Transport and Permeation Properties of a Ternary Gas Mixture in a Medium-Size Polysulfone Hollow Fiber Permeator

Abstract

Permeation properties were analyzed for a mixture of CO₂, O₂, and N₂ in a medium-size polysulfone hollow fiber permeator with a net permeation area of 4.22 m². Measurements were conducted as a function of feed composition, reject flow rate, and feed pressure. Results included variations in species permeability, separation factor, permeate enrichment, reject depletion, and stage cut as a function of system parameters. Variations in permeation properties show strong dependence on feed composition, reject flow rate, and feed pressure. Permeability of carbon dioxide was higher at larger feed pressures and higher carbon dioxide content in the feed stream. Effect of increasing the reject flow rates on the permeability of carbon dioxide was affected by the system pressure and the carbon dioxide content in the feed stream. At low pressures, increase of the reject flow rate resulted in a decrease of carbon dioxide permeability. The opposite behavior was obtained at higher feed pressures. Increase of the reject flow rate reduced the gas residence time within the permeator. Increase of reject flow rate reduced species residence within the permeator and in turn increased resistance to species transport within the permeator. However, higher system pressures and carbon dioxide content in the feed stream resulted in larger levels of membrane plasticization, which increased the permeation rates of all species. The combined efféct of reducing the species residence time within the permeator and the level of membrane plasticization favored the permeation of carbon dioxide versus the other two species. Variations in other permeation properties, which include oxygen and nitrogen permeabilities, stage cut, permeate enrichment in carbon dioxide, and reject depletion in carbon dioxide, were also explained in terms of resistances encountered within the permeator and the membrane.     

Understanding the performance of membrane for direct air capture of CO2

Direct air capture (DAC) of CO₂ is becoming increasingly important for reducing greenhouse gas concentrations in the atmosphere. However, the cost and energy requirements associated with DAC make it less economically feasible than carbon capture from flue gases. While various methods like solid sorbents and gas–liquid absorption have been explored for DAC, membrane processes have only recently been investigated. The objective of this study is to examine the separation performance of a membrane unit for capturing CO₂ from ambient air. The performance of a membrane depends on several factors, including the composition of the feed gas, pressure ratio, material selectivity, and membrane area. The single-stage separation process with the co-current flow and constant permeability flux model is evaluated using a commercial module integrated with a process simulator to separate a binary mixture of carbon dioxide and nitrogen to assess the sensitivity of selectivity on purity and recovery of CO₂ in permeate, and power requirement. Additionally, three levels of CO₂ reduction from the feed stream to the retentate stream (25%, 50%, and 75%) are studied. A trade-off between purity and recovery factor is observed, and achieving high purity in permeate requires high concentration in the retentate.     

A Novel Rig Design for Ultra- and Microfiltration Experiments

Abstract

The versatile rig for crossflow ultrafiltration and microfiltration experiments described in this paper can be operated at various concentrations of the feed stream by using a feed-and-bleed mode, either at controlled permeation flux or at controlled transmembrane pressure. Transmembrane pressure can be set as a static counterpressure through a bleed valve, or as a dynamic counterpressure achieved by circulating the permeate cocurrent to the retentate, to maintain an equal transmembrane pressure profile along the filtration path. The rig is equipped with extra independent controls (retentate and permeate temperature, retentate tangential flow velocity, retentate pressure) to enable to master filtration procedures by setting variables to the desired values through any operational pathway. It allows real time data monitoring and storing by a computer through a multichannel analyzer.     

Permeability of paint films towards chloride ion

An apparatus for determining the permeability of paint films towards chloride ion is described. This set-up implements the time-lag, method and consists of a permeation cell made up of two chambers divided by a supported paint film. The upper chamber contains an aqueous sodium chloride solution and the lower one, water. The permeability is obtained from the conductivity history read at the lower chamber. Osmotic pressure issue is addressed and the reproducibility of the results reported. The time-lag, method is not described in any standard. The requirement concerning “surface protection systems for concrete” for chloride ion permeability is not quantified in prEN 1504-2. The standard establishes that this requirement is “subject to national standards and national regulations” but when the capillary adsorption of water is lower than 0.01 kg/(m²h^0.5) the diffusion of chloride ion is not to be expected. Some experimental results prove this is not correct and, in Portugal, the National Laboratory of Civil Engineering (LNEC) has proposed a threshold permeability value of 10⁻¹⁴ m²/sec for coatings claiming to be corrosion protective.     

Permeability and separability of methane and carbon dioxide across meso-porous Mg-Al hydrotalcite and activated carbon media

Hydrotalcite and activated carbon (AC) are known to exhibit certain level of affinity for CO₂. If the materials are constructed for use as an adsorptive film or adsorbent in gas separation application, more of CO₂ can be permeated and separated from the other component gas mixture. In this study, permeability of carbon dioxide across the materials was found to increase almost linearly with increase in the respective gas flow rate but the permeability was nearly independent of pressure, attesting to their meso-porosity. The permeability remained constant at ≈6×10⁻³ mol m/m² s Pa, apparently due to the dominance of Knudsen diffusion mechanism. The separability of gas increased with increase in the inlet flow rate and pressure. Hydrotalcite film deposited on porous alumina substrate demonstrated the highest separability factor of 91, followed by bast AC (separability factor=13) and core AC (separability factor=11). Methane was found to permeate preferentially through the three porous media due to hindered diffusion of CO₂ as a result of the affinitive force attributed to high charged density in the interlayer spacing of Mg-Al hydrotalcite structures that sequestered CO₂.     

Selective permeation across a blend film of cellulose acetate and polymer or copolymer of c-(Nε-AcrLys-Sar)

A blend film of cellulose acetate and the homopolymer (PCP) or the copolymer with styrene [P(CP_ST)] or 4-vinylpyridine [P(CP_VP)] of $\text{cyclo(}\text{N}{}^{\mathrm{\epsilon }}\text{-}\text{acryloyl-}\text{l}\text{-lysylsarcosyl}\text{)}$ [c-(N^ε-AcrLys_Sar)], which is a vinyl compound carrying a cyclic dipeptide in the side chain, was prepared and investigated as a selectively permeable film for ions and polar substances. For the permeation of alkali metal chlorides, the solubility coefficient S increased in proportion to the content of PCP in the blend film, whereas the diffusion constant D_s increased up to 20 wt% of PCP content and levelled off beyond it. D_s of Rb⁺ was greatest for any blend film regardless of the composition. It was considered that the hydrophilic PCP forms water channels in the blend film and metal salts diffuse by coordination with cyclic dipeptide ligand groups which are arrayed along the water channels. In this process, the cooperative interaction of the ligand groups with a metal ion along the flexible polymer chain should work most efficiently with Rb⁺, leading to the Rb⁺ selectivity in the permeation. A similar ion selectivity was observed with the blend film of P(CP_ST). For the blend film of P(CP_VP), S increased in proportion to the content of P(CP_VP), where D_s was a minimum at 20 wt% of P(CP_VP) content. The ion selectivity was not observed with either S or D_s. For the permeation of alkali metal salts across the blend film of PCP, D_s and the ion selectivities were compared for chlorides and thiocyanates, and no remarkable difference was observed. D_s for the permeation of alkaline earth metal salts across various blend films were smaller than those for alkali metal salts. A blend film containing 20 wt% of PCP was found to permeate l-phenylalanine about three times as fast as d-phenylalanine. The optical resolution of racemic phenylalanine by the permeation across the blend film was possible. With increasing content of PCP in the blend film, the urea permeability increased but the oxygen permeability decreased.     

Preparation and Oxygen Permeation Properties of BaCrOx Coated Ba0.5Sr0.5Co0.8Fe0.2O3- Tubular Membrane

Barium-chromium oxide (BaCrO_x) coated Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) tubular membranes were successfully prepared and evaluated for oxygen separation applications under high pressure–temperature conditions. The oxygen permeation flux was measured in accordance with the temperature, air pressure, and retentate flow rate, ranging from 750–950°C, 3–9 atm, and 200–1000 mL/min, respectively. The permeation testing on the BaCrO_x coated BSCF tubular membranes showed that the oxygen flux increased as the temperature, pressure, and retentate flow rate increased. The oxygen permeation flux was 5.7 mL/(min cm²) with temperature, pressure, and retentate flow rate of 900°C, 9 atm, and 1000 mL/min, respectively. The temperature dependence of the oxygen permeation process is further investigated, and the Arrhenius pre-exponential factor, as well as the apparent activation energy, is determined.     

Experimental validation of hybrid distillation‐vapor permeation process for energy efficient ethanol–water separation

BACKGROUND: The energy demand of distillation‐based systems for ethanol recovery and dehydration can be significant, particularly for dilute solutions. An alternative separation process integrating vapor stripping with a vapor compression step and a vapor permeation membrane separation step, termed membrane assisted vapor stripping (MAVS), has been proposed. The hydrophilic membrane separates the ethanol–water vapor into water‐rich permeate and ethanol‐enriched retentate vapor streams from which latent and sensible heat can be recovered. The objective of this work was to demonstrate experimentally the performance of a MAVS system and to compare the observed performance with chemical process simulation results using a 5 wt% ethanol aqueous feed stream as the benchmark. RESULTS: Performance of the steam stripping column alone was consistent with chemical process simulations of a stripping tower with six stages of vapor liquid equilibria (VLE). The overhead vapor from the stripper contained about 40 wt% ethanol and required 6.0 MJ of fuel‐equivalent energy per kg of ethanol recovered in the concentrate. Introduction of the vapor compressor and membrane separation unit and recovery of heat from both membrane permeate and retentate streams resulted in a retentate ethanol concentrate containing ca 80 wt% ethanol, but requiring only 2.2 MJ fuel kg^?1 ethanol, significantly less than steam stripping alone. CONCLUSION: Performance of the experimental unit with a 5 wt% ethanol feed liquid corroborated chemical process simulation predictions for the energy requirement of the MAVS system, demonstrating a 63% reduction in the fuel‐equivalent energy requirement for MAVS compared with conventional steam stripping or distillation. Published 2009 by John Wiley & Sons, Ltd.     

Effects of preparation conditions on the morphology and gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films

In this study, the effect of film preparation conditions on the gas permeation properties of polyethylene (PE) and ethylene vinyl acetate (EVA) films (containing 18 and 28 wt% vinyl acetate) was investigated. Film blowing and phase inversion methods were applied in the production of PE and EVA films, respectively. The permeation of pure oxygen and carbon dioxide gases was measured at room temperature. The results indicated that with the increase of PE film thickness, permeability and solubility of O₂ and CO₂ in these films decreased; but the diffusivities of gases through PE films increased. In addition, in the case of EVA copolymers, by increasing the content of vinyl acetate, the permeability of CO₂ increased. The rate of increase in CO₂ permeability was different for samples having different preparation conditions. For example, the samples prepared using chloroform as the solvent instead of THF, showed lower CO₂ permeability. Also, the morphological studying of film structure indicated that the higher CO₂ permeability for the samples made from THF solvent is due to the existing of higher porosity in the under layer polymer area. Also scanning electron microscopy (SEM) micrographs showed that with the usage of phase inversion method, there will be a thin dense layer near to the glass substrate.     

Effect of pressure drop on performance of hollow-fiber membrane module for gas permeation

The pressure drop mainly due to viscous friction inside hollow fibers is taken into consideration by nondimensionalization and numerical simulation of governing equations. For pure gas, the permeation pressure and velocity of actual situations with a viscous fluid deviate significantly from those of the corresponding inviscid or no-pressure-drop cases. The apparent permeability estimated from the relation of permeate flow rate and pressure difference is considerably underestimated in actual situations, and more severely for the region of small pressure difference and large module length. Numerical simulation shows that the estimated permeability behaves as if it were an increasing function of pressure difference for a constant permeability and roughly a constant for a dual-sorption-type permeability, respectively. For binary-mixture permeation the cut ratio and purity of permeate stream are mainly governed by two dimensionless parameters standing for pressure drop and permeability, respectively. The cut ratio and corresponding product composition are predictable without the rigorous simulation of the governing equations.     

Reduction of the Lactose Content of Skim Milk by Continuous Countercurrent Cascade Ultrafiltration

Abstract

Lactose was continuously removed from skim milk using two ultrafilters in series, with intermediate recycle. Reduced recycle flow rates at constant lactose stream (permeate product) flow rate resulted in slightly better removal of lactose from the milk feed, although this mode of operation increased the protein loss from the final milk retentate product. Increased permeate flow rate at constant recycle rate removed more lactose from the feed but also resulted in more loss of protein. However, at its maximum, the loss of protein reprented only about 6% of the nutritional value of the milk. Under the experimental conditions studied, 58% of the lactose in the original skim milk could be continuously removed for the best combination of recycle and permeate flow rates. The experimental values of flow rates and compositions were reasonably well predicted by a mathematical model of the process.     

Oxygen enrichment from air through multilayer thin low‐density polyethylene films

Several multilayer thin low‐density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 μm and an area of 130 cm². They were characterized for their oxygen‐enrichment performance from air by a constant pressure–variable volume method in a round permeate cell with an effective area of 73.9 cm². The relationship between oxygen‐enrichment properties, including oxygen‐enriched air (OEA) flux, oxygen concentration, permeability coefficients of OEA, oxygen, nitrogen, as well as separation factor through the multilayer LDPE films, and operating parameters, including transfilm pressure difference, retentate/permeate flux ratio, temperature, as well as layer number, are all discussed in detail. It is found that all of the preceding oxygen‐enrichment parameters increase continuously with an increase of transfilm pressure difference from 0.1 to 0.65 MPa, especially for the trilayer and tetralayer LDPE films. The oxygen concentration and separation factor appear to rapidly increase within the retentate/permeate flux ratio below 200, and then become unchangeable beyond that, whereas the OEA flux and the permeability coefficients of OEA, oxygen, and nitrogen seem to remain nearly constant within the whole retentate/permeate flux ratio investigated, especially for the monolayer and bilayer LDPE films. The selectivity becomes inferior, whereas the permeability becomes superior, as the operating temperature increases from 23 to 31°C. The highest oxygen concentration was found to be 44.8% for monolayer LDPE film in a single step with air containing oxygen of 20.9% as a feed gas and operating pressure of 0.5 MPa at a retentate/permeate flux ratio of 340 and 23°C. The results demonstrate a possibility to prepare an oxygen‐enriching membrane directly from air, based on the easily obtained thin LDPE films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3013–3021, 2002; DOI 10.1002/app.2331     

Oilfield Produced Water Treatment by Ceramic Membranes: Mass Transfer and Process Efficiency Analysis of Model Solutions

This work evaluated the performance of ceramic membranes in removing dispersed oil present in oilfield produced water, seeking to advance knowledge of the process, and identify the conditions for its application. The effect of the operating conditions and effluent characteristics were evaluated across a wide range, enabling establishment of operational limits for the permeation process. It was demonstrated that a flow regime corresponding to a Reynolds number (Re) greater than 6,000 does not imply significant improvements in membrane permeability. It was further found that the permeate flux exhibits a slight linear dependence with the salt concentration (C_S).     

Measurement of gas permeability of polymers. II. Apparatus for determination of permeabilities of mixed gases and vapors

A gas permeability apparatus has been constructed to facilitate the study of permeation of mixtures of gases and vapors. The apparatus utilizes the carrier gas method with gas-chromatographic analysis to determine individual permeation values and in-line thermal conductivity detectors to provide simultaneous overall diffusion and permeability data. The effects of film type, structure, and morphology on permeability may be studied from atmospheric to 100 psi feed pressure and from ambient to 300°C. Feed stocks may be custom mixed, and a vaporizing bath permits introduction of vapors either as contaminants or as primary permeants in an inert carrier. The experiments which illustrate the use of the equipment suggest that the noninteracting gases H₂ and CH₄ permeate a number of polymer films independently over a wide concentration range and that water vapor retards their permeation in polyimide films.     

Enrichment of helium by asymmetric hollow-fiber membrane of cellulose triacetate

The permeation behavior of pure He and separation characteristics of He–air mixtures were examined using asymmetric hollow-fiber-type membrane modules of cellulose triacetate. The module was operated in a feed-outside mode. In permeation of pure He, the permeation rate coefficients slightly increased with increasing upstream pressure, and they agreed fairly well with those calculated on the basis of the assumption that the permeate flow inside the fiber is governed by the Hagen-Poiseuille equation. In the single-stage hollow-fiber module used, the molar fraction of He in the permeate stream was increased to 0.99 and 0.999 at the stage cuts of lower than 0.3 when the molar fraction in the feed stream was 0.90 and 0.99, respectively. The molar fractions of He in the permeate stream were numerically evaluated for various combinations of operating conditions in terms of a countercurrent plug flow model. © 1994 John Wiley & Sons, Inc.     

Performance study on ultrafiltration of Kraft black liquor and membrane characterization using Spiegler-Kedem model

Ultrafiltration of Kraft black liquor was carried out by using an asymmetric membrane in a stirred batch cell, modified to work on a continuous mode. Spiegler-Kedem (SK) model from irreversible thermodynamics was used for the estimation of different membrane-solute parameters, like solute permeability (P_m) and reflection coefficient (Σ). The P_m andΣ so calculated from the above model were used to study the variation of these parameters with other process variables, like bulk concentration, pressure difference and stirrer speed. Finally, a simulation model was developed with the objective to predict permeate flux and rejection, which coupled the film theory, osmotic pressure model and SK model. The simulation results obtained from this study were validated with the experimental data using cellulose acetate membrane of 5,000 Da MWCO. Reasonably good agreements between the predicted and experimental values were observed and the average absolute deviation (AAD) for the prediction of flux and rejection using SK model was found to be 6.3%.     

Ultrafiltration of a Textile Plant Effluent

Abstract

This preliminary study was initiated to determine the feasibility of using ultrafiltration to remove dyes and other contaminants from industrial textile plant waste streams. Various runs were conducted on samples of the waste stream by using a lab-scale UF unit fitted with a polysulfone XM50 hollow fiber membrane. The effects of temperature and pressure on permeate flow rate and rejection coefficient were investigated. Spectrophotometric analysis was used to determine the rejection coefficients. The average rejection coefficients ranged from 30 to 90%. The permeate-to-feed ratios ranged from 1.4 to 15.2%. Increasing the pressure increased the permeate flow rate, but also decreased the rejection coefficient. The effect of temperature was inconclusive. Fouling varied with the waste solutions, but could be enough to clog the whole unit. The pH remained at the same value of 10 for the permeate, retentate, and feed in all the runs.     

Cyclic Operation of Forced Flow Electrokinetic Separation for Simultaneous Separation and Concentration of Charged Molecules

Abstract

A new cyclic operation of membrane separation in the presence of an electric field is developed. The microporous membrane/filter acts as a barrier between two adjacent solutions (i.e., the solution in the membrane cell and in the permeate). An electric field is applied across the membrane to induce electromigration of charged molecules whose molecular weights are much smaller than the molecular weight cutoff of the membrane used. The charged molecules move freely through pores of the membrane without hindrance. In the presence of an electric field, the concentration of charged molecules in the permeate stream is determined by the electromigration velocity and the permeation flow rate through the membrane. The permeation rate is controlled by the applied pressure drop, and the electro-migration velocity can be controlled by the electric field strength applied. By applying a high electric field and a low pressure drop, the concentration in the permeate stream can be increased, thus resulting in enrichment of the charged molecules in the permeate. By applying an electric field such that the electromigration is in the opposite direction to the permeation flow, the permeate is depleted of the charged molecules. A continuously supplied feed stream to the membrane cell can be processed into a concentrated solution and a depleted solution by alternating the polarity of an electric field. This paper presents the experimental results of a cyclic operation for the simultaneous separation/recovery and concentration of acetate, phenylalanine, glycine, and aspartic acid.     

Polystyrene photodegradation with a novel titanium dioxide/poly(ethylene oxide)/methyl linoleate paint photocatalyst system

The photodegradation of a polystyrene (PS) film was performed by a titanium dioxide (TiO₂)/poly(ethylene oxide) (PEO)/methyl linoleate (ML) paint photocatalyst system. The PS surface was catalytically photodegraded by the TiO₂/PEO component, and a conjugated carbon–carbon double bond was partially produced. A crosslinking reaction occurred between the PS carbon–carbon double bond and radical spices; as a result, the photodegradation diffusion into the inner region was blocked. The additional ML component certainly blocked the crosslinking reaction and accelerated the photodegradation rate. The fraction of less than 10,000 molecular weight of the 4‐h‐photodegaraded film with the TiO₂/PEO/ML paint was 15.1%, and its photodegradation yield increased four times compared with that with the TiO₂/PEO one. The weight loss values of the photodegraded PS part were 9.9, 10.7, and 11.7% at 4, 8, and 12 h, respectively, and gradually increased with increasing irradiation time. Some part of the film was violently photodegraded by the paint, and its photocatalytic effect lasted. The ML was graft‐polymerized into the film, and a phase separation was caused. The photodegradation behavior between the 0.05‐ and 0.1‐mm films was remarkably different; this showed that the diffusion of the ML radical was affected by the film thickness. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Production of a Highly Concentrated CaCO3 Suspension by Cross‐Flow Microfiltration in the Presence of a Dispersant

Abstract

This article presents the study of the cross‐flow microfiltration of an aqueous calcium carbonate suspension in the presence of dispersant in order to obtain the highly concentrated retentate. In the absence of a dispersant, the cross‐flow microfiltration with cylindrical ceramic membrane permitted to increase the CaCO₃ suspension concentration from 27 to 36.5%. The retentate concentration is increased markedly in the presence of the dispersant (up to 70%). In the presence of the dispersant, the productivity of cross‐flow microfiltration of CaCO₃ suspension is almost 30% higher than the productivity of dead‐end microfiltration of this suspension at the same pressure of 1 bar. However, the permeate contamination by the dispersant could not be avoided and a subsequent separation must be provided to purify the permeate.