Thiophene conversion under mild conditions over a ZSM-5 catalyst

Abstract

Refiners are nowadays actively considering the post-treating FCC gasoline processes as a viable and less costly approach for meeting sulfur environmental regulations. Most promising catalytic desulfurization processes do not require hydrogen addition, including between others the use of zeolites as adsorbents/catalysts. This type of desulfurization leads to the formation of significant amounts of coke, requiring keeping high catalyst activity a continuous twin fluidized bed system (fluidized-bed reactor, fluidized bed regenerator). This study evaluates the catalytic conversion of thiophene and/or thiophene in n-octane mixtures. Catalytic experiments are carried out in the CREC riser simulator under mild conditions, using H-ZSM5 zeolite dispersed in a silica matrix. The experimental results obtained demonstrate a higher selective conversion of thiophene over n-octane. It is shown that thiophene conversion proceeds via ring opening and alkylation yielding H2S, alkyl-thiophenes, benzothiophene, and coke, with no measurable thiophene saturation or dimerization reactions observed. The experimental results are also supported with an extensive thermodynamic analysis that includes all the possible thiophene conversion pathways over zeolites. On this basis and using as a reference the observable measurable species, a reaction network is proposed to represent the thiophene catalytic conversion under the suggested gasoline post treatment conditions.