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This study investigated the enhancement in bioethanol recovery from mixed matrix membranes (MMMs) by functionalizing zeolite framework-8 (ZIF-8) with imidazolate. This study focused on the separation of ethanol from low-concentration ethanol/water mixtures (typical post-fermentation concentrations of 5–10 wt%). Specifically, ZIF-8 was modified by the shell–ligand exchange reaction (SLER) with 5,6-dimethylbenzimidazole (DMBIM), resulting in ZIF-8-DMBIM particles with improved hydrophobicity, organophilicity, larger size, and adjustable pore size. These particles were incorporated into a PEBAX 2533 matrix to produce ZIF-8-DMBIM/PEBAX MMMs using a dilution blending method. The resulting membranes showed significant performance enhancement: 8 wt% ZIF-8-DMBIM loading achieved a total flux of 308 g/m2·h and a separation factor of 16.03, which was a 36.8% increase in flux and 176.4% increase in separation factor compared with the original PEBAX membrane. In addition, performance remained stable during a 130 h cycling test. These improvements are attributed to the enhanced compatibility and dispersion of ZIF-8-DMBIM in the PEBAX matrix. In conclusion, the evaluation of nanofiller content, feed concentration, operating temperature, and membrane stability confirmed that ZIF-8-DMBIM/PEBAX MMM is ideal for ethanol recovery in primary bioethanol concentration processes. [ABSTRACT FROM AUTHOR]

In this study, Principal Component Analysis (PCA) was applied to discern the underlying trends for 31 distinct MFI (Mobil No. 5)-zeolite membranes of 11 textural, chemical, and operational factors related to manufacturing processes. Initially, a comprehensive PCA approach was employed for the entire dataset, revealing a moderate influence of the first two principal components (PCs), which collectively accounted for around 38% of the variance. Membrane samples exhibited close proximity, which prevented the formation of any clusters. To address this limitation, a subset acquisition strategy was followed, based on the findings of the PCA for the entire dataset. This resulted in an enhanced overall contribution and the revelation of diverse patterns among the membranes and the considered manufacturing factors (total variance between 55% and 77%). The segmentation of the data unveiled a robust correlation between silica (SiO2) concentration and pervaporation conditions. Additionally, a notable clustering of the chemical compositions of the preparation solutions underscored their significant influence on the operational efficacy of MFI zeolite membranes. On the other hand, an exclusive chemical composition of the preparation solution was noticed. This highlighted the high influence of the chemical composition on the operational efficiency of MFI zeolite membranes. The coupling of PCA with experimental results can provide a data-driven enhancement strategy for the manufacturing of MFI-type zeolite membranes used for ethanol/water separation. [ABSTRACT FROM AUTHOR]

Inorganic based membranes are promising candidates for a variety of applications, including adsorption and separation due to their large surface area, high pore volume, tunable structure, and strong resistance against aggressive operation conditions, such as high temperature and pressure. Many research groups have investigated zeolite, micro- or mesoporous silica, and hybrid materials (organic and inorganic materials) as advanced membrane configurations in liquid separation applications. Especially, hydrophobic inorganic membranes have potential to separate ethanol from aqueous solution via pervaporation, ultimately producing ethanol, but several important challenges such as reliable synthesis, fabrication, or functionalization are yet to be solved. More specifically, a novel, high throughput process for the fabrication of continuous and defect-free hydrophobic inorganic membranes is required. Then, functionalization of pore structures of the membrane, if necessary, is desirable in order to tailor even more advanced hydrophobic properties for ethanol. Finally, the separation characteristics and performance of inorganic membranes must be further investigated to implement in the industry. Herein, the synthesis and normalized separation performance of diverse hydrophobic inorganic membranes with respect to selective layer material basis, such as zeolite, functionalized mesoporous silica, and mixed matrix, are comprehensively reviewed and the future direction is presented with a focus on ethanol recovery. [ABSTRACT FROM AUTHOR]

The use of pervaporation membranes has shown great potential in the extraction of bioethanol. However, a simple, continuous, and controllable alcohol perm-selective membrane manufacturing process is needed for practical applications. In this study, the slot-die coating technique was utilized to deposit low-viscosity vinyl-polydimethylsiloxane (vinyl-PDMS) and crosslinker onto a porous substrate. A defect-free separation layer could be created within just 20 min, which includes the membrane forming and drying process, due to the rapid hydrosilylation reaction between vinyl-PDMS and the crosslinker. Therefore, the efficient fabrication process is suitable for continuous roll-to-roll industrial production. Additionally, by optimizing the slot-die parameters, the thickness of the separation layer could be regulated from 0.4 to 15 μm. The obtained vinyl-PDMS composite membrane demonstrated a total flux of 2.8 kg m−2 h−1 and a separation factor of 10.3 for 5 wt% ethanol/water mixture at 60 °C. [Display omitted] • Slot-die coating was used to prepare an alcohol-selective pervaporation membrane. • The thickness of the separation layer could be regulated between 0.4 μm and 15 μm. • A defect-free separation layer could be formed within just 20 min. [ABSTRACT FROM AUTHOR]

• A new strategy to prepare ultrathin silicone composite membrane was proposed. • A PDMDES active layer was fabricated with its low-surface-energy monomer DMDES. • The PDMDES active layer possessed sub-micrometer sized thickness. • A high flux of 7565.6 g·m−2·h−1 was achieved for 9 wt% ethanol/water separation. • Stable intrinsic separation ability was achieved under different conditions. Silicone-based polymers are the most popular materials to prepare pervaporation (PV) membranes for bioethanol recovery from fermentation process. However, the existing silicone composite membranes mostly exhibited limited permeance for ethanol/water separation, which can be attributed to the thick active silicone layers resulting from insufficient spreading of the polymer casting solution on the porous substrate. In the present study, we propose the use of low-surface-energy monomer into casting solution to enhance its spreading ability for ultrathin silicone membrane fabrication. In specific, a poly(dimethyldiethoxylsilane) (PDMDES) casting solution was prepared by limited polymerization of its low-surface-energy monomer dimethyldiethoxylsilane (DMDES), and was then casted on a porous substrate. We show that the surface energy of the partially polymerized casting solution maintained low, and an ultrathin PDMDES active layer with thickness of sub-micrometer size was obtained. The physicochemical properties of the PDMDES membrane were further characterized by ATR-FTIR, XRD and TGA, respectively. Upon optimized preparation and operation conditions, the PDMDES composite membrane exhibited a superior flux of 7565.6 g·m−2·h−1, while maintained a comparable separation factor when compared to traditional PDMS membranes. Our strategy provides new insights into the development of ultrathin silicone membranes for enhanced bioethanol recovery. [ABSTRACT FROM AUTHOR]

Abstract Pervaporation (PV) has emerged as a robust membrane-based separation technology for liquid mixtures. For the development of high-performance PV membranes, it is crucial to quantitatively understand the separation mechanism from a molecular level. Nevertheless, molecular simulation of PV is challenging due to the practical requirements of preserving a vapor-liquid equilibrium (VLE) in the feed side, and simultaneously an extremely low permeate pressure throughout the simulation. In this study, we develop a molecular simulation protocol for PV by rigorously incorporating these two practical requirements and demonstrate its applications in three separations: (1) Seawater desalination through a zeolitic-imidazolate framework (ZIF-8) membrane. Water permeability and salt rejection predicted are in excellent agreement with experiment. (2) Ethanol/water separation through a polymer of intrinsic microporosity (PIM-1). The normalized-fluxes of ethanol and water match remarkably well with experimental data. (3) Ethanol/water separation through a zeolite (MFI) membrane. The separation factors of ethanol/water agree fairly well with measured data. In all the three separations, a VLE is preserved in the feed side, while a vanishingly low pressure is maintained in the permeate side (< 10 mbar as in experiments). The simulation protocol reliably mimics practical PV processes and can be generally applied to simulate the PV separations of other liquid mixtures. Graphical abstract A molecular simulation protocol for membrane pervaporation is developed. fx1 Highlights • A molecular simulation protocol is developed for membrane pervaporation. • The simulation protocol is demonstrated for three separations. • Water permeability predicted through ZIF-8 is in excellent agreement with experiment. • Ethanol and water fluxes predicted through PIM-1 match remarkably well with experimental data. • Ethanol/water separation factors predicted through MFI agree well with measured data. [ABSTRACT FROM AUTHOR]

Silicalite-1 zeolite membranes were prepared on porous tubular α-Al 2 O 3 supports by a secondary growth method. The influences of the Si/Al ratio and the amount of deposited MFI (silicalite-1 and ZSM-5) seed crystals on membrane pervaporation (PV) performance for the separation of ethanol/water (binary) and ethanol/water/succinic acid (ternary) mixtures were investigated. The prepared membranes were characterized by X-ray diffraction and scanning electron microscopy, and the Si and Al distributions in the membrane layers were determined by energy-dispersive X-ray line scanning. Each silicalite-1 membrane was composed of two layers: an MFI-seed-crystal layer that grew on the support surface, and another gel-derived silicalite-1 top layer that formed on the seed crystal layer. The texture of the MFI seed layer (i.e., the deposited amount and the Si/Al ratio) was found to play an important role in the separation process. When silicalite-1 seed crystals were used, the ethanol separation factor was high in the binary ethanol/water system, but lower in the presence of succinic acid. However, when ZSM-5 seeds were used, the ethanol separation factor in the ternary system improved. These results suggest that silicalite-1 membranes prepared using ZSM-5 seed crystals are effective for the recovery of ethanol in the presence of organic acids. [ABSTRACT FROM AUTHOR]

Silicalite-1 membranes with high pervaporation performance were prepared successfully on a silica-particle-coated tubular silica support using a gel-free steam-assisted conversion (SAC) method. The effects of the silica-particle layer formed on the top surface of the silica support and the physical properties of the silica particles themselves on the membrane-formation process were investigated. The silica particles coated served as the additional silica source for growing the silicalite-1 seed crystal layer into the silicalite-1 membrane. As a result, it was possible to form a dense and continuous membrane even under gel-free conditions. Furthermore, it was found that the properties of the silica particles, such as their primary particle diameter, had a determining effect on their solubility during the steam treatment, that is, on the supply rate of the silica source. The silicalite-1 membrane obtained using the spherical-silica-particle-coated support had an approximately 9-μm-thick separation layer and showed very high pervaporation performance, exhibiting a separation factor of 105 and a flux of 3.72 kg m−2 h−1 for a 10 wt % ethanol/water mixture at 323 K. Thus, the gel-free SAC method can be used with a silica support coated with silica particles to readily prepare high-performance membranes without producing any chemical waste.

Composite alginate membranes filled with various amount of iron ferroferric oxides (Fe 3 O 4 ) 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 Fe 3 O 4 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 . [ABSTRACT FROM AUTHOR]

Pervaporation is a membrane separation technology applied especially for the dehydration of organic solvents. Since its excellent permselectivity toward water, sodium alginate has been identified as the promising membrane material for the pervaporative dehydration of ethanol. Hybrid alginate membranes filled with various amount of magnetite (Fe 3 O 4 ) and crosslinked using four different agents, i.e. calcium chloride (AlgCa), phosphoric acid (AlgP), glutaraldehyde (AlgGA) and citric acid (AlgC) were prepared and applied in pervaporative dehydration of ethanol. In this paper, the correlation between chemical composition, structure and morphology, and separation properties of membranes is discussed. [ABSTRACT FROM AUTHOR]

• LDDLT plasma was used to etch the surface of MMMs for PV separation. • The thickness of separation layer reduced and more ZIF-L nanosheets were exposed. • The PV performance for ethanol separation was greatly improved by plasma etching. • Plasma etched-ZIF-L/PDMS MMMs had long-term stability for ethanol recovery. Mixed matrix membranes (MMMs) have been shown great performance and remarkable stability for diverse molecular separations. Considering that the density of MOFs is usually higher than that of polymer doping solution, the upper separation layer surface of MMMs is enriched by the polymer matrix, compromising the membrane performance. In this study, the asymmetric separation layer of MOF-filled MMMs was etched by the long-distance and dynamic low-temperature (LDDLT) plasma for enhanced ethanol permselective pervaporation. The thickness of separation layer decreased and the MOF amount on surface increased after the LDDLT plasma etching, which dramatically reduced the molecular permeation resistance and improved the membrane performance. Under optimal plasma conditions, the etched MMMs exhibited the superior permeation flux of 1120 g·m−2·h−1 (60% more than that of unetched membrane) and the separation factor of 12.3 (1.16 times as much as that of unetched membrane) in separation of 5 wt% ethanol aqueous solution at 40 °C. [ABSTRACT FROM AUTHOR]

BACKGROUND Polybenzoxazine ( PBZ) membranes have received increasing attention for serving as a high performance membrane for pervaporation processes owing to their good mechanical properties, high chemical resistance, high thermal stability, and low synthesis cost. This study aims to develop PBZ membrane and NaA-PBZ mixed matrix membrane ( MMM) for purification of ethanol/water mixtures using a pervaporation process and to investigate the effects of preparation parameters on the membrane performance, including precursor concentrations, number of dippings, amount of NaA zeolite loading, temperature, and ethanol concentration. RESULTS It was found that PBZ membrane and NaA-PBZ MMM exhibited excellent stability in all feed ethanol concentrations tested, with a low degree of swelling. The highest separation factor of the pure PBZ membrane was more than 10 000 while the NaA-PBZ MMM was even higher, up to and, in some cases, higher than 100 000 with the highest permeation flux of 1071 g m−2 h−1 when using 25 wt% PBZ precursor with 15 wt% NaA zeolite loading. The permeation flux of MMM increased with increase in temperature or a decrease in the feed ethanol concentration. Swelling increased when the ethanol concentration was increased, revealing the hydrophobic behavior of NaA-PBZ MMM. CONCLUSION The membranes are capable of purifying ethanol over a wide feed ethanol concentration range with excellent performance and properties that promise great potential for use in bioethanol purifying applications. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The silicalite-1/PDMS hybrid membranes have been widely studied in alcohol perm-selective pervaporation separations. However, the poor compatibility between silicalite-1 particles and PDMS has already rebated the separation performance of these hybrid membranes. In this paper, two approaches were investigated to improve/tune the compatibility of the silicalite-1 particles and PDMS matrix. Firstly, silicalite-1 crystal particles with different sizes were synthesized. The effects of the particle size on the compatibility between silicalite-1 and PDMS were investigated. It was found that smaller silicalite-1 crystals (about 100 nm) have a better compatibility with PDMS matrix, thereby an enhanced separation performance of their hybrid membranes. Subsequently, the surface of silicalite-1 particles were modified through three kinds of silane coupling agents with different functional groups, which was confirmed to be feasible in increasing the compatibility with PDMS. In ethanol/water pervaporation separation, a higher selectivity was achieved in the PDMS hybrid membrane with TMDS-modified small silicalite-1 crystals. Moreover, silicalite-1 crystals provide many separate channels, so that the separation performance of the hybrid membrane has dramatically increased. [ABSTRACT FROM AUTHOR]

Composite chitosan membranes filled with various amount of iron ferroferric oxides (Fe3O4) cross-linked by two different agents, i.e. sulphuric acid (CHSA) and glutaraldehyde (CHGA) were prepared, and the pervaporation of water/ethanol mixture was investigated. The influence of cross-linking agents and iron oxide powder content on the transport properties were discussed. Permeation of water after addition of iron oxide nanoparticles to the polymer matrix for both types of cross-linking agents gradually increased. Furthermore, it was observed that the difference between permeation coefficients for ethanol and water was larger for membranes cross-linked by glutaraldehyde then for membranes cross-linked by sulphuric acid. Maximal evaluated the separation factor for CHGA membranes was about 2.5 times larger than for CHSA, and selectivity coefficient was 3.5 times larger. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane pervaporation membrane was employed to remove ethanol from aqueous solutions. The influences of feed flow rate, temperature, permeate-side pressure, and ethanol concentration on the membrane performance were investigated. The feed flow rate was shown to have no significant effect on either flux or ethanol selectivity whereas the feed concentration, temperature, and permeate-side pressure had highly significant effects. Sorption and desorption experiments were also performed to provide data for analysis of mass transport based on resistance-in-series model. The analysis of transport resistances revealed that the mass transport of the system was controlled by the transport resistance of components in the membrane active layer. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane (PDMS) is a benchmarked membrane material for pervaporation, gas separation, and nanofiltration, remaining challenges in achieving high-flux membrane. Herein, we proposed a high-flux PDMS membrane with corrugated morphology realized by simply coating PDMS solution on nanofiber substrate. It was demonstrated that the electrospun nanofiber substrate with highly interconnected and porous structures could generate a corrugated PDMS membrane layer with highly increased surface area and meanwhile remarkably reduce transport resistance of the membrane. By optimizing the pore structure of nanofiber substrate and reducing the membrane thickness to sub-micrometer, the corrugated PDMS membrane exhibited up to one order of magnitude higher permeation flux compared with state-of-the-arts PDMS membranes for pervaporation separation of ethanol/water mixtures. Specifically, using a 5 wt% ethanol/water mixture as feed at 60 °C, a total flux of 8.7 kg m −2 h−1 and a separation factor of 7.2 were obtained. This work provides a facile approach to develop nanostructured membranes with highly enhanced transport properties. [Display omitted] ➢ Corrugated membrane surface is created by coating PDMS on nanofiber substrate ➢ Highly porous and interconnected nanofiber substrate reduce transport resistance ➢ Corrugated PDMS/nanofiber membrane show significantly enhanced pervaporation flux [ABSTRACT FROM AUTHOR]

Abstract: High-performance silicalite membranes were successfully prepared on porous tubular silica supports by in situ hydrothermal synthesis without seeding. The separation performance of the as-synthesized silicalite membranes was evaluated by separating ethanol/water mixtures. It was found that both the aging temperature and aging time had a significant influence on the performance of silicalite membranes when the silica tubes and synthesis solution were aged together. The tubular silica supports were filled with glycerol/water mixtures to reduce the penetration of synthesis solution, and it was found that this solution-filling method could effectively improve the membrane flux by about 27% with a higher separation factor. By using two-step hydrothermal synthesis, the silicalite membrane with a total flux of 0.58kg/m2 h and ethanol/water separation factor of 95 at 333K was obtained. The method in this work has been demonstrated a simple and effective way to skip the deposition of pre-formed nanosized seeds on tubular supports before the secondary growth of silicalite membrane. [Copyright &y& Elsevier]

Emerging pervaporation technology is very promising to realize clean and renewable bioethanol recovery from biomass fermentation broth. The huge challenge of this technology is the need for a pervaporation membrane with high separation performance. Based on the solution-diffusion mechanism, pervaporation membrane for ethanol recovery should possess hydrophobic selective layer to improve sorption ability toward ethanol molecules, thereby enhancing the separation performance. In this study, a superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer with a nano-level bud-like surface morphology was grown on polydimethylsiloxane (PDMS) composite membrane via ZIF-8 particle dip-casting, secondary seeded growth, and hydrophobic modification by n-octadecylphosphonic acid for highly efficient ethanol/water separation. The mole ratio of 2-methylimidazole and zinc nitrate (Hmim/Zn2+) in the process of ZIF-8 secondary growth was systematically studied to construct appropriate micro-nano structure on PDMS composite membrane. The resultant optimal composite membrane exhibited a water contact angle of about 163° and an ethanol contact angle of 0°. In addition, it also displayed an outstanding separation factor of 17.4 corresponding to a total flux of 0.64 kg/m2 h with 5 wt% ethanol aqueous solution at 30 ℃, and thus the superior pervaporation performance to most other reported PDMS-based mixed matrix membranes. The strategy of constructing superhydrophobic layer on PDMS composite membrane may provide a meaningful guidance for preparing high-performance pervaporation membrane for organic recovery from aqueous solution. ga1 • Superhydrophobic membranes prepared via ZIF-8 secondary growth and OPDA modification. • These composite membranes show a nano-level bud-like surface morphology. • Hmim/Zn2+ ratio of 4 endows the membrane with higher hydrophobicity and selectivity. • Optimal membrane shows the highest separation factor (17.4) and comparable flux. [ABSTRACT FROM AUTHOR]

• Robust hybrid PVA membranes filled with particles of chitosan derivatives. • Impact of enhanced hydrophilicity on the ethanol/water separation. • Membrane with 3 wt% of phosphorylated or sulphated CS showing the highest PSI. • Comparison of PVA_CS membranes with congruent Alg_CS and other hybrid PVA membranes. The series of novel hybrid poly(vinyl alcohol) (PVA) membranes filled with chitosan particles (CS) and its four derivatives: phosphorylated (CS-P), crosslinked with glutaraldehyde (CS-GA), glycidol-modified (CS-G) and sulphated (CS-SO 3) chitosan were prepared and tested in the pervaporative separation process of a water/ethanol mixture. The influence of various types of chitosan particles, as well as their loadings, on transport properties of the membranes was discussed. Consequently, the addition of chitosan particles into the PVA matrix was found to significantly change its hydrophilicity and have a positive impact on the efficiency of ethanol dehydration. The best performance in terms of the highest separation factor (263.3) and PSI (380.3 kg·m−2·h−1) was shown for a PVA membrane filled with the phosphorylated chitosan particles (3 wt% CS-P), which significantly outperformed not only other materials considered in this study, but also other hybrid PVA-based membranes described in the literature. [ABSTRACT FROM AUTHOR]

In this study, silicalite-1 membranes were prepared on seeded tubular silica supports using a gel-free steam-assisted conversion (SAC) method. The effects of seed crystal type on the growth and microstructure of the membranes were investigated. The morphologies of the membranes obtained by this preparation method reflected the orientation of the seed crystal layer covering the tubular support; when spherical seed crystals were used, the membrane surface was composed of randomly oriented crystals; whereas when coffin-type seed crystals were used, the membrane surface was composed of crystals arranged in a relatively b -axis orientation. This suggests that membrane layers can be grown with the same orientation as the seed crystals on the tubular support. That is, the gel-free SAC method is able to suppress changes in the orientation of zeolite crystals during membrane formation, which is a problem in conventional hydrothermal syntheses. This is a very interesting phenomenon that occurs only under gel-free SAC conditions, and accounts for the successful growth of the b -oriented silicalite-1 membrane layer on the tubular support. Our findings successfully demonstrate approaches for the formation of membrane layers that retain the orientation of zeolite seed crystals on tubular supports, and for the synthesis of oriented zeolite membranes with high permeability. Image 1 • Silicalite-1 membranes prepared on tubular silica supports via gel-free steam-assisted conversion. • Effects of seed crystal type on membrane growth and microstructure are analyzed. • The membrane orientation reflects the orientation of the seed crystal used. • The prepared membranes exhibit high flux for separating ethanol/water mixtures. [ABSTRACT FROM AUTHOR]

A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure MFI zeolite membranes based on "like grows like" principle. Through covalent modification of the porous ceramic supports by using 1H,1H,2H,2H-perfluoroalkyltriethoxysilanes (POTS), the support surface was changed from hydrophilic to hydrophobic, which promotes the nucleation and growth of hydrophobic MFI zeolite membranes. Thin, well-intergrown and phase-pure MFI zeolite membranes, with a thickness of about 2.0–3.0 μm, can be facilely prepared on POTS-modified supports like Al 2 O 3 and TiO 2 at 175 °C for 24 h. No cracks, pinholes or other visible macroscopic defects are observed in the membrane layer. The MFI zeolite membranes were evaluated in the hydrophobic separation of 5.0 wt% ethanol/water mixture at 75 °C by pervaporation. The MFI zeolite membrane prepared on the POTS-modified TiO 2 disk shows high pervaporation separation for ethanol recovery. At 75 °C, a separation factor of 103 and total flux of 2.56 kg/m2h can be obtained, which is promising to extract bio-alcohols from the fermentation broth. Image 1 • A novel strategy is developed for seeding-free synthesis of MFI zeolite membranes based on "like grows like" principle. • Hydrophobic MFI membranes tend to grow well on the hydrophobic support surface. • Thin and well-intergrown MFI membranes can be easily prepared on POTS-modified supports. • The MFI membranes prepared on POTS-modified TiO 2 supports show high pervaporation performance. [ABSTRACT FROM AUTHOR]

Silicalite-1 membranes with high pervaporation performance were prepared successfully on a silica-particle-coated tubular silica support using a gel-free steam-assisted conversion (SAC) method. The effects of the silica-particle layer formed on the top surface of the silica support and the physical properties of the silica particles themselves on the membrane-formation process were investigated. The silica particles coated served as the additional silica source for growing the silicalite-1 seed crystal layer into the silicalite-1 membrane. As a result, it was possible to form a dense and continuous membrane even under gel-free conditions. Furthermore, it was found that the properties of the silica particles, such as their primary particle diameter, had a determining effect on their solubility during the steam treatment, that is, on the supply rate of the silica source. The silicalite-1 membrane obtained using the spherical-silica-particle-coated support had an approximately 9-μm-thick separation layer and showed very high pervaporation performance, exhibiting a separation factor of 105 and a flux of 3.72 kg m−2 h−1 for a 10 wt % ethanol/water mixture at 323 K. Thus, the gel-free SAC method can be used with a silica support coated with silica particles to readily prepare high-performance membranes without producing any chemical waste. [ABSTRACT FROM AUTHOR]

A procedure to estimate the diffusion coefficient in solution–diffusion models of hydrophilic membranes used in pervaporation-based purification experiments is presented. The model is based on a series solution of the general permeation problem. It considers a membrane that can be filled with water or with the feed solution before the measurement. Furthermore, the length of the tubing between the permeation cell and the place of cold traps is also addressed. To illustrate the parameter estimation procedure, we have chosen the data for the separation of water and ethanol by chitosan membranes. It is shown that the diffusion coefficient can be estimated effectively from the time course of the transported mass and by the analysis of certain well defined time lags of the permeation curve. [ABSTRACT FROM AUTHOR]