ADSORPTION OF ALKANES AND OTHER ORGANIC-MOLECULES IN LIQUID-PHASE ANDIN THE DENSE VAPOR-PHASE - INFLUENCE OF POLARITY, ZEOLITE TOPOLOGY, AND EXTERNAL FLUID DENSITY AND PRESSURE

Adsorption of alkanes, aromatics, and other organic molecules in liqui d phase and the dense vapor phase was studied on FAU and MFI zeolites at temperatures ranging from 25 to 300 degrees C. On faujasites, no co mpetitive adsorption between n-alkanes of different carbon number was observed at room temperature. At higher temperatures and lower fluid d ensities, longer n-alkanes start being adsorbed preferentially over sh ort n-alkanes on faujasites. On MFI zeolites, longer n-alkanes have la rger partition coefficients than short n-alkanes. The difference in co mpetitive adsorption behavior resides in the different pore structures of these zeolites: mutual interactions of several molecules adsorbed in the supercages of the faujasites dominate over direct interaction w ith the zeolites' force field, while on MFI zeolites, only one n-alkan e molecule fits in the cross diameter of the pore, thereby strongly re ducing the adsorbate-adsorbate interactions. On MFI zeolites, small n- alkanes have unrestricted access to both channel types, while long n-a lkanes have restricted access to part of the micropore structure. Sepa ration by selective adsorption in liquid phase on faujasites depends t o a high extent on differences in building blocks of the molecules.