Improving the uniformity and tailoring the crystal size of silicoaluminophosphate and aluminosilicate zeolites as well as effectively converting methanol to olefins over the resulting silicoaluminophosphate zeolite

The crystal size and uniformity of zeolites are crucial for their excellent performance in various industrial applications. Here, by utilizing commercial micrometer-sized zeolites as seeds and adjusting the weight percentage of seeds from 0 % to 5 %, the crystal sizes of silicoaluminophosphate SAPO-34 samples first decrease from 12.47 μm (S0) to 3.04 μm (S4), then increase to 5.34 μm (S5). Correspondingly, their relative crystal size deviations first decrease from 183.32 % to 60.53 %, then increase to 115.17 %, and the crystal size uniformity factors first increase from 0.33 to 1, then decrease to 0.53. The crystal size uniformity factor of sample S4 equals 1, indicating that it exhibits the best crystal size uniformity. This method is also applicable to aluminosilicate zeolites. By adjusting the weight percentage of seeds from 0 % to 3 %, the crystal sizes of ZSM-5 samples first decrease from 13.61 μm (Z0) to 2.49 μm (Z2), then increase to 4.46 μm (Z3); correspondingly, their crystal size uniformity factors first increase from 0.42 to 1, then decrease to 0.71. In addition, this route significantly enhances the yields and relative crystallinities of both SAPO-34 and ZSM-5 zeolites. Specifically, the yield and relative crystallinity of SAPO-34 zeolite increase by 40.71 % and 8.45 % respectively, while the yield and relative crystallinity of ZSM-5 zeolite improve by 24.05 % and 12.55 % individually. Notably, in the methanol to olefins (MTO) reaction, the propylene selectivity to butene selectivity ratio is inversely related to the crystal size; this suggests that crystal size may play a primary role in the formation of propylene and butene, with smaller crystal sizes being more favorable for the formation of propylene compared to butene. Furthermore, sample S4, which has a crystal size uniformity factor of 1 and a crystal size of 3.04 μm, exhibits excellent MTO performance; its catalytic lifetime increases by 69 %, and selectivity for ethylene plus propylene increases by 6.3 % in comparison to conventional sample S0.