Simulation of transient adsorption in MFI films

The ability of zeolites to adsorb many gases is an important application for such a ceramic material. Specific channel size enables zeolites to act as molecular gas sieves and selectively adsorb such gases as Xylenes and carbon dioxide. Zeolites have the potential of providing precise and specific separation of gases where applied in conjunction with properly engineered systems. Due to the heat effects on adsorption, nonisothermal kinetics may have to be used for the evaluation of diffusivities from rate of sorption measurements. A general analytical solution is derived, taking into account both the thermal conductivity within the adsorbent and the heat exchange with the surroundings. In this work a simulation for the transient adsorption of CO2 (and others molecules) in thin MFI films has been performed. Combined heat and mass transfer problem is modelled and simulated using the software packet MATLAB® (MATrix LABoratory). Mass transfer is described by micropore diffusion, while heat transfer is described in terms of conduction and convection. The temperature dependence of the diffusion coefficient, as well as the Henry law constant, is defined by an Arrhenius relationship. It was found that for a high diffusion coefficient, the assumption of isothermal conditions was not a realistic model. Since the adsorption is extremely quick, heat generated inside the adsorbent cannot be easily exchanged with the surroundings in sufficient rate yielding an increase in the temperature. On the other hand, for a low diffusion coefficient, the time required to reach the maximum amount of the component is high and thus is relatively easy to exchange the heat formed during the adsorption with the surroundings. In that case, it is obvious that the temperature within the solid will remain almost constant and it can be consider as isothermal system. It is also known that CO2 has a high diffusion coefficient. It will be appropriate to use a nonisothermal system. On the other hand, p-Xylene and isomers have lower diffusion coefficients. By comparing plots for each component, it will be made that topic clear.Validerat; 20101217 (root