HZSM-5上正己烷酸催化裂解反应路径及机理的研究  

Insight into reaction path and mechanism of catalytic cracking of n-hexane in HZSM-5 zeolites

作　　者：翟鹏 郑健 张锦研 王焕[1,2] 秦玉才 刘宏海[3] 宋丽娟 ZHAI Peng;ZHENG Jian;ZHANG Jin-yan;WANG Huan;QIN Yu-cai;LIU Hong-hai;SONG Li-juan(Key Laboratory of Petrochemical Catalytic Science and Technology,Liaoning Petrochemical University,Fushun 113001,China;College of Chemistry and Chemical Engineering,China University of Petroleum(East China),Qingdao 266555,China;PetroChina Petrochemical Research Institute Lanzhou Petrochemical Research Centre,Lanzhou 730060,China)

机构地区：[1]辽宁石油化工大学辽宁省石油化工催化科学与技术重点实验室,辽宁抚顺113001 [2]中国石油大学(华东)化学工程学院,山东青岛266555 [3]中国石油石油化工研究院兰州化工研究中心,甘肃兰州730060

出　　处：《燃料化学学报》2021年第10期1522-1530,共9页Journal of Fuel Chemistry and Technology

基　　金：国家自然科学基金(21902068,U20A20120);中国石油科技创新基金(2020D-5007-0401);辽宁省教育厅科学研究经费优青培育计划项目(L2019035)资助。

摘　　要：以正己烷为模型化合物,通过产物分布分析,探讨HZSM-5分子筛上烷烃酸催化裂解反应路径及机理。研究结果表明,反应温度为300℃,不存在热裂解过程的条件下,只有基于碳正离子机理的酸催化反应。催化剂裂化活性与B酸(Brönsted acid)量成正相关。由裂解产物的分布特点,其中,丙烯的选择性与催化剂硅铝比和剂油比正相关,而乙烷、乙烯和丙烷的选择性呈负相关性,证实了低酸密度有利于单分子裂解路径的进行。值得注意的是,正己烷直接裂解所得C4产物的总选择性明显高于C_(2)产物,结合量化计算,证实正己烷裂解生成的C_(2)H^(+)_(5)碳正离子难以通过氢转移反应生成乙烯和乙烷,而是更倾向于与正己烷分子形成新的碳鎓离子(C_(8)H^(+)_(19)),继续发生裂解反应生成更多C4产物,揭示了轻烃催化裂解产物中乙烯选择性低的理论本质。综上可知,通过改变催化剂酸密度和剂油比,可实现反应路径的控制,从而调控轻烃酸催化裂解产物的选择性。本研究可为石脑油催化裂解催化剂和工艺开发提供重要的理论支撑。The n-hexane was used as a model compound to study the catalytic cracking behavior of light hydrocarbon in HZSM-5 zeolites,and the law of product selectivity of real acid-catalyzed reaction was investigated by analyzing the product distributions.The results showed that no pyrolysis reaction was found at 300℃.Only the acid catalytic reaction took place by the mechanism of carbocation,whose activity was positively correlated to the amount of Brønsted(B)acid sites.The selectivity of ethane,ethylene and propane was negatively correlated,while that of propylene was positively correlated with the Si/Al ratios and catalyst to oil ratios,suggesting that low acid density might be more favorable for monomolecular cracking reactions.It was worth nothing that the total selectivity of C4 products was much higher than that of C_(2)products.Combined with the quantum chemistry calculation results,it could be confirmed that the super-stability of C_(2)H^(+)_(5)carbenium ion from the monomolecular cracking of n-hexane made it difficult to produce ethylene and ethane through hydrogen transfer reaction.It’s easier to form a C8 carbenium ion(C_(8)H^(+)_(19))with another n-hexane molecule,and then to generate more C4 products.These results revealed the nature of the low selectivity of ethylene in light hydrocarbon catalytic cracking products.It could be concluded that the product selectivity of catalytic cracking of light hydrocarbons could be modulated by controlling reaction paths depending on the catalyst acid properties and the catalyst to oil ratios.This work will provide important theoretical support for the catalyst design and process development of naphtha catalytic cracking.

关 键 词：HZSM-5 催化裂解 Brønsted酸中心 选择性 碳正离子 

分 类 号：O643[理学—物理化学]