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Nonlinear kinetics of oxygen and nitrogen sorption on carbon molecular sieves

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Abstract

Equilibrium and kinetics of oxygen and nitrogen sorption in two different carbon molecular sieves (CMS) have been modeled. In both CMS materials, equilibrium characteristics are adequately described by the Langmuir model. However, for kinetics of sorption, one CMS followed classic Fickian diffusion, while the other sample did not. A mathematical model was developed which accurately describes both pure component as well as binary uptakes in both materials. Simple manipulation of the boundary condition of the diffusion process allows the model to accurately predict both Fickian and surface barrier diffusion. All parameters needed to estimate binary uptake rates are obtained from pure component uptakes and isotherms. In addition, the model predicts both pure component and binary diffusion rates with diffusion coefficients which are not concentration dependent.

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Abbreviations

b,b 0 :

Constants in Langmuir isotherm [1/atm]

Bi :

Dimensionless parameter of H-844 CMS

C p :

Heat capacity of the pellet [kJ/kg °C]

D :

Diffusion coefficient [M2/sec]

E :

Activation energy [kJ/mole]

j, j,16-1 J16-2 :

Moles flow in the pellet [mole · m/kg · sec]

N,N (−),N (+) :

Moles concentration in the pellet [mole/kg]

P :

Pressure [atm]

q :

Dimensionless parameter of non-isothermal sorption

q :

Isosteric heat of adsorption [kJ/mole]

r :

Dimension coordinate

R :

Gas constant, 8.314 [kJ/mole °C]

R p :

Linear size of the pellet [m]

S n :

Roots of Eqs. (19) and (22)

T,T (−),T (+) :

Temperature [°C]

t :

Time

V d,V s :

Volumes of dosing and sample vessels

x :

Oxygen mole fraction

m :

Langmuir saturation capacity [mole/kg]

α :

Coefficient of heat transfer [kJ/m2 sec °C]

ß, γ :

Dimensionless parameters of non-isothermal sorption

ν :

Kinetic coefficient [1/sec]

ψ (−),ψ (+) :

Probabilities of a “jump” from one adsorption site to another adsorption site [1/sec]

λ :

Characteristic length between adsorption sites [m]

λ :

Thermal conductivity of CMS pellet [dg/m sec °C]

ρ p :

Density of the pellet [kg/m3]

τ :

Non-dimensional time,tD/R 2p

η :

Non-dimensional coordinate,r/R p

i :

Variable with this index corresponds to i-component

1:

Variable with this index corresponds to first component in binary mixture (O2 for mixture of oxygen and nitrogen)

2:

Variable with this index corresponds to second component in binary mixture (N2 for mixture of oxygen and nitrogen)

eq:

Equilibrium value of the variable indexed

0, in:

Initial value of the variable indexed : Dimensionless variable

p :

Variable with this index corresponds to one averaged over the pellet bulk at timet.

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Authors and Affiliations

  1. Russian Academy of Sciences, Siberian Branch, Institute of Thermophysics, Novosibirsk, Russia

    Y. Y. Trifonov

  2. Air Products and Chemicals, Inc., 18195, Allentown, PA

    T. C. Golden

Authors
  1. Y. Y. Trifonov
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  2. T. C. Golden
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Trifonov, Y.Y., Golden, T.C. Nonlinear kinetics of oxygen and nitrogen sorption on carbon molecular sieves. J Porous Mater 3, 5–16 (1996). https://doi.org/10.1007/BF01135356

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  • DOI: https://doi.org/10.1007/BF01135356

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