【作者】 颜卫；

【导师】 辛峰；

【作者基本信息】 天津大学 ， 化学工程， 2007， 硕士

【摘要】 分子筛是绿色化学与化工中常用的环境友好材料,在催化反应中的应用也日渐广泛。钛硅分子筛TS-1催化环己酮液相氨肟化合成环己酮肟是分子筛催化的典型反应之一。Enichem公司开发成功的钛硅分子筛TS-1催化环己酮氨肟化新工艺,合乎绿色化工发展的要求,具有重要的工业推广价值。但对于该反应的机理,还存在着争论,所建立的动力学模型也缺乏足够的研究依据。本文采用分子模拟的方法,对环己酮催化氨肟化的吸附、反应和扩散机理进行了研究。首先建立合理的分子筛簇模型来模拟分子筛活性中心,并通过从头计算方法研究了过氧化钛反应活性中心的生成过程。根据环己酮催化氨肟化反应体系的特点,在传统的过氧化钛反应活性中心基础上,用氨水作为过渡金属钛原子的配位体重新定义适用于该反应体系的反应活性中心。体系能量计算结果表明,新建立的反应活性中心模型能量比传统的过氧化钛模型低3.3kcal/mol,更加稳定和合理。确定活性中心的分子结构后,根据能量最小化原理计算了各个反应物吸附在反应活性中心模型上不同位点时的体系能量,并以能量最低处的吸附状态作为各反应物吸附位置;在此基础上,运用过渡态理论,对按亚胺机理和羟胺机理所进行的反应过程进行了具体分析。结果表明,从量子化学角度分析,环己酮氨肟化反应的亚胺机理和羟胺机理均可以发生。反应过程中可以生成环己亚胺和羟胺。亚胺是由吸附态的氨分子和环己酮作用生成,过程中只有一种过渡态产生;而羟胺的形成是由反应活性中心和氨水分子反应得到,过程中有两个过渡态连续产生,生成第一个过渡态后会形成O-NH4+结构作为中间结构,随后继续反应生成羟胺。从环己亚胺或羟胺形成产物环己酮肟的反应也可以进行,过程中均只找到一个过渡态。同时发现羟胺和环己酮可在分子筛不参与反应条件下,生成环己酮肟。运用化学反应动力学的理论对各个基元过程的活化能以及化学反应速率常数进行计算。分析出亚胺机理中环己酮的吸附和环己亚胺的形成是该反应的速率控制步骤,分别需要跨越61.5kcal/mol和46.61kcal/mol的能垒;羟胺机理中生成羟胺的反应为速率控制步骤,需要跨越65.19kcal/mol的能垒。通过比较能量变化可知,羟胺机理在能量上要优先于亚胺机理,即羟胺机理的反应过程较易发生。最后,使用分子动力学和蒙特卡洛的方法,对环己酮分子在和TS-1具有相同MFI拓扑结构的ZSM-5分子筛中的扩散进行了初步的研究,发现环己酮分子和分子筛骨架间相互作用的势能是控制环己酮分子在分子筛中扩散速度的主要因素;环己酮分子在晶内扩散时,斥力是分子间主要的相互作用力。更多还原

【Abstract】 Molecular sieve, applied in catalyzed reaction widely, is a kind of environmental friendly material and frequently used in the field of“Green chemistry”. Titanium Silicalite-1 (TS-1) catalytic ammoximation of cyclohexanone in the liquid phase, developed by Enichem Co., is one of the typical processes in molecular sieve catalysis, and is advantageous from the environmental point of view and meets the requirement of“Green Chemical Engineering”. Notwithstanding several studies on this process, there is not a general agreement about the catalytic reaction mechanism, and the theoretical bases for existing kinetic models are also absent.In this paper, the mechanism of catalytic ammoximation of cyclohexanone with H2O2 to cyclohexanone oxime over TS-1 catalyst was investigated by the method of molecular simulation. The adsorption、reaction and diffusion mechanisms were discussed respectively. The formation of active complex was studied by the ab-initio method based on the establishment of proper cluster model of TS-1. According to the characters of this reaction system, a novel active complex was proposed by incorporated ammonia water in the catalyst model as a ligand of Ti atom. The newly-developed active complex was found to be more stable than the conventional one by lower 3.3kcal/mol of overall energy.After the establishment of active complex model, the interaction between reactant and the catalyst was estimated by calculating the overall energy when reactants adsorbed on different positions of the active complex. The final adsorption states of reactants were found at the minimum of calculated energy profiles. Then the reaction pathways of cyclohexanone ammoximation were investigated by transition state theory based on the final sorption states. The results revealed that the imine mechanism and hydroxylamine mechanism were both existed in the reaction. The intermediate, imine and hydroxylamine, were all attainable from perspectives of quantum chemistry. Only one transition state could be found during imine formation which caused by the interaction between adsorbed ammonia and cyclohexanone. Meanwhile, two transition states could be found consecutively during hydroxylamine formation by the interaction between the ammonia water and the reaction active center. One intermediate structure, which represented O-NH4+, was also found and it was generated after the first transition state formed. Then the intermediate could subsequently formed hydroxylamine. The formation of cyclohexanone oxime was also attainable from both imine and hydroxylamine with only one transition state found in each of the procedures. It also could be found that the hydroxylamine and cyclohexanone could generate cyclohexanone oxime without zeolite participating.The activation energy and rate constant of each elementary reaction were also estimated by chemical dynamics. The results indicated that the formation of imine and the adsorption of cyclohexanone were the rate control steps in the imine mechanism procedure with the activation energy barrier of 61.5kcal/mol and 46.61kcal/mol respectively. The formation of hydroxylamine was the rate control step in the hydroxylamine mechanism with the activation energy barrier of 65.19kcal/mol. The energy changes were compared, and it was found that the hydroxylamine mechanism was the energy-preferred pathway in cyclohexanone ammoximation, which means the hydroxylamine mechanism was the main pathway to produce oxime during the reaction.At last, the diffusion mechanism of cyclohexanone in ZSM-5 zeolite with MFI topology was studied by Molecular Dynamics and Kinetic Monte Carlo. The calculate energy profiles and diffusivity coefficients shows that the potential energy between cyclohexanone and zeolite framework was the main factor of rate control while duffusion and the repulsion was the major factor for the interaction among cyclohexanones.更多还原