Kinetics of Ag+ contained polymeric complex membranes for facilitated olefin transport

The reactions of silver ion complexes with polyethylene-graft-poly(acrylic acid) (PE-g-AA) and the olefin reversible coordinates with the PE-g-AA–Ag⁺ complex membranes were studied. Infrared and nuclear magnetic resonance spectra confirmed the complex formation between the carboxylic acid of the PE-g-AA and the Ag⁺ ion. Also, the Ag⁺ ion in PE-g-AA-Ag⁺ membrane was assumed to be a fixed carrier that adsorbs and transports olefin, thereby causing a selective olefin/paraffin separation. A theoretical model of the PE-g-AA-Ag⁺ (olefin) complex was proposed. The coordination number of Ag⁺ ion binding to the carboxylic acid of PE-g-AA is about 1.6 in glycerol solution. The coordination number of olefin binding to the Ag⁺ in the PE-g-AA–Ag⁺ complex membrane is 1. Moreover, the kinetics of olefin binding to the PE-g-AA–Ag⁺ complex membranes were studied. The equilibrium, association, and dissociation constants were also presented. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 909–917, 1997     

Nanocomposite membranes containing positively polarized gold nanoparticles for facilitated olefin transport

Positively polarized gold nanoparticles have been demonstrated for use as stable olefin carriers for facilitated olefin transport membranes. The formation and size of gold nanoparticles stabilized by 4-dimethylaminopyridine (DMAP) were monitored using X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy. Nanocomposite membranes that deliver high separation performance for olefin/paraffin mixtures were prepared by dispersing gold nanoparticles stabilized by DMAP in a polymer matrix, poly(vinyl pyrrolidone) (PVP). X-ray photoelectron spectroscopy (XPS) and zeta potential measurements revealed that gold nanoparticles stabilized by DMAP exhibited a high positive polarity, which is responsible for the reversible interaction between the gold nanoparticles and olefin molecules. Compared to neat PVP membranes, the composite membranes consisting of PVP and the polarized gold nanoparticles showed stable and enhanced separation of olefin/paraffin mixtures.     

An ab initio study of ionic liquid silver complexes as carriers in facilitated olefin transport membranes

Liquid phase isoprene/n-pentane mixtures can be separated through the use of facilitated transport membranes containing complexes of silver ions with an ionic liquid (IL). 1-Butyl-3-methyl imidazolium tetrafluoroborate and zwitterion-type imidazolium compounds containing covalently-bound sulfonate groups form complexes with AgX (X = BF₄, NO₃, and ClO₄). Facilitated isoprene transport has been observed with selectivities that depend on the counteranion of the silver salt. The facilitated transport phenomena of the olefin and IL/silver complexes were investigated theoretically by calculating their complexation energies (i.e., the energy of formation of the silver complexes with the olefin) with the density functional theory method. Among polymer/silver salt systems, the polymer/AgBF₄ system has been found to be generally more favorable for facilitated olefin transport than the polymer/AgNO₃ system because of the low lattice energy of AgBF₄. However, there is a different trend for IL/AgX systems. This difference may arise because the positively charged components of the IL can interact with the anions of the silver salt, which changes the olefin complexation activity. For IL/AgX systems, the selectivity varies inversely with the complexation energy, which implies that the diffusion of the carrier may be the significant factor affecting isoprene/n-pentane separation, once the appropriate complexation has occurred between olefin molecules and the ILsilver complexes.     

π-complexes of polystyrene with silver salts and their use as facilitated olefin transport membranes

π-Complexes of silver salts with polystyrene (PS) were prepared and tested in the separation of propylene/propane mixtures. After the incorporation of silver ions into the PS matrix, both the pure propylene gas permeance of the membrane and its olefin selectivity with respect to the propylene/propane mixtures were remarkably higher than those of the pure PS membrane, demonstrating facilitated propylene transport through the solid-state membrane. The remarkable separation performance of the PS/silver salt membranes was attributable to the unusually high solubility of the silver salts in the PS matrix, which was possibly due to the formation of π-complexes between the silver ion and aromatic CC bond of PS. The coordination properties and dissolution behavior of the silver salts in PS were investigated with Fourier transform infrared, Fourier transform Raman, and X-ray photoelectron spectroscopy. The values for the intersegmental d-spacing, determined by wide-angle X-ray scattering, also showed that significant transient crosslinks arose between the PS chains when the silver salts were added to the PS matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2263–2269, 2004     

Transient response of facilitated transport membranes

The transient flux of permeate is determined for one-dimensional facilitated transport in flat plate, cylindrical, and spherical geometries. The results are presented graphically. The flux is a function of four parameters. The graphical results allow one to determine the permeate flux as a function of time for given set of operating conditions, determine the steady-state value of the permeate flux and the time to reach steady-state.     

Amino acid ionic liquid-based facilitated transport membranes for CO2 separation

Supported liquid membranes incorporating amino acid ionic liquids remarkably facilitate CO(2) permeation under dry and low humid conditions.     

Competitive facilitated transport through liquid membranes

A mathematical model is presented which solves the dimensionless, transient, non-linear partial differential equations governing the competitive facilitated transport of two gases through a liquid membrane. The model incorporates the mass transfer coefficients in the boundary conditions for the free gas concentrations. Several studies were carried out. A comparison of this model with a steady-state “equilibrium core” model was excellent. Through varying the dimensionless parameters, it was found that gas I would have a higher steady-state facilitation factor than gas 2 if k₁ >k₂ and k_-1k_-2. The boundary conditions and mass transfer coefficients were also varied to see their effects on the facilitation factors. The idea of pumping one of the gases against its concentration gradient was shown to be theoretically possible.     

Transient behaviour of facilitated transport through liquid membranes

During the transient period of facilitated transport of a permeant across a thin liquid film, the ratio of the concentrations of the carrier at the two ends of the film as a function of time has a shape which is sensitive to the values of the physicochemical parameters. In certain systems involving ionic carriers, the above concentration ratio can be related to a conveniently measurable electrical potential difference, ΔV, across a pair of electrodes attached to the two faces of the liquid film. Bdzil et al. measured ΔV vs. time for NO FeCl₂FeCl₃—formamide system and observed that it goes through a maximum (ΔV_max), before reaching the asymptotic value corresponding to the steady state, ΔV_s.In the present paper, we solve numerically the species conservation equations, which describe the transients of the facilitated transport in the film, when the reversible reaction occurring in the film is of the form: A↑ + B = P (where A is the permeant and B and P are the carrier and permeant—carrier complex, respectively). The analysis takes into account: (i) the electrical effects which arise when B and P are ions of different diffusion coefficients and (ii) the effect of a second electrolyte added to the film to provide the cations which participate in an electrode reaction with the carrier ions. On this basis, an explanation is provided for the overshoot observed experimentally by Bdzil et al. in the ΔV vs. time curve. Such a maximum is exhibited by systems for which the time scales of diffusion and backward reaction in the film are of comparable magnitude. (Of course, for viable facilitation, the characteristic times of the forward and backward reactions should also be comparable.)The profile of ΔVvs. time is very sensitive to the values of the kinetic constants as well as the diffusion coefficients of the species A, B, and P. Therefore, measurements of ΔV vs. time (or equivalently the ratio of concentrations of the carrier on the two sides of the film as a function of time) can provide a more accurate method of determining the above parameters than those based on flux measurements.     

Structure and coordination properties of facilitated olefin transport membranes consisting of crosslinked poly(vinyl alcohol) and silver hexafluoroantimonate

The high selectivity of solid‐state crosslinked poly(vinyl alcohol) (CPVA) membranes containing silver hexafluoroantimonate (AgSbF₆), with respect to olefin/paraffin mixtures, was previously reported. The structure and coordination properties of CPVA/AgSbF₆ complexes were investigated in this study with wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), and theoretical ab initio calculations, and they were compared with those of poly(vinyl alcohol) (PVA)/AgSbF₆ complexes. Contrary to expectations, the measurements of the intersegmental d‐spacings and glass‐transition temperatures indicated that the chain mobility in the PVA/AgSbF₆ membranes was lower than that in the CPVA/AgSbF₆ membranes. The different extents of transient crosslinking in the two systems were attributed mostly to their different coordination structures; silver ions in PVA/AgSbF₆ were coordinated with hydroxyl oxygens located near the polymer main chains, whereas those in CPVA/AgSbF₆ were coordinated with aldehyde oxygens located far from the main chains. According to WAXS spectra, AgSbF₆ was completely dissolved in both PVA and CPVA, and this disrupted the crystallinity of the polymers. However, our DSC study showed that the silver ions dissolved in both polymer matrices recrystallized into silver oxide at elevated temperatures. The binding energy of Ag3d_5/2, as determined from XPS spectra, shifted to lower values with the addition of increasing amounts of the polymer matrix, indicating the increasing coordination of silver ions with polymer chains. The presence of various oxygen species with and without coordination to silver ions was confirmed from O1s XPS spectra of CPVA membranes containing silver ions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 621–628, 2004     

Complexation mechanism of olefin with silver ions dissolved in a polymer matrix and its effect on facilitated olefin transport

Remarkable separation performance of olefin/paraffin mixtures was previously reported by facilitated olefin transport through silver-based polymer electrolyte membranes. The mechanism of facilitated olefin transport in solid membranes of AgCF3SO3 dissolved in poly(N-vinyl pyrrolidone) (PVP) is investigated. In silver polymer electrolyte membranes, only free anions are present up to the 2:1 mole ratio of [C=O]:[Ag], and ion pairs start to form at a ratio of 1:1, followed by higher-order ionic aggregates above a ratio of 1:2. At silver concentrations above 3:1, the propylene permeance increases almost linearly with the total silver concentration, unexpectedly, regardless of the silver ionic constituents. It was also found that all the silver constituents, including ion pairs and higher order ionic aggregates, were completely redissolved into free anions under the propylene environment; this suggests that propylene can be a good ligand for the silver cation. From these experimental findings, a new mechanism for the complexation reaction between propylenes and silver salts in silver-polymer electrolytes was proposed. The new mechanism is consistent with the linearity between the propylene permeance and the total silver concentration regardless of the kind of the silver constituents. Therefore, the facilitated propylene transport through silver-polymer electrolytes may be associated mainly with the silver cation weakly coordinated with both carbonyl oxygen atoms and propylene.     

Polymeric complex membranes for olefin/paraffin separation

Semi-crystalline polyethylene (PE), rubbery silicone rubber (SR) and glassy poly[(l-trimethylsilyl)-l-propyne] (PTMSP) were modified for olefin/paraffin separation. The polymers were first grafted with the acrylic acid (AA) and then incorporated with silver ions for forming the complex membranes such as PE-g-AA-Ag⁺, SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺ The complex membranes were activated by glycerol solvation and subsequently showed high selectivity in olefin/paraffin separation. The silver ion distribution, the kinetics of olefin binding to PE-g-AA-Ag⁺, the gas permeation properties and the sorption behaviors were studied. A novel dry complex membrane for olefin/paraffin separation based on AgClO₄ complexing with PTMSP main-chain was also studied.     

Mechanism of facilitated saccharide transport through plasticized cellulose triacetate membranes

Mechanistic insight is gained for saccharide transport through plasticized cellulose triacetate (CTA) membranes containing lipophilic ion-pair transport carriers. The molecular structures of the different membrane components are systematically varied and diagnostic transport characteristics such as saccharide–carrier diffusion constant and saccharide extraction constant are determined. The observed percolation thresholds support a jumping mechanism, however, the diffusion constants are found to decrease as the size of the saccharide, carrier cation, and carrier anion increase, indicating that the rate-limiting step in the transport process involves diffusion of a complex comprised of all three components. The data is reconciled in terms of mobile-site jumping mechanism where the saccharide is relayed along a sequence of ion-pair carriers that are locally mobile. In an attempt to improve saccharide selectivity, calix-[4]-arene dicarboxylates were evaluated as potential ditopic transport carriers. This produced no major change in saccharide extraction constants.     

Coordination structure of various ligands in crosslinked PVA to silver ions for facilitated olefin transport

The most effective ligand among -OH, -O- and -CHO for facilitated olefin transport by silver ions in room temperature crosslinked poly(vinyl alcohol) membrane has been evaluated.     

Swollen polymeric complex membranes for olefin/paraffin separation

Swollen complex membrane of linear low density polyethylene-graft-poly(acrylic acid)-Ag⁺ (LLDPE-g-AA-Ag⁺) were studied and compared with the corresponding membranes based on silicone rubber (SR) and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), such as SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺. The polymeric matrix was first grafted with acrylic acid (AA) and then incorporated with silver ions (Ag⁺) in glycerol solution for forming the swollen complex membrane. Various metal ions and swollen agents in membranes for isobutene/isobutane separation were presented. The swelling of the complex membrane containing Ag⁺ with glycerol shows a higher olefin/paraffin selectivity than those membranes containing Cu⁺ or Cu²⁺ ions and/or other swelling agents. The gas permeability coefficients and the isobutene/isobutane selectivity of LLDPE-g-AA-Ag⁺ membrane were compared with those of SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺ membranes. The PTMSP-g-AA-Ag⁺ complex membrane was found to reach high gas permeability and high olefin/paraffin selectivity. The effects of solubility and diffusivity in membranes are compared with the corresponding non-Ag membranes. The sorption properties in these complex membranes were also included.     

Silver nanoparticles stabilized by crosslinked poly(vinyl pyrrolidone) and its application for facilitated olefin transport

Positively polarized silver nanoparticles by poly(vinyl pyrrolidone) (PVP) have been demonstrated for use as stable olefin carriers for facilitated olefin transport membranes. The formation and size of silver nanoparticles stabilized by PVP were monitored using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nanocomposite membranes consisting of polymer and silver nanoparticles stabilized by PVP exhibited the high separation performance for olefin/paraffin mixtures. X-ray photoelectron spectroscopy (XPS) showed that silver nanoparticles stabilized by PVP exhibited a high positive polarity, resulting in the reversible interaction between the surface of silver nanoparticles and olefin molecules.     

Carbon dioxide separation from hydrogen and nitrogen by fixed facilitated transport in swollen chitosan membranes

The separation of carbon dioxide from hydrogen and nitrogen at high temperatures would be valuable to fuel cell, flue gas purification, and ammonia processes. A feed gas mixture of carbon dioxide, hydrogen and nitrogen (10% CO₂, 10% H₂, and 80% N₂) was used to evaluate water-swollen chitosan as a facilitated transport membrane for these applications. The amino group of the chitosan repeating unit could be the fixed carrier that facilitates carbon dioxide transport in the presence of water.     

Influence of oxygen-containing hydrocarbons on the separation of olefin/paraffin mixtures using facilitated transport

Perfluorosulfonated ionomer (PSI) membranes were used to investigate the separation of olefin/paraffin mixtures by means of silver-based facilitated transport of olefins. Pentene and pentane were used as model compounds and separation factors as high as 33 were obtained. Influence of linear C₃C₆ alcohols and ketones on the separation of the pentene/pentane mixtures was investigated. The presence of oxygenates increases the fluxes of olefins and paraffins, resulting in lower selectivity for hydrocarbon separation.     

Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes

Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Sn²⁺ and In³⁺ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn²⁺ and Cd²⁺ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.     

Active and passive transport of amino acid derivatives via metal complex carriers

A new class of carrier, lipophilic copper complex, mediated active and passive transport of a variety of amino acid derivatives as carboxylate anion.