【作者】 洪哲；

【导师】 朱志荣；

【作者基本信息】 同济大学 ， 化学， 2022， 博士

【摘要】 苯乙烯在石油化工领域有着重要的应用。目前工业上主要通过苯和乙烯发生烷基化反应得到乙苯,随后将乙苯脱氢制得苯乙烯。相较于传统的工艺路线,采用来源广泛且成本相对较低的甲苯、甲醇为原料,通过甲醇与甲苯的侧链发生烷基化反应合成苯乙烯,具有工艺流程简单、能耗低和成本低等优点,是一条具有工业应用前景的苯乙烯生产路线。本论文首先对甲苯与甲醇侧链烷基化反应的催化剂以及反应机理等方面的研究背景进行了系统的综述。随后,深入地研究了吡啶碱辅助的Cs改性X分子筛催化剂的甲苯甲醇侧链烷基化反应性能、高分散的Pt纳米粒子改性的Cs X催化剂的甲苯甲醇侧链烷基化催化性能、X分子筛的酸蚀后处理对甲苯甲醇侧链烷基化反应性能的影响,以及Cs改性的中空ZSM-5催化剂的2-甲基吡啶与甲醛的侧链烷基化催化性能等几个方面。具体研究内容如下:首先,本文设计制备并表征了一系列Cs改性的X分子筛催化剂,并考察了甲苯甲醇侧链烷基化催化性能。同时采用在反应体系中引入有机碱性化合物甲基吡啶辅助催化方法,探究其对反应活性的影响。此外,进一步考察了不同浓度的2-甲基吡啶对Cs改性X分子筛催化性能的影响,并深入探究了不同2-甲基吡啶浓度下的甲苯甲醇烷基化反应路径。实验结果表明,不同浓度2-甲基吡啶的引入对Cs改性X催化剂的催化活性具有重要影响。在0-10 mol%的2-甲基吡啶浓度范围内,催化活性随着2-甲基吡啶的浓度先提高随后显著降低。低浓度2-甲基吡啶的引入有利于促进甲醇脱氢生成甲醛,甲醛作为与甲苯直接发生反应的烷基化试剂有利于侧链烷基化反应生成苯乙烯。但当2-甲基吡啶浓度较高,较强的碱性使甲醇深度分解为CO并释放大量H₂,导致甲醇的利用率降低,同时苯乙烯与H₂加氢生成了更多的乙苯,因而不利于甲苯的转化和苯乙烯产物的生成。此外,低浓度2-甲基吡啶的引入有利于单齿甲酸盐中间物种的形成,而高浓度的2-甲基吡啶则导致单齿甲酸盐转变为对侧链烷基化反应不利的双齿甲酸盐。在CsX催化剂的基础上,通过真空浸渍法引入高分散的Pt纳米粒子,设计制备了一系列Pt改性的Cs X催化剂,并系统考察了Pt改性Cs X催化剂的物理化学性质和甲苯甲醇侧链烷基化反应催化性能。研究表明,当Pt负载量为0.5 wt%并250 ^oC H₂还原处理的Pt改性Cs X催化剂（0.5Pt/Cs X-540-R250）表现出优于母体Cs X的催化性能,其甲苯转化率和苯乙烯选择性分别可以达到9.7%和72.4%,同时0.5Pt/Cs X-540-R250相比于Cs X也表现出更好的反应稳定性。结合相关表征结果认为,在Cs X催化剂表面引入高分散的Pt⁰物种能够有效促进甲苯侧链甲基C-H键的活化,进而有利于提高侧链烷基化反应的甲苯转化率,同时Pt⁰物种良好的加氢特性能够使反应过程中生成的烯烃（积碳前驱体）氢化为烷烃,从而在一定程度上抑制积碳的生成,进而延缓催化剂失活,提高催化剂的反应稳定性。同时本文进一步通过NH₄F后处理的方法制备了一系列具有不同微孔/介孔特性的X分子筛,并通过离子交换、以及离子交换与浸渍结合的方法对其改性处理,考察了不同铯改性X催化剂上的甲苯与甲醇侧链烷基化反应性能。研究发现,相较于未进行后处理的母体X分子筛,NH₄F酸蚀30 min的样品的催化活性有所提高,而随着酸蚀时间进一步增加为60 min和120 min,样品的催化性能与未处理的X分子筛相比均有不同程度的降低。碱金属改性的X分子筛的催化性能与其孔结构密切相关。NH₄F酸蚀30 min的样品（X-FT-30）在保留了X分子筛固有微孔结构的同时疏通并增加了部分孔道,拥有比未处理的X分子筛（X-C）更大的比表面积,可反应利用的活性中心数量增加,因而表现出更优异的催化性能。当酸蚀后处理时间较长,使X分子筛固有微孔结构被破坏,则导致催化活性的降低。最后通过研究不同催化剂上2-甲基吡啶与甲醛的侧链烷基化反应,加深了对于侧链烷基化反应过程的理解。在四丙基氢氧化铵（TPAOH）溶液的的作用下,经过“脱硅溶液-重结晶”策略成功合成了中空ZSM-5分子筛,并对其进行铯改性处理,比较了Cs改性的中空ZSM-5催化剂和传统ZSM-5催化剂上2-甲基吡啶与甲醛侧链烷基化催化性能的差异。结果表明,Cs改性的中空ZSM-5催化剂（Cs₂O/Cs-h ZSM-5）表现出更优的催化性能,其2-甲基吡啶转化率在320 ^oC时可以达到50.1%,同时2-乙烯吡啶的选择性达62.5%。此外,Cs₂O/Cs-h ZSM-5催化剂也表现出更优的反应稳定性。结合XRD、N₂物理吸附、TEM、CO₂-TPD和NH₃-TPD等表征结果与反应活性数据关联分析,发现催化剂的侧链烷基化反应活性与其载体内部结构和酸碱性质都有关系。Cs₂O/Cs-h ZSM-5催化剂具有更大的BET比表面积和孔体积、更强的碱性中心以及适宜的弱酸性中心,有利于反应物的扩散、吸附和活化,因而表现出更加优异的催化性能。更多还原

【Abstract】 Styrene has an important application in the petrochemical field.The most conventional route for the large-scale production of styrene is based on a homogeneous Friedel-Crafts alkylation reaction,typically starting from benzene alkylation with ethylene,followed by the dehydrogenation of ethylbenzene.Recently,a potential route for styrene production by toluene side-chain with methanol is proposed.This process of producing styrene offers advantages,such as simple process,lower energy consumption and less environmental pollution compared with the traditional styrene production route.This thesis firstly focused on the review on catalysts and reaction mechanism in side-chain alkylation of toluene with methanol.Furthermore,this thesis explore the side-chain alkylation of toluene with methanol to styrene over the Cs-modified X zeolite by the assistance of basic compounds（2-picoline）as a co-catalyst,the promoting effect of highly dispersed Pt nanoparticles in side-chain alkylation of toluene with methanol,the catalytic activity of X zeolite obtained by post treatment methods,and the cesium-modified hollow ZSM-5 catalyst for side-chain alkylation of 2-picoline with formaldehyde.Firstly,a series of cesium modified zeolite catalysts were synthesized,characterized and the catalytic activities for side-chain alkylation of toluene with methanol were studied.A new way is introduced to improve the catalytic activity by means of assisting basic compounds as co-catalysts during the reaction.Moreover,the effect of 2-picoline concentration on the activity was investigated.With the increase of the 2-picoline concentration from 0 to 2 mol%,both the toluene conversion and styrene selectivity were increased.However,further increase of 2-picoline rapidly caused a drop of catalytic activity.The results indicated that the addition of 2-picoline with low and high concentration have different effects on the toluene side-chain alkylation reaction.Two possible reaction routes on Cs-modified zeolite under the different 2-picoline concentration were proposed:when the concentration of2-picoline is low,the methanol firstly dehydrogenated to formaldehyde,and then attacked the methyl group of toluene to form styrene;while in the high concentration range of 2-picoline,the formaldehyde prefer to further decompose into CO and H₂,thereby dropping the reaction activity.The styrene would be undesirably hydrogenated by H₂ to form excessive ethylbenzene.In addition,the addition of low concentration of 2-picoline is beneficial to the formation of monodenate formate,while bidentate formate is more easily to form under the high concentration of2-picoline.Secondly,a series of Pt-modified CsX catalysts were prepared by vacuum impregnation method and investigated for the physicochemical properties and activities in the reaction of toluene side-chain alkylation with methanol.Among which,the 0.5Pt/Cs X-540-250R catalyst demonstrated superior catalytic activity,leading to a toluene conversion of 9.7%and styrene selectivity of 72.4%.Meanwhile,this Pt modified catalyst exhibited better reaction durability than Cs X.The high performance mainly lies in two aspects:（1）the highly dispersed Pt nanoparticles could assist C-H bond activation in the methyl group of toluene more efficiently to promote the toluene conversion;（2）the inhibition of coke formation by Pt modification to retard the catalyst deactivation.Thirdly,a series of X zeolites with different micro/mesoporosity were synthesized through the post treatment of NH₄F,and then modified by cesium ion exchange and impregnation methods.By comparing the catalytic performance of these Cs modified samples,it was found that the sample with 30 min of NH₄F post treatment exhibited higher catalytic activity than that of the parent sample.However,further increase of etching time to 60 min and 120 min rapidly caused a drop of catalytic activity.We considered that the microporous structure of X zeolites play the critical role in the process of side-chain alkylation of toluene.The sample with 30 min of NH₄F post treatment（X-FT-30）showed larger microporous surface area than parent X,resulting in the increase of available active sites.When etching time is long during the post treatment process,the inherent micropore structure would be destroyed.And the losing microporosity caused the decreasing of catalytic activity.Finally,by studying the side chain alkylation reaction of 2-picoline with formaldehyde on different catalysts,the understanding of the side chain alkylation process is deepened.Hollow ZSM-5 was synthesized by tetrapropylammonium hydroxide（TPAOH）alkali treatment for parent ZSM-5.The side-chain alkylation activity was investigated on the Cs-modified ZSM-5 catalysts.Among these catalysts,Cs₂O/Cs-hollow ZSM-5（Cs₂O/Cs-h ZSM-5）was found to display the highest catalysis performance,which showed the highest 2-picoline conversion of 50.1%and2-vinylpyridine selectivity of 62.5%.Meanwhile,the Cs₂O/Cs-hollow ZSM-5displayed excellent reaction durability.Combining catalytic performance with characterization results（including XRD,N₂ adsorption/desorption,TEM,CO₂-TPD and NH₃-TPD）,the larger BET surface area,increased mesoporous channels and harmonious acid-base property of the Cs modified hollow ZSM-5 catalysts facilitates the transport,adsorption and activation of reactant,thus endowed them with excellent catalytic performance.更多还原