The adsorption isotherms of F-11(trichloro-fluoromethane), F-12 (dichloro-difluoromethane) and F-22( chloro-difluoromethane) were measured at various temperatures on hydrophobic high silica MFI and FAU zeolites in order to investigate thermal effect of the adsorption. The isosteric adsorption heat Qst(C) and average isosteric adsorption heat Qst^*(△Ha) under various coverage of the adsorbates were calculated by using Clapeyron-Clausious equation on the isotherms of adsorption. The order of the adsorption heats for all adsorbates on the zeolites investigated is △Ha(MFI)＞△Ha(FAU). The order of the adsorption heats of certain adsorbate on each zeolite is as follows: △Ha (F-11)＞△Ha(F-12)＞△Ha(F-22). The molecules of the adsorbate can get in and out the cavities of FAU zeolite freely. In such cases it is found that the larger the molecule size the higher of the adsorption capacity and the △Ha according to the comparison of △Ha at low pressure and the isotherms measured at 298K. On the other hand, the relationship of △Ha, molecule size and the saturated adsorption capacity (Vm) is uncertain in the situation of MFI zeolite, since there exists a space restriction for the adsorbed molecules. Two factors. △Ha and Vm should be considered simultaneously for searching the effective adsorbent to remove chloro- fluoro-hydrocabons.

Key words: SILICALITE, ADSORPTION