浓差极化对正渗透膜通量影响研究

采用两种正渗透膜HTI-ES和HTI-NW膜研究了浓差极化对膜通量的耦合作用,阐述了浓缩的外浓差极化和稀释的内浓差极化对膜通量的影响。结果表明内浓差极化是造成膜通量减小的主要原因,在此基础上同时结合浓差极化模型,求得了外浓差极化系数k和内浓差极化系数K,并对实验数据进行了拟合,该模型计算出的HTI-ES水通量与实验吻合良好。     

操作条件对正渗透分离性能的影响

正渗透是以渗透压差为驱动力的新型膜分离过程。采用水流分布较佳的膜池结构,研究了膜朝向、流动方式对正渗透水通量性能的影响,结果表明PRO模式（当膜的活性层朝向驱动液时）的水通量明显高于FO模式（当膜的活性层朝向原料液时）,但其衰减程度较大;在溶液浓度差相同的条件下,逆流操作更利于水通量的提高。针对FO模式和逆流条件,探讨了溶液温度对水通量和反向盐通量的影响,结果表明：膜两侧溶液温度同步升高时,正渗透过程的水通量和反向盐通量均增加,且水通量的增加幅度大于反向盐通量;单侧增加溶液的温度时,驱动液侧温度升高对水通量性能的提升效果优于原料液侧。综合考虑过程能耗和系统性能,认为单独升高驱动液温度更具实用价值。     

隔网对正渗透膜压力延迟渗透性能影响的研究

针对压力延迟渗透(PRO)过程中正渗透膜片的性能表现,采用无隔网、单隔网和双隔网相互对照的方法考察了过程中正渗透膜片的水通量和盐通量的变化情况。结果发现,实验过程中无隔网时浓差极化现象对水通量的影响比较明显;单隔网能有效减弱浓差极化现象,水通量平均提升10%左右,盐通量下降幅度为3.4%左右;双隔网虽然在一定程度上可以减弱浓差极化现象,但实验过程中出现的阴影效应,导致膜片有效渗透面积减少及水通量快速下降。经过比较发现PRO过程中在膜片两侧添加单隔网可以使膜的水渗透性能和盐截留性能达到较好的状态。     

纳米材料用于薄层复合正渗透膜的制备

正渗透是一种以渗透压为驱动力的膜分离技术,它具有低污染、低能耗、在常温常压下运行等优点,因而被广泛地应用于水处理和脱盐。然而,正渗透技术依然存在一些瓶颈,包括浓差极化现象、膜污染、溶质的反向扩散和新的膜材料以及汲取液的设计。纳米材料的快速发展为解决这些问题提供了一种有效的途径,将无机纳米材料作为填料,添加到薄层复合(TFC)膜中能够有效地增正渗透性能。这篇综述概括了纳米无机材料作为填料用于薄层复合正渗透膜的制备。     

卷式正渗透膜组压力延迟渗透性能实验研究

利用卷式醋酸纤维素正渗透膜组,以Na Cl溶液和自来水分别作驱动液和料液,考察了进口压力、溶液流量、驱动液浓度和跨膜压差等因素对膜组性能的影响,并对以上4个因素进行单因素实验。结果表明,相同流速下料液流道阻力明显大于驱动液流道;随着料液和驱动液流量的增加,膜组水通量呈缓慢上升趋势,料液流量改变对水通量的影响更明显一些,但和膜片相比,膜组的单位面积水通量有所下降;通过增加驱动液浓度能够较大幅度提升膜组水通量和功率密度,但浓差极化现象的抑制作用也逐渐增加。随着跨膜压差的升高,水通量呈逐渐下降趋势,当其达到渗透压的一半时,膜组功率密度达到最大。     

正渗透基本原理及其工程应用

介绍了正渗透基本原理及其在海水淡化、绿色能源方面的应用,通过对正渗透和减压渗透过程的通量模型的分析,指出内、外浓差极化是导致通量衰减的主要因素,并依据模型提出了减弱内、外浓差极化影响的思路,为正渗透技术的工程应用提供了参考。     

正渗透膜材料的研究进展

正渗透技术因其低能耗、耐污染等优势受到国际和国内众多学者的关注,尤其近几年来,取得了迅速发展。本文对正渗透过程中的影响因素以及浓差极化现象作了简要分析,结果表明,内浓差极化是影响正渗透技术效率低下的重要因素,而制备适当的膜材料是有效改善内浓差极化的关键技术。回顾了正渗透分离技术在国内外的发展历程,通过不懈的探索和研发,先后成功制备得到不同材料和结构的正渗透膜。重点讲述膜材料在正渗透领域所取得的最新研究进展,最后指出众多正渗透膜材料由于条件限制难以推广应用,希望在未来的研究过程中突破这项技术难题,缩短科研理论与实际应用之间的差距,在膜材料的实际应用方面取得创新性成果。     

正渗透—纳滤耦合处理苦咸水脱盐工艺

以2 000 mg/L氯化钠模拟苦咸水,采用二价无机盐作为汲取液,研究了正渗透淡化苦咸水时的水通量;通过软件计算和试验研究了不同组成汲取液的纳滤性能,并且设计了二级纳滤系统用于汲取液的回收。结果表明:相同浓度时硫酸镁汲取液正渗透水通量最低,而氯化镁汲取液水通量最高;相反在纳滤过程中,硫酸镁汲取液性能最佳,氯化镁最差;稀释硫酸钠汲取液浓度为30 g/L时,二级纳滤过程可以将汲取液浓缩至初始浓度(60 g/L),并制得浓度低于500 mg/L的产水。     

碳酸氢铵为汲取液正渗透海水淡化研究

正渗透技术因低能耗、低膜污染和高回收率等优点逐渐成为膜分离技术的研究热点。本文以碳酸氢铵溶液为汲取液、0.6mol/L氯化钠溶液为模拟海水进行了正渗透实验,研究了不同操作条件下正渗透水通量的变化规律和汲取液部分解吸-吸收过程中氨解吸率、氨吸收率以及解吸能耗的变化。结果表明,提高进料流量和汲取液浓度,正渗透过程水通量增加;提高吸收塔进料流量,氨吸收率增加,操作条件对氨解吸率影响较小;海水淡化正渗透系统能耗主要用于汲取液解吸过程,降低解吸塔进料浓度可以降低解吸过程的能量消耗。在优化的工艺条件下,正渗透过程水通量为13.6L/(m~2·h),汲取液回收利用率达到99%,海水淡化产水总溶解固体(TDS)不高于1000mg/L,系统吨水耗电量约为195kW·h。实验结果对正渗透过程的工业化应用具有指导意义。     

压力延迟渗透发电技术的影响因素探究

压力延迟渗透技术作为提取盐差能的一种有效方法,已在海洋新能源开发方面展现出巨大潜力,提高盐差能发电效率是目前压力延迟渗透技术尚需解决的重要问题之一。以压力延迟渗透过程膜的水通量和功率密度为评价指标,重点研究了料液流动方式、流速和浓度等因素对压力延迟渗透过程性能的影响。结果表明,采用逆流方式、增大浓度差、提高流速均有利于提高压力延迟渗透过程中的水通量和功率密度,其中,单侧增加原料液浓度,水通量和功率密度均呈逐渐降低趋势;单侧增加驱动液浓度,水通量和功率密度均呈逐渐上升趋势。选取河水-正渗透浓盐水模拟体系,采用逆流操作,在压力差为1 200 kPa条件下,提升原料液流速效果更优;驱动液流速为1.0 L·min^-1,原料液流速从0.5 L·min^-1提升到2.0 L·min^-1时,水通量提升了17.3%,功率密度也从8.01 W·m^-2增加到9.39 W·m^-2。     

正向渗透膜分离技术及其应用综述

正向渗透是一项新型的利用半透膜两侧溶液渗透压差作为驱动力的膜分离技术。文章介绍了正向渗透膜分离技术的原理和影响因素,对其在各个领域(包括海水淡化、废水处理、橙汁浓缩、水袋)的研究进展进行了综述。现有的研究表明,可用于正向渗透工艺的膜不同于常规的反渗透膜,需要从膜结构开发适合的膜组件;采用NH3和CO2制备提取液是目前研究中具有应用前途的方式之一,具有产水率高且易于分离浓缩的优点。     

A novel ammonia—carbon dioxide forward (direct) osmosis desalination process

A novel forward (direct) osmosis (FO) desalination process is presented. The process uses an ammonium bicarbonate draw solution to extract water from a saline feed water across a semi-permeable polymeric membrane. Very large osmotic pressures generated by the highly soluble ammonium bicarbonate draw solution yield high water fluxes and can result in very high feed water recoveries. Upon moderate heating, ammonium bicarbonate decomposes into ammonia and carbon dioxide gases that can be separated and recycled as draw solutes, leaving the fresh product water. Experiments with a laboratory-scale FO unit utilizing a flat sheet cellulose tri-acetate membrane demonstrated high product water flux and relatively high salt rejection. The results further revealed that reverse osmosis (RO) membranes are not suitable for the FO process because of relatively low product water fluxes attributed to severe internal concentration polarization in the porous support and fabric layers of the RO membrane.     

温度对正向渗透的影响机制与数值模拟

正向渗透(FO)是一种以溶液自身渗透压作为推动力的膜分离技术。温度对溶液、膜的性质以及溶液与膜之间的相互作用有很大影响,进而影响FO的水通量。利用数值模拟与试验研究了温度对FO性能的影响。结果表明,当膜两侧等温时,FO水通量随着温度的升高而增大;当膜两侧不等温时,原液(FS)一侧温度的影响比提取液(DS)一侧更大,主要是因为温度升高降低了溶液黏度,强化了过膜扩散过程,而温度对DS渗透压的影响不明显。在不同温度条件下,FO水通量和热通量随流量的增大而增大,主要是由于流速的增大压缩膜表面的流体边界层,强化了传质和传热过程。     

正渗透水处理关键技术研究进展

正渗透是一种新型的膜分离技术,其分离的驱动力来源于原料液和汲取液之间自然存在的渗透压差,近年来正渗透技术已在国际上得到广泛关注。简述了基于此技术的正渗透水处理过程的基本原理,指出了这种新型水处理过程的关键技术——正渗透膜和汲取液,根据各自的技术特点对其进行分类概述,并从实验室基础研究和技术的商业化进程两方面介绍了这两项关键技术取得的最新研究进展。从水通量角度对不同体系进行了简单比较,分析了各材料和方法的优缺点,并对它们的应用前景进行了展望。     

An agent-based simulation with NetLogo platform to evaluate forward osmosis process (PRO Mode)

Forward osmosis (FO), as an emerging technology, is influenced by different factors such as operating conditions, module characteristics, and membrane properties. The general aim of this study was to develop a suitable (flexible, comprehensive, and convenient to use) computational tool which is able to simulate osmosis through an asymmetric membrane oriented in pressure retarded osmosis (PRO) mode in a wide variety of scenarios. For this purpose, an agent-based model was created in NetLogo platform, which is an easy-to-use application environment with graphical visualization abilities and well suited for modeling a complex system evolving over time. The simulation results were validated with empirical data obtained from literature and a great agreement was observed. The effect of various parameters on process performance was investigated in terms of temperature, cross-flow velocity, length of the module, pure water permeability coefficient, and structural parameter of the membrane. Results demonstrated that the increase in all parameters, except structural parameter of the membrane and the length of module led to the increase of average water flux. Moreover, nine different draw solutes were selected in order to assess the influence of net bulk osmotic pressure difference between the draw solution (DS) and feed solution (FS) (known as the driving force of FO process) on water flux. Based on the findings of this paper, the performance of FO process (PRO mode) can be efficiently evaluated using the NetLogo platform.     

High performance forward osmosis cellulose acetate (CA) membrane modified by polyvinyl alcohol and polydopamine

Cellulose acetate (CA) is a low cost and readily available material widely used in forward osmosis (FO) membranes. However, the performance of pure CA membranes is not good enough in salt separation and the traditional modification methods are generally multistep and difficult to control. In this paper, we reported high performance cellulose acetate (CA) composite forward osmosis (FO) membranes modified with polyvinyl alcohol (PVA) and polydopamine (PDA). PVA was first cross-linked onto the surface of CA membranes, and then PDA was coated with a rapid deposition method. The membranes were characterized with respect to membrane chemistry (FTIR and XPS), surface properties comprising wettability (by water contact angle), and osmosis performance. The modified membrane coated by PVA and PDA shown better hydrophilicity and exhibited 16.72 LMH osmotic water flux and 0.14 mMH reverse solute flux with DI water as feed solution and 2.0 M NaCl as draw solution and active layer facing the feed solution. This simple and highly effective modification method makes it as an excellent candidate for further exploration for FO.     

Synthesis and application of ethylenediamine tetrapropionic salt as a novel draw solute for forward osmosis application

The development of suitable draw solutes for forward osmosis (FO) process is a big obstacle on the way of its real industrialization. In this work, a novel draw solute, ethylenediamine tetrapropionic (EDTP) acid (salt) is developed for FO application. The successful synthesis is confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high resolution mass spectrum. By optimizing the pH of EDTP solution, its composition is varied, and therefore, its water solubility and osmotic pressure are effectively improved. The effects of EDTP concentration on the osmotic pressure and FO performance are also investigated. Its outstanding osmotic pressure and big molecular size result in a high water flux of 22.69 LMH and a low salt flux of 0.32 gMH with 0.8 M EDTP draw solution (water as the feed solution, pressure retarded osmosis mode). The good stability and easy recovery by nanofiltration of EDTP solution also demonstrate its great potential as the draw solute for future FO applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1309–1321, 2015     

Osmotic concentration of succinic acid by forward osmosis: Influence of feed solution pH and evaluation of seawater as draw solution

In this study, we investigated the essential role of feed solution pH so as to gain insights into the transport mechanisms of succinic acid concentration by osmotically-driven forward osmosis(FO) process. FO performances including water flux and bidirectional transport of succinate and chloride anions were systematically examined using cellulose triacetate-based FO membrane. Additionally, real seawater was explored as draw solution. Experimental results revealed that the p H-dependent speciation of succinic acid can affect the FO performances. Ionization of succinic acid at higher solution p H enhanced the osmotic pressure of feed solution, thus leading to lower water flux performance. A strong effect was pointed out on the succinate rejection for which nearly 100% rejections were achieved at p H above its pK_(a2) value. The rejection of succinate increased in the following order of chemical form: C_2H_4 C_2O_4H_2 C_2H_4C_2O_4H~ˉ C_2H_4C_2O_4~(2-).With real seawater as the draw solution, low to moderate water fluxes(4 L·m~(-2)·h~(-1)) were observed.The divalent succinate anion was highly retained in the feed side despite differences in the succinic acid feed concentration at p H of approximately 6.90.