Dehydration from alcohols by polyion complex cross-linked chitosan composite membranes during evapomeation

This study describes the dehydration of an ethanol/water azeotrope during evapomeation using polyion complex cross-linked chitosan composite (q-Chito-PEO acid polyion complex/PES composite) membranes, constructed from quaternized chitosan (q-Chito) and poly(ethylene oxydiglycolic acid) (PEO acid) on a porous poly(ether sulfone) (PES) support. Both the q-Chito/PES composite and the q-Chito-PEO acid polyion complex/PES composite membranes showed high water permselectivity for an ethanol/water azeotrope. Both the permeation rate and the water permselectivity of the q-Chito/PES composite membranes were enhanced by increasing the degree of quaternization of the chitosan molecule because the affinity of the q-Chito/PES composite membranes for water was increased by introducing a quaternized ammonium group into the chitosan molecule. q-Chito-PEO acid polyion complex/PES composite membranes prepared from an equimolar ratio of carboxylate groups in the PEO acid versus quaternized ammonium groups in the q-Chito showed the maximum separation factor for water permselectivity without lowering the permeation rate. With an increasing molecular weight of PEO acid, the separation factor for water permselectivity increased, but the permeation rate almost did not change. The mechanism responsible for the separation of an ethanol/water azeotrope through the q-Chito-PEO acid polyion complex/PES composite membranes was analyzed by the solution-diffusion model. The permeation rate, separation factor for water permselectivity, and evapomeation index of q-Chito-PEO acid 400 polyion complex/PES composite membrane with an equimolar ratio of carboxylate groups in PEO acid 400 and ammonium groups in q-Chito were 3.5 x 10(-1) kg/(m(2) hr), 6300, and 2205, respectively, and very high membrane performance. The separation factor for water permselectivity for aqueous solutions of n-propyl and isopropyl alcohol was also maximized at an equimolar ratio of carboxylate groups and ammonium groups and was greater than that for an ethanol/water azeotrope. The above results were discussed from the viewpoint of the physical and chemical structure of the q-Chito-PEO acid polyion complex/PES composite membranes and the permeants.     

Phosphorylated chitosan membranes for the separation of ethanol-water mixtures by pervaporation

Dense membranes of chitosan were prepared and ionically crosslinked with phosphoric acid for varying intervals of time. The membranes were characterized by FTIR and XRD to confirm cross-linking. TGA and IEC studies were conducted to assess the thermal stability and estimate the number of interactive groups left in the membrane after crosslinking. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the membranes in pure liquids as well as binary mixtures. The phosphorylated chitosan membrane crosslinked for 2 h showed good mechanical strength and strong potential for breaking the azeotrope of 95.58 wt% ethanol by exhibiting a high pervaporation selectivity of 213 with substantial water flux of 0.58 kg/(m² h). Pervaporation experimental parameters such as feed composition, membrane thickness and permeate pressure were varied to identify optimum operating conditions.     

Highly concentrated aqueous ethanol solutions by pervaporation using silicalite membrane — Improvement of ethanol selectivity by addition of sugars to ethanol solution

Pervaporation performance using silicalite membranes in the separation of an ethanol/water solution was affected by the addition of sugars, sugar alcohols or yeast cells. Although the membrane flux drastically decreased to about 30% of that for an aqueous ethanol solution with increasing glucose or lactose concentration, the selectivity towards ethanol was inversely enhanced by the addition of glucose from 23 to 137. The accumulated proteins and acidic by-products in the fermentation broth caused the decline in the performance.     

Performance of butyrylcellulose membranes for benzene/cyclohexane mixtures containing a low benzene concentration by pervaporation

Butyrylcellulose (BuCell) with different degrees of butyrylation was synthesized as a membrane material for the separation of benzene/cyclohexane (Bz/Chx) mixtures. A BuCell membrane with a degree of butyrylation of 2.3 showed high benzene/cyclohexane selectivity for Bz/Chx mixtures by pervaporation. Both the permeation rate and the benzene/cyclohexane selectivity of the BuCell membrane increased with increasing benzene concentration in the feed mixture. The increase in the permeation rate resulted from an increase in the swelling of the membrane, and the increase in the benzene/cyclohexane selectivity can be attributed to an increase in the diffusion selectivity. With increasing degree of butyrylation of BuCell, the permeation rate increased; on the other hand, the benzene/cyclohexane selectivity decreased slightly. This result can qualitatively be explained by the degree of swelling, the density, and the contact angle of the BuCell membranes. The permeation and separation mechanism of Bz/Chx mixtures through BuCell membranes by pervaporation is discussed on the basis of the solution-diffusion model, which is typically applied for permeation through dense, nonporous membranes.     

Dehydration of 1,4-dioxane by pervaporation using modified blend membranes of chitosan and nylon 66

The pervaporation separation of 1,4-dioxane/water mixtures was carried out using crosslinked blend membranes of chitosan (CS) and nylon 66 (NYL). These membranes were characterized by FTIR, TGA, XRD, and tensile strength to assess intermolecular interactions, thermal stability, crystallinity and mechanical strength, respectively. Sorption studies were carried out in pure liquids and binary mixtures of different compositions to evaluate polymer–liquid interactions. The effects of CS/NYL ratio, membrane thickness, feed concentration on the transmembrane permeation rate and separation factor were investigated. Optimum CS/NYL ratio was determined as 90/10 (w/w) for 4.3 wt% feed water concentration at 40 °C. Increasing barrier from 30 to 120 μm improved the separation factor from 767 to 1123 at the cost of flux, which lowered from 0.118 to 0.028 kg/m² h. The membrane performance was also investigated for the separation of various feed compositions of 1,4-dioxane–water mixtures and permeate pressures. The azeotrope formed at 82-wt% dioxane was easily broken with a selectivity of 865 and water flux of 0.089 kg/m² h.     

Pervaporation behavior and integrated process for concentrating lignocellulosic ethanol through polydimethylsiloxane (PDMS) membrane

The effects of by-products from ethanol fermentation and hydrolysates of lignocelluloses on ethanol diffusion through polydimethylsiloxane (PDMS) membranes with/without silicalite-1 were investigated. A pervaporation process was integrated with lignocellulosic fermentation to concentrate bioethanol using bare PDMS membranes. Results showed that yeasts, solid particles, and salts increased ethanol flux and selectivity through the membranes (PDMS with/without silicalite-1), whereas glucose exerted negative effects on the performance. On bare PDMS membrane, the performance was not obviously affected by the existence of aliphatic acids. However, on PDMS-silicalite-1 membrane, a remarkable decrease in ethanol selectivity and a rapid growth of total flux in the presence of aliphatic acids were observed. These phenomena were due to the interaction of acids with silanol (Si–OH) groups to break the dense membrane surface. On the PDMS membranes with/without silicalite-1, degradation products of lignocellulosic hydrolysates such as furfural and hydroxyacetone slightly influenced separation performance. These results revealed that an integrated process can effectively eliminate product inhibition, improve ethanol productivity, and enhance the glucose conversion rate.     

Phase separation of cholesterol and the interaction of ethanol with phosphatidylserine-cholesterol bilayer membranes

Thermotropic and structural effects of ethanol on phosphatidylserine (PS) membranes containing up to 0.4 mol fraction cholesterol were investigated by differential scanning calorimetry, X-ray diffraction and fluorescence spectroscopy. It was found that in the presence of cholesterol, 10% (v/v) added ethanol depresses the melting temperature of the phospholipid by approximately 2 degrees C, similar to what was observed in the absence of cholesterol. Below the melting temperature the progressive disordering effect of added cholesterol is weakly enhanced by the presence of ethanol. In the liquid crystalline state, the marked decrease in the thickness of the bilayer which ethanol causes in the absence of cholesterol (Chem. Phys. Lipids 92 (1998) 127), is also observed in its presence. We conclude that, in contrast to what has been observed for zwitterionic phospholipids, high concentrations of cholesterol do not diminish the interaction of ethanol with PS membranes. With addition of 10% (v/v) ethanol, crystalline cholesterol diffraction, an indication of phase separation of the sterol, appears at mol fraction cholesterol 0.34, as compared to 0.3 in the absence of ethanol (Chem. Phys. Lipids 92 (1998) 71).     

Hybrid Membranes Dispersed with Superhydrophilic TiO2 Nanotubes Toward Ultra‐Stable and High‐Performance Vanadium Redox Flow Batteries

The vanadium redox flow battery (VRFB) is a large‐scale energy storage technique and has been regarded as a promising candidate to integrate intermittent renewable energy with the grid. Its long‐term stability has so far been limited by the core component, an ion exchange membrane with low ion selectivity. Here a hybrid membrane with superhydrophilic TiO₂ nanotubes dispersed in a Nafion matrix is reported. The VRFB single cell with the hybrid membrane exhibits an impressive performance with high coulombic efficiency (CE, ≈98.3%) and outstanding energy efficiency (EE, ≈84.4%) at 120 mA cm^?2, which is higher than that of the commercial Nafion 212 membrane (CE, ≈94.5%; EE, ≈79.2%). More importantly, the cell maintains a discharge capacity of ≈55.7% after 1400 cycles (over 518 h), in obvious contrast to that of ≈20% after only 410 cycles for the one using commercial Nafion 212. This is attributed to the high ion selectivity of the hybrid membrane, because of, 1) the blocked and elongated ion diffusion pathway induced by the dispersed nanotubes and 2) binding and alignment of the sulfonic acid groups on nanotube surface. The high‐performance membranes may also find important applications in other fields, such as fuel cells, dialytic batteries, and water treatment.     

Osmotic gradient-induced water permeation across the sarcolemma of rabbit ventricular myocytes

The mechanism of water permeation across the sarcolemma was characterized by examining the kinetics and temperature dependence of osmotic swelling and shrinkage of rabbit ventricular myocytes. The magnitude of swelling and the kinetics of swelling and shrinkage were temperature dependent, but the magnitude of shrinkage was very similar at 6 degrees, 22 degrees, and 37 degrees C. Membrane hydraulic conductivity, Lp, was approximately 1.2 x 10(-10) liter.N-1.s-1 at 22 degrees C, corresponding to an osmotic permeability coefficient, Pf, of 16 microns.s-1, and was independent of the direction of water flux, the magnitude of the imposed osmotic gradient (35-165 mosm/liter), and the initial cell volume. This value of Lp represents an upper limit because the membrane was assumed to be a smooth surface. Based on capacitive membrane area, Lp was 0.7 to 0.9 x 10(-10) liter.N-1.s-1. Nevertheless, estimates of Lp in ventricle are 15 to 25 times lower than those in human erythrocytes and are in the range of values reported for protein- free lipid bilayers and biological membranes without functioning water channels (aquaporin). Evaluation of the effect of unstirred layers showed that in the worst case they decrease Lp by < or = 2.3%. Analysis of the temperature dependence of Lp indicated that its apparent Arrhenius activation energy, Ea', was 11.7 +/- 0.9 kcal/mol between 6 degrees and 22 degrees C and 9.2 +/- 0.9 kcal/mol between 22 degrees and 37 degrees C. These values are significantly greater than that typically found for water flow through water-filled pores, approximately 4 kcal/mol, and are in the range reported for artificial and natural membranes without functioning water channels. Taken together, these data strongly argue that the vast majority of osmotic water flux in ventricular myocytes penetrates the lipid bilayer itself rather than passing through water-filled pores.     

Biodegradable polylactide/chitosan blend membranes

Biodegradable blend membranes based on polylactide and chitosan with various compositions were prepared via a two-step processing pathway. In the first step, solutions of each component were properly mixed and cast into a gelatinous membrane, and in the second step, the obtained membrane was immersed into a mixed solution for the solvent extraction followed by a drying procedure to finally generate a well-blended membrane. An acetic acid-acetone solvent system was selected for poly(DL-lactide)/chitosan membranes, and another solvent system for poly(L-lactide)/chitosan membranes consisted of acetic acid and dimethyl sulfoxide. Some processing parameters, such as the concentration of component solutions and the composition ratio of mixed solvents and extraction solvents, were optimized by primarily considering whether the directly visible phase separation occurred during the processing procedures. Morphologies of these blend membranes were viewed using SEM. It was found that the processing parameters exerted quite notable impacts on the morphology of the membranes. The hydrophilicity of membranes was examined by measuring their water contact angle and swelling index. These blend membranes were also investigated for their miscibility using IR spectra, X-ray diffractograms, TG, DSC, and dynamic mechanical analysis methods. Although the presence of phase separation at a microscopic level was detected for these membranes, pronounced interactions between components were confirmed. The obtained results shown that some membranes prepared under optimized processing conditions had a partially miscible structure.     

Neutron diffraction studies of oral stratum corneum model lipid membranes

In this work we have investigated model lipid mixtures simulating a lipid component of oral stratum corneum (OSC). Neutron diffraction experiments on oriented samples have revealed that SM (bovine brain)/dipalmitoylphosphatidylethanolamine/dipalmitoylphosphatidylcholine (DPPE/DPPC) mixtures at molar ratios of 1/2/1 and 1/1/1 are one-phase membranes. The incorporation of low concentrations of ceramide 6 and cholesterol into SM/DPPC/DPPE bilayers does not result in a phase separation, affecting membrane hydration. The model OSC membrane composed of ceramide 6/cholesterol/fatty acids/cholesterol sulfate/SM (bovine brain)/DPPE/DPPC is characterized by coexistence of several lamellar phases, that behave differently during their hydration in water excess. The phase with lamellar repeat distance of about 45 Å is likely a ceramide-rich phase and shows a restricted swelling in water, while another phase with repeat distance of 50 Å swells very quickly on 15 Å and then disappears. Our results indicate that phospholipid-rich and ceramide-rich domains could possibly coexist in the intercellular space of oral epithelium.     

Molecular simulation of permeation behaviour of ethanol/water molecules with single-layer graphene oxide membranes

Graphene oxide (GO)-based materials have shown promise as water-permeating membranes in pervaporation separation. However, the feed permeation and surface affinity of single-layer nanoporous GO sheet for liquid mixtures remain unresolved. Here, the pressure-driven molecular transport of pure ethanol and pure water, as well ethanol-water mixtures, crossing through single-layer nanoporous GO sheet was studied by non-equilibrium molecular dynamics simulations. We show that single-layer GO sheet with controlled pore sizes can effectively reject ethanol and allow water permeation with high permeability. This means that porous GO sheets could act as an effective dehydration membrane, therefore providing the initial barrier for ethanol passage in GO-based membrane. The pore size effect was considered as the separation mechanism. Both ethanol and water molecules in the mixture show comparable affinity with GO surfaces. The hydrogen-bonding coupling interaction between mixture and surface functional groups provide addition influence on the molecular transport through GO pores.     

Comparative effects of cholesterol and cholesterol sulfate on hydration and ordering of dimyristoylphosphatidylcholine membranes.

The comparative effect of cholesterol (CH) versus cholesterol sulfate (CS) on dimyristoylphosphatidylcholine (DMPC) membranes has been investigated by optical microscopy, freeze-fracture electron microscopy, x-ray diffraction, and solid state 2H and 31P nuclear magnetic resonance (NMR). The sulfate analogue extends the lamellar phase domain toward high water contents, and substitution of 30 mol % CH by CS in DMPC lamellae induces the trapping of 30 wt % additional water. The greater swelling of the CS-containing systems is evidenced by determination of lamellar repeat distances at maximal hydration: 147 +/- 4 A and 64 +/- 2 A in the presence of CS and CH, respectively. 2H-NMR of heavy water demonstrates that CS binds approximately 12 more water molecules at the interface than CH whereas NMR of deuterium-labeled DMPC chains reveals that 30 mol % CS orders the membrane as 15 mol % CH at high temperature and disorders much more than CH at low temperatures. The various effects of CS versus CH are discussed by taking into account attractive Van der Waals forces and repulsive steric/electrostatic interactions of the negatively charged sulfate group.     

Solute effects on the colloidal and phase behavior of lipid bilayer membranes: ethanol-dipalmitoylphosphatidylcholine mixtures.

By means of the scanning differential calorimetry, x-ray diffractometry, and the dynamic light scattering, we have systematically studied the phase and packing properties of dipalmitoylphosphatidylcholine vesicles or multibilayers in the presence of ethanol. We have also determined the partial ternary phase diagram of such dipalmitoylphosphatidylcholine/water/ethanol mixtures. The directly measured variability of the structural bilayer parameters implies that ethanol binding to the phospholipid bilayers increases the lateral as well as the transverse repulsion between the lipid molecules. This enlarges the hydrocarbon tilt (by up to 23 degrees) and molecular area (by < or = 40%). Ethanol-phospholid association also broadens the interface and, thus, promotes lipid headgroup solvation. This results in excessive swelling (by 130%) of the phosphatidylcholine bilayers in aqueous ethanol solutions. Lateral bilayer expansion, moreover, provokes a successive interdigitation of the hydrocarbon chains in the systems with bulk ethanol concentrations of 0.4-1.2 M. The hydrocarbon packing density as well as the propensity for the formation of lamellar gel phases simultaneously increase. The pretransition temperature of phosphatidylcholine bilayers is more sensitive to the addition of alcohol (initial shift: delta Tp = 22 degrees C/mol) than the subtransition temperature (delta Ts reversible 5 degrees C/mol), whereas the chain-melting phase transition temperature is even less affected (delta Tm = 1.8 degrees C/mol). After an initial decrease of 3 degrees for the bulk ethanol concentrations below 1.2 M, the Tm value increases by 2.5 degrees above this limiting concentration. The gel-phase phosphatidylcholine membranes below Tm are fully interdigitated above this limiting concentration. The chain tilt on the fringe of full chain interdigitation is zero and increases with higher ethanol concentrations. Above Tm, some of the lipid molecules are solubilized by the bound ethanol molecules. More highly concentrated ethanol solutions (> 7 M) solubilize the phosphatidylcholine bilayers with fluid chains fully and result in the formation of mixed lipid-alcohol micelles.     

Chronic and acute ethanol treatment modifies fluidity and composition in plasma membranes of a human hepaic cell line (WRL-68)

The aim of this study was to compare the effects of chronic (0.1 mol/L ethanol exposure during 30 days) and acute (0.5 mol/L ethanol exposure during 24 h) ethanol treatment on the physical properties and the lipid composition of plasma membranes of the WRL-68 cells (fetal human hepatic cell line). Using fluorescence polarization we found that ethanol treatment reduced membrane anisotropy due to disorganization of acyl chains in plasma membranes and consequently increased fluidity, as measured with the diphenylhexatriene probe. Addition of ethanolin vitro reduced anisotropy in control plasma membranes, whereas chronically ethanol-treated plasma membranes were relatively tolerant to thein vitro addition of ethanol. Acutely ethanol-treated plasma membranes exhibited a smaller anisotropy parameter value than control plasma membranes. We found a decrease in total phospholipid content in acute ethanol WRL-68 plasma membranes. Cholesterol content was increased in both ethanol treatments, and we also found a significant decrease in phosphatidylinositol and phosphatidylcholine and an increase in phosphatidylethanolamine content in ethanol-treated plasma membranes. Our data showed that ethanol treatment decreased the anisotropy parameter consistently with increased fluidity, while increasing the cholesterol/phospholipid ratio of plasma membranes of WRL-68 cells, but only chronically ethanol-treated plasma membranes exhibited tolerance to thein vitro addition of ethanol. It is important to note that some changes that were interpreted as a result of chronic ethanol treatment were also present in short-period ethanol treatments.Abbreviations DPH diphenylhexatriene - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PS phosphatidylserine - SPH sphingomyelin     

Ethanol production in an integrated fermentation/membrane system. Process simulations and economics

Four systems comprising of an ethanol fermentation integrated with microfiltration and/or pervaporation, and a conventional continuous culture, were compared with respect to the performance of the fermentation and economics. The processes are compared on the basis of the same kinetic model. It is found that cell retention by microfiltration leads to lower production costs, compared to a conventional continuous culture. Pervaporation becomes profitable at a high selectivity of ethanol/water separation and low membrane prices.     

Investigation of stratum corneum lipid model membranes with free fatty acid composition by neutron diffraction

The outermost epidermal layer, the stratum corneum (SC), is the main skin barrier. Studies of SC model systems enable characterization of the influence of individual lipids on the organization of the SC lipid matrix, which is the main pathway of water through the skin. This work presents a neutron diffraction study of the SC model membranes based on short-chain ceramide 6 with nearly realistic composition of free fatty acids (FFA) at physiological temperature of the SC. The influence of FFA and the effect of cholesterol–cholesterol sulfate substitution on the structure and hydration of the SC model membranes are described. The structure of the SC membrane with FFA is close to the structure of the earlier studied SC membrane based on short-chain palmitic acid (PA) and does not vary significantly under changes of the ratio of the main membrane components. FFA accelerates membrane swelling at the same low level of hydration of both PA- and FFA-containing membranes. The substitution of cholesterol sulfate by cholesterol in the membrane composition decreases membrane swelling and leads to phase separation in the model system.     

The role of OH…O and CH…O hydrogen bonds and H…H interactions in ethanol/methanol–water heterohexamers

Bioethanol is one of the world’s most extensively produced biofuels. However, it is difficult to purify due to the formation of the ethanol–water azeotrope. Knowledge of the azeotrope structure at the molecular level can help to improve existing purification methods. In order to achieve a better understanding of this azeotrope structure, the characterization of (ethanol)₅–water heterohexamers was carried out by analyzing the results of electronic structure calculations performed at the B3LYP/6-31+G(d) level. Hexamerization energies were found to range between ?36.8 and ?25.8 kcal/mol. Topological analysis of the electron density confirmed the existence of primary (OH…O) hydrogen bonds (HBs), secondary (CH…O) HBs, and H…H interactions in these clusters. Comparison with three different solvated alcohol systems featuring the same types of atom–atom interactions permitted the following order of stability to be determined: (methanol)₅–water > (methanol)₆ > (ethanol)₅–water > (ethanol)₆. These findings, together with accompanying geometric and spectroscopic analyses, show that similar cooperative effects exist among the primary HBs for structures with the same arrangement of primary HBs, regardless of the nature of the molecules involved. This result provides an indication that the molecular ratio can be considered to determine the unusual behavior of the ethanol–water system. The investigation also highlights the presence of several types of weak interaction in addition to primary HBs.

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Graphical Abstract Water-ethanol clusters exhibit a variety of interaction types between their atoms, such as primary OH...O (blue), secondary CH...O (green) and H...H (yellow) interactions as revealed by Quantum Chemical Topology

     

Ethanol withdrawal provokes mitochondrial injury in an estrogen preventable manner

We investigated whether ethanol withdrawal (EW) oxidizes mitochondrial proteins and provokes mitochondrial membrane swelling and whether estrogen deprivation contributes to this problem. Ovariectomized female rats with or without 17β-estradiol (E2)-implantation received a control diet or a liquid ethanol diet (6.5%) for 5 weeks and were sacrificed during EW. Protein oxidation was assessed by measuring carbonyl contents and was visualized by immunochemistry. Mitochondrial membrane swelling as an indicator of mitochondrial membrane fragility was assessed by monitoring absorbance at 540 nm and was compared with that of male rats. Compared to the control diet group and ovariectomized rats with E2-implantation, ovariectomized rats without E2-implantation showed higher carbonylation of mitochondrial proteins and more rapid mitochondrial membrane swelling during EW. Such rapid mitochondrial membrane swelling was comparable to that of male rats undergoing EW. These findings demonstrate that EW provokes oxidative injury to mitochondrial membranes in a manner that is exacerbated by estrogen deprivation.     

Membrane separations using molecularly imprinted polymers

This review presents an overview on the promising field of molecularly imprinted membranes (MIM). The focus is onto the separation of molecules in liquid mixtures via membrane transport selectivity. First, the status of synthetic membranes and membrane separation technology is briefly summarized, emphasizing the need for novel membranes with higher selectivities. Innovative principles for the preparation of membranes with improved or novel functionality include self-assembly or supramolecular aggregation as well as the use of templates. Based on a detailed analysis of the literature, the main established preparation methods for MIM are outlined: simultaneous membrane formation and imprinting, or preparation of imprinted composite membranes. Then, the separation capability of MIM is discussed for two different types, as a function of their barrier structure. Microporous MIM can continuously separate mixtures based on facilitated diffusion of the template, or they can change their permeability in the presence of the template ("gate effect"). Macroporous MIM can be developed towards molecule-specific membrane adsorbers. Emerging further combinations of molecularly imprinted polymers (MIPs), especially MIP nanoparticles or microgels, with membranes and membrane processes are briefly outlined as well. Finally, the application potential for advanced MIM separation technologies is summarized.