微波加热水溶液及化学反应的分子动力学模拟研究

发布时间：2018-03-23 22:05

本文选题：微波化学　切入点：分子动力学模拟　出处：《电子科技大学》2014年硕士论文

【摘要】：微波具有高效、高渗透性、选择性加热等特点并已广泛运用于化工、石油、环境治理等众多领域。但是,人们对微波与化学反应体系的相互作用机理和相关基础问题的认识和理解尚不深入,其相互作用过程中产生的特殊效应如非热效应、热点、热失控等现象也一直是人们关注的焦点和理解的难点,这导致微波能技术在工业应用中的瓶颈。本文就微波与水溶液、微波与化学反应体系相互作用过程中产生的一些特殊效应,从分子动力学模拟到理论分析进行深入探讨,这些研究对进一步理解微波与化学反应相互作用的机理、探讨其特殊效应及进一步的工程应用提供科学依据。本论文主要研究内容和创新点如下:(1)本文研究了频率为20 GHz微波加热氯化钠水溶液的过程。发现分子动力学模拟下微波加热氯化钠溶液的温度与微波的电场强度、溶液浓度存在一定的内在联系,并在此基础上通过数据拟合得到分子动力学模拟时间量程内,频率为20 GHz的微波加热氯化钠溶液的经验性温升公式。这有助于探究微波加热溶液及化学反应的温升机理并提供一定的实验支持和理论参考。(2)在对微波加热裂解甲苯和非交联环氧树脂的ReaxFF反应分子动力学模拟过程中观察到热失控现象。经过分析,出现这种温升突变现象的原因是整个体系内极性基团数量的突然增多导致体系对微波能的吸收能力突然增强,使体系的温升速率迅速升高,从而产生温度突变。(3)观察到微波作用于物质时的非热效应,并进一步基于碰撞理论和熵效应分析该现象。在研究微波加热NaCl溶液的过程中,发现微波能并没有如传统理论认为那样会被全部转化为系统的动能,而是有一部分转变为系统的势能,该结果有助于从分子层面揭示和理解非热效应。而相比于传统加热,微波加热下的甲苯裂解以及环氧树脂高温分解过程中部分产物的生成速率会降低。通过分析模拟结果并结合反应动力学研究,确定这种反应速率降低的现象属微波的非热效应。同时,本文对微波加热至高温后,部分极性分子电偶极矩的旋转特性进行了统计和分析。结果表明反应体系中的小尺寸极性基团如水、甲醇等的旋转特性依然能够与外电场的时变性保持一致。而对于大尺寸的极性基团(≥C7),其旋转特性相比于外加电场有一定的滞后效应,即相位延迟。(4)本文基于ReaxFF分子动力学方法对葡萄糖水溶液在超临界环境中气化的工程应用进行了探讨。相关文献表明,微波加热纯水至超临界状态后温升速率会降低,因此,理论上不会出现热失控现象。本文研究结果表明,在微波高温气化葡萄糖水溶液过程中,没有出现热失控现象,微波场也未对气化后最终产物的组分和产量有明显影响,这与预期相符。因此,本文认为微波应用于葡萄糖超临界气化是可行的。总体而言,从国内外的研究现状及公开报道来看,本文首次基于分子动力学模拟探讨微波作用下的若干化学反应体系,并揭示和解释了其中一些特殊现象如热失控、非热效应等的作用机理和规律,这在一定程度上突破了其发展和应用中面临的某些技术瓶颈。这些成果在微波加快化学反应以及微波能在化学工业中的大规模潜在应用方面具有重要的指导意义和参考价值,同时也为国家节能环保的重大社会需求进一步提供技术支持。
[Abstract]:The microwave has the advantages of high efficiency, high permeability, selective heating characteristics and has been widely used in chemical, petroleum, many areas of environmental governance. However, understanding the interaction mechanism of microwave and chemical reaction and related basic problems is not deep, special effects produced the interaction process such as non the effect of heat, hot, thermal runaway phenomenon is also a difficult focus of attention and understanding, which leads to microwave energy bottleneck technology in industrial application. In this paper, microwave and water solution, some special effects of interaction between microwave and chemical reaction system, from molecular dynamics simulation to the theory are discussed analysis of these studies, to further understand the mechanism of the interaction between microwave and chemical reaction, to provide a scientific basis to explore its special effects and further engineering application. This paper mainly studies The content and innovation are as follows: (1) this paper studies the frequency of 20 GHz microwave heating process of sodium chloride aqueous solution. It is found that the field strength of molecular dynamics simulation of temperature under microwave heating and microwave Sodium Chloride Solution, there are some relations between the concentration of the solution, and on the basis of the data obtained by molecular dynamics simulation time range. The frequency of microwave heating temperature experience Sodium Chloride Solution 20 GHz liter formula. This helps to explore the microwave heating solution and reaction temperature rise mechanism and provide some experimental support and theoretical reference. (2) in the ReaxFF reaction kinetics of microwave heating pyrolysis of toluene and non crosslinked epoxy resin was observed during thermal simulation the phenomenon of out of control. After analysis, the temperature rising of mutation phenomenon is the number of the whole group polarity within the system suddenly increase system of microwave energy The absorption ability suddenly increased, so that the system's temperature rise rate increased rapidly, resulting in sudden temperature. (3) observed that the non thermal effect of microwave irradiation in substance, and further analysis based on the collision theory and the entropy effect of this phenomenon. In the process of microwave heating of NaCl solution, found that microwave energy is not as traditional theory think that all will be transformed into the kinetic energy of the system, but there is a part of change for the potential energy of the system, the results help from the molecular level to reveal and understand the non thermal effect. Compared with conventional heating, the formation rate of part of the product under microwave heating and epoxy resin in high temperature cracking of toluene decomposition process will reduce by. Analysis of simulation results and combined with the study of reaction kinetics, determine the non thermal effect of this phenomenon is the microwave reaction rate decreases. Meanwhile, the microwave heating to high temperature, part of the polar molecule dipole The polar moment rotation characteristics were collected and analyzed. The results show that the small size of the reaction system of polar groups such as water, methanol and other rotating characteristics of time-varying and external electric field can still keep the same. But for the polar groups of large size (more than C7), the rotation characteristics compared to the external electric field has lagged behind the effect of the phase delay. (4) the ReaxFF molecular dynamics method based on engineering application of glucose solution gasification in supercritical environment were discussed. The literature shows that the microwave heating water to a supercritical state after the temperature rise rate will be reduced, therefore, the thermal runaway phenomenon does not occur in this theory. The results show that the microwave high temperature gasification of glucose solution process, no thermal runaway phenomenon, has obvious effect of microwave is not on gasification of final product components and production, which in line with expectations. Therefore, this paper Microwave application in glucose supercritical gasification is feasible. Overall, the research status at home and abroad and publicly reported, this is the first research on some chemical reactions under microwave irradiation based on molecular dynamics simulation, and reveal and explain some special phenomena such as thermal runaway, the mechanism and laws of non thermal effect etc. this, some breakthrough technology bottlenecks facing its development and application to a certain extent. These results have important guiding significance and reference value in the large-scale potential application of microwave and microwave can accelerate chemical reactions in the chemical industry, but also a major social demand as the national energy saving and environmental protection to provide technical support.

【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：O643.1;TM924.76

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