【作者】 韩海波；

【导师】 郭斌；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2013， 博士

【摘要】 在世界上很多国家和地区，水资源短缺是限制社会经济可持续发展的一个重要因素，由于海水资源储量丰富，海水淡化是解决水资源问题的重要途径，对现有海水淡化技术的任何改进将显著提高人们的生活质量。目前，效率最高的海水淡化方法是反渗透法，但仍存在需要高压和经常更换膜组件的问题，因此急需对现有海水淡化技术进行改进。考虑到磁场在水处理方面的优势，我们提出了基于旋转电磁效应海水淡化技术，该方法具有抑垢、缓蚀、杀菌、灭藻，能源利用率高和设备动力损耗低等优点，但其中磁场对海水微观结构和动力学性质以及海水淡化过程中水分子和盐离子在反渗透膜中传质行为的作用效果和机制，旋转电磁效应涉及的主要因素对磁场作用效果的影响规律并不明确，因此本文开展了该方面的分子动力学模拟和实验研究。采用分子动力学模拟方法，以扩散系数为依据，选择与实验数据最接近的SPCE水分子模型和合适的势能参数，研究磁场对纯水和NaCl溶液中水分子扩散系数、对相关函数、配位数等的影响。模拟结果表明，磁场作用下，纯水中水分子之间的氢键网络增强、结构有序性增强、分子簇平均尺寸增加；NaCl溶液中两种离子与水分子之间作用均减弱、水合离子尺寸减小、水合数目减少，水分子之间氢键作用减弱、水分子簇减小，接触离子对增加而桥接离子对减少。进一步通过研究磁场大小、浓度、温度、盐种类和磁场类型对溶液中磁场作用效果的影响，发现随着磁场、浓度和温度的增加，磁场作用效果均增强，而磁场对不同种类盐离子组成溶液呈现不同的作用效果，交变磁场和脉冲磁场的作用效果均不如静磁场明显，并随着磁场变化频率的增加而减弱。实验测量了磁场对NaCl溶液红外光谱、紫外光谱、表面张力、渗透压和粘度的影响，结果表明磁处理后，钠离子和氯离子与水分子之间的作用力均减弱，水合离子的尺寸减小，水合数目减少，钠离子的结构有序性和氯离子的结构无序性均降低，并且磁场对氯离子比对钠离子的作用效果更明显，磁场打乱了溶液中原本的氢键网络结构，溶剂水的摩尔体积增大，溶液中水分子簇减小，水分子之间的氢键作用减弱。与磁场对NaCl溶液影响的分子动力学模拟结果一致，验证了分子动力学模拟用于NaCl溶液微观结构和动力学性质分析的可靠性，可以用来预测磁场大小、浓度、温度、盐种类和磁场类型对磁场作用效果的影响。通过分子动力学模拟MPD和TMC单体的“聚合”过程，得到交联密度、密度、孔径均与实验值吻合较好的聚酰胺膜。模拟水分子和盐离子在膜中的扩散行为，磁场使聚合物之间以及水分子和聚合物之间的作用减弱，而离子和聚合物之间的作用增强，聚酰胺膜中水分子扩散系数增加，离子移动性减弱，这将导致海水淡化过程中水分子更容易而盐离子更难通过反渗透膜，有利于提高产水量和脱盐率。采用分子动力学模拟方法，以水分子和盐离子扩散行为为依据，研究磁场大小、温度、盐种类和磁场类型对磁场作用效果的影响。随着磁场强度增加，磁场作用效果呈渐近线趋势增强；温度较高时，磁场对水分子扩散系数和离子移动性的影响更明显；由不同种类盐离子组成的模拟系统，磁场对由二价离子组成的且水分子与聚合物之间作用较弱的系统中的传质行为影响较大，而对由一价离子组成的且水分子与聚合物之间作用较强的系统中的传质行为影响较小；与静磁场相比，交变磁场和脉冲磁场的作用效果分别增强和减弱，随频率增加，两种磁场的作用效果均增强。为进一步提高海水淡化产水量和脱盐率，可以采取增强磁场，升高温度和增加磁场变化频率的措施。设计渗透和反渗透实验装置，分析磁场对BW30、LE和XLE三种聚酰胺反渗透膜中传质过程的影响。由于膜表层的差异，三种反渗透膜呈现出的磁场作用效果不同。磁场作用下，渗透过程中吸附系数Kwater和Ksalt均增大，水和盐在膜中的传质速率均增加，而反渗透过程中，水和盐的传质速率主要由扩散系数决定，Dwater增加，Dsalt减小，水在膜中的传质速率增加而盐的减小，水通量和脱盐率均增加。实验结果与磁场对水和盐在聚酰胺膜中传质行为影响的分子动力学模拟结果一致，说明分子动力学模拟可以有效地分析磁场对反渗透海水淡化影响的作用效果和机制，预测磁场大小、温度、盐种类和磁场类型对磁场作用效果的影响规律。基于旋转电磁效应海水淡化技术中，引入磁场有益于海水淡化过程，并且可以通过增强磁场，适当调控旋转速率升高温度和增加磁场变化频率进一步提高海水淡化效率。更多还原

【Abstract】 Fresh water shortage is one of the main factors that restraint the sustainabledevelopment of socio-economy in many regions and countries of the world. Due tothe vast reserves of seawater available, seawater desalination is an important way tosolove the problem. Any improvement of the currently used seawater desalinationtechnologies can improve the quality of people’s lives. Recently, the most efficientseawater desalination technology is reverse osmosis, whereas, it requires highpressures and frequent replacement of membrane module. It is therefore an urgentneed to improve the current seawater desalination method. Considering theadvantages of magnetic fields in water treatment, we proposed a seawaterdesalination method based on the rotating electromagnetic effect. It has the merits ofscale and corrosion inhibition, sterilization and removal algae, high energyefficiency and low device power loss, etc. But the magnetic effect on themicrostructure and dynamics properties of seawater and the transport behavior ofwater molecules and salt ions in the reverse osmosis membrane during seawaterdesalination process, and the influence mechanism, as well as the influence ofrelated main factors of rotating electromagnetic effect on the magnetic effect isunknown. Therefore, it is studied in this paper by molecular dynamics simulationsand experiments.Molecular dynamics simulation is used to choose the proper water model andpotential, then SPCE model is adopted because the corresponding diffusioncoefficient is close to the experiment value. The effect of magnetic field on diffusioncoefficients, pair correlation functions and running integration numbers of purewater and NaCl solution is investigated. With the effect of magnetic field, thehydrogen network between water molecules and the relevant order are bothenhanced, and the mean sizes of water clustes increase in pure water. In NaClsolution, the interaction between ions and water molecules is weakened. The meansizes of both Na+and Cl-ions and the corresponding hydration numbers aredecreased. The hydrogen interaction between water molecules is weakened and themean sizes of water clustes decrease. Besides, Magnetic field makes the contactpairs increase and the solvent separated ones decrease.The influence of magnetic intensity, concentration, temperature, salt speciesand the type of magnetic field on the magnetic effect is performed. With the increaseof magnetic intensity, concentration and temperature, the magnetic effect isenhanced. The magnetic effect on various solutions is different and it depends on thesalt species. The magnetic effect of pulse and alternating field is less significant than that of static field, and it weakens with the frequency of magnetic feld.Magnetic effect on the infrared spectra, ultraviolet spectra, surface tension,osmosis pressure and viscosities of NaCl solution is studied. The results show that,under the influence of magnetic field, the interaction between ions and watermolecules is weakened. The mean sizes of both Na+and Cl-ions and thecorresponding hydration numbers are decreased. The structure–ordering propertyof Na+ions and the structure–disordering property of Cl-ions are both weakened.the magnetic effect on the Cl-ions is more obvious than that on the Na+ions.Magnetic field disrupts the hydrogen network in the solution and the molar volumeof the solvate water increases. The mean sizes of the water clusters decrease and thehydrogen interaction between water molecules is weakened. These agree well withthe molecular dynamics simulation results of magnetic effect on NaCl solution. Itreveals that molecular dynamics simulation can be used to ayalyze the magneticeffect and predict the influence of magnetic intensity, concentration, temperature,salt species and the type of magnetic field on the magnetic effect.Molecular dynamics simulation is carried out to investigate the polymerizationprocess of MPD and TMC monomers to form the PA. The crosslinking density,density and pore diameter of the modled PA all agree well with the experimentresults. The diffusion behavior of water molecules and salt ions in the membrane issimulated. With the effect of magnetic field, the interaction between polymer andthat between water molecules and polymer is weakened, while the interactionbetween ions and polymer is enhanced. These lead to increased diffusioncoefficients of water molecules and weakened mobility of ions in the PA. Inseawater desalination, the water molecules and salt ions would permeate membranemore readily and hardly, respectively. Magnetic field is beneficial to improve thewater production and salt rejection.Based on the transport behavior of water molecules and salt ions in themembrane, molecular dynamics simulation is performed to study the influence ofmagnetic intensity, temperature, salt species and the type of magnetic field on themagnetic effect. With the increase of magnetic intensity, the diffusion coefficientincreases and the asymptotic behavior is observed. Magnetic effect on the diffusioncoefficients of water molecules and mobility of ions is more obvious at highertemperatures. For the simulation systems composed with different salt species, themagnetic effect on the transport behavior of the system composed of divalent ionsand in which the water molecules interact strongly with polymer is more obvious,while it is less on the transport behavior of the system composed of monovalent ionsand in which the water molecules interact weakly with polymer. Compared with thestatic magnetic field, the magnetic effect of pulse and alternating field is enhancedand weakened, respectively. Moreover, both the effect turns significantly with the frequency of magnetic feld. In seawater desalination, the water production and saltrejection can be further improved by increasing magnetic intensity and properlyregulating rotating rate to raise temperture and increase magnetic frequency.Osmosis and reverse osmosis devices are designed to investigate the magneticeffect on the transport processes of BW30, LE and XLE membranes. The magneticeffect on the three membranes is different from each other and the diversities aredue to the various membrane surface characters. With the influence of magneticfield, the adsorption coefficients Kwaterand Ksaltboth increase, and the transport rateof both water and salt is increased in the osmosis process. However, the diffusioncoefficients Dwaterincrease and Dsaltdecrease. The transport rate of water and salt isincreased and decreased respectively, and water flux and salt rejection are bothincreased in the reverse osmosis process. Thses are in accordance with the moleculardynamics simulation results of magnetic effect on water and salt transport in the PAmembranes. This indicates that molecular dynamics simulation can effectivelyanalyze the effect of magnetic field on the reverse osmosis seawater desalinationand the influence machnism, as well as predict the influence of magnetic intensity,temperature, salt species and the type of magnetic field on the magnetic effect. Inthe seawater desalination method based on the rotating electromagnetic effect,magnetic field is beneficial to the seawater desalination process. Desalinationefficiency can be improved by increasing magnetic intensity and properly regulatingrotating rate to raise temperture and increase magnetic frequency.更多还原