论文标题:超临界苯烷基化反应体系在分子筛中吸附行为的分子模拟
Adsorption of Benzene Alkylation System in Zeolites under Supercritical Condition by Molecular Simulation
论文作者 陈小明
论文导师 汪文川,论文学位 硕士,论文专业 化学工程
论文单位 北京化工大学,点击次数 79,论文页数 96页File Size2096k
2004-05-26论文网 http://www.lw23.com/lunwen_202344377/ 超临界;苯的烷基化;Monte Carlo 模拟;ZSM-5
supercritical;benzene alkylation;Monte Carlo simulation;ZSM-5
本文研究的内容包含三个方面。一是超临界苯烷基化体系在ZSM-5 中吸附行为的分子模拟;二是超临界苯-丙烯烷基化体系在ZSM-12、Mordenite、ZSM-5、β、MCM-22、ITQ-14 一系列分子筛中吸附行为的分子模拟;三是纯组分苯和纯组分丙烯在全新分子筛ITQ-22 中吸附行为的分子模拟。 在苯的烷基化反应中,传统的生产工艺以固体磷酸或三氯化铝为催化剂,设备腐蚀和环境污染严重。解决的方法是以固体酸分子筛催化剂来取代。由于烯烃的齐聚以及苯的深度烷基化等原因,容易堵塞分子筛孔道,导致分子筛催化剂的失活,这是分子筛催化苯烷基化新工艺亟待解决的问题。针对这个问题,本文提出了两种解决的途径。一是将反应条件设置在超临界条件下,这是由于超临界流体具有优良的传热、传质及溶解萃取性能,能有效萃取焦前驱体,可望延缓催化剂结焦失活;二是使用新的分子筛,这是因为不同的分子筛本身有不同的选择性,有不同的稳定性和使用寿命,因此,应用新的对苯烷基化反应有更高选择性的分子筛也不失为一个解决的好方法。本文采用分子模拟的方法探讨这两条途径的可行性。 i北 京 化 工 大 学 硕 士 学 位 论 文 第一条途径是将反应条件设置在超临界条件下,也即本文第一部分的内容。模拟计算 ZSM-5 分子筛中苯-丙烯体系和苯-乙烯体系在超临界条件下的吸附行为,比较分析五个相区中苯烷基化混合体系的吸附,最终认为超临界条件是有利于苯的烷基化反应产物的生成,有利于延缓分子筛催化剂失活的。 第二条途径是选择新的分子筛作为催化剂,也即本文第二部分的内容。模拟计算了超临界条件下在 ZSM-12、Mordenite、ZSM-5、β、MCM-22、ITQ-14 这一系列分子筛中苯-丙烯体系的吸附行为。比较分析模拟的结果和试验结果发现新分子筛ITQ-14中苯的吸附选择性最高,对于苯烷基化反应来说应有很好的稳定性,可延缓催化剂结焦失活。 本文第三部分的内容是探讨全新分子筛ITQ-22的吸附特性及应用前景。由于芳烃及烯烃涉及多种涉及多种催化和分离过程,因此,研究它们在分子筛中的吸附行为具有重要的意义。本文选择苯和丙烯作为代表,探讨它们在 ITQ-22 分子筛中的吸附行为。
This thesis contains three parts.The first part is the molecular simulation of adsorption behaviors of benzene alkylation system in supercritical condition.The second part investigates the adsorption of benzene alkylation with propylene in several zeolites,including ZSM一12,Mordenite,ZSM一5,p,MCM一22 and ITQ-14. Then,the adsorption behaviors of benzene and propylene in new type zeolite,ITQ一22, iS discussed. According to the benzene alkylation with olefins,the polymerization of olefins and further alkylation of benzene contribute to the deactivation of zeolites.In order to resolve this problem,there are two ways recommended by this thesis.One is to undergo the reaction in supercritical condition,because chemical reactions in supercritical conditions can be accelerated,the product selectivity can be improved and more importantly,catalyst coking can be reduced.The other way is using new type zeolites,because different zeolites have different selectivity of molecules and different stability of catalyst to the benzene alkylNion reaction.This thesis investigated the feasibility of the two ways mentioned above using molecular simulation method. Benzene alkylation reaction in supercritical condition is first way mentioned above,and the discussion of adsorption behavior of the benzene— propylene and benzene-ethylene alkylation system in ZSM一5 under supercritical condition is the first part of this thesis.The adsorption behaviors of benzene—propylene system in variety of conditions,including subcritical and supercritical conditions show that benzene alkylation reaction in supercritical condition increases the yield of products and improves the stability of zeolite.The result of this part consists of four points,(1)In vapor phase,the equilibrium ratio of benzene/propylene in simulation decreases and is close to 1:1 with the decrease of temperature,which is interestingly similar to the experimental results,where the selectivity of cumene is close to 100%with the decrease of temperature.It suggests that a high yield for benzene alkylation with propylene to produce cumene,the equilibrium ratio Of benzene/prOpylene,close to 1:1 in the pores of ZSM一5.This is in agreement with the reaction mechanism of benzene alkylation with propylene.(2)The adsorption behaviors in five different phases, including supercritical,near supercritical,gas,vapor,and liquid phases,are discussed。 The simulation results show that the equilibrium ratio of benzene/propylene is closer to 1:1 in supercritical and near supercritical phases than that in other phases.This is corresponding to the experimental results,where the selectivity of cumene is highest in supercritical condition.(3)The effect of the feed ratio of benzene/propylene(or ethylene)in supercritical condition is investigated.On the one hand,according tO benzene-propylene system,the equilibrium ratio of benzene/propylene is nearest to 1:1 when the feed ratio of benzene/propylene is 5:1.On the other hand,according to benzene— ethylene system,the equilibrium ratio of benzene/ethylene is nearest to 1:1 when the feed ratio of benzene/ethylene is 3:1.It suggests that the proper feed ratio is 5:1 to benzene--propylene system and 3:1 to benzene-ethylene system for the high values of the selectivity of cumene.(4)The adsorption isotherm of benzene and the localization of benzene molecules in ZSM一5 suggest that benzene molecules is ‘commensurate freezing’in the interconnection of sinusoidal and straight channels. Using a new zeolite as the catalysit of benzene alkylation is another way mentioned above,and the discussion of adsorption behavior of the benzene— propylene system in several zeolites,including ZSM一5,ZSM一12,Mordenite,ZSM一5,p, MCM一22 and ITQ一14 under supercritical condition is the second part of this thesis. The simulation results,comparing with the experimental data,show that the new zeolite,ITQ一14,has the highest adsorption selectivity of benzene,and sugg
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