UNIFICATION OF FRUIT WATER SORPTION ISOTHERMS USING ARTIFICIAL NEURAL NETWORKS

The chemical composition, water activity, temperature and equilibrium moisture content (EMC) for 10 selected fruits were determined. Two methods of water sorption modeling, the GAB equation and the artificial neural network (ANN) method, were compared for their ability to predict water sorption behavior. Unlike the GAB equation, which uses only physical data for modeling, the ANN method uses both physical and chemical compositional data to make predictions. The ANN was superior, in most cases, to that of the GAB equation, in predicting EMC. This superiority was due to the availability of the additional chemical compositional information. The ANN method could predict EMC with a mean relative error of 9.85% and a standard error (S _x ) of 1.59% EMC. The correlation coefficient (r ²) of the relationship between the actual and predicted values of equilibrium moisture content obtained by the ANN was 0.9938. The ANN model was able to show a temperature dependent crossing of water sorption isotherms, due to the dissolution of sugar crystals in the fruit. The ANN was also able to predict the extent of crossing, depending upon differences in the individual fruit chemical composition.     

Experimental study of vapor permeation of C5C7 alkane through PDMS membrane

Vapor permeation through dense membrane is regarded as an effectively way to separate volatile organic compounds (VOC) from industrial gas stream. This study proposes a new method to get the solubility and diffusivity of pure VOC vapor in dense membrane. C₅H₁₂, C₆H₁₄ and C₇H₁₆ were selected as sample VOC components to conduct newly developed sorption experiment with polydimethylsiloxane (PDMS) membrane. For each considered VOC component, its solubility was obtained from measured sorption equilibrium concentration in PDMS membrane, and its diffusivity was determined by fitting diffusion equation to the measured transient concentration of VOC component. The permeation behavior of VOCs in PDMS membrane was analyzed in terms of their solubility, diffusivity and permeability. Furthermore, the obtained solubility of these VOC components was utilized to get the vapor–membrane interaction parameters in UNIQUAC model. This opens an effective way to obtain the activity coefficient of VOC components for predicting their permeation performance in PDMS membrane.     

Investigations on the ability of di‐isopropanol amine solution for removal of CO2 from natural gas in porous polymeric membranes

In this study, capture of CO₂ and H₂S from natural gas mixture using porous polymeric membranes has been investigated numerically to assess the capacity of a novel absorbent, di‐isopropanol amine (DIPA), in CO₂ removal. Diffusion of acid gases through porous polymeric membranes was simulated by employing CFD techniques and considering a gas feed stream, a porous membrane and a reaction medium. For solving conservation equations, finite element method was applied to calculate the rate of CO₂ and H₂S absorption in the membrane. The type of membrane in this work is a hollow‐fiber module. According to the modeling results, a high H₂S removal can be achieved by DIPA absorber. Moreover, CO₂ was captured from natural gas in an efficient manner in low gas/liquid flow rates. POLYM. ENG. SCI., 55:598–603, 2015. © 2014 Society of Plastics Engineers     

Sorption and permeation behavior for a gas in glassy polymer membrane near the glass transition temperature

The deviation from the conventional dual-mode sorption and mobility model for a gas in glassy polymer membranes has separately been studied thus far, and to simulate sorption and diffusion behavior, an extended dual-mode sorption model and a modified dual-mode mobility model, respectively, have been proposed independently. However, simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in cases of CO₂in poly-4-methyl-1-pentene membrane at 20°C and in polystyrene membrane at 60 and 70°C. The plasticization effect of sorbed CO₂ on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed gas molecules exists. © 1996 John Wiley & Sons, Inc.     

Gas permeation in miscible homopolymer–copolymer blends. I. Poly(methyl methacrylate) and styrene/acrylonitrile copolymers

Gas transport properties in homogeneous blends of PMMA with each of two SAN random copolymers, containing 13.5 and 28% by weight of acrylonitrile respectively, have been measured at 35°C for He, H₂, O₂, N₂, Ar, CH₄, and CO₂. For all cases, the permeability and diffusion coefficients are higher than that expected from the semilogarthmic additivity rule. On the other hand, the solubility coefficients and the ideal gas separation factors follow this rule well. These results for PMMA/SAN blends differ from those observed recently for other miscible blend systems; however, they agree well with recent theories proposed to describe gas sorption and permeation behavior in polymer mixtures. The composition dependence of gas transport properties observed in PMMA/SAN blends is attributed to the very weak net interactions between PMMA and SAN produced by repulsions between styrene and acrylonitrile units in the SAN random copolymers. Gas transport properties in phase-separated PMMA/SAN blends have also been studied. The phase-separated blends show sorption and permeation properties very similar to the corresponding homogeneous blends which can be explained by an isotropic, interconnected, two-phase model proposed by Kraus and Rollmann. Gas permeabilities for the solution cast PMMA films used here are compared with melt-extruded specimens used previously, and the differences are attributed to molecular orientation.     

Pervaporation of methanol–water mixture by poly(γ-methyl L-glutamate) membrane and synergetic effect of their mixture on diffusion rate

The pervaporation behaviors of methanol–water by poly(γ-methyl L -glutamate) (PMLG) membrane at non-steady- and steady-state permeation were investigated. The values of t_1/2 (time required to reach a half value of steady-state permeation flux) for methanol and water changed and did not change with the component in feed, respectively. Both of the average diffusion coefficients for methanol–and water–PMLG from the mixture changed exponentially with the sorption amount of methanol by the synergetic effect on diffusion. The difference in behavior of non-steady and steady state diffusion was explained by whether D_o (diffusion coefficient at zero penetrant concentration) was influenced by the concentration distribution of penetrant in PMLG membrane.     

Mathematical modeling of solid oxide fuel cells at high fuel utilization based on diffusion equivalent circuit model

Mass transfer and electrochemical phenomena in the membrane electrode assembly (MEA) are the core components for modeling of solid‐oxide fuel cell (SOFC). The general MEA model is simply governed with the Stefan‐Maxwell equation for multicomponent gas diffusion, Ohm's law for the charge transfer and the current‐overpotential equation for the polarization calculation. However, it has obvious discrepancy at high‐fuel utilization or high‐current density. An advanced MEA model is introduced based on the diffusion equivalent circuit model. The main purpose is to correct the real‐gas concentrations at the triple‐phase boundary by assuming that the resistance of surface diffusion is in series with that of the gaseous bulk diffusion. Thus, it can obtain good prediction of cell performance in a wide range by avoiding the decrement of effective gas diffusivity via unreasonable increment of the electrode tortuosity in the general MEA model. The mathematical model has been validated in the cases of H₂? H₂O, CO? CO₂ and H₂? CO fuel system. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Permeation through CO2selective glassy polymeric membranes in the presence of hydrogen sulfide

Minor components present in feed gas streams can have a significant influence on the separation performance of polymeric membranes. Hydrogen sulfide is present in many of the processes where CO₂ capture is possible and can therefore undergo competitive sorption with CO₂ for transport through the membrane, as well as influence the membrane morphology inducing plasticization. This study investigates the change in CO₂ permeability and CO₂/N₂ selectivity of two glassy polymeric membranes; polysulfone and 6FDA‐TMPDA, when 500 ppm H₂S is present in the gas mixture. The outcomes of this study reveal that H₂S in trace amounts has a strong influence on the separation performance of both membranes. For both membranes, a plasticization partial pressure ～0.5–0.6 kPa H₂S is observed. H₂S competitive sorption is also observed and is modeled by competitive dual‐sorption theory. Results suggest that mixed gas permeation influences the amount of each gas immobilized within the Langmuir voids in addition to the expected competitive sorption effects. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

H2S absorption at high pressure using hollow fibre membrane contactors

In this article, the removal of H₂S from natural gas at high pressure using hollow fibre membrane contactors and water as the absorbent solvent was described and validated by a 2D comprehensive mathematical model. The modelling predictions were in a good agreement with the experimental data at low pressure of 1 bar under non-wetting conditions. However, the experimental behaviour at high pressure in the range of 10–50 bar was always lower than the modelling predictions. And thus, a sensitivity analysis was carried out to study the influence of gas, liquid, membrane diffusion and solubility coefficients of H₂S at high pressure upon the modelling behaviour compared with the experimental trend. The modelling results confirmed that these parameters were still insensitive as the model predictions changed slightly with altering these coefficients. Conversely, membrane wetting was confirmed to be an important factor even for small ratios, i.e. pseudo-wetting (1–3%). The model was able to predict the absorption of H₂S at higher pressures under 3% pseudo-wetting. Although the type of membranes used in this study was highly hydrophobic (ePTFE) and thus membrane wetting was not expected, pseudo-wetting phenomenon was confirmed to be an important factor at high pressure.     

Theoretical investigation of a water‐gas‐shift catalytic membrane for diesel reformate purification

The novel application of a catalytic water‐gas‐shift membrane reactor for selective removal of CO from H₂‐rich reformate mixtures for achieving gas purification solely via manipulation of reaction and diffusion phenomena, assuming Knudsen diffusion regime and the absence of hydrogen permselective materials, is described. An isothermal, two‐dimensional model is developed to describe a tube‐and‐shell membrane reactor supplied with a typical reformate mixture (9% CO, 3% CO₂, 28% H₂, and 15% H₂O) to the retentate volume and steam supplied to the permeate volume such that the overall H₂O:CO ratio within the system is 9:1. Simulations indicate that apparent CO:H₂ selectivities of 90:1 to >200:1 at H₂ recoveries of 20% to upwards of 40% may be achieved through appropriate design of the catalytic membrane and selection of operating conditions. Under these conditions, simulations predict an apparent hydrogen permeability of 2.3 × 10^?10 mol m^?1 Pa, which compares favorably against that of competing hydrogen‐permselective membranes. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4334–4345, 2013     

UNIFICATION OF FRUIT WATER SORPTION ISOTHERMS USING ARTIFICIAL NEURAL NETWORKS

The chemical composition, water activity, temperature and equilibrium moisture content (EMC) for 10 selected fruits were determined. Two methods of water sorption modeling, the GAB equation and the artificial neural network (ANN) method, were compared for their ability to predict water sorption behavior. Unlike the GAB equation, which uses only physical data for modeling, the ANN method uses both physical and chemical compositional data to make predictions. The ANN was superior, in most cases, to that of the GAB equation, in predicting EMC. This superiority was due to the availability of the additional chemical compositional information. The ANN method could predict EMC with a mean relative error of 9.85% and a standard error (S_x) of 1.59% EMC. The correlation coefficient (r²) of the relationship between the actual and predicted values of equilibrium moisture content obtained by the ANN was 0.9938. The ANN model was able to show a temperature dependent crossing of water sorption isotherms, due to the dissolution of sugar crystals in the fruit. The ANN was also able to predict the extent of crossing, depending upon differences in the individual fruit chemical composition.     

Measurement and prediction of diffusion coefficients of supercritical CO2 in molten polymers

The solubility and diffusivity of supercritical carbon dioxide (sc‐CO₂) in low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polypropylene (PP), ethylene‐ethylacrylate copolymer (EEA) and polystyrene (PS) were measured at temperatures from 150°C to 200°C and pressures up to 12 MPa by using the Magnetic Suspension Balance (MSB), a gravimetric technique for gas sorption measurements. The solubility of CO₂ in each polymer was expressed by Henry's constant. The interaction parameter between CO₂ and polymer could be obtained from the solubility data, and it was used to estimate the Pressure‐Volume‐Temperature relationship and the specific free volume of polymer/CO₂ mixtures. The diffusion coefficients were also measured by the MSB for each polymer. The resulting diffusion coefficients were correlated with the estimated free volume of polymer/CO₂ mixture. Combining Fujita's and Maeda and Paul's diffusion models, a model was newly developed in order to predict diffusion coefficients for the polymers studied. Polym. Eng. Sci. 44:1915–1924, 2004. © 2004 Society of Plastics Engineers.     

Mathematical modeling of mass transfer in multicomponent gas mixture across the synthesized composite polymeric membrane

This study presents a new mathematical model to investigate the ternary gas mixture permeation across a synthesized composite PDMS/PA membrane. A novel algorithm is introduced for direct determination of diffusion coefficients. It pertains to study gas permeation through concentration dependent systems and comparing with traditional time lag method confirms the precision of this approach. Feature is that this method does not require physical properties of the membrane. Accordingly, it can be used as a general comprehensive model. In addition, molecular pair and molecular trio interactions were taken into account and in order to investigate the deviation of gas mixture from ideality, fugacities were calculated. The results showed that permeabilites of H₂ and CH₄ increase with increasing feed temperature and fugacity, while that of C₃H₈ decreases. Moreover, increasing C₃H₈ concentration improved permeation properties of all components. The results demonstrated that considering the concentration dependent system (CDS) leads to the small deviation of about less than 10%, while the deviation of 50–100% by the concentration independent system (CIS) was acquired. Additionally the results indicated that permeability of the lighter gases is specially affected by diffusivity, while solubility is dominant on permeability of the heavier gases.     

Pervaporation of benzene–cyclohexane mixture by poly(γ-methyl L-glutamate) membrane and synergetic effect of their mixture on diffusion rate

The pervaporation of binary liquids mixture of benzene and cyclohexane was examined by use of poly(γ-methyl L -glutamate) (PMLG) membrane. The permeation rate–time curve for each of benzene and cyclohexane from their mixtures changed to the longer times side by increasing the cyclohexane in the mixtures. t_1/2 (the time required to reach a half-value of the steady state permeation rate) for the each component increased exponentially with increasing of cyclohexane, which has a smaller plasticizing effect on PMLG membrane than benzene, in the mixtures. The apparent diffusion coefficients, obtained from the steady state permeation and the sorption experiments, for benzene–PMLG and cyclohexane–PMLG are dependent exponentially on the sorbed amounts of benzene. This result was explained on the bases that the diffusion of cyclohexane was enhanced synergetically with benzene coexisting in the system. This effect influenced negatively the separation of the liquids mixture by pervaporation.     

The Recovery of Hydrogen from Binary Gas Mixtures Using a Membrane Module Based on a Palladium Foil Taking into Account the Deactivation of the Membrane

The recovery of hydrogen from binary gas mixtures with active (deactivating the surface of the membrane) and passive impurities has been studied. Experiments have been carried out on a multifunctional membrane module, the operating area of which consists of gas chambers separated by a thin foil palladium membrane. A dimensionless coefficient of the deactivation of the surface of the membrane has been introduced. An analytical formula has been obtained for the hydrogen flux from binary mixtures at its preset pressures on the opposite sides of the membrane that takes into account adsorption–desorption, breaking to protons on the surface, the diffusion of the latter in the metal lattice, and the recombination of Н⁺. In the case when the condition are fulfilled, the Н₂ flux can be calculated by the modifiable Sieverts equation. This equation and an assumption about the complete mixing of the mixtures in the chambers of the membrane module have made it possible to develop a theoretical model for the recovery of hydrogen from binary mixtures in the membrane module. An analytical dependence for the Н₂ flux as a function of the fluxes of the mixtures at the inlet of the chambers, ratio of the pressures on the opposite sides of the membrane, initial composition of the hydrogen mixture, and the coefficient of deactivation has been found. Utilizing this dependence, a procedure for finding this coefficient using additional experiments has been proposed. As an example, the coefficients of deactivation for the products of steam reforming of methane (CO, СО₂, СН₄, and water vapor) have been calculated for a palladium membrane with a composition Pd–6%Ru. The theoretical model has been subjected to the experimental verification on Н₂–5%CO and Н₂–20%CO binary mixtures.     

Study of transport of pure and mixed CO2/N2 gases through polymeric membranes

The permeations of pure CO₂ and N₂ gases and a binary gas mixture of CO₂/N₂ (20/80) through poly(dimethylsiloxane) (PDMS) membrane were carried out by the new permeation apparatus. The permeation and separation behaviors were characterized in terms of transport parameters, namely, permeability, diffusion, and solubility coefficients which were precisely determined by the continuous‐flow technique. In the permeation of the pure gases, feed pressure and temperature affected the solubility coefficients of CO₂ and N₂ in opposite ways, respectively; increasing feed pressure positively affects CO₂ solubility coefficient and negatively affects N₂ solubility coefficient, whereas increasing temperature favors only N₂ sorption. In the permeation of the mixed gas, mass transport was observed to be affected mainly by the coupling in sorption, and the coupling was analyzed by a newly defined parameter permeation ratio. The coupling effects have been investigated on the permeation and separation behaviors in the permeation of the mixed gas varying temperature and feed pressure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 179–189, 2000     

Rolltruded Poly(Aryl Ether Ether Ketone) (PEEK) for Membrane Applications

Abstract

An investigation of the transport and separation of several permanent gases (CO₂, N₂, CH₄, and H₂) and vapors (H₂O and ethanol) in unprocessed and rolltruded poly(aryl ether ether ketone) (PEEK) thin films has been conducted to evaluate PEEK for membrane applications requiring thermally and chemically stable materials. Transport coefficients and separation factors have been determined at permeation temperatures ranging from 40 to ca. 180°C. The gas transport coefficients were found to increase by up to 30% depending on the processing conditions. Actual separation factors, determined for a CO₂/N₂ gas mixture (24.6 vol% CO₂), were depressed slightly in comparison to the ideal values obtained from pure component data. In contrast, water and ethanol vapor permeabilities declined between 10 and 15% as a result of processing. For a 39.1 wt% vapor mixture of H₂O in EtOH, ideal and actual separation factors, determined at 130°C, were in good agreement. In contrast, order of magnitude improvements in the actual versus ideal separation factors were found for 11.7 and 7.6 wt% mixtures of H₂O in EtOH in both unprocessed and rolltruded PEEK. A comparison with other membranes considered for high temperature vapor dehydrations suggests that PEEK may be an excellent polymer for these applications.     

Gas permeation in miscible homopolymer-copolymer blends: II. Tetramethyl bisphenol-A polycarbonate and a styrene/acrylonitrile copolymer

Gas sorption and transport properties for He, H₂, O₂, N₂, Ar, CH₄, and CO₂ at 35°C near atmospheric pressure have been obtained for miscible blends of tetramethyl bisphenol-A polycarbonate (TMPC) and a random copolymer of styrene with acrylonitrile (SAN) containing 9.5% by weight of acrylonitrile. All gas permeability, diffusion, and solubility coefficients obtained are lower than that calculated from the semilogarithmic additivity rule. These results are qualitatively interpreted by ternary solution theory and activated state theory which have been proposed to describe gas sorption and diffusion in miscible blends. The negative deviation of gas permeabilities for the blends from this rule can be explained semiquantitatively by free volume theory which takes volume contraction on mixing into account. The negative deviation increases with gas molecular size which results in larger ideal gas separation factors than that calculated from the additivity rule. For He/CH₄ and H₂/CH₄ pairs, the permselectivities for the blends are higher than that for either pure TMPC or SAN. The deviation from additivity for gas transport properties of TMPC/SAN blends is the opposite of that observed in the first paper of this series for PMMA/SAN blends. This can be attributed to the stronger interactions in TMPC/SAN blends than in PMMA/SAN blends.     

An extension of the group contribution method for estimating thermodynamic and transport properties part II. Polyatomic gases (F2, Cl2, CS2, H2S, NO and N2O)

Earlier work on the group contribution method applied to the Kihara potential is extended to polyatomic gases for the calculation of second virial coefficients, viscosities and diffusivities of dilute gases with a single set of gas group parameters. Functional group parameters are evaluated from the simultaneous regression of second virial coefficient and viscosity data of pure gases. Parameters for gas groups (F₂, Cl₂, CS₂, H₂S, NO, nd N₂O) are found to provide good predictions of second virial cross coefficients, mixture viscosities and binary diffusion coefficients of gas-gas mixtures. Application of the model shows that second virial coefficient data can be represented with good results comparable to the values by means of the corresponding states model. The reliability of the present model in viscosity predictions is proved by comparison with the Lucas method. Predictions of binary diffusion coefficients are in excellent agreement with experimental data and compare well with values obtained by means of the Fuller method.     

Influence of a monomeric plasticizer on the water-sorption behaviour of food-grade plastics packaging materials

The interaction of water with poly(vinylchloride) and poly(vinylidene chloride-vinylchloride) (p(VdC-VC)) plasticized with different amounts of a monomeric plasticizer (dioctylphthalate) has been studied using inverse gas chromatography. The present work was focused on the effect of temperature and plasticizer content on the water sorption behaviour of these plastics packaging materials. Values for thermodynamic parameters such as Gibb's free energy (ΔG_s), enthalpy (ΔH_s), entropy (ΔS_s) and activity coefficient (γ) corresponding to sorption of water by the polymers have been calculated using chromatographic retention data. It was found that the sorption of water vapours increases with increasing the amount of plasticizer and decreases with increasing temperature. The Van Deemter equation was found to be applicable to these systems and was used to determine diffusion coefficients and activation energies for diffusion. Diffusion coefficient values increase with increasing amounts of plasticizer and they also increase with increasing temperature; this latter increase is accompanied by a decrease in the activation energy for diffusion. Present results were also compared to our own previous data, using a polymeric plasticizer.