Permselective Properties for Aqueous Ethanol Solutions through Copolymer Membranes from Benzyl Methacrylate and Polyethylene Glycol Dimethacrylate

Abstract

Copolymer membranes prepared by bulk copolymerization of polyethylene glycol dimethacrylates of three different degrees of polymerization as macromonomer and benzyl methacrylate as comonomer were used for the separation of aqueous ethanol solutions in both pervaporation and evapomeation. The copolymer membranes preferentially permeated water from an aqueous ethanol solution in evapomeation. In pervaporation, ethanol was predominantly permeated from an aqueous ethanol solution through the copolymer membranes containing a long polyethylene glycol (PEG) chain above about 20 wt% PEG content in a copolymer. This result was attributed to a remarkable swelling of the copolymer membrane containing a long PEG chain by the aqueous ethanol solution in pervaporation. In evapomeation, both the separation factors and the permeation rates through these membranes are not much affected by the ethanol concentration in the feed vapor. In pervaporation, they were significantly dependent on the ethanol concentration in the feed solution. The above results are discussed from the viewpoint of the physical structure of the membrane in evapomeation and pervaporation.     

Pervaporation for the Separation of Methyl Ethyl Ketone from Binary Process Mixtures

Abstract

The separation of methyl ethyl ketone (MEK) from binary process mixtures containing water and ethanol has been examined. These studies demonstrate the capability of pervaporation membranes to effectively separate MEK from various process streams in industry. Extensive organic permeation studies were performed using silicone composite membranes to evaluate the effect of temperature, permeate-side pressure, and feed concentration on flux and selectivity. Two organophilic membranes, a high selectivity low flux membrane and a low selectivity high flux membrane, were compared. Dehydration of a MEK-water mixture was also effectively performed with a polyvinyl alcohol composite membrane. MEK was separated only slightly from an ethanol mixture using a silicone membrane.     

Analysis of Parameters for Ion Permeation in Immobilized Liquid Membranes. I. Perfect-Mix Stages and Cascades

Abstract

This study is concerned with the engineering design and analysis of systems for which the basis for separation is the selective permeation of dissociated salts from aqueous feed to strip solutions through immobilized liquid membranes. Theoretical equations are derived for binary mixtures, assuming Fick's law, to model perfect-mix permeation stages, and separation cascades containing perfect-mix stages. The results should apply both to passive (ordinary) diffusion and macrocycle-mediated transport. Important stage variables include the ratio of total dissociated salt concentrations in the stage feed and strip solutions, the total concentration in the stage strip solution, the stage cut, and the ratio of permeability coefficients for the two species in the separation mixture, i.e., the ideal separation factor. The stage separation factor is a complex function of these variables, and may be much less than the ideal separation factor, depending on values of these variables. Severe stagewise diffusional limitations can exist, particularly if the feed solution must be stripped to very low concentration levels. A conceptual design for an ion permeation cascade is presented which suggests that the overall ion permeation process is quite complex and may be energy intensive. For many separations, cascading is required to achieve desired separations, even with very large ideal separation factors.     

Effect of the Addition of Fructose on the Pervaporation of Ethanol/Water Mixtures by Silicone-Rubber-Coated Polyethersulfone Membranes

Abstract

Composite hollow fiber membranes were prepared by coating polyethersulfone hollow fibers with silicone rubber. The hollow fiber membranes so produced were found to be water selective when they were used for the separation of feed ethanol/water mixtures by pervaporation. When fructose was added to feed ethanol/water mixtures, a decrease in permeation rate and an increase in water selectivity were observed. The decrease in the permeation rate was possible to assume, but the noticed increase in water selectivity was against our expectation, since the vapor pressure of water decreases while that of ethanol increases when sugars are added to mixtures of ethanol and water. Water selectivity of the membrane was enhanced with an increase in the amount of fructose in the feed.     

On the Permeability of Silicone Rubber to Acetylene

Abstract

Very high rates have been reported for the permeation of acetylene through silicone rubber. Measurements in this laboratory, while consistent with the reported data for the permeation of other gases through silicone rubber, do not confirm the rates reported for acetylene.     

Separation of Pyridine/Water Solutions Using Pervaporation

Abstract

Studies were performed on the separation of pyridine/water solutions using pervaporation. Organic permeation experiments were performed using a ‘silicalite»-filled silicone composite membrane. Effects of feed concentration, feed temperature, and permeate side pressure were examined. Benchmark conditions of 5.0 wt% pyridine, 50°C, and 2 torr were chosen. At the benchmark conditions, an organic selectivity of 34 and a permeate flux of 0.428 kg/m²h was achieved. An increase in feed concentration caused an increase in both the permeate concentration and flux, but caused a decrease in the selectivity. Also, permeate compositions far exceeded standard vapor—liquid equilibrium. Temperature had an Arrhenius-type relationship with regard to flux, but had no effect on the selectivity. Increasing the permeate pressure caused a steady decrease in permeate flux and also decreased the permeate composition and selectivity.     

Selective separation of n‐butanol from aqueous solutions by pervaporation using silicone rubber‐coated silicalite membranes

BACKGROUND: To use butanol as a liquid fuel and feedstock, it is necessary to establish processes for refining low‐concentration butanol solutions. Pervaporation (PV) employing hydrophobic silicalite membranes for selective recovery of butanol is a promising approach. In this study, the adsorption behavior of components present in clostridia fermentation broths on membrane material (silicalite powder) was investigated. The potential of PV using silicone rubber‐coated silicalite membranes for the selective separation of butanol from model acetone–butanol–ethanol (ABE) solutions was investigated. RESULTS: The equilibrium adsorbed amounts of ABE per gram of silicalite from aqueous solutions of binary mixtures at 30 °C increased as follows: ethanol (95 mg) < acetone (100 mg) < n‐butanol (120 mg). The amount of butanol adsorbed is decreased by the adsorption of acetone and butyric acid. In the separation of ternary butanol/water/acetone mixtures, the enrichment factor for acetone decreased, compared with that in binary acetone/water mixtures. In the separation of a model acetone–butanol–ethanol (ABE) fermentation broth containing butyric acid by PV using a silicone rubber‐coated silicalite membrane, the permeate butanol concentration was comparable with that obtained in the separation of a model ABE broth without butyric acid. The total flux decreased with decreasing feed solution pH. CONCLUSION: A silicone rubber‐coated silicalite membrane exhibited highly selective PV performance in the separation of a model ABE solution. It is very important to demonstrate the effectiveness of PV in the separation of actual clostridia fermentation broths, and to identify the factors affecting PV performance. Copyright © 2011 Society of Chemical Industry     

Separation Characteristics of Dimethylformamide/Water Mixtures through Alginate Membranes by Pervaporation,Vapor Permeation and Vapor Permeation with Temperature Difference Methods

Abstract

In this study permeation and separation characteristics of dimethylformamide (DMF)/water mixtures were investigated by pervaporation (PV), vapor permeation (VP), and vapor permeation with temperature difference (TDVP) methods using alginate membranes crosslinked with calcium chloride. The effects of membrane thickness (30–90 µm), feed composition (0–100 wt%), operating temperature (30–50°C) on the permeation rates and separation factors were investigated. The permeation rate was found to be inversely proportional to the membrane thickness whereas separation factor increased as the membrane thickness was increased. It was observed that the permeation rates in VP and TDVP were lower than in PV however the highest separation factors were obtained with TDVP method. Alginate membranes gave permeation rates of 0.97–1.2 kg/m² h and separation factors of 17–63 depending on the operation conditions and the method. In addition, sorption‐diffusion properties of the alginate membranes were investigated at the operating temperature and the feed composition. It was found that the sorption selectivity was dominant factor for the separating of DMF/water mixtures.     

Effect of coating procedure on composite gas separation membrane performance

The influence of different coating procedures on the transport and separation properties of composite gas separation membranes was studied. The composite membrane (CM) comprises a coating material (silicone rubber) in occluding contact with an asymmetric polysulfone flat membrane (AM). Permeabilities, ideal separation factors and structure of the CM were found to depend strongly on the evaporation time, volume and concentration of the coating solutions. Gas permeation experiments (H₂, N₂, CO₂, CH₄) indicated that gas permeabilities decreased rapidly with an increasing amount of coating. A maximum in the H₂/N₂, H₂/CH₄ ideal separation factor was reached as the amount of coating was increased. Scanning electron microscopy (SEM) studies revealed the presence of a dense isotropic layer of coating material above an anisotropic layer comprised of a mixture of polysulfone nodules and silicone material. The results showed that the CM prepared with a concentration of 6% silicone solution and contact time of 1 min has the best gas separation performance.     

Effect of operation conditions in the pervaporation of ethanol–water mixtures with poly(1‐trimethylsilyl‐1‐propyne) membranes

Poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) is known to show preferential permeation of ethanol in the pervaporation of ethanol–water mixture. Although this polymer presents good characteristics for the separation of organic–water solutions, operation conditions and membrane characteristics, such as thickness, affect its pervaporation performance. The effect of temperature and feed concentration on pervaporation was studied. During pervaporation of 10 wt % ethanol–water solution, the separation factor (α_H2O^EtOH) remains almost constant, whereas the permeation flux (F) increases exponentially with operation temperature. On the other hand, the separation factor decreases, whereas the permeation flux increases with ethanol content in the feed mixture. The membrane thickness also affects the performance of PTMSP polymer films: selectivity increases sharply with membrane thickness up to 50 μm, whereas it remains constant for thicker membranes. The permeation flux decreases with membrane thickness in the whole range studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94:1395–1403, 2004     

Permeation Properties in Laminated Membranes

Abstract

The response of laminated membranes to permeation was investigated using simple permeation equations. The intrinsic permeability constant of the membrane was shown to be between the maximum or minimum intrinsic permeability constant of all component membranes. Thus the separation factor of the laminated membrane for any type of permeating molecules will be between the values of maximum and minimum separation factors of the component membranes. Permeation through the laminated membrane for a given species will depend on the direction of permeation if the intrinsic permeability constant of any permeating molecule is dependent on the concentration. A simple example for the concentration dependence of permeability constant shows the limits of anisotropic flow ratio.     

Permeation and Separation Characteristics of Acetic Acid‐Water Mixtures by Pervaporation through Acrylonitrile and Hydroxy Ethyl Methacrylate Grafted Poly(vinyl alcohol) Membrane

Abstract

In this study, acrylonitrile (AN) and hydroxyl ethyl methacrylate (HEMA) were grafted onto poly(vinyl alcohol) (PVA) using cerium (IV) ammonium nitrate as initiator at 30°C. The graft copolymer was characterized using the Fourier transform infrared spectroscopy (FTIR) and elemental analysis. The grafted PVA membranes (PVA‐g‐AN/HEMA) were prepared by a casting method, and used in the separation of acetic acid‐water mixtures by pervaporation. The effects of the membrane thickness, operating temperature, and feed composition on the permeation rate and separation factor for acetic acid‐water mixtures were studied. Depending on the membrane thickness, the temperature and feed composition PVA‐g‐AN/HEMA membranes gave separation factors 2.26–14.60 and permeation rates of 0.18–2.07 kg/m²h. It was also determined that grafted membranes gave lower permeation rates and greater separation factors than PVA membranes. Diffusion coefficients of acetic acid‐water mixtures were calculated from permeation rate values. The Arrhenius activation parameters were calculated for the 20 wt.% acetic acid content in the feed using the permeation rate and the diffusion data obtained at between 25–50°C.     

Reliable production of highly concentrated bioethanol by a conjunction of pervaporation using a silicone rubber sheet‐covered silicalite membrane with adsorption process

For the production of highly concentrated bioethanol by pervaporation using an ethanol‐permselective silicalite membrane, pervaporation performance was investigated using a silicalite membrane entirely covered with a silicone rubber sheet to prevent direct contact with acidic compounds. By using a resistance model for membrane permeation, the separation factor of the covered silicalite membrane towards ethanol can be estimated from the individual pervaporation performances of the silicalite membrane and the silicone rubber sheet. No decrease in the ethanol concentration through the silicone rubber sheet‐covered membrane was caused when ethanol solutions containing succinic acid were supplied. By directly passing the permeate‐enriched ethanol vapor mixed with water vapor through a dehydration column packed with a molecular sieve of pore size 0.3 nm, highly concentrated bioethanol up to 97% (w/w), greater than the azeotropic point in the ethanol/water binary systems, can be obtained from 9% (w/w) fermentation broth. Copyright © 2004 Society of Chemical Industry     

Liquid Permeation of Isopropanol and Water in a Silicone Rubber

Abstract

The feasibility of using a silicone rubber membrane to separate mixtures of isopropyl alcohol and water, including the azeotropic composition, has been demonstrated and a quantitative measure of efficiency of separation has been developed.

One of the problem areas in studying liquid permeation is the variability in the polymer membrane structure. Such factors as the presence of solvents and plasticizers, previous thermal history, previous solvent history, and the degree of crystallinity of the polymer behavior affect membrane behavior. However, as the polymers are better understood, these drawbacks for the researcher may be of advantage to those tailoring a polymer to a specific use.     

Separation of Water/Ethanol Vapor Mixtures through Chitosan and Crosslinked Chitosan Membranes

Abstract

The separation of water/ethanol vapor mixtures through chitosan membranes and crosslinked chitosan membranes was studied by means of the vapor permeation technique. The permeation performance was discussed in terms of separation factor and permeation flux. Crosslinking the chitosan membrane by glutaraldehyde enhanced the selectivity. The highest separation factor obtained was 6000 for a crosslinked chitosan membrane with a degree of deacetylation of 100%.     

Perstraction of Phenolic Compounds from Aqueous Solution Using a Nonporous Membrane

Abstract

An exploratory study of nondispersive extraction of various phenolic solutes using a nonporous membrane has been carried out. Sorption and permeation data for these solutes have been obtained using a silicone rubber membrane. The effects of hydrodynamic factors, concentration of phenols, and temperature on the trans-membrane flux are discussed. A film model is used to determine the intrinsic mass transfer characteristics of the membrane. Comparison of sorption of phenolic solutes from the membrane into the organic solvent indicates that methyl isobutyl ketone is a better solvent than butyl acetate.     

STRIPPING RATE OF PROPIONIC ACID FROM STYRENE-DIVINYLBENZENE COPOLYMERIC MICROCAPSULES WITH TRI-W-OCTYL AMINE AS CORE MATERIAL

ABSTRACT

The stripping rate of propionic acid from microcapsules containing tri-n-octyl amine was investigated using distilled water and aqueous NaOH as stripping solutions. The experiments were conducted at 303K. The stripping rate was found to be controlled by diffusion through porous microcapsule membrane and increased with an increase in the concentration of propionic acid in the microcapsules for each solution system. It was found that the stripping rates in aqueous NaOH solution system was higher than in distilled water at the same concentration of propionic acid in microcapsules. The experimental results in the NaOH solution system could be analyzed using a permeation model considering mass transfer accompanied by irreversible instantaneous neutralization reaction between NaOH and the propionic acid/tri-n-octyl amine complex in the microcapsule membrane.     

Selective Separation of Gallium from Acidic Leach Solutions by Emulsion Liquid Membranes

Abstract

The separation and concentration of gallium from acidic leach solutions, containing various other ions such as iron, cobalt, nickel, zinc, cadmium, lead, copper, and aluminium, by an emulsion liquid membrane (ELM) technique using tributyl phosphate (TBP) as carrier has been presented. Liquid membrane consists of a diluent, a surfactant (ECA 4360J), and an extractant (TBP), and 0.1 M HCl or 0.1 M H₂SO₄ were used as the stripping solution. The important variables governing the permeation of gallium and their effect on the separation process have been studied. These variables were membrane type and composition, mixing speed, diluent type, surfactant concentration, extractant concentration, HCl concentration in the feed, acid type of stripping phase, feed concentration, and treatment ratio. The optimum conditions were determined. It was possible to selectively extract 96.0% of gallium from the acidic leach solutions, containing Fe, Co, Ni, Zn, Cd, Pb, Cu, and Al, at the optimum conditions.     

Swollen-Dry-Layer Model for the Pervaporation of Ethanol-Water Solution through Hydrophilic Membranes

Abstract

A swollen-dry-layer model is presented for the pervaporation of ethanol-water solution through hydrophilic polymer membranes: poly(vinyl alcohol) and carboxymethyl cellulose. Independent measurements were conducted of the sorption equilibrium, the hydraulic permeation rates through the swollen membranes, and the permeabilities of ethanol and water vapors. The hydraulic permeabilities were estimated from the mutual diffusion coefficients of solution in the swollen membrane. Sorption behavior and hydraulic permeabilities showed a dependence on feed concentration. Vapor permeabilities of water and ethanol through dry membranes differ by a factor of about 20. Comparisons between the experimental data from the pervaporation run and the results calculated from the model were made. The model offers a quantitative explanation for the dependency of selectivity and flux on feed concentration. The model explained that the flux dependency caused by a change in the swollen-dry-layer ratio, and that the selectivity is governed by vapor permeabilities through the dry layer.     

Selective and Simultaneous Extractions of Zn and Cu Ions by Hollow Fiber SLM Modules Containing HEH(EHP) and LIX84

Abstract

The selective extractions of Zn²⁺ and Cu²⁺ from their mixed solutions of sulfate medium have been studied using hollow fiber supported liquid membranes (HFSLM). The HFSLM contained two kinds of extractants; one contained 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester [HEH(EHP)], the commercial name of which is PC88A, for Zn extraction; the other contained the hydroxy oxime reagent LIX84 for Cu extraction. Individual runs of each HFSLM were made to determine the effect of operational variables on the permeation rates of metal ions and their separation factors. In addition, the simultaneous and selective extractions of both Zn²⁺ and Cu²⁺ from their mixed solutions were demonstrated using the PC88A and LIX84 HFSLMs together. The performance of simultaneous extraction was compared with those of the individual runs.