甲醇制芳烃反应过程中纳米ZSM-5分子筛催化剂性能演变与结构性质的关系研究  

Variance in the catalytic performance of nano-ZSM-5 zeolites during the reaction process of methanol to aromatics and its relation to the structural properties

作　　者：李晗 付廷俊[1] 张亮亮 马倩 崔丽萍[1] 李忠[1] LI Han;FU Ting-jun;ZHANG Liang-liang;MA Qian;CUI Li-ping;LI Zhong(Key Laboratory of Coal Science and Technology,Ministry of Education and Shanxi Province,Taiyuan University of Technology,Taiyuan 030024,China)

机构地区：[1]太原理工大学煤科学与技术教育部和山西省重点实验室,山西太原030024

出　　处：《燃料化学学报》2021年第4期483-494,共12页Journal of Fuel Chemistry and Technology

基　　金：国家重点研发计划(2018YFB0604901);国家自然科学基金(21978191,21878207)资助。

摘　　要：ZSM-5分子筛催化甲醇制芳烃反应中,存在产品选择性低和催化稳定性差等问题。本研究通过XRD、物理吸附、NH3-TPD、TEM、TG及27Al MAS NMR等手段表征分析反应过程中ZSM-5的结构变化,结合催化性能演变,探讨不同反应阶段影响其结构与性能的关键因素。结果表明,反应初期19 h内高温水热对铝结构的破坏使酸量由0.41 mmol/g明显降至0.17 mmol/g,低碳烯烃选择性显著增加,液烃收率由14.7%快速增至19.3%。稍后的24 h稳定反应阶段中,积炭速率增加,催化剂比表面积由340 m2/g显著降至275 m~2/g,酸量继续下降至0.10 mmol/g;液烃收率仍维持在19.5%,说明该反应仅需少量酸即可维持。之后31 h内积炭不断累积,虽然积炭速率明显降低,但催化剂逐渐失活;外表面积炭显著增加,比表面积和酸量继续缓慢减小,液烃收率降至17.3%,芳烃选择性也随之降低。反应末期的7 h里,积炭严重覆盖了ZSM-5酸位并堵塞孔道,液烃收率突降至12.2%,CH_4选择性由13.2%骤增至24.2%;积炭对外表面酸的覆盖减少了表面异构化,对二甲苯在二甲苯中选择性由24.4%增至33.1%。考虑到积炭对失活后团聚晶粒的整体包裹,应设法减少晶粒外表面间的接触,以提升分子对反应活性位的可接近性和催化剂的容碳能力。该研究为芳构化催化剂制备时酸性和形貌的控制提供了依据。Low selectivity to target products and poor catalytic stability remain two crucial issues for the conversion of methanol to aromatics(MTA)catalyzed by ZSM-5 zeolites.In this work,the variance in catalytic performance of ZSM-5 zeolites with the time on stream during a long term MTA test was monitored and related to the structural changes which were characterized by XRD,physisorption,NH3-TPD,TEM,TG and 27Al MAS NMR;the key structural factors affecting the catalytic performance and structure were then investigated.The results illustrate that within the early 19 h after starting the reaction,the amount of acid sites decreases significantly from 0.41 to 0.17 mmol/g due to the damage to the structure of aluminum species under high temperature hydrothermal conditions;the selectivity to light alkenes increases significantly,accompanying with a rapid increase of the liquid hydrocarbons yield from 14.7%to 19.3%.In the next stable reaction stage of 24 h,the rate of coke formation increases and the surface area decreases significantly from 340 to 275 m2/g,whilst the amount of acid sites decreases continuously to 0.10 mmol/g;the liquid hydrocarbon yield keeps above 19.5%,suggesting that a small amount of acid sites will be sufficient to stably bolster the MTA reaction.In contrast,in the next 31 h,although the rate of coke formation decreases obviously,the catalyst is deactivated gradually,dominantly by the coke deposition on the external surface;in this period,the surface area and the amount of acid sites decreases continuously and slowly and the liquid hydrocarbon yield drops to 17.3%,accompanying with a decrease in the selectivity to aromatics.At the end of the reaction of 7 h,the liquid hydrocarbon yield drops to 12.2%,due to the complete coverage of the acid sites and serious blockage of the pore by coke deposition;meanwhile,the selectivity to CH4 increases significantly from 13.2%to 24.2%,whereas the fraction of p-xylene in xylenes increases from 24.4%to 33.1%,owing to the suppression of isomerization on the external sur

关 键 词：甲醇 芳烃 ZSM-5分子筛 积炭 反应过程 结构变化 

分 类 号：O643.3[理学—物理化学]