ZSM-5分子筛酸分布对丁烯裂解制丙烯性能的影响

Effect of ZSM-5 Zeolite Acid Distribution on Butene Cracking to Propylene

以硝酸钙为改性剂处理ZSM-5分子筛孔道内及外表面的酸中心,得到一系列酸分布不同的钙改性ZSM-5分子筛催化剂,并采用XRD,SEM,BET,XRF,NH_3-TPD等技术对催化剂的物化性质进行表征;在连续流动固定床反应器上研究了分子筛孔道内及外表面的酸分布对丁烯裂解制丙烯反应性能的影响。实验结果表明,钙改性ZSM-5分子筛的酸量是丁烯裂解活性的决定因素,酸量越多,催化剂催化丁烯裂解的活性越高;丙烯选择性主要受催化剂酸强度的影响,降低酸强度有利于提高丙烯选择性;ZSM-5分子筛外表面酸中心在丁烯催化裂解制丙烯过程中起主要作用,改性时保留外表面酸中心有利于提高丙烯选择性。

A series of ZSM-5 catalysts with different acid distribution were prepared by the treatment of the acid centers located on the zeolite channel and/or outer surface with calcium nitrate as the modifier. The catalysts were characterized by means of XRD, SEM, BET, XRF and NH^3-TPD. The effect of the ZSM-5 acid distribution on butene cracking to propylene was investigated on a continuous fixed-bed reactor. The results manifested that the butane conversion was determined by the acid amount and raised with increasing of the acid amount. Propylene selectivity was influenced mainly by the acid strength and low acid strength was beneficial to the improving of propylene selectivity. The acid centers located on the outer surface played a more important role in butene cracking to propylene than those located in the zeolite channel, the propylene selectivity was improved by the treatment of the ZSM-5 zeolite with the modifier, and at the same time the acid centers located on the outer surface were protected.