减压膜蒸馏法稀碱液浓缩过程研究

以聚偏氟乙烯疏水膜为材料,采用减压膜蒸馏技术在较高真空度下浓缩硫化钠溶液,研究了各种条件对膜通量的影响.结果表明,当进料温度80℃、真空度为80kPa、流速为0.99m·s~(-1)时,质量分数4.6%的硫化钠溶液VMD膜通量为23.7 kg·m~(-2)·h~(-1);连续运行时,将稀碱液浓缩5倍后,膜通量仍维持在10.6kg·m~2·h~(-1),用稀盐酸清洗后膜通量恢复到初始值的95.6%;浓缩过程产水电导维持在10μS·cm~(-1)以下,脱盐率大于99.99%.     

Vacuum membrane distillation simulation of desalination using polypropylene hydrophobic microporous membrane

Numerical simulation is an effective method to get the optimal operating parameters in the chemical engineering process. In this work, the transport mechanism of vacuum membrane distillation (VMD) process was simulated and predicted by mathematical model, which was established based on the convective heat transfer coefficient, and 0.5M aqueous NaCl solution was concentrated with isotactic polypropylene (iPP) hydrophobic microporous membrane prepared via thermally induced phase separation (TIPS) in the VMD process. The as‐presented mathematical model simulated the effects of different operating parameters on the VMD performances for aqueous NaCl solution, such as feed temperature, feed flow rate, absolute pressure of membrane permeate side, temperature coefficient, membrane thickness, and porosity. A comparison between experimental data and simulated data was also considered to verify the proposed mathematical model. Additionally, the salt rejection of aqueous NaCl solution production water in VMD was higher than 99.9%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41632.     

Evaluation of membrane fouling and flux decline related with mass transport in nanofiltration of tartrazine solution

BACKGROUND: This work was carried out to investigate and analyze the interrelated dynamics of mass transport, membrane fouling and flux decline during nanofiltration of tartrazine. A combined application including pore diffusion transport model and a material balance approach was used to model an experimental flux data obtained from different values of pH (3, 5, 7 and 10), feed‐dye concentration (25, 100 and 400 mg L^?1), and transmembrane pressure (1200, 1800 and 2400 kPa). RESULTS: Almost 100% dye solution removal and a permeate flux of 135 L m^?2 h^?1 were obtained for 25 mg L^?1 and 1200 kPa at pH 10. At pH 10, lower membrane fouling was obtained due to the increase of electrostatic repulsion between anionic dye molecules and the more negatively charged membrane surface. Flux decline and membrane fouling increased together with transmembrane pressure and dye concentration. Fouling was found to be directly related to proportional‐permeation coefficient (k_O′) of dye which was identified as the solute passing into the permeate with respect to the amount transported into the membrane from the feed. CONCLUSIONS: For a decrease of pH (10 to 3) and transmembrane pressure (2400 to 1200 kPa) or an increase of feed‐dye concentration (25 to 400 mg L^?1), fewer dye molecules passed into the permeate with respect to the amount transported into the membrane from the feed. This situation depended mainly on the combined influences of the gel layer and fouling in the membrane. Copyright © 2010 Society of Chemical Industry     

Application of Membrane Deliquoring Technology in Ginkgo Biloba Extract Production

To displace the original vacuum hypothermia triple effect evaporation technology, save energy, and enhance product activity, nanofiltration technology is applied in getting rid of most solvent of macro porous resin eluent, which is generated in producing Gingko biloba extract. Membrane K and membrane L are studied systematically in this experiment. The results indicate that permeate flux increases with the accretion of operating pressure, operating temperature, and recycle flux, and decreases with the increase of feed concentration. An increased operating pressure and recycle flux resulted in a decreased permeate concentration, and increased operating temperature and feed concentration lead to an increased permeate concentration. Active components content in permeate almost does not change with operating condition. However, the cutoff ratio is about 99%, which can meet the need of production. Optimized operating condition was assured and small field experiment was done. It was shown that nanofiltration membrane technology could effectively eliminate solvent of macro porous resin eluent. Elementary estimation indicates that nanofiltration membrane technology can reduce 90% energy and 70% cost over the original technology.     

Treatment of Liming Effluent from Tannery using Membrane Separation Processes

Abstract

A treatment method of liming effluent of a tannery is tested using hybrid membrane separation processes. The effluent after gravity settling and alum coagulation is subjected to ultrafiltration followed by nanofiltration. The optimum alum dose is obtained by analyzing the effluent using various concentrations of alum. The membrane separation processes are conducted in a continuous cross flow mode. The effects of operating conditions e.g., transmembrane pressure difference, and cross flow velocity (Reynolds number) on the permeate flux are analyzed. Effects of change in hydrodynamic conditions in various flow regimes, e.g., laminar, laminar with turbulent promoter, and turbulent flow on flux improvement have been studied. A resistance‐in‐series model for flux decline during the filtration process is proposed. COD, BOD, TDS, TS, pH, Ca²⁺ concentration, Cl^? concentration and conductivity are measured before and after each operation. The potential of the dried sludge as organic fertilizer is also explored.     

Nanofiltration Membrane Process for the Removal of Arsenic from Drinking Water

The removal of arsenic from drinking water by nanofiltration membranes was investigated. Experiments were conducted with tap water to which arsenate and arsenite were added. Two types of nanofiltration membranes, i.e., NF‐90 and NF‐200, have been tested. The effect of various operating conditions, e.g., applied pressure, feed concentration, pH and temperature, were also investigated. The pH and arsenic concentration in the feed and the operating temperature are found to be decisive factors in determining the arsenic concentration remaining in the permeate. The level of removal of As(V) was higher than 98 % for both membranes, but that of As(III) was much lower. It can be concluded that by controlling the operating parameters, source water containing As(V) may be recovered as drinking water to EPA maximum contaminant level quality standards, but that water containing As(III) must undergo a pre‐oxidation treatment before passing through the nanofiltration membrane in order to maintain drinking water quality.     

气液两相流强化卷式纳滤膜分离硫酸镁水溶液

气液两相流强化卷式纳滤膜分离实验是针对DK2540卷式纳滤膜,采用气液两相流强化分离技术,对硫酸镁溶液进行研究,较系统地研究了温度、料液浓度、过膜压力、料液流速、气体流速等因素在分离硫酸镁溶液时,对膜通量、截留率和膜通量增加率的影响,并总结了气液两相流强化效果。结果表明,气液两相流强化卷式纳滤膜分离有明显的效果。温度宜在30~40℃。料液浓度越大、过膜压力越小、气液比越大,气液两相流强化效果越明显。     

有机废水中盐含量对膜蒸馏处理性能的影响

采用真空膜蒸馏技术对高盐有机废水进行浓缩回收。考察了废水进料温度、真空度、进料流速、废水盐度、废水的进料方式等因素对膜通量和截留率的影响。结果表明,在常压循环方式进料,透过侧真空度0.04～0.095 MPa,进料温度为30～80℃,进料流量为40～160 L/h的条件下,通过实验设计的膜蒸馏过程,可以将质量分数为10%盐度的有机废水,COD〉7 500×10^-6,浓缩至质量分数为30%盐度的有机废水,透过水的盐度〈0.01%,COD〈20×10^-6,通过盐结晶方法去除相应有机物后,可获得纯度较高的工业盐。     

Application of Membrane Deliquoring Technology in Ginkgo Biloba Extract Production

To displace the original vacuum hypothermia triple effect evaporation technology, save energy, and enhance product activity, nanofiltration technology is applied in getting rid of most solvent of macro porous resin eluent, which is generated in producing Gingko biloba extract. Membrane K and membrane L are studied systematically in this experiment. The results indicate that permeate flux increases with the accretion of operating pressure, operating temperature, and recycle flux, and decreases with the increase of feed concentration. An increased operating pressure and recycle flux resulted in a decreased permeate concentration, and increased operating temperature and feed concentration lead to an increased permeate concentration. Active components content in permeate almost does not change with operating condition. However, the cutoff ratio is about 99%, which can meet the need of production. Optimized operating condition was assured and small field experiment was done. It was shown that nanofiltration membrane technology could effectively eliminate solvent of macro porous resin eluent. Elementary estimation indicates that nanofiltration membrane technology can reduce 90% energy and 70% cost over the original technology.     

Separation of Diacteone Alcohol‐Water Mixtures by Membrane Pervaporation

Abstract

A study was conducted to evaluate membrane pervaporation for the separation of diacetone alcohol‐water mixtures using commercially available membranes for organic enrichment and dehydration. Empirical correlations for the effect of the process parameters of feed concentration, feed temperature, permeate‐side pressure, and scale‐up were developed. The solvent‐water mixture was successfully separated with a poly(vinyl alcohol) based Sulzer PERVAP 2210 dehydration membrane. Various dehydration membranes were evaluated and a comparison of the flux and separation factor was made. The membrane performance in separating acetone‐water mixtures was also studied. An overall model to predict the membrane area needed for a scale‐up was developed based on the results.     

An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part II: Experiments on the ultrafiltration unit and combined operation

A batch-recirculated photoreactor was combined with a hollow-fibre membrane ultrafiltration (UF) unit for heterogeneous photocatalysis applications. This paper focuses on the operation and modelling of the UF process component and on the performance of the integrated photoreactor–UF process assembly. Methylene blue and titanium dioxide (Degussa P-25) were used as the test pollutant and photocatalyst, respectively. The influence of cross-flow velocity, transmembrane pressure, and TiO₂ dose on the permeate flux through the hollow fibre membrane is described. These data are modelled on the basis of concentration polarization and gel layer formation at the membrane surface/feed slurry boundary. The operation of the integrated photoreactor–UF assembly over ten repeat cycles is described. Photocatalyst separation was complete as gauged by nephelometric turbidity measurements. However, a systematic degradation in the photocatalyst performance was noted with each repeat cycle. Dynamic laser light scattering data are consistent with agglomeration of the TiO₂ particles as a result of the UF process, and suggest a possible factor in the degraded photocatalytic activity. Possible solutions to this problem are finally presented.     

减压膜蒸馏传热传质过程

对减压膜蒸馏传热传质机理进行了研究,在已有理论模型的基础上,考虑温度极化和浓差极化的影响,引入减压膜蒸馏传热传质理论模型,并对模型进行了计算,结果表明:随温度的升高,传质系数Km升高,温度极化系数TPC减小,浓差极化系数CPC增大,通量呈近指数倍增加;随流速的增加.TPC增大,膜表面传热系数hf增大,CPC略有降低,K...     

运行条件对N-乙酰化壳聚糖超滤膜污染的影响

考察了N-乙酰化壳聚糖超滤膜运行过程中分离介质浓度、pH值、膜面流速、操作压力和操作时间对膜污染的影响。实验结果表明:分离介质浓度越高、pH值越低、膜面流速越小、操作压力越高和操作时间越长,膜受到的污染越严重;当印染废水色度120ppm以下,pH值6.5左右、膜面流速0.8m/s左右、操作压力0.6MPa以下,可使膜在五天时间内的污染度降低到20%。     

Influence of Membrane Intrusion on Permeate‐Sided Pressure Drop During High‐Pressure Reverse Osmosis

By replacing thermal concentration processes, high‐pressure reverse osmosis has the potential to contribute to cost and energy savings regarding concepts for industrial water reuse. To provide a better understanding of the spiral‐wound element behavior during high‐pressure operation, this study focusses on the investigation of their performance by scrutinizing the crucial effect of the permeate‐sided pressure drop induced by membrane‐spacer interactions. The experiments show a considerable influence of membrane intrusion on the element performance with a strong dependence on the feed pressure.     

VMD处理反渗透浓水操作参数及水质评价

利用VMD进行了处理反渗透(RO)浓水的试验研究,考察了VMD过程中操作参数对产水量的影响,并利用离子色谱仪与气相色谱-质谱联用仪对RO浓水与VMD产水中所含阳离子与有机物进行了进一步分析.试验结果表明,VMD产水量均随着冷侧真空度、料液线速度以及料液温度的升高而增大,但增长趋势各不相同;VMD除对NH4+截留率相对较低外,对于其它阳离子的截留率均达到99.9％以上;VMD对RO浓水的TOC截留率可达86.4％,其产水中主要含有低分子量有机物.     

Exploring the spinning and operations of multibore hollow fiber membranes for vacuum membrane distillation

Hollow fiber membranes with a multibore configuration have demonstrated their advantages with high mechanical strength, easy module fabrication, and excellent stability for membrane distillation (MD). In this work, the microstructure of multibore fibers was optimized for vacuum MD (VMD). A microstructure consisting of a tight liquid contact surface and a fully porous cross‐section is proposed and fabricated to maximize the wetting resistance and VMD desalination performance. The new membrane exhibited a high VMD flux of 71.8 L m^?2 h^?1 with a 78°C model seawater feed. Investigations were also carried to examine various effects of VMD operational conditions on desalination performance. The 7‐bore membrane showed higher flux and superior thermal efficiency under the VMD configuration than the direct contact MD configuration. Different from the traditional single‐bore hollow fiber, the VMD flux of multibore membrane at the lumen‐side feed configuration was higher than that of the shell‐side feed due to the additional evaporation surface of multibore geometry. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1078–1090, 2014     

Separation of Liquiritin from Glycyrrhizic Acid in Licorice Root Extract by Nanofiltration Membrane

The aim of this work was to study the separation of liquiritin (LQ) from glycyrrhizic acid (GA), in licorice aqueous solutions using nanofiltration (NRT-7450) membrane. The LQ and GA components are the main active ingredients of licorice root extract with various pharmacological effects, The effects of transmembrane pressure, feed temperature, feed pH, and cross-flow velocity on permeate flux and recovery were determined. A lab scale cross-flow set up using flat-sheet configuration membrane was employed for all experiments. SEM micrographs showed the changes in the fouled surface during operating time. The applied transmembrane pressure, feed temperature, feed pH, and cross-flow velocity were varied from 4 to 10 bars, 30 to 40°C, 3 to 9, and 0.8 to 3.1 m s^?1 respectively. The obtained recoveries for GA and LQ varied between 0.65 to 1.86% and 16.89 to 41.65%, respectively. The optimum operating conditions for separation LQ from GA in licorice aqueous solutions using NRT-7450 nanofiltration membrane were 1.8 m s^?1cross-flow velocity, 8 bars transmembrane pressure, 40°C of feed temperature and pH 7.     

PERFORMANCE CHARACTERISTICS OF A CERAMIC MEMBRANE SYSTEM FOR MICROFILTRATION OF CORN STARCH HYDROLYSATE

A ceramic microfiltration membrane was used for the clarification of corn starch hydrolysate, having a dextrose equivalence of 95, to study the effect of process variables (transmembrane pressure, cross-flow velocity, and feed concentration) on permeate flux. Flux increased with increased cross-flow velocity for all transmembrane pressures and feed concentrations up to a volume concentration ratio of 100. Flux became asymptotic at pressures of 200-375kPa, indicating that microfiltration performance was limited by concentration-polarization. The optimum transmembrane pressure was higher at higher cross-flow velocities. A process model based on the resistances-in-series concept adequately described the observed variation of permeate flux with process variables such as transmembrane pressure, cross-flow velocity and feed concentration. Resistance due to concentration polarization decreased linearly with increase in cross-flow velocities for all feed concentrations, while fouling resistance increased linearly with increase in feed concentration.     

Application of ultrafiltration hybrid membrane processes for reuse of secondary effluent

This study evaluates the factors affecting pretreatment conditions for hybrid UF membrane processes for reuse of secondary effluent from the sewage treatment plant. The experimental results obtained from the ultrafiltration (UF) membrane process showed that the particles of the size range between 0.2 and 1.2 μm caused a significant impact on membrane fouling in all cases even with or without the coagulation process. As pretreatment of UF membrane process, the coagulation significantly improved the permeate flux. Optimal flux improvement was seen at an alum dose of 50 mg/L. In addition, it was found that the permeate flux was least declined under the coagulation condition of charge neutralization (pH 5.0). Also, the powdered activated carbon (PAC) adsorption enhanced the permeate flux. Application of the direct filtration as a pretreatment of UF membrane process was also very effective in reducing the UF membrane fouling.     

真空膜蒸馏浓缩反渗透浓盐水的工艺研究

分别采用聚乙烯、聚丙烯微孔膜对反渗透海水淡化浓盐水进行真空膜蒸馏的研究。考察了膜下游真空度、浓盐水温度、浓度、流速对膜通量及截留率的影响。结果表明,真空度增大,膜通量和截留率呈增长趋势。料液温度升高,膜通量增加,截留率呈减少趋势。料液流速增加会使通量增加,截留率呈减少趋势,但影响相对不大。随着料液浓度的增加,膜的通量下降,截留率基本保持不变。本实验条件下最大截留率可达99．99％,表明利用真空膜蒸馏技术可有效实现反渗透海水淡化浓盐水的浓缩。