Pervaporation Process Research Articles

Investigation into Ethanol Purification Using Polymeric Membranes and a Pervaporation Process

AbstractA comprehensive computational fluid dynamics simulation was developed for the rational design of a bioethanol purification system using a pervaporation process by tailoring the hydrodynamics of the process. The process involves the removal of water from a water/ethanol liquid mixture using a dense polymeric membrane. The model domain was divided into two compartments comprising the feed and the membrane. To describe water transport in the feed solution, the Maxwell‐Stefan approach was used, whereas for mass transfer inside the membrane the molecular diffusion mechanism was adopted. The governing equations were solved numerically by using a finite element method. The model was capable of predicting mass transfer along with momentum transfer in the feed and membrane compartments.

Development of a Scale-up Tool for Pervaporation Processes.

In this study, an engineering tool for the design and optimization of pervaporation processes is developed based on physico-chemical modelling coupled with laboratory/mini-plant experiments. The model incorporates the solution-diffusion-mechanism, polarization effects (concentration and temperature), axial dispersion, pressure drop and the temperature drop in the feed channel due to vaporization of the permeating components. The permeance, being the key model parameter, was determined via dehydration experiments on a mini-plant scale for the binary mixtures ethanol/water and ethyl acetate/water. A second set of experimental data was utilized for the validation of the model for two chemical systems. The industrially relevant ternary mixture, ethanol/ethyl acetate/water, was investigated close to its azeotropic point and compared to a simulation conducted with the determined binary permeance data. Experimental and simulation data proved to agree very well for the investigated process conditions. In order to test the scalability of the developed engineering tool, large-scale data from an industrial pervaporation plant used for the dehydration of ethanol was compared to a process simulation conducted with the validated physico-chemical model. Since the membranes employed in both mini-plant and industrial scale were of the same type, the permeance data could be transferred. The comparison of the measured and simulated data proved the scalability of the derived model.

Molecular Dynamics Simulation of Pervaporation of an Ethanol–Water Mixture on a Hybrid Silicon Oxide Membrane

A molecular-statistical method for simulating the process of pervaporation on hybrid silicon oxide membranes is proposed. This method is a development of the control volume method. Models of three membrane samples with different densities and pore sizes were obtained. These samples were used for the molecular-dynamics simulation of pervaporation of a 95 mol % aqueous solution of ethanol at a temperature of 343 K. It is shown that the membrane is selective with respect to water; the component flow is found to exponentially depend on the pore size.

A composable module-type cyanide microfluidic sensor based on polydimethylsiloxane membrane pervaporative sampling with sodium bicarbonate internal-pressure regulation and dual fluorescence/potentiometric monitoring

This paper demonstrates a reliable and safe microfluidic sensor on the monitoring of weak-acid dissociable cyanide (WAD-CN−) from environmental waters. The sensor chip consists of three parts: a pervaporative membrane sampling module, a fluorescence labelling/detection module and a cyanide ion selective-electrode (CN−-ISE) potential detection module. Cyanide pervaporation was achieved by in situ sample acidification to produce hydrogen cyanide (HCN) through a gas-diffusing polydimethylsiloxane (PDMS, 4–5 μm thickness) membrane. HCN was recovered using a lye solution and subsequently split into two streams for the dual fluorescence/potentiometric monitoring. Dual fluorescence and CN−-ISE potential monitoring were performed by applying two indispensable treatment to the split streams with naphthalene-2,3-dicarboxaldehyde (NDA)-glycine (Gly) and total-ionic-strength-adjustment buffer solution (TISAB), respectively. The parameters in the pervaporation process and both detections were optimized. To increase the sensitivity at low concentrations, a sodium bicarbonate solution was introduced into the sample stream as a chemical pressure regulator, which maintained a constant pressure in the channel by continuously producing CO2. To prevent the loss of produced gas, the channels, except for the membrane, were coated by a polyvinylsilazane (PVSZ) polymer solution and cured. Under an HCl donor stream (0.5 mol L−1; 15 μL min−1) and a sodium hydroxide acceptor stream (0.1 mol L−1; 20 μm/min), 65.7% of transmission rate (RSD = 0.86%; n = 3 for 0.1 mg L−1 CN−) was achieved. The pervaporative sampling method effectively minimized the interferences (except organic thiols) from the environmental matrices during the detection of cyanide in both detection modules. The validity and quality of the assay were assessed in terms of the linearity 5–500 μg L−1 (R2 = 0.9992) and limit of detection (cL) 0.015 μg L−1 with the fluorescence method and those are 2.6–1000 μg L−1 (R2 = 0.998), and 1.1 μg L−1 with the CN−-ISE potentiometric detection. The cyanide levels in waste waters were determined using the standard addition method and verified using the EPA method OIA-1677. Furthermore, a microchip electrophoresis (MCE) analysis was performed to investigate the systemic errors from the mercapto-interferences of the samples. The developed microfluidic sensor was applied to monitor WAD-CN− in waste waters. The sensor is a flexible, extensible, and environmentally friendly alternative for WAD-CN− monitoring.

Using of Artificial Neural Network and COMSOL Multiphysics for Modeling of Pervaporation Process

Using of Artificial Neural Network and COMSOL Multiphysics for Modeling of Pervaporation Process

Effects of structural crystallinity and defects in microporous Al-MOF filled chitosan mixed matrix membranes for pervaporation of water/ethanol mixtures

A new two-dimensional microporous metal organic framework (MOF), Al-MOF, [Al(OH)(MBA)] (CYCU-7, MBA = diphenylmethane-4,4′-dicarboxylate anion) and its reported analogue, [Al(OH)(SBA)] (CAU-11, SBA = 4,4′-sulfonyldibenzoate anion), have been synthesized using hydrothermal and solvothermal methods, respectively, and their structural crystallinities and defect porosities were carefully controlled and characterized by N2 sorption isotherms and 27Al solid-state nuclear magnetic resonance measurements. Interestingly, the MOF synthesized by the ethanol-based solvothermal method (CYCU-7) show a significant degree of linker-missing defects compared to that synthesized by the water-based hydrothermal method (CAU-11). We further incorporated the synthesized CYCU-7 and CAU-11 with chitosan (CS) biopolymer to make [email protected] and [email protected] mixed matrix membranes (MMMs) with the loading amount of MOF 2.5, 5.0, or 10 wt%. The as-prepared [email protected] and [email protected] MMMs were applied for separation of water/ethanol mixtures through the pervaporation process, and the effects of the structural properties (e.g. crystallinity and defects) of CYCU-7 and CAU-11 on the separation performance are studied. It is found that defect-rich [email protected] MMMs exhibit higher flux, while [email protected] MMMs with higher crystallinity exhibit a higher separation factor. In addition, the [email protected] MMM with 5.0 wt% loading of CAU-11 displays the best separation performance (separation factor = 2741 and flux = 458 g/m2 h).

A compositional model based on SAFT-VR and Maxwell-Stefan equations for pervaporative separation of aroma compounds from aqueous solutions

In this study, the SAFT-VR equation of state combined with the Maxwell-Stefan theory was employed to develop a mass transfer model for the pervaporation process. For this purpose, the SAFT-VR equation of state was used for thermodynamic modeling of the sorption step as one of the main steps of the mass transfer in the pervaporation process and the Maxwell-Stefan theory was applied to describe the transport of permeating compounds through the membrane. The Maxwell-Stefan diffusion coefficients were estimated based on the free volume theory. The model was then validated using the experimental data obtained from the sorption and pervaporative separation of volatile aroma compounds like 3-methyl butanal, isoamyl acetate and n-hexanol from their binary aqueous solutions with the polydimethylsiloxane (PDMS) membrane. The proposed model was successfully able to predict the influence of feed aroma concentration and operating temperature on the aroma and water partial fluxes and aroma separation factors. The predicted partial and total fluxes of 3-methyl butanal, isoamyl acetate and n-hexanol aqueous solutions showed good agreement with the measured fluxes at various feed aroma concentrations and operating temperatures. Therefore, the proposed mass transfer model based on the SAFT-VR and Maxwell-Stefan equations satisfactorily described the mass transport in the hydrophobic pervaporation process without the need of any adjustable parameters dependent on the sorption and pervaporation experiments.

Mechanistic Modeling of Organic Compounds Separation from Water via Polymeric Membranes

A mathematical model considering mass and momentum transfer was developed for simulation of ethanol dewatering via pervaporation process. The process involves removal of water from a water/ethanol liquid mixture using a dense polymeric membrane. The model domain was divided into two compartments including feed and membrane. For a description of water transport in the feed solution, Maxwell-Stefan approach was used, while for mass transfer inside the membrane the molecular diffusion mechanism was assumed. The governing equations were solved numerically using finite element method. The concentration profile inside the membrane showed a linear decrease and a parabolic fully developed velocity profile was obtained on the feed side. The results also confirmed that formation of concentration layer can be easily predicted using Maxwell-Stefan approach in dewatering of organic compounds using pervaporation process.

Modeling of the pervaporation process for isobutanol purification from aqueous solution using intelligent systems

ABSTRACTIn this study, intelligent systems (ANN-GA and GMDH) was employed to develope a model based on experimental data to predict the performance of the pervaporation process. The ANN system was coupled with the genetic algorithm (GA) to choose initial connection weights and biases of the multi-layer feed forward neural network (FFNN). The input parameters were the feed concentration, membrane thickness, and Reynolds number, while the outputs were total flux and permeate concentration. The RMSE of the estimated total flux for the ANN-GA and GMDH were 0.09170 and 0.0903, respectively. Also, the RMSE of estimated permeate concentration for the ANN-GA and GMDH were 0.0994 and 0.0975, respectively. The results indicated that the models had sufficient accuracy, but that GMDH could provide a better outcome. Finally, the relative importance of input variables on the network outputs was determined. Sensitive analysis showed that the membrane thickness and feed concentration are the most effect on the total flux and permeate concentration, respectively. Other variables also have important effect on the PV process and cannot be ignored.

Dehydration of waste cutting oil using a pervaporation process

Abstract A commercial polyvinyl alcohol (PVA)/polyacrylonitrile (PAN) hybrid membrane (B3 membrane) was tested to evaluate its ability to dehydrate waste cutting oil by pervaporation (PV). The major material and the water content of the waste cutting oil were analyzed by TGA, NMR, and Karl Fisher titrator. A preliminary PV experiment that involved treatment with 15 wt% aqueous diethylene glycol (DEG) was carried out at various temperatures, and 85 °C was found to be the optimal temperature. The separation factor increased from around 530 to 1140 and the total flux decreased from approximately 0.88 to 0.01 kg/m2/h as the water concentration in the feed solution decreased. Then, a PV experiment that involved treating the waste cutting oil was carried out at 85 °C and the obtained results were almost the same as those in the preliminary experiment, indicating that PV is an effective method for recycling waste cutting oil.

Enhanced butanol selectivity of pervaporation membrane with fluorinated monolayer on polydimethylsiloxane surface

A facile approach to fabricate fluorinated molecular monolayer on the surface of polydimethylsiloxane (PDMS) membrane was conducted using fluoroalkylsilane (FAS) as cross-linking agent. In detail, hydroxyl terminated PDMS were cross-linked with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane and cast on porous polysulfone support to prepare PDMS membranes. X-ray photoelectron spectroscopy showed that fluorinated alkyl chains were enriched at the surface of the membranes. Moreover, the surface fluorine concentration increased with the increasing of FAS and plateaued at around 55at% (close to that of FAS molecules) when the surface was fully covered by fluorinated monolayers. The surface hydrophobicity was proportional to the surface fluorine content as revealed by water contact angle measurement. When applied in pervaporation separation of 1wt% n-butanol/water mixture at 60°C, the membrane prepared with a FAS ethoxy to PDMS hydroxyl equivalents ratio of 35 (PDMS-FAS-35) exhibited a flux of 843g−2h−1 and an enhanced permeate n-butanol concentration of 34.3wt% compared with PDMS cross-linked with traditional TEOS (1375g−2h−1, 24.4wt%). The decrease of permeate flux was because of the reduced water partial flux without sacrificing the butanol partial flux on the consequence of water repellency of FAS monolayer. The results indicated that the FAS cross-linked PDMS could increase the separation efficiency of the membrane, thereby reducing the cost and energy consumption of the pervaporation process.

Pervaporative dehydration of ethanol/water mixture through hybrid alginate membranes with ferroferic oxide nanoparticles

Abstract Composite alginate membranes filled with various amount of iron ferroferric oxides (Fe3O4) and cross-linked by four different agents, i.e. calcium chloride (AlgCa), phosphoric(V) acid (AlgP), glutaraldehyde (AlgGA) and citric acid (AlgC) were prepared. Alteration of the separation performance related to the membrane’s composition was examined by the pervaporative dehydration process of water/ethanol mixture. The observed influence of the nature of chosen crosslinking agent and the contents of Fe3O4 on the transport parameters was discussed in detail. Among all the tested membranes, the alginate membrane loaded with 15 wt% of magnetite and crosslinked with phosphoric(V) acid (AlgP), showed the highest PSI of 33.86 kg·m−2·h−1·μm−1.

Biobutanol concentration by pervaporation using supported ionic liquid membranes

Abstract ABE fermentation uses anaerobic bacteria to produce acetone, butanol and ethanol from carbohydrates. Nowadays, ethanol is used as a petrol additive but butanol, due to its unique properties, can become a future biofuel. To recover n -butanol from the fermentation broth, pervaporation can be used. However, separation performance of pervaporation is limited by the polymeric membrane. This problem can be overcome by using an ionic liquid, immobilized in the active layer of the membrane. This paper investigates the performance of supported ionic liquid membranes (SILMs) employed for the pervaporative concentration of n- butanol. In the study, two ionic liquids (ILs), i.e. trihexyl(tetradecyl)phosphoniumtetracyanoborate (P 6,6,6,14 tcb) and 1-hexyl-3-methylimidazolium hexafluorophosphate (Im 6,1 hfp), were used. The ILs were immobilized with the help of polyether block amide (PEBA). To prevent the ionic liquids from leaching out, additional polymeric coating was necessary. For this purpose, an additional amount of PEBA was applied directly on the IL-PEBA layer. The pervaporation process was carried out at 29, 37 and 50 °C. The aqueous feed solution contained three organic components, i.e. acetone, butanol and ethanol in a 3:6:1 mass ratio. The concentration of butanol in the feed was 1.5, 3 and 5 wt%. It was found that the permeation fluxes as well as selectivity of the SILMs could be influenced by different ILs. The highest permeation flux, equal to 6,5 kg/(m 2 h), was observed for the membrane without an ionic liquid due to a higher water flux. However, the highest concentration of butanol in the permeate was achieved with the P 6,6,6,14 tcb membrane and the enrichment factor was found to be 14.93 while the selectivity for butanol in relation to water was equal to 8.34.

Fabrication and Characterization of Chitosan/Alginate Multilayer Composite Membrane Supported by a Porous Poly (Acrylonitrile) Substrate for Pervaporation Dehydration of Alcohol

Chitosan (CS) and alginate (Alg) are complementary in their membrane performance, but the combination of them is normally difcult to use due to their different solubilities. Layer-by-Layer deposition appears to be an effective method for improving the separation efciency of a composite membrane. In this work, the polyelectrolyte multilayer composite membranes (PEMCMs) were fabricated by depositing CS and Alg solutions alternatively onto a hydrolyzed porous poly(acrylonitrile) (PAN) substrate under a reduced pressure, as evidenced by Attenuated total reflectance Fourier transform infrared spectroscopy, contact angle and zeta potential measurement. Pervaporation results showed that the water selectivity increased while the flux decreased with the growth of CS/Alg-based polyelectrolyte layer. It was interesting that the sorption process dominated the pervaporation process when the numbers of polyelectrolyte layers were less than 7. However, the diffusion effect was more profound than the sorption effect as more than 8 polyelectrolyte layers were deposited on the PAN substrate. In particular, the prepared CS/Alg PEMCMs exhibited highly improved water selectivities towards alcohol/water mixtures, and a good compromise between flux and separation factor was observed when compared to other polyelectrolyte-based membranes. For separating 90% IPA/water mixtures at 60 oC, the (CS/Alg)4 composite membrane displayed a separation factor of 4491 and a flux of 596 g/m2.h, respectively. These results indicate that the fabricated CS/Alg composite membranes are excellent waterpermselective ones for alcohol dehydration.

Mixed matrix membranes applications: Development of a resistance-based model

In this study, a model for the prediction of the mass transport through ideal mixed matrix membranes (MMMs) for pervaporation and gas separation processes has been introduced. A Resistance-Based (RB) model was used in conjunction with a three-directional Finite Difference (FD) numerical solution to derive a semi-empirical model for calculating the effective permeability of ideal mixed matrix membranes. Predictions of the effective permeability obtained with the proposed model were compared with the estimated permeability for ideal MMMs using numerous analytical solutions such as Maxwell, Lewis-Nielsen, Bruggeman and Hennepe models. The extended RB model was theoretically able to predict accurately the effective permeability of ideal MMMs over a large range of filler volume fraction. Higher deviations were observed between the predictions of the extended RB model and the estimations of the majority of the other models in the case of MMMs containing higher permeable fillers and larger amount of filler material.

Polymeric Nanocomposite Membranes for Next Generation Pervaporation Process: Strategies, Challenges and Future Prospects.

Pervaporation (PV) has been considered as one of the most active and promising areas in membrane technologies in separating close boiling or azeotropic liquid mixtures, heat sensitive biomaterials, water or organics from its mixtures that are indispensable constituents for various important chemical and bio-separations. In the PV process, the membrane plays the most pivotal role and is of paramount importance in governing the overall efficiency. This article evaluates and collaborates the current research towards the development of next generation nanomaterials (NMs) and embedded polymeric membranes with regard to its synthesis, fabrication and application strategies, challenges and future prospects.

High performance pervaporative desalination of saline waters using Na-X zeolite membrane

A high quality Na-X zeolite membrane was synthesized on a seeded a-alumina disc by the secondary growth method. Structural characterization was done by X-ray spectroscopy, FT-IR spectroscopy, SEM and AFM imaging. The performance evaluation of the membrane was firstly tested in separation of glucose/water solutions by pervaporation process. There was obtained a separation factor 182.7+-8.8, while the flux through the membrane was 3.6+-0.3 kg m-2 h-1. The zeolite membrane was then used for desalination of aqueous solutions consisting of Na+, Ca2+, Cs+ and Sr2+ because of the importance of these ions in water and wastewater treatments. The effects of some parameters such as temperature and solution concentration on the desalination process were studied for investigating of diffusion/adsorption mechanism in membrane separation. Finally, high water fluxes ranged from 2 up to 9 kg m-2 h-1 were obtained and the rejection factors were resulted more than 95% for Na+ and Ca2+ and near to 99% for Cs+ and Sr2+. Based on the results, fluxes were significantly improved due to convenient passage of water molecules from large pores of NaX, while the fouling was declining dramatically. Based on the results, NaX zeolite can efficiently use for the removal of different cations from wastewaters.

Novel approach to determination of sorption in pervaporation process: a case study of isopropanol dehydration by polyamidoimideurea membranes

Development of novel membranes with optimal performance, selectivity, and stability is a key research area in membrane technology. In the present work aromatic polyamidoimideurea (PAIU) is synthesized and tested as promising membrane material for separation of water and alcohol mixtures. The PAIU membrane structure, density, and transport properties are studied. Mass transfer of water and isopropanol through the membrane is estimated by sorption and pervaporation tests to determine equilibrium sorption degree, diffusion coefficients, flux through the membrane, and separation factor. Two techniques of sorption study from liquid and from vapor phases are used as novel approach to experimental study of mass transfer. The vapor sorption calorimetry permits to analyze the behavior of the polymer material in sorption process. In pervaporation of water–isopropanol mixture, almost pure water mainly permeates through PAIU membrane. To improve the performance, a double layer membrane containing a thin PAIU layer on the surface of porous poly(phenylene oxide) support is developed. The double layer membrane is extremely effective in dehydration of isopropanol.

Performance of commercial composite hydrophobic membranes applied for pervaporative reclamation of acetone, butanol, and ethanol from aqueous solutions: Binary mixtures

Abstract In this study the efficiency of three various commercial membranes based on poly(octylmethyl siloxane), poly(ether-block-amide), and poly(dimethylsiloxane) polymers were investigated in pervaporative separation of acetone, butanol, and ethanol from aqueous binary solutions (0–5 wt% of organics) at 60 °C. The influence of fermentation broth microfiltration on membrane performances in pervaporative removal of ethanol was also investigated. The use of microfiltration improved the effectiveness of the removal of ethanol from the broth comparing with the unfiltered one. Molar ratios of organics to water fluxes and Pervaporative Separation Index (PSI) values were employed to discuss membranes' performance in removal of organic solvents from binary aqueous mixture. It was found that PDMS based (Pervap4060) membrane shows the best separation efficiency in all tested binary aqueous mixtures. Modelling of the process proved the feasibility of pervaporation process for the removal of acetone, butanol and ethanol from binary and quaternary aqueous mixtures.

Hydrothermal stability of silica, hybrid silica and Zr-doped hybrid silica membranes

Abstract Hybrid silica membranes have demonstrated to possess a remarkable hydrothermal stability in pervaporation and gas separation processes allowing them to be used in industrial applications. In several publications the hydrothermal stability of pure silica or that of hybrid silica membranes are investigated. To gain deeper insight into the mechanism of hydrothermal stability of silica-based membranes we report a comparison under identical conditions of the gas permeation performance of silica (TEOS), hybrid silica (BTESE) and Zr-doped BTESE (Zr-BTESE) membranes before and after hydrothermal treatments. First, a fast and straightforward hydrothermal stability test at 100 °C was applied to screen these membranes. The BTESE and Zr-BTESE membranes maintained their excellent performance after this test, though the TEOS membranes lost their selectivity. Second, hydrothermal tests under water gas shift (WGS) conditions were performed at different temperatures. No significant changes in permeance and selectivity were observed for BTESE derived membranes after a hydrothermal treatment at 300 °C. Surprisingly, a large reduction in carbon dioxide permeance was observed for Zr-BTESE hybrid silica membranes after a hydrothermal treatment at 200 or 300 °C, resulting in a significant increase of the H 2 /CO 2 permselectivity from 12 to 35.