Pervaporation of esters with hydrophobic membrane

Surface-modified alumina membrane (A1₂O₃) was used for ester flavor recovery by pervaporation. This study focused on the permeation characteristics of ester compounds (ethyl acetate, EA; ethyl propionate, EP; ethyl butyrate, EB) through tube-type hydrophobic membrane. Experiments were performed to evaluate the effects of the feed concentration (0.15-0.60 wt%) and temperature (30-50 ‡C) on separation of EA, EP, and EB from aqueous solutions. It was found that the permeation flux increased with increasing feed ester concentration and operating temperature. The fluxes of EA, EP, and EB at 0.60wt% feed concentration and 40 ‡C were 254, 343, and 377 g/m² hr, which was much higher than those of polymer membranes. It was reported that the permeate flux of EA with PDMS was 1.1-58 g/m²Phr at feed concentration of 90-4,800 ppm and 45 ‡C. The separation factors for the 0.15-0.60 wt% feed solution of EA, EP, and EB at 40 ‡C were in the range of 66.9-78.9, 106.5-97.3, and 120.5-122.8, respectively. Due to the high separation factor, phase separation occurred in permeate stream because the ester concentration in permeate was much above the saturation limit.     

Recovery of ionic liquids from dilute aqueous solutions by electrodialysis

Ionic liquid/s (IL/ILs) are ideal solvents for many separation processes, such as cellulose dissolution, extraction of heavy metal ions and coal liquefaction residues, etc. During the above processes, ILs would inevitably remain in effluents. Due to their high costs and potential detrimental impacts on environment, it is extremely important to recycle ILs from dilute aqueous solutions. Electrodialysis (ED) was used for primary separation and recycling ILs. In order to evaluate the performance of ED process, the effects of initial concentration, applied voltage and initial volume of the dilute solutions on the overall current efficiency (η), recovery ratio (R) and concentration ratio (ω) were investigated. Among these experimental results, the highest recovery ratio could reach 85.2% and the highest overall current efficiency could reach 80.9%. The ED energy consumption is also discussed and the highest specific energy consumption (R_e) could reach about 1350 g/kW h. The effects of IL cation and anion sizes on concentrating process are also evaluated. The experimental results indicate that ED is an effective method to concentrate IL aqueous solutions.     

Gas permeation characteristics of silica/alumina composite membrane prepared by chemical vapor deposition

Amorphous silica membranes were deposited by thermal decomposition of tetraethoxysilane at 600–650 ‡C on a porous α-alumina tube with pore size of 110–180 nm or γ-alumina coated α-alumina tube with pore size of 6–8 nm.The forced cross-flow through the porous wall of the support was very effective in plugging macropores. The membranes formed on γ-alumina coated oc-alumina tube showed H₂ permeances much higher than the SiO₂ membranes formed on the α-alumina tube. This indicated that the γ-alumina film was effective in improving the H₂ permeance and H₂/N₂ selectivity. The permeation tests with CO₂, N₂, CH₄, C₃H₈ and i-C₄H₁₀ showed that a very small number of mesopores remained unplugged by the CVD. Permeation of hydrogen was explained by activated diffusion, and that of the other gases by Knudsen diffusion through the unplugged pores. Thus, the total permeance was composed of permeances due to the activated and Knudsen diffusion mechanisms. The contribution of Knudsen diffusion pores decreased to 0.02 when the γ-alumina film was modified at 650 ‡C until P_fe=50 Pa.     

用电去离子过程从稀溶液中回收镍离子并制备纯水

利用基于EDI工艺的单个过程实现了低浓度废水中镍的回收并同时制备纯水.研究表明:当原水镍含量为55ppm时,镍去除率可达99.9%以上,淡水产水中镍的浓度低于0.05mg·L-1,其电阻率稳定在2.02～2.59MΩ•cm,浓水中镍浓度则可高达1263mg·L-1.该研究充分证明了EDI可用于回收低浓度含镍废水中的镍离子且同时产生优质纯水,从而可实现如电镀等行业的清洁生产和闭路循环。     

Removal of zinc from dilute aqueous solutions by galvanochemical treatment

The possibility of zinc removal, a common toxic metal, from simulated liquid effluents by the application of a novel treatment method, termed galvanochemical, was investigated. The galvanochemical process is considered as a simple, economic, friendly to the environment, method, which does not create harmful end‐products. Synthetic wastewaters were examined, these contained concentrations of zinc commonly found in real wastewaters from small‐to‐medium size industrial units, such as metal‐plating or metal‐treatment plants. These liquid wastes pose an important environmental problem, due to the content of heavy metals. The optimization of the main operating parameters was the objective of the study. The galvanic pair scrap ratio iron:coke was used for these investigations. It was found that the use of the galvanic pair mixture of 80 g dm^?3 (weight per solution volume ratio), agitated at 160 rpm for 5 h, removed more than 90% of zinc from the initial solution, containing initially 50 mg dm^?3 of zinc. The scanning electron microscopy/energy disperse spectrometry (SEM/EDS) analysis performed on the products showed that zinc was adsorbed onto the coke to a small extent and that the zinc removal was mainly based on the adsorption of zinc onto the surface of active iron oxides formed as a result of galvanochemical reactions. Copyright © 2005 Society of Chemical Industry     

渗透汽化-结晶耦合分离稀溶液中的香兰素

以聚醚嵌段共聚酰胺（PEBA2533）为膜材料,采用干法相转化法制备性能优异的高分子膜,用于渗透汽化-结晶耦合（PVCC）分离系统中回收稀水溶液中的香兰素。采用扫描电子显微镜（SEM）对PEBA2533膜的形貌进行表征。考察原料液浓度、温度对膜渗透汽化性能的影响。结果表明：随着溶液浓度的增加,PEBA2533膜溶胀性能增加,说明PEBA2533能够优先吸附香兰素;随原料液浓度增加,香兰素渗透通量增加,分离因子略微下降;原料液温度增加,香兰素渗透通量和分离因子都增加;并通过Arrhenius方程计算得到香兰素比水对温度更加敏感。PVCC系统中控制一级冷凝器温度为2℃时,一级冷凝器中结晶态香兰素通量为39.52 g·m^-2·h^-1,纯度在99%以上。     

Characteristics of gas permeation using two-layered alumina membrane prepared by anodic oxidation

The microporous alumina membrane with asymmetrical structure, having upper layer with pore diameter of 10 nm under and lower layer with pore diameter of 36 nm, was prepared by anodic oxidation using DC power supply of constant current mode in an aqueous H₂SO₄ solution as a electrolyte. The aluminum plate was pretreated with thermal oxidation, chemical polishing and electrochemical polishing before anodic oxidation. The membranes were prepared by controlling the current density such as a very low current density for upper layer and a high current density for lower layer of membrane. By controlling the cumulative charge density, the thickness of upper layer of membranes was about 6 Μm and the total thickness of membranes was about 80–90 Μm. We found from gas permeation experiments with the membranes prepared by above method that the mechanism of gas permeation of the all membranes prepared under each condition complied with model of the Knudsen diffusion.     

用膜分离技术从合成氨弛放气中回收氢气

论述了中空纤维氮氢分离膜的应用以及从合成氨驰放气中回收氢。     

醇类稀溶液的溶剂萃取研究

介绍了醇类稀溶液的溶剂萃取研究进展。在此基础上 ,提出了醇类稀溶液的萃取分离途径 ,并进行了实验研究。     

Experimental studies on extraction of cobalt ions from dilute aqueous solutions by using complexation-ultrafiltration process

The extraction of cobalt ions from dilute aqueous solutions was investigated by ultrafiltration with the help of poly(acrylic acid) sodium salt (PAASS). Polysulfone and polyethersulfone hollow fiber ultrafiltration membranes were employed in this process. The kinetics of complexation reaction was studied for PAASS with Co²⁺. Results showed that, under a large excess of PAASS, it takes 65, 55 and 40 min at pH 5, 6 and 7, respectively, to get the equilibrium of complexation. The reaction kinetics can be described by a pseudo-first-order equation. Then, the effects of various parameters on the extraction of Co²⁺ were examined in detail. Results indicated that loading ratio, pH value and low-molecular competitive complexing agent affect significantly cobalt rejection coefficient R. Furthermore, a concentration experiment was carried out at pH 7. With increasing volume concentration factor, membrane flux declines slowly, and R value is always about 1. The concentrated retentate was used further for a decomplexation experiment. The decomplexation ratio of cobalt-PAASS complex reaches as high as 90.1%. After the decomplexation step, a diafiltration experiment was performed at pH 2.5. Cobalt ions can be extracted satisfactorily from the retentate, and a purified PAASS is obtained.     

Experimental studies on extraction of cobalt ions from dilute aqueous solutions by using complexation-ultrafiltration process

The extraction of cobalt ions from dilute aqueous solutions was investigated by ultrafiltration with the help of poly(acrylic acid) sodium salt (PAASS). Polysulfone and polyethersulfone hollow fiber ultrafiltration membranes were employed in this process. The kinetics of complexation reaction was studied for PAASS with Co²⁺. Results showed that, under a large excess of PAASS, it takes 65, 55 and 40 min at pH 5, 6 and 7, respectively, to get the equilibrium of complexation. The reaction kinetics can be described by a pseudo-first-order equation. Then, the effects of various parameters on the extraction of Co²⁺ were examined in detail. Results indicated that loading ratio, pH value and low-molecular competitive complexing agent affect significantly cobalt rejection coefficient R. Furthermore, a concentration experiment was carried out at pH 7. With increasing volume concentration factor, membrane flux declines slowly, and R value is always about 1. The concentrated retentate was used further for a decomplexation experiment. The decomplexation ratio of cobalt-PAASS complex reaches as high as 90.1%. After the decomplexation step, a diafiltration experiment was performed at pH 2.5. Cobalt ions can be extracted satisfactorily from the retentate, and a purified PAASS is obtained.     

Separation and purification of isobutanol from dilute aqueous solutions by a hybrid hydrophobic/hydrophilic pervaporation process

In this study, a hybrid hydrophobic/hydrophilic pervaporation process was employed to separate and purify isobutanol from its dilute aqueous solutions. For this purpose, composite polydimethylsiloxane membranes were initially used for the recovery of isobutanol by hydrophobic pervaporation. Then the hydrophilic pervaporation with a composite polyvinyl alcohol membrane was utilized to separate water from the organic phase of the permeate stream of the hydrophobic pervaporation. The effect of feed flow rate on the performance of pervaporation was investigated. The resistance in series model was also applied to calculate the transport resistances through the composite membranes. It was observed that an enhancement in the feed flow rate led to higher permeation flux and selectivity of the more permeable component, while the flux of the less permeable component was almost constant. Also, the ratio of liquid boundary layer resistance to membrane layer resistance decreased by an increase in the feed flow rate. The isobutanol with a purity of higher than 99 wt.% was produced by the hybrid hydrophobic/hydrophilic pervaporation technique from a 2 wt.% aqueous isobutanol solution.     

Removal of organics from aqueous solutions by commercial RO and NF membranes of characterized porosities

Removal of organic pollutants of petrochemical and agrochemical origin by some commercial reverse osmosis (RO) and nanofiltration (NF) membranes of characterized porosity was investigated. The rejection of organics was shown to depend on both the membrane properties like pore size, membrane material, membrane charge and solute characteristics such as molecule size, charge and polarity. The rejection of the small nonionized organic molecules by the tight pore membranes is influenced by both the sieving parameters (solute and pore size) and by the physicochemical interactions. The rejection of the same pollutants by the wider pore membranes is dominantly influenced by the physicochemical interactions. The rejection of pesticides is prevalently governed by the sieving mechanism based on the size of the solute molecule and the membrane pore size. However, the physicochemical effects cannot be totally neglected, and they can contribute to the rejection of some pesticides by certain membranes.     

Chemical cleaning of reverse osmosis and nanofiltration membranes fouled by licorice aqueous solutions

The aim of this work was finding optimum cleaning agents and conditions for cleaning reverse osmosis (RO) and nanofiltration (NF) membranes fouled by licorice aqueous solutions. The effect of various chemicals on flux recovery (FR) and resistance removal (RR) of the fouled membranes was investigated. For both membranes the results indicate that a combination of ethylene diamine tetra acetic acid (EDTA), sodium dodecyl sulphate (SDS) and sodium hydroxide may be used as cleaning agents to achieve an optimum cleaning efficiency. Zeta potential and contact angle measurements indicate the changes in charge and hydrophilicity of the surface of RO and NF membranes at various pH solutions, respectively. The effect of surface characteristics is evident in efforts to select the optimal operating conditions. The effect of cleaning condition such as concentration, temperature, pH and cleaning time was studied. The optimum temperature, cleaning time, pH and concentration were found as 35 ± 1 °C, 20 min, 12 and 0.1 wt.%, respectively. SEM pictures showed the surface morphology of RO and NF membrane.     

Cobalt(III) EDTA complex removal from aqueous alkaline borate solutions by nanofiltration

At the PWR Paks diluted low-level radioactive waste water (LLW) contains the long-lived ⁶⁰Co isotope in EDTA complex form, which has no simple separation procedure. In this research nanofiltration(NF) was studied for selective removal of the cobalt(III) EDTA complex from a drain waste water model solution, which contains mainly sodium borate at an alkaline pH. A suitable NF membrane was chosen to separate the cobalt complex from the borate solution. The NF experiments were performed at constant temperature (25°C) and pressure range 1-10 bar. The cobalt complex and the borate ion rejection (R) as well as the permeate flux of the membrane was investigated as a function of pH. The rejection of the cobalt(III) EDTA complex ion and especially the borate were strongly pH dependent. The rejection of the complex ion and the borate was increased at alkaline pH (at pH 8, R = 73%; at pH 11.5, R = 96% for the cobalt complex; at pH 8, R = 7%; at pH 11.5, R = 59% for borate). NF seems to be a suitable separation method for the removal of the Co(III) EDTA complex from nuclear power plant waste streams. The removal of the cobalt complex ion from an alkaline borate solution by NF is possible in two ways: at slightly alkaline pH by a two-step separation, or at a more alkaline pH (pH > 9.5) by a one-step separation.     

Influence of operation parameters on the separation of mixtures by pervaporation and vapor permeation with inorganic membranes. Part 2: Purely organic systems

The performance of commercially available tubular Y-type zeolite membranes was studied for organic separations by vapor permeation. The separation characteristics were determined as function of operating conditions such as concentration, temperature, permeate and feed pressure. The production quality of the tested membranes, in terms of flux and selectivity, was reproducible within a range of 10%. The partial flux of both the preferentially permeating and the retained components generally increase with partial pressure difference in feed and permeate. A constant permeance model may be used to estimate the flux of lower alcohols in mixtures with various non polar organics. Y-type zeolite membranes exhibit permeance values of 2.5 and , respectively for methanol and ethanol and a separation factor over toluene of 100 for methanol and 70 for ethanol, both determined at moderate to high alcohol concentration. There are, however, considerable differences between ideal and mixture selectivities and the error for the flux of the retained component may become large at small concentrations of the preferentially permeating component. The most remarkable abnormality in flux behavior can be observed for a partially Ca-exchanged NaY-Zeolite that shows strongly preferential permeation for methanol at higher methanol concentrations and a marked selectivity in favor of toluene at low methanol concentration. The flux increases with temperature according to an Arrhenius-function, while selectivity does not change significantly. The selectivity can be changed by ion-exchange of the incorporated counter-ions in the zeolite lattice. The separation mechanism is mainly based on preferential adsorption and differences in mobility rather than on size or shape selectivity. With regard to the operation stability of the membranes when separating purely organic systems with the Y-type zeolite, pore blocking, adsorption and coking occurred and reduced the measured flux rates with operation time. The membrane could be partly regenerated by thermal treatment with a nitrogen sweep at 200 °C under vacuum. The installation of a wire mesh demister to reject droplets of heavy boilers in the feed vapor solved the problem.     

Removal of Fe(III) ions from dilute aqueous solutions by alginic acid‐enhanced ultrafiltration

The removal of Fe(III) ions from aqueous solutions was studied using membrane filtration. A water‐soluble polymer alginic acid (AA) was used to bind the metal ions, which was followed by batch ultrafiltration using poly(methyl methacrylate‐methacrylic acid) membranes modified with poly(ethylene glycol) (PMMA‐MA‐PEG). The complexation behavior of AA and the effect pH on the rejection of iron were investigated. Maximum recovery of 87.13% was obtained when the filtration was carried out in the presence of AA at pH 3.1. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1096–1101, 2000