Catalytic Cracking Of Mixed C₄ Hydrocarbon To Propylene And Ethylene

Propylene and ethylene are the most important organic chemical materials used in the production of polypropylene, acrylonitrile and acrylic. With a higher growth rate for propylene derivatives, demands for propylene strongly increases per year. C4 hydrocarbons have been produced abundantly in the process of steam cracking and catalytic cracking, using industrially abundant and less valuable C4 hydrocarbons as feedstock, combining the merits of catalytic cracking to produce valuable ethylene and propylene is a hot and difficult research. HZSM-5 catalyst has been used for most of research because of its special pore structure, well shape-selective, strong acidity. However, non-modified HZSM-5 catalyst show bad catalytic performance. So research have been paid attention to modifying HZSM-5 zeolites enhance the performance of catalytic cracking.In this work, mixed C4 hydrocarbons catalytic cracking and joint transformation of mixed C4 hydrocarbons and methanol over catalyst and catalytic performance has been investigated.(1) The mixed C4 hydrocarbons catalytic cracking to propylene and ethylene over modified HZSM-5 catalyst. The catalytic performance of HZSM-5(SiO2/Al2O3=25,50,200) and HZSM-5(SiO2/Al2O3=50) modified with P was investigated. The result indicated that HZSM-5(SiO2/Al2O3=50) favored catalytic performance; PHZSM-5(ion-exchange method) gave 92.0% conversion of C4, yield of ethylene and propylene is 5.5% and 34.4% at 450℃, 0.8 h-1, atmosphere pressure. Then, adding other additives over P-modified HZSM-5(SiO2/Al2O3=50) was investigated. The catalytic performance associate with the type and loading of additives. The 0.5%ZrPHZSM-5 catalyst with 0.5 wt% Zr content performed best, giving 94.8% conversion of C4 and yield of ethylene and propylene is 5.9% and 36.5% at 450℃,0.8 h-1, atmosphere pressure. The reaction condition of C4 hydrocarbons catalytic cracking over 0.5%ZrPHZSM-5 catalyst was studied. The result showed that increasing temperature, lowing space velocity properly and adding suitable steaming can improve conversion, yield of propylene. stability of catalyst.Then, the physicochemical features of catalysts were characterized by means of XRD. N2 adsorption isotherms. Py-FTIR. The results indicated P and Zr reduced the surface area and pore volume of catalyst, highly dispersed on surface and framework of catalyst, adding Zr decreased the amount of PHZSM-5 acidic sites. The enhanced performance of the catalyst for C4 cracking to propylene and ethylene can be correlated to the synergistic effect between the doped Zr and P on the reaction network of the cracking process. This synergistic effect regulated the catalyst acidic sites, consequently, catalyst with suitable amount was favorable for enhancing C4 hydrocarbons catalytic cracking to propylene and ethylene.(2) The process of the joint catalytic transformation of mixed C4 hydrocarbons and methanol not only obtained propylene but also under in energy neutral. The influence of reaction conditions based on HZSM-5(SiO2/Al2O3=50) were studied. At the temperature of 48℃.0.6 h-1. methanol/C4 molar ratio 0.3:1, the conversion of mixed C4 hydrocarbons was 95.5%, yield of ethylene and propylene is 16.8%.39.0%. respectively. This integrated process has been studied based on HZSM-5(SiO2/Al2O3=50) doped with La. At the temperature of 450℃.0.3 h-1. methanol/C4 molar ratio 0.3:1,1.5%LaHZSM-5 catalysts showed excellent catalytic performance, the conversion of mixed C4 hydrocarbons was 98.6%, yield of ethylene and propylene was 17.7% and 48.9%. The influence of reaction conditions based on 1.5%LaHZSM-5 zeolites were studied. The results showed that appropriate methanol/C4 molar ratio, high reaction temperature, low space velocity can improve C4 conversion, the yield of propylene and anti-coking ability.In addition, the physicochemical features of catalysts were characterized by means of XRD. N2 adsorption isotherms. Py-FTIR. The results indicated that surface area and pore volume was found to be decreased with increasing La loading, acid density and the acid strength of HZSM-5 catalyst decreased with the modification of HZSM-5 zeolite by La. La modification with suitable amount was favorable for constraining the reaction of aromatization and hydrogen transfer, enhancing the selectivity and yield to propylene.