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作 者:赵勤 李芳 张鹏鹤 刘月明 Zhao Qin;Li Fang;Zhang Penghe;Liu Yueming(State Key Laboratory of Petroleum Molecular&Process Engineering,Shanghai Key Laboratory of Green Chemistry and Chemical Processes,School of Chemistry and Molecular Engineering,East China Normal University,Shanghai 200062,China)
机构地区:[1]华东师范大学化学与分子工程学院、石油化工分子转化与反应工程全国重点实验室、上海市绿色化学与化工过程绿色化重点实验室,上海200062
出 处:《化学学报》2024年第10期1013-1021,共9页Acta Chimica Sinica
基 金:国家自然科学基金(Nos.22072044,21673076);华东师范大学“幸福之花”基金(No.2020ST2203)资助。
摘 要:庚烯(C_(7)^(=))是一种重要的化工中间原料.C_(7)^(=)催化裂解制乙烯/丙烯(C_(2)^(=)/C_(3)^(=))过程是烯烃碳资源高值化利用的有效途径,然而其裂解反应路径及其调控原理仍有待厘清.本工作根据正碳离子机理和β-裂解机理,首先建立了C_(7)^(=)催化裂解反应路径网络,并考察了不同拓扑结构分子筛催化剂的催化裂解性能,发现ZSM-5分子筛是C_(7)^(=)催化裂解的高效催化剂.在此基础上,系统研究了ZSM-5分子筛的酸性质(酸量、酸强度)对反应的影响.结果表明,ZSM-5分子筛酸量、酸强度的降低,均抑制了生成非烯烃类产物的氢转移、芳构化等反应路径,进而提高了烯烃碳资源利用率.特别的是,ZSM-5分子筛的酸强度控制了C_(7)^(=)单分子裂解反应路径Ⅰ(C_(7)^(=)→C_(3)^(=)+C_(4)^(=))和路径Ⅱ(C_(7)^(=)→C_(2)^(=)+C_(5)^(=)),强酸中心促进裂解路径Ⅱ而多产乙烯,弱酸中心利于裂解路径Ⅰ而多产丙烯.本研究为C_(7)^(=)催化裂解制C_(2)^(=)/C_(3)^(=)过程中碳资源高效利用的催化剂设计提供了新思路.Heptene(C_(7)^(=))is an important chemical intermediate.The C_(7)^(=)catalytic cracking to ethylene/propylene(C_(2)^(=)/C_(3)^(=))represents an effective approach for the high-value utilization of carbon resources.However,the reaction pathways involved in the catalytic cracking of C_(7)^(=)and the principles governing their modulation remain to be thoroughly analyzed and clarified.In this study,we established a reaction network for C_(7)^(=)catalytic cracking based on the carbenium ion mechanism andβ-scission mechanism.We investigated the catalytic performance of various zeolite catalysts with different topological structures and found that ZSM-5 zeolite,characterized by its unique pore structure,served as an efficient catalyst for C_(7)^(=)catalytic cracking.On this basis,a series of ZSM-5 zeolites(ZSM-5(I)to ZSM-5(V))with comparable acid density and varying acid strength were synthesized via hydrothermal processes using phosphorus-modified and ammonium fluorosilicate-modified methods.The effects of the acidity(acid amount and acid strength)of the ZSM-5 zeolites on the catalytic cracking reaction of C_(7)^(=)were systematically investigated under 550℃.The results indicated that the C_(7)^(=)catalytic cracking primarily involved unimolecular cracking,hydrogen transfer,dehydrogenative aromatization,and decarbonylation reactions.The reduction of both acid amount and acid strength in ZSM-5 suppressed the reaction pathways for generating non-olefinic products,such as hydrogen transfer and aromatization,while enhancing the cracking pathways that produce olefins,thereby increasing the carbon resource utilization efficiency.Specifically,the acid strength of ZSM-5 played a crucial role in controlling the unimolecular cracking reaction pathways:pathwayⅠ(C_(7)^(=)→C_(3)^(=)+C_(4)^(=))and pathwayⅡ(C_(7)^(=)→C_(2)^(=)+C_(5)^(=)).An increase in strong acid sites within ZSM-5 enhanced pathwayⅡ,leading to increased ethylene yields.Conversely,a higher number of weak acid sites promoted pathwayⅠ,resulting in greate
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