Study On Alkylation Of Benzene With Short-chain Olefins

In this paper,the alkylation of short-chain olefins(ethylene/propylene)in benzene and hydrocarbon mixtures to synthesize alkylbenzenes(ethylbenzene/cumene)as the object,the screening of alkylation catalysts and process conditions were carried out.Using ethylene as raw material,based on the experimental evaluation of fixed-bed reactor and the characterization results of NH3-TPD and BET,the alkylation of benzene and ethylene on the five molecular sieves ZSM-5,BETA,MCM-22,MCM-49 and Y were compared and analyzed.Relatively speaking,ZSM-5 molecular sieve has better ethylene alkylation performance.The relatively suitable alkylation conditions determined are:temperature 380?,pressure 0.2 MPa,benzene/ethylene molar ratio 6 and ethylene mass space velocity 2 h-1.Under this condition,complete conversion of ethylene can be achieved,and ethylbenzene selectivity reaches about 90%.Using propylene as raw material,the selected three molecular sieves ZSM-5,BETA and MCM-22 were evaluated.The results showed that:BETA molecular sieve has better catalytic performance for alkylation of benzene and propylene.The relatively suitable alkylation conditions determined are:temperature 180??200?,pressure 0.8 MPa,benzene/propylene molar ratio 6 and propylene mass space velocity 1 h-1.Under these conditions,the conversion rate of propylene can be stabilized above 98%,and the selectivity of cumene can reach about 84%.Using mixed ethylene+propylene as raw material,the alkylation performance of mixed short-chain olefins and benzene on ZSM-5,BETA and MCM-22 molecular sieves are compared and analyzed.The results show that:BETA molecular sieve has better comprehensive alkylation performance.The law of the alkylation process with the change of conditions is as follows:with the increase of temperature,the ethylene conversion rate does not change much,the propylene conversion rate increases significantly,the cumene content in the product gradually increases,and the ethylbenzene content decreases gradually;as the molar ratio of benzene to mixed olefins increases,the mixed olefins conversion rate increases significantly,the content of ethylbenzene and cumene in the product increased;With the increase of space velocity,the conversion rate of olefin significantly decreased,but the space velocity had little effect on the product distribution.The final conditions for the alkylation of mixed short-chain olefins are:pressure 0.8 MPa,temperature 200??220?,benzene to mixed olefins molar ratio 10 and mixed olefins mass space velocity 0.5 h-1,?1 h-1.Under this condition,propylene is almost completely converted,the ethylene conversion rate is about 80%,and the total content of ethylbenzene and cumene in the product is kept at about 95%.Based on the above research results,a series alkylation scheme for a double fixed bed reactor containing a mixture of ethylene and propylene hydrocarbons was determined.Among them,the first reactor is filled with BETA molecular sieve for complete conversion of propylene and most of ethylene conversion,and the second reactor is filled with ZSM-5 molecular sieve for complete conversion of remaining ethylene.The simulation analysis of the alkylation of ethylene and propylene in the exhaust gas of a 100,000 ton/year methanol aromatization device shows that:with this scheme and under suitable conditions,complete conversion of ethylene and propylene can be achieved,with total selectivities of ethylbenzene and cumene reaching 90%and 94%.