Copolyimide Brushes as a Component of a Hybrid Poly(phenylene Oxide) Membrane for Controlling Gas Separation: Effect of Water, Methanol, and Hexane Vapors.

The effect of water, methanol, and hexane vapors on gas permeability was studied in a hybrid membrane containing 5 wt% copolyimide brushes with poly(methyl methacrylate) side chains (PI-g-PMMA) in a poly(phenylene oxide) (PPO) matrix, and in a pristine PPO membrane. These membranes in the form of dense nonporous films were further examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), as well as by measuring their mechanical and gas transport properties. A gas separation study of the membranes in a dry state and the membranes saturated with water, methanol, and hexane vapors was performed to estimate the effect of each vapor on the H2, CO2, N2 permeability and selectivity in the separation of H2/N2 and CO2/N2 pairs. In general, saturation with water, methanol, and hexane vapors caused a decrease in the gas permeability of both membranes. The hybrid membrane containing copolyimide brushes demonstrated enhanced selectivity in the separation of H2/N2 and CO2/N2 pairs. It was found that a special effect of the vapors used for membrane saturation is associated with their molar volume. The solubility and diffusion coefficients of N2 and CO2 were obtained by Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations.

The Effect of Complex Modifier Consisting of Star Macromolecules and Ionic Liquid on Structure and Gas Separation of Polyamide Membrane.

A novel hybrid membrane was developed on the basis of poly(m-phenylene isophthalamide) (PA) by introducing an original complex modifier into the polymer; this modifier consisted of equal amounts of heteroarm star macromolecules with a fullerene C60 core (HSM) and the ionic liquid [BMIM][Tf2N] (IL). The effect of the (HSM:IL) complex modifier on characteristics of the PA membrane was evaluated using physical, mechanical, thermal, and gas separation techniques. The structure of the PA/(HSM:IL) membrane was studied by scanning electron microscopy (SEM). Gas transport properties were determined by measuring He, O2, N2, and CO2 permeation through the membranes based on PA and its composites containing a 5 wt% modifier. The permeability coefficients of all gases through the hybrid membranes were lower than the corresponding parameters for the unmodified membrane, whereas the ideal selectivity in the separation of He/N2, CO2/N2, and O2/N2 gas pairs was higher for the hybrid membrane. The position of the PA/(HSM:IL) membrane on the Robeson's diagram for the O2/N2 gas pair is discussed.

Novel Design of Co-Poly(Hydrazide Imide) and Its Complex with Cu(I) for Membrane Separation of Methanol/Dimethyl Carbonate Mixture.

Poly(2,2'-biquinoline-6,6'-dicarbohydrazide)-co-(bistrimelliteimide)methylene-bisanthranylide (PHI) and its metal-polymer complex PHI-Cu(I) containing several types of functional groups (hydrazide, carboxyl, amide, and imide fragments) were synthesized to prepare two types of dense nonporous membranes. The study on morphology using scanning electron microscopy (SEM), measurements of mechanical, thermal, and transport properties of the membrane samples was carried out. The main mechanical properties of both membranes do not differ significantly, but the values of ultimate deformation differ palpably as a result of a non-uniform character of the deformation process for the PHI membrane. The thermal analysis based on the curves of thermogravimetric (TGA) and differential thermal (DTA) analyses of the PHI and PHI-Cu(I) membranes revealed peculiarities of the membrane structure. Transport properties were studied in pervaporation (PV) of methanol (MeOH) and dimethyl carbonate (DMC) mixtures including an azeotropic point. Intrinsic properties of the penetrant-membrane system were also determined. It was found that the total flux is higher through the PHI membrane, but the PHI-Cu(I) membrane exhibits a higher separation factor. Calculation of the pervaporation separation index (PSI) allowed to conclude that the PHI-Cu(I) membrane exhibits better transport properties as compared with the PHI membrane.

Effect of ionic liquid on formation of copolyimide ultrafiltration membranes with improved rejection of La3.

Ultrafiltration (UF) as a widely used industrial separation method with optimal selection of membrane materials can be applied to extract rare earth metals from dilute solutions formed during the processing of electronic waste by hydrometallurgical methods. In the present work, promising UF copolyimide membranes were prepared using [hmim][TCB] ionic liquid (IL) co-solvent which can be considered as an environmentally friendly alternative to conventional solvents. The membranes were characterized by ATR-FTIR, TGA, SEM and quantum chemical calculations. A significant difference in morphology of these membranes was revealed by SEM of membrane cross-sections; the P84 membrane has finger-like structure of porous substrate in contrast to spongy structure of substrate for the P84/IL membrane due to a higher dynamic viscosity of the casting solution. The transport parameters were determined in ultrafiltration tests with pure water and an aqueous solution of bovine serum albumin. The addition of ionic liquid to the P84 casting solution increases the performance of the membrane. The rejection capacity was evaluated with respect to La3+ in the form of a lanthanum alizarin complex (LAC) in aqueous acetone solution. The P84 membrane prepared using IL showed a high rejection (98.5%) with respect to LAC, as well as a significant productivity.

Application of Cyclized Polyacrylonitrile for Ultrafiltration Membrane Fouling Mitigation.

In this study, novel composites were produced by blending partially cyclized polyacrylonitrile (cPAN) and poly(amide-imide) (PAI) in N-methylpyrrolidone in order to fabricate asymmetric membranes via phase inversion method. The compatibility of PAI and cPAN through possible intermolecular interaction was examined by quantum chemical calculations. The composite membranes were characterized by FTIR, SEM, contact angle measurements, etc. A considerable reduction in the contact angles of water and ethylene glycol (EG) was observed after adding cPAN to the PAI membrane, which is evidence of improved membrane hydrophilicity. Membrane transport properties were investigated in ultrafiltration tests by measuring the pure water flux, rejection of proteins, and flux recovery ratio (FRR). The best properties were found for the membrane containing 5 wt% cPAN; an increase in BSA rejection and a remarkable increase in FRR were observed, which can be explained by the hydrophilization of the membrane surface provided by the presence of cPAN.

Impact of Layered Perovskite Oxide La0.85Yb0.15AlO3 on Structure and Transport Properties of Polyetherimide.

This study aims to improve properties of Ultem® polyetherimide (PEI) by incorporating up to 2 wt% additives of the perovskite oxide La0.85Yb0.15AlO3 (LYA). The structure of dense PEI/LYA films was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in combination with an analysis of their elemental composition using energy-dispersive spectroscopy (EDS). The PEI/LYA films exhibit a two-layer structure. Contact angle measurements revealed hydrophilization of the membrane surface enriched with the perovskite. The transport properties were tested via gas separation and pervaporation processes. The separation selectivity of He/N2 and O2/N2 gas pairs increased with the growth of the LYA content in the membranes. Pervaporation of a methanol(MeOH)-cyclohexane(CH) mixture was effective due to the high sorption of MeOH in the PEI/LYA membranes. The maximal pervaporation separation index was found for the PEI/LYA(2%) membrane.

Enhancing Pervaporation Membrane Selectivity by Incorporating Star Macromolecules Modified with Ionic Liquid for Intensification of Lactic Acid Dehydration.

Modification of polymer matrix by hybrid fillers is a promising way to produce membranes with excellent separation efficiency due to variations in membrane structure. High-performance membranes for the pervaporation dehydration were produced by modifying poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to facilitate lactic acid purification. Ionic liquid (IL), heteroarm star macromolecules (HSM), and their combination (IL:HSM) were employed as additives to the polymer matrix. The composition and structure of hybrid membranes were characterized by X-ray diffraction and FTIR spectroscopy. Scanning electron microscopy was used to investigate the membranes surface and cross-section morphology. It was established that the inclusion of modifiers in the polymer matrix leads to the change of membrane structure. The influence of IL:HSM was also studied via sorption experiments and pervaporation of water‒lactic acid mixtures. Lactic acid is an essential compound in many industries, including food, pharmaceutical, chemical, while the recovering and purifying account for approximately 50% of its production cost. It was found that the membranes selectively remove water from the feed. Quantum mechanical calculations determine the favorable interactions between various membrane components and the liquid mixture. With IL:HSM addition, the separation factor and performance in lactic acid dehydration were improved compared with pure polymer membrane. The best performance was found for (HSM: IL)-PPO/UPM composite membrane, where the permeate flux and the separation factor of about 0.06 kg m-2 h-1 and 749, respectively, were obtained. The research results demonstrated that ionic liquids in combination with star macromolecules for membrane modification could be a promising approach for membrane design.

Strongly Selective Polymer Membranes Modified with Heteroarm Stars for the Ethylene Glycol Dehydration by Pervaporation.

Hybrid membranes based on poly (2,6-dimethyl-1,4-phenylene oxide) modified with heteroarm stars (HAS) were developed to separate ethylene glycol/water mixtures by pervaporation. The HAS consist of a small branching center fullerene C 60 and twelve arms of different nature, six arms of nonpolar polystyrene and six arms of polar poly-tert-butyl methacrylate. The changes of structure and physical properties with HAS inclusion were systematically studied using SEM, X-ray diffraction analysis, TGA, and contact angle measurements. Mass transfer of ethylene glycol and water through membranes was studied by sorption and pervaporation tests. It was found that the growth of HAS content up to 5 wt% in the membrane leads to an increase in the total flux and a strong increase in the separation factor. To evaluate intrinsic properties of the penetrant ‒membrane system, permeability and selectivity were calculated. Overall, utilizing star-shaped macromolecules as a filler can be a promising way to improve the separation performance of diffusion membranes.

Novel Polyester Amide Membranes Containing Biquinoline Units and Complex with Cu(I): Synthesis, Characterization, and Approbation for n-Heptane Isolation from Organic Mixtures.

The wide possibilities of designing a chemical structure and creating complexes with transition metals make polymers of heteroaromatic structure interesting objects, from both scientific and practical aspects. In this work, modern biquinoline-containing polymers, namely polyester amide (PEA) and its metal-polymer complex (PEA-Cu(I)), were synthesized and used to form dense flat membranes. A comparative study of their morphology, same physical properties (density, free volume, and contact angles), and thermomechanical characteristics was carried out. The transport properties of the modern membranes were studied during pervaporation, to solve a problem of n-heptane isolation from its binary mixtures with thiophene and methanol. It was shown that only the PEA membrane is selective for the separation of thiophene impurities from the mixture with n-heptane. In pervaporation of methanol/n-heptane mixture, the РЕА-Cu(I) membrane exhibits significantly higher pervaporation separation index, as compared with that of the РЕА membrane.

Asymmetric Membranes Based on Copolyheteroarylenes with Imide, Biquinoline, and Oxazinone Units: Formation and Characterization.

Modern ultrafiltration requires novel perfect membranes with narrow pore size, high porosity, and minimal pore tortuosity to achieve high separation performance. In this work, copolyamic acid (co-PAA) was synthesized and used for the preparation of asymmetric porous membranes by phase inversion technique. Several co-PAA membranes were heated up to 250 °C; during heating, they undergo solid-phase transformation into co-polybenzoxazinoneimide (co-PBOI) via dehydration and cyclization. Comparative characterization of both co-PAA and co-PBOI membranes was realized by scanning electron microscopy, mechanical testing, thermogravimetric analysis, and ultrafiltration experiments. Membrane calibration was carried out using a mixture of seven proteins with different molecular weights. During heat treatment, the molecular weight cut-off of the membranes decreased from 20 × 103 g/mol (co-PAA) to 3 × 103 g/mol (co-PBOI). Abnormally low dispersions of rejection (0.3 for co-PAA and 0.45 for co-PBOI) were observed for the studied membranes; this fact indicates that the membranes possess enhanced resolving power.

Improved Hydrogen Separation Using Hybrid Membrane Composed of Nanodiamonds and P84 Copolyimide.

Membrane gas separation is a prospective technology for hydrogen separation from various refinery and petrochemical process streams. To improve efficiency of gas separation, a novel hybrid membrane consisting of nanodiamonds and P84 copolyimide is developed. The particularities of the hybrid membrane structure, physicochemical, and gas transport properties were studied by comparison with that of pure P84 membrane. The gas permeability of H2, CO2, and CH4 through the hybrid membrane is lower than through the unmodified membrane, whereas ideal selectivity in separation of H2/CO2, H2/CH4, and CO2/CH4 gas pairs is higher for the hybrid membrane. Correlation analysis of diffusion and solubility coefficients confirms the reliability of the gas permeability results. The position of P84/ND membrane is among the most selective membranes on the Robeson diagram for H2/CH4 gas pair.

Impact of Endometallofullerene on P84 Copolyimide Transport and Thermomechanical Properties.

Novel polymer composite materials, including unique nanoparticles, contribute to the progress of modern technologies. In this work, the endohedral fullerene C60 with incapsulated iron atom (endometallofullerene Fe@C60) is used for modification of P84 copolyimide. The impact of 0.1, 0.5, and 1 wt % endometallofullerene on the structure and physicochemical properties of polymer films is studied through scanning electron microscopy, thermogravimetric analysis, and thermomechanical tests. Transport properties are estimated through sorption and pervaporation techniques toward methanol and methyl acetate mixture. The inclusion of endometallofullerene into the copolyimide matrix improves membrane permeability and selectivity in the separation of methanol-methyl acetate mixtures. The maximal effect is achieved with a composite containing 0.5 wt % Fe@C60. The developed composites are effective for energy and resource saving purification of methyl acetate by pervaporation.

Aromatic Copolyamides with Anthrazoline Units in the Backbone: Synthesis, Characterization, Pervaporation Application.

Copolyamides with anthrazoline units in the backbone (coPA) were synthesized and dense nonporous films were prepared by solvent evaporation. Glass transition temperature, density, and fractional free volume were determined for the dense nonporous films composed of polyamide and two of its copolymers containing 20 and 30 mol % anthrazoline units in the backbone. Transport properties of the polymer films were estimated by sorption and pervaporation tests toward methanol, toluene, and their mixtures. An increase in anthrazoline fragments content leads to an increasing degree of methanol sorption but to a decreasing degree of toluene sorption. Pervaporation of a methanol⁻toluene mixture was studied over a wide range of feed concentration (10⁻90 wt % methanol). Maximal separation factor was observed for coPA-20 containing 20 mol % fragments with anthrazoline units; maximal total flux was observed for coPA-30 with the highest fractional free volume.