【作者】 段作山；

【导师】 姚杰；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2010， 硕士

【摘要】 中空纤维膜萃取是膜过程与液液萃取相结合的新型分离技术,特别适用于金属离子、热敏性物质和难分离物质的分离与提取。与传统的液液萃取过程相比,膜萃取具有传质面积大、萃取效率高、能耗低、环境污染少及无液泛和返混、萃取剂损失少等优势。目前,该技术处于工业化应用的初始阶段,是环保领域研究的热点之一。因此有很多问题值得研究。本论文以疏水性PVDF中空纤维膜为传质界面,用高效萃取剂Cyanex 923-煤油-NaOH溶液体系对模拟苯酚废水进行了萃取-反萃取实验,研究了两相传质方式、水相和有机相流速、进水初始浓度、膜组件装填因子、离子强度、膜组件串联和反萃取相浓度等操作条件对萃取率和传质性能的影响。并在此基础上对实际煤气化废水进行了萃取实验。实验结果拟合出了萃取平衡曲线,并计算了分配系数与苯酚在水相中浓度的关系:logD=1.62-0.077caq。pH值对分配系数有重要影响,当pH>8时,分配系数下降很快。增大水相流速能显著加快萃取过程和提高传质系数,而改变有机相流速基本不影响传质系数。这说明水相边界层阻力是总传质阻力的控制因素,计算结果也表明有机相边界层阻力和膜相阻力所占比例不到20%。在水相流速为0.002m/s~0.016m/s的范围内,膜组件的传质单元高度为0.17m~0.75m,明显小于传统萃取设备。增大进水初始酚浓度,总传质系数反而降低,一方面,分配系数随初始浓度的增大而减小,另一方面,浓度升高加剧了传质界面两侧的浓差极化现象。膜组件装填因子和膜的均匀分布及疏密程度对传质有很大影响。增大装填因子能提高传质面积,但同时使膜丝间距变小,容易发生挤压现象,使传质系数降低。串联低装填因子的膜组件能缩短萃取时间,节省投资。盐析效应能够促进萃取传质过程。因此可以通过增大水相离子强度来强化传质。当NaOH浓度由0.1mol/L升高到0.5mol/L时,反萃取系数由4.83×10-7m/s增大到5.93×10-7m/s。酚回收率达到93%以上。反萃取传质系数比萃取传质系数小一个数量级,这是由于在反萃取传质界面不存在溶质的预吸附作用优势。实际废水中SS的含量对萃取率有明显的影响,经混凝预处理后,传质加快。在连续逆流萃取实验中,水相流速在一定范围内的增大能够提高萃取率,但超过这一范围萃取率开始降低。膜组件串联延长了两相间的接触时间,萃取率升高。对长时间使用过的膜进行SEM测试,没有发现膜污染,说明膜萃取抗污染能力很强。更多还原

【Abstract】 Hollow fiber membrane extraction process is combined with liquid-liquid extraction of new separation technologies, especially for metal ions, heat-sensitive material and difficult to separate physical separation and extraction. With the traditional liquid-liquid extraction process, compared with membrane extraction mass transfer area, extraction efficiency, low consumption, little environmental pollution and flooding and no back mixing, extraction and less loss of advantage. Currently, the technology applied in the initial stage of industrialization, is one of the hot research field of environmental protection. So many problems are worth studying.In this thesis, the hydrophobic PVDF hollow fiber membrane for the mass transfer interface, with efficient extractant Cyanex 923-kerosene-NaOH aqueous solution was simulated Phenol extraction- stripping experiments to study the mass transfer of two ways, water phase and organic phase flow rate, initial concentration of water, membrane loading factor, ionic strength, membrane modules in series and anti-phase extraction and concentration of operating conditions on the extraction rate and mass transfer properties. And on this basis, the actual extraction of coal gasification wastewater was experimental.The results of the extraction equilibrium curve fitting and calculating the distribution coefficient and the concentration of phenol in the aqueous phase relationship: logD=1.62-0.077caq. pH values have a major impact on the distribution coefficient, when the pH>8, the distribution coefficient decreased rapidly. Increase the water phase flow rate can significantly speed up the extraction process and increase the mass transfer coefficient, the organic phase flow rate change is not effected by the mass transfer coefficient. It shows that the water phase boundary layer mass transfer resistance is the resistance of the controlling factors, the results also show that the organic layer resistance and membrane phase resistance account for less than 20%. In the water phase flow rate of 0.002m/s~0.016m/s within the modules and mass transfer unit height of 0.17m~0.75m, significantly less than traditional extraction equipment. Increasing initial concentration of water, However, reduce the overall mass transfer coefficient. On the one hand, distribution coefficients with the initial concentration decreases, on the other hand, increasing the concentration and mass concentration polarization on both sides of the interface phenomenon. Membrane packing factor and uniform distribution of film and the density levels have a significant impact on mass transfer. Increase the filling factor can increase the mass transfer area, but the membrane smaller wire spacing, prone to compression phenomena, mass transfer coefficient decreased. Series of low packing factor of the membrane can reduce the extraction time, save the investment. Salt effect can promote the mass transfer process. Therefore, by increasing the ionic strength to reinforce the water phase mass transfer.When the NaOH concentration from 0.1mol/L increased to 0.5mol/L, the anti-extraction coefficient was 4.83×10-7m/s increased to 5.93×10-7m/s. Phenol recovery of more than 93%. Mass transfer coefficient against mass transfer coefficient than an order of magnitude, which is due to stripping of solute mass transfer interface, there is no pre-adsorption edge.SS content in the actual waste water on the extraction rate significantly affected by coagulation pretreatment, mass transfer speed. In the continuous countercurrent extraction experiments, the water phase flow rate increases within a certain range can increase the extraction rate, but the extraction rate over the range began to decrease. Membrane modules in series to extend the contact time between the two phases, extraction rates increased. On the membrane long used SEM tests found no membrane fouling, indicating a strong antifouling membrane extraction.更多还原