聚丙烯腈纳滤膜的制备及对造纸废水的截留性能

以聚丙烯腈膜为基膜 ,壳聚糖为改性剂 ,采用紫外辐射法制备了一种新型纳滤膜。研究了纳滤膜的制备工艺及性能 ,并将纳滤膜用于处理蓝桉化学热磨机械浆 (CTMP)废水。研究结果表明 :在所选择的条件下制备的 #4纳滤膜 ,其离子交换容量和膜电阻分别为 3 5× 1 0 - 3 mmol/cm2 、3 52× 1 0 3 Ω ;采用 #4纳滤膜处理CTMP废水 ,其对钠的截留率为 40 1 % ,并且浓缩液中的固形物含量、燃烧热比原废液大大增加 ,可以满足碱回收工段的要求。     

PVA/SiO2/GO复合夹层结构纳滤膜的制备及其性能

为了提高氧化石墨烯(GO)纳滤膜的纳滤性能,采用静电喷涂技术制备了大面积的GO纳滤膜,进一步结合静电纺丝技术,设计并制备了PVA/GO复合夹层结构纳滤膜,极大地提高了纳滤膜的结构稳定性。此外,为了进一步提高PVA/GO纳滤膜的纳滤性能,采用亲水性二氧化硅(SiO₂)纳米粒子插层GO,增大了GO纳滤膜的层间距。最后,对所制备的PVA/SiO₂/GO复合夹层结构纳滤膜(PS@GS-NF)的纳滤性能、结构稳定性、可重复利用性能和吸附性能进行研究。结果表明:PS@GS-NF的稳态纯水渗透系数高达21.1 L/(m²·h·bar),有机染料截留率的保持率高达98%。同时夹层结构还保证了PS@GS-NF具有较高的结构稳定性。此外,PS@GS-NF还具有良好的可重复利用性能和对带正电荷的有机染料分子具有良好的吸附性能,其纯水渗透系数恢复率可达92%,对带正电荷的亚甲基蓝有机染料分子的吸附率可达96%。     

纳滤膜的应用及过程中的污染控制

纳滤技术是一种介于超滤和反渗透之间的新型分离技术.本文简单介绍了纳滤膜的特性及其独特分离特点,高分子纳滤膜的几种主要分类、分离机理及理论模型.介绍了纳滤膜在水处理、食品、化工和医药等领域的应用.同时较详细的阐述了4种主要的减轻污染的方法:膜清洗、改变物料的性质、改变操作方式及膜面改性.指出今后的发展将着重于传质机理、新的膜材料及集成工艺开发等方面.     

振动超滤的原理和应用研究

引言以逆渗透、超滤和精密过滤为代表的液体膜分离法在分离液体时没有相的变化,它作为节能分离技术而得到普通应用,特别是它可避免食品加热浓缩时的品质劣化、可提高饮用水的品质而     

食用油脂膜分离超滤脱胶的研究进展

综述了食用油脂膜分离超滤脱胶的研究进展.分析了超滤脱胶的主要优点,介绍了超滤脱胶的工艺条件和膜材料.展望了超滤脱胶的工业化前景.     

纳滤浓缩西番莲果汁的研究

根据西番莲原汁中的有机物组成及分子量,选择合适的纳滤膜对西番莲澄清果汁的浓缩过程进行研究.通过系统考察影响膜通量的因素,发现适当提高温度、压力可以提高膜通量.在不破坏西番莲果汁中的芳香成分及Vc等营养成分和不超过膜的压力操作范围的前提下,得到较适的操作温度和压力.选择在操作温度为28 ℃左右,压力为3 MPa时,分离效果最好,此时实际膜通量达17 L/(m2.h).经过纳滤浓缩,西番莲澄清汁可溶性固形物从13oBx提升到30oBx左右.本实验可以达到较好的膜通量和截留率,为在工业化浓缩西番莲澄清汁过程中,利用膜技术大大减少芳香成分及Vc等营养成分损失提供参考.     

再生纤维素基交联改性纳滤膜的制备及对无机盐截留性能的研究

以竹纤维素再生膜为基膜,海藻酸钠和羧甲基纤维素的共混溶液为涂覆液,环氧氯丙烷为交联剂,采用交联法制备了一种新型纤维素复合纳滤膜。研究了纳滤膜的制备工艺和对NaCl、Na_2SO_4、MgCl_2、MgSO_4、CaCl_2(500 mg/L)的截留性能。结果表明,在海藻酸钠与羧甲基纤维素共混溶液质量分数2.0%、共混比1∶3、环氧氯丙烷质量分数3.0%条件下,纤维素复合纳滤膜的膜通量为13.75 L/(m~2·h),Na Cl截留率为48.15%,较纤维素再生膜的膜通量(487.81 L/(m~2·h))下降明显,较纤维素再生膜的截留率(1.52%)有明显提高。对几种无机盐的截留性能顺序为:Na_2SO_4﹥Mg SO4﹥Na Cl﹥Mg Cl2﹥Ca Cl2。相比纤维素再生膜,纤维素复合纳滤膜的抗张力为83.31 N,比纤维素再生膜的抗张力(46.65 N)提高了44.0%,膜伸长量4.7 mm,伸长率9.40%,抗张强度5.554 k N/m,机械性能相对提高。     

纳滤浓缩古龙酸提取液的研究

纳滤膜能在常温下将超滤提取后的古龙酸提取液浓缩,替代了原有的蒸发浓缩。既降低了能耗,又防止了料液被高温分解破坏,提高了产品的收率和成品质量,经济效益可观。现纳滤膜已成功地运用到维生素C大生产中。污染后的膜用加酶复合型清洗剂进行清洗,其效果优于单一型酸、碱清洗剂。     

RO反渗透膜、纳滤膜和超滤膜的对比

一种最通用的广义定义是“膜”为两相之间的一个不连续区间。因而膜可为气相、液相和固相,或是他们的组合。简单的说,膜是分隔开两种流体的一个薄的阻挡层。描述膜传递速率的膜性能是膜的渗透性。一、反渗透基本原理1.反渗透过程反渗透是利用反渗透膜选择性的只能通过溶剂(通常     

Purification of pectate oligosaccharides showing root-growth-promoting activity in lettuce using ultrafiltration and nanofiltration membranes

Pectate oligosaccharides were separated from enzymatically hydrolyzed pectate by using ultrafiltration (UF) and nanofiltration (NF) membranes. The UF treatment was performed at a transmembrane pressure of 0.15 MPa and flow velocity of 0.6 m.s(-1), and nonhydrolyzed pectate was removed almost completely. The NF treatment was carried out at a transmembrane pressure of 0.5 MPa and flow velocity of 0.6 m.s(-1), and large amounts of monogalacturonic acid and sucrose, the contaminants included in the UF permeate were separated. Pectate oligosaccharides obtained by the diafiltration treatment of the NF concentrate were mainly composed of di- to pentasaccharides and exhibited root-growth-promoting activity in lettuce (approximately 1.8-fold) compared with the control. In particular, penta-, tetra-, and disaccharides were found to have strong activity.     

超滤、纳滤技术分离大枣功效成分的研究

以大枣汁为材料,研究不同截留分子量(10000、5000、800、500 u)的超滤和纳滤膜分离大枣中粗多糖、粗低聚糖和单糖糖浆的效果,筛选了不同截留分子量的超滤膜和纳滤膜,并分别优化操作条件,得到适宜的工艺条件。结果表明:选用10000 u超滤膜,大枣汁可溶性固形物含量为3%,操作压力0.12 MPa;选用500 u纳滤膜,可溶性固形物含量为1.0%,操作压力0.54MPa。在此条件下,粗多糖、粗低聚糖和单糖糖浆的得率依次为5.21%、19.24%和58.27%,纯度可达到52.61%、54.78%和84.00%。     

Selective removal of cobalt species using nanofiltration membranes

Selective removal of cobalt species from simulated nuclear liquid waste was investigated with different nanofiltration (NF) membranes at various solution pH levels, initial cobalt concentrations, and background ion concentrations. This study provides insight into the understanding of the relationships between rejections of a target compound (cobalt) and chemical equilibria of various species in the feed solution during NF. Particularly, the ratio of electrostatic rejection to steric rejection for different membranes used was quantitatively evaluated to find outthe relative significance in NF. Substantial cobalt rejection by NF was achieved along with partial separation of monovalent ionic species, although it depended on the level of liquid pH and the presence of background species. Greater cobalt rejection at increased pH was attributed to the precipitation of CoCO3(s) associated with natural carbonates originating from atmospheric CO2 gas rather than that of Co(OH)2(s). A loose NF membrane (e.g., NTR7410) gave as high a rejection as other tighter ones due to the stronger influence of electrostatic rejection, particularly at low pH where no cobalt precipitation was occurring. The decrease of cobalt rejection with the addition of boric acid was found to occur due to the formation of complexes between cobalt and boric acid, which was verified by the analyses of solution turbidity and near-infrared spectroscopy.     

Concentration and purification of galacto‐oligosaccharides using nanofiltration membranes

This study was aimed at using nanofiltration to purify the galactooligosaccharides (GOS) found in a commercial mixture containing lactose, glucose and galactose, whose compositions were similar to that obtained through transgalactosylation reactions catalysed by β‐galactosidase from Kluyveromyces marxianus CCT 7082. NP030 polyethersulphone membrane was selected for the purification processes, once it differed statistically from other membranes due to the higher purification factor and permeate flux under the optimised temperature and pressure conditions of 35 °C and 3 MPa, respectively. Results indicate that NP030 membrane can be employed as a preliminary technique for the GOS purification with approximately 61% (w/w) of recovery.     

Selecting ultrafiltration and nanofiltration membranes to concentrate anthocyanins from roselle extract (Hibiscus sabdariffa L.)

Ten nanofiltration flat-sheet membranes and eight tight ultrafiltration membranes with nominal MWCOs ranging from 0.2 to 150 kDa were tested to concentrate anthocyanin extract from roselle. A pilot system was used, which featured a membrane cell with an effective area of 0.0155 m². Permeate fluxes were recorded for transmembrane pressures between 0.5 and 3.0 MPa, while keeping all other operating conditions constant (volumetric reduction ratio 1, 35 °C). Retention values of total soluble solids, acidity and anthocyanins increased with transmembrane pressure. With similar permeate fluxes at average transmembrane pressure, retention of anthocyanins is significantly higher for nanofiltration membranes than for ultrafiltration membranes. A membrane was then selected for an industrial trial on the basis of its flux, retention of compounds of interest and energy consumption per liter of permeate. The trial using a 2.5-m² filtration surface, could concentrate roselle extract from 4 to 25 g total soluble solids per 100 g, with 100% retention of anthocyanins. No significant damages were observed when comparing concentrate quality with the initial roselle extract.     

Fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes by protein mixtures: the role of inter-foulant-species interaction

Protein fouling of nanofiltration (NF), reverse osmosis (RO), and ultrafiltration (UF) membranes by bovine serum albumin (BSA), lysozyme (LYS), and their mixture was investigated under cross-flow conditions. The effect of solution chemistry, membrane properties, and permeate flux level was systematically studied. When the solution pH was within the isoelectric points (IEPs) of the two proteins (i.e., pH 4.7-10.4), the mixed protein system experienced more severe flux decline compared to the respective single protein systems, which may be attributed to the electrostatic attraction between the negatively charged BSA and positively charged LYS molecules. Unlike a typical single protein system, membrane fouling by BSA-LYS mixture was only weakly dependent on solution pH within this pH range, and increased ionic strength was found to enhance the membrane flux as a result of the suppressed BSA-LYS electrostatic attraction. Membrane fouling was likely controlled by foulant-fouled-membrane interaction under severe fouling conditions (elevated flux level and unfavorable solution chemistry that promotes fouling), whereas it was likely dominated by foulant-clean-membrane interaction under mild fouling conditions. Compared to nonporous NF and RO membranes, the porous UF membrane was more susceptible to dramatic flux decline due to the increased risk of membrane pore plugging. This study reveals that membrane fouling by mixed macromolecules may behave very differently from that by typical single foulant system, especially when the inter-foulant-species interaction dominates over the intra-species interaction in the mixed foulant system.     

Efficient degumming of crude canola oil using ultrafiltration membranes and bio-derived solvents

Vegetable oils derived from rapeseed and its genetic variant canola, are conventionally extracted from oilseeds by means of an organic solvent, typically hexane. Concerns regarding the toxicity of hexane have meant safer and more environmentally friendly solvents such as terpenes are becoming attractive. In this research, the degumming of canola oil/terpene mixtures using ultrafiltration is considered as a critical step in such an extraction process. Polysulfone (PSF) and polyethersulfone (PES) membranes were found to be ineffective in this application, as the oil appeared to cause swelling of the membrane structure. This meant that the original flux could not be restored after cleaning. Conversely, a ceramic membrane (MWCO 5 kDa) provided stable behaviour over several cycles of operation when cleaned with pure solvent at high cross-flow velocity at 40 °C. This membrane showed high phospholipid retention (95 ± 2%), although some oil was also retained (16 ± 3%). Cymene emerged as the most attractive of the three terpenes tested, with higher permeate flux and phospholipid rejection than limonene or pinene.Industrial relevanceWhile hexane has been traditionally used for oilseed extraction, toxicity concerns are likely to restrict its industrial use in the future. This article provides information to engineers and food scientists on the use of terpenes as an alternative solvent. In particular, the potential for ultrafiltration to be used in degumming of canola oil/terpene mixture is assessed. Our research shows that polymeric membranes are unlikely to be useful at scale in this application, as they are not readily cleaned for reuse. Conversely, a ceramic membrane of 5 kDa pore size provides the necessary rejection of phospholipids. There is some oil retention, that might require a downstream recovery step. The best results were obtained with cymene, suggesting this is a good target for industrial use.     

Preparation and antioxidative activity of hoki frame protein hydrolysate using ultrafiltration membranes

Hoki frame protein, which is normally discarded as an industrial by-product in fish plants, was hydrolyzed with various enzymes. The antioxidative activity of the hydrolysates was investigated, and the results showed that pepsin hydrolysate has the highest activity. Hoki frame protein hydrolysates (HPH) prepared by pepsin were fractionated according to the molecular mass into four major types, HPH I (5–10 kDa), HPH II (3–5 kDa), HPH III (1–3 kDa), and HPH IV (below 1 kDa), using an ultrafiltration membrane. HPH III showed a higher antioxidative activity than the other hydrolysates in a linoleic acid emulsion system. In addition, the free-radical scavenging activities of the fractionated hydroysates were evaluated using electron spin resonance spectroscopy. The results showed that HPH III has the highest scavenging effects for 1,1-diphenyl-2-picrylhydrazyl, hydroxyl, alkyl and superoxide anion radicals, and the inhibition pattern was dose-dependent.     

Influence of flocculation and adsorption as pretreatment on the fouling of ultrafiltration and nanofiltration membranes: application with biologically treated sewage effluent

Membrane fouling is a critical limitation on the application of membranes to wastewater reuse. This work aims to understand the fouling phenomenon which occurs in ultrafiltration (UF; 17500 molecular weight cutoff (MWCO)) and nanofiltration (NF; 250 MWCO) membranes, with and without pretreatment. For this purpose, the molecular weight (MW) distribution of the organics has been used as a parameter to characterize the influent, the permeate, and the foulant on the membrane surface. The variation of foulant concentration on the membrane due to pretreatment of the influent by flocculation and/or adsorption was investigated in detail. With the UF membrane, the peak of the MW distribution of organics in the permeate depended on the pretreatment; for example, the weight-averaged MW (Mw) of 675 without pretreatment shifted down to 314 with pretreatment. In the case of the NF membrane, the Mw of organics in the permeate was 478 (without pretreatment) and 310 (with flocculation followed by adsorption). The Mw of the organics in the foulant on the membrane surface was 513 (UF) and 192 (NF) without pretreatment and 351 (UF) and 183 (NF) after pretreatment with flocculation followed by adsorption, respectively. Without the pretreatment, the foulant concentration was higher on both membranes. The difference was more significant on the UF membrane than on the NF membrane. For both membranes, the flocculation-and-then-adsorption pretreatment proved very effective.     

Power generation using different cation, anion, and ultrafiltration membranes in microbial fuel cells

Proton exchange membranes (PEMs) are often used in microbial fuel cells (MFCs) to separate the liquid in the anode and cathode chambers while allowing protons to pass between the chambers. However, negatively or positively charged species present at high concentrations in the medium can also be used to maintain charge balance during power generation. An anion exchange membrane (AEM) produced the largest power density (up to 610 mW/m2) and Coulombic efficiency (72%) in MFCs relative to values achieved with a commonly used PEM (Nafion), a cation exchange membrane (CEM), or three different ultrafiltration (UF) membranes with molecular weight cut offs of 0.5K, 1K, and 3K Daltons in different types of MFCs. The increased performance of the AEM was due to proton charge-transfer facilitated by phosphate anions and low internal resistance. The type of membrane affected maximum power densities in two-chamber, air-cathode cube MFCs (C-MFCs) with low internal resistance (84-91 omega for all membranes except UF-0.5K) but not in two-chamber aqueous-cathode bottle MFCs (B-MFCs) due to their higher internal resistances (1230-1272 omega except UF-0.5K). The UF-0.5K membrane produced very high internal resistances (6009 omega, B-MFC; 1814omega, C-MFC) and was the least permeable to both oxygen (mass transfer coefficient of k(O) = 0.19 x 10(-4) cm/s) and acetate (k(A) = 0.89 x 10(-8) cm/s). Nafion was the most permeable membrane to oxygen (k(O) = 1.3 x 10(-4) cm/s), and the UF-3K membrane was the most permeable to acetate (k(A) = 7.2 x 10(-8) cm/s). Only a small percent of substrate was unaccounted for based on measured Coulombic efficiencies and estimates of biomass production and substrate losses using Nafion, CEM, and AEM membranes (4-8%), while a substantial portion of substrate was lost to unidentified processes for the UF membranes (40-89%). These results show that many types of membranes can be used in two-chambered MFCs, even membranes that transfer negatively charged species.