The effect of casting solvent on the sorption and diffusion of water vapor in poly(γ-methyl L-glutamate)

Water vapor permeability of poly(γ-methyl L -glutamate) (PMLG) membranes prepared by using dichloroethane, trifluoroacetic acid, and formic acid as solvents was studied. The membranes prepared by casting dichloroethane and trifluoroacetic acid solutions of the polymer, designated as PMLG–DCE and PMLG–TFA, respectivley, had α-helical structures according to infrared absorption spectra, while the membranes prepared by allowing the PMLG–TFA membranes to swell in formic acid, designated as PMLG–FA, had mainly a β-sheet structure. The amounts of water sorbed by PMLG–DCE, PMLG–TFA, and PMLG–FA increased in that order. The isotherms of PMLG–TFA and PMLG–FA were sigmoidal-shaped isotherms, and the heat of sorption for PMLG–TFA and PMLG–FA was larger than that for PMLG–DCE, which suggested the presence of the sorption sites. The diffusion coefficients of water for PMLG–DCE increased and then decreased with increasing concentration. On the other hand, the diffusion coefficients for PMLG–TFA and PMLG–FA increased with concentration. The activation energies of diffusion for PMLG–DCE, PMLG–TFA, and PMLG–FA increased in that order. These results were discussed in connection with the molecular conformations of poly(γ-methyl L -glutamate) in the membranes. From these results, it is assumed that the molecular chains in the PMLG–TFA membranes are mainly in α-helical and partly random-coil conformations.     

Preparation and permeability of a block copolymer dialysis membrane by poly(γ-methyl-L-glutamate) and poly(ethylene glycol)

The block copolymer (PMLG-b-PEG) of poly(γ-methyl-L -glutamate) (PMLG) and isocyanate-terminated poly(ethylene glycol) was synthesized. Membranes were prepared by casting 2% 1,2-dichloroethane solutions of the polymer onto a glass plate and by evaporating the solvent at room temperature. The structure and microdomain morphologies of the membranes were observed with IR spectroscopy and scanning electron microscopy, respectively. Measurement of the contact angles of deionized water on polymer membrane surfaces was made. The mechanical properties of the membranes were also determined. The permeability of the PMLG-b-PEG and PMLG membranes toward urea and creatinine was studied in a dialyzer. In all cases, the block membranes showed improved permeability toward those solutes in comparison with the PMLG membranes. The permeation coefficients of urea, through the PMLG-b-PEG300 and PMLG-b-PEG1000 membranes, were about 2.3 and 3.2 times larger than that of PMLG membranes, and for creatinine through PMLG-b-PEG300 and PMLG-b-PEG1000 membranes, were about 1.0 and 2.0 times larger than that of PMLG membranes. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:75–82, 1998     

Permeability of synthetic poly(α-amino acid) membranes to oxygen dissolved in water

Membranes of synthetic poly(α-amino acids), namely, poly(γ-methyl L -glutamate) (PMLG), poly(γ-benzyl L -glutamate) (PBLG), poly(L -glutamic acid) (PLGA), poly(L -methionine) (PLM), and poly(N^?-carbobenzoxy-L -lysine) (PCLL), were prepared and their permeabilities of oxygen dissolved in water were measured in the 8–50°C temperature range using an oxygen electrode. Permeation curves for the poly(α-amino acid) membranes did not approach steady-state currents because of membrane degradation. To eliminate this, the membranes were laminated between polystyrene membranes; thus, the poly(α-amino acid) membranes came in direct contact with neither cathode surface nor electrolyte solution. No effect of membrane thickness on the permeability was observed. The Arrhenius plots of permeability coefficients for PCLL appear to change slope at about 22°C. This is consistent with the diffusion of oxygen in PCLL through the side-chain regions between helices. Comparisons between the permeability of oxygen dissolved in water and permeability of gaseous oxygen obtained by the high-vacuum method and between the activation energy of permeation of dissolved oxygen and that of gaseous oxygen were made in order to elucidate the effect of water on the oxygen permeation of each polymer. The permeability of the poly(α-amino acid) membranes to dissolved oxygen appears to depend on the properties of the side chains of the polymers.     

Pervaporation of benzene–cyclohexane mixture by poly(γ-methyl L-glutamate) membrane and synergetic effect of their mixture on diffusion rate

The pervaporation of binary liquids mixture of benzene and cyclohexane was examined by use of poly(γ-methyl L -glutamate) (PMLG) membrane. The permeation rate–time curve for each of benzene and cyclohexane from their mixtures changed to the longer times side by increasing the cyclohexane in the mixtures. t_1/2 (the time required to reach a half-value of the steady state permeation rate) for the each component increased exponentially with increasing of cyclohexane, which has a smaller plasticizing effect on PMLG membrane than benzene, in the mixtures. The apparent diffusion coefficients, obtained from the steady state permeation and the sorption experiments, for benzene–PMLG and cyclohexane–PMLG are dependent exponentially on the sorbed amounts of benzene. This result was explained on the bases that the diffusion of cyclohexane was enhanced synergetically with benzene coexisting in the system. This effect influenced negatively the separation of the liquids mixture by pervaporation.     

Gas transport properties in chlorosulfonated polyethylene‐acrylate based adhesives

The permeability and diffusivity properties of four gases—oxygen, nitrogen, carbon dioxide and methane—have been obtained for membranes prepared by the photocrosslinking of a mixture of chlorosulfonated polyethylene, acting as a binder, and a series of acrylic and methacrylic monomers. These measurements have been performed in the range 20°C to 50°C, and the activation energies have also been determined. These data are presented in comparison with those previously obtained in a crosslinked system in which the binder was not chlorosulfonated polyethylene but an aliphatic polyurethane. Both polymeric systems show similar permselectivities for the gas pairs O₂/N₂ (near 5) and CO₂/CH₄ (near 12), though overall permeability is about three times lower in the chlorosulfonated polyethylene—based polymer because of the smaller diffusion coefficients. The permeation and diffusion results are discussed in terms of the final structure of the photocrosslinked polymeric system, and it is concluded that it is the binder which is mostly responsible for the gas transport properties of these crosslinked materials.     

Permeability of polyglutamic acid ester membranes to benzene vapor

Permeability of poly(γ-methyl L -glutamate) (PMLG), poly(γ-hexahydrobenzyl L -glutamate)-(PHBLG), and poly(γ-n-amyl L -glutamate) (PALG) membrane to benzene vapor was studied. Permeability coefficients of all the membranes were large, of the order of 10^?9–10^?6 cm³(STP) cm/cm² sec cm Hg, and increased markedly with increasing relative vapor pressure and temperature. The large permeability was due to the large diffusion coefficient. The sorption behavior of the PALG–benzene system was interpreted in terms of the theory of the mixing of solvent with side chains. The Arrhenius plots of diffusion coefficients for PMLG and PHBLG showed a break at about 29 and 40°C, respectively, where the volume-expansion curves of each polymer also showed a break, which is thought to be related to the side-chain motion. The diffusivity data for PALG were examined in terms of Fujita's free-volume theory, and it was found that the value of the average free-volume fraction in the pure polymer for PALG was much larger than that for vinyl polymers. This means that the side-chain motion of PALG is easy and is the reason that the diffusion coefficients for PALG are large. These results indicate that the diffusion of benzene in these polypeptides takes place in the side-chain regions between helices.     

Pervaporation of methanol–water mixture by poly(γ-methyl L-glutamate) membrane and synergetic effect of their mixture on diffusion rate

The pervaporation behaviors of methanol–water by poly(γ-methyl L -glutamate) (PMLG) membrane at non-steady- and steady-state permeation were investigated. The values of t_1/2 (time required to reach a half value of steady-state permeation flux) for methanol and water changed and did not change with the component in feed, respectively. Both of the average diffusion coefficients for methanol–and water–PMLG from the mixture changed exponentially with the sorption amount of methanol by the synergetic effect on diffusion. The difference in behavior of non-steady and steady state diffusion was explained by whether D_o (diffusion coefficient at zero penetrant concentration) was influenced by the concentration distribution of penetrant in PMLG membrane.     

Probing anodic reaction kinetics and interfacial mass transport of a direct formic acid fuel cell using a nanostructured palladium-gold alloy microelectrode

The anodic reaction kinetics and interfacial mass transport of a direct polymer electrolyte membrane formic acid fuel cell have been investigated in an all solid-state electrochemical cell using a highly active nanostructured palladium-gold alloy microelectrode as an in situ probe. Well-defined “S-shaped” steady-state cyclic voltammograms exhibiting current-rising region at lower overpotentials and limiting current region at higher overpotentials have been first obtained for the electrochemical oxidation of formic acid at varying temperature. The “S-shaped” steady state polarization curves and chronoamperometric curves enable convenient measurements of the anodic reaction kinetics and interfacial mass transport of formic acid under real polymer electrolyte membrane conditions. It is encouragingly found that formic acid can be directly oxidized to CO₂ with the first electron transfer being the likely rate-determining step and the formation of surface poison can be neglected. The exchange current density for the electrooxidation of formic acid is on the order of magnitude of 10⁻⁷ A cm⁻² in the temperature range of 20-60 °C. The permeability and diffusion coefficient of formic acid through a Nafion^® 117 membrane are of the order of magnitude of 10⁻⁹ mol cm⁻¹ s⁻¹ and 10⁻⁶ cm² s⁻¹, respectively. The combination of a nanostructured microelectrode and an all solid-state electrochemical cell offers a versatile approach to evaluate potential electrocatalysts for fuel cells and electrochemical sensors employing polymer electrolyte membranes.     

Pebax membrane for CO2/CH4 separation: Effects of various solvents on morphology and performance

In this study, the effects of different solvents on the morphology and permeation of poly(ether‐block‐amide) (Pebax‐1657) membranes were investigated. Pebax membranes were fabricated via a solution casting method with five different solvents, that is, N,N‐dimethyl formamide (DMF), N,N‐dimethyl acetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), formic acid, and a mixture of ethanol (EtOH) with water (H₂O). Cross‐sectional scanning electron microscopy analysis of the membranes was performed to investigate the morphology of the prepared membranes. X‐ray diffraction and Fourier transform infrared analysis were also carried out to characterize the membranes. The interactions of the polymer and various solvents were evaluated with Hansen solubility parameters. Permeation experiments for CO₂ and CH₄ gases were performed to study the effects of the solvents on the permeation properties of the membranes. The solvent properties, such as the molar volume, boiling point, and solubility parameters, were investigated as were the membranes characteristics, such as the crystallinity, d‐spacing, and fractional free volume. The results obtained from the experiments show that the CO₂ permeability for the membranes prepared with different solvents followed this order: NMP > DMF > Formic acid > DMAc > H₂O/EtOH mixture. With increasing molar volume, the gas permeability increased for all of the membranes, except for DMAc, which showed a lower permeability because of its highly crystalline structure. DMF showed a higher CO₂/CH₄ ideal selectivity compared to the other membranes and, consequently, could be introduced as the best solvent from all aspects for the Pebax‐1657 membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44531.     

Electrochemical polymerization of β‐naphthalene sulfonic acid

β‐Naphthalene sulfonic acid (β‐NSA) has been electrochemically polymerized in a mixed electrolyte of boron trifluoride diethyl etherate (BFEE) solution mixed with a certain amount of trifluoroacetic acid (TFA) or concentrated sulfuric acid (SA). The poly(β‐naphthalene sulfonic acid) (PNSA) film prepared from the medium of BFEE+TFA was partly soluble in methanol. On the other hand, the polymer obtained from the system of BFEE+SA was soluble in water and general polar organic solvents such as methanol, alcohol, and acetone. The structure of PNSA was examined by infrared and UV spectra. Fluorescent spectral studies indicate that the polymer is a blue light emitter with fluorescence quantum efficiency of ～ 4%. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1939–1944, 2004     

Post-synthesis amination of polymer of intrinsic microporosity membranes for CO2 separation

Membrane separation is an energy-saving technology for carbon capture. However, it is subjected to permeability-selectivity trade-off limitation. Although chemical functionalization is proposed to boost separation efficiency, controlling sorption–diffusion process remains extremely challenging. In this study, a facile, controllable, and versatile chemical vapor amination strategy is reported to simultaneously tune gas sorption and diffusion in polymer of intrinsic microporosity (PIM)-based membranes for improving carbon capture performance. Through simple exposure in amine vapors under mild conditions, nucleophilic substitution of amines toward ether and halogen groups induce grafting, ring-opening, terminal replacement, chain-scission, and crosslinking of PIM-1, thereby underpinning CO₂-philicity and tailoring passageway. The prepared CO₂-philic membranes exhibit substantially improved CO₂/N₂ selectivity over 30.8, about 226% as that of original one, accompanied by high CO₂ permeability of 2590 Barrer, which can surpass the trade-off upper bound of polymer membranes. Our results reveal that post-synthesis amination is an effective route to obtain high-performance membranes.     

Interaction between carboxylic acids and the peptide group

The interaction between the peptide group and carboxylic acids is one of either protonation or hydrogen bonding. Both interactions will affect the vibrational frequency of the peptide group, resulting in changes in the characteristic amide vibrations. Infra-red spectroscopy has been used to examine the change in the amide I and II absorption bands of the model compound N-methylacetamide (NMA) when it is dissolved in deuterochloroform and various deuterochloroform/carboxylic acids, such as acetic, formic, dichloroacetic and trifluoroacetic acid. The results indicate that the interaction is one of hydrogen bonding except when NMA is dissolved in the strongest acid used, trifluoroacetic acid (TFA). Studies on the interaction between TFA and the peptide group of poly(l-alanine) various poly(dl-alanines) and poly(γ-benzyl-l-glutamate) show that the hydrogen bond interaction occurs, with little evidence of protonation taking place. In poly(γ-benzyl-l-glutamate) it was found that the TFA interacted both with the peptide group and the side chain carboxyl group.     

Polyether-segmented nylon hemodialysis membranes. IV. Membrane morphologies and permeability characteristics of dialysis membrane composed of poly(ethylene oxide)-segmented Ny69/M10

Dialysis membrane was prepared by a phase inversion method using a new polyether-segmented nylon which dissolves in common organic solvents such as dimethylsulfoxide. The polyether-segmented nylon contained poly(ethylene oxide) block and nylon block (random copolyamide: Ny69/M10) prepared by sebacic acid, azelaic acid, m-xylenediamine, and hexamethylenediamine. The morphologies and permeability characteristics of the membranes were investigated. It was shown by scanning electron microscope observation that the membrane had a fingerlike structure when dimethylsulfoxide was used as a polymer solvent, and a spongelike structure when an additive such as calcium chloride was added to the polymer solution. The high permeability for the solutes such as urea and vitamin B₁₂ were observed in comparison with the polyether-segmented Ny610 membranes prepared by a phase inversion method. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1731–1737, 1997     

Acetic Acid Extraction by Solvent Membrane

Abstract

Solvent extraction of acetic acid at low concentrations from aqueous solutions was studied. Decalin was found to be the optimal solvent and trioctyl phosphine oxide an effective carrier species. Phase equilibrium constants were measured and the results agree with the theoretical equation in the low carrier concentration range. The polymer supported solvent membranes carrying the same solvent and carrier, under various physical and chemical conditions, were prepared and the apparent diffusion coefficients of acetic acid through these membranes were measured and the results were discussed. The apparent diffusion coefficient of acetic acid in these tests was not interfered with by the existence of hydrochloric acid in the feed stream.     

Papain immobilization onto porous poly(λ-methyl L-glutamate) beads

Water-insoluble papain was prepared by immobilizing papain onto the surface of porous poly(λ-methyl L -glutamate) (PMLG) beads with and without spacer. The mode of the immobilization between papain and porous PMLG beads was covalent fixation. The relative activity and the stability of the immobilized papain was investigated. The retained activity of the papain covalently immobilized by the azide method was found to be excellent toward a small ester substrate, N-benzyl L -arginine ethyl ester (BAEE), compared with that of the peptide binding method. The values of the Michaelis constant K_m and the maximum reaction velocity V_m for free and immobilized papain on the PMLG beads were estimated. The apparent K_m was larger for immobilized papain than for the free enzyme, while V_m was smaller for the immobilized papain. The thermal stability of the covalently immobilized papain was higher than that of the free papain. The initial enzymatic activity of the covalently immobilized papain remained approximately unchanged with storage time, when the batch enzyme reaction was performed repeatedly, indicating the excellent durability.     

Polyether-segmented nylon hemodialysis membranes. I. Preparation and permeability characteristics of polyether-segmented nylon 610 hemodialysis membrane

The effect of the coagulation condition in the phase inversion method on the permeability characteristics of poly(propylene oxide) or poly(tetramethylene oxide)-segmented nylon 610 (PPO-Ny610 or PTMO-Ny610) hemodialysis membranes, the stability of the membrane performance, and the mechanical strength were investigated. The polymers were dissolved in a solvent such as formic acid and methanol saturated with calcium chloride, and thus PPO-Ny610 and PTMO-Ny610 membranes were prepared using formic acid and a calcium chloride/methanol/water mixture as a polymer solvent and a coagulant, respectively. It is concluded that PPO-Ny610 membrane has better permeability characteristics than PTMO-Ny610 membrane, and possesses additional properties for hemodialysis membranes such as mechanical properties and permeability stability in the drying and sterilizing processes. Furthermore, the blood compatibilities of PPO-Ny610 and PTMO-Ny610 membranes were superior to regenerated cellulose membranes on the basis of the result of platelet adhesion test. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1703–1711, 1997     

Kinetic Study of Formic Acid Oxidation on Highly Dispersed Carbon Supported Pd–TiO2 Electrocatalyst

The highly dispersed carbon supported Pd–TiO₂ catalyst was prepared by a liquid phase reduction method with intermittent microwave irradiation. The kinetic parameters, such as the charge transfer parameter (α) and the apparent diffusion coefficient (D) of formic acid electrooxidation on a carbon supported Palladium Titanium dioxide (Pd–TiO₂/C) electrode were obtained under the quasi steady-state conditions. The dependence on temperature of the formic oxidation at a Pd–TiO₂/C electrode was also investigated and the activation energy (E _a) at different potentials was obtained.     

Investigating the membrane morphology of water/solvent/nylon 6 systems

In this study, nylon 6 membranes were prepared in a water coagulation bath with two types of solvents, CaCl₂–methanol (CaClMe) and formic acid (FA). The morphology of the membranes, which was controlled by the phase behavior of their solutions, were connected to the mechanism of demixing, including liquid–liquid and liquid‐crystallization. Ternary phase diagrams showed that the CaClMe system coagulated significantly faster than the FA system. As observed by scanning electron microscopy, the CaClMe membrane had a porous, interconnected pore structure with macrovoids, whereas the FA membrane had a dense, spherulitic surface with a closed cell morphology. The high reaction surface of the CaClMe membrane with dye molecules provided outstanding dye rejection. Also, thermal analysis by differential scanning calorimetry showed that the slow coagulation of the FA system facilitated the formation of stable α‐form crystals rather than a metastable γ‐form structure. The results show that the phase‐separation mechanism was switched from liquid–liquid to liquid‐crystallization through a change in the solvent type from CaClMe to FA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Intensification of the Sulfuric Acid Alkylation Process with Trifluoroacetic Acid

H₂SO₄ alkylation of isobutane and butene is one of the primary commercial processes used to produce alkylates. This work presents a technology for the intensification of sulfuric acid alkylation with the addition of trifluoroacetic acid (TFA). The addition of TFA increased the solubility of isobutane in H₂SO₄, decreased its viscosity, and adjusted the acidity of H₂SO₄. With the addition of TFA, the selectivity of C8 was dramatically improved from 36.8 to 95.7%. The TFA content, stirring speed, reaction temperature, volume ratio of acid to hydrocarbon (H/C), molar ratio of isobutane to 2-butene (I/O), reaction time, and reuse of H₂SO₄/TFA were also investigated in this work. Compared with the conventional process, the new technology provided a considerably higher quality alkylation with considerably lower energy consumption. © 2018 American Institute of Chemical Engineers AIChE J, 65: 113–119, 2019     

Electrochemical comparison of IrO2 prepared by anodic oxidation of pure iridium and IrO2 prepared by thermal decomposition of H2IrCl6 precursor solution

Surface redox activities, oxygen evolution reaction (OER), oxidation of formic acid (FA), and anodic stability were investigated and compared for IrO₂ electrodes prepared by two techniques: the thermal decomposition of H₂IrCl₆ precursor (TDIROF) and the anodic oxidation of metallic iridium (AIROF). Surface redox activities involved on the AIROF were found to be much faster than those involved on the TDIROF. Concerning the oxygen evolution reaction, both films show a similar mechanism and specific electrocatalytic activities. The situation seems to be different for FA oxidation. In fact, on TDIROF, the oxidation of FA and the OER compete involving the same surface redox couple Ir(VI)/Ir(IV) contrary to FA oxidation on AIROF, where the Ir(V)/Ir(IV) surface redox couple is involved. Finally, electrode stability measurements have shown that contrary to TDIROF, which are very stable under anodic polarization, the AIROF are rapidly corroded under anodic treatment. This corrosion is enhanced even further in the presence of formic acid.