Abstract: The MTO (methanol-to-olefins) process using SAPO-34 as the active component of catalyst has been successfully industrialized on a large scale. Research on the recycling of solid and liquid waste from SAPO-34 synthesis is essential for promoting the sustainable development of the MTO process. Herein, we explored the utilization of crystallization mother liquor obtained from SAPO-34 synthesis and demonstrated its effectiveness for synthesizing both SAPO-34 and SAPO-18. For SAPO-34, under identical gel molar compositions, increasing the amount of mother liquor led to similar product Si content and Si coordination environments, but resulted in reduced crystallite sizes and decreased Si enrichment on crystal surface. In the case of SAPO-18, an increased addition of mother liquor produced materials with comparable Si content but induced a notable change in Si coordination environment from a complex mixture to a predominant Si(4Al) species. Concurrently, the crystal morphology evolved from elongated to rhombohedral crystals, consistent with the formation of an AEI/CHA intergrowth. In MTO catalytic tests, mother liquor-derived SAPO-34 showed enhanced selectivity toward ethene and propene, attributable to reduced surface Si enrichment and consequently enhanced mass transport. Meanwhile, mother liquor-derived SAPO-18 samples exhibited a prolonged catalytic lifetime and high overall selectivity toward ethene, propene, and butene.

Key words: Molecular sieve synthesis, Mother liquor, SAPO-18, SAPO-34, Methanol to olefins (MTO)