EFFECTS OF PECTINASE IMMOBILIZATION DURING HOLLOW FIBER ULTRAFILTRATION OF APPLE JUICE

The immobilization of commercial pectinases by physical adsorption on hollow fiber ultrafiltration (HFUF) membranes was studied in view of its possible application in fruit juice clarification. The optimal pH during immobilization and washing was investigated, as well as the effects of enzyme and pectin concentrations and retentate flow on the operation. Results indicated that permeate flux was not initially increased when pectin solution or apple juice was ultrafiltred through pectinase immobilized on HFUF membranes. However, enzyme immobilization greatly extended the membrane operation, by keeping permeate flux constant during prolonged periods at a reasonable yield.     

Removal of natural hormones by nanofiltration membranes: measurement, modeling, and mechanisms

The removal mechanisms of four natural steroid hormones-estradiol, estrone, testosterone, and progesterone-by nanofiltration (NF) membranes were investigated. Two nanofiltration membranes with quite different permeabilities and salt retention characteristics were utilized. To better understand hormone removal mechanisms, the membrane average pore size was determined from retention data of inert organic solutes of various molecular weights and a pore transport model that incorporates steric (size) exclusion and hindered convection and diffusion. Results indicate that, at the early stages of filtration, adsorption (or partitioning) of hormones to the membrane polymer is the dominant removal mechanism. Because the adsorptive capacity of the membrane is limited, the final retention stabilizes when the adsorption of hormones into the membrane polymer has reached equilibrium. At this later filtration stage, the overall hormone retention is lower than that expected based solely on the size exclusion mechanism. This behavior is attributed to partitioning and subsequent diffusion of hormone molecules in the membrane polymeric phase, which ultimately results in a lower retention. Hormone diffusion in the membrane polymeric matrix most likely depends on the size of the hormone molecule, hydrogen bonding of hormones to membrane functional groups, and hydrophobic interactions of the hormone with the membrane polymeric matrix.     

Novel method for treatment of hollow fiber membranes using hypochlorite

A novel hypochlorite treatment method that enhances hydraulic permeability of hollow fiber membranes used in ultra-filtration was successfully devised and tested. Dope containing polysulfone/poly vinyl pyrrolidon (PVP-K90)/N-methyl-2-pyrrolidone (NMP) in mass ratio of 15:5:80, respectively, were used to produce hollow fibers via dry-jet wet spinning process. NMP in 1:1 ratio and distilled water were used as bore fluid. Hollow fiber membrane samples were post-treated using the novel, 95°C water and traditional hypochlorite treatments. State of membranes before and after post-treatment were morphologically compared using SEM microphotographs of fiber cross-section in conjuncton with image proceesing techniques. It was observed that in general both the novel and the traditional methods results in elimination of PVP swelling alone with alteration of pore size and pore distribution. This was confirmed by an increase in water flux of the hollow fibers that were subjected to these two post-treatment methods. Atomic force microscopy analysis vividly pointed to an intense increase in the roughness of the inner and outer surfaces of the membranes. This was attributed to the effect of post-treatment methods. It was found that in general post-treatments involving hypochlorite, increases the surface roughness of the membranes. However, increase in rate of the roughness of inner surface of traditionally hypochlorite treated hollow fiber membrane was found to be much higher than those subjected to the novel treatment method. It was established that the developed novel hypochlorite treatment method can be successfully used for production of high permeable hollow fiber membranes which have vast potential in therapeutic applications.     

聚丙烯腈基中空碳纤维膜制备及结构研究

研究了在不同工艺条件下制备的聚丙烯腈(PAN)基中空碳纤维膜和预氧化膜及其结构特征。通过实验得出,基膜的拉伸使预氧化膜和碳化膜致密化,在制备PAN基膜时加入聚甲基丙烯酸甲酯(PMMA)和聚酰亚胺YJ-16添加剂,有助于保持中空纤维膜的指状孔结构,得到孔结构较好的预氧化中空纤维膜和中空碳纤维膜。     

Interface treatment and performance study on fiber tube reinforced polyvinylidene fluoride hollow fiber membranes

Abstract

The fiber tube reinforced hollow fiber membranes are widely used in membrane bioreactor (MBR) due to their excellent mechanical and filtered properties. However, the poor adhesive power between fiber tubes and membranes restricted their service life in practice applications. Herein, we supply a facile and feasible surface coating modification methods for optimizing the interfacial bonding ability. The outer surfaces of the braided and knitted tubes were modified with silane coupling agent KH570 and acrylate adhesive before the fiber tube reinforced hollow fiber membranes were fabricated. The effects of different modifiers dosages on the morphology, tensile strength, bursting strength, pure water flux, porosity and mean pore size of the braided and knitted tubes reinforced hollow fiber membranes were evaluated respectively. Moreover, the effects of different modifiers on the fabric tubes with different structure were analysed. The results showed that the optimum dosage of the two modifiers was 3?g/5m. It is revealed that the minute quantities of modifiers applied to the tubes could improve not only the interfacial combination of the reinforced membrane, but also their strength and penetration performance.     

编织管增强PVDF中空纤维膜界面处理及性能研究

为解决污水处理过程中PVDF中空纤维膜易剥离和分层问题,以两种涤纶编织管作为中空纤维膜的增强体,分别使用硅烷偶联剂KH570和丙烯酸酯黏合剂对编织管外表面进行预处理,以增强编织管与PVDF铸膜液的结合性能。通过测试编织管增强PVDF复合膜的水通量、孔隙率及爆破强度,分析复合膜表面及截面微观形貌,对比两种改性剂用量对两种编织管增强复合膜性能的影响。结果表明:随着改性剂用量增加,经硅烷偶联剂KH570及丙烯酸酯粘合剂处理后的复合膜与未处理的复合膜相比较,水通量略有下降;孔隙率呈逐渐减小的趋势;拉伸强度及爆破强度均有较大幅度的提高;综合比较,两种整理剂用量达到3 g/5 m时,增强复合膜各项性能最优,其中线密度为42.79 tex的2#编织管增强复合膜性能好于线密度为27.78 tex的1#编织管增强复合膜。     

增强型中空纤维多孔膜研究进展

介绍了提高中空纤维膜力学性能的方法,即通过增强体增强法制备兼具增强体力学性能优异和分离层分离精度高特点于一体的增强型中空纤维膜,解决传统单质中空纤维力学性能与分离性能 不能兼顾的矛盾。分析了增强型中空纤维膜的及其制备方法,包括连续纤维增强型中空纤维膜、编织管增强型中空纤维膜和多孔基膜增强型中空纤维膜,阐述了3种增强型中空纤维膜的制备技术路线和致孔机制,回顾了其研究进展,并展望了增强型中空纤维膜的发展及应用前景。     

膜分离和聚酰胺吸附对金花茶多酚的纯化

结合中空纤维膜分离与聚酰胺吸附对金花茶中的茶多酚进行纯化研究,考察金花茶提取液分别经过分子量为300,100,10,3 k的中空纤维膜分离后,各透过液和截流液中茶多酚的含量情况.当提取液透过分子量为10 k的中空纤维膜时,茶多酚含量提高到39.36%;透过液再经聚酰胺吸附纯化,茶多酚的纯度可提高到79.42%.     

高强度聚氯乙烯中空纤维膜的制备及其性能

针对溶液相转化法制备的聚氯乙烯(PVC)膜存在强度及通透性能难以同步提高的问题,以MT-I型复合粉为成孔剂,邻苯二甲酸二辛酯为稀释剂,采用螺杆挤出法制备了PVC中空纤维膜,研究了拉伸和萃取过程对纤维膜形貌及结构的影响,并通过水通量、碳素墨水截留率及拉伸强力测试分析了纤维膜的分离性能和力学性能。结果表明:随着拉伸倍数的增加,PVC中空纤维膜的断裂强度增大,断裂伸长率减小;经乙醇萃取后纤维膜表面出现了更多微孔,纤维膜的通透性能提高;当拉伸倍数为3时,纤维膜具有较高通透性和较好的力学性能,水通量为798 L/(m²·h),拉伸断裂强度为17.7 MPa,断裂伸长率为70.67%。     

EFFECTS OF CO-IMMOBILIZATION OF PECTINASE AND AMYLASE ON ULTRAFILTRATION OF APPLE JUICE SIMULATE

In view of its possible application in apple juice clarification, the potential of co‐immobilized pectinase/amylase by physical adsorption on a polysulfone ultrafiltration hollow fiber was examined. Solutions containing different concentrations of pectin and starch were used. The effect of various operational parameters on the production of reducing compounds, mainly galacturonic acid and maltose, was investigated. Results indicated that relative permeate flux, during ultrafiltration of starch‐pectin solutions, was up to 35% higher when commercial pectinase and amylase were co‐immobilized on a hollow fiber membrane. Although the concentration of reaction products increased up to 50% with the pectin concentration, the same was not verified when the starch content changed from 3.85 to 5.00 mg/mL. However, the reference permeate flux was improved when starch was added to substrate, independently of its concentration. Considering the size of an average starch granule, this increase in permeate flux was attributed to the removal of pectin gel by dragging. Permeate fluxes were comparable for both batch and permeate recycling operations.     

Removal of the natural hormone estrone from aqueous solutions using nanofiltration and reverse osmosis

The ability of a variety of nanofiltration and reverse osmosis membranes to retain the natural hormone estrone are examined here as a function of solution conditions. While size exclusion dominates retention with the tighter membranes, both size exclusion and adsorptive effects appear to be instrumental in maintaining high retention on nanofiltration membranes that otherwise exhibit relatively low ion retentions. These adsorptive effects may be driven by hydrogen bonding between estrone and the membrane. Electrostatic attraction appears to aid retention with an apparent slight decrease in retention at high NaCl concentrations. Deprotonation of estrone leads to a significant decrease in retention, most likely as a result of the effect of strong electrostatic repulsive forces decreasing the proximity of the negatively charged estrone to the negatively charged membrane surface and thus lowering the potential for adsorptive retention. This deprotonation effect is absent for tight RO membranes. The results reported here indicate that while open nanofiltration membranes may be effective in retaining estrone under some conditions, the extent of retention may be very susceptible to maintenance of adsorptive capacity at the membrane surface and depend on solution chemistry.     

聚醚砜中空纤维膜的制备及其性能

聚醚砜（PES）中空纤维膜已被广泛使用在许多领域,如超滤,微滤,反渗透,液体/液体或液体/固体分离,气体分离,血液透析等。本文制备了聚醚砜中空纤维膜,并研究了膜的结构和性能。通过研究的成分和工艺条件对聚醚砜中空纤维膜的形态和性能的影响,从而掌握膜的结构和性能的关系。采用了浸入沉淀相转化法,通过改变聚合物溶液浓度,空气浴时间,凝固浴组成等参数来调节膜的性能。运用孔隙率、纯水通量和扫描电子显微镜（SEM）对膜的形态和性能进行表征。研究表明,膜的形态受到聚合物溶液浓度、凝固浴组成等工艺参数的较大影响,通过工艺条件的组合,制得具有良好的性能和理想结构的中空纤维膜。     

组合式中空纤维膜澄清杨梅果酒的研究

杨梅果酒是不稳定性胶体溶液,为提高其澄清度和稳定性,采用超滤膜过滤的方法,进行了单一中空纤维膜工艺和组合式中空纤维膜工艺澄清杨梅果酒的研究。以超滤压力、时间、温度和料液流速为影响因素,探讨超滤工艺条件及膜处理方式对杨梅果酒的澄清效果和品质的影响。结果表明:在温度为28℃,压力为0.08MPa,料液流速为6L/h下,用分子截留量为80000u与50000u的组合式中空纤维膜处理后得到的杨梅果酒色度值A520为0.301,澄清度T680为96%,膜通量为25L/(m2.h),蛋白质与单宁含量明显减少,且总酸、总糖、酒精度等含量几乎无变化。     

冷却温度对聚偏氟乙烯/超高分子量聚乙烯共混中空纤维膜结构与性能的影响

针对聚偏氟乙烯(PVDF)膜强度与渗透性能难以同步提高的问题,以矿物油和邻苯二甲酸二丁酯为复合稀释剂,通过热致相分离法制备了PVDF/超高分子量聚乙烯(UHMWPE)共混中空纤维膜,探究不同冷却温度对膜形貌及孔结构的影响,并通过气通量、水通量及拉伸强力测试表征了中空纤维膜的渗透性能与力学性能。结果表明:原纤状UHMWPE增加了PVDF球晶聚集体的连接性;冷却温度对共混中空纤维膜的结构与性能影响显著;随着冷却温度的升高,PVDF/邻苯二甲酸二丁酯和UHMWPE/矿物油的相分离与结晶时间均延长,纤维膜的平均孔径和孔隙率增加,渗透性能改善,但大孔的出现和UHMWPE原纤数量的减少使纤维膜的力学性能下降。     

中空纤维超滤膜在水处理中的应用

为了测试不同的中空纤维超滤膜在污水处理方面的性能,本文采用三种不同材料的中空纤维超滤膜：聚醚砜、聚丙烯和聚丙烯腈超滤膜,分别过滤了自来水和污水。讨论了过滤前后,水的色度、浊度、PH值、电导率、氨氮含量、化学需氧量和水流量的变化,并通过扫描电镜观察过滤前后三种超滤膜的表面和横截面微观形态的变化。试验结果表明：在三种超滤膜中,聚醚砜超滤膜在污水处理中表现出了最好的综合应用性能。三种超滤膜对污水中的氨氮和化学需氧量的去除率有限,采用二级或三级过滤可以提高过滤效果。电镜实验还说明,指状结构比孔状结构的防污性能好。     

Hyperbranched polyethyleneimine induced cross-linking of polyamide-imide nanofiltration hollow fiber membranes for effective removal of ciprofloxacin

This study aims to develop a positively charged nanofiltration (NF) hollow fiber membrane for effective removal of ciprofloxacin from water. A novel NF membrane was fabricated by hyperbranched polyethyleneimine (PEI) induced cross-linking on a polyamide-imide hollow fiber support. The spongy-like, fully porous membrane support provides minimal transport resistance and sufficient mechanical strengths for water permeation under high pressures. It is found that the PEI modification significantly influences NF performance through the mechanisms of size exclusion, charge repulsion, and solute-membrane affinity. Specifically, after PEI induced cross-linking, the membrane pore size is significantly reduced. The membrane surface becomes more hydrophilic and positively charged. As a result of these synergic effects, the rejection of ciprofloxacin is substantially enhanced. Furthermore, experimental results show that the molecular weight of PEI has tremendous effect on NF performance of the as-modified membrane. The NF membrane modified by a high molecular weight PEI_60K exhibits the highest rejection, the lowest fouling tendency, and keeps a constant flux over the whole pH range. This study may have great potential for developing high-performance antifouling NF hollow fiber membranes for various industrial applications.     

凝固条件对PVDF/PVA共混中空纤维膜结构及性能的影响

采用干湿法纺丝工艺制备聚偏氟乙烯(PVDF)/聚乙烯醇(PVA)共混中空纤维膜,讨论凝固条件对膜结构及性能的影响,旨在选择适当的凝固条件,制备性能较优的PVDF/PVA共混中空纤维膜。结果表明,凝固浴为液氮时,孔结构非常致密;凝固浴为水时,随凝固浴温度升高,外皮层界面孔数量较少但尺寸增大,且由裂缝状转变为圆孔状,靠近外层的指状孔延长,孔结构变疏松;凝固浴温度升高,水通量增大,卵清蛋白截留率降低;较高的凝固浴温度有利于PVDF结晶和拉伸强度的提高。     

熔纺PU/PVDF共混中空纤维膜研究

以聚氨酯(PU)与聚偏氟乙烯(PVDF)共混,经熔体纺丝及后拉伸得到具有聚合物界面微孔的中空纤维膜。分析PU/PVDF的混溶性,讨论膜孔结构的形成,并对其形貌进行观察。结果表明,随PU/PVDF混溶性的改善,共混物可纺性提高,成孔性则有所下降;拉伸使膜界面微孔张开,随拉伸倍数的增加膜通量先增加再略有下降后迅速增加,共混物晶区的规整性也有所提高;所得膜为对称结构,且高倍拉伸后膜表面形成大量界面微孔。     

高中空生物质活性碳纤维制备及其对亚甲基蓝的吸附性能

为提高活性碳纤维对有色废水的吸附效率,以牛角瓜纤维为前驱体,采用磷酸活化、高温炭化工艺制备了具有高中空结构的活性碳纤维.采用扫描电镜/能谱仪、红外光谱仪等表征其微观形貌及化学结构,分析了所制备活性碳纤维对水溶液中亚甲基蓝的吸附性能与吸附机制.结果表明:牛角瓜活性碳纤维的平均中空度大于92％,具有粗糙表面和发达介孔结构,...     

几种澄清方法对梨汁理化和感官等指标的影响

本文研究了无机陶瓷微滤膜微滤、中空纤维超滤以及果胶酶对梨汁的澄清效果、理化及感官指标的影响。采用三种孔径的氧化铝膜和自制的加压微滤装置、外购中空纤维超滤装置以及果胶酶进行澄清实验。实验结果表明:(1)0.2μm孔径无机陶瓷膜微滤对梨汁的可溶性固形物含量、VC含量和还原糖含量影响不大,澄清梨汁得率较高,并且基本保持了梨汁的原有风味,适合梨汁澄清生产。(2)50nm无机陶瓷膜微滤和中空纤维超滤因孔径太小,不适合梨汁澄清生产。(3)0.8μm孔径无机陶瓷膜微滤和果胶酶澄清处理梨汁的浊度太大,短时间出现分层或沉淀,不适合梨汁澄清生产。