有机分子在渗透汽化膜中溶解扩散过程的实验及模拟研究

发布时间：2018-04-09 14:58

本文选题：渗透汽化　切入点：分子模拟　出处：《北京化工大学》2017年硕士论文

【摘要】：有机溶剂的脱水及回收在精细化工,医药化工,日用化工及新能源等领域是非常重要的,传统上采取精馏,萃取或者分子筛等技术来达到分离有机物和水的目的。作为新的膜分离技术,渗透汽化现在已经迅速发展并成为高效的产业化分离技术。从分子水平上研究不同基团及聚合物对膜分离性能的影响对设计特定功能和性质的渗透汽化膜至关重要。通过在分子层面上研究小分子在膜上的吸附及扩散,可以更好的在微观角度了解渗透气化膜溶解吸附机理。本文使用分子模拟软件Materials Studio,主要采用巨正则蒙特卡洛法以及分子动力学法,主要针对研究聚合物二甲基硅氧烷渗透汽化膜改性及添加新材料(ZIF,COF)对有机物的水溶剂分离性能的影响。主要工作如下:1、研究3%糠醛的水溶液在PDMS膜与PDMS/VTES膜中的溶解扩散情况。发现当PDMS:VTES=1: 1即引入乙烯基量是Si的摩尔量的一半时,膜的自由体积增加为原PDMS膜的两倍,聚合物链跨链距离由原先的7.05埃变为7.59埃,这些都是有利于小分子扩散的因素。通过MSD曲线斜率可以看出糠醛在vinyl:Si=1/2的膜中扩散最快,模拟糠醛和水的吸附发现,膜中引入乙烯基的量越多,糠醛的吸附量越大,而水几乎不变。最后实验发现vinyl:Si=1/2的膜的选择性为49.85,远大于纯PDMS膜的30.67,证实了前面模拟结论。2、由于具有较好的热力学稳定性,灵活的网络结构和超疏水性,ZIF材料已经被很多研究者运用到构建以PDMS为基础的混合基质膜中。本课题主要运用动力学模型,研究各种ZIF结构对丁醇的吸附性能的差异以及ZIF材料在汽油脱硫方面的应用。结果表明ZIF-3,ZIF-6和ZIF-8对丁醇的具有较好的吸附性能,且吸附量远远大于PDMS对丁醇的吸附。在对噻吩/苯/异辛烷模拟方面,发现ZIF-3, ZIF-6, ZIF-8对噻吩和苯的吸附量均高于对异辛烷的吸附量,但是在中高压下,异辛烷在ZIF-8中几乎不吸附,这一点上要优于ZIF-3和ZIF-6。3. COF-300具有大孔洞,疏水性的特点,预期添加到PDMS膜中会很好的改善膜对有机物的分离效果。通过分子模拟的方法研究了COF-300材料对丁醇/水的吸附扩散性能以及汽油脱硫方面的应用,结果表明COF-300对丁醇的吸附性能不仅远远高于PDMS,而且要比ZIF材料更好一些,虽然水的扩散速率要比丁醇的扩散速率增加更大,但是总体上,COF-300对丁醇/水的分离性能要好与PDMS。在对噻吩/苯/异辛烷吸附方面,发现COF-300对三种组分单独吸附时吸附量均很高,但是三种组分同时吸附时,异辛烷会随着总压的增加而急剧下降,在中高压区几乎吸附量为零,证明可以有效的在异辛烷中分离出噻吩和苯。
[Abstract]:Dehydration and recovery of organic solvents are very important in the fields of fine chemicals, pharmaceutical chemicals, daily chemicals and new energy. Traditionally, distillation, extraction or molecular sieve are used to separate organic matter and water.As a new membrane separation technology, pervaporation has developed rapidly and become a highly efficient industrial separation technology.It is very important to study the effects of different groups and polymers on membrane separation performance at molecular level for the design of pervaporation membranes with specific functions and properties.By studying the adsorption and diffusion of small molecules on the membrane at the molecular level, the mechanism of dissolution and adsorption of permeable gasification membrane can be better understood from the microscopic perspective.In this paper, we use the molecular simulation software Materials Studio, mainly using the grand regular Monte Carlo method and the molecular dynamics method.The effect of polymer dimethylsiloxane pervaporation membrane modification and the addition of a new material, ZIFCOF, on the water solvent separation of organic compounds was studied.The main work is as follows: 1. The dissolution and diffusion of 3% furfural aqueous solution in PDMS and PDMS/VTES films are studied.It is found that the free volume of the film increases by twice as much as that of the original PDMS film, and the transchain distance of the polymer chain changes from 7.05 to 7.59A, which is beneficial to the diffusion of small molecules, when the amount of vinyl is half of Si when the ratio of PDMS: VTE is 1: 1, which is beneficial to the diffusion of small molecules.The slope of MSD curve shows that furfural diffuses fastest in the membrane of vinyl:Si=1/2. The simulated adsorption of furfural and water shows that the more vinyl is introduced into the membrane, the larger the adsorption capacity of furfural is, but the water is almost unchanged.Finally, it was found that the selectivity of vinyl:Si=1/2 membrane was 49.85, which was much higher than that of pure PDMS membrane.Flexible network structure and superhydrophobic ZIF materials have been used by many researchers to construct PDMS based mixed matrix membranes.In this paper, the kinetics model is used to study the difference of the adsorption properties of butanol by various ZIF structures and the application of ZIF materials in gasoline desulfurization.The results show that ZIF-3H ZIF-6 and ZIF-8 have better adsorption performance for butanol, and the adsorption capacity is much larger than that of PDMS for butanol.COF-300 has the characteristics of large pores and hydrophobicity. It is expected that adding it to the PDMS membrane will improve the separation effect of organic matter.The adsorption and diffusion properties of butanol / water and the application in gasoline desulfurization of COF-300 were studied by molecular simulation. The results showed that the adsorption of butanol by COF-300 was not only much higher than that of ZIF, but also better than that of ZIF.Although the diffusion rate of water is higher than that of butanol, the separation performance of COF-300 for butanol / water is better than that of PDMS.It is proved that thiophene and benzene can be effectively separated from isooctane.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ028.8

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