乙醇一步法制乙酸乙酯铜铬催化剂吸附性能分子模拟研究

发布时间：2018-05-31 08:05

本文选题：乙酸乙酯 + 分子模拟　；参考：《天津大学》2010年硕士论文

【摘要】：乙酸乙酯是一种用途广泛的大宗化学品。乙醇一步法制备乙酸乙酯可采用单一生物乙醇作原料,无污染腐蚀性小,近些年来广受关注。该方法所使用的催化剂主要是铜铬催化剂,可以应用于工业化生产。对于该反应吸附方面的研究目前只是借助实验手段,由于实验手段的局限性,有些方面无法探测,并且缺乏深入的认识,亟待展开研究。本文采用分子模拟方法研究了乙醇一步法制备乙酸乙酯反应中各物种在Cu、Cr_2O_3和Cu/Cr_2O_3催化剂上的吸附行为,深入探究和解释影响催化剂不同吸附性能的原因,并设计了验证性实验,以期更好地指导实践。采用蒙特卡罗和分子动力学模拟方法研究乙醇一步法制备乙酸乙酯反应中的物种CH_3CH_2OH、CH_3CHO、CH_3CH_2OOCCH_3、CH_3CH_2O、CH_3CO、H_2和H在Cu、Cr_2O_3和Cu/Cr_2O_3催化剂上的吸附行为。结果表明物种在三种催化剂上均有明显的吸附作用,吸附量随温度升高而降低;在相同条件下乙酸乙酯吸附量最大,吸附能数值也较大,吸附比较强,脱附困难;各物种在Cu/Cr_2O_3催化剂上的吸附量均大于Cu催化剂,吸附能数值也增大,这表明添加Cr_2O_3后加强了物种的吸附作用。采用量子力学和分子动力学方法研究了Cu、Cr_2O_3和Cu/Cr_2O_3催化剂的构型,通过构型分析深入地探讨了影响催化剂的吸附性能的因素,在剖析结构的基础上,进一步研究了负载催化剂中载体Cr_2O_3的作用。Cu、Cr_2O_3和Cu/Cr_2O_3催化剂的Mulliken、态密度和前线轨道的组成互不相同,这些构型特点决定了催化剂吸附性能的不同。Cu/Cr_2O_3催化剂由于Cu与载体Cr-2O_3发生了相互作用,引起了催化剂电荷分布和前线轨道能量的改变,使得吸附性能加强;Cu是反应的活性中心,物种吸附在Cu上发生反应,生成新物种,该新物种最终迁移到载体Cr_2O_3的酸性位上,形成更稳定的构型;载体Cr_2O_3的作用之一是提供酸性位,在乙醇一步法制乙酸乙酯反应过程中,各物种均倾向于吸附在催化剂酸性位上。在常压、313.15~433.15K下测定了乙醇在Cu催化剂上的吸附量,并与模拟结果进行了对比分析。模拟与实验结果较为接近,两者趋势一致,这表明本研究中所采用的分子模拟方法是可靠的。本文系统地研究了吸附,深入探讨了影响吸附性能的因素,对该反应过程有了更进一步的认识,为设计和改进催化剂提供了有力的理论依据。
[Abstract]:Ethyl acetate is a widely used chemical. One-step ethanol preparation of ethyl acetate can use single biological ethanol as raw material with little pollution and corrosion, so it has attracted much attention in recent years. The main catalyst used in this method is copper-chromium catalyst, which can be used in industrial production. At present, the research on the reaction adsorption is only by means of experiment. Because of the limitation of the experimental means, some aspects can not be detected, and there is a lack of deep understanding, so the research needs to be carried out urgently. In this paper, molecular simulation method was used to study the adsorption behavior of various species on CutiCr _ 2O _ 3 and Cu/Cr_2O_3 catalysts in the one-step ethanol synthesis of ethyl acetate. The reasons affecting the different adsorption properties of the catalysts were deeply explored and explained, and confirmatory experiments were designed. In order to better guide the practice. Monte-Carlo and molecular dynamics simulations were used to study the adsorption behavior of the species of Ch _ 3CH _ 2OH _ 2O _ H _ (Ch _ 3CHO) _ (Ch _ 3CH _ 2O) _ (Ch _ 3CHO) _ (Ch _ 3CHO _ 2O) _ C _ 3C _ 2O _ H _ 3 and H on Cutir _ 2O-Stack3 and Cu/Cr_2O_3 catalysts by means of Monte Carlo and molecular dynamics simulation methods in the preparation of ethyl acetate by one-step ethanol-ethanol method. The results show that the species have obvious adsorption on the three catalysts, and the adsorption capacity decreases with the increase of temperature, and under the same conditions, the adsorption capacity of ethyl acetate is the largest, the value of adsorption energy is larger, the adsorption is relatively strong, and the desorption is difficult. The adsorption capacity of each species on Cu/Cr_2O_3 catalyst was higher than that on Cu catalyst, and the adsorption energy was also increased, which indicated that the addition of Cr_2O_3 enhanced the adsorption of species. The configuration of Cu-Cr2O3 and Cu/Cr_2O_3 catalysts was studied by quantum mechanics and molecular dynamics methods. The factors affecting the adsorption properties of the catalysts were discussed through configuration analysis. On the basis of the analysis of the structure, the structure of the catalysts was analyzed. The function of supported Cr_2O_3 in the supported catalyst. The Mulliken, density of states and the composition of the front-line orbitals of the supported catalysts, CuCU / Cr2O3 and Cu/Cr_2O_3 catalysts, are further studied. These configuration characteristics determine the different adsorbability of the catalyst. Cu- / Cr2O3 catalyst is the active center of the reaction because of the interaction between Cu and Cr-2O_3, which leads to the change of catalyst charge distribution and frontier orbital energy. The species reacts on Cu to form a new species, which eventually migrates to the acidic site of the carrier Cr_2O_3 to form a more stable configuration. One of the functions of the carrier Cr_2O_3 is to provide acidic sites for the one-step synthesis of ethyl acetate from ethanol. Each species tended to adsorb on the acidic site of the catalyst. The adsorption capacity of ethanol on Cu catalyst was determined at 313.15C 433.15K, and the results were compared with the simulated results. The simulation results are close to the experimental results, which indicates that the molecular simulation method used in this study is reliable. In this paper, the adsorption is systematically studied, the factors affecting the adsorption performance are discussed, and the reaction process is further understood, which provides a strong theoretical basis for the design and improvement of the catalyst.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：TQ225.241

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