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Alkali-treatment of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios and light olefin production by heavy oil cracking

Zhao, Liang, Gao, Jinsen, Xu, Chunming, Shen, Baojian
Fuel processing technology 2011 v.92 no.3 pp. 414-420
alkali treatment, catalysts, catalytic cracking, cracking, feedstocks, industry, oils, olefin, sodium hydroxide, yields, zeolites
Four kinds of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios are alkali-treated in 0.2M NaOH solution for 300min at 363K. Changes to the compositions, morphologies, pore sizes, and distributions of the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO₂/Al₂O₃ ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO₂/Al₂O₃ ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.