A 3-PHASE MODEL FOR SORPTION ISOTHERM IN ZEOLITE ADSORBENTS

A three-phase model for adsorption in zeolite cavities is proposed. Th e adsorbed molecules are taken to be distributed between a surface lay er and a dense phase filling the rest of the cavity volume. This model is a more realistic representation of molecules in zeolite cages espe cially at high pressures. The equation for the adsorption isotherm, ba sed on this model, has two contributions: a surface term and a dense p hase term. The dense phase contribution was estimated from a simple eq uation that obeys the limiting values at low and high pressures. The s urface contribution can be estimated from the existing surface adsorpt ion models. When all model parameters are estimated from molecular and literature data, the combination of the two terms was found to be an improvement over traditional treatment of adsorption data of a number of gases in zeolite-A for a wide range of pressures. However, new mode ls for the adsorbed phase that account for sorbate-sorbate repulsive f orces correctly are needed for accurate prediction of adsorption data.