PVA杂化膜中小分子吸附和扩散行为的分子模拟

doi:10.11949/0438-1157.20240632

摘要/Abstract

摘要：

无机粒子掺杂聚乙烯醇（PVA）改性膜材料在渗透汽化酯化体系脱水方面展现出良好工业应用前景，但还缺乏微观层面的机理探究和基础理论数据。采用分子模拟手段构建了ZSM-5和ZIF-67两种粒子分别与PVA混合后的杂化材料分子结构模型，得到了无机粒子在PVA链段间的分布情况；利用Monte Carlo（MC）方法模拟了乙酸乙酯、水在PVA杂化材料中的吸附行为，考察了掺杂比例和温度对吸附量、吸附等温线的影响；利用分子动力学（MD）方法模拟了乙酸乙酯、水在杂化材料中的扩散行为，计算了杂化材料内部的自由体积分数（FFV），考察了掺杂比例和温度对小分子在杂化材料中扩散系数的影响。结果表明，两种杂化材料对水的吸附量显著高于酯，且ZSM-5/PVA材料对水的吸附量高于ZIF-67/PVA材料；水在两种杂化材料中的扩散系数大于乙酸乙酯，且由于ZSM-5/PVA材料具有更大的FFV，小分子在ZSM-5/PVA中的扩散系数远大于在ZIF-67/PVA中的扩散系数。本研究为PVA材料改性及传质分离提供了理论指导。

关键词: 分子模拟, ZSM-5, ZIF-67, PVA杂化膜, 吸附, 扩散, 渗透汽化

Abstract:

The inorganic particle-doped modified polyvinyl alcohol (PVA) membrane materials have promising industrial application prospects in pervaporation dehydration from esterification system. However, it is still lack of mechanism exploration in microscopic view and fundamental theoretical data. In this study, the molecular structure models of two types hybrid PVA materials doped with ZSM-5 and ZIF-67 respectively were constructed using molecular simulation method to elucidate distribution of inorganic particles in PVA chains. The Monte Carlo (MC) method was used to simulate the adsorption behavior of ethyl acetate and water in PVA hybrid materials, and the effects of doping ratio and temperature on adsorption amount and adsorption isotherm were investigated. The diffusion behavior of ethyl acetate and water in the hybrid materials and the fraction of free volume (FFV) within the hybrid materials were simulated by molecular dynamics (MD) method, and the influence of doping ratio and temperature on the diffusion coefficients of small molecules through the hybrid materials were investigated. The results showed that the adsorption of water in the two hybrid materials was significantly higher than that of ethyl acetate, and the adsorption of water in the ZSM-5/PVA was higher than that in ZIF-67/PVA. The diffusion coefficient of water in the two hybrid materials was significantly higher than that of ethyl acetate, and moreover, the diffusion coefficients of small molecules in ZSM-5/PVA were higher than those in ZIF-67/PVA because ZSM-5/PVA has higherFFV. It provides theoretical guidance for the modification of PVA materials and the mechanism of mass transfer separation.

Key words: molecular simulation, ZSM-5, ZIF-67, PVA hybrid membrane, adsorption, diffusion, pervaporation

中图分类号:

TQ 028.8

付敏, 陈子健, 汤帅, 钱锡亮, 危增曦, 邹昀, 童张法. PVA杂化膜中小分子吸附和扩散行为的分子模拟[J]. 化工学报, 2024, 75(11): 4152-4161.

Min FU, Zijian CHEN, Shuai TANG, Xiliang QIAN, Zengxi WEI, Yun ZOU, Zhangfa TONG. Molecular simulation of small molecule adsorption and diffusion behavior in PVA hybrid membranes[J]. CIESC Journal, 2024, 75(11): 4152-4161.

图/表 12

图1 小分子及PVA杂化体系的分子结构模型

Fig.1 Molecular structure models of small molecules and PVA hybrid systems

表1 用于吸附模拟的不同杂化比例的无机粒子/PVA体系

Table 1 Inorganic particle/PVA system with different hybridization ratios for adsorption simulation

项目	ZSM-5/PVA				ZIF-67/PVA
项目	0%ZSM-5/PVA	3%ZSM-5/PVA	6%ZSM-5/PVA	9%ZSM-5/PVA	0%ZIF-67/PVA	3%ZIF-67/PVA	6%ZIF-67/PVA	9%ZIF-67/PVA
PVA链段数	150	150	150	150	50	50	50	50
无机粒子个数	0	1	2	3	0	1	2	3

图2 ZSM-5/PVA和ZIF-67/PVA模型结构

Fig.2 Model structure of ZSM-5/PVA和ZIF-67/PVA

图3 ZSM-5/PVA和ZIF-6/PVA对乙酸乙酯/水分子的吸附量

Fig.3 Adsorption of EtOAc/H2O by ZSM-5/PVA and ZIF-6/PVA

图4 不同温度下ZSM-5/PVA以及ZIF-67/PVA对水分子的吸附等温线

Fig.4 Adsorption isotherms of H2O on ZSM-5/PVA and ZIF-67/PVA at different temperatures

图5 不同分子结构模型内的自由体积

Fig.5 Free volume within different molecular structure models

表2 ZSM-5/PVA以及ZIF-67/PVA中的自由体积分数

Table 2 FFV in ZSM-5/PVA and ZIF-67/PVA

无机粒子掺杂比例/%(质量)	FFV/%
无机粒子掺杂比例/%(质量)	ZSM-5/PVA	ZIF-67/PVA
0	15.21	25.44
3	35.46	27.13
6	35.76	30.34
9	16.80	28.43

图6 ZSM-5/PVA、ZIF-67/PVA中的水、乙酸乙酯分子的运动轨迹

Fig.6 Trajectory of H2O and EtOAc in ZSM-5/PVA and ZIF-67/PVA

图7 无机粒子含量对纯酯、水分子在ZSM-5/PVA、ZIF-67/PVA中的扩散系数的影响

Fig.7 Effect of inorganic particle content on diffusion coefficient of pure ester and water molecules in ZSM-5/PVA and ZIF-67/PVA

表3 纯PVA中水分子的扩散系数D

Table 3 Diffusion coefficient D of water molecules in pure PVA

体系	水分子的扩散系数D×10¹²/(m²/s)
体系	模拟结果	实验结果^[35]
纯PVA	10~300	480~12670

图8 温度对纯酯、水分子在ZSM-5/PVA、ZIF-67/PVA中的扩散系数的影响

Fig.8 Effect of temperature on diffusion coefficient of pure ester and water molecules in ZSM-5/PVA and ZIF-67/PVA

图9 不同组成酯水二元体系在ZSM-5/PVA、ZIF-67/PVA中的扩散系数

Fig.9 Diffusion coefficients of ester and water binary system in ZSM-5/PVA and ZIF-67/PVA at different concentration

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