【作者】 董艳萍；

【导师】 董秀芹；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 硕士

【摘要】 超临界水氧化法是近年来发展起来的一种新型、高效的废物处理技术,特别适用于难处理的有机废水。但由于超临界水体系高温高压等苛刻条件,实验研究有较大难度。本文采用分子动力学模拟方法,对超临界水氧化硝基苯体系进行了研究。首先通过对比分析,确定了适用于研究超(亚)临界水体系的模拟过程参数,计算得到的亚临界水和超临界水的自扩散系数与文献实验值相比,相对偏差均小于5%。在此基础上,进一步系统研究了温度373.2~863.2K、压力5~29MPa范围内水自扩散系数的变化规律,扩散系数随温度的升高而增大,随压力的增大而减小,温度和压力的影响在超临界状态下比亚临界状态下明显;同时考察了水中氢键及水分子的几何构型随温度压力的变化规律。根据超临界水氧化硝基苯过程中的自由基反应机理,硝基苯和?OH自由基首先结合生成[OHC6H5NO2]π?,这一步骤受扩散控制,其反应速率常数可通过硝基苯和?OH自由基在超临界水中的无限稀释扩散系数求得。本文在温度643.2~843.2K、压力23~29MPa范围内,计算了硝基苯和?OH自由基在超临界水中的无限稀释扩散系数,进而由Smoluchowski方程计算了硝基苯与?OH自由基反应扩散控制步骤的速率常数,为超临界水氧化硝基苯过程的反应动力学研究提供了必要的参考数据。为验证MD模拟方法的可靠性,采用超临界相平衡设备,在温度308.15~328.15K范围内测定了CO2-乙醇二元混合体系的泡点压力,并通过MD模拟方法在相同温度范围内计算了该体系的内聚能密度,以预测泡点压力范围,模拟结果与实验结果吻合较好。在此基础上,通过模拟预测了乙醇摩尔分数为0.5的H2O-乙醇二元体系相变点范围,513.2K时,相变压力范围为5.74~5.78MPa;523.2K时,相变压力范围为6.70~6.75MPa。更多还原

【Abstract】 Supercritical water oxidation (SCWO) is a newly-developed, highly-effective technology for the treatment of hazardous organic wastewater. However, there are disadvantages in the experimental study due to the high reaction temperature and pressure condition requirements. In this paper, the properties of supercritical water oxidation system with nitrobenzene were investigated using the Molecular Dynamics (MD) simulation method.The suitable parameters of MD simulation for the sub-critical and supercritical water system were optimized. The calculated results of self-diffusion coefficients of water were in good agreement with the experimental results. The relative errors were no more than 5 percent. The self-diffusion coefficients of sub-critical and supercritical water were investigated systemically. The effects of temperature and pressure on hydrogen bond and the geometry of water molecules were investigated respectively.Based on the mechanism of hydroxyl radical reactivity with nitrobenzene in supercritical water, the formation of [OHC6H5NO2]π?, which is diffusion-controlled, is the first step. However,the diffusion-controlled rate constant of this step is related to the infinite dilute diffusion coefficients of the reactants. Therefore, the infinite dilute diffusion coefficients of nitrobenzene and hydroxyl in supercritical water were first investigated by MD simulation in the temperature range of 643.2~843.2K and pressure range of 23~29MPa, by which, the diffusion-controlled rate constant for the addition of hydroxyl radical to nitrobenzene could be calculated by the Smoluchowski equation. The results provided valuable information to the reaction kinetics of nitrobenzene in SCWO processes.Cohesive Energy Density (CED) is an important property of a substance which can characterize intermolecular force. In this paper, the changing trend of Cohesive Energy Density was investigated to estimate the phase behaviour of the binary mixture. In order to ensure the validity of the simulation method, the CO2-ethanol system was chosen as an instance, and the results agreed with the experiment results. Henceforth, the phase behaviour of H2O-ethanol system was simulated.更多还原