【作者】 李睿；

【导师】 王连军；

【作者基本信息】 南京理工大学 ， 环境工程， 2010， 博士

【摘要】 本文以含苯废气作为研究体系,开展了膜吸收工艺在VOCs净化领域的研究,研究内容主要包括工艺性能研究和传质理论研究。工艺性能研究方向主要围绕工艺参数的优化、膜材质与吸收剂的兼容性研究等方面展开。传质理论方向则以双膜理论为基础,结合传质阻力方程,建立了传质微分模型,模拟膜吸收传质过程,预测传质相关系数。同时,对减压膜蒸馏工艺再生吸收剂性能也进行了初步的研究,建立了膜吸收-减压膜蒸馏新型组合工艺。首先,根据膜吸收工艺的特点、吸收剂循环利用以及与膜材质的兼容性等因素,结合传统吸收工艺对VOCs吸收剂的要求,对含苯废气吸收剂进行筛选,最终选取工业用于芳烃提纯的N-甲酰吗啉(NFM, n-Formyl morpholine)水溶液作为吸收剂,测定了不同浓度的NFM水溶液的密度、粘度、表面张力和亨利定律常数(苯)等物性参数,通过线性拟合得到不同条件下物性常数的计算公式；采用扫描电镜观察了使用前后膜表面形态的变化,结果表明：NFM水溶液具有较高的表面张力,难以湿润有机高分子膜表面,能与有机高分子膜很好地兼容,有效的避免了因膜孔润湿带来的膜相传质阻力增大对传质过程的影响,该溶液是膜吸收良好的吸收剂。设计并搭建了膜吸收-减压膜蒸馏组合工艺装置,以亲水性有机溶剂NFM水溶液为吸收剂,疏水性多孔聚丙烯中空纤维膜组件为气、液膜接触器,在实验装置上开展了膜吸收净化含苯废气性能的研究：分析了气、液流量、吸收剂温度、吸收剂浓度和进口气中苯初始浓度等操作条件对去除率和传质系数的影响；采用传质阻力方程对总传质系数进行模拟计算,并将模型值与实验值进行对比；同时计算了传质过程中的传质阻力,研究了气液传质过程的控制因素,结果表明：膜吸收净化含苯废气具有较高的传质效率,在NFM体积分数为40%,吸收剂流量20-100 mL·min-1,进口气流量40-300 mL-min-1,进口气浓度10.2 mg·L-1的条件下,C6H6去除率为65.0%-99.5%,总体积传质系数为0.0157-0.08412 s-1；膜吸收工艺在实验时间内具有较高的稳定性和可操作性；传质阻力模型值与实验值符合较好,能够较好的反映膜吸收传质过程,在实验条件下,实验值与模型计算值之间的平均误差为7.9%,最大误差为20.2%；通过对传质阻力计算发现,在NFM水溶液吸收C6H6的体系中,液相传质阻力占总传质阻力的99%以上,气相阻力与膜相阻力可忽略不计,传质过程主要受液膜控制。在双膜理论的基础上建立了气相在中空纤维膜管程流动的膜吸收过程的非线性微分方程,提出了微分方程的数值求解方法；在非润湿条件下,模拟了C6H6在膜丝管程及膜孔内的传质过程,求解出组分在管程及膜孔内的浓度分布,预测传质相关系数,并将模拟结果与实验结果进行了对比,结果表明：对不同气、液流量条件下膜吸收净化含苯废气效率进行模拟,模型计算值与实验值平均误差为1.81%；吸收速率模型值与实验值平均误差为1.9%,总传质系数模型值与实验值平均误差为12.16%。模型可以较准确地描述中空纤维膜吸收C6H6的过程,可作为膜吸收技术工业放大的理论依据。在相同的操作条件下,比较了膜吸收与传统的传质设备填料塔的传质特性和传质性能,结果表明：通过吸收剂流量、进口气流量、进口气浓度及吸收剂NFM体积分数对两种装置的净化效果的影响,膜吸收的吸收效率和总体积传质系数KGa值高于填料塔；膜吸收过程中的传质单元高度HTUG (the height of a transfer units)值明显低于填料塔的HTUG值。膜接触器与传统的传质设备相比具有自身独特的传质特性,这些独特的传质特性使膜接触器具有比传统的传质设备等更好的应用潜力和市场。最后,采用减压膜蒸馏(VMD, vacuum membrane distillation)工艺再生吸收剂,实现吸收剂的循环利用,疏水性聚丙烯中空纤维膜为再生膜接触器,研究了减压膜蒸馏过程中,各操作参数对吸收剂再生性能的影响。实验结果表明减压膜蒸馏技术对含苯NFM水溶液具有较高的再生效率和传质通量。减压膜蒸馏具有体积小,再生效率高,能耗少和膜通量高等优点。更多还原

【Abstract】 Removal VOCs from waste gas using membrane-based gas absorption process was firstly studied in this paper. The systemic investigations are performed about process performance and mass transfer theory. The study of process performance was mainly including optimization of process parameters, compatibility research between membrane materials with absorbent. The study of mass transfer theory, based on the double film theory, was mainly including establishment of a differential model of mass transfer combining with mass transfer resistance equation, prediction of mass transfer parameters. Meanwhile, the process performance of membrane-based gas absorption process and traditional technology packed tower was compared. A new combined process, membrane-based gas absorption combining vacuum membrane distillation, was established, and the process performance of vacuum membrane distillation for the regeneration of absorbent was also studied here.In the first, combined with the request of VOCs absorbent in traditional absorbent absorption process, the works focused on the selection of absorbent which could be easy to regeneration and has good compatibility with the membrane material in the membrane-based gas absorption. As a result, the N-Formyl morpholine which is used as aromatics extraction solution was selected as the absorbent in this study. Density, viscosity, surface tension and benzene henry’s law constant in different concentration and temperature were determined experimentally. Fitting equations of experimental data were obtained. Compatibility of NFM and microporous hollow fiber polypropylene membrane was studied, and the results show that the NFM aqueous solution was provided with high surface tension and difficult to wet the PP membrane. It had compatibility with PP membrane, which could be efficiently to decrease the effect of the increasing of membrane resistance caused by the wetting of membrane pore. The NFM aqueous was suitable absorbent for the absorption benzene in membrane-based gas absorption process.An experimental scale device combining membrane-based gas absorption with vacuum membrane distillation for benzene separation from mixture gas was designed and built up. Using NFM aqueous solution as absorbent and PP as the membrane contactor, the performance of membrane-based gas absorption process was studied. Effects of gas and liquid flow rate, absorbent temperature, absorbent concentration, benzene initial concentration in feed gas et al. on the removal efficiency and mass transfer coefficient were studied. Mathematical model based on resistance-in-series concept was presented to predict the value of the overall mass transfer coefficient ko(?), which was compared with experimental value, and the mass transfer resistance was also calculated to study the domain factor in mass transfer process. The results show that the characteristics of separation of C6H6/N2 by membrane contactor are of quicker mass transfer velocity and higher efficiency of separation. The removal efficiency achieves 65.0%-99.5%, and the overall volumetric mass transfer coefficient kGa achieves 0.0157-0.08412 s-1, when following conditions were used:volume ratio of NFM,40%; flow rate of absorbent,20-100 mL-min-1; flow rate of feed gas,40-300 mL-min-1. It was proved that membrane-based gas absorption process has high stability and operability. Prediction values of the overall mass transfer coefficient are in better agreement with experimental values, the average error is 7.9%, and maximal error is 20.2%. For all practical purposes, the resistance of liquid phase can be assumed as approximately 99% of the total resistance to calculate the area required for the absorption system design. The resistance of gas phase and membrane can be neglected. The resistance of liquid phase is the domain factor of mass transfer process.Based on the double-film theory, nonlinear differential equations were established to simulate the process of mass transfer process while the gas phase flow in the tube side. The mass transfer process in the membrane tube side and membrane pore were simulated using differential equations, and the distribution of benzene in the tube side and membrane pore were also simulated, mass transfer coefficient were predicted, which were compared with those of experiment. The results showed that the average error of benzene removal efficiency was 1.81% between simulate values with those of experimental values, and the average error of absorption rate was 1.9%, the average error of overall mass transfer coefficient was 12.16%. The mass transfer process could be accurately simulated by the differential equations, which can be used as the theory basis for the industrial enlargement of membrane-based gas absorption technology.Under same conditions, the performance of membrane-based gas absorption process were compared with those of traditional packed tower, and the results showed that the membrane contactor had significantly higher absorption efficiency, overall volumetric mass transfer coefficient and lower values of height of a transfer units based on the studies of effects of absorbent and gas flow rate, initial concentration and absorbent concentration on the mass transfer performance using two technology. It could be conclude that the membrane-based gas absorption process own unique mass transfer characteristics, which meant this technology had more market potential for the removal of VOCs from gas mixtures of industrial emission.In order to regenerate and recycle absorbent, vacuum membrane distillation process was introduced. Microporous hollow fiber polypropylene membrane was used as the membrane contactor. Studies of effects of operational parameter on the regeneration performance were carried out, and the results showed that the characteristics of regeneration by VMD process were of higher regeneration efficiency and mass transfer flux. VMD had the advantages such as high efficiency and flux, low power consume, which was the best technology for the removal VOCs from exhaust gas combining with the membrane-based gas absorption.更多还原