Effects of ionic dissociation of membrane polymer on pervaporation performance

Pervaporation of a water/alcohol mixture through a membrane which has ion-exchange capacity has been investigated. Theoretical equations are introduced which relate the degree of ionic dissociation of the polymer to quantities of water and alcohol dissolved in the polymer. From these equations, an equation for selective dissolution R is derived which does not contain an explicit term for ionic dissociation. Dissociation affects selective dissolution only by changing the degree of swelling of the polymer. Reformulating R asymptotically obtains a reciprocal relationship between permselectivity and permeability for a water-selective membrane. Experiments to check the validity of the relationship have been carried out using chitosan membranes neutralized by several acids. The effect of degree of neutralization also has been investigated. Results can be well understood on the supposition that ionic dissociation depends upon the water/alcohol composition, the kind of acid, and the degree of neutralization. Experimental results indicate that the reciprocal relationship is maintained over an appropriate range of feed compositions which confirm the validity of the theoretical equations for the swelling equilibrium of an ionic membrane. © 1994 John Wiley & Sons, Inc.     

A study of pervaporation of aqueous benzyl alcohol solution by polydimethylsiloxane membrane

Pervaporation of dilute benzyl alcohol solutions was attempted using polydimethylsiloxane (PDMS) membranes. The effects of temperature, downstream pressure and the solution concentration as operating variables on the membrane performance were investigated. It was possible to concentrate benzyl alcohol ten fold in the permeate at the downstream pressure of 66.7 Pa (0.5 mmHg) activity coefficient of benzyl alcohol in the aqueous solution. The permeate concentration, however, decreased and became even less than the feed concentration at high downstream pressures. An increase in the operating temperature increased the vapor pressure of benzyl alcohol and, consequently, increased the permeate concentration. As a result, more than seventy fold increase of benzyl alcohol in the permeate was possible at an operating temperature of 40°C.     

Prediction of pervaporation separation characteristics for the ethanol-water-nylon-4 membrane system

The modified Fels and Huang model has been extended to predict the separation factors and permeabilities more accurately for the system of ethanol-water-nylon-4 membranes. In this system, the binary interaction parameters, g₁₃ and g₂₃, are assumed to be concentration dependent. In order to evaluate these binary interaction parameters, the relationship of the prediction of sorption capability for a given binary mixture into the membrane is developed with and without the consideration of osmotic equilibrium between the polymeric membrane and the binary mixture. The permeabilities of each component for the entire range of the feed mixture at various operating temperatures are then calculated using the predicted sorption capabilities. The experimentally determined diffusion coefficient at zero concentration and the solubility of the pure component are compared with the actual experimental permeabilities. When the osmotic pressure term was taken into consideration, it was found that the calculated individual permeabilities are fairly close to the experimental permeabilities.     

Low-gradient magnetic separation of magnetic nanoparticles under continuous flow: Experimental study,transport mechanism and mathematical modelling

Low-gradient magnetic separation (LGMS) of magnetic nanoparticles (MNPs) has been proven as one of the techniques with great potential for biomedical and environmental applications. Recently, the underlying principle of particle capture by LGMS, through a process known as magnetophoresis, under the influence of hydrodynamic effect has been widely studied and illustrated. Even though the hydrodynamic effect is very substantial for batch processes, its impact on LGMS operated at continuous flow (CF) condition remained largely unknown. Hence, in this study, the dynamical behaviour of LGMS process operated under CF was being studied. First, the LGMS experiments using poly(sodium 4-styrenesulfonate)-functionalized-MNP as modelled particle system were performed through batchwise (BW) and CF modes at different operating conditions. Here BW operation was used as a comparative study to elucidate the transport mechanism of MNP under the similar environment of CF-LGMS process, and it was found out that the convection induced by magnetophoresis (timescale effective is ∼1200 s) is only significant at far-from-magnet region. Hence, it can be deduced that forced convection is more dominant on influencing the transport behaviour of CF-LGMS (with resident time ≤240 s). Moreover, we found that the separation efficiency of CF-LGMS process can be boosted by the higher number of magnets, the higher MNP concentration and the lower flowrate of MNP solution. To better illustrate the underlying dynamical behaviour of LGMS process, a mathematical model was developed to predict its kinetic profile and separation efficiency (with average error of ∼2.6% compared to the experimental results).     

On-line water removal during enzymatic triacylglycerol synthesis by means of pervaporation

Triacylglycerols can be synthesized from glycerol and fatty acids. During this equilibrium reaction water is produced, therefore a mixture of mono-, di- and triesters is obtained. One way to produce an excess of triacylglycerols is to remove the water produced during synthesis. This can be realized in an immobilized enzyme pervaporation system. The enzyme is immobilized onto the lumen side of a cellulose membrane where the organic phase is present. Air circulates at the shell side and the water activity is controlled with the use of a condenser. The lipase catalyzed esterification of decanoic acid and partial glycerides is studied in this reactor. The system is reaction limited. Only at low water activity conditions, an excess of triacylglycerols is obtained. The enzyme activity at the start of the experiments is independent of the water activity within the range studied. Stability is influenced: After 600 hours the activity is 26% of the activity at the start at a_w = 0.1 and 71% at a_w = 0.45.     

Preparation and pervaporation performance of high-quality silicalite-1 membranes

High-performance silicalite-1 membranes were successfully synthesized on novel porous silica tubes by two-step in-situ hydrothermal synthesis.The flux and separation factor towards ethanol/water mix- ture at 60℃were 0.56 kg/(m2·h)and 84,respectively.The as-synthesized silicalite-1 membranes were characterized by scanning electron microscopy(SEM).The influence of different synthesis conditions on the separation performance of the silicalite-1 membranes was investigated.It was found that the average flux of silicalite-1 membranes was improved by about 26?ter filling the silica tubes with mixed solution containing glycerol and water.After calcinating at 400℃for 5 h repeatedly,membrane synthesized on silica tube still showed high pervaporation performance towards ethanol/water mixture even at a calcination rate of 4℃/min,which suggested that silica support was more suitable for pre- paring high-performance silicalite-1 membranes.     

Preparation of plasma-grafted polymer membranes and their morphology and pervaporation properties toward benzene/cyclohexane mixtures

Composite membranes were prepared by plasma-induced graft polymerization of vinyl monomers onto porous substrates of high density polyethylene, and the relationship between the polymerization conditions and morphological structure and pervaporation performance toward benzene/cyclohexane mixtures was investigated in detail. The morphological structures of the plasma-grafted membranes depended on the monomer reactivity, plasma treatment manner, and graft polymerization conditions. Pervaporation properties were closely related to the graft monomers and the morphological structures. The poly(glycidyl methacrylate)-grafted membranes prepared by homogeneous both sides plasma treatment and under mild polymerization conditions showed the highest pervaporation performance with a permeation flux of 0.3 kg/(m² h) and separation factor of 22 at 60 wt % benzene and 70°C. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2247–2259, 1998     

Recent advances in sodium alginate-based membranes for dehydration of aqueous ethanol through pervaporation

Sodium alginate (SA) is a progressive material for membrane fabrication. The technological development of SA-based membranes has made a significant contribution to the separation techniques, especially in aqueous organic solutions. The outstanding performance of SA is attributed to its outstanding structural flexibility and hydrophilicity. In view of structural characteristics, SA membranes have immense utilization in the pervaporation separation of organics. Among various organics, dehydration of aqueous ethanol is employed as a standard to check the success of pervaporation (PV) membrane. Because ethanol and water have comparable molecular sizes, thus difficult to extract water from aqueous ethanol mixtures than it is for other organics. A literature survey shows that wide-ranging data are available on the PV performance of SA and its modified membranes. In this context, the present review addresses the recent advances made in SA membranes for enhanced ethanol dehydration performance during the last decade. Available data since 2010 has been compiled for grafted, crosslinked, blend, mixed matrix, and composite hybrid sodium alginate membranes in terms of separation factor, permeation flux, and pervaporation separation index PSI. The data are assessed with reference to the effect of feed composition, membrane selectivity, flux, and swelling behavior.     

Sorption and pervaporation properties of sulfonyl‐containing polyimide membrane to aromatic/non‐aromatic hydrocarbon mixtures

Sorption of single‐component vapors of benzene (Bz), n‐hexane (Hx), and cyclohexane (Cx), and of binary liquid mixtures of Bz/Hx and Bz/Cx in a polyimide from 3,3′,4,4′‐diphenylsulfone‐tetracarboxylic dianhydride (DSDA) and 2,8(6)‐dimethyl‐3,7‐diaminobenzothiophene‐5,5‐dioxide (DDBT) were investigated in detail at 333 K. Sorption and desorption of vapors followed the non‐Fickian kinetics and the sorption isotherms were concave to the vapor activity. For the binary liquids, the sorption isotherms of the Bz component were concave to the Bz composition in feed, whereas those of Hx and Cx were convex because of competitive sorption. As a result, the solubility selectivity was much larger than the sorption ratio of pure liquids. The concentration‐averaged diffusion coefficients of Bz (D̄_Bz) and Hx (D̄_Hx) were evaluated using the sorption and pervaporation data of the polyimide membrane toward the binary mixtures. A kind of coupling effect of the coexisting component on D̄ was observed. That is, D̄ of penetrant with smaller molecular size (Hx and Bz for Bz/Hx and Bz/Cx systems, respectively) was reduced by the presence of penetrant with larger molecular size (Bz and Cx, respectively) and vice versa. D̄_Bz was similar to D̄_Hx, but much larger than D̄_Cx. The difference in PV behavior between Bz/Hx and Bz/Cx systems for glassy polymer membranes was understood based on the aforementioned features of sorption and diffusion. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2954–2964, 2000     

Sorption and pervaporation properties of crosslinked membranes of poly(ethylene oxide imide) segmented copolymer to aromatic/nonaromatic hydrocarbon mixtures

Poly(ethylene oxide imide) segmented copolymer (PEO‐PI) membranes were crosslinked by the chemical reaction between ethylene glycol diglycidyl ether and benzylalcohol groups of diamine moieties in polyimide segments at high temperatures. Sorption and diffusion of penetrants took place in poly(ethylene oxide) segment microdomains. Sorption and desorption behavior of pure vapors such as benzene (Bz), cyclohexane (Cx) and n‐hexane (Hx) was classified as the Fickian diffusion. Sorption isotherms of binary liquid mixtures could be represented by the Flory–Rehner model, but the model overpredicted the sorption amounts of Cx and Hx, leading to small predictions of sorption selectivity α_S for Bz/Cx and Bz/Hx systems. UNIFAC‐FV model fairly well predicted the sorption amounts of aromatic hydrocarbons, but significantly overestimated those of nonaromatic ones, leading to too small predictions of α_S. Pervaporation (PV) behavior of PEO‐PI membranes was governed by sorption behavior followed by membrane swelling. Diffusion coefficient weakly depended on the minimum cross section of a penetrant. The diffusivity selectivity α_D hardly depended on the feed composition and was about 1.4 and 0.75 for Bz/Cx and Bz/Hx, respectively. PV selectivity α_PV was larger for Bz/Hx than for Bz/Cx because of larger α_S. PEO‐PI membranes displayed high specific permeation flux Ql and reasonably high α_PV for aromatic/nonaromatic hydrocarbons; for example, Ql = 60 Kg μm/(m² h) and α_PV = 8 for a feed mixture containing Bz, Tol, Hx, n‐Ot and i‐Ot of 20 wt % at 353 K. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1800–1811, 2000     

两步变温晶种法制备丝光沸石膜及其渗透汽化乙酸脱水性能

在水热晶种法基础上采用两步变温晶化以高水硅比(n_H2O/n_SiO2)稀溶液配方为合成液,研制用于渗透汽化(PV)乙酸脱水的丝光沸石膜(MOR膜),考察了变温晶化各段时间、水硅比与氟离子对 MOR膜的形貌与分离性能的影响规律。结果表明：高温段晶化时间、水硅比与氟离子对MOR膜的形貌、结晶度和膜层厚度产生显著影响,并影响MOR膜渗透气化分离性能;在高温段(150 ℃)和低温段(120 ℃)的晶化时间分别为 18和 6 h,在水硅比为 60且含氟离子体系中所制备的 MOR膜的性能最佳,其对质量分数50%的乙酸水溶液的渗透通量和分离系数分别为1.45 kg·m^-2·h^-1和1 008。     

两步变温晶种法制备丝光沸石膜及其渗透汽化乙酸脱水性能

在水热晶种法基础上采用两步变温晶化以高水硅比(n_H2O/n_SiO2)稀溶液配方为合成液,研制用于渗透汽化(PV)乙酸脱水的丝光沸石膜(MOR膜),考察了变温晶化各段时间、水硅比与氟离子对MOR膜的形貌与分离性能的影响规律。结果表明：高温段晶化时间、水硅比与氟离子对MOR膜的形貌、结晶度和膜层厚度产生显著影响,并影响MOR膜渗透气化分离性能;在高温段(150℃)和低温段(120℃)的晶化时间分别为18和6 h,在水硅比为60且含氟离子体系中所制备的MOR膜的性能最佳,其对质量分数50%的乙酸水溶液的渗透通量和分离系数分别为1.45 kg·m^-2·h^-1和1 008。     

填充Silicalite—I沸石的PDMS橡胶醇—水分离膜

Ｓｉｌｉｃａｌｉｔｅ－Ｉ沸石经过酸处理或水热处理可完善其晶体结构，提高对乙醇的吸附选择性，由此提高对乙醇－水混合物的分离系数，特别是先经过酸处理再经过水解处理的Ｓｉｌｉｃａｌｉｔｅ－Ⅱ沸石填充聚二甲基硅氧烷橡胶膜，乙醇－水的分离系数可达３０左右。     

改性壳聚糖渗透蒸发膜分离叔丁醇-水

改性壳聚糖渗透蒸发膜分离叔丁醇-水;壳聚糖; 渗透蒸发; 膜分离; 叔丁醇-水     

Computer simulation for the pervaporation process of wate/ethanol mixture through interpenetrating polymer network (IPN) membranes

In this study, the pervaporation behavior of EtOH-water mixture through interpenetrating polymer network (IPN) membranes was predicted. The pervaporation characteristics of single component membranes were modelled according to the “six coefficients model” proposed by Brun [J. Membrane Sci., 23 (1985) 257]. In the case of the IPN membrane, two models were proposed according to the phase structure of the IPN. For a uniphase membrane with no phase separation, the compositional averages of the single component membrane coefficients were used. In the case of the phase separated IPN, two cases exist. The first is the island and sea model: one phase is continuous and the other is discrete. The second is the cocontinuous model, in which two continuous phases exist. For these cases the permeation rate and separation factor of the IPN membrane were calculated using the experimental sorption data and pure component values for each IPN composition. Comparison with the experimental data indicates that these models could be to predict the performances of IPN membranes depending on the morphology of the IPN.     

Synthesis of thianthrene‐5,5,10,10‐tetraoxide‐containing polyimides via Yamazaki–Higashi phosphorylation method and their pervaporation properties to aromatic/nonaromatic hydrocarbon mixtures

High molecular weight polyimide was successfully prepared from thianthrene‐2,3,7,8‐tetracarboxylic acid‐5,5,10,10‐tetraoxide (TADATO‐4A) and 3,7‐diamino‐2,8(6)‐dimethyldibenzothiophene sulfone (DDBT) via the Yamazaki–Higashi phosphorylation method in the presence of triphenyl phosphite (TPP) and pyridine (Py). The obtained polyimide showed about 3–4 times larger inherent viscosity than that prepared by the conventional two‐step method in which the anhydride form (TADATO) of TADATO‐4A was used. The combination of the conventional two‐step method and Yamazaki–Higashi phosphorylation method, in which a dianhydride monomer [3,3′,4,4′‐diphenylsulfonetetracarboxylic dianhydride (DSDA)] was allowed to react with excessive DDBT to form an amine end‐capped polyamic acid oligomer and subsequently the oligomer was further polymerized with TADATO‐4A in the presence of TPP and Py, succeeded in giving the high molecular weight copolyimide, TADATO/DSDA(1/1)‐DDBT. However, both TADATO‐DDBT and TADATO/DSDA(1/1)‐DDBT showed fairly poor thermal stability due to the highly rigid structures. The pervaporation (PV) properties of the prepared polyimide membranes for benzene/cyclohexane (Bz/Cx) and benzene/n‐hexane (Bz/n‐Hx) mixtures were investigated. TADATO‐DDBT showed similar PV performance to DSDA‐DDBT at 60 °C. The sorption measurement revealed that these two kinds of polyimide membranes had a similar sorption amount, solubility selectivity, and diffusivity selectivity. The PV performance of TADATO/DSDA(1/1)‐DDBT was also found similar to DSDA‐DDBT for Bz/Cx mixture. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 895–906, 2000     

表面作用力孔流通模型计算高分子滤过膜孔径大小及分布的方法

综述了一种建立在表面作用力孔流通模型基础上计算高分子多孔滤过膜孔径大小及分布的方法。     

Synthesis and separation performance of silicalite-1 membranes on silica tubes

High-performance silicalite-1 membranes were synthesized on silica tubes by in-situ hydrothermal synthesis. By using the "solution-filling (SF)" method, the average flux of membranes with the SF method was improved by about 25% compared to that of the membranes without using the SF method; the flux and the separation factor of the membranes prepared with the SF method for an ethanol/water mixture at 60 ℃ were 0.99 kg/(m2·h) and 73, respectively. It was found that the membranes synthesized on silica tubes ex...     

Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid) (PE-g-AA) and the olefin reversible coordinates with the PE-g-AA–Ag⁺ complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag⁺ ion. Also, the Ag⁺ ion in PE-g-AA-Ag⁺ membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag⁺ (olefin) complex was proposed. The coordination number of Ag⁺ ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag⁺ in the PE-g-AA–Ag⁺ complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA–Ag⁺ complex membranes were studied. The equilibrium, association, and dissociation constants were also presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 909–917, 1997