Catalytic desulfurization of thiophene on H-ZSM5 using alkanes as co-reactants

Abstract

Propane, n-hexane, n-decane, and hydrogen were used as co-reactants in the desulfurization of thiophene catalyzed by H-ZSM5 at 673 K. These co-reactants lead to hydrogen-rich intermediates, which are required for the removal of unsaturated fragments formed in thiophene decomposition reactions. Thiophene desulfurization rates increased with increasing alkane chain size, suggesting that the availability of hydrogen-rich intermediates increases with increasing alkane reactivity. Desulfurization rates with alkane co-reactants were significantly higher than those achieved with hydrogen. Sulfur is predominately removed as hydrogen sulfide (>80% S-selectivity) in the presence of alkane co-reactants, but much lower hydrogen sulfide selectivities were obtained when hydrogen was used and when thiophene decomposed in the absence of any co-reactants. The presence of thiophene did not alter the nature of the cracking, dehydrogenation, oligomerization, and cyclization pathways typical of alkane reactions or the overall rates of propane conversion on H-ZSM5. The selectivity for alkane conversion to aromatics, however, increased when alkane reactions occur concurrently with thiophene desulfurization, indicating that thiophene-derived intermediates contribute to the formation of aromatics by scavenging alkene intermediates formed from the alkane co-reactants. The higher alkene/alkane ratios observed during alkane reactions in the presence of thiophene are consistent with the scavenging of hydrogen-rich intermediates by thiophene-derived species via reactions that form aromatic molecules containing carbon atoms from both alkane and thiophene reactants.