Pervaporation Dehydration Of Acetic Acid Research Articles

Novel view at hybrid membranes containing star macromolecules using neutron scattering and pervaporation dehydration of acetic acid

Hybrid membranes based of polyphenylene oxide matrix and star macromolecules (up to 5 wt%) containing six polystyrene and six poly-2-vinylpyridine arms attached to a common fullerene C60 center were prepared and successfully used for pervaporation separation of acetic acid – water mixtures. The peculiarities of the hybrid membrane structure and properties were studied by small-angle neutron scattering in two states (dry and swollen in deuterated acetic acid). It was established that star macromolecules are non-uniformly distributed in the matrix and form aggregates; they increase in the size up to ~60% during swelling of membranes in deuterated acetic acid. In pervaporation, the total flux through the membrane rises with increasing both the star macromolecule content in membrane and water concentration in the feed. Separation factor reaches its greatest value when the hybrid membrane contains 5 wt% star macromolecules.

All-silica DD3R zeolite membrane with hydrophilic-functionalized surface for efficient and highly-stable pervaporation dehydration of acetic acid

A novel strategy of all-silica zeolite membrane with hydrophilic-functionalized surface was proposed for efficient and highly-stable pervaporation dehydration of acetic acid. 3-aminopropyltriethoxysilane (APTES) was used to graft onto the surface of hollow fiber supported DD3R membrane to enhance its surface hydrophilicity and therefore improve its water/AcOH separation factor. Both pristine DD3R and obtained APTES-DD3R membranes were characterized extensively in terms of water contact angle (WCA), SEM, XRD, FT-IR and XPS for comparison. When the DD3R membrane was grafted with APTES for 1 h, the membrane surface turned from hydrophobic to hydrophilic. Under the synergetic effect of enhanced water adsorption on membrane surface and intrinsic molecule-sieving property of DD3R zeolitic pores, the APTES-DD3R membrane showed an improved separation factor of 1700 rather than that (196) of pristine DD3R membrane in separation of 10 wt% water/AcOH mixture at 348 K. Moreover, the APTES-DD3R membrane exhibited excellent stability during the PV separation, even in the presence of strong inorganic acids (HCl and H2SO4).

Pervaporation dehydration of acetic acid through hollow fiber supported DD3R zeolite membrane

Abstract All-silica Decadodecasil 3R (DD3R) zeolite membranes were prepared on four-channel ceramic hollow fibers by seeding with ball-milled Sigma-1 zeolites and hydrothermal synthesis method. Effect of synthesis time on membrane structure and morphology was investigated and the membrane quality was evaluated by CO2/CH4 binary gas separation. The as-prepared membranes were further used in pervaporation dehydration of acetic acid (AcOH) for the first time. Although behaving strong hydrophobicity, the defect-free DD3R zeolite membrane exhibited a good water-selective permeability based on molecular-sieving mechanism. A water permeation flux of 0.58 kg m−2 h−1 as well as a separation factor of 800 was achieved in dehydration of 70 wt% water/AcOH mixture at 368 K. Both experimental and molecular simulation studies were explored to investigate the influence of pervaporation condition on membrane separation performance. The results showed that both high temperature and feed water content were beneficial for improving the water flux and separation factor. The long-term pervaporation test revealed that hydrophobic DD3R zeolite membrane behaved stable permeation flux and separation factor in dehydration of AcOH, even in the presence of inorganic acid, confirming the excellent acid-resistance of its all-silica framework structure.

Pervaporation dehydration of acetic acid using NH 2 -UiO-66/PEI mixed matrix membranes

Abstract Acetic acid dehydration is significant in chemical industry. Pervaporation has attracted increasing attention due to its low energy consumption and environmentally friendly process. However, there is still lack of efficient membrane materials for the pervaporation separation of acetic acid/water mixtures. Therefore, developing new material to prepare pervaporation membrane is currently the main task. In this study, an acid stable Zr-MOF NH2-UiO-66 was synthesized and incorporated into poly(ethyleneimine) (PEI) to form mixed matrix membranes (MMMs) for separating acetic acid/water mixtures. The NH2-UiO-66/PEI MMMs were deposited on the surface of NaA zeolite tubular substrate to form composite membranes using dip-coating method. The morphologies and structures of the particles and composite membranes were characterized by SEM, EDX, FTIR and contact angle. The effects of membrane preparation conditions on the separation performance were investigated. The results indicated that the NH2-UiO-66/PEI composite membranes showed good acetic acid dehydration behavior, because of the high porosity and hydrophilicity of the particles. Moreover, the particles had good compatibility with polymer and strong combination with substrate. Therefore, this study may provide a new material and facile strategy for preparing composite membrane in the separation of acetic acid/water mixtures.

Separation of acetic acid/water mixtures by pervaporation with composite membranes of sodium alginate active layer and microporous polypropylene substrate

A new kind of composite membrane for the pervaporation dehydration of acetic acid was prepared by casting sodium alginate (NaAlg) solution onto a microporous polypropylene membrane (MPPM) which possessed well-controlled porosity and excellent solvent resistance. The MPPM surface was modified by N2 plasma prior to the fabrication of the corresponding NaAlg-based composite membrane in order to improve its compatibility with the NaAlg active layer. The active layer of the NaAlg/MPPM composite membrane was then cross-linked with multivalent ions. This cross-linking behavior restricted the mobility of the polymer chains in the active layer and accordingly increased their relaxation time. Interestingly, the activation energy of the pervaporation process increased linearly with the relaxation time. Pervaporation results indicated that the prepared composite membranes exhibited desirable separation properties, and a good compromise between flux and separation factor was observed. For the separation of an 80/20wt% acetic acid/water mixture at 50°C, the Ca2+ cross-linked composite membrane (Ca-Alg/MPPM) displayed a separation factor of 631 and a flux of 653g/m2h, which surpassed most NaAlg-based homogeneous membranes and other composite membranes reported in the literature. These results suggest that the prepared composite membranes have promising potential for acetic acid dehydration.

Sulfonated polybenzimidazole membranes for pervaporation dehydration of acetic acid

Abstract In this study, a novel sulfonated polybenzimidazole (SPBI) membrane has been developed and investigated for pervaporation dehydration of acetic acid, via a two-step sulfonation modification technique—sulfonation with sulfuric acid followed by a thermal treatment at 450 °C. Both steps are found indispensible in order to produce a stable SPBI membrane with enhanced acid resistance and superior separation performance. Effects of the sulfuric acid concentration and thermal treatment duration have been investigated and found to have significant impact on the pervaporation performance of the resultant SPBI membranes. Various characterizations (FTIR, XPS, TGA and XRD) are employed to elucidate the physicochemical changes of membranes as a function of chemical and thermal modifications. In addition, effects of pervaporation temperature and feed composition are studied not only in terms of flux and separation factor, but also of membrane intrinsic permeance and selectivity. The best pervaporation performance of the SPBI membrane has a flux of 207 g/m 2 /h and a separation factor of 5461 for dehydration of a 50/50 wt% acetic acid/water feed solution at 60 °C, which not only outperforms the conventional distillation process, but also surpasses most other polymeric pervaporation membranes reported in literature. It is therefore believed that the novel developed SPBI membrane may have great potential for pervaporation dehydration of acidic organics, as well as other applications that demand acid-proof materials.

Microstructural optimization of mordenite membrane for pervaporation dehydration of acetic acid

Abstract The crystallization of defect-free, acid-proof film microstructure is consistently pursued for making hydrophilic pervaperation (PV) membranes popular in process industries. We show that a novel modified secondary growth method can fabricate high-PV-performance, excellent-acid-stability mordenite membranes by eliminating grain boundary defects, dramatically by optimizing film microstructure. This method consists of growing the assembled nanocrystals of an ultrathin seed layer to a well-intergrown film directly on a macroporous support at a relatively low crystallization temperature (150 °C) by avoiding events that lead to an acid nonresistant film microstructure, such as the formation of Al-rich film surface and grain boundaries. Fluoride anions are used as mordenite crystal structure modifiers to optimize distribution of aluminum atoms in zeolitic film, so grain boundaries can be kept intact for long-term acidic corrosion. The polycrystalline films are ultrathin (3–4 μm), and oriented with different Si/Al ratios (5.6–20.1). Comparison with conventional synthesized membranes shows that these microstructurally optimized membranes have superior PV performance and acid stability for the dehydration of high-concentration acetic acid (AcOH) mixtures.

Fabrication of poly(1-vinylimidazole)/mordenite grafting membrane with high pervaporation performance for the dehydration of acetic acid

A novel hydrophilic poly(1-vinylimidazole)/mordenite (PVI/MOR) grafting membrane was prepared by free-radical graft polymerization of 1-vinylimidazole (VI) onto the as-synthesized mordenite zeolite membrane. The surface property and the morphology of the membranes were analyzed by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), diffuse reflectance FT-IR spectroscopy (DRIFTS) and thermogravimetric analysis (TGA). The effects of VI concentrations in the grafting medium, separation temperature, feed concentration on selectivity and flux of the obtained membranes for pervaporation dehydration of acetic acid were examined. The PVI/MOR grafting membrane with the VI solution of 15 wt.% astonishingly exhibited the ideal selectivity with water contents in permeates reaching 100.00 wt.% over acetic acid feed concentrations from 71 to 94 wt.% at 80 °C. Both the total fluxes and selectivity for this membrane increased with temperature ranging from 40 to 80 °C. It was suggested that an in situ formed complex between the poly(1-vinylimidazole) (PVI) moiety of the membrane and the acetic acid in the feed played an important role in the separation performance. It not only blocked the permeation of acetic acid through the grain boundary defects but also facilitated the transport of the water molecules, resulting in an ideal selectivity of water over acetic acid.

Dehydration of acetic acid by pervaporation using SPEK-C/PVA blend membranes

Sulfonated cardo polyetherketone (SPEK-C) and poly(vinyl alcohol) (PVA) blend membranes were prepared by solution casting method and used in pervaporation (PV) dehydration of acetic acid. The membranes were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle meter. The results show that thermal crosslinking occurred to the membrane under high temperature annealing. The effective d-spacing (inter-segmental spacing) decreased with PVA content decreasing. The hydrophilicity of the blend membrane increased with SPEK-C content increasing. Swelling and sorption experiments show that the swelling degree of the blend membrane increased, however both the sorption and diffusion selectivities decreased with increasing PVA content. The diffusion selectivity is higher than the sorption selectivity. This suggests that PV dehydration of acetic acid is dominated by the diffusion process. The pervaporation separation index (PSI) of the membrane increases with increasing PVA content and arrives at a maximum when the SPEK-C/PVA ratio is 3/2, then decreases with further addition of PVA. The membrane has an encouraging separation performance with a flux of 492 g m −2 h −1 and separation factor of 59.3 at 50 °C at the feed water content 10 wt%.

Aluminum-rich zeolite beta incorporated sodium alginate mixed matrix membranes for pervaporation dehydration and esterification of ethanol and acetic acid

Mixed matrix membranes of sodium alginate (NaAlg) were prepared by solution casting by incorporating 2.5, 5, 7.5 and 10 wt.% of zeolite beta particles. The membranes thus prepared were crosslinked with glutaraldehyde and tested for the pervaporation (PV) dehydration of ethanol and acetic acid at 30–60 °C. The aluminum-rich zeolite beta, with its hydrophilic nature as well as molecular sieving effect and its favorable interaction with hydrophilic NaAlg, was responsible to enhance the PV dehydration of acetic acid and ethanol in terms of separation factor, flux, pervaporation separation index (PSI) and enrichment factor ( β). Thermodynamic model for sorption process was investigated typically for water + ethanol mixtures based on Flory–Huggins theory to explain the PV performance. Based on these results, permeance and driving force mechanisms were also elucidated. Extraction or dissolution of zeolite beta from mixed matrix membranes is confirmed by equilibrium sorption. Additionally, the changes in the dimension of pristine and mixed matrix membranes are compared to provide the influence of swelling on the stabilities of mixed matrix membranes. Arrhenius parameters for the process of permeation were calculated using these data at different temperatures to investigate their effects on the nature of the mixed matrix membrane. The plots of ln J p vs. 1/ T were constructed and found to follow the linear trends in the studied range of 30–60 °C for both the feed mixtures, indicating that flux followed the Arrhenius trend. PV experiments were also carried out for 5 and 10 wt.% incorporated NaAlg mixed matrix membranes at 70 °C to verify the suitability of the membranes at the esterification temperature. PV-aided catalytic esterification of acetic acid with ethanol was studied at 70 °C, which led to a considerable increase in ethyl acetate conversion with a reduction in reaction time as compared to the blank reaction due to continuous removal of water permeating through the barrier membrane.

Highly water selective silicotungstic acid (H 4SiW 12O 40) incorporated novel sodium alginate hybrid composite membranes for pervaporation dehydration of acetic acid

Silicotungstic acid incorporated sodium alginate (STA-NaAlg) hybrid composite membranes were prepared by incorporating 1, 2, 3 and 5 wt.% of silicotungstic acid (STA) into sodium alginate (NaAlg) and crosslinked with glutaraldehyde. Scanning electron microscopy and universal testing machine were used to investigate the morphology and the mechanical strength properties of the membranes. These membranes were tested for pervaporation (PV) dehydration of acetic acid at lower water concentrations of 10–25 wt.% in the feed. Addition of STA into NaAlg could result in a dramatic increase of water selectivity over that of plain NaAlg membrane dehydrating acetic acid for lowest STA containing NaAlg membrane. Thus, infinite selectivity was observed for STA-NaAlg membrane containing 1 wt.% of STA for all feed mixture compositions ranging from 10 to 25 wt.% water. With increasing STA content from 2, 3 and 5 wt.% in NaAlg membranes, selectivities ranged from 22,491 to 288, 12,848 to 192 and 6914 to 108, respectively for the studied composition range of the feed mixtures. PV performances of STA-NaAlg hybrid composite membranes were also tested at 40, 50, 60 and 70 °C typically in case of 10 wt.% water-containing feed mixture, which indicated a decrease in selectivity and increase in flux for all hybrid composite membranes. Arrhenius plots of flux data versus reciprocal of temperature exhibited linear trends. The hydrophilic STA is responsible to offer increased selectivity and flux to water as compared to plain NaAlg membrane for the feed mixtures studied. Of all the membranes tested, the 1 wt.% STA containing NaAlg membrane exhibited the best PV performance characteristics. Temperature did not influence much the selectivity data of STA-NaAlg membrane containing 1 wt.% of STA up to 50 °C, but flux increased with increasing temperature for all membranes. The results of this study are far superior to the previously reported data on acetic acid dehydration by the PV technique.

Novel carbohydrate polymeric blend membranes in pervaporation dehydration of acetic acid

Due to the widespread usage of carbohydrate polymers in a variety of areas, the present study is undertaken to develop novel graft copolymers of hydroxyethylcellulose and acrylamide (HEC- g-AAm). Grafting reaction was confirmed by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The graft copolymers were blended in different ratios with a natural polymer, sodium alginate (NaAlg). Using these polymers, membranes were prepared by solution casting and were crosslinked with glutaraldehyde for testing in pervaporation (PV) dehydration of acetic acid. Swelling experiments have been performed on the blend membranes at 30 °C to test their stability in water–acetic acid mixtures. The present membranes, being hydrophilic, were able to successfully recover 89% of water from acetic acid solutions when tested for feed mixtures ranging from 10% to 50% (w/w) of water. Membrane flux and selectivity to water was increased at increasing amount of HEC- g-AAm grafted copolymer in the mixed blend of NaAlg. The membranes of this study showed selectivity of 27.9 with a flux of 0.058 kg/m 2 h to dehydrate 10% (w/w) water from aqueous acetic acid feed mixture through the blend membrane. Flux values increased with increasing concentration of water in the feed, while selectivity decreased considerably. To the best of our knowledge, this is indeed the first example of the use of this type of combination carbohydrate polymers for pervaporation dehydration of acetic acid, which is a well-known industrial solvent.