A green approach to improve the yield of SAPO-34 crystal as well as its methanol-to-olefin performance

Abstract

Nowadays, large amounts of aluminosilicophosphate SAPO-34 zeolite are produced in industrials annually. Here, a green strategy is developed to increase SAPO-34 crystal's yield and its catalytic performance in methanol-to-olefin (MTO) reaction. Tuning the pH value of mother liquor from alkaline to acid by rationally decreasing the environmentally unfriendly organic amine to only 57%, surprisingly the yield of SAPO-34 zeolite increases from 31% to 78%; the weak acid environment at the initial stage generates more AlPO4 precursors, which then are converted into the zeolite framework. For the first time, we found that the yield and crystallinity of the SAPO-34 crystal are positively correlated with the pH difference between gels before and after crystallization. Furthermore, the sample with the largest pH difference of about 2, showing hierarchical pore structure and mild acidity, presents excellent MTO performance: a longer lifetime of 381 ​min and a higher selectivity for ethylene plus propylene of 84.91%, compared to the conventional microporous sample of 131 ​min and 78.89%. This green approach uses less environmentally detrimental amine but enhances the yield of zeolite, in favor of the completion of the world's carbon neutrality.