非电解质溶液扩散系数的理论研究评述

许多过程都涉及扩散控制的传质,相应的扩散速率计算对过程工程的精确量化具有重要意义.本文简述了扩散速率的理论表述模型,并着重介绍了非电解质溶液内扩散系数的理论分析计算途径.分子动力学模拟正处于发展中,并用于估算自扩散系数,但进入实用化阶段尚需时日,唯象模型仍为最重要的理论计算手段.作为最常用的方法,由无限稀释浓度下的扩散系数以及合适的插值方法可计算特定浓度下的扩散系数;自由体积理论是半经验性模型,可以计算自扩散系数,并借助混合规则计算相互扩散系数;最后,对扩散系数的理论研究作了展望.     

Maxwell-Stefan方程及其在多元相间传质中的应用

多元物系传质过程与二元物系传质过程有着本质的区别 ,由于组分间的交互作用 ,多元物系传质各组分传质效率不相等 ,其分布范围可在 -∞至 +∞之间 ,某些组分可能产生逆向传质、渗透传质、传质障碍等传质奇异现象 ,这些现象用传统的二元物系传质规律无法作出解释 ,必须用Maxwell Stefan方程进行描述。该文综述了Maxwell Stefan方程的由来、求解方法及其在多元相间传质中的应用。     

MFI型沸石膜的渗透分离性能及应用

综述了ＭＦＩ型沸石分子筛的渗透分离性能,探讨了其可能的分离机理,并介绍了包括膜分离与经在内的前沿进展。     

MFI型沸石分子筛膜的研究进展及应用

综述了MFI型沸石分子筛膜制备方法的研究进展,突出介绍了较为成熟的水热合成法、微波合成法以及气相转移法,讨论了MFI型沸石分子筛膜在应用方面具有优势的有机物提纯、气体分离以及催化反应的研究进展,并提出了MFI型沸石分子筛膜制备和应用方面一些亟待解决的问题。     

二元液体混合物扩散系数的理论计算

许多化工过程涉及扩散控制的质量传递,扩散系数的获取对过程工程的精确量化具有重要意义.今提出了基于局部组成的扩散系数模型,以估算Maxwell-Stefan扩散系数随浓度的变化.仅通过无限稀释下的扩散系数,以及溶液的Wilson或NRTL参数,能够预测二元混合物的扩散系数.与文献发表的实验数据比较,对15种二元组分溶液的计算结果平均误差是6.35%.结果显示,这种模型优于目前常用的Darken模型.     

Maxwell-Stefan理论模拟NaA沸石膜分离一氯甲烷中微量水的渗透特性

通过热浸渍晶种法制备了高质量的NaA沸石膜,并将其应用于蒸汽渗透脱除一氯甲烷中的微量水. 实验结果表明,NaA膜对该体系显示了优异的分离性能,水对一氯甲烷的分离系数高达74831,产品中的水含量从0.2582%(w)降低到0.005%(w). 将基于Maxwell-Stenfan理论和Langmuir理想吸附理论推导的吸附-扩散模型用于模拟水渗透流速与渗透侧真空度和进料温度的关系,预测趋势与实验值吻合很好,且拟合得到的参数与文献报道较接近,表明水蒸汽在NaA沸石膜中的传递为表面扩散机制,水蒸汽的吸附对渗透速率的贡献很大. 水蒸汽的吸附热为-34.15 kJ/mol.     

ZLC技术测定沸石晶内扩散系数研究进展

简介了测定沸石晶内扩散系数的各种方法,重点介绍了零长柱（ZLC）技术基本原理、实验方法和测定探针分子在沸石晶内扩散系数的研究进展,对采用ZLC技术表征探针分子在新型多孔材料中的扩散行为进行了展望。     

C02，CH4在全硅MFI型沸石中吸附的分子模拟

采用巨正则蒙特卡洛（GCMC）分子模拟方法研究了CO2,CH4分子在全硅MFI型沸石中的吸附行为,计算得到了纯组分和两组分的混合物在不同温度时的吸附等温线;分析了全硅MFI型沸石对混合组分的选择性吸附;模拟还得到了COz,CHt分子在全硅MFI型沸石中的吸附位。     

沸石催化剂内液相交互扩散系数的测定

采用简单实用的试验方法研究了苯和异丙苯在沸石内的交互扩散情况,通过测定不同时间点的扩散质的浓度,利用适宜的数学模型和最小二乘法关联出两种体系中各扩散质在沸石催化剂内的交互扩散系数。可以为苯烷基化反应的工业模拟提供重要的基础数据。     

CO_2,CH_4在全硅MFI型沸石中吸附的分子模拟

采用巨正则蒙特卡洛(GCMC)分子模拟方法研究了CO2,CH4分子在全硅MFI型沸石中的吸附行为,计算得到了纯组分和两组分的混合物在不同温度时的吸附等温线;分析了全硅MFI型沸石对混合组分的选择性吸附;模拟还得到了CO2,CH4分子在全硅MFI型沸石中的吸附位。     

An investigation of the characteristics of Maxwell-Stefan diffusivities of binary mixtures in silica nanopores

Diffusion of pure components (hydrogen (H₂), argon (Ar), krypton (Kr), methane (C1), ethane (C2), propane (C3), n-butane (nC4), and n-hexane (nC6)) in silica nanopores with diameters of 1, 1.5, 2, 3, 4, 5.8, 7.6, and 10 nm were investigated using molecular dynamics (MD). The Maxwell-Stefan (M-S) diffusivity (?_i,s) and self-diffusivities (D_i,self,s) were determined for pore loadings ranging to 10 molecules nm⁻³. The MD simulations show that zero-loading diffusivity ?_i,s(0) is consistently lower, by up to a factor of 10, than the values anticipated by the classical Knudsen formula; the differences increase with increasing adsorption strength. Only when the adsorption is negligible does the ?_i(0) approach the Knudsen diffusivity value.MD simulations of diffusion in binary mixtures C1-H₂, C1-Ar, C1-C2, C1-C3, C1-nC4, C1-nC6, C2-nC4, C2-nC6, and nC4-nC6 in the different pores were also performed to determine the three parameters ?_1,s, ?_2,s, and ?₁₂, arising in the M-S formulation for binary mixture diffusion. The ?_i,s in the mixture were found to be practically the same as the values obtained for unary diffusion, when compared at the same total pore loading. Also, the ?_i,s of any component was practically the same, irrespective of the partner molecules in the mixture. Furthermore the intermolecular species interaction parameter ?₁₂, could be identified with the binary M-S diffusivity in a fluid mixture at the same concentration as within the silica nanopore. The obtained results underline the overwhelming advantages of the M-S theory for mixture diffusion in nanopores.Our study underlines the limitations of the commonly used dusty-gas approach to pore diffusion in which Knudsen and surface diffusion mechanisms are considered to be additive.     

Monte Carlo simulation of complex isomerization. I. Effect of diffusivity on product selectivity

A Monte Carlo method by which actual situations can be approached was developed. The complex isomerization A=B=C in a regular network was simulated, and the effects of intracrystalline diffusivities of molecules on the product selectivity were also investigated.     

A NEW METHOD OF CALCULATING TERNARY MASS TRANSFER WITH A NON TRANSFERRING SPECIES BASED ON GILLILAND'S PARAMETRIC SOLUTION OF THE MAXWELL-STEFAN EQUATIONS FOR THE FILM MODEL

This paper presents a solution for the problem of multiple roots in Gilliland's parametric solution of the Maxwell-Stefan equations. Based on it a new algorithm for calculating ternary mass transfer with a non transferring species is obtained. This new algorithm demonstrates rapid and stable convergence. In contrast to the well known calculation of mass transfer in multicomponent mixtures using the matrix solution of the Maxwell-Stefan equations the new algorithm simplifies the calculation by avoiding any matrix operations.     

Monte Carlo simulation of xylene isomerization over zeolite catalysts

The isomerization reaction of xylene was simulated by means of the Monte Carlo method based on the experimentally observed parameters, including the diffusivity, equilibrium adsorption constant and intrinsic rate constant. The dependence of the product selectivity upon the Thiele modulus was examined and the results were satisfactorily consistent with those of the continuous model as well as the experiments. This suggests that the Monte Carlo method is helpful for investigating the nature of shape selectivity in zeolite-catalyzed reactions.     

多组分冷冻保护剂导入神经干细胞球的传质模拟

基于Maxwell-Stefan方程和两参数模型构建了神经干细胞球多组分保护剂导入模型,并模拟了多组分保护剂导入过程中细胞内外浓度及细胞膜两侧浓差的时空分布。在此基础上系统分析了多组分浓度配比、神经球尺寸、保护剂导入方式对传质渗透过程的影响。结果表明,多组分保护剂导入神经球过程中出现"逆梯度扩散"现象,胞内浓度变化总是滞后于胞外浓度变化,细胞膜两侧浓差呈现先增大后减少的趋势。改变保护剂组分的浓度配比时,不同组分的渗透特性变化规律不同。此外,神经球尺寸对中心处细胞的浓度时空分布影响显著,分步导入和连续导入能够减缓保护剂扩散,降低细胞内外浓差。本研究结果可用于指导神经球冷冻保存的实验研究,优化保护剂导入程序。     

丙烯聚合的Monte Carlo模拟(Ⅰ)活性杂质对丙烯聚合的影响

A comprehensive mechanism for propylene polymerization was proposed by considering the effects of main impurities in the material on propylene polymerization. According to the proposed mechanism, Monte Carlo simulation was employed to investigate the polymerization kinetics in order to determine the effects of the main impurities on the polymerization. Significant influences of the main impurities on the rate, number-average degree and controlling capability of hydrogen of the polymerization were analyzed.     

丙烯聚合的Monte Carlo模拟(Ⅰ)活性杂质对丙烯聚合的影响

1 INTRODUCTION Polypropylene is a popular thermoplastic polymer, and produced via bulk polymerization in petroleum chemical industry. The molecular configuration of polypropylene and the characteristics of polymer can be controlled by the catalyst and polymerization method. Furthermore, other factors, such as impurities in the material and polymerization conditions, also influence the industrial production. Catalyst influences the rate and the quality of polymer, is a key factor of the in…