Insight into the competitive adsorption mechanism of ethylbenzene and octane on zeolite NaY with different SAR

Abstract

The Si/Al molar ratio (SAR) of zeolites is crucial for separating unsaturated hydrocarbon components, but it was difficult to rule out the impact of changes in pore properties. In this work, a GCMC method was developed to investigate the effect of varying SAR (2.4, 20, and 50) using a module of NaY zeolite. The deviation of pore properties is less than 5%. When using ethylbenzene and n-octane as probe molecules, increasing the SAR is not conducive to improving the selectivity of ethylbenzene in single component adsorption, but in the two components, the selectivity increases from 76.0% to 92.6% when SAR increasing from 2.4 to 50. The increase of diffusion coefficient in two component is also significantly different. The NH3 radial distribution functions (RDF) method was used to investigate the number of acid sites and acid strength, it can be observed that the adsorption capacity of ammonia decreases with SAR increasing but slightly when the SAR exceed 50. However, the number of ammonia molecules adsorbed per site significantly increases, the II site exhibits stronger acidity than III site. To distinguish different preferences of adsorbate onto zeolites with different SAR, concentration distribution combined with RDF was used. During single-component adsorption, both ethylbenzene and n-octane could be freely adsorbed on the II and III sites, however in binary situation, ethylbenzene tended on the II sites, while n-octane on the III sites. As the SAR increased, the adsorption of ethylbenzene, which displaced the original adsorption sites occupied by n-octane and consequently improved the selectivity of ethylbenzene. To investigate the interaction between adsorbents with different polarities, different feed concentration and RDF between the adsorbates were used, which revealed that polarities may have a greater impact on selectivity. Through the Monte Carlo series of tools, the structure-performance relationship between complex adsorbates and adsorbed molecules can be studied clearly.