【作者】 肖敏；

【导师】 周集体；

【作者基本信息】 大连理工大学 ， 环境工程， 2007， 博士

【摘要】 渗透萃取是一种新型膜分离技术，适用于恒沸物或近沸物、挥发性有机物、热敏性物质及低沸点物系的分离。其中，利用具有弱酸、碱性芳香类化合物水解平衡的特点，以无机碱／酸溶液作萃取液、均质硅橡胶膜（对芳香类化合物具有选择透过性）作为分离膜的新型渗透萃取技术，具有效率高、能耗低、过程简单等优点。目前，该技术正处于工业化应用初始阶段，但仍有许多问题值得深入研究。因此，本文以此类化合物中酚类的代表——苯酚，为模型污染物，以氢氧化钠溶液为萃取液，利用均质致密硅橡胶膜（聚二甲基硅氧烷（PDMS）、聚甲基乙烯基硅氧烷（PVMS））及平板复合膜（PDMS／聚偏氟乙烯（PVDF）），构造渗透萃取系统，对这两种体系渗透萃取含酚水溶液的特性、传质过程与机理进行了研究，主要开展了以下几个方面的工作：（1）采用均质硅橡胶膜卷绕式膜组件，对含酚水溶液进行渗透萃取研究。对比了两种膜材料PDMS、PVMS的渗透萃取性能及运行稳定性。结果表明：PVMS用于渗透萃取含酚水溶液的性能优于PDMS，但前者不适宜在强碱性条件下长期使用。分析探讨了料液流量、料液与萃取液及盐浓度、运行温度、萃取液pH值等因素对渗透萃取性能的影响。其中，萃取液pH值对处理效果影响显著。在料液流量2.0L／d、浓度范围5.0～20.0g／L、萃取液温度323.2K及pH值12.5～13.0的条件下，料液中苯酚的去除率可达95％以上，出水含酚浓度低于500mg／L。萃取液浓度的变化对苯酚去除率无显著影响；总传质系数(K_ov)随盐离子含量的增高而增大。研究表明本体系适于处理高浓度、高盐度含酚废水（0～300g／L NaCl），过程较适宜的料液流量范围1.0～3.0 L／d，水力停留时间2min左右。（2） PDMS渗透萃取吉化双苯厂含酚废水，在料液流量2.0L／d、萃取液温度323.2K及pH值12.5～13.0的条件下，对于初始浓度4.3～10.7g／L的苯酚废水，苯酚的去除率大于97％，出水含酚浓度低于150mg／L，运行效果稳定。表明新型渗透萃取技术分离回收含高浓度苯酚废水具有良好的技术可行性。（3）针对渗透萃取过程中液膜边界层传质、膜内扩散传质及支撑层中传质的特点，探讨了硅橡胶均质膜以及复合膜的渗透萃取传质过程与机理，确定了相应的传质表达式。基于液-膜-液串联传质阻力模型，通过实验测定了体系的总传质系数。（4）以PDMS卷绕式及管束式两种膜组件，研究了连续稳态和循环非稳态操作中均质膜渗透萃取过程的传质。考察了稳态下该体系的K_ov及苯酚在硅橡胶膜中的渗透系数（P）；特别针对膜面上液体流动状况、温度及料液浓度对传质的影响进行了探讨，得到了K_ov与雷诺数（Re）及温度之间关系的数学模型，并将理论值与实验值进行比较。分析了非稳态条件下，萃取液pH值、萃取液流动状态及两相压力对K_ov的影响。研究表明：对于氢氧化钠-苯酚-水实验体系，化学反应对苯酚传质速率的增强作用不显著，传质由膜阻控制，K_ov为3.5×10^-7m／s；pH＞13时，保持萃取液湍流状态，可忽略萃取液侧传质阻力。苯酚溶液初始浓度在5.0～20.0g／L范围内，K_ov与其浓度无关，苯酚的传质通量（J）与其初始浓度呈线性关系，J为1.6～7.7×10^-6kg／m²·s。致密膜体系中两相压差的存在不利于传质的进行。K_ov与运行温度呈直线关系。苯酚在硅橡胶膜中的渗透系数与萃取液温度之间的关系符合Arrhenius型方程。并分析了液相边界层传质阻力及膜扩散传质阻力对K_ov的影响。（5）利用新型PDMS／PVDF平板复合膜构造含酚水溶液渗透萃取体系（料液与萃取液均呈放射状流型），研究了非稳态过程的复合膜渗透萃取传质问题。采用对比差值法将K_ov拆分为液膜传质系数与膜内扩散传质系数。探讨了料液与萃取液的浓度及流量、运行温度、萃取液pH值和膜两侧压差等操作条件对膜渗透萃取性能的影响，回归求得了传质模型中不同操作条件对应的参数。苯酚的液膜传质系数与Re^0.46成正比，传质通量与温度的关系符合Arrhenius方程。讨论了活性层厚度对传质过程的影响，并确定总传质阻力与活性层厚度的关系式。在此基础上得到了复合膜渗透萃取的传质模型，并将理论值与实验值进行比较。研究表明：pH＞13时，K_ov不随流量及萃取液浓度变化而变化；化学反应的增强作用完全可克服支撑层的传质阻力及萃取液侧传质阻力。在苯酚初始浓度5.0～15.0g／L范围内，K_ov为定值。膜两侧压差的存在不利于传质的进行。活性皮层厚度为4、6、8μm的膜扩散传质系数分别为15.0、9.9及7.5×10^-7m／s（323.2K），较均质膜提高了2～4倍。苯酚在复合膜中的传质仍属膜控制的传质。在本研究的4个月的试验周期中，膜的分离性能维持相对稳定。然而，使用3周后的复合膜材料被压密，膜的使用寿命较短。（6）与传统的分离技术比较，这项新型渗透萃取技术具有简单高效、产品纯度高、运行条件温和、环境污染少等优点，是一项先进有效、具有较佳环境与经济效益的含芳香化合物废水分离与回收技术。更多还原

【Abstract】 Pertraction is a new membrane-based separation process to remove azeotropic compounds, volatile organic compounds, and thermosensitive and low boiling point materials from aqueous solution. By means of hydrolytic equilibrium of aromatic acid or base, combined nonporous membrane （permeable for the aromatic compounds but impermeable for the ionic species） and caustic or acidic stripping solution, the new pertraction process could be provided with high efficiency, low energy consumption, simpleness and conveniency and so on. Presently, this technology is being at the initial industrialization application stage, still many problems need to be investigated. In this study, phenol was chosen as model compound which is the representation of phenolic compounds to study and caustic stripping solution （sodium hydroxide） was as stripping solution. Two kinds of pertraction system were constructed by nonporous membrane （Poly （dimethylsiloxane）, i.e. PDMS and Poly （methyl vinyl） siloxane, i.e. PVMS） and flat sheet composite membrane （PDMS/PVDF, Polyvinylidene Fluoride, i.e. PVDF）. The characteristic, mass transfer process and mechanism of the systems were investigated, and the following studies were carried out:1) Membrane pertraction process to the removal of phenol from aqueous solution was investigated, where the apparatus with spiral wound silicone rubber membrane was applied. The pertraction ability and stability of PDMS and PVMS water-phenol mixtures were compared. PVMS performed better than PDMS but was not suitable for long-term operation under strong base condition. The role of operative conditions on the process performance was widely investigated, and flow rate of liquid feed, composition （phenol, stripping solution and salt）, temperature and pH in the stripping solution were the main operative variables. Among these, the pH in the stripping solution was the major factor since it greatly affected the separation efficiency. The phenol removal efficiency was over 95% under the conditions of flow rate 2.0 L/d, phenol concentration 5.0-20.0 g/L, 323.2 K and pH 12.5-13.0, which was independent of initial stripping concentration. Phenol concentration in the outlet was lower than 500 mg/L. The overall mass transfer coefficient (OMTC, K_ov) increased as salt concentration increased. That indicated the system was especially fit for high phenol concentration and high salinity （0-300 g/L） wastewater. The feasible range of flow rate was from 1.0 to 3.0 L/d and hydraulic retention time was about 2 minutes.2) The phenolic wastewater from double benzene factory of Jilin Petrochemistry Corporation had been disposed with pertraction technique under PDMS system. The technical feasibility of the process was obviously: Over 97% of phenol could be removed from the wastewater under the conditions of flow rate 2.0 L/d, phenol 4.3-10.7 g/L, 323.2 K and pH 12.5-13.0, and phenol concentration in the outlet was lower than 150 mg/L, the system ran steadily.3) As for the mass transfer character of liquid film boundary layer, membrane and support layer, pertraction mass transfer mechanism and process of phenol through membrane of nonporous and composite silicone rubber were investigated. Mathematical models descriptions of the two kinds of processes were developed respectively. Based upon the resistance-in-series model, OMTC was measured.4) Using spiral wound and single tubular PDMS nonporous silicone rubber membrane modules respectively, mass transfer process of pertraction was researched at steady state and non-steady state. At steady state, the effects of liquid flow status, initial phenol concentration and system temperature on the surface of membrane on OMTC and the permeability for phenol through the membrane were discussed. A correlation between OMTC and Reynolds number （Re） as well as system temperature were obtained, and the results were compared with the experiments. The effects of stripping solution pH value, stripping solution flow status on the surface of membrane and liquid phase pressure difference between opposite membrane sides on OMTC were analyzed at the non-steady state. The experiment results indicated that chemical reaction enhancement was not remarkable, and mass transfer was dominated by membrane resistance (K_ov=3.5×10^-7 m/s). Liquid film resistance of stripping solution （pH>13） could be negligible under turbulent condition. In the initial phenol concentration ranges （5.0-20.0 g/L）, OMTC was nearly, constant, and mass flux of phenol displayed linearly with initial concentration (1.6-7.7×10^-6 kg/m²·s). The presence of liquid phase pressure difference between opposite membrane sides went against permeability of phenol. K_ov was in direct proportion to the temperature of the process. And the experimental data conformed to Arrhenius relationship for the temperature dependence of the permeability of phenol through the polymer. Especially, the effects of liquid film boundary layer resistance and membrane resistance on OMTC were analyzed.5) At non-steady state, pertraction mass transfer characteristic of phenol from aqueous solution through a novel flat sheet composite membrane （PDMS/PVDF） with radial flow in both feed and stripping sides was investigated. OMTC was split into liquid film and membrane mass transfer coefficient, by conducting a calculation from the experimental data with different nonporous selective layer thickness of membranes. The experiments were carried out to investigate the effects of composition and flow rate （feed and stripping solution） temperature, pH value and liquid phase pressure difference between opposite membrane sides on the pertraction performance. The parameters according to different operation conditions were regressed. It appeared that feed-side boundary layer mass transfer coefficient was proportional to Re^0.46, and mass flux increased exponentially with increasing temperature, that is, Arrhenius relationship. A correlation between the thickness of selective layer and the mass transfer resistance was established. On the basis of above results, a pertraction mass transfer model of composite membrane was achieved, and the results were compared with the experiments. The experimental results showed that OMTC was independent of stripping solution flux and concentration （pH>13）. The support layer and stripping side resistance to mass transfer could be eliminated completely due to chemical reaction enhancement. OMTC was independent of initial phenol concentration （5.0-15.0 g/L）. The presence of liquid phase pressure difference between opposite membrane side counteracted permeability of phenol. Membrane diffusive mass transfer coefficients of selective layer （thickness 4, 6 and 8μm） were 15.0, 9.9 and 7.5×10^-7 m/s respectively（323.2 K）, which exhibited 2-4 times higher than that of nonporous silicone rubber. Mass transfer resistance in membrane was also dominant for composite memebrane system. In a continuous experimental period of four months, the membrane had been behaving well. However, after being used for three weeks, composite membrane was compressed obviously and short life-span.6) The new pertraction technology offers an excellent combination of Simplicity, high efficiency, sufficient final product purity, low energy consumption, mild operation conditions and less pollution compared with traditional ones. As a Consequence, it is an advanced, effective, economical and environment amity for recovery of aromatic acids and bases from wastewater streams.更多还原