EFFECT OF CATALYST MODIFICATION ON THE CONVERSION OF METHANOL TO LIGHT OLEFINS OVER SAPO-34

The catalytic activity and selectivity of as-prepared and modified sam ples of SAPO-34 and Me-APSO-34 (Me = Co, Ni) for the conversion of met hanol to olefins has been investigated. The catalytic performance for the conversion of methanol to light olefins of all the catalyst sample s prepared was found to be closely related to the number of strong aci d sites present. Mild steaming, encountered during deep-bed calcinatio n, increased the lifetime of SAPO-34 due to the formation of stronger acid sites probably on the external surface of the crystallites. Selec tivities to light olefins were typical of those previously reported an d was essentially constant for all the catalysts investigated. The abs ence of C-5+ olefins is ascribed to the 'cage effect'. Dilution of the methanol with water as opposed to nitrogen increased the catalyst uti lization value threefold and reduced the rate of coke formation during reaction. Treatments such as steaming, silanization and poisoning of strong sites by ammonia all reduced the number of strong acid sites an d, thus, reduced catalytic performance.