A study on the load-dependent enthalpy of adsorption and interactions in adsorption of C5 and C6 hydrocarbons on zeolites 13X and ZSM-5 and an activated carbon

Abstract

In a systematic experimental work, the adsorption of linear, branched and cyclic C5 and C6 hydrocarbons on the zeolites 13X-APG and HiSiv 3000 and the activated carbon Norit R1 Extra is studied. By simultaneous measurement of adsorption capacities and load-dependent enthalpies of adsorption using a self-developed sensor gas calorimeter a deep knowledge about the energetic strength of interactions in adsorption is gained. A special focus is laid on the discussion of the influence of pore geometry and surface chemistry of the adsorbents as well as the molecular structure and binding types of the adsorptives used. Depending on the pore geometry and the surface chemistry of the adsorbents, the load-dependent enthalpies of adsorption show different shapes. While the enthalpies of adsorption on the Faujasite zeolite increase with loading, they are independent of loading on the ZSM-5 zeolite and decrease on the activated carbon. On both zeolites the cyclic and branched adsorptive molecules show lower enthalpies of adsorption compared to the linear molecules due to a less favorable arrangement on the surface. On activated carbon, the enthalpies of adsorption of linear and cyclic hydrocarbons are comparable and significantly higher than those of branched hydrocarbons. For molecules with C=C double bonds only 13X-APG showed higher enthalpies of adsorption and thus stronger interactions.