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
c...
