(93h) Comparison of Experimental and Predicted Adsorption Isotherms of Mixtures

Comparison of experimental and predicted adsorption
isotherms of mixtures

Julian Butz,
Sabine Enders

Karlsruhe Institute of Technology, Institute of Technical
Thermodynamics and Refrigeration Engineering, Engler-Bunte-Ring 21, D-76131 Karlsruhe,
Germany.

Email: julian.butz@kit.edu;
sabine.enders@kit.edu

Key words: adsorption
isotherms of mixtures, prediction

Abstract:

Multicomponent
substances who build close-boiling system are a huge challenge for the separation
through distillation. In such systems adsorption often is a lucrative
separation alternative. The foundation for a good estimation of the outcome of
the adsorption process is the adsorption equilibrium which can be described via
adsorption isotherms. Unfortunately, measurements of adsorption isotherm for
mixtures are still seldom while the measurement of pure component adsorption
isotherms are a common but tedious method. Because of that it is suitable to
predict the mixtures adsorption isotherms from only one adsorption isotherm for
each pure component. The density functional approach [1] in combination with an
convenient equation of state gives an excellent opportunity to do so. The
solid-liquid interactions are modelled with a Steele 10-4-3 potential [2] in a slit
pore while the liquid-liquid interactions are modelled with the PC-SAFT
equation of state [3]. While the parameters of the PC-SAFT EOS for a lot pure
components are listed in the literature [3] the parameters of the energy
parameters of the Steele potential and the geometry parameters of the slit pore
must be extracted from all pure component adsorption isotherms at one
temperature. In terms of parameters this means one interaction solid-fluid
energy parameter for every component ε_sf,i one interaction distance
for the adsorbent σ_ss, the mean pore width H as well as the
mean pore volume V_p. For a pure component system that are 4
parameters while a ternary system needs 6 parameters. Having these parameters
fitted to the pure components it is now possible to examine broad parameter
studies. For the case of a varying feed composition in the adsorption process
it is possible to pretend the adsorption isotherms for the possible feed
configurations. Furthermore, a prediction of adsorption for temperatures yields
a good opportunity to choose a good process window. It was found that a
comparison to experimental multicomponent adsorption data [4] at different
temperatures yields a very good compliance to the calculated predictions.

[1] C. Lastoskie, K.E.
Gubbins, N. Quirke, J. Phys. Chem. 97 (1993) 4786.

[2] W.A. Steele, Surf.
Sci. 36 (1973) 317.

[3] J. Gross, G.
Sadowski, Ind. Eng. Chem. Res 40 (2001) 1244.

[4] R. Reich, W. T.
Ziegler, K.A. Rogers, Ind. Eng. Chem. Process Des. Dev. 19 (1980) 336.