Process for preparing silicoaluminoposphate (SAPO) molecular sieves, catalysts containing said sieves and catalytic dehydration processes using said catalysts

A new process for producing a SAPO molecular sieve is disclosed wherein a mixture of a P source with an Al source is subjected to a digestion step under stirring before adding a Si source and a template. The slurry resulting after addition of all chemicals is subjected to a pH adjustment followed by the usual hydrothermal treatment at higher temperature in an autoclave. In this way, very pure highly crystalline SAPO molecular sieves such as SAPO-34 are obtained with a very high yield. In addition, the SAPOs produced this way have an exceptional activity in the dehydration reactions and can be employed as a active component of catalysts for the production of valuable dehydration products from methanol such as, but not limited to, olefins and dimethylether (DME).