Direct and Highly Selective One-Step Production of Ethylbenzene from Syngas and Benzene

Abstract

Due to cost and energy consumption constraints, converting benzene into ethylbenzene using low-cost syngas instead of ethylene as an alkylation reagent is significant. However, when using syngas as the reaction raw material, generating ethylated side chains on the benzene ring is challenging. Instead, toluene/xylene becomes the primary product. We used a three-bed series connection method in a reactor, achieving one-step high selectivity of syngas and benzene to produce ethylbenzene. In the first bed layer (ZnAl2O4/SAPO-34), the syngas was first converted into methanol/dimethyl ether (DME) on ZnAl2O4. Then, it was further converted into low-carbon olefins on SAPO-34, with the microporous shape-selective effect of SAPO-34, inhibiting the generation of toluene/xylene in the alkylation of benzene with methanol/DME. At the same time, we proved that the absence of microporous shape-selective effect acid sites on the outer surface of S34 can lead to the occurrence of side reactions of benzene and methanol/DME methylation. In the second bed layer, SAPO-34 could continue to convert unconverted methanol/DME in the first bed layer into low-carbon olefins. In the third layer (ZSM-5), ethylene and benzene underwent highly selective alkylation on ZSM-5 to convert it into ethylbenzene. We found a “volcanic” curve relationship between the selectivity of ethylbenzene and the Brønsted acid site density of ZSM-5. On the one hand, Brønsted acid could catalyze the formation of ethylbenzene from benzene and ethylene; On the other hand, excessive Brønsted acid could lead to the isomerization of ethylbenzene to toluene/xylene. When the Brønsted acid showed a site density of 0.7 mmol/g, the selectivity of ethylbenzene was as high as 87%, with a byproduct of xylene showing only 0.3%, which is usually difficult to separate from ethylbenzene. Finally, the three-bed catalytic system showed no deactivation after 100 h.