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  • Chemistry  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Reaction rates in fractal vs. uniform catalysts with linear and nonlinear kinetics (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1691-1699 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pore fractal objects are expected to be optimal catalysts, since material is supplied to the narrower pores, which are also shorter through the larger pores where diffusion resistance is smaller. To demonstrate this, diffusion and reaction were simulated on Sierpinski-gasket-type fractal objects and on the corresponding nonfractal uniform-pore structures of the same size, porosity and reactive area. Positive order reactions limited by Knudsen diffusion were shown to exhibit larger rates in fractal than in uniform-pore objects. Fractal catalysts also exhibited a new intermediate domain in which the rate depends only weakly on the kinetics parameters. In nonmonotomic kinetics the branching point (bifurcation point) was extremely sensitive to the pore structure.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430706
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  • 2
    Electronic Resource
    Electronic Resource
    Mass transfer studies using cloned-luminous strain of Xanthomonas campestris (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 34 (1989), S. 671-680 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Measurements of mass transfer in a highly viscous pseudoplastic broth, which is typical to Xanthomonas campestris fermentations, are difficult to obtain by conventional methods and little data is available. A novel research method that uses bioluminescence for mass transfer studies has been developed. A plasmid carrying the luminescence operon of marine luminous bacteria is introduced into an industrial bacteria, X. campestris. Besides producing the polysaccharide xanthangum, the bioluminescent X. campestris emits measurable light. Monitoring the luminescence is a simple, noncontaminating nondestructive and very sensitive indicator of the metabolic activity of the culture during fermentation. Energy drain due to bioluminescence is very low; growth rate and polysaccharide production rate are close to those of the wild-type strain.Oxygen and substrate mass transfer are determined by inducing step or periodic fluctuations in their concentration and measuring the resultant luminescence response. Oxygen mass transfer coefficients show linear dependence on Reynolds number and an exponential dependence on the average shear rate. Viscosity effect is small at high viscosities but increases rapidly below 10 Pa-s. The influence of oxygen uptake rate is studied.Mass transfer of the limiting component (ammonium ions) is analyzed under pulsating feed conditions. The luminescence declines, following a feed pulse, due to energy investment in active transport of ammonium ions through the cell membrane, it regenerates then to its baseline. The relation between mass transfer and luminescence fluctuation is elucidated.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260340511
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of polymer synthesis rates during steady-state growth of X. campestris (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 37 (1991), S. 383-385 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260370413
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  • 4
    Electronic Resource
    Electronic Resource
    Methods of deterministic chaos applied to the flow of thin wavy films (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 481-489 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The structure of thin, wavy falling films was studied to evaluate whether the random-appearing wave structure is a result of deterministic chaos or a purely stochastic process. The time-varying film thickness was obtained at different spatial locations near the point of wave inception for flow rates in the range of Re=3-10. Under all conditions the wave structure was aperiodic in nature and displayed none of the known transitions to chaos. However, the power spectra followed an exponential decay law at high frequencies that is characteristic of chaotic systems. The estimated attractor dimension, used to characterize the complexity of a chaotic system, was much higher than those of known model chaotic systems. It is demonstrated that these high values could be explained due to small levels of noise present in experimental situations. Since experimental data are seldom noise free, a basic limitation in applying these methods to experimental measurements is demonstrated.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370402
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of commensalistic systems with self- and cross-inhibition (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 22 (1980), S. 2557-2577 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Up to three stable steady states are possible in a simple commensalistic system, taking place in an open-loop mixed reactor when the growth rates of the two species are inhibited by the substrates they prey on (Self-inhibition). Two stable states are possible in a system with noncompetitive inhibition of the species by the substrate they are not preying on (cross-inhibition). A large number of steady states as well as oscillatory states are possible when both self- and cross-inhibition are strong. Multiplicity of steady states is also possible in a reactor with biomas recirculation for these kinetics. Yet, the latter is more stable than the open-loop reactor in the sense that the domain of steady-state multiplicity is narrower. The stability of steady states and the dynamics of the systems for each of the investigated kinetics are summarized in a qualitative phase plane. The importance of the analysis for improving the selectively and yield of the system and for predicting the response of the system to changes in the operating conditions, is discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260221206
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  • 6
    Electronic Resource
    Electronic Resource
    Role of exocellular polymer in the design of activated sludge (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 28 (1986), S. 1564-1576 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This research is aimed at understanding the reactor-settler interaction. The reactor operating conditions affect the sludge-settling properties due to (a) production of exocellular polymer that serves as a flocculant in the settler and (b) population shift from flocculating bacteria to filamentous microorganisms that do not settle. A structured kinetic model that accounts for stored substrate and production of polymers, biomass, and inerts was constructed and applied to various open and closed reactor configurations. It is based on our observation that, in a batch reactor, the polymer is produced during endogenous respiration. The model describes well the observed temporal variation in substrate, biomass, and polymer concentration. Application of the model to continuous operation predicts increasing polymer concentration with sludge age, which is in good agreement with one study in the literature. Our study in a once-through reactor, as well as others, suggests an inverse dependence. The difference is probably due to different operating modes. Our study confirmed the role of the polymer in the sedimentation process. Under some conditions, however, a slow population shift to filamentous growth becomes the dominant factor.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260281015
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  • 7
    Electronic Resource
    Electronic Resource
    Steady state analysis of a continuous clarifier-thickener system (1986)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 32 (1986), S. 1516-1525 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Kynch's theory of sedimentation is adopted to solve for the attainable steady state concentration in a vertical continuous sedimentation basin incorporating a thickener and a clarifier. The limiting flux solution corresponding to the local minimum at the flux concentration curve is proved to have a limited range of validity and is shown to apply only to the intermediate range of feed concentrations. This limit is replaced by a five-region diagram; the solution is determined by the feed coordinates in the flux concentration plane, with respect to the flux concentration curve. Each section exhibits different characteristic solutions for both the clarifier and the thickener.The analysis, which combines dispersion, dynamics, and stability considerations, reveals new possible ranges of operating conditions where the flux exceeds the limiting flux and solids are not entrained. The results, contradicting previous published work, are verified by a finite-difference dynamic simulator.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690320912
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  • 8
    Electronic Resource
    Electronic Resource
    Phase plane and bifurcation analysis of thin wavy films under shear (1989)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 177-186 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A long-wave equation for film thickness as a function of position is derived for a general case incorporating viscous, surface tension, and interfacial shear effects. The derivation considers both the parabolic and the power-law velocity profiles. The analysis is aimed at revealing the wave velocity that induces infinitely long (homoclinic) periods as well as substrate thickness and wave peak amplitude. Phase plane analysis shows that at Re ≫ 1, due to time-scale separation, the homoclinic velocity is near that at the Hopf bifurcation. That enables analytical derivation of the wave characteristics.Comparison with experimental results in the range of Re-310-3, 100 with countercurrent gas flow, shows encouraging agreement. At very high Re the wave velocity suggests the onset of turbulence, in agreement with theory. Phase plane analysis predicts also that the wave shape consists of a simple peak with a steep front, with short waves riding on the main wave at low Re.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690350202
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  • 9
    Electronic Resource
    Electronic Resource
    Oscillatory states in the oxidation of carbon-monoxide on platinum (1981)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 27 (1981), S. 20-25 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The trend observed on variation of the operating conditions during CO oxidation on platinum in a CSTR is as follows: stable states → simple oscillations → multipeak oscillations → stable states. Analysis of the experimental results indicates that a third or higher order system of differential equations is necessary to describe most of the observations.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690270105
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