The potential use of multivalent-cation-exchanged Y zeolites as selective adsorbents for hydrogen sulfide (H2S) from Claus process tail gas was examined; previous work suggested Zn(II)Y, Ni(II)Y, and Ga(III)Y were chosen as representative candidates. The adsorption energies of H2S and other Claus tail gas components (CO, H2O, N2, and CO 2) were computed on zeolite cluster models with density functional theory (DFT). It was found that these multivalent cation-exchanged zeolites are subject to strong adsorption of water. The trend in adsorption energy does not change with the cation type and Al distribution, and is similar to that on alkali metal exchanged zeolites found in our previous study. However, the reason for water selectivity is different for the multivalents than for the alkali metal Y's, and this is revealed by absolutely localized molecular orbital energy decomposition analysis (ALMO EDA). The difference between the adsorption energies of CO and H2S on GaY is the largest among all the cation-exchanged Y zeolites we have studied so far. Therefore, a two-step process, where the H2S adsorption follows the removal of H 2O, might be a good strategy for adsorptive desulfurization.
Bibliographical noteFunding Information:
This work was funded in part by the Nanostructural Materials and Processes Program through IPRIME at University of Minnesota, by ADGAS and GASCO, UAE, and by ADMIRE (AbuDhabi-Minnesota Institute for Research Excellence). We are also grateful to the Minnesota Supercomputing Institute for providing resources necessary to perform this study.
- Cation-exchanged zeolite
- Claus process
- Density functional theory
- Selective adsorption