Effect of membrane preparation conditions on solute permeability in chitosan membrane

Chitosan membrane was prepared in various conditions and diffusive permeabilities of theophylline and vitamin B₁₂ were investigated. The membrane preparation procedure consists of dissolving chitosan in acid solution, cast on the glass plate, drying the dope solution, and immersion of the plate in the gelating agent. Effects of the kinds of acids to dissolve chitosan, chitosan concentration, drying time of the dope solution, and the kinds of the gelating agent on the membrane structure and performance were studied in detail. With increasing the chitosan concentration, the solute permeability decreased, while the selectivity of theophylline to vitamin B₁₂ increased. The membrane changed from the wholly porous structure to the asymmetric structure by the increase of the chitosan concentration. Furthermore, the use of ethanol as the gelating agent brought about the wholly porous structure with the high permeability and the low selectivity. The asymmetric structure and the wholly dense structure were obtained in the cases of the gelating agents, such as aqueous NaOH solution and dimethyl sulfoxide (DMSO), respectively. Thus, the membrane structure can be controlled by the kinds of gelating agent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2715–2725, 1999     

SEPARATION AND ENRICHMENT OF WEAK ORGANIC ACIDS OR BASES BY IMMOBILIZED LIQUID MEMBRANES

A new and effective liquid membrane process to achieve both separation and enrichment simultaneously of weak organic acids or bases was developed. The process utilizes effectively the difference in the apparent partition coefficient of the constituent species between the aqueous and organic phases, and uses the change of the apparent partition coefficients with the hydrogen ion concentration of the aqueous phase. For such a fundamental model apparatus as a diaphragm diffusion cell being operated batch wise, the effects of pK value of solutes, permeability of solutes through the membrane, volume ratio of liquids in two aqueous phases, and pH value of aqueous phase on enrichment factor and selectivity for the solute to be concentrated were discussed analytically. Separation and enrichment were demonstrated using aqueous mixed solutions of fumaric acid and L-malic acid. The results were in good agreement with the theoretical predictions.     

Permselectivities of some aromatic compounds in organic medium through cellulose acetate membranes by reverse osmosis

Reverse osmosis of some aromatic compounds in 1-propanol solution using porous cellulose acetate membranes and some factors which influence the organic solute permeability were investigated. Reverse osmosis data for a number of benzene derivatives showed that only phenol was rejected and the others were enriched. For the compounds with various substituent groups, the solute permeabilities have the following order; OH < CH₃ < H < Cl < NH₂ < NO₂. In the series of benzene, naphthalene, and anthracene, the permeability is related to the molar volume of solutes and varied as follows: benzene < naphthalene < anthracene. Generally speaking, there are two factors—a partition coefficient and a diffusion coefficient—for governing the permeation behavior through the membrane. Under the condition that no steric effect is exerted, the partition coefficient exclusively is a dominant factor. A good correlation between the partition coefficient of a particle and that of the membrane was pound. The partition coefficients are closely related to the dipole moment of solutes.     

Simulation of Solute Diffusion through Porous Media

Abstract

Simulation of solute diffusion through porous media (membrane) was carried out by a random walk procedure. The porous media used were three kinds of two-dimensional square networks of channels with almost the same average pore diameters and porosities, but with different pore size distributions. In the simulation the partition equilibrium of solute between the bulk feed phase and the membrane phase was established, and the apparent permeability in the steady state was evaluated. First, only the steric interaction between the solute and the pore wall was considered. In spite of the similar average pore diameters and porosities of the networks, the apparent permeability and selectivity were dependent on the kinds of networks. The network with more small pores showed the smaller permeability and the higher selectivity. When the diameter of solute which can be actually transported is fairly smaller than the average pore diameter, the network with broad pore distribution and with more small pores is found to be useful for obtaining higher selectivity. Next, the electrostatic and dispersion (van der Waals) interactions between the solute and the pore wall were introduced in this simulation. By such long-range interactions the selectivity increased while the apparent permeability decreased. This result showed that the introduction of the repulsive electrostatic interaction between membrane and solute is one useful method for enhancing the selectivity. The effects of the kinds of networks on transport properties in the presence of long-range interactions were similar to those in the absence of such interactions.     

Synthesis,properties, and permeation of solutes through hydrogels based on poly(ethylene glycol)-co-poly(lactones) diacrylate macromers and chitosan

Triblock copolymers from poly(ethylene glycol) (PEG) and D,L -lactide or ε-caprolactone were synthesized to prepare semi-interpenetrating polymer networks (semi-IPNs) with chitosan by ultraviolet (UV) irradiation method. Then, the solute permeation through these semi-IPNs hydrogels were investigated. The structures of semi-IPNs were confirmed by Fourier transform infrared (FTIR) spectroscopy and wide-angle X-ray diffractometer (WAXD). The equilibrium water content (EWC) of these hydrogels was in the range of 67–75%. The crystallinity, thermal properties, and mechanical properties of semi-IPNs hydrogels were studied. All the hydrogels revealed a remarkable decrease in crystallinity as compared with the PEG macromer itself. The tensile strengths of semi-IPNs hydrogels in a dry state were rather high, but those of hydrogels in a wet state decreased drastically. The permeabilities of solutes of hydrogels followed the swelling behaviors and were regulated by solute size. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2151–2158, 1999     

Preparation and properties of negatively charged ultrafiltration membrane: Photografted sodium styrene sulfonate onto brominated polyacrylonitrile membrane

Charged ultrafiltration membranes were prepared by photografting sodium styrene sulfonate onto photosensitive polyacrylonitrile membrane containing bromine atoms. The degree of the photografting was characterized by contact angles of air or n-octane in water and FTIR spectra for the negatively charged membrane. Permeations of dextran and dextransulfate through the negatively charged membranes were studied by ultrafiltration in the aqueous solutions of both solutes. With an increase of photoirradiation, the permeability of the solutes decreased. Also, an electrostatic repulsion of the solute and the membrane was confirmed by direct comparison between the permeability of the solutes, dextran, and dextransulfate, each having similar molecular size.     

A Numerical Study of the Apparent Selectivity in the Fractionation of Two Macromolecules by Ultrafiltration

The fractionation of two macromolecules by ultrafiltration in a parallel plate cell was studied by computational fluid dynamics (CFD). The in-house code developed takes on account of the pressure drop, the variation of the permeate velocity along the cell, the concentration polarization over the membrane, and the variation of the transport properties and of the osmotic pressure with the concentration of the solutes. A convective-diffusive model, to simulate the solute transmission, was also adopted. The real and apparent selectivity, local and mean, were determined, in order to study the effect of transmembrane pressure, Reynolds number, inlet solute concentrations, specific area of the membrane pores, and membrane resistance. The code was applied to study the separation of Bovine Serum Albumin (BSA) and Dextran-T10 macromolecules. The mean apparent selectivity increases with increasing transmembrane pressures until it reaches a maximum after which it decreases. The mean apparent selectivity increases with increasing Reynolds number consequence of a polarization decrease. Moreover, the selectivity increases with a decrease of the pore size and, also, with an increase of the membrane resistance. For low inlet concentrations of the solutes, the variation of the physical properties with the concentration does not produce any appreciable effect on the apparent selectivity.     

Permeation of solutes through interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylic acid)

The swelling behaviors of poly(vinyl alcohol)–poly(acrylic acid) (PVA–PAAc) interpenetrating networks (IPN) hydrogels in the presence of electrolytes were studied. The ionized carboxylic group within IPN hydrogels at pH 7 strongly interacted with electrolytes in the medium and caused anomalous swelling pattern. The permeabilities of 5 representative solutes were regulated as a function of temperature, pH, ionic strength, solute size, and ionic properties of solutes. The permeation of nonionic solutes followed the swelling behaviors dependent on external stimuli, including the above factors. However, the ionic solutes showed different trends in their permeation through IPN hydrogels. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 479–486, 1998     

Solubility / retention relationships in supercritical-fluid chromatography

The effects of temperature, pressure and supercritical fluid density on solubility-retention relationship of solutes in supercritical fluid partition chromatography are investigated. New retention data for naphthalene and phenanthrene are obtained as a function of pressure at different temperatures. The mobile-phase partial molar volumes of the solutes are determined from infinite-dilution fugacity coefficients and used to model the pressure dependence of solute retention that reveals the nature of interactions between the stationary phase and the solute. Relationships between pressure and temperature dependence of solubility and retention of solutes are also illustrated.     

Prediction of Equilibrium Partitioning of Nonpolar Organic Solutes in Water‐ Surfactant Systems by UNIFAC and COSMO‐RS Models

In the present study the potential of two thermodynamic‐based models (the group‐contribution UNIFAC model and the a priori predictive COSMO‐RS model) to predict solute partitioning in aqueous surfactant solutions is evaluated. In order to take into account the small size of micelles, the UNIFAC model was extended by the interfacial contribution based on the Gibbs‐Thompson equation. The applicability of the approach was successfully proved for the partitioning of nonpolar solutes (toluene, p‐xylene) in aqueous solutions of nonionic surfactants. The original COSMO‐RS model underestimates the concentration of the solute in the aqueous phase in the case of micellar systems since it does not account for the small size of micelles. At the same time, this model gives quantitative results for the octanol/water partition coefficients of both solutes under study leading to the conclusion that the affinity of both solutes to a certain solvent is well described. Thus, extending the COSMO‐RS by the interfacial term seems to be promising.     

Permeability through cellulose membranes grafted with vinyl monomers in a homogeneous system. VIII. N-vinylpyrrolidone-grafted cellulose membranes

The homogeneous grafting of N-vinylpyrrolidone (NVP) onto cellulose was carried out in a dimethyl sulfoxide/paraformaldehyde (DMSO/PF) solvent system. The diffusive permeabilities of solutes through the NVP-grafted cellulose membranes, apparent activation energy for solute permeation through them, states of water in them, and their microphaseseparated structures were investigated. The solute permeability through the grafted membranes was superior to that through the cellulose membrane cast from the DMSO/PF solution of cellulose. The total water and nonfreezing water contents of the grafted membranes were larger than those of the cellulose membrane. The difference in permeability through the membranes was not correlated quantitatively with the amount of each state of water in them. Activation energies for permeation of solutes through the grafted membranes were similar to those through the cellulose membrane. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of hydrophobically modified poly(vinyl alcohol) hydrogel membrane

Hydrophobically modified poly(vinyl alcohol), [PVA] was synthesized by graft copolymerization of N-tertiary butyl acrylamide [NTBA] onto PVA by free radical polymerization. The incorporation of NTBA onto PVA chains was confirmed by elemental analysis, FT-IR and NMR spectroscopy. A series of graft copolymers with different contents of NTBA were prepared and membranes were casted from these copolymer solutions in dimethyl sulfoxide. The increase in hydrophobicity with an increase in NTBA content was investigated by contact angle measurements. The swelling behaviour of membranes as a function of temperature, hydrophobic content, annealing temperature and period was studied. Permeability of solutes through these membranes was investigated as a function of solute size, membrane hydrophobicity and temperature. The swelling behaviour of the copolymer membranes showed that the lower content of NTBA gives discontinuous volume transition with respect to temperature whereas, the presence of higher amounts of NTBA showed decreased swelling ratios with very little influence of temperature on the swelling. The permeabilities of solutes through these membranes were strongly dependent on the size of the solute, solution temperature and hydrophobicity of the membrane. The copolymer membranes were further characterized using DSC, DMA and XRD. The peak becomes broader as the NTBA content increases.     

Controlled release of riboflavin and insulin through crosslinked poly(vinyl alcohol)/chitosan blend membrane

The permeation of riboflavin and insulin through poly(vinyl alcohol) (PVA) and chitosan blend membrane was conducted. The permeability coefficients of both solutes through the crosslinked PVA and chitosan blend membrane were in the order of 10^?6?10^?7 cm³ cm/cm²s and showed a pH dependence. The pH-dependent permeation behavior was discussed in terms of water content and water structure inside of the swollen membrane. Riboflavin and insulin were presumed to permeate through the free water region in the swollen blend membrane. The DSC thermograms of these membranes indicated that the content of free water and the amount of freezing bound water increased with the water content in the membrane. The greater permeation rate of solutes in acidic solution rather than in neutral solution was due to an increase in both water content and the amount of free water and freezing bound water.     

Amphiphilic graft copolymer latex membranes. VI. Poly(vinyl alcohol)–acrylonitrile–N-hydroxyethyl acrylamide graft copolymer latex membranes

Poly(vinyl alcohol)(PVA)–acrylonitrile(AN)–N-hydroxyethyl acrylamide (HEAAm) graft copolymer latex membranes were prepared and properties of the membranes were compared with those of PVA–AN graft latex membranes and Cuprophane PT-150. The physical constants of HEAAm were determined and the tautomerization between hydroxyethyl amide group and aminoethyl ester group upon pH changes was ascertained by infrared spectrum of poly(HEAAm) film. An increase in HEAAm content in the membrane enhanced permeabilities of solute in aqueous solutions in comparison with PVA–AN graft latex membranes, maintaining good mechanical properties in wet state. With pH variation, the permeability of the nonionic solute was unchanged, but that of the anionic solute in acidic condition was superior to that in basic condition, and the permeability of the cationic solute exhibited the opposite trend. The behavior of ionic solute were attributable to the effect of the tautomerization of the functional group in the membrane.     

Prediction of partition coefficients using COSMO-RS: Solvent screening for maximum conversion in biocatalytic two-phase reaction systems

Many biocatalytic reaction systems are biphasic with a reactive and an immiscible non-reactive phase. The reactive, mostly aqueous phase provides a natural enzyme environment and the non-reactive phase serves for delivery of dissolved substrates at high concentrations and for extraction of products. The proper choice of the non-reactive phase will have manifold influence on the catalytic parameters, such as activity, selectivity, and stability, but also on the maximum obtainable conversion or yield.

Conversion or yield constitutes a concise target of practical relevance for rational solvent screening which requires thermodynamic information on coupled reaction and phase equilibria as input information. As long as the reactive phase is kept constant, only the partition equilibrium of each solute in any solvent combination has to be determined. The experimental determination of these data requires a considerable laboratory effort. Therefore, an in-silico screening of solvents for maximal conversion of alcohol dehydrogenase-catalysed oxidoreductions of prochiral ketones was evaluated. COSMO-RS was used for the prediction of solute partitioning between organic solvents and aqueous reaction medium.

Although significant absolute deviations were found, COSMO-RS still predicted the correct trends for the partition coefficients of solutes in different solvents. The calculated overall reaction equilibrium using these partition coefficients again resulted in the prediction of the correct best solvent regarding conversion.     

高取代度氰乙基纤维素膜及其共混膜的研究——Ⅱ.高取代度氰乙基纤维素反渗透膜

本文对高取代度氰乙基纤维素(HCEC)的制膜工艺进行了初步研究,并考察了膜的化学稳定性和渗透选择性。结果表明,HCEC膜除有优良的耐微生物分解性能外,在耐酸、碱水解和耐活性氯氧化性能上也远胜于醋酸纤维素(CA)膜。在对溶质的渗透选择性能方面,HCEC膜对荷负电溶质有较高的截留性能,并表现出类似于荷电型阳离子反渗透膜的某些特征。     

Properties of dynamically formed membranes

Although it is known that the so-called dynamically formed membranes are easy to make, resistant to high temperature and have large water permeabilities , their precise properties have not been fully analysed. Also it has been found that reproducible membranes were different to make. In this work first we tried to define conditions to make reproducible membranes having wide ranges of permeability, by using zirconium hydroxide and polyacrylic acid.Next we determined properties of these membranes under various conditions, such as pH, temperature, concentration and pressure using not only sodium chloride but also other non-electrolytes as solutes. It became clear that pH affects both water and solute permeabilities and the membrane stability very much. Membranes that have low water permeability have high rejection at high concentration, for example 80% at 3.5% NaCl solution at 70 bar. Such a membrane can reject sucrose over 90%, phenol 80%, urea 35%. All these fact show that the dynamic membrane acts as a porous membrane, in which the preferential sorption has an important role, as well as a charged membrane.     

Partitioning of Charged Solutes in Poly(Ethylene Glycol)/Potassium Phosphate Aqueous Two-Phase Systems

Abstract

A mathematical model based on the dissociation of charged compounds and the pH of each phase is developed to describe the partitioning of charged compounds in aqueous two-phase systems. Observed partition coefficients of several charged and uncharged compounds, including three pairs of oppositely charged analogs (tryptamine/indole 3-acetic acid, 5-methoxytryptamine/5-methoxyindole 3-acetic acid and 2-(p-tolyl) ethylamine/p-tolyl acetic acid), are compared in identical poly-(ethylene glycol)/potassium phosphate aqueous two-phase systems over the pH range of 5.5 to 9.2. Among these pairs, the partition coefficients of the acids increased with increasing pH, from 8.4 to 33.3 for indole 3-acetic acid, from 11.4 to 53.9 for 5-methoxyindole 3-acetic acid, and from 4.2 to 17.7 for p-tolyl acetic acid. The amine partition coefficients also increased with increasing pH, from 4.0 to 7.8 for tryptamine, from 5.8 to 12.2 for 5-methoxytryptamine, and from 1.6 to 3.0 for 2-(p-tolyl) ethylamine, respectively. Consistent with the derived model, the greatest rate of increase in the partition coefficients of the acids occurs at low pH, while the greatest rate of increase in amine partition coefficients occurs at high pH. The ratio of partition coefficients for these pairs predicted by the model agrees with the observed partition ratio. The results indicate that charge, in addition to hydrophobic effects previously described, plays a major role in the partitioning of biological compounds.     

Synthesis and characterization of polyamphoteric hydrogel membrane based on chitosan

Polyamphoteric hydrogel membranes were synthesized by graft copolymerization of N‐isopropylacrylamide (NIPAm) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) onto chitosan (CS). The incorporation of poly(NIPAm) (PNIPAm) and poly(AMPS) (PAMPS) into CS was confirmed by FTIR spectroscopy. The swelling behavior of membranes as a function of pH, temperature, and ionic strength was studied. Permeability of solutes through these membranes was investigated at different temperatures. The results showed the dual sensitivity of membranes toward pH and temperature. The formation of the polyelectrolyte complex between CS and PAMPS showed influence on the lower critical solution temperature of PNIPAm. The permeabilities of solutes through these membranes were strongly dependent on the size of solutes, solution temperature, and hydrophilicity of the membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1454–1461, 2004     

Water/ethanol pervaporation performance of asymmetric polyelectrolyte complex membrane constructed by the diffusion of poly(acrylic acid) in chitosan membrane

Asymmetric polyelectrolyte complex (PEC) membranes composed of chitosan membrane and absorbed poly(acrylic acid) (PAA) were constructed. Absorption and therefore PEC formation were performed by bringing a chitosan membrane into contact with a PAA aqueous solution. The mean molecular weight (MW) of PAA employed was 5,000, 25,000 or 250,000. Absorption of PAA and asymmetry of PEC membranes were confirmed and evaluated by Fourier transform infrared (FTIR) spectra and electron spectroscopy for chemical analysis (ESCA). The absorption quantity of PAA decreased while the water selectivity of the PEC membrane increased with an increase in the MW of constituent PAA. In a pervaporation experiment, the water selectivity of the membrane was so high that no ethanol was detected by gas chromatography (GC). Such selectivity was attained by just a small quantity of PEC formation at the surface of the chitosan membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 265–271, 2002