Patent ID: 8268277

Claim:
A method of preparing a silicoaluminophosphate molecular sieve having a desired crystal size, the method comprising: (a) providing a synthesis mixture comprising a source of aluminum, a source of phosphorus, a source of silicon, and at least one organic template containing (i) a 4- to 8-membered cycloalkyl group, optionally substituted by 1-3 alkyl groups having from 1-3 carbon atoms, or (ii) a 4- to 8-membered heterocyclic group having from 1-3 heteroatoms, said heterocyclic group being optionally substituted by 1-3 alkyl groups having from 1-3 carbon atoms, and said heteroatoms in said heterocyclic groups being selected from the group consisting of O, N, and S, wherein the synthesis mixture exhibits a Si/Al 2 ratio less than 0.33; (b) inducing crystallization of a silicoaluminophosphate molecular sieve, which exhibits 90% or greater CHA framework type character, from said synthesis mixture by heating said synthesis mixture at a heating rate of more than 20° C./hr to a crystallization temperature; and (c) crystallizing said silicoaluminophosphate molecular sieve at the crystallization temperature for between 16 hours and 350 hours, such that a yield of silicoaluminophosphate molecular sieve greater than 8.0% is attained, wherein the crystallized silicoaluminophosphate molecular sieve exhibits a Si/Al 2 ratio less than 0.33 and has a crystal size distribution such that its average crystal size is not greater than 1.0 μm; and wherein step (a) comprises: (i) combining the source of phosphorus and the source of aluminum, optionally with a liquid mixture medium, to form a primary mixture; (ii) aging the primary mixture for an aging time and under aging conditions sufficient to allow homogenization of the primary mixture, physico-chemical interaction between the source of phosphorus and the source of aluminum, or both; and (iii) adding the source of silicon, the at least one organic template, and optionally additional liquid mixture medium, to the aged primary mixture to form the synthesis mixture, wherein said source of silicon is combined with said primary mixture prior to adding said at least one organic template.