Synthesis of chabazite-containing molecular sieves and their use in the conversion of oxygenates to olefins

Abstract

In a method of synthesizing a mostly CHA-type silicoaluminophosphate sieve, a reaction mixture comprises sources of water, silicon, aluminum, phosphorus, and a template. In one aspect, the inorganic phosphorus and silicon sources are first combined to form a primary mixture that is aged. Then, the aluminum source is added, followed optionally by any organic phosphorus source, and then the template, to form the synthesis mixture. After heating at <10° C./hr to induce crystallization, in this aspect, both the crystallized sieve has an average crystal size ≦1.5 μm and/or is recovered in a yield of ≧10.0 wt %. In another aspect, when the synthesis mixture Si/Alratio is <0.33, crystallization is induced. Advantageously, the sieve so crystallized has a template efficiency of ≧0.5 and/or is recovered in a yield of ≧10.0 wt %. The molecular sieve from both aspects can be used in a hydrocarbon (oxygenates-to-olefins) conversion process.