Experiment and Simulation Study of Multi-component Gas Adsorption On MSC3A By Volumetric method Kazuyuki. Chihara, Shohei. Koide, Masashi Nomoto, Yuzo. Amari, Meiji University,Kawasaki,Japan Abstruct Equilibria and rates of adsorption of carbon dioxide (CO 2 ), methane (CH 4 ),Nitrogen (N 2 ) and binary CO 2 -CH 4 -N 2 mixtures into molecular sieving carbon 3A, which had been used for air separation to get carbon dioxide, were studied by the volumetric technique. Equilibrium of single component was correlated by Langmuir or Toth equation. Equilibrium of binary gas mixture was expressed by Markham-Benton or IAS correlation. Kinetics of single component was analyzed by fitting with theoretical curves. Kinetics of binary gas mixture was studied by computer simulation. Introduction MSC (Molecular Sieving Carbon) has slit like micropores, which separate different size molecules by molecule s different diffusivity. In this study, the adsorption experiment was conducted by the volumetric technique. MSC 3A (KURARAY CHEMICAL CO., LTD) was used as adsorbent at 303K, 313K and 323K. Experimental adsorption of binary mixtures was compared with the simulation using the data obtained in equilibria and rates of adsorption of the single component. The characteristic value of MSC was shown in Table1. 2.1Experimental Method The experimental apparatus was shown in figure1. The apparatus was similar to Volumetric method. MSC (Molecular Sieving Carbon) has slit like micropores, which separate different size molecules by molecule s different diffusivity. In this study, the adsorption experiment was conducted by the volumetric technique. MSC 3A (KURARAY CHEMICAL CO., LTD) was used as adsorbent at 303K, 313K and 323K. Experimental adsorption of binary mixtures was compared with the simulation using the data obtained in equilibria and rates of adsorption of the single component.
2.2 Study on gas phase adsorption by a volumetric method. Equilibria and rates of adsorption of nitrogen, methane and binary N 2 -CH 4 mixtures into molecular sieving carbon(msc3a) were studied by the volumetric method. Micropore diffusion, mass transfer coefficient are obtained by making an ideal curve and curve fitting of the pressure change about the analysis of the adsorption rate. 2.3Stop & Go Simulation Numerical solution for multi component chromatogram in time domain could be obtained by appropriate model equations with experimental conditions. This simulated chromatogram can be compared with experimental chromatogram to determine the equilibrium and the adsorption kinetic parameters. Here Markham-Benton equation as for adsorption equilibrium and linear driving force (LDF) approximation as for adsorption kinetics were adapted for numerical calculation, which was based on stop & go method (Chihara et al. 1986, Chihara and Kondo 1986). In particular, LDF model of adsorption kinetics was based on non-equilibrium thermodynamics. For binary adsorbates, adsorption rate equations are q t γ 1 = Ksav ( q q ) + Ksav ( q * q ) (1) 2 1,1 1 * 1 1, q γ = Ksav2,1( q1 * q1) + Ksav2,2( q2 * q2) t (2) where Ksav= Overall mass transfer coefficients. Overall mass transfer coefficients (Ksav) for LDF model were determined. Then,
micropore diffusivities were obtained by subtracting other mass transfer effects from overall resistance ( /Ksav). Thus obtained micropore diffusivities were correlated with chemical potential driving force by consideration of Fick s diffusion equation, non-equilibrium thermodynamics and extended Langmuir equation (Karger and Bulows 1975). D ' ln ' 1 θ = D p = D a a q a 11 1 1 1 2 ln 1 1 θ1 θ2 D D ' q ln p D ' (3) 12 1 1 1 1 1 = = a a q2 ln q2 a 1 θ1 θ2 θ (4) D ' ln ' = D q p = D a a q q a 21 2 2 1 ln 1 1 θ1 θ2 θ D D ' ln p D ' 1 θ (5) 2 2 1 = = a a ln q2 a 1 θ1 θ2 (6) For instance, Ksav is related to D in single adsorbate case as 2 2 1 a R R = + K * + (7) Ksav 15D 3k f 15εD a For binary case, when using Equation (15), apparent K* could be determined by appropriate slope of adsorption isothermal plane at perturbation point. 3.Result And Discussion Equiblibria for single component Showed adsorbent of MSC3A, 303.15K,313.15K, 323.15K, adsorption isotherm of the CO 2,CH 4 and N 2 in Fig2. From fig2, quantity of adsorption increase as temperature is low. It is thought that this is because adsorption is a fever process. (a)methane
(b)carbon dioxide (c) nitrogen Figure2 (a) Adsorption isotherm(ch 4 ),(b)adsorption isotherm(co 2 ) Table2 The value of the parameters of Langmuir and Toth equation were shown in Table 2
Kinetics for single component Below of the pressure decayon the course of adsorption ( CO 2 and CH 4 ) in 313.15K. As column temperature rose, it becomes early that temperature dependence occurs and reaches the adsorption equilibrium. CO 2 is the number when comparaed by gas distinction, but adsorption speed is earlier than CH 4. It is thought that adsorption speed of the big CH4 of the molecular diameter becomes slow to provide molecular sieve in a micro-aperture diffusion limited access of MSC3A. (a) (b) Figure3 (a) Pressure decay(ch 4 ) course of adsorption (b) Pressure decay(co 2 ) on the Kinetics of single component was analyzed by curve fitting the pressure decay on the course of adsorption with the theoretical curves, to get k s a p, D/a 2 and K s a p, which means micropore mouth mass transfer coefficient, micropore diffusivity and over all mass transfer coefficient, respectively. A graph of fitting with theoretical curves was shown in Figure 4 as example. The dependencies of K s a p on amount adsorbed were shown in Figure 5-(a) and (b). As quantity of adsorption increased K s a p in CH4, CO2, a tendency to increase together was obtained.
(a) (b) 4.Conclusion When I think that the data by the single ingredient experiment are used by the multicomponent experiment, in getting reproducibility having higher precision by a single ingredient experiment, it is supposed that the accurate simulation of the multicomponent experiment is provided. References Chihara K. et al; Simulation of Pressure Swing Adsorption for Air Separation Proc. 7 th Int. zeolite Conf.,563(1986) Chihara K. and Kondo A.; Simulation of Pressure Swing Adsorption Three Gas Components and Three Adsorption Columns- 2 nd FOA, 165 (1986) Karger J. and Bulows M.; Chem. Eng. Sci., 30, 893(1975) Kumar R., Duncan R.C. and Ruthven D.M.; A Chromatographic Study of Diffusion of Single Components and Binary Mixtures of Gases in 4A and 5A Zeolites Can.J.Chem.Eng., 57, 342 (1982) Ruthven D.M,; Principle of Adsorption and Adsorption Process Wiley, 146 (1984)