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大多数天然水中合有带负电荷的胶体,在电渗析器中,这种胶体在阴膜表面沉淀析出,造成阴膜的“受污”。阴膜的受污都发生在膜的淡水室一侧,无机化合物的沉淀结垢如CaCO_3、MgCO_3、Mg(OH)_2、CaSO_4等都发生在阳膜浓水室的一侧,当多价离子或分子量较大的离子进入膜中井固定在膜中时,称为“中毒”。阴膜的“受污”是电渗析中一个较普遍的问题,它导致阴膜电压增高,电渗析效率降 相似文献
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本文以海洋开发工程深入发展的角度出发,从海水淡化和海水综合利用,浓缩海水直接制碱和制盐工业三个方面论述离子交换膜电渗析法浓缩海水在我国的应用价值。指出这项技术在我国是具有应用前景的。同时阐述随着离子交换膜性能不断提高,电渗析装置不断改进,以及与闪蒸法海水淡化工厂联合,与发电厂联合。都必将使此法能耗有较大辐度降低。离子交换膜电渗析法浓缩海水会显示出越来越大的优越性。 相似文献
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离子交换膜是电渗析技术的心脏。五十年代末叶,电渗析技术尚处于萌芽时期,许多国家都致力于这项工作的研究。自六十年代以来,由于离子交换膜的合成有了很大进展,质量及品种基本上能满足实用要求,电渗析技术才迅速发展起来。现在,有的国家将电渗析技术应用于大规模海水制盐,有些国家的干旱地区和天然资源废水区,则大规模用于含盐浓度500 相似文献
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高盐废水“零排放”是当今很多企业需要面临的非常严峻的环保问题,而离子膜电渗析由于其独特的分离机制能够实现高盐废水中无机盐的分离、浓缩和资源化利用,从而实现水和盐的回收利用。本文综述了离子膜电渗析目前在高盐废水“零排放”盐浓缩工艺中的应用情况;展望了电渗析在高盐高COD废水中的应用前景以及新型的电渗析技术如选择性电渗析和双极膜电渗析在混盐分离和盐的资源化利用中的机遇;同时指出离子膜电渗析在大规模应用中仍存在很多挑战,如离子膜性能的提高、电渗析工艺的优化和电渗析设备的投资成本和能耗如何降低。本文将为高盐废水“零排放”提供新思路,同时为离子膜电渗析在高盐废水“零排放”中的规模化应用奠定基础。 相似文献
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为了达到最大限度回收离子液体循环再利用的目的,用电渗析-真空膜蒸馏集成膜法浓缩低浓度质量分数(下同)为1%~5%的离子液体水溶液,实现了有效可操作的膜集成浓缩过程控制。分析了膜集成过程中电渗析施加电压、料液初始浓度和料液体积比等操作参数对优化工艺的影响,获得了此电渗析过程的最高浓缩浓度。当电渗析可浓缩[AMIM]Cl至最大浓度时,即可切换至真空膜蒸馏过程深度浓缩,最终可将[AMIM]Cl水溶液浓缩至48.2%。 相似文献
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Vacuum membrane distillation (VMD) is considered an effective method for concentration of herbal aqueous solutions (HAS). However, membrane fouling and flux decline are complex problems in such concentration processes. The concept of threshold flux was proposed for optimizing the membrane process. Whether it is useful for guiding optimization of the VMD process on HAS concentration needs further investigation. The Semen Raphani aqueous solution (SRAS) was taken as an example to investigate the membrane flux behavior during SRAS concentration by VMD. The results confirmed that the threshold flux concept is applicable to concentrate HAS by VDM. At or below the threshold flux, the total resistance was independent of the flux, while above it membrane fouling increased with higher membrane flux. Moreover, limiting the flux should be avoided in the membrane process because of strong fouling and flux decline. 相似文献
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针对直接接触式膜蒸馏(direct contact membrane distillation,DCMD)过程存在的膜通量小及膜污染问题,设计了一种新型结构的膜蒸馏组件。以蔗糖溶液为处理液,考察了膜组件装填密度Φ、膜曝气量q、蔗糖浓度c与温度T0对DCMD过程的影响。结果表明:随着Φ、q的增加,DCMD过程的膜通量先增大,后逐渐降低,Φ、q均存在最优值;随着c的增加,膜通量逐渐降低;随着T0的增加,膜通量增大;对c为30%(mass)的蔗糖溶液进行DCMD法处理330 min时,膜曝气可使DCMD的初始膜通量Jinitial提升24.7%、膜通量衰减率ΔJ降低55.0%,维持高膜通量的连续运行时间t0延长4倍。主要原因是膜曝气强化了DCMD过程的传热传质,进而强化过程的分离性能;有效控制了DCMD过程的浓差极化,进而延缓过程的膜污染进程。研究结果有利于推进DCMD的工程化应用。 相似文献
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提出将陶瓷膜与流化床反应器耦合构成一体式流化床膜反应器,用于直接法合成二甲基二氯硅烷。实验考察了催化剂浓度、脉冲反吹对反应效率和膜分离性能的影响,并对反应前后的触体及陶瓷膜进行了表征。结果表明,催化剂浓度小于4%(质量)时,二甲基二氯硅烷的选择性均可维持在85%以上,硅粉转化率随催化剂浓度的增大而增大;催化剂浓度在4%~8%时,二甲基二氯硅烷的选择性随催化剂浓度增加而略有下降,当催化剂浓度大于8%时,二甲基二氯硅烷选择性明显下降。触体失活后粒径减小,硅粉表面积碳随催化剂浓度的增加而升高。陶瓷膜表面形成内外两层滤饼,内层滤饼主要成分为铜,外层滤饼主要成分为碳;不同催化剂浓度下,陶瓷膜对粉尘的截留率均可达100%,反应过程中跨膜压差随时间变化较小,脉冲反吹可增加硅粉转化率。 相似文献
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《分离科学与技术》2012,47(4):517-535
ABSTRACT The pervaporation transport process of H2O-EtOH solution was studied on a chitosan membrane and on a H2SO4 crosslinked chitosan membrane. The influence of concentration, temperature, and crosslinking was also studied. The dependence of permeation fluxes on feed concentration showed strong coupling effects existed in the permeation process. That the thermodynamic swelling—distribution relationship changed with the feed concentration also showed that a strong coupling effect existed in the thermodynamic swelling process. The permeation fluxes and thermodynamic swelling processes showed analogous relationships versus the concentration in the feed. The high swelling ratio and the high selectivity of the membrane in the thermodynamic swelling distribution process was the basis ofhigh flux and high permselectivity of pervaporation. With an increase of temperature, the permeation fluxes increased quickly, but the swelling ratio of water and EtOH in the membrane scarcely changed. This showed that an increase of temperature promoted the diffusion process but had little influence on permselectivity. The permselectivity of pervaporation depended strongly on the thermodynamic swelling process. 相似文献
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研究了VO2+在Nafion117质子交换膜中的传质过程, 重点考察了不同操作工况下浓度场和电场的协同作用。定量了电场对钒离子透膜传质过程的影响大小, 并根据实验数据拟合出了VO2+在Nafion117膜中的表观电迁移率。结果表明:电场对高浓度电解液的离子透膜过程影响较大, 升高温度和增加电解液对流均强化了电场作用在钒离子透膜传质的影响, 加入的正向电场越强, 跨膜渗透越剧烈, 且电场因子随着时间的增加而增加。反向电场有利于缓解钒离子透膜传递过程。 相似文献
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CO2捕集作为温室气体排放控制的有效手段已成为重要研究课题。作为新兴捕集技术之一,低温CO2捕集因产品纯度高、无附加污染等优势受到关注。然而,该技术能耗和捕集率对于气体中CO2浓度十分敏感,对于高CO2浓度气体可获得较高的CO2捕集率和较低能耗水平。基于此,本文提出了耦合膜分离的新型CO2低温捕集系统,通过膜材料选择渗透性实现待捕集气体CO2浓度主动调控,并在最优浓度下进行CO2低温捕集。首先基于不同传统低温捕集系统特点,对比分析了不同耦合系统模式,从而确定了最优耦合系统结构。针对最优耦合系统进行了运行参数优化,并分别基于实现系统捕集能耗最低与捕集率最高的目标,获得了膜渗透侧CO2浓度与进气CO2浓度间的关系式,为该耦合系统中膜组件选型提供指导。研究表明,本文提出的耦合系统捕集能耗为1.92MJ/kgCO2,相比于传统单一低温系统捕集能耗可降低16.5%。 相似文献
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The development of energy saving membrane separation processes is finding a unique position in process industries. One of the important areas where they are employed is the biotechnology industry. This industry has its own specifications and requirements, e.g., levels of diluteness, thermal, chemical and shear fragility. Membrane separation processes have the characteristics necessary to match these specifications and needs. In this research, the determination of the experimental concentration of L‐Lysine monohydrochloride (L‐lysine‐HCl) syrup was investigated using ultrafiltration (UF) and vacuum membrane distillation (VMD) hybrid membrane processes. Four parameters that are known to have significant influence on the UF process were examined, i.e., pressure difference across the membrane, feed concentration of L‐lysine‐HCl, feed velocity on the membrane surface, and pH. For the VMD unit, pressure difference and pH were replaced with feed temperature and vacuum pressure on the permeate side of membrane. Each process was carried out separately and the results were used to design a bench‐scale process. In order to save time and money, the Taguchi method of experimental design was employed. The effects of feed concentration, pressure difference across the membrane, feed velocity on the membrane surface, and pH on the target variable, i.e., the membrane flux, in the UF process were 39.93, 38.65, 9.36, and 9.59 %, respectively. For the VMD process, these values were 64.79, 22.16, 6.21, and 2.14 % for feed temperature, feed concentration, vacuum pressure on the permeate side, and feed velocity on the membrane surface, respectively. 相似文献