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  • Industrial Chemistry  (437)
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  • crystal structure  (134)
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  • 1995-1999  (796)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of cluster science 8 (1997), S. 521-531 
    ISSN: 1572-8862
    Keywords: Zirconium clusters ; isocyanide ; synthesis ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The first isocyanide ligated hexanuclear zirconium halide cluster is reported. The unoxidized [(Zr6Be)Cl12(CNXyl)6] (CNXyl = 2,6-dimethylphenyl isocyanide) was obtained from the solid state precursor K3Zr6Cl15Be by dissolution in CH3CN in the presence of CNXyl. The CNXyl ligands occupy all the axial positions on the cluster. The compound was recrystallized from CH2Cl2 and Et2O. [(Zr6Be)Cl12(CNXyl)6].2CH2Cl2 crystallizes in the space group $${\text{P}}\overline {\text{1}} $$ (#2) with a = 12.092(5) Å, b=12.728(5) Å, c = 14.102(8) Å, α = 104.98(4)°, β =107.11°, γ = 100.94°, V = 1919(2) Å3, Z = l, R = 11.3% and R W = 27.0%. For the bound isocyanide ligands, v CN increases to 2140 cm−1.
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  • 2
    ISSN: 1572-8862
    Keywords: Rhenium ; dirhenium complexes ; rhenium–rhenium multiple bonds ; isocyanide ligands ; carbonyl ligand ; structural isomers ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reaction of the unsymmetrical, coordinatively unsaturated dirhenium(II) complex [(XylNC)(OC)CIRe(μ-dppm)2ReCl2]O3SCF3 (dppm = Ph2PCH2PPh2) with one equivalent of XylNC in CH2Cl2 affords a fifth structural isomer of the [Re2Cl3(μ-dppm)2(CO)(CNXyl)2] + cation; this is believed to have a CO-bridged structure of the type [(XylNC)ClRe(μ-Cl)(μ-CO)(μ-dppm)2ReCl(CNXyl)]+. The latter complex reacts with a further equivalent of XylNC in the presence of Tl+ to form the [Re2Cl2(μ-dppm)2(CO)(CNXyl)3]2+ cation, which has been shown by IR spectroscopy, and by the X-ray crystallographic characterization of its neutral congener Re2Cl2(μ-dppm)2(CO)(CNXyl)3, to contain a very weak and unsymmetrical CO bridge.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 50 (1997), S. 569-586 
    ISSN: 1572-8943
    Keywords: crystal structure ; metal(II) picolinate and quinaldinate ; thermal degradation of imidazole and pyrazole complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Complexes of the type M(Pa)2(HAz)2 and M(QA)2(HAz)2 (M=cobalt(II) and nickel(II); HPa=picolinic acid, HQa=quinaldic acid; HAz=azoles like imidazole (Him), pyrazole (HPz), benzimidazole (HBzIm) etc.) show a similar thermal behaviour. In the first step of decomposition the corresponding azolinium picolinates or quinaldinates (H2AzPa, H2AzQa) are split off with formation of polymeric mixed ligand complexes M(Pa)(Az) or M(Qa)(Az). X-ray analysis of Co(Qa)2(HBzIm)2 XIIIa illustrates a proton transfer and a subsequent thermal removal of benzimidazolinium quinaldinate (H2BzImQa): Hydrogen bridges from pyrrole nitrogen of the benzimidazole to the non-coordinated oxygen of the quinaldinate predetermine the thermal initiated proton transfer. The high volatility of the heterocyclic acids and the nitrogen coordination are responsible for the formation of the mixed ligand complex Co(Qa)(BzIm) XIVa. Exceptions are the complexes M(Pa)2(HPz)2 XIa-b and M(Qa)2(HIm)2 XVIIa-b. Pyrazole is eliminated from the complexes XIa-b with formation of the solvent-free inner complex M(Pa)2 XIIa-b. From compounds XVIIIa-b quinaldic acid or their decomposition products are split off and a high temperature modification of M(Im)2 XVIIIa-b is formed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)2 similarly to the thermal behaviour of Cu(Im). In the first step the thermal degradation of imidazole and pyrazole adducts of copper(II) picolinates and quinaldinates is characterized by the elimination of azoles. The reason for this thermal behaviour is the weaker coordination of the azole heterocycles in copper chelate compounds.
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  • 4
    ISSN: 1572-9001
    Keywords: Tautomerism ; anthraquinone ; crystal structure ; semiempirical computations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Substituted 1-hydroxy-9,10-anthraquinone-9-imines have been found to exhibit tautomeric interconversions between the 9,10- and 1,10-quinonoid forms in the solid state as well as in solution. Single-crystal X-ray crystallography was used to study the structures of 4-(N-acetyl-p-tolylamino)-9-amino-1,10-anthracenedione and 4-hydroxy-1-phenylamino-10-mesitylimino-9(10H)-anthracenone at ambient and low temperatures. The former compound gave crystals belonging to the monoclinic space group P2l/c and, at 295 K,a=9.684(2),b=16.371(3),c=12.097(2) å,Β=110.41(1)
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  • 5
    ISSN: 1572-9001
    Keywords: Benzopsoralen ; photochemotherapeutic agent ; crystal structure ; molecular mechanics ; AM1 theoretical calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 5-Methoxy-4-methyl-2H-benzofuro[3,2-g]benzo-1-pyran-2-one was synthesized and its crystal structure was determined and compared with the optimal conformation arrived at by MM and AM1 theoretical calculations. The latter indicated that the tetracyclic skeleton is planar with total length (C2–C8) 9.23 å, and that the line joining the conters of the terminal-benzene and furan rings makes an angle of 30.5
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Glycoconjugate journal 14 (1997), S. 677-690 
    ISSN: 1573-4986
    Keywords: molecular dynamics ; crystal structure ; cellulose I and II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The paper describes molecular dynamics (MD) simulations on the crystal structures of the Iβ and II phases of cellulose. Structural proposals for each of these were made in the 1970s on the basis of X-ray diffraction data. However, due to the limited resolution of these data some controversies remained and details on hydrogen bonding could not be directly obtained. In contrast to structure factor amplitudes in X-ray diffraction, energies, as obtained from MD simulations, are very sensitive to the positions of the hydroxyl hydrogen atoms. Therefore the latter technique is very suitable for obtaining such structural details. MD simulations of the Iβ phase clearly shows preference for one of the two possible models in which the chains are packed in a parallel orientation. Only the parallel-down mode (in the definition of Gardner and Blackwell (1974) J Biopolym 13: 1975-2001) presents a stable structure. The hydrogen bonding consists of two intramolecular hydrogen bonds parallel to the glycosidic linkage for both chains, and two intralayer hydrogen bonds. The layers are packed hydrophobically. All hydroxymethyl group are positioned in the tg conformation. For the cellulose II form it was found that, in contrast to what seemed to emerge from the X-ray fibre diffraction data, both independent chains had the gt conformation. This idea already existed because of elastic moduli calculations and 13C-solid state NMR data. Recently, the structure of cellotetraose was determined. There appear to be a striking similarity between the structure obtained from the MD simulations and this cellotetraose structure in terms of packing of the two independent molecules, the hydrogen bonding network and the conformations of the hydroxymethyl group, which were also gt for both molecules. The structure forms a 3D hydrogen bonded network, and the contribution from electrostatics to the packing is more pronounced than in case of the Iβ structure. In contrast to what is expected, in view of the irreversible transition of the cellulose I to II form, the energies of the Iβ form is found to be lower than that of II by 1 kcal mol-1 per cellobiose.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Structural chemistry 8 (1997), S. 141-147 
    ISSN: 1572-9001
    Keywords: Dibenzanthracene ; trinitrobenzene complex ; trinitrobenzene complex ; π-complex ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The crystal structure of the complex between the polycyclic aromatic hydrocarbon di-benz[a,c]anthracene and 1,3,5-trinitrobenzene is reported. The crystals are triclinic, space group P¯1 with unit cell dimensionsa=7.277(2) å,b=11.237(6) å, andc=13.902(5) å,α= 104.13(4)
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  • 8
    ISSN: 0887-3585
    Keywords: small-angle scattering ; x-rays ; allosteric enzymes ; crystal structure ; rigid body modeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Solution scattering curves evaluated from the crystal structures of the T and R states of the allosteric enzyme aspartate transcarbamylase from Escherichia coli were compared with the experimental x-ray scattering patterns. Whereas the scattering from the crystal structure of the T state agrees with the experiment, large deviations reflecting a significant difference between the quaternary structures in the crystal and in solution are observed for the R state. The experimental curve of the R state was fitted by rigid body movements of the subunits in the crystal R structure which displace the latter further away from the T structure along the reaction coordinates of the T→R transition observed in the crystals. Taking the crystal R structure as a reference, it was found that in solution the distance between the catalytic trimers along the threefold axis is 0.34 nm larger and the trimers are rotated by 11° in opposite directions around the same axis; each of the three regulatory dimers is rotated by 9° around the corresponding twofold axis and displaced by 0.14 nm away from the molecular center along this axis. Proteins 27:110-117 © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 0887-3585
    Keywords: bactericidal antibody ; crystal structure ; Neisseria meningitidis ; peptide-fluorescein conjugate ; PorA outer membrane protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Class 1 outer membrane protein PorA of Neisseria meningitidis is a vaccine candidate against bacterial meningitis. Antibodies against PorA are able to induce complement-mediated bacterial killing and thereby play an important role in protection against meningococcal disease. Bactericidal antibodies are all directed against variable regions VR1 and VR2 of the PorA sequence, corresponding to loops 1 and 4 of a two-dimensional topology model of the porin with eight extracellular loops. We have determined the crystal structure to 2.6 Å resolution of the Fab fragment of bactericidal antibody MN12H2 against meningococcal PorA in complex with a linear fluorescein-conjugated peptide TKDTNNNL derived from the VR2 sequence of sero-subtype P1.7,16 (residues 180-187) from meningococcal strain H44/76. The peptide folds deeply into the binding cavity of the Fab molecule in a type I β-turn, with the minimal P1.16 epitope DTNNN virtually completely buried. The structure reveals H-bonds and van der Waals interactions with all minimal epitope residues and one essential salt bridge between Asp-182 of the peptide and His-31 of the MN12H2 light chain. The key components of the recognition of PorA epitope P1.16 by bactericidal antibody MN12H2 correspond well with available thermodynamic data from binding studies. Furthermore, they indicate the structural basis of an increased endemic incidence of infection by group B meningococci in England and Wales since 1981 associated with the occurrence of an Neisseria meningitidis escape mutant (strain MC58). The observed three-dimensional conformation of the peptide provides a rationale for the development of a synthetic peptide vaccine against meningococcal disease. Proteins 29:113-125, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 10
    ISSN: 0887-3585
    Keywords: Brownian dynamics ; molecular recognition ; site-directed mutagenesis ; facilitated diffusion ; crystal structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Key charged residues in Cu,Zn superoxide dismutase (Cu,Zn SOD) promote electrostatic steering of the superoxide substrate to the active site Cu ion, resulting in dismutation of superoxide to oxygen and hydrogen peroxide. Lys-136, along with the adjacent residues Glu-132 and Glu-133, forms a proposed electrostatic triad contributing to substrate recognition. Human Cu,Zn SODs with single-site replacements of Lys-136 by Arg, Ala, Gln, or Glu or with a triple-site substitution (Glu-132 and Glu-133 to Gln and Lys-136 to Ala) were made to test hypotheses regarding contributions of these residues to Cu,Zn SOD activity. The structural effects of these mutations were modeled computationally and validated by the X-ray crystallographic structure determination of Cu,Zn SOD having the Lys-136-to-Glu replacement. Brownian dynamics simulations and multiple-site titration calculations predicted mutant reaction rates as well as ionic strength and pH effects measured by pulse-radiolytic experiments. Lys-136-to-Glu charge reversal decreased dismutation activity 50% from 2.2 × 109 to 1.2 × 109 M-1 s-1 due to repulsion of negatively charged superoxide, whereas charge-neutralizing substitutions (Lys-136 to Gln or Ala) had a less dramatic influence. In contrast, the triple-mutant Cu,Zn SOD (all three charges in the electrostatic triad neutralized) surprisingly doubled the reaction rate compared with wild-type enzyme but introduced phosphate inhibition. Computational and experimental reaction rates decreased with increasing ionic strength in all of the Lys-136 mutants, with charge reversal having a more pronounced effect than charge neutralization, implying that local electrostatic effects still govern the dismutation rates. Multiple-site titration analysis showed that deprotonation events throughout the enzyme are likely responsible for the gradual decrease in SOD activity above pH 9.5 and predicted a pKa value of 11.7 for Lys-136. Overall, Lys-136 and Glu-132 make comparable contributions to substrate recognition but are less critical to enzyme function than Arg-143, which is both mechanistically and electrostatically essential. Thus, the sequence-conserved residues of this electrostatic triad are evidently important solely for their electrostatic properties, which maintain the high catalytic rate and turnover of Cu,Zn SOD while simultaneously providing specificity by selecting against binding by other anions. Proteins 29:103-112, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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  • 11
    ISSN: 0887-624X
    Keywords: 1,4-benzenedithiol ; 1,4-diethynylbenzene ; crystal structure ; solid-state polymerization ; layer structure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of 1,4-benzenedithiol (BDT) was determined by the Rietveld method based on the calculation of the atomic coordinates of the BDT molecule using the Molecular Mechanics Program (MMP2). The refined crystal structure of BDT was monoclinic P21/c with dimensions, a = 7.795, b = 7.290, c = 5.955 Å, β = 92.16°, z = 2. The R factor of the refined structure was 0.038. Using above results, the mechanism of solid-state addition polymerization of BDT to 1,4-diethynylbenzene (DEB) was studied. Sublimed BDT piles up onto glass plate substrate and forms the layer structure along with the a axis. An inclination angle of the piled BDT column was 60° toward the substrate surface. DEB crystal structure was also monoclinic P21/c with a = 4.007, b = 6.018; c = 15.340 Å, β = 91.42°, z = 2. Sublimation of equimolar mixture of BDT and DEB gave a crystal having 1 : 1 composition, in which DEB column is situated between the columns of BDT. Relative arrangement of both monomers was suitable for the addition of —SH and —C=CH groups, since the distance between the two groups is 3.3 Å by CERIUS II calculation. Therefore, the addition polymerization of BDT to DEB easily proceeded by UV irradiation and the resulting polymer had a highly layer structure along with the a axis of BDT crystal. Tentatively estimated crystal structure of polymer obtained is monoclinic with a = 7.73, b = 7.30, c = 5.95 Å, β = 92.16°. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1621-1625, 1997
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 27 (1997), S. 169-178 
    ISSN: 1573-1111
    Keywords: Bridged calix[4]arene ; ditopic receptor ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The crystal structures of a new solvate of the ditopic receptor 1,3-calix[4]-bis-crown-6, Bis-C6, and of 1,3-calix[4]-bis-(benzo-crown-6), Bis-benzoC6, are reported. Bis-C6.3 CH3CN (1) crystallizes in the monoclinic space group P21/n, a = 14.388(3), b = 26.947(8), c = 14.707(4) Å, β = 113.19(3)°, V = 5241(5) Å3, Z = 4. Refinement led to a final conventional R value of 0.092 for 2723 reflections. The structure of (1) differs from the previously reported structure of Bis-C6.4 CH3CN by the conformation of one crown either chain. Two acetonitrile molecules are in the close neighbourhood of the crown ether cavities. Bis-benzoC6.3 CH3CN (2) crystallizes in the monoclinic space group P21/c, a = 10.391(4), b = 17.264(11), c = 30.426(9) Å, β = 94.62(3)°, V = 5440(7) Å3, Z = 4. Refinement led to a final conventional R value of 0.106 for 2965 reflections. Two acetonitrile molecules are located near the crown ether cavities, as in (1). One of the crown ether conformations is the same as in the binuclear caesium complex of Bis-benzoC6, supporting the hypothesis of a preorganization of this ligand towards the complexation of this ion; the second crown ether chain is partially disordered.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 28 (1997), S. 125-140 
    ISSN: 1573-1111
    Keywords: X-ray ; crystal structure ; Li-complex ; triamides ; 1H-NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The structure of the lithium complex with1,3,5-tris[oxymethylene(N,N-dicyclohexyl)carboxyamido]cyclohexanehas been determined by the X-ray method.The compound is triclinic, space group P¯1,a = 15.623(3), b = 19.279(4),c = 19.295(4)Å α = 102.32(3), β = 92.45(3),γ = 105.67(3)0, V = 5436(2)Å3, Z = 4. Itscomposition is represented by the formulaC48H82N3O6LiI 0.5H2O. The lithium cationis encapsulated in a polar pseudo-cavity of six oxygen atoms of the ligandmolecule and displays a distorted trigonal prism coordination. The conformationof the ligand in the solid state complex has been compared with the conformationof the complex in solution determined by 1H-NMR measurements. Supplementary data relevant to this publication have been deposited with the British Library, No. SUP 82224 (21 pages).
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 28 (1997), S. 17-32 
    ISSN: 1573-1111
    Keywords: Azocrown ether ; azoxycrown ether ; sodium complexes ; crystal structure ; X-ray analysis ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sodium iodide complexes of 13-membered azo-(I)and azoxycrown ethers (II) have been synthesized. Compound I[Na(L1 trans)2]⋅I⋅H2O is triclinic witha = 11.53(2), b = 15.74(2), c = 19.17(2) Å,α = 98.93(9), β = 105.51(9),γ = 89.20(9) deg.; Z = 4, space groupP1. Compound II [Na(L2)2]⋅I is orthorhombic witha = 12.451(2), b = 13.796(3), c = 18.667(4)Å; Z = 4, space group P212121. In bothcomplexes the cation is coordinated tochain oxygen atoms and to one nitrogen atom of the azoor azoxy unit. The ability of bothligands to form complexes in relation to thegeometry of the azo or azoxy subunit of themacrocycle is discussed.
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  • 15
    ISSN: 1573-1111
    Keywords: β-Dimorph ; crystal structure ; dianilinegossypol ethylacetate 1 : 1 clathrate ; packing motifs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Depending on crystallization conditions, dianilinegossypol and ethylacetate form low (ambient temperature, α-phase) and high temperature (t = 35°C, β-phase) clathrate modifications. The structure of the α-phase has been discussed earlier [1]. Crystals of the 1 : 1 β-phase complex, C42H40O6N2·C4O2H8, are monoclinic, space group P21/c, a = 11.362(6), b = 19.479(9), c = 19.085(9) Å, β = 103.21(4)°, V = 4112(3)Å3, Z = 4, R = 0.084 for 3210 observed reflections. In these complexes centrosymmetric dimers of dianilinegossypol molecules formed via O(5)—H···O(3) hydrogen bonds are associated into columns by a weak O(8)—H···O(7) H-bond. A difference in the structure of these two phases is in the packing mode of the columns. The angle formed by intersecting host columns is about 126° for the α-phase and 104° for the β-modification. Guest molecules are hydrogen bonded to the host molecules via an O(1)—H···O(10) bond and are accommodated in channels in α-phase complex and in cavities in β-phase complex.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 27 (1997), S. 13-20 
    ISSN: 1573-1111
    Keywords: Uranyl complexes ; calixarenes ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The synthesis and crystal structure of the inclusion complex between uranyl and p-tert-butylcalix[5]arene are reported. [UO2 (p-tert-butylcalix[5]arene-4H]2- · $${\text{2HNE}}_{{\text{t}}_{\text{3}} }^{\text{ + }} $$ &·2MeOH(1) crystallizes in the monoclinic space group C2/c, a = 30.06(2), b = 18.20(3), c = 31.35(2) Å, β = 128.51(6)°, V = 13423(40) Å3, Z = 8. Refinement led to a final conventional R value of 0.043 for 4155 reflections. The uranyl ion is bonded, in its equatorial plane, to the five oxygen atoms of the calixarene, four of which are deprotonated. A protonated triethylamine molecule is located inside the calixarene cavity and hydrogen bonded to a uranyl oxygen atom, and another one outside and hydrogen bonded to a calixarene oxygen atom. The calixarene conformation is the usual cone one.
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  • 17
    ISSN: 1573-1111
    Keywords: Calix[4]arene ; polyether ; crystal structure ; alkali metal ion binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The ligand 5,11,17,23-tetra-t-butyl-25,27-di(phenylmethoxy)-26,28-di(2-methoxy-ethoxy)calix[4]arene,designed as an analogue of some calixcrown speciesin order to evaluate possible origins of their selectivity in alkali metal ion binding, has been synthesised and structurally characterised by X-ray crystallography. The crystals are monoclinic, P21/n, a = 15.940(6), b = 19.388(5), c = 20.020(5) Å,β = 109.10(2) deg., Z = 4, conventional R on |F| being 0.073 for 3454 independent, ’observed‘ (I 〉 3σ(I)) reflections. 1H-NMR studies in 1:1 CD3CN/CDCl3solvent have shown that the ligand exerts a strong preference for the lighteralkali metal ions (Li+ and Na+) contrary to the binding behaviour of knowncalixcrowns. This may reflect interactions restricted to the lower rim donor atoms without concomitant interaction with the calixarene π-electrons, perhaps because the latter interactions are substituted by those with the benzyl group π-electrons.
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  • 18
    ISSN: 1573-1111
    Keywords: Dianilinegossypol ; crystal structure ; host–guest complexes ; H-bond ; α- and β-dimorphs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dianilinegossypol forms a 1 : 2 host-guest complex with DMSO:monoclinic, space group P21/n, a = 8.522(3), b = 18.034(4), c= 28.462(6) Å, β = 94.14(2)°, V = 4362Å3, Z = 4, D x = 1.26 g cm-3, T = 295 K.Final R value is 0.102 for 1793 observed reflections. A 1 : 1 : 1 adduct ofdianilinegossypol with 1,4-dioxane and 1,2-dichloroethane is found to beisostructural with the dianilinegossypol complex with DMSO: monoclinic,space group P21/n, a = 8.281(2), b = 19.245(3), c = 27.970(7)Å, β = 95.18°, V = 4439 Å3, Z = 4, D x =1.28 g cm-3, T = 295 K. Final R value is 0.114 for 2458observed reflections.The host molecules are associated by O(4)—H ...O(3) H-bonds toinfinite chains running in the direction of the c-axis The chains areincorporated into layers through 1,4-dioxane or DMSO molecules havingH-bonds with dianilinegossypol molecules. Another DMSO or 1,2-dichloroethanemolecule is included as a guest in the channels formed between the layers.At 60 °C a cryptate-type inclusion complex of dianilinegossypol isformed with DMSO or 1,4-dioxane. It is isostructural with the acetonecomplex reported in Part IV of the present series.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 29 (1997), S. 175-185 
    ISSN: 1573-1111
    Keywords: p-tert-Butylcalix[5]arene ; synthesis ; complexation ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of p-tert-butylcalix[5]arene by the opening ofp-tert-butyldihomooxacalix [4]arene and the addition of a monomer has beenstudied. Various facets, including the effects of bases and the nature ofthe monomer added to the p-tert-butyldihomooxacalix[4]arene, have beeninvestigated. p-tert-Butylcalix[5]arene can be prepared in yields up to30%. The structure of its 1 : 2 complex with DMF has been determinedby X-ray crystallography. Crystals are triclinic, space group P¯1, a =1428.2(3) pm, b = 1837.3(3) pm, c = 1276.1(2) pm, α = 108.98(1)°,β = 105.02(2)°, γ = 95.21(1)°, Z = 2, D c = 1.059 kg m-3,final R value = 0.087. The macrocycle adopts a cone conformation, one guestenclosed inside the cavity, the other one outside.
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 29 (1997), S. 335-346 
    ISSN: 1573-1111
    Keywords: Glycophane ; macrocycle ; carbohydrate ; crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Preparation of two new glycophanes is reported. These compounds arecomprised of two glucose molecules linked by hydrocarbon units at the 1,1′ and 3, 3′ or 3, 3′ and 6, 6′ positions. Thecrystal structure of one of the glycophanes is also described.
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  • 21
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 22
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    Chemical Engineering & Technology - CET 20 (1997), S. 17-22 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mass transfer with chemical reaction by liquid/liquid phase tranfer catalysis (LLPTC) for an isothermal batch reactor was analyzed. The results for the phase transfer catalyzed reaction system can be generally described by a pseudo first-order hypothesis, whereas the reaction system can be controlled by simultaneous mass transfer of the catalysts between two liquid phases and chemical reaction in the organic phase. The mass transfer limitation is mainly from the mass transfer step of QX from the organic phase to the aqueous phase. The concept of catalyst-effectiveness vs. physically meaningful parameters in a liquid/liquid phase transfer catalyzed reaction is introduced. The catalyst effectiveness is increased as the mass transfer factors increase, the ratio of reaction rate coefficients of aqueous forward reaction to organic increases, and the equilibrium constant in the aqueous solution increases.
    Additional Material: 7 Ill.
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  • 23
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    Chemical Engineering & Technology - CET 20 (1997), S. 40-42 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The use of ozone and hydrogen peroxide for the simultaneous oxidation of nitrogen and sulfur oxides was studied in experiments carried out in a stirred cell. It was found that in a gas mixture, containing both nitrogen and sulfur oxides, only the nitrogen oxides are oxidized by ozone. Contrary to earlier results, sulfur dioxide does not disturb the oxidation of nitrogen oxides under dry conditions. The consumption of ozone in the oxidation of nitric oxide was slightly below the stoichiometric level because the ozone was introduced into the reactor in the oxygen flow. When the molar ratio between ozone and nitric oxide was more than 0.4, some of the nitric oxide was oxidized to higher oxides of nitrogen, the final product being a solid mixture of N2O5 and (NO)2S2O7. Some nitrosyl sulfuric acid was formed in the aqueous solution of hydrogen peroxide in addition to sulfuric acid under wet conditions. Some white solid was found on the walls of the reactor. This solid is said it the literature to consist of H2SO4, HNOSO4 and (NO)2S2O7.
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  • 24
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 25
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    Chemical Engineering & Technology - CET 20 (1997), S. 564-570 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The modern urea plants are using a stripping process to reduce the energy consumption. The potential, very severe corrosion problems have been mastered by special grades and strict process control. The different grades are reviewed. After more than 20 years operation the results are very satisfying.In ammonia plants, an often forgotten corrosion problem is found in the heat exchangers. After about 3-6 years failures caused by chloride continuing cooling water may appear on carbon steel or low alloyed austenitic stainless steels. Corrosion mechanism is reviewed. Duplex stainless steels has been used with success and the properties are presented. An example of life-cycle cost shows that duplex stainless steel is an inexpensive way to solve chloride related corrosion problems.Condensation and evaporation of nitric acid in heat exchangers in nitric acid plants cause severe corrosion on conventional stainless steel grades. Low impurity in combination with high chromium content has proved to result in stainless steel with improved corrosion resistance.
    Additional Material: 5 Ill.
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  • 26
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    Chemical Engineering & Technology - CET 20 (1997), S. 550-556 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Bubble break-up, gas holdup, and the gas-liquid volumetric mass transfer coefficient are studied in a bubble column reactor with simultaneous injection of a gas and liquid through a T-junction nozzle. The theoretical dependence of bubble break-up and the volumetric mass transfer coefficient on liquid velocity in the nozzle is developed on the basis of isotropic turbulence theory. It is shown that correlations which are developed based on liquid jet kinetic power per nozzle volume explain average gas holdup and the volumetric mass transfer coefficient within an error of 15% for all gas and liquid flow rates and nozzle diameters used. Experiments with a larger scale column, height 4.64 m and diameter 0.98 m, show a transition from homogeneous to heterogeneous flow at a certain liquid flow rate through the nozzle. Liquid composition was found to have a significant effect on gas-liquid mass transfer. A phenol concentration of 10-30 mg/l in water increases the volumetric mass transfer coefficient of oxygen by 100%. This phenomenon may have significance in the chemical oxidation of wastewater.
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  • 27
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    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 28
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    Chemical Engineering & Technology - CET 20 (1997), S. 582-588 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The shape-selective transalkylation of biphenyl with pentamethylbenzene over ultrastable Y-faujasites to produce para-methylated biphenyls was studied in the liquid slurry phase. The reaction was carried out in a discontinuously operated stainless steel autoclave using n-heptane as the solvent with a temperature range of 513 to 533 K and a pressure of 3 MPa. As for the progress of the reaction the presence of strong Brønsted acid sites was essential, an ultrastable faujasite treated with aqueous hydrochloric acid having a high content of those sites was used as the catalyst. Thus, a yield of the target product 4,4′-dimethylbiphenyl of above 11% referring to biphenyl could be achieved. The effect of the operating conditions on the formation of the target product was investigated. The decisive influence was acted out by the molar ratio of biphenyl to alkylating agent, in so far as a surplus of pentamethylbenzene of 7:1 referring to biphenyl enhanced the yield of the target product to 14%. The kinetics of the reaction could be successfully descibed with a lumped reaction scheme, introducing pseudo components, summarizing structural isomers, and pseudo reactions, such as the formation of coke.
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  • 29
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    Chemical Engineering & Technology - CET 20 (1997), S. 624-632 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The oxidation of sulfide in oxygen-saturated aqueous solutions is accelerated by dissolved or silica-bonded cobalt phthalocyanines. On the basis of thermodynamical considerations it is postulated that the catalyst enhances the formation of disulfide as the initial elementary reaction step. The following reaction steps are largely unaffected by the catalyst, as indicated by a product ratio sulfate/thiosulfate=0.86, comparable to that of the uncatalyzed autoxidation. A Langmuir-Hinshelwood formalism is developed for the catalytic reaction step and is demonstrated to fit best with the kinetics. In addition, from the kinetic data free enthalpies for the adsorption of HS- (i) at the dissolved phthalocyanine (ΔG = -17.6 kJ/mole) and (ii) at the immobilized complex (ΔG = -20.0 kJ/mole) are calculated.
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  • 30
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    Chemical Engineering & Technology - CET 20 (1997), S. 641-645 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An In-HZSM 5 honeycomb catalyst is used for the experimental investigations of the NO reduction with methane. The catalyst is prepared by the ion-exchange method. The influence of temperature and concentration of oxygen and methane is studied. In addition to methane, natural gas is used as reductant for the reduction of nitric oxide. The results are compared with those of other authors who use zeolithe pellets.
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  • 31
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chemical engineering is taught at German universities in three different types of curricula: chemical engineering proper, process engineering (“Verfahrenstechnik”), and industrial chemistry (“Technische Chemie”). Independent departments resp. faculties of chemical engineering exist at four universities. At other universities process engineering is offered as a complete curriculum with a smaller amount of chemistry than chemical engineering curricula, mostly by the departments of mechanical engineering. Industrial chemistry is an essential component of chemistry courses at most technical universities and optional subject at several classical universities. The cause of this diversity of approaches to chemical engineering can be traced back to the beginning of the production of high-value organics (dyes, pharmaceuticals) in Germany in the second half of the 19th century.
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  • 32
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    Chemical Engineering & Technology - CET 20 (1997), S. 293-296 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When mechanical foambreakers are used in chemical engineering processes to control an undesired primary foam, a secondary foam is often produced. Secondary foams consist of small bubbles, have a high liquid hold-up, and cannot be condensed further by mechanical foambreakers. Secondary foams can be converted into liquid and gas in a coalescence column by drainage, diffusion, and breakage of the lamellas. This paper presents a new model to determine the velocity of bubble growth and the time of coalescence of secondary foams. The experimental investigations have been carried out with surfactants in aqueous solutions.
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  • 33
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    Chemical Engineering & Technology - CET 20 (1997), S. 309-312 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Errors caused by the use of sensitivity tables may become very large in some cases because of the tables' total disregard of nonlinearities and interaction effects. We introduce a new and improved approach which calculates the effect of disturbances simultaneously by solving a set of linear equations. The approach offers simplicity, speed, insight and accuracy.
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  • 34
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A ‘carbon source controlled shift technique’ was developed for fermentation medium optimization in continuous culture with the objective to maximize growth rate and growth-linked product formation of a biological system. An automatic culture medium preparation system was operated together with 2 parallel stirred tank reactors and a HPLC system for on-line analysis of the carbon source concentration in the reactors. A genetic algorithm was applied for experimental design. The concentrations of 7 medium components (mineral salts and vitamins) were optimized automatically within 40 continuous experiments to result in a maximum growth rate of the methylotrophic yeast Candida boidinii and growth-linked production of the formate dehydrogenase enzyme (FDH). The specific growth rate of Candida boidinii and the specific activity of the FDH enzyme at a set-point of 420 mM methanol in the reactor were, thus, improved by 19% to 0.16 h-1 and 26% to 164 U g-1, respectively, compared to the previously used medium, which has already been previously optimized in shake flask experiments. The results of the continuous medium optimization were evaluated with a full second order seven-dimensional polynomial model (regression coefficient 96.8%).
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  • 35
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    Chemical Engineering & Technology - CET 20 (1997), S. 414-418 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the present work, we employ a fuzzy logic controller (FLC) to control the unstable state of a nonlinear biological reaction. The state variable vectors consist of cell density and substrate concentration. The dilution rate is used as a manipulated variable to control the reaction dynamics. An analytic form of FLC employing Zadeh AND logic along with Center of Mass defuzzification method is considered. Simulations reveal that for servo response test, the FLC shows satisfactory performance for natural unsteady states for which a conventional PI controller is known to fail. Further simulations also show that the FLC gives satisfactory regulatory response and is relatively insensitive to the deviations in model parameters.
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  • 36
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    Chemical Engineering & Technology - CET 20 (1997), S. 429-433 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When in contact with water, organoalkoxysilanes and other alkoxy metal compounds react to organofunctionalized polysiloxanes or heteropolysiloxanes. A new method for the continuous preparation of porous organopolysiloxane spheres was developed. Droplets of the precursor mixture are injected into the vertical reactor column. Movement of the gelating droplets is controlled by flow of the aqueous reaction medium. Advantages are adjustable residence time, minimized coalescence and low reactor height. An example shows typical product characteristics like narrow particle size distribution and macroporosity.
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  • 37
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    Chemical Engineering & Technology - CET 20 (1997), S. 462-468 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The autoxidation of aqueous sulfide solutions by dioxygen is studied at pH 9 and 14 and at initial sulfide concentrations between 1 and 100 mM. Disulfide as a primarary intermediate is proposed to enhance the sulfide oxidation by autocatalytically forming polysulfies. The postulate is supported by the observed acceleration of the process at increasing pH favoring the presence of disulfide rather than that of sulfur. The final reaction products thiosulfate and sulfate are proposed to result from the hydrolysis of the highly instable intermediate polythiosulfite in parallel parallel reaction pathways, assuming probabilities for breaking the sulfur chain at the α (sulfate) and β (thiosulfate) positions to be responsible for the selectivity. A reaction scheme is proposed, considering all experimental observations.
    Additional Material: 7 Ill.
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  • 38
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    Chemical Engineering & Technology - CET 20 (1997), S. 485-490 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dynamic model of the liquid fluidized bed containing two or more solid particle species of different size and density is presented. The model incorporates the particle mass transport mechanisms of the convection and the dispersion. The movement of the upper interface of the bed subject to a change in the liquid velocity is specified using the mass balance constraint. The particle velocities and dispersion coefficients are evaluated using correlations. The model is capable of describing the bed expansion, concentration profiles of the individual particle species, the bulk density profile, and the occurrence of layer inversion.
    Additional Material: 7 Ill.
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  • 39
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    Chemical Engineering & Technology - CET 20 (1997), S. 221-229 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: To review mass transfer trays from a process point of view, the dependence of efficiency on the loadings, the loading range and the maximum loadings with an acceptable tray efficiency have to be known. Comparing the results taken from experiments on Dualflex trays and from other types of trays which have been in industrial applications for many years and which are recognized as “industrial standard”, has been evaluated in this review.
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  • 40
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    Chemical Engineering & Technology - CET 20 (1997), S. 259-267 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In this study, a scale-down approach has been used for the simulation of the imperfect mixing on the growth processes by considering several configurations of continuous stirred tank reactor (CSTR, aerated) and plug flow tubular reactor (PFTR, not aerated). The steady-state concentrations of biomass and enzyme in a continuous culture were calculated as a function of dilution rate using modified Monod growth kinetics. A mathematical model for each combination of two bioreactors was developed to account for growth, substrate utilization (oxygen and glucose) and enzyme synthesis and decay. The model was then used to investigate biomass production and enzyme expression in relation to the volumetric fraction Uf = VPFTR/(VCSTR + VPFTR) and the recirculation ratio R = fr/(f + fr) of the fermentation system. These two mixing parameters were found to be significant factors in the biomass and enzyme production from the fermentation system. This model was also compared with some of the existing models.
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  • 41
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    Chemical Engineering & Technology - CET 20 (1997), S. 23-28 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the present study, a mass transfer model for Type-1 facilitated transport in liquid surfactant membrane is developed by taking into consideration a size distribution of emulsion drops, and analytical solution of the model equations has been presented. The model takes into account the continuous phase and outer liquid membrane phase resistances along with diffusion through composite emulsion drop. Effort has been made to highlight the effect of the various system parameters on the extraction rate including computation of reaction front position. The results of this work are found to be in good agreement with the published experimental results on batch extraction of phenol using NaOH as internal reagent. The model would thus provide an insight of the separation mechanism involved in the mass transfer processes in this type of system.
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  • 42
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    Chemical Engineering & Technology - CET 20 (1997), S. 43-46 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Liquid-phase cyclohexanone ammoximation over titanium silicate was carried out in a batch reactor. The influence of the solvent, duration of kinetic run, catalyst amount and reactant concentrations was investigated. Byproducts were formed in considerable amounts, leading to catalyst deactivation by pore blocking. The values of initial reaction rates were calculated taking into account deactivation phenomenon. Theses values indicated that within the range of studied concentration (Ccyclohexanone = 0.4 to 1.70 mol/l; Cammonia = 1 to 4 mol/l; Chydrogen peroxide = 0.4 to 1.8 mol/l) the reaction rates plotted as a function of all the reagent concentrations go through a maximum. Special experiments on hydrogen peroxide decomposition and cyclohexanone oximation by hydroxylamine demonstrated that the rates of these reactions are essentially higher than the ammoximation rates.A kinetic equation for initial ammoximation rates was developed on the basis of a mechanistic model. The advanced model permits description of the observed kinetic regularities.
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  • 43
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The following deliberations are concerned with the application of economy criteria to the optimization of process-engineering plants. We are therefore not concerned here with criteria for investment decisions, i.e., decisions on the implementation orabandonment of an investment project, nor with criteria for the selection of the most profitable investment options from a series of alternatives. Instead, we are interested here in the question of how a plant, while at the planning stage, can best be designed, i.e., the most rational method of selecting process parameters, such as throughputs, pressures, temperatures, concentrations, etc. The problem of plant optimization only occurs, however, when there are design parameters which can be selected at will or can, at least, be varied within certain limits. This is however, virtually always the case. There is then a need for an optimization strategy in the form of an objective function which is either reduced to a minimum, where lowest possible production costs are the target, for instance, or advanced to a maximum, where high profitability is the aim. The inclusion of engineering economy functions, in the form, namely, of the net present value function and the internal rate of return function for definition of such objective functions, provides better defined information on the best possible choice of process parameters than was possible with methods previosly used, such as the annuity method, for instance. One obtains different values for the process parameters to be optimized, depending on the objective functionused, and therefore different investment costs and utility consumptions. These differences are delineated and quantified using a process-engineering example in the course of the following discussion. The example selected is a gas scrubber, the function of which is to remove and recover useful components from a flow of gas. The specific problem examined is one of heat recovery.
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  • 44
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    Chemical Engineering & Technology - CET 20 (1997), S. 90-92 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of sodium lauryl sulphate (anionic) and Triton X-100 (nonionic) on the solid-liquid mass transfer at a gas-sparged fixed bed of copper Raschig rings was studied by measuring the diffusion-controlled dissolution of copper rings in acidified chromate solution. The variables studied were the nitrogen flow rate, the type of surfactant, and the surfactant concentration. It was found that an increase occurs in the solid-liquid mass transfer coefficient with increasing the nitrogen flow rate. Increasing the surfactant concentration was found to decrease the mass transfer coefficient. For a given surfactant concentration, it was found that Triton X-100 reduces the mass transfer coefficient more than sodium lauryl sulphate.
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  • 45
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    Chemical Engineering & Technology - CET 20 (1997), S. 118-130 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dynamic model is developed for a fluid catalytic cracking (FCC) unit to describe the dynamic behavior of both the riser and the regenerator reactors and their interactions. The cracking reactions are simulated by the four-lumped kinetic model [1]. The reactions in the riser occur in a transported bed with the fluid and the solids in ideal plug flow. The two-phase nature of the regenerator-fluidized bed is considered and the kinetic model for the coke combustion on the cracking catalyst [2,3] is incorporated. The proposed model is validated using steady-state plant data from an industrial unit and the results are found to be in good agreement. One of the main advantages of the model is that it does not include any partial differential equations. This facilitates the solution of the equations and makes the model particularly suitable for control studies. Simulation studies are performed to investigate the effect of changing various process variables, such as catalyst circulation rate, gas oil feed rate, and oxygen feed concentration.
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  • 46
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    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 47
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    Chemical Engineering & Technology - CET 20 (1997), S. 182-191 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The uncatalyzed esterification of acetic acid is described in the literature as a typical example of reactive distillation. Many rigorous models were validated using this esterification as an example. Process proposals for the production of pure ethyl acetate from ethanol and acetic acid have been determined using short-cut methods with the assumption of chemical equilibrium only. In this publication, the limitations of this esterification are clarified, using a rigorous model that was developed. The reasons why reactive distillation appears to be unfavorable for this esterification are explained. It is, however, theoretically possible to obtain ethyl acetate in high purity with different variants of the process. Different process variants are examined in this work. Construction variables that are important for the design of reactive columns, such as the number of reactive separation stages and the holdup in the column, are analyzed. Furthermore, the influence of variables dependent on the component system, such as the phase equilibrium of the reactive system and the reaction kinetics on the conversion in the column, are described. It can be shown that the short-cut methods published so far for reactive distillation, which assume chemical equilibrium, are inadequate.
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  • 48
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    Chemical Engineering & Technology - CET 20 (1997), S. 203-207 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Transient heat transfer in a mechanically agitated vessel is studied in the case of an anchor and an helical ribbon impeller using Newtonian and shear thinning fluids. Temperature stratification is found more pronounced with the anchor, making this impeller clearly inadequate for heat transfer. The impact of natural convection is evaluated first using the classical Gr/Re2 ratio. It is shown that the use of this criterion in viscous mixing is somewhat misleading. A new Grashof number is then proposed to assess the significance of the viscous and buoyancy effects in non-isothermal, non-Newtonian mixing applications. It is shown that the interpretation of this new number is strongly related to the concept of process viscosity.
    Additional Material: 6 Ill.
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  • 49
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    Chemical Engineering & Technology - CET 20 (1997), S. 240-246 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The rate of the homogenous exothermic hydrolysis reaction of acetic anhydride catalyzed by sulfric acid in solvent acetic acid was estimated from nonisothermal experimental batch reactor transient temperature data. Rate equations based on three different reaction mechanisms of hydrolysis published in the literature were fitted to the experimental rate data. The experimental results on runaway and limit cycle behavior obtained with this reaction were explained by using the mechanism-based rate equations for hydrolysis in the reactor dynamic models, and good agreement was obtained between the predicted and the experimental dynamic data.
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  • 50
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    Chemical Engineering & Technology - CET 20 (1997), S. 282-284 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 51
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    Chemical Engineering & Technology - CET 20 (1997), S. 268-276 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: As an alternative to the existing bioheat transfer models a new system of two energy equations is proposed by considering the human body as a deformable porous medium. One equation is developed for the blood and the other for the peripheral skeletal tissue. It includes such significant factors as the vascular geometry and size, the blood flow and direction, thermal diffusion and the local thermal nonequilibrium between the blood and peripheral tissue. Discussion and application of both equations are given.
    Additional Material: 5 Ill.
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  • 52
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    Chemical Engineering & Technology - CET 20 (1997), S. 285-286 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An ortho-experiment design and the analysis method of mathematical statistics are adopted to study the conversion of gypsum and potassium chloride to potassium sulfate in the system of K+, Ca2+, NH4+ ‖ Cl-, SO42- in H2O. Optimal reaction parameters and engineering mean are acquired to attain a conversion yield of potassium chloride of 94.52%.
    Additional Material: 2 Tab.
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  • 53
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    Chemical Engineering & Technology - CET 20 (1997), S. 297-303 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Electrochemical gas absorption or biotechnical purification processes using structured packing as electrode or as biological support, respectively, may operate in bubble columns in presence of suspended solids. In both systems the knowledge of mass transfer rates from the liquid to the packing is important for the design of equipment. In the present investigation, the fluid dynamic behavior of a simple bubble column and a bubble column containing small size particles, both in presence of structured packing, was studied. Furthermore, mass transfer coefficients between the liquid and the structured packing were obtained by the electrochemical method. The influence of physical properties of the liquid phase, gas flow rate, kind and concentration of the suspended particles on both gas holdup and mass transfer was investigated. Correlations of the experimental data of mass transfer using dimensionless groups were derived and compared to previous correlations. Similarity with a heat transfer expression already used in two-phase systems was found.
    Additional Material: 9 Ill.
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  • 54
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    Chemical Engineering & Technology - CET 20 (1997), S. 333-337 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The reaction of anisole hydroxylation with hydrogen peroxide to form methoxyphenols over TS-1 was studied. Four C1-C3 alcohols and the two aprotonic solvents acetone and acetonitrile were used. Product conversion was almost proportional to the titanium content of the catalyst sample. The highest conversion and p-selectivity were observed in ethanol. Some speculations, based on the formation of substrate-solvent or titanium-solvent-oxidant complexes, about the role of the solvent are presented. It was found that in all the solvents studied the p/o ratio increased with time.
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  • 55
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    Chemical Engineering & Technology - CET 20 (1997), S. 378-383 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Catalytic decontamination of waste gases in a fixed bed reactor, operating at non-steady state conditions achieved by periodic gas flow reversal, is simulated on the basis of a mathematical model. The opportunity to utilize a significant part of the reaction heat is discussed and the effect of catalyst inactivation upon reactor performance is analyzed. Stable temperature regime and conversion exceeding 99.5% could be ensured by a more than eightfold reduction of catalyst activity.
    Additional Material: 7 Ill.
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  • 56
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    Chemical Engineering & Technology - CET 20 (1997), S. 396-402 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A packed column has been used to study the absorption of nitrogen oxide in an alkaline solution of potassium permanganate. The reactions taking place during the absorption have been examined and the rate constants have been estimated from experimental data. The experiments show that potassium permanganate is an excellent absorbent for nitrogen oxide. However, to avoid formation of MnO2, the hydroxide concentration has to be very high, i.e. 〉 3 mol/l. It was found that the reaction could be expressed as first-order with respect to NO and with respect to KMnO4. The rate constant may be expressed in terms of the hydroxide concentration as follows: kmn = 6114.9 101.9208 10-4 CNaOH m3 mol-1 s-1.
    Additional Material: 8 Ill.
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  • 57
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    Chemical Engineering & Technology - CET 20 (1997), S. 424-428 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In paper coating make-down, a poor dispersion of pigments in coating colors may lead to coater runnability problems. This is manifested by coat defects at the paper surface, excessive coater blade wear, and an over-consumption of pigments. For this reason, high shear impellers operated at high speed are used, yielding a high energy consumption. A new method to disperse high solids mix at low energy consumption is presented. This method based on the use of a rod impeller scraping the fluid surface in the vessel, is tested on a slurry composed of calcined and delaminated clays up to a solids content of 66.7 wt.% without dispersing aids.
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  • 58
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    Chemical Engineering & Technology - CET 20 (1997), S. 445-454 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two different layouts for the liquid-liquid extraction section of an industrial caprolactam process are evaluated. Laboratory mass transfer measurements on streams obtained from an industrial and a demonstration plant with different extraction sections are interpreted by a model describing the effect of surface contaminants on mass transfer coefficients. Indications of the impact of these layouts on the complexity of the extraction section, quality of products and efficiency of the extraction processes are given.
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  • 59
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    Chemical Engineering & Technology - CET 20 (1997), S. 469-474 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Bubble columns are commonly used in industry for polluted gas treatment. Based on the same principle, the droplet column which is not widely known in the literature, uses much higher gas velocities, up to 14 m/s. This study concerns the hydrodynamics and mass transfer in this apparatus, in presence or absence of solid particles. Our results have demonstrated the impact of dusts on mass transfer performance giving rise to an increase in the kL aL coefficient with decreasing particle size. However, no influence of dust on the hydrodynamics of the column has been demonstrated within the studied particle size range.A study of liquid holdups obtained by three different methods is also carried out. Our results are comparable, thus validating the methods used.
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  • 60
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    Chemical Engineering & Technology - CET 20 (1997), S. 491-494 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experiments were carried out in a conventional circulating fluidised bed to measure the axial pressure profile and total pressure drop, which covered a wide range of operating conditions. Material belonging to the Geldart A (fine material) as well as the Geldart B (course material) categories have been used in the present work. Slip velocity is determined from the total pressure drop and noticed that the slip velocity is much higher than the free fall velocity of single particle for Geldart A type material, while it is approximately equal to the free fall velocity of single particle for the Geldart B type materials.A model is developed for slip velocity taking into account all the hindrance effects: particle-particle, and particle-wall, and particle agglomeration. Predictions of the present model are validated with the data due to present study and the data reported in the literature.
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  • 61
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    Chemical Engineering & Technology - CET 20 (1997), S. 502-509 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dust explosion hazard exists in plants and facilities wherever combustible dusts are hardled. Minimum explosible concentration of dust clouds is an important factor requiring special attention for hazard evaluation if any technological equipment is to be protected by inertisation. The mathematical models available for prediction of this parameter have been analysed for their application to organic dust clouds. Solution of the most general mode for determination of minimum explosible concentration of dust clouds proposed by Mitsui and Tanaka is presented, together with the comparison with experimental data. It has been found that the model is not successful in predicting the minimum explosible concentration for organic dusts. Recommendations on requirement of development of a new model for prediction of minimum explosible concentration of an organic dust such as polyethylen have been given.
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  • 62
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    Chemical Engineering & Technology - CET 20 (1997), S. 557-563 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Capillary viscometry is used to characterize viscosity, entrance pressure loss and apparent wall slip of paper coating colors at high shear rates. Special emphasis is laid on the dependence of these phenomena on solids content in order to account for changes in the rheology due to the dewatering of the color during the coating process. Coating colors with substantially different runnability have been investigated. Differences in apparent wall slip and high shear viscoelasticity (manifesting itself in extremely high entrance pressure losses) are observed at increased concentration, even if these phenomena do not show up at the initial solids content. Poor runnability is observed when viscosity, entrance pressure loss and wall slip increase strongly with increasing solids content. But all rheological features change simultaneously with the coating color recipe and it is not possible to separate out the contribution of the particular rheological features on the runnability of the coating colors or to correlate the runnability to a single rheological prorameter. Future work will have to focus on a numerical analysis of the blade coating process taking into account all the rheological features described here. First simulations including slip at the color/blade interface indicate that wall slip may cause severe runnability problems, at least when the apparent slip velocity exceeds the web velocity.
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  • 63
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    Chemical Engineering & Technology - CET 20 (1997), S. 581-581 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 64
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    Chemical Engineering & Technology - CET 20 (1997), S. 589-595 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: New data of gas-liquid mass transfer for cocurrent downflow through packed beds of non-porous particles are presented. Mass transfer parameters for air/carbon dioxide/water and air/carbon dioxide/sodium hydroxide systems were evaluated by least squares fit of the calculated CO2 concentration profiles in the gas phase to the experimental values. The dependence of kGa on gas and liquid flow rates is caused by the dependence of gas-liquid interfacial area, not by the gas-side mass transfer coefficient kG. In the case of the absorption of dilute carbon dioxide the gas-side resistance is considerably smaller than the liquid-side resistance. In the pulse flow regime, gas-liquid interfacial area calculated from kLa and kL values obtained by physical, respectively, chemical absorption are lower than the gas-liquid interfacial area evaluated from the measurements under reaction conditions.
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  • 65
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    Chemical Engineering & Technology - CET 20 (1997), S. 617-623 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Designing an appropriate methanol steam reformer requires detailed knowledge about the processes within such a reactor. Thus, the axial temperature and concentration gradients and catalyst ageing were investigated. It was found that for a fresh catalyst load, the catalyst located in the reactor entrance was most active during the experiment. The activity of this part of the catalyst bed decreased after some time of operation due to ageing. With further operation, the most active zone moved through the catalyst bed. From the results concerning hydrogen production and catalyst degradation, the necessary amount of catalyst for a mobile PEMFC-system can be estimated.
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  • 66
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    Chemical Engineering & Technology - CET 20 (1997), S. 633-640 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The size-dependent breeding of sodium chlorate crystals can be determined by carrying out experiments with seed crystals of optical antipodes of different sizes that undergo absolutely identical experimental conditions. Small portions of right- and left-handed seed crystals of different sizes were used. The number density distributions of the two opposite forms led to the total numbers of D- and L-crystals. The nucleation from different seed sizes under identical experimental conditions was found to be proportional to L4 in agreement with Clontz et al. [1] and Bennett et al. [2]. A computer program for the modelling of batch crystallization was used to calculate the development of the nucleation process. The data for the supersaturation course and for the development of the population of the right- and left-handed crystals are in good agreement with the experimental results. Only few generations (one or two) of secondary nucleation are being built during the process because of the strong influence of the size of crystals on the nucleation rate. The formation of two generations of secondary nuclei could be observed during three-hour batch crystallization runs.
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  • 67
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    Particle and Particle Systems Characterization 14 (1997), S. 283-289 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The influence of the surface roughness of solid conducting spheres on the response of a phase-Doppler anemometer (PDA) is described by using a ray theory model. A rough particle surface is modeled as an ensemble of distorted spheres. First- and second-order reflection and diffraction are considered for far-field calculations of the PDA phase difference. The numerical simulations are accompanied and supported by experimental results. Single rough Sn spheres are captured inside an electro-dynamic trap and investigated with a standard phase-Doppler system.
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  • 68
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    Particle and Particle Systems Characterization 14 (1997), S. 295-303 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new method is introduced to analyze the accuracy of phase-Doppler anemometry (PDA) for sizing large particles in two-phase flows. The method is based on Fourier optics theory (FOT) and geometrical optics theory (GOT) to calculate the intensity ratio of refractive and reflective light scattered by a sphere under a slit constraint. To examine the accuracy in calculating the light intensity, the results from the GOT method were compared with those of the direct simulation based on the generalized Lorenz-Mie theory (GLMT). This newly developed FOT/GOT method also predicts the results of phase jump due to the slit constraint. The performance of dual-mode phase-Doppler anemometry can also be simulated by this method.
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  • 69
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    Particle and Particle Systems Characterization 14 (1997), S. 290-294 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A compact and commercial aerosol generator capable of generating narrowly size-distributed aerosols with high mass concentrations was designed, fabricated and tested. The aerosol generator, consisting of a Delavan simplex nozzle (Model 30610-4), an L-shaped settling chamber and a virtual impactor with a clean air core, was modified and improved from Chein and Lundgren's work [20] to be more compact and readily commercial. The performance of the aerosol generator was evaluated using corn-oil, sodium chloride and uranine solutions. The results indicated that the cornoil droplets produced by the generator had a mass medium aerodynamic diameter (MMAD) of 7.20 ± 0.32 μm with a geometric standard deviation (GSD) of 1.48 ± 0.01 and the aerosol generation rate was 13.8 ± 1.3 mg/min. Solid aerosols generated from NaCl solution were found to have an MMAD in the range 1.39-4.88 μm with a GSD of 1.34-1.47 with the volumetric solution concentration varying from 0.1% to 9%. At the same time, the aerosol generation rate varied from 0.27 ± 0.05 to 15.8 ± 1.8 mg/min. depending on the solution concentration and the particle size produced. In addition, a 0.01% uraniane solution was tested to generate a submicron aerosol with an MMAD of 0.93 μm and a GSD of 1.48.
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  • 70
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    Particle and Particle Systems Characterization 14 (1997), S. 307-309 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 71
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    Particle and Particle Systems Characterization 14 (1997), S. 304-306 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 72
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    Chemical Engineering & Technology - CET 20 (1997), S. 93-100 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Distillation columns with multiple feeds are often used in processes for the separation of multicomponent mixtures. The minimum energy demand of such columns is determined via the minimum reflux and reboil, respectively.A novel method for directly calculating the minimum reflux ratio is presented in this paper. Applicable to ideal, nonideal and azeotropic mixtures the method is based merely on the knowledge of vapor-liquid equilibrium of the feed mixtures. This knowledge allows the determination of the internal concentration profile near the feed entry and, in turn, the calculation of both minimum reflux and optimal sequence of feeds. This sequence of feeds depends on feed compositions and product compositions, as well. Surprisingly, sometimes a multiple feed entry requires a higher energy demand than premixing the feed streams.
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  • 73
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    Chemical Engineering & Technology - CET 20 (1997), S. 131-137 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Hydrogenation of 10% aqueous solution of 3-hydroxypropanal (HPA) was adiabatically carried out over cylindrical Ni/SiO2/Al2O3-catalyst pellets (∅ 0.8 + 5 mm) in a trickle bed (∅ 76 × 5200 mm) at 2.6 to 8.0 MPa. The concentration and temperature profiles in the trickle-bed were measured at different flow rates of liquid. A mathematical model was developed under consideration of heat transfer, interphase mass transfer, intraparticle diffusion and deactivation of catalyst pellets at partial wetting with different wetting geometries. The model fits the measured data satisfactorily when its kinetics of deactivation is modified by a factor determined by regression of data measured in the trickle bed.
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  • 74
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    Chemical Engineering & Technology - CET 20 (1997), S. 171-181 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Hydrodynamic parameters have been determined in common equipment, i.e., same column and liquid and gas distributors, for cocurrent and countercurrent two-phase flow through fixed beds. The piston/dispersion exchange model (PDE) with usual Danckwerts' boundary conditions (closed/closed system) has been used to describe the liquid flow. A new imperfect pulse method has been used to estimate the PDE model parameters directly from the experimentally nonideal input and output response. The transition between trickle flow and pulse flow, for two-phase downflow, and the occurrence of flooding, for countercurrent flow, has been investigated using a macroscopic model for the two-phase flow.
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  • 75
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    Chemical Engineering & Technology - CET 20 (1997), S. 192-198 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two devices were developed, mechanical and electrical, to measure the mechanical power relative to superficial gas velocity and stirring speed in a mechanically agitated reactor. Two bubble regimes were demonstrated. The study of gas holdup, obtained from the residence time distribution, and the bubble size, determined by interfacial area measurement, confirm these two regimes of flow. Our results show that the gas holdup, the interfacial area, and the liquid-side mass transfer coefficient are increasing functions of the energy dissipated in the solution.
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  • 76
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    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 77
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    Chemical Engineering & Technology - CET 20 (1997), S. 230-239 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In this contribution, a new method is proposed for determining effective macropore diffusion coefficients in porous media by digitized microphotographs of porous support materials and random walk simulations. The method introduced allows calculation of the effective diffusion coefficient as a function of the mean free path length over a wide variety of values. A versatile method for the preparation of porous substances for light microscopy is described.The frequently applied model of an active shell, which is used to model particle/solid collisions, was found to give incorrect results in conjunction with the application of the first passage time algorithm, which was applied to save computing time in the simulation of gas diffusion. It was possible to show that more realistic results are obtained if a Knudsen layer is used to model particle/solid collisions. Furthermore, in investigating diffusion in two- and three-dimensional representations of capillary tubes, it was found that results of simulations performed to calculate transport properties of fluids in porous media, based on two-dimensional model systems, cannot in any case be transferred to the corresponding three-dimensional systems.
    Additional Material: 15 Ill.
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  • 78
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    Chemical Engineering & Technology - CET 20 (1997), S. 85-89 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A comparative study of reported theoretical and experimental investigations evaluating the numbers and sizes of bubbles emerging from submerged orifices reveals that the lack of consistency can be attributed largely to faulty experimental techniques. Errors are attributed to an inadequate knowledge of the influence of the surface properties of the solid and liquid media on the emission process and to the lack of standardization of the equipment geometries especially regarding the pressure chambers and orifice plates. The analyses provide guidance to designing standardized equipment to produce reproducible bubbles.
    Additional Material: 1 Ill.
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  • 79
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    Chemical Engineering & Technology - CET 20 (1997), S. 108-117 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: On the basis of the balance of forces acting on droplets falling down inside a co- or counter-current spray tower, a model of scrubber aerodynamic characteristics was developed. Relations between pressure drop caused by spray, droplet concentration and residence time distribution of the dispersed phase were found analytically for slurry droplet motion in the range of 400〈Re〈2500. The differences between the simplified model solutions and complete solutions are presented. The model was verified by the experimental data collected in two large pilot plant scrubbers applied for flue gas desulfurization (FGD).
    Additional Material: 14 Ill.
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  • 80
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    Chemical Engineering & Technology - CET 20 (1997), S. 138-143 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The gas-phase hydrogenation of buta-1,3-diene to but-1-ene, trans- and cis-but-2-ene and butane has been performed over 0.5% Pd/γ-Al2O3 catalyst. The reaction has been investigated at atmospheric pressure and 0°C over a wide range of conversions. The kinetic model based on the present day knowledge of reaction mechanism has been advanced. The parameters of the kinetic model have been estimated through statistical data fitting. The kinetic model provides a fairly good description of selectivity in the whole range of conversions.
    Additional Material: 4 Ill.
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  • 81
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    Chemical Engineering & Technology - CET 20 (1997), S. 149-161 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The following article concerns emulsification reaction in a continuous screw loop reactor. The influence of hydrodynamics on the emulsification process as well as the influence of some specific substances were examined. We produced oil/water model emulsions under different test conditions and we determined the correlations between the mixing behavior of the reactor and the characteristic features of the obtained emulsion. Special consideration was given to the droplet size and its distribution. Variable operating conditions of the reactor are the residence time and the rotational speed of the screw, both of which have a decisive influence on the recycle factor and the number of passages through the rotor/stator system. In addition we determined the dependence of the obtained droplet size distribution on the viscosity of the continuous and dispersed phase, on the interfacial surface tension and on the phase proportions. The influence of the specific type of emulsifying agent and its concentration has been examined as well. The positive effect of the mixing and of the recirculation on the emulsification in the screw loop reactor was particularly evident with low emulsifier concentrations and with emulsifiers with slow adsorption kinetics. The established theories for emulsion formation (Kolmogoroff, Taylor) were used for a quantitative description of the experimental results. The screw loop reactor was compared to an agitated tank reactor and a toothed-ring dispersing machine (Ultra Turrax) based on the comminution energy which is produced per unit volume of emulsion. The agitated tank reactor produced only coarsely dispersed emulsions through the entire rotational speed range, wheras the screw loop reactor and the Ultra Turrax, particularly at high rotational speeds and, therefore, high power densities, showed a similar emulsification and produced much finer dispersed emulsions.
    Additional Material: 18 Ill.
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  • 82
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    Chemical Engineering & Technology - CET 20 (1997), S. 208-211 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The results of a process analysis and an experimental exploratory study of supercritical water oxidation (SCWO) show that elements of combustion technology are suitable to overcome the technical problems of SCWO. The Film Cooled Hydrothermal Burner (FCHB) which operates at 25 MPa up to 2000 K in the reaction zone keeping wall temperature under stress at 300 to 400 K shows further development potential of the Wallcooled Hydrothermal Burner (WHB) concept for SCWO, a still promising waste treatment process.
    Additional Material: 6 Ill.
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  • 83
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    Chemical Engineering & Technology - CET 20 (1997), S. 576-580 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper presents a fuzzy control system for electroplating of gold which was developed to solve the problems of non-linearity and to overcome difficulties in establishing a mathematical model of the pH of the industrial gold electroplating process. Operating results show that the fuzzy controller effectively counteracts the non-linearity of the plant.
    Additional Material: 7 Ill.
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  • 84
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    Chemical Engineering & Technology - CET 20 (1997), S. 606-611 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Based on experiments, this paper describes that the vibration energy imported to a packed bed is through the collision between the vibration plate and the bed, and the vibration energy imported to a fluidized bed is through continuous wave propagation. A new type sensor was used to measure the wave signals in VFB. The wave characteristics are affected by bed properties. By analyzing the wave frequency spectrum, the bubble's behavior in the bed can be followed.
    Additional Material: 10 Ill.
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  • 85
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 86
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    Chemical Engineering & Technology - CET 20 (1997), S. 371-377 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fluctuation solution theory relates thermodynamics partial derivatives to integrals of molecular direct correlation functions from statistical mechanics. This paper describes an application of that theory for correlating and predicting solubilities of light gases in heavy n-paraffins. Two of the solvents are complex waxes. Equations from the theory represent the liquid phase, and additional hypothesis are adopted to build a model for the high pressure vapor-liquid equilibrium. In the correlation mode, the model, based in the fluctuation solution theory, produces a molar fraction of the gas in the liquid phase with an average absolute relative deviation under 3% in a large number of cases. In the prediction mode, when binary parameters are used, errors are on the order of 10%. Overall for n-paraffins solvents, the model presented in this paper shows a good capacity to correlate experimental solubility and an adequate power to extrapolate lower pressure data when a binary parameter value has been chosen.
    Additional Material: 6 Ill.
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  • 87
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    Chemical Engineering & Technology - CET 20 (1997), S. 391-395 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The H2O2 concentration for the nonlinear process of the iron-catalysed hydrogen peroxide decomposition in a continuous stirred tank reactor is estimated using a time-variant Extended Luenberger-Observer. The asymptotic stability of the observer, designed by adequate pole-placement, is demonstratéd by simulation and comparison of the transient behavior of the estimated concentration profiles with those of the nonlinear system. Comparison with measured H2O2 concentrations indicates satisfactory observer dynamics and accuracy with respect to a lower stationary state of the nonlinear process.
    Additional Material: 5 Ill.
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  • 88
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    Chemical Engineering & Technology - CET 20 (1997), S. 419-423 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: By applying the macroscopic conservation laws to a simplified jet downstream from a sudden enlargement, a new correlation of the two-phase subcritical pressure recovery is obtained. Comparisons with the set of existing data (air-water and steam-water subcritical flows) show that the predictions obtained by means of this formula are more accurate than the ones given by available analytical models. The proposed correlation presents an important improvement of the pressure recovery predictions in the case of small mass velocities. However, it can not be applied in the conditions of quality too close to one.
    Additional Material: 6 Ill.
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  • 89
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    Chemical Engineering & Technology - CET 20 (1997), S. 435-444 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes how gain scheduling control is applied to a continuous stirred tank reactor model. The CSTR process, equipped with a cooling system, is modelled. Based on the resulting nonlinear model, a gain scheduling controller is designed. The gain scheduling follows a scheme denoted bias compensation. Compared to earlier reported gain scheduling schemes, the proposed scheme results in a controller that is less complex, which is advantageous in the controller implementation stage. Numerous simulations are performed, using the gain scheduling controller and two choices of control input to the reactor model. The simulation results indicate that a gain scheduling controller performs better than a linear controller. Simulations using different choices of control input to the reactor model indicate that proper process design is crucial for the controlled process performance.
    Additional Material: 9 Ill.
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  • 90
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    Chemical Engineering & Technology - CET 20 (1997), S. 475-477 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simple and new model for the prediction of drop velocity as a function of dispersed phase volume fraction has been proposed on the basis of experimental knowledge of onset time of complete separation between two phases as function of the initial hold-up.
    Additional Material: 1 Ill.
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  • 91
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    Chemical Engineering & Technology - CET 20 (1997), S. 478-484 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two important structural factors that affect distillation efficiencies, the outlet weir heigh and the liquid flowpath length, are investigated. Performance and efficiency data of an industrial scale i-butane/n-butane distillation column equipped with two-pass trays are used as a basis for the calculations. A mathematical development for a new method for predicting the numbers of vapor and liquid phase transfer units is given. This method together with some other NTU calculation methods is used to assess the effect of the outlet weir height on efficiencies. The effect of outlet weir height on the Murphree tray efficiencies is investigated using the observed point efficiencies and different point efficiency to the Murphree tray efficiency relation methods. The effect of varying liquid flowpath lengths on efficiencies is studied by calculating the Murphree tray efficiencies for one-pass and two-pass trays. The results obtained using the NTU calculation method presented in this study show that a certain outlet weir height point efficiency reaches its maximum. Most of the other methods give opposite results giving a minimum for point efficiency at a certain outlet weir length. The results also show that the Murphree tray efficiencies for one-pass trays are higher than for two-pass trays. Obviously, this is caused by the longer liquid flowpath length of one-pass trays. The Murphree tray efficiencies are also calculated for an industrial-scale MTBE purification column. The column is equipped with two-pass trays in the stripping section and with one-pass trays in the rectifying section. The Murphree tray efficiencies of one-pass trays are considerably higher than the two-pass tray Murphree tray efficiencies.
    Additional Material: 5 Ill.
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  • 92
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 20 (1997) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 93
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    Chemical Engineering & Technology - CET 20 (1997), S. 571-575 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For a specific combustion problem involving calculations of several species at equilibrium, it is much simpler to write a special computer program and calculate the concentrations, rather than to use a generalized computer program. To calculate these concentrations, one must solve a set of non-linear algebraic equations. This work describes a procedure in which the Newton-Raphson method and the successive substitution method are combined. It is was found that for these types of problems the value of unknowns and the nature of the equations are such that by adopting the two procedures simultaneously a much faster and reliable convergence is achieved. This study also shows what possible species should be considered for these calculations.
    Additional Material: 4 Ill.
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  • 94
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    Chemical Engineering & Technology - CET 20 (1997), S. 10-16 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The performance of an upflow packed-bed biofilm reactor has been analyzed under dual substrate limitation conditions. The numerical solution of the proposed equations defining the system has been obtained for a wide range of operating conditions for a case of practical significance involving glucose and oxygen as dual substrates. The results show that the inlet glucose concentration defines the limiting substrate at a position near the inlet of the reactor. For inlet glucose concentrations up to 300 mg/l, glucose acts as the limiting substrate. However, for inlet concentrations of 400 mg/l of glucose or higher, oxygen assumes the role of the limiting substrate at that position. For all other positions in the reactor, glucose acts as the limiting substrate, irrespective of its inlet concentration. Extensive computations were performed in order to define regions where glucose, oxygen or both are limiting. The predicted results have been found to be in agreement with the theoretical criteria, proposed in the literature, of determining the limiting substrate.
    Additional Material: 8 Ill.
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  • 95
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    Chemical Engineering & Technology - CET 20 (1997), S. 36-39 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In order to reduce the B2O3 content in sintered magnesium oxide as much as possible, in precipitation with 80% of the stoichiometric quantity of dolomite lime, the effect of the pH of the agent used for rinsing the magnesium hydroxide precipitate was examined, as well as the effect of mannitol in sea water before precipitation. Mannitol binds orthoboric acid present in sea water into a weakly dissociated complex acid HB(OC)4. Experiments have shown that the B2O3 content in the sintered magnesium oxide samples is satisfactorily low. The lowest B2O3 content is obtained when mannitol is added; no B2O3 was found in these samples after sintering. Magnesium oxide samples were sintered at 1500°C; duration of isothemal sintering was one hour. Values for density and porosity of individually sintered samples are listed. The ratio CaO/SiO2 indicates that forsterite (Mg2SiO4), monticellite (CaMgSiO4) and mervinite (Ca3MgSi2O8) are formed during sintering of the samples.
    Additional Material: 1 Ill.
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  • 96
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    Chemical Engineering & Technology - CET 20 (1997), S. 53-62 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The minimum ignition temperature of dust clouds is one of the important factors required for the design of preventive measures against dust explosion. The mathematical models available to predict this parameter have been analyzed for thier application to organic dust clouds. A solution of the most general model proposed by Mitsui and Tanaka is presented, together with its comparision with experimental data. It has been found to be quite successful in predicting the minimum ignition temperature for metal dusts but not for organic dusts. Recommendations for the development of a new model to predict the minimum ignition temperature of an organic dust, such as polyethylene, have been given.
    Additional Material: 12 Ill.
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  • 97
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    Chemical Engineering & Technology - CET 20 (1997), S. 76-84 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: During recent years in chemical engineering processes for instance with aerated stirred tanks containing surface-active components foams and their mechanical control have become very important. However, there are still no rules for calculating mechanical foam breakers. As a contribution to foam control the present paper discusses the fundamentals of foam breaking by means of foam densities and gives a physical model for the mechanisms of a mechanical foam breaker when the main breaking effect is based on impact. The mechanisms were proved by measuring pressures in a foam breaker box. Diameters of secondary foam bubbles produced by foam breakers are calculated and discussed. Experimental investigations were made with different surfactants in aqueous solutions. The paper points out their influence on the process of foam breaking.
    Additional Material: 17 Ill.
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  • 98
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    Chemical Engineering & Technology - CET 20 (1997), S. 101-107 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A vapor pressure calculation procedure based on a lattice equation is applied to several compounds. Originally, the method was used to predict low vapor pressures of heavy hydrocarbons. In this work, the method is used at low vapor pressure for nonhydrocarbons, and a modified version is employed at high vapor pressure for n-alkanes. As the procedures require the knowledge of one vapor pressure datum only, they work in a predictive mode. Prediction for hydrocarbons is good and for nonhydrocarbons is poor. Prediction of n-alkanes high vapor pressure is good with an overall average relative absolute deviation under 6 percent.
    Additional Material: 5 Ill.
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  • 99
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    Chemical Engineering & Technology - CET 20 (1997), S. 144-148 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics of the liquid phase hydrogenation of 4-tert-butylphenol to form cis- and trans- 4-tert-butylcyclohexanol at 1.0-10.0 MPa and 40°C in isopropanol over a Rh catalyst has been studied. The kinetic behavior of this parallel system is described by a proposed reaction network. Keto-enol tautomeric transformation of adsorbed 4-tert-butyltetrahydrophenol and 4-tert-butylcyclohexanone is thought to be a key step, which governs the stereoselectivity of the overall complex reaction of alkylphenol hydrogenation.
    Additional Material: 4 Ill.
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  • 100
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    Chemical Engineering & Technology - CET 20 (1997), S. 162-170 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The performance of an upflow packed-bed biofilm reactor has been analyzed under multisubstrate limitation by considering simultaneous carbon oxidation and nitrification reactions. The fasting shock load of inlet methanol concentration has a much more pronounced effect on the response of the system compared to that of inlet NH4+ -nitrogen concentration. The exit concentration of NH4+ -nitrogen drops very close to zero, thereby showing essentially complete nitrification during methanol fasting condition. Further, the concentration profiles of oxygen within the biofilm show significant variation during methanol fasting and nonfasting conditions whereas during NH4+ -nitrogen fasting conditions the oxygen concentration profile in the biofilm remains essentially unaffected.
    Additional Material: 6 Ill.
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