Pervaporation Separation Process Research Articles

Rigid-flexible coupled organosilica membranes toward high-efficiency molecules separation

Membrane-based technology has garnered significant interest in the separation and purification of molecules due to its inherent advantages, such as high efficiency, low energy consumption, and ease of operation. In this study, rigid-flexible coupled organosilica membranes were fabricated through co-polymerization using 1,2-bis(triethoxysilyl)acetylene (BTESA) containing rigid acetylene bridges and 1,2-bis(triethoxysilyl)propane (BTESP) containing flexible propane bridges. The incorporation of flexible propane bridges into BTESA networks allowed for precise adjustment of the network structures, resulting in composite BTESA-P membranes with improved molecular sieving properties. BTESA-P membrane demonstrated significant promise for applications in both CO2 capture and pervaporation (PV) dehydration due to its high potential. BTESA-P30 membrane, fabricated using the rigid-flexible coupled strategy, demonstrated a CO2 permeance of 3807 GPU and a CO2/N2 selectivity of approximately 40. These results surpassed those of numerous previously reported membranes, indicating significant potential for CO2 capture applications. BTESA-P30 membrane exhibited significant competitiveness in the decarbonization process of natural gas. More significantly, analogous occurrences are evident in gas permeation and PV separation process, where the permeation mechanism of gas and PV separation is primarily governed by molecular sieving. The utilization of diverse organosilica precursors in the rigid-flexible coupled strategy proposed in this study offers increased potential for membrane structure design and energy-efficient separation of molecules.

Co-gallate MOF Membrane for Efficient Pervaporation Separation of MeOH from MTBE

The pervaporation (PV) technology is attractive for azeotrope component separation of the MeOH/MTBE mixture due to the reduced energy and cost relative to the traditional ternary distillation process. However, the membrane separation performance is largely affected by its microstructure including pore size and shape as well as its surface properties such as hydrophilicity. Herein, we report a Co-gallate MOF membrane that features preferential adsorption and diffusion of methanol (MeOH) relative to the methyl tert-butyl ether (MTBE) molecules during the PV separation process. The high-quality Co-gallate MOF membrane has been prepared by introducing a regulator of KOH. The MeOH flux of the Co-gallate MOF membrane was 0.565 kg m−2 h−1 and the separation factor was up to 721 at 15 wt% MeOH/MTBE feed composition. It is worth noting that the separation performance exceeds most of the reported membrane materials for MeOH/MTBE separation in the PV process. Furthermore, the separation performance of the Co-gallate MOF membrane for MeOH/MTBE mixtures remained almost unchanged over 70 h, indicating the reliable long-term stability of the membrane. Thus, the Co-gallate MOF membrane demonstrated a potential practical application for MeOH/MTBE separation.

Cellulose nanofiber and halloysite nanotubes embedded polyvinyl alcohol membranes for pervaporation dehydration of epichlorohydrin–isopropanol–water ternary feed mixture

AbstractThe dehydration of epichlorohydrin (ECH)–isopropanol (IPA)–water mixtures was conducted by using pervaporation separation process. Two types of crosslinked polyvinyl alcohol (PVA) membranes, PVA‐Glu and PVA‐TEOS, were prepared using glutaraldehyde (Glu) and tetraethyl ortho silicate (TEOS), then mixed with cellulose nanofiber (CNF) and halloysite nanotube (HNT) fillers, respectively. They characterized using field emission scanning electron microscopy to observe surface morphology, Fourier‐transform infrared spectroscopy to study the filler–polymer interactions and chemistries of membranes, and X‐ray diffraction experiment for the analysis of membrane crystallinity. Finally, a pervaporation test was carried out to dehydrate the ECH–IPA–water feed solution at the azeotropic feed composition. From the result, the membrane of PVA‐Glu, including 4% w/w CNF filler, showed a flux of 0.17 kg (m2h)−1 and a separation factor of 456. However, the membrane of PVA‐TEOS with 5% w/w HNTs filler indicated a flux of 0.15 kg (m2h)−1 and a separation factor of 4158. The higher pervaporation performance of the HNTs‐added PVA‐TEOS membrane is attributed to the smaller size and more porous nature of HNTs than CNFs.

Breakthroughs on tailoring membrane materials for ethanol recovery by pervaporation

• Mixed matrix membranes (MMMs) with well-designed membrane structures may provide both high permeability and membrane selectivity to break trade-off effect due to the better control over physi-/chemical micro-environment and cavity/pore size as well as size distribution. • Fillers should be orderly arranged in polymer matrix and form continuous transport channels for ethanol to full play the synergistic effect of polymer and fillers. • Building firm bonding interactions between filler and polymer is one of the most promising methods to strengthen the PV performance of MMMs. • The development of bioinspired materials and structures provides enlightening ideas for the construction of ethanol perm-selective membranes. Bioethanol, as a clean and renewable fuel, has gained increasing attention due to its major environmental benefits. Pervaporation (PV) is a promising and competitive technique for the recovery of ethanol from bioethanol fermentation systems due to the advantages of environmental friendliness, low energy consumption and easy coupling with fermentation process. The main challenge for the industrial application of ethanol perm-selective membranes is to break the trade-off effect between permeability and selectivity. As membrane is the heart of the pervaporation separation process, this article attempts to provide a comprehensive survey on the breakthroughs of ethanol perm-selective PV membranes from the perspectives of tailoring membrane materials to enhance PV separation performance. The research and development of polymeric and organic/inorganic hybrid membranes are reviewed to explore the fundamental structure-property-performance relationships. It is found that mixed matrix membranes with well-designed membrane structures offer the hope of better control overphysi-/chemical micro-environment and cavity/pore size as well as size distribution, which may provide both high permeability and membrane selectivity to break the trade-off effect. The tentative perspective on the possible future directions of ethanol perm-selective membranes is also briefly discussed, which may provide some insights in developing a new generation of high-performance PV membranes for ethanol recovery.

Review of Pervaporation and Vapor Permeation Process Factors Affecting the Removal of Water from Industrial Solvents.

A recent review article (J Chem Technol Biotechnol 94: 343-365 (2019)) identified several commercially-available permselective materials for drying organic solvents with pervaporation (PV) and vapor permeation (V·P) separation processes. The membrane materials included polymeric and inorganic substances exhibiting a range in the performance characteristics: water permeance, water/solvent selectivity, and maximum use temperature. This paper provides an overview of the factors affecting the design of PV/V·P processes utilizing these membranes to remove water from common organic solvents. Properties of the specific membrane and of the solvent substantially affect the PV/V·P separation. Equally important is the impact of operating parameters on the overall separation. To study these impacts, simplified process performance equations and detailed spreadsheet calculations were developed for single-pass and recirculating batch PV systems and for single-pass V·P systems. Estimates of membrane area, permeate concentration, solvent recovery, permeate condenser temperatures, and heating requirements were calculated. Process variables included: solvent type, water permeance, water/solvent selectivity, initial and final water concentrations, operating temperature (PV) or feed pressure (V·P), temperature drop due to evaporation (PV) or feed-side pressure drop (V·P), and permeate pressure. The target solvents considered were: acetonitrile, 1-butanol, N,N-dimethyl formamide, ethanol, methanol, methyl isobutyl ketone, methyl tert-butyl ether, tetrahydrofuran, acetone, and 2-propanol.

Zeolitic imidazolate framework membranes for gas and water purification

Zeolitic imidazolate frameworks (ZIF) have a flexible structure, controllable pore size, and thus adjustable properties, which make them effective materials for membrane separation. They have been used as a pure membrane in about 55% of cases, and as a structure modifier of mixed matrix membranes in other cases. ZIF-based membranes have been applied in pervaporation, nanofiltration, reverse osmosis and gas separation processes. This manuscript reviews the role of ZIF in promoting the membrane performance. A new performance parameter is defined based on permeability and selectivity, in order to compare the results of published reports. Findings show that the presence of ZIF in mixed matrix membranes improves the performances of pervaporation by 70%, nanofiltration by 211%, and reverse osmosis by 30%. ZIF also improved 11 times the membrane performance in gas separation, compared to the raw membrane.

Novel thin-film composite pervaporation membrane with controllable crosslinking degree for enhanced water/alcohol separation performance

Thin-film composite (TFC) pervaporation membranes is of widespread interest for the alcohol dehydration, since the thin selective layer allows a high permeation flux. However, how to obtain the desired flux and separation selectivity simultaneously is still the bottleneck of industrial application with pervaporation technology. In this study, a novel ultrathin multi-layer polyurea or polyamide pervaporation membrane was designed and assembled via layer-by-layer (LBL) interfacial polymerization (IP) method on the hydrolyzed polyacrylonitrile (HPAN) substrate membrane. During the LBL assembly process, the controllable crosslinking degree of the separation layer formed through changing the concentration of the oil phase monomer while remaining the concentration of the aqueous phase monomer constant based on the solution-diffusion mechanism of pervaporation separation process. The surface characterization revealed that the tris(2-aminoethyl) amine (TAEA)1.5-toluene 2,4-diisocyanate (TDI)1-0.5-0/HPAN composite membrane exhibited much rougher surface than that of the membranes with the same crosslinking degree. The optimized composite membrane exhibited a high separation factor of 844.6 with a desirable permeation flux of 1284.3 g·m−2·h−1 for the pervaporation dehydration 95 wt% ethanol aqueous solution at 80 °C, which was 10-fold increase of separation factor compared with the control membrane. Moreover, the excellent operation stability of the TFC membrane demonstrated the promising prospect for the alcohol dehydration separation. This preparation methodology has potential application in other membrane separation process on the basis of solution-diffusion mechanism, such as gas separation and reverse osmosis membrane.

Optimization of the in situ recovery of butanol from ABE fermentation broth via membrane pervaporation

Butanol produced via the ABE fermentation is plagued with low final concentrations and low yield. The selective removal of butanol from the fermentation broth by integrating a separation process to the fermenter for the in situ recovery of butanol has been proposed by many researchers. In this investigation, the integration of a membrane pervaporation separation process with the continuous ABE fermentation system has been simulated and optimized using a multi-objective genetic algorithm. The ABE fermentation model proposed by Mulchandani and Volesky was used and the multi-objective optimization problem was defined to simultaneously maximize the butanol productivity, the overall butanol concentration and the sugar conversion. The three objective functions, if non-dominated, define the Pareto domain of the optimization problem along with the four decision variables, namely the dilution rate, the feed sugar concentration, the cell retention factor and the membrane surface area. The optimal solutions of the integrated process for two different pervaporation membrane models were compared to the stand-alone continuous fermentation. By adding an in situ separation system to the continuous ABE fermentation, the optimal butanol productivity and overall butanol concentration increased by approximately 250% compared to those of the non-integrated fermenter. Furthermore, the sugar conversion also increased.

Study on CO2 Desorption Behavior of a PDMS-SiO2 Hybrid Membrane Applied in a Novel CO2 Capture Process.

In this present work, a novel approach has been proposed by which a solvent absorption and membrane desorption methods can significantly reduce the carbon dioxide (CO2) emission and energy consumption. In this method, the CO2 capture processing is based on the combination of membrane and physical solvent. Here, dimethyl carbonate and polydimethylsiloxane (PDMS)-SiO2 nanocomposite were used as the physical solvent and desorption membrane, respectively. However, the main focus of this research was on the CO2 desorption behavior of PDMS-SiO2 hybrid membrane. To do so, the influence of the operating conditions and membrane properties on the pervaporation process to capture CO2 have been investigated. The PDMS-SiO2 hybrid membrane containing 10 wt % SiO2 was the most effective membrane. Results revealed that increase in CO2 concentration from 1.5 to 3 wt % led to decrease in the selectivity from 94 to 47 and increase in flux from 1.7 to 5.38 (kg/m2·h). In addition, an increase in temperature increased the flux and reached the highest level (8.17 kg/m2·h) at 40 °C. However, the selectivity decreased to 36.13. It was found that the addition of SiO2 nanoparticles to the PDMS membrane not only enhanced the membrane performance but also decreased the energy consumption about 75% compared with gas stripping method and mass transfer about 49% compared with pure PDMS membrane. Finally, these results illustrated that such a novel technique used for pervaporation separation process is a green and promising alternative to separate CO2 from the physical solvent.

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.

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.

Graphitic carbon nitride nanosheets embedded in poly(vinyl alcohol) nanocomposite membranes for ethanol dehydration via pervaporation

Abstract Graphitic carbon nitride (g-C 3 N 4 ) is an innovative soft two-dimensional (2D) nanomaterial. Due to its lamellar structure, similar to graphite layers, g-C 3 N 4 has attracted significant interest as a new class of filler for the fabrication of novel polymeric nanocomposite membranes. In this study, highly water-selective hybrid membranes with excellent water/ethanol separation performance and superior water channels were fabricated by incorporating g-C 3 N 4 nanosheets into a poly(vinyl alcohol) (PVA) matrix. g-C 3 N 4 was synthesized via thermal oxidation “etching”, using melamine as a precursor. The ultrathin and nanoporous structures formed were characterized through transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. Due to the strong interfacial interactions among g-C 3 N 4 , succinic acid (Sa) and the PVA matrix, the hybrid nanocomposite membranes showed both high swelling resistance and mechanical stability. Furthermore, the addition of g-C 3 N 4 can significantly improve the membrane’s hydrophilicity and heat-resistance properties. Importantly, membrane permeability improved greatly because the ordered alignment and the regular pore structure of g-C 3 N 4 resulted in ordered water channels for rapid transportation of water molecules. The total flux and separation factor of this new membrane can reach about 6332 g/(m 2 h), and 30.7 for 90% wt.% ethanol, respectively. Compared with the cross-linked pure PVA membrane (2337 g/(m 2 h) and 11.2), the flux and separation factor can be improved simultaneously. Namely, the composite membrane can break the “trade-off effect” effectively. Furthermore, the nanocomposite membrane exhibited an excellent long-term operating stability. After operating for over 120 h with a 90 wt% ethanol/water system at 75 °C, the total flux and separation factor remained at their initial values. This is a step forward in the application in pervaporation separation processes of organic-inorganic hybrid membranes with superior properties incorporating 2D porous fillers (e.g., g-C 3 N 4 ).

Structure–property tuning in hydrothermally stable sol–gel-processed hybrid organosilica molecular sieving membranes

Supported microporous organosilica membranes made from bridged silsesquioxane precursors by an acid-catalyzed sol–gel process have demonstrated a remarkable hydrothermal stability in pervaporation and gas separation processes, making them the first generation of ceramic molecular sieving membranes with sufficient performance under industrially relevant conditions. The commercial availability of various α,ω-bis(trialkoxysilyl)alkane and 1,4-bis(trialkoxysilyl)benzene precursors facilitates the tailoring of membrane properties like pore size and surface chemistry via the choice of precursor(s) and process variables. Here, we describe the engineering of sols for making supported microporous thin films, discuss the thermal and hydrothermal stability of microporous organosilicas and give a short overview of the developments and applications of these membranes in liquid and gas separation processes since their first report in 2008.

Preparation of ultra-thin poly(vinyl alcohol) membranes supported on polysulfone hollow fiber and their application for production of pure water from seawater

Pervaporation membrane process using polymeric membrane is promising for production of high-quality water from seawater. The use of membrane support is necessary for improvements in the membrane performance. In this work, preparation of thin poly(vinyl alcohol) (PVA) membranes over polysulfone hollow fiber support and their application for production of pure water from seawater through pervaporation separation process is reported. The uniformly thin PVA membrane coating over the cylindrical hollow fiber support of about 1.10mm diameter was obtained by an automatic dip-coating method. The coating solution was a dilute aqueous solution of PVA (61,000g/mol, molecular weight) and maleic acid having a molar composition in the range of 1 C2H4O (vinyl alcohol): 0.05–0.20 C4H4O4 (maleic acid): 61–815 H2O. The conductance of produced water by the membranes from desalination of saline water of 30,000ppm NaCl concentration was in the conductance range of pure water grade. The thinnest coated membrane exhibited permeate flux of about 7.4L/m2/h from the feed water of 30,000ppm NaCl at 344K. The apparent activation energy of the pervaporation desalination based on the volume flux of the membranes was determined as about 23.1–25.8kJ/mol.

Cetyltrimethylammonium bromide–silica membrane for seawater desalination through pervaporation

A simple preparation of mesostructured cetyltrimethylammonium bromide (CTAB)–silica membrane is reported. It effectively desalinates seawater to pure water through pervaporation separation process. The membrane thickness was of nanometer-length-scale obtained by deposition of CTAB–silica colloids on porous polysulfone support. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) studies were performed to characterize the membrane while the structure of the colloids in coating solution was probed by small-angle neutron scattering (SANS). The prepared membranes exhibited excellent salt rejection efficiency of 99.9% in desalination of synthetic seawater of 40,000 ppm NaCl by pervaporation at 25∘C. The pure water flux was in the range of 1–2.6 kg m−2 h depending upon the membrane configuration and thickness. The flux could be greatly enhanced by operating the process at higher temperatures of 40–80∘C but it was at the cost of decreased salt-rejection efficiency. The initial rejection efficiency and flux of the membrane was found to be restored upon cooling the membrane back to room temperature.

Polysulfonamide Thin-Film Composite Membranes Applied to Dehydrate Isopropanol by Pervaporation

To dehydrate the isopropanol (IPA) by the pervaporation separation process at 25°C, the polysulfonamide thin-film composite (TFC) membranes were prepared via the interfacial polymerization of diamines including 1,3-diaminopropane (DAPE), 1,3-cyclohexanediamine (CHDA) and m-phenylenediamine (MPDA) with 1,3-benzenedisulfonyl dichloride (BDSC) on the surface of modified asymmetric polyacrylonitrile (mPAN) membrane. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectrometry, atomic force microscope (AFM) and water contact angle (WCA) measurements were applied to analyze chemical structure, surface roughness and hydrophilicity of the polymerized layer of composite membrane. In the dehydration of aqueous isopropanol solutions, the DAPE-BDSC/mPAN membrane had the higher permeation flux and the similar water concentration in permeate compared with the CHDA-BDSC/mPAN and MPDA-BDSC/mPAN membranes. The pervaporation performance of the composite membrane was affected by the chemical structure of the polysulfonamide polymer.

Effects of the polymerization and pervaporation operating conditions on the dehydration performance of interfacially polymerized thin‐film composite membranes

AbstractThe disadvantage of dense polyamide membranes when applied in the pervaporation separation process is their low permeation rates. To improve the pervaporation performance, polyamide thin‐film composite membranes were prepared via the interfacial polymerization reaction between ethylenediamine (EDA) and trimesoyl chloride (TMC) on the surface of modified polyacrylonitrile (mPAN) membranes. These composite membranes were applied in the pervaporation separation of alcohol aqueous solutions. On the basis of the best pervaporation performance, the desired polymerization conditions for preparing the polyamide thin‐film composite membranes (EDA–TMC/mPAN) were as follows: (1) the respective concentration and contact time of the EDA aqueous solution were 5 wt % and 30 min and (2) the respective concentration of and immersion time in the TMC organic solution were 1 wt % and 3 min. The polyamide thin‐film composite membranes (EDA–TMC/mPAN) exhibited membrane durability when applied in the pervaporation separation of a 90 wt % isopropyl alcohol aqueous solution at 70°C, which indicated that the polyamide thin film composite (TFC) membranes were suitable for the pervaporation separation process at a high operating temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Modeling and multi-response optimization of pervaporation of organic aqueous solutions using desirability function approach

The factorial design of experiments and desirability function approach has been applied for multi-response optimization in pervaporation separation process. Two organic aqueous solutions were considered as model mixtures, water/acetonitrile and water/ethanol mixtures. Two responses have been employed in multi-response optimization of pervaporation, total permeate flux and organic selectivity. The effects of three experimental factors (feed temperature, initial concentration of organic compound in feed solution, and downstream pressure) on the pervaporation responses have been investigated. The experiments were performed according to a 2 3 full factorial experimental design. The factorial models have been obtained from experimental design and validated statistically by analysis of variance (ANOVA). The spatial representations of the response functions were drawn together with the corresponding contour line plots. Factorial models have been used to develop the overall desirability function. In addition, the overlap contour plots were presented to identify the desirability zone and to determine the optimum point. The optimal operating conditions were found to be, in the case of water/acetonitrile mixture, a feed temperature of 55 °C, an initial concentration of 6.58% and a downstream pressure of 13.99 kPa, while for water/ethanol mixture a feed temperature of 55 °C, an initial concentration of 4.53% and a downstream pressure of 9.57 kPa. Under such optimum conditions it was observed experimentally an improvement of both the total permeate flux and selectivity.

Selective removal of acetone and butan-1-ol from water with supported ionic liquid–polydimethylsiloxane membrane by pervaporation

Abstract The use of ionic liquid–polymer in supported ultrafiltration membrane in vacuum pervaporation has been verified. The ultrafiltration membranes were impregnated by two ionic liquids (1-ethenyl-3-ethyl-imidazolium hexafluorophosphate and tetrapropylammonium tetracyano-borate) and polydimethylsiloxane. These new and very stable supported ionic liquid–polymer membranes were used for separation of ternary mixtures butan-1-ol–acetone–water by vacuum pervaporation. In comparison with polydimethylsiloxane membranes, the average enrichment factor of butan-1-ol increased in both cases. This higher selectivity shows a good potential for improving pervaporation separation process.

Pervaporation studies of gaseous plasma treated PVA membrane

Nonporous polyvinyl alcohol (PVA) membrane was modified in gaseous plasma to improve the separation efficiency for water-isopropanol (IPA) mixtures. Method of pervaporation separation process was adopted to assess the permselectivity after plasma processing. Membranes were exposed to plasma of air, nitrogen and oxygen for 2–15 min, and, their performances was evaluated at 75 °C for separation of azeotropic mixture of water–IPA. The optimized treatment time thus obtained for modification of PVA membrane was specifically used to further investigate the pervaporation performance over the selected water–IPA concentration range. Separation process at this stage was carried out at 25 and at 75 °C. The modified membrane was characterized by ATR-FTIR spectrometry, thermal analyses using DSC and wide angle X-ray diffraction. It has been found that the nitrogen plasma processing induces cross-linking on membrane surface leading to effective improvement in separation performance of membrane.