CAS OpenIR
分子筛内有机小分子吸附扩散行为的分子模拟研究
张禹佳
Subtype硕士
Thesis Advisor徐俊波
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword分子模拟,分子筛,蒙特卡罗方法,分子动力学方法
Abstract

分子筛是具有微孔结构的硅酸盐晶体,具有独特的孔道结构和择形选择性,同时还具有比表面积高、孔径大小可调和水热稳定性好等众多优良特性,可用作吸附剂、催化剂、分离剂及离子交换剂等,在化工等领域有着广泛应用。本文采用分子模拟方法,针对典型化工过程需求,对作为分离材料和催化剂的分子筛中有机小分子的吸附扩散行为进行了深入研究与分析。第2章针对氯丙烷、氯丙烯物性相近、精馏分离能耗高、效率低的问题,采用Monte Carlo方法计算获得了氯丙烷、氯丙烯在不同种类分子筛内的吸附等温线,筛选得到了4类仅吸附氯丙烯的分子筛。进一步以分子筛膜为研究对象,采用非平衡分子动力学方法分析了氯丙烯在上述分子筛中的扩散路径,计算了其扩散通量,研究结果显示AHT型分子筛有着最佳的吸附扩散表现。本文从热力学角度对这种超高选择性的分离机理进行了探讨,并结合氯丙烷、氯丙烯二面角——分子势能变化等数据,提出了基于孔道形状的构象识别机理,为今后探索烷烃和烯烃混合物的分离过程提供了新的思路与途径。第3、4章针对异丁烷/丁烯烷基化反应中分子筛催化剂迅速失活的现象,对催化剂失活机理及如何减缓分子筛催化剂失活两个问题进行了研究与分析。第3章获得了烷基化反应各组分在Y型分子筛上的吸附等温线和扩散系数等数据,确定适宜烷基化反应的烷烃烯烃进料比及分子筛硅铝比等条件。在此基础上,对分子筛中吸附副产物C12H26产生的影响进行了系统分析,对比不同条件下各组分的扩散系数及活性位点可接近性等数据,结果表明C12H26及更高碳数副产物覆盖活性位点并影响反应物扩散性质是催化剂迅速失活的主要原因。第4章初步探讨了Y型分子筛内介孔结构对烷基化反应混合物吸附扩散的影响规律,结果表明介孔能有效提升反应位点附近异丁烷与2-丁烯的浓度和C12H26大分子的扩散速率,从而减缓孔道堵塞,延长分子筛催化剂使用寿命。介孔孔径为4 nm时反应物异丁烷扩散表现良好,采用等级孔道分子筛是解决烷基化反应中分子筛催化剂迅速失活的有效途径;Zeolites are silicate crystals with microporous structure. They have unique pore structure, selectivity and many excellent properties such as high specific surface area, adjustable pore size and good hydrothermal stability. Zeolites can be used as adsorbents, catalysts, separation materials and ion exchangers. They are widely used in chemical industry and other fields. In this work, the adsorption and diffusion behavior of small organic molecules in zeolites as separation materials and catalysts were analyzed by molecular simulation method in order to meet the needs of typical chemical processes.In chapter 2, focused on the similar physicochemical properties of 1-chloropropane and allyl chloride, high energy consumption and low efficiency of distillation separation, Monte Carlo method was used to calculate the adsorption isotherms of 1-chloropropane and allyl chloride in different kinds of zeolites, and four kinds of zeolites were screened out which can only adsorb allyl chloride. Furthermore, the diffusion path of allyl chloride in the above zeolites was analyzed by non-equilibrium molecular dynamics method, and the diffusion flux was calculated. The results show that the AHT zeolite has the best adsorption and diffusion performance. In this chapter, the mechanism of the ultra-high selectivity separation is discussed by thermodynamic analysis, combining with the data of dihedral angle-molecular potential energy change of 1-chloropropane and allyl chloride, a conformation recognition mechanism based on the pore geometry is proposed, which provides a new avenue to explore the separation of mixtures of alkanes and olefins in the future.In chapter 3 and chapter 4, focused on the rapid deactivation of zeolite catalysts in isobutane/butene alkylation, the mechanism of deactivation and the way to slow down the deactivation of zeolite catalysts were studied. In Chapter 3, the adsorption isotherms and diffusion coefficients of alkylation components in Y zeolite were obtained, and the suitable feed ratios of isobutane and olefin and the silicon-aluminium ratio of zeolite were determined. On this basis, the influence of by-product C12H26 in zeolites was analyzed. Comparing the diffusion coefficients of components and the accessibility of active sites under different conditions, the results showed that the main reason for rapid deactivation of catalyst was that C12H26 and higher carbon number by-products covered active sites and affected the diffusion properties of reactants. In Chapter 4, the influence of hierarchical of Y zeolite on the adsorption and diffusion properties of mixture in alkylation reaction is discussed. The results show that the mesopores can effectively increase the concentration of isobutane and 2-butene near the active site and the diffusion rates of C12H26. Thus mesopores can slow down the blockage of pores and prolong the life of zeolite catalyst. Isobutane diffuses well when the diameter of mesopore is 4 nm. The application of hierarchical Y zeolite is an effective way to solve the problem of rapid deactivation of zeolite catalysts in alkylation reaction

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40699
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
张禹佳. 分子筛内有机小分子吸附扩散行为的分子模拟研究[D]. 中国科学院大学,2019.
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