Preparation Of Modified ZSM-5/Cordierite Monolithic Catalyst And Their Catalytic Performance Of Methanol To Olefin

Ethylene and propylene is an important raw material for chemical industry. In recent years, demand of the national economy in various fields for synthetic materials and organic materials is continuously growing. That makes ethylene and propylene market capacity increase with higher speed. Methanol to olefin technology is a new process that uses raw coal or natural gas to make methanol, and then after prepare ethylene, propylene, low carbon olefins etc with methanol. Traditional way of producing low carbon olefins is by oil cracking. Because of the shortage of oil resources and the limit of price, methanol to olefin technology opens a new line of preparing low carbon olefins, so more and more researchers pay an attention to that.Methanol olefin process is focused on the preparation and screening of catalyst. In this paper, direct method of synthesizing ZSM-5 catalyst without templates was used, different modified M-HZSM-5 (M=Al, Mg, Ca, Sr, Ba) catalyst were prepared, and a series of the HZSM-5/cordierite monolithic catalysts with different HZSM-5 molecule sieve contents were prepared using pretreated monolithic cordierite as support. The structure of the catalysts was characterized by XRD and BET technique. The catalytic performance of the catalysts for the methanol to olefins was evaluated in a fixed-bed micro-reactor and best technological conditions were ascertained.For modification catalyst, the effects of the metal contents, reaction temperature, feed gas space velocity and reaction time on the olefin composition distribution were investigated. The results indicated with the increase of metal contents, the BET surface area and the pore volume of the catalysts decreased and pore diameter took place the corresponding change. Metals influenced crystallinity of HZSM-5 molecule sieve more or less, but its basic skeleton was retained including features diffraction peak of some metals (Mg, Ca). Al, Mg modified HZSM-5 molecule sieve better than others. Modification catalysts improved the best selectivity of the ethylene and the propylene and made total amounts of low carbon olefins at around 70%. The Al-HZSM-5 catalyst with 6.0% Al contents exhibited the best catalytic performance for the methanol to olefins. Methanol conversion rate is 99.3%. The selectivity of the ethylene and the propylene can reach 42.7% and 26.6%, respectively, under the reaction condition at 380℃and 786 ml/g-h. The Mg-HZSM-5 catalyst with 15.0% Mg contents exhibited the best catalytic performance for the methanol to olefins. Methanol conversion rate is 97.7%. The selectivity of the ethylene and the propylene can reach 35.3% and 38.9%, respectively, under the reaction condition at 500℃and 612 ml/g-h. In reaction process, reaction activity of Al-HZSM-5 catalysts and Mg-HZSM-5 catalysts declined with the growth of the reaction time, and ethylene, propylene selectivity gradually decreased.The result is better than before when Ca and Ba modified HZSM-5 molecule sieve. The total amount of low carbon olefins is about 45%. Effect of Sr modification is poorer. Methanol conversion rate is 100% when Ca contents is 12.0% under the reaction condition at 575℃and 786ml/g·h. The selectivity of the ethylene and the propylene can reach 17.2% and 26.6%, respectively. Methanol conversion rate is 100% when Ba contents is 6.8% under the reaction condition at 400℃and 786ml/g-h. The selectivity of the ethylene and the propylene can reach 21.0% and 24.5%, respectively. Conversion of Sr-HZSM-5 including 18% of Sr is 57.3% under the condition at 375℃and 786ml/g·h. The selectivity of the ethylene and the propylene can only reach 20.6% and 16.1%, respectively.For the research of monolithic catalysts, the effects of the HZSM-5 molecule sieve contents, reaction temperature, feed gas space velocity, different coating and reaction time on the olefin composition distribution were investigated. The results indicated the structure of HZSM-5 molecule sieve was retained in the HZSM-5/cordierite monolithic catalysts. The BET surface area and the pore volume of the catalysts increased with the increase of HZSM-5 molecule sieve contents. The HZSM-5/cordierite monolithic catalyst with 22.5% HZSM-5 molecule sieve contents and coating of Al sol exhibited the best catalytic performance for the methanol to olefins. Conversion rate is 99.5%. The selectivity of the ethylene and the propylene can reach 35.22% and 30.95%, respectively, under the reaction condition at 380℃and 820 ml/g-h.