Sustainable synthesis of AEI/CHA intergrowth zeolites for methanol-to-olefins conversion

The conventional hydrothermal synthesis of zeolites is inevitably accompanied by the production of mother li-quors containing plentiful unreacted raw materials and organic templates. The direct emission or improper use of these mother liquors will cause not only the environmental contamination but also the waste of resources. Here we report a promising synthetic strategy for the effective recycle of mother liquors produced from the industrial production of SAPO-34 zeolites. Mother liquors with the addition of extra Si, P and Al were spray-dried and subsequently converted to the crystal seeds by vapor-phase-transport (VPT) method. Zeolite products with improved porosity and altered acidity were eventually acquired by VPT-Seeds-assisted hydrothermal crystalli-zation, in which the topologic structures (e.g., CHA, AEI or AEI/CHA intergrowth) of zeolites depended signif-icantly on the crystalline phase of VPT-Seeds. We demonstrated further via FT-IR and kinetics study that VPT-Seeds accelerated the crystallization of zeolites dramatically without the severe dissolution during the whole stage of synthesis. The as-synthesized AEI/CHA intergrowth zeolites showed the enhanced catalytic lifetime (increased at least by 27.6%) and higher selectivity in (C2H4+C3H6) (increased by 2.5%) during methanol-to -olefins (MTO) reactions than the pure CHA zeolites synthesized by the conventional hydrothermal method. Zeolites synthesized using the secondary recycled mother liquors in the same way also showed the comparable catalytic performances in MTO process, again verifying the feasibility of our methods to recycle mother liquors. The sustainable synthesis route developed in this work should be applicable to the industrial production of a wide variety of zeolites.

Automated summary

A synthetic strategy for the effective recycling of mother liquors produced from industrial production of SAPO-34 zeolites is reported. By using vapor-phase-transport method, spray-dried mother liquors with added Si, P and Al were converted to crystal seeds, leading to the acquisition of zeolite products with improved porosity and acidity. The topological structures of the zeolites significantly depended on the crystalline phase of the vapor-phase-transport seeds. The as-synthesized zeolites showed enhanced catalytic performance in methanol-to-olefins reactions compared to conventional hydrothermal synthesized zeolites.