Selective adsorption for removing sulfur from jet fuel over zeolite-based adsorbents

Adsorbents based on transition metal ion-exchanged Y zeolites (with Cu, Ni, Zn, Pd, and Ce ions) were synthesized and evaluated for the adsorptive desulfurization of a model jet fuel (MJF) and a real jet fuel (JP-8). Among the adsorbents tested, Ce-exchanged Y zeolites exhibited better adsorption capacity of about 10 mg of sulfur/g of adsorbent at 80 degreesC with a MJF containing 510 ppmw sulfur. The same adsorbent exhibited a sulfur adsorption capacity of about 4.5 mg/g for the real JP-8 jet fuel containing about 750 ppmw sulfur. Desulfurization of MJF under flow conditions at 80 degreesC showed a breakthrough capacity of about 2.3 mg/g of adsorbent. Ce-exchanged zeolites exhibited higher selectivity for sulfur compounds as compared to the selectivity of aromatics, for which a comparative study indicated that the sulfur compounds are adsorbed over Ce-exchanged Y zeolites via direct sulfur-adsorbent (S-M) interaction rather than via pi-complexation. While the selectivity for 2-methyl benzothiophene (2-MBT) was higher in the static adsorption studies, the adsorption selectivity decreased in the order 5-methyl benzothiophene (5-MBT) > benzothiophene (BT) > 2-MBT under dynamic conditions. This trend was correlated to the electron density on sulfur atoms derived from computer-aided molecular orbital calculations.