Propylene-induced plasticization in silver polymer electrolyte membranes

Silver polymer electrolyte membranes consisting of AgBF₄ or AgCF₃SO₃ dissolved in poly(2-ethyl-2-oxazoline) (POZ) or poly(N-vinyl pyrrolidone) (PVP) have previously shown outstanding separation performance for propylene/propane mixtures. The ideal separation factor (i.e. pure gas selectivity) of propylene over propane reached 15,000, but the actual selectivity (i.e. mixed gas selectivity) was approximately 50. In this study, the origin of large difference between pure and mixed gas selectivities has been elucidated in terms of membrane plasticization by propylene molecules. The membrane plasticization was confirmed by the decrease of selectivity with increasing propylene concentration in the feed, resulting from the increase of both propylene and propane permeances. The decrease of glass transition temperature (T_g) in silver polymer electrolytes upon the sorption of propylene also supported the membrane plasticization, determined by in situ high-pressure differential scanning calorimetry (HPDSC). Further analysis of configuration entropy model revealed that the interaction of propylene/silver ion in POZ/AgBF₄ was approximately 2-fold stronger than that in POZ/AgCF₃SO₃, which is in good agreement with the results of propylene solubility and FT-IR spectra.     

Effect of coordination number on the formation of silver nanoparticles in polymer/silver salt complex membranes

Polymer/silver salt complex membranes consisting of AgBF₄ dissolved in poly(2-ethyl-2-oxazoline) (POZ) exhibited higher separation performance for propylene/propane mixtures but gradual decrease of separation properties, primarily due to the reduction of silver ions to silver nanoparticles. In this study, the effect of salt concentration on the formation of silver nanoparticles in POZ/AgBF₄ complex membranes was investigated. Separation test showed that 1/0.5 POZ/AgBF₄ complex membrane exhibited improved long-term stability on the membrane separation performance for propylene/propane mixtures compared to 1/1 POZ/AgBF₄ complex membrane. The stability improvement would be attributed to the suppression of the reduction of silver ions to silver metal nanoparticles, resulting from the higher coordination number of silver ions to carbonyl oxygens of POZ in 1/0.5 POZ/AgBF₄ membrane than 1/1 membrane. Transmission electron microscopy (TEM) and UV–visible spectra results confirmed that the rate of silver metal nanoparticle formation in the 1/0.5 POZ/AgBF₄ complex membrane was significantly retarded compared to that of 1/1 POZ/AgBF₄ complex membrane. It is therefore concluded that the coordination number of silver ions for carbonyl oxygens is of pivotal importance in controlling the reduction reaction of silver ions to silver metals and consequently improving the membrane separation performance for propylene/propane mixtures.     

Facilitated propylene transport in mixed matrix membranes containing ZIF-8@Agmim core-shell hybrid material

The ZIF-8@Agmim core-shell hybrid material was synthesized via a favorable post-modification method of ion exchange (PMIE). This infrequent ZIF-8@Agmim core-shell structure maintains a well-integrated pore size that is almost the same as ZIF-8. The similar equilibrium isotherms with ZIF-8 and better kinetic separation toward propylene/propane than ZIF-8 render ZIF-8@Agmim to be an interesting candidate for propylene/propane separation. The core-shell hybrid nanomaterial was further used as nanofillers in the polymer of intrinsic microporosity matrix (PIM-1) for propylene/propane separation. The resultant mixed-matrix membranes (MMMs) exhibited a simultaneous increase in C₃H₆ permeability and C₃H₆/C₃H₈ ideal selectivity compared to pure polymer membrane owing to a synergistic effect of molecular sieving from ZIF-8 and π-complexation of Ag⁺ with propylene. The separation performance of the prepared MMM surpasses the upper bound line of polymer membranes. Furthermore, the hybrid materials possess superb photochemical stability and the corresponding MMMs exhibit excellent anti-aging property and long-term stability.     

Structure and properties of semiinterpenetrating polymer networks based on polyurethane and nitrochitosan

Two semiinterpenetrating polymer networks (semi‐IPNs) based on trihydroxyl methylpropane–polyurethane (T‐PU) or castor oil–polyurethane (C‐PU) were prepared by curing the mixed solution of the polyurethane prepolymer and nitrochitosan (NCH). During the curing process, crosslinking and grafting reaction between the molecules of the PU prepolymer and NCH occurred, because of the high reactivity of remaining hydroxyl groups in the NCH with ? NCO groups of PU. The structure of the original semi‐IPN sheets and the sheets treated with acetone were studied by infrared, ¹³C‐NMR, scanning electron microscopy, and dynamic mechanical analysis, showing interpenetration of NCH molecules into the PU networks. When nitrochitosan content (C_NCH) was lower than 10 wt %, the semi‐IPN sheets T‐PU and C‐PU had higher density and tensile strength (σ_b) than the systems with C_NCH more than 20%. The trihydroxymethyl propane‐based PU reacted more readily with nitrochitosan to form the semi‐IPNs than castor oil‐based PU. The semi‐IPN coatings T‐PU and C‐PU were used to coat cellophane, resulting in intimate interfacial bonding. The mechanical strength and water resistivity of the cellophane coated with T‐PU coating were improved remarkably. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3109–3117, 2001     

Electrospun polyurethane membrane with Ag/ZnO microparticles as an antibacterial surface on polyurethane sheets

A method of antibacterial modification of the polyurethane (PU) surface is presented in this article. An electrospun PU membrane with an incorporated antibacterial agent was applied as a coating of the PU sheets. As an antibacterial agent, a hybrid bimetallic filler was used; it combined the antibacterial effects of silver and zinc oxide. With an electrospun submicrometer‐fiber membrane, the filler was uniformly and thinly applied on the PU surface by compression molding. The antibacterial activities of three filler concentrations were tested, and they demonstrated an effective antibacterial action against Staphylococcus aureus and Escherichia coli. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43020.     

Propylen/Propan‐Trennung im Festbettadsorber und durch Membranpermeation

The metal‐organic framework Mg₂(dhtp) with the linker dihydroxyterephthalate is known as MOF‐74 or CPO‐27. Mg₂(dhtp) has been synthesized as powder to measure breakthrough curves in a fixed‐bed adsorber and adsorption isotherms, and as a supported thin membrane layer for permeation studies. The measurement of the breakthrough curves of the binary propylene/propane mixture shows that separation with the fixed bed adsorber is possible. Propylene shows a higher affinity to Mg₂(dhtp). Although the single gas propane flux is slightly higher than the one of propylene, the binary propane/propylene mixture is not separated.     

Synthesis and characterization of poly(urethane‐co‐imidine)s having pendent phenyl and benzylidene groups using bisphthalides,bislactones and blocked polyurethane prepolymers

Poly(urethane‐co‐imidine)s were prepared using amine blocked polyurethane (PU) prepolymer. The PU prepolymer was prepared by the reaction of poly(propylene glycol) (PPG₂₀₀₀) and 2,4‐tolylene diisocyanate (TDI) and end capped with N‐methyl aniline. The PU prepolymer was then reacted with bisphthalides and bislactones, until the evolution of carbon dioxide ceased. Polymerization reactions with bispthalides and bislactone took more time than with dianhydrides. Polymers were characterized by FTIR, GPC, TG and DSC analyses. Molecular weights of the poly(urethane‐co‐imidine)s were found to be lower than that of poly(urethane‐co‐imide)s. Compared to poly(urethane‐co‐imide)s all poly(urethane‐co‐imidine)s showed high glass transition temperature and crystallization peak in DSC. The thermal stability of the polyurethanes was found to increase with the introduction of imidine component. © 2001 Society of Chemical Industry     

Membranes of triphenylsilyl substituted polyphenylene oxide in the permeation of propylene and propane gases

Poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) was chemically modified by the attachment of a bulky triphenylsilyl (TPS) group substituent (～30 mol %) to study its impact on hydrocarbon gas permeation. A membrane of the modified PPO (TPS–PPO) was tested for the permeation of pure propylene and propane gas and that of their 55:45 binary mixture at 30 ± 2°C. Gravimetric single‐gas equilibrium sorption studies were carried out to determine the gas solubility coefficients and diffusion coefficients to assess their role in the gas permeation mechanism of the membranes. Characterization studies were done to determine the interrelationship between the transport properties and the polymer structure. The studies included density, fractional free volume, Fourier transform infrared spectroscopy, ¹H‐NMR, differential scanning calorimetry, wide‐angle X‐ray diffraction, tensile testing, and scanning electron microscopy. The TPS–PPO membrane was found to be 3 times more permeable to propylene and 3.8 times more permeable to propane with a small decrease in the propylene/propane ideal permselectivity (3.37) when compared to that of unmodified PPO (4.25). TPS–PPO could be a potential membrane material for the efficient recovery of propylene and propane from mixtures with permanent gases such as those found in refinery off‐gas. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and viscoelasticity of anisotropic polyurethane composites filled with TiO2 particles

An anisotropic structure arranged by fillers is an effective method to make composites possess special properties, but the conventional particle-reinforced polyurethane (PU) composites usually have an isotropic 0-3 structure. In this study, a precipitation method was used to synthesize TiO₂ particles. The particles were dispersed in a PU matrix, and the structures were observed by scanning electron microscopy. The results indicate that in the presence of an applied electric field, 1-3-like composites with TiO₂ particles in an oriented arrangement were prepared, while 0-3 PU composites were prepared without an electric field. Dynamic viscoelasticity test results show that the PU-TiO₂ composites with a 1-3-like structure have a higher storage and loss modulus. The creep properties of these two kinds of PU composites were measured and further fitted with a Findley power law and Weibull model. It was found that the creep resistance and recovery properties of the PU composites were enhanced by the anisotropic structures of the filler particles in the matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47450.     

Pervaporation performance of surface-modified zeolite/PU mixed matrix membranes for separation of phenol from water

Polyurethane (PU) is a kind of promising pervaporation membrane material and silica-rich zeolite is a potential modifier to PU, but the pristine zeolite particles suffer from the bad dispersion in the polymer. This work presents a new route to modify zeolite (ZSM-5) particles via bridging with isocyanate to prepare a membrane for the recovery of phenol from the water. Zeolite ZSM-5 particles were successfully grafted by TDI, β-cyclodextrin, and oleyl alcohol, consecutively. The corresponding zeolites filled PU membranes were prepared and characterized by FTIR, TGA and SEM techniques. The effects of the grafted structures on the pervaporation performances of the zeolites/PU membranes were investigated in the recovery of phenol from the water. The results showed that the modified ZSM-5 particles had a good dispersion in PU, while the pristine ones demonstrated an obvious sedimentation. The modified zeolite/polyurethane membranes achieved better comprehensive separation performance than the neat PU and pristine ZSM-5 modified PU membranes. Depending on the good affinity of the β-cyclodextrin to phenol, ZSM-5 particles grafted by toluene diisocyanate and β-cyclodextrin (ZSM-TC) showed the optimal separation performance with the flux of 46.03 kg μm m^?2 h^?1 and the separation factor of 15.64 for the 0.3 wt% aqueous phenol solution at 80 °C. With the increase in the zeolite loading from 5 to 25%, ZSM-5/PU membrane showed the decreased separation factor and flux comparing to the neat PU. However, ZSM-TC/PU membrane showed higher flux and better selectivity than the neat PU and pristine ZSM-5 filled PU membranes.     

Effects of simultaneous chemical cross-linking and physical filling on separation performances of PU membranes

The novel modified polyurethane (PU) membranes were prepared by β-cyclodextrin (CD) cross-linking and SiO₂/carbon fiber filler, simultaneously. The structures, thermal stabilities, morphologies, and surface properties were characterized by FTIR, TGA, SEM, and contact angle. The results showed that the addition of inorganic particles increased the thermal stabilities of PU membranes. The modified PU membranes possessed more hydrophobic surfaces than pure PU. In the swelling investigation, PU and its modified membranes were swelled gradually with increasing phenol content in the mixture. The membranes modified by CD cross-linking (PUCD) demonstrated the highest swelling degree. Pervaporation (PV) performances were investigated in the separation of phenol from water. Three kinds of modified membranes obtained better permeability and selectivity than PU membranes. With the feed mixture of 0.5 wt% phenol at 60 °C, the modified PU membrane by CD cross-linking and SiO₂ filler (PUCD-S) obtained the total flux of 5.92 kg μm m^?2 h^?1 which was above doubled that of PU (2.90 kg μm m^?2 h^?1). The modified PU membrane by CD cross-linking and carbon fiber filling (PUCD-C) obtained the separation factor of 51.31 which was nearly tripled that of PU (17.72). The PUCD membranes showed both better permeability and selectivity than the pure PU membranes. The increased phenol content induced an increased separation factor of PUCD and PU, but a decreased selectivity of PUCD-S and PUCD-C. The methods of CD cross-linking and inorganic particle filling were effective to develop the overall separation performances, greatly.     

Supported liquid membrane separation of propylene-propane mixtures using a metal ion carrier

Experimental results for the separation of propylene from a propylene/propane mixture using facilitated transport membrane system with silver nitrate as carrier are presented. The equilibrium constant of the reaction between propylene and silver ion (Ag⁺) at different operating conditions was determined, experimentally. For a 50:50 (vol.%) propylene-propane mixture, at feed pressure of 50-120 kPa, the separation performance of a facilitated transport membrane system was evaluated. It was observed that increasing carrier concentration and trans-membrane pressure, separation factor was increased. At feed pressure of 120 kPa and the carrier concentration of 20 wt.%, a separation factor of 270 was obtained.     

Pervaporation of Acetaldehyde Aqueous Solution through Zeolite 3A-Polyurethane (PU) Composite Membrane

3A-filled hydrophilic polyurethane (PU) membranes were prepared by incorporating zeolite 3A into PU for pervaporation separation of acetaldehyde and water mixtures (acetaldehyde concentration 2 wt%–20 wt%). The composite membranes were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The morphology and thermal stability of these membranes were also investigated. The effects of zeolite 3A on the sorption, diffusion, and pervaporation performance were evaluated. The swelling study showed that 3A-PU membrane had higher swelling degree in acetaldehyde aqueous solution than in pure water. And the swelling degree of the composite membrane in acetaldehyde solution increased with the 3A content. The permeation flux and water/acetaldehyde separation factor first increased and then decreased with increasing 3A content. The reason may be that a proper quantity of 3A will enlarge the free volume fraction of PU while excessive 3A lead to its poor dispersion. The highest permeation flux of the composite membrane could reach 223 g · m^?2 · h^?1 and the maximum water/acetaldehyde selectivity achieved 7.5. The calculation of sorption selectivity and diffusion selectivity showed that diffusion played a more important role in this process.     

Carbon Isotope Separation by Absorptive Distillation

Abstract

The feasibility of separating carbon isotopes by absorptive distillation has been studied for CO absorption by cryogenic solvents. Phase equilibrium, isotopic separation, and mass transfer data were taken between 77.4 and 114.3 K for the following solvents: propane, propylene, 1:1 propane-propylene, 1-butene, isobutane and nitrogen.

Carbon monoxide solubility followed Henry's Law, with a maximum experimental solubility of 6.5 mole per cent. Isotopic separation between CO in the gas and liquid phases using hydrocarbon solvents was several times that for pure CO vapor-liquid equilibrium. The maximum observed isotopic separation factor was 1.029 at 77.4 K with the propane-propylene solvent mixture. Mass transfer measurements yielded calculated HTU's of 2 to 5 cm for a possible separation system.

An attempt has been made to correlate isotopic separation data using Hildebrand's theory of solutions. The differential absorption of isotopic CO species is expressed as a difference in solubility of the isotopic CO molecules. Data for propane, propylene, and 1-butene show approximately the same behavior at varying temperatures.     

Pervaporation separation of benzene/cyclohexane through AAOM-ionic liquids/polyurethane membranes

Supported ionic liquids/polyurethane (PU) membranes were prepared by immobilizing ionic liquids on a porous anodic aluminum oxide membrane (AAOM) support that was coated on one side with polyurethane (PU). The microstructure of all membranes was characterized using scanning electron microscopy (SEM). The pervaporation separation performance of the supported ionic liquids/polyurethane membranes was investigated for benzene/cyclohexane (Bz/Cy) mixtures. The SEM results demonstrated that the porous surface of the AAOM support was sealed by the dense polyurethane membrane and the pores of the AAOM support were impregnate with ionic liquids. The ionic liquids filling in the AAOM support enhanced the separation selectivity of Bz/Cy. The separation factor of Bz to Cy increased from 5 to 34.4 and the largest PSI of AAOM-[C₄mim]PF₆/PU membrane reached 452.54 g m⁻² h⁻¹ at 55 °C for a 50 wt.% Bz/Cy mixture. Because the polyurethane prevented the leakage of ionic liquids filled in the AAOM support, the supported ionic liquids/polyurethane membranes exhibited excellent stability.     

Preparation and Characterization of C60‐Filled Ethyl Cellulose Mixed‐Matrix Membranes for Gas Separation of Propylene/Propane

Mixed‐matrix membranes (MMMs) consisting of ethyl cellulose as continuous matrix and inorganic particle C₆₀ as dispersed phase were prepared for propylene/propane separation. The impact of the C₆₀ content on the separation properties of MMMs without and with ultraviolet cross‐linking was investigated. The increment of decomposition temperature and single glass temperature of ethyl cellulose/C₆₀ MMMs indicates a strong interfacial interaction between polymer and fullerenes. After UV irradiation, the gas permeability coefficient of propylene and ideal separation factor of propylene/propane decreased, and new features appeared in scanning electron microscopy and atomic force microscopy images, testifying the photopolymerization reaction of C₆₀ at a depth near to the surface. C₆₀ could be acted as a possible replaced carrier for the separation of olefin/paraffin using membrane separation technology.     

Effects of hard-segment compositions on properties of polyurethane–nitrolignin films

Segmented polyurethane (PU) films from castor-oil-based PU prepolymer with different hard-segment compositions and nitrolignin (NL) were synthesized. Diisocyanates (DIs), such as 2,4-tolylene DI (TDI) and 4,4′-diphenylmethane DI (MDI), 1,4-butanediol (BDO) as a chain extender, and trimethanol propane (TMP) as a crosslinker were used to obtain PU films containing NL (UL) which were named as UL–TB for TDI and BDO, UL–TT for TDI and TMP, UL–MB for MDI and BDO, and UL–MT for MDI and TMP, respectively. The mechanical properties and thermal stability of the films were characterized by a tensile test and thermogravimetric analysis, respectively. The MDI-based UL films exhibited a higher tensile strength (σ_b) and thermal stability than TDI-based UL. However, the recoverability of the TDI-based UL films was better than that of others. The UL films with TMP (UL–TT and UL–MT) had higher σ_b and lower breaking elongation (ϵ_b) than the UL films with BDO (UL–TB and UL–MB), caused by enhancement in the crosslinking network of hard segments and microphase separation between soft and hard segments. The values of σ_b and ϵ_b of the UL films that contained NL were much higher than those of the PU films, which indicates that the introduction of NL increased the interaction between hard segments by crosslinking. The hydrogen bonding in the UL films was studied by infrared spectroscopy, which indicated that MDI favored the formation of hydrogen bonds, especially in the ordered domain. Differential scanning calorimetry, dynamic mechanical analysis, and wide-angle X-ray diffraction indicated that the UL films were compatible as a whole, but microphase separation existed between soft and hard segments and significantly affected the mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3251–3259, 2001     

Semiinterpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. I. Thermodynamic state and dynamic mechanical analysis

Semiinterpenetrating polymer networks (semi‐IPNs) based on polyurethane (PU) and polyvinylpyrrolidone (PVP) have been synthesized, and their thermodynamic characteristics, thermal properties, and dynamical mechanical properties have been studied to have an insight in their structure as a function of their composition. First, the free energies of mixing of the two polymers in semi‐IPNs based on crosslinked PU and PVP have been determined by the vapor sorption method. It was established that these constituent polymers are not miscible in the semi‐IPNs. The differential scanning calorimetry results evidence the T_g of polyurethane and two T_g for PVP. The dynamic mechanical behavior of the semi‐IPNs has been investigated and is in accordance with their thermal behavior. It was shown that the semi‐IPNs present three distinct relaxations. If the temperature position of PU maximum tan δ is invariable, on the contrary, the situation for the two maxima observed for PVP is more complex. Only the maximum of the highest temperature relaxation is shifted to lower temperature with changing of the semi‐IPNs composition. It was concluded that investigated semi‐IPNs are two‐phase systems with incomplete phase separation. The phase composition was calculated using viscoelastic properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 852–862, 2001     

Kinetic modeling of oxidative dehydrogenation of propane with CO2 over MoOx/La2O3–Al2O3 in a fluidized bed

A 4-step kinetic model of CO₂-assisted oxidative dehydrogenation (ODH) of propane to C₂/C₃ olefins over a novel MoO_x/La₂O₃–γAl₂O₃ catalyst was developed. Kinetic experiments were conducted in a CREC Riser Simulator at various reaction temperatures (525–600 °C) and times (15–30 s). The catalyst was highly selective towards propylene at all combinations of the reaction conditions. Langmuir-Hinshelwood type kinetics were formulated considering propane ODH, uni- and bimolecular cracking of propane to produce a C₁-C₂ species. It was found that the one site type model adequately fitted the experimental data. The activation energy for the formation of propylene (67.8 kJ/mol) is much lower than that of bimolecular conversion of propane to ethane and ethylene (303 kJ/mol) as well as the direct cracking of propane to methane and ethylene (106.7 kJ/mol). The kinetic modeling revealed the positive effects of CO₂ towards enhancing the propylene selectivity over the catalyst.     

Molecular transport of n‐alkanes into PU/PBMA interpenetrating polymer network systems

The methylene diisocyanate (MDI) and toluene diisocyanate (TDI) based polyurethane/polybutyl methacrylate (PU/PBMA‐50/50) interpenetrating polymer network (IPN) membranes have been prepared. The molecular migration of n‐alkane penetrants such as hexane, heptane, octane, nonane, and decane through PU/PBMA (50/50) membranes has been studied at 25, 40, and 60°C using a weight gain method. From the sorption results, diffusion (D) and permeation (P) coefficients of n‐alkane penetrants have been calculated. Molecular migration depends on membrane‐solvent interactions, size of the penetrants, temperature, and availability of free volume within the membrane matrix. Attempts have been made to estimate the parameters of an empirical equation and these data suggest that molecular transport follows Fickian mode. From a study of temperature dependence of transport parameters, activation energy for diffusion (E_D) and permeation (E_P) have been estimated from the Arrhenius relation. Furthermore, sorption results have been interpreted in terms of enthalpy (ΔH) and entropy (ΔS) of sorption. The liquid concentration profiles have been computed using Fick's equation with appropriate initial and boundary conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 739–746, 2003