Exclusive SAPO-seeded synthesis of ZK-5 zeolite for selective synthesis of methylamines

Abstract

The selectivity for monomethylamine plus dimethylamine is desired to be improved in the selective synthesis of methylamines due to their high value as chemical intermediates. ZK-5, a small-pore zeolite, shows high selectivity for monomethylamine plus dimethylamine, while conventional synthetic methods of ZK-5 involve a long crystallization time and/or expensive organic structure-directing agents/explosive nitrates. Herein, ZK-5 is rapidly synthesized with Na⁺ and K⁺ and the exclusive silicoaluminophosphate SAPO-34 seed. The indispensable role of the as-synthesized SAPO-34 seed is disclosed. The as-synthesized SAPO-34 seed is dissolved in the initial mixture, forming Si(3Al), P-containing species, and morpholine. Further research studies reveal that the Si(3Al) species and morpholine play a synergistic role in the synthesis of ZK-5. The obtained H-ZK-5 zeolite exhibits superior selectivity for monomethylamine plus dimethylamine (94.4%) compared to the traditional H-ZK-5 (K, Cs) zeolite and other small-pore zeolites (SAPO-34, DNL-6, H-rho, and H-PST-29), showing great potential for industrial synthesis of monomethylamine and dimethylamine.