乙烯在催化裂解催化剂上的低聚反应

HETEROGENEOUS OLIGOMERIZARION OF ETHYLENE OVER CATALYTIC CRACKING CATALYST

以Y和ZSM-5分子筛催化裂解催化剂为研究对象,采用N_(2)吸附-脱附、氨气程序升温脱附(NH_(3)-TPD)和吡啶吸附红外(Py-FTIR)对其进行表征,研究了反应温度和反应压力对其催化乙烯低聚反应性能的影响。结果表明:催化裂解催化剂富含3~4 nm介孔,以弱L酸中心为主;在500~550℃和常压条件下,乙烯不易于转化,主要经低聚、裂化反应生成C_(3)~C_(4)烯烃,且丙烯的选择性高于丁烯;当反应温度高于550℃时,丙烯和丁烯的环化脱氢反应使焦炭的选择性大幅增加;与常压条件相比,在0.5~1.0 MPa反应压力下,乙烯在催化裂解催化剂上低聚反应的转化率明显升高;提高反应压力有利于C_(3)~C_(4)烯烃的氢转移反应,丙烷和丁烷的选择性升高,而焦炭的选择性降低。

The Y and ZSM-5 zeolite catalyst was characterized by N_(2) physical adsorption-desorption,pyridine adsorption Fourier-transform infrared spectrum(Py-FTIR)and temperature-programmed desorption of ammonia(NH_(3)-TPD),and the effects of reaction temperature and pressure on catalytic performance in heterogenous oligomerization of ethylene were investigated.The results showed that the catalytic cracking catalyst was rich in mesoporous 3—4 nm and weak Lewis acid sites.At 500—550℃ and atmospheric pressure,ethylene was not easy to be converted,C_(3)—C_(4) olefin was mainly produced by oligomerization and cracking,and the selectivity of propylene was higher than that of butylene.When the reaction temperature was higher than 550℃,the selectivity of coke was greatly increased by the cyclization dehydrogenation of propylene and butylene.Compared with the normal pressure,the catalytic cracking catalyst with weak Lewis acid sites could effectively catalyze ethylene oligomerization with the conversion higher than 70%at reaction pressure of 0.5—1.0 MPa.Increasing the reaction pressure was beneficial to the hydrogen transfer reaction of propylene and butylene,increasing the selectivity of propane and butane,while decreasing the selectivity of coke.