Highly selective and efficient transport of toluene in bulk ionic liquid membranes containing Ag as carrier

Ionic liquids have very low vapour pressure and a very high boiling temperature and are therefore a potentially environmentally friendly solvent. In this paper, room-temperature ionic liquids are used as a bulk liquid membrane for separation of toluene from n-heptane. Aromatic hydrocarbon, toluene, is successfully transported through the ionic liquid membrane based on 1-methyl-3-octyl imidazolium chloride. Using silver ion as a carrier in 1-methyl-3-octyl imidazolium chloride membranes, batch wise extraction experiments are carried out. The separation performances, represented by the permeation rate and separation factor, are analyzed systematically by varying the operating parameters: the contact time, concentration of Ag⁺, stirring effect, initial feed phase concentration and temperature.     

Selective Separation of Toluene from n‐Heptane via Emulsion Liquid Membranes Containing Substituted Cyclodextrins as Carrier

Abstract

The selective separation of toluene from n‐heptane is investigated using unsubstituted α‐cyclodextrin (αCD), β‐cyclodextrin (βCD) and also with two substituted CDs as a carrier in oil/water/oil‐type emulsion liquid membranes. The separation factor for toluene to n‐heptane is evaluated from the extraction of an equimolar mixture of toluene and n‐heptane. βCD shows the highest selectivity followed by αCD, hydroxypropyl‐αCD and hydroxypropyl‐βCD. The separation performances, represented by the permeation rate and separation factor, are analyzed systematically by varying the operating parameters: contact time, concentration of carriers, volume fraction of the membrane phase, and the relative amount of solvent. In this paper the effects of carriers and interfacial tension on dispersed phase drop size, internal droplets size, and size distribution are also systematically investigated.     

Pervaporation separation of dimethyl carbonate/methanol mixtures with regenerated perfluoro‐ion‐exchange membranes in chlor‐alkali industry

The waste perfluoro‐ion‐exchange membranes (PFIEMs) in chlor‐alkali industry were regenerated and used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) mixtures by pervaporation process. The energy‐dispersive spectrum (EDS) demonstrates that the impurities on the surfaces of waste PFIEMs can be effectively cleared by the regeneration process. The degree of swelling, sorption, and pervaporation properties of the regenerated PFIEMs with different counter ions were investigated. The results indicate that the counter ions of PFIEMs conspicuously influence the degree of swelling, sorption, and pervaporation properties for DMC/MeOH mixtures. The degree of swelling and solubility selectivity both decreases with the alkali metal counter ions in the sequence: Li⁺ > Na⁺ > K⁺ > Cs⁺. The degree of swelling increases with MeOH concentration increasing in feed liquid. The pervaporation measurements illustrate that the permeation flux decreases and the separation factor increases with the rising in ion radius of counter ions. The increase of feed concentration (MeOH) and feed temperature is advantageous to improve permeation flux while at the cost of separation factor decreasing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

CO2‐Switchable Oil/Water Emulsion for Pipeline Transport of Heavy Oil

By mixing an aqueous solution of tertiary amine, N,N‐dimethylethanolamine (DMEA), with naphthenic acid (RCOOH) derived from heavy oil, a CO₂ switchable zwitterionic surfactant (RCOO^?DMEAH⁺) aqueous system was constructed. The CO₂ switchability of this zwitterionic surfactant was confirmed by visual inspection, pH measurements, and conductivity tests, i.e., the RCOO^?DMEAH⁺ decomposed into RCOOH, DMEAH⁺ and HCO₃^? after bubbling CO₂ through but switched back to its original state by subsequent bubbling N₂ through at 80 °C to remove the CO₂. The interfacial tension tests of heavy oil in DMEA aqueous solutions indicated that the solution containing 0.5 wt% of DMEA and 0.2 wt% of NaCl resulted in the lowest interfacial tension. The O/W emulsion formed when aqueous solutions of DMEA were used to emulsify heavy oil exhibited the best performance when the oil/water volume ratio, DMEA concentration, and NaCl concentration were 65:35, 0.5 and 0.2 wt%, respectively. The feasibility of pipeline transport of the O/W heavy oil emulsion was evaluated. The results illustrated that the demulsification of the O/W emulsion after transport could be easily realized by bubbling CO₂ through. Although demulsification efficiency still needs to be improved, the recycling of the aqueous phase after demulsification by removal of CO₂ looks promising.     

Effect of Receiving Phase Anion on Macrocycle-Mediated Cation Transport Rates and Selectivities in Water—Toluene—Water Emulsion Membranes

Abstract

Relative transport rates of metal nitrates (Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, T1⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, and Pb²⁺) were measured alone and in combination with either Pb²⁺, Ag⁺, or T1⁺ in a water-toluene-water emulsion membrane system. The toluene phase contained the surfactant Span 80 and the crown ether dicyclohexano-18-crown-6 (DC18C6). The aqueous receiving phase contained the lithium salt of one of the following anions: pyrophosphate, thiosulfate, hydroxide, chloride, formate, nitrate. In the case of the metal combinations, chloride and formate ions were not studied. Unless significant complexation occurred both between the transported cation and the anion in the receiving phase and between the cation and DC18C6 in the membrane phase, there was little or no transport of the cation from the source phase to the receiving phase. Selective removal of Pb²⁺ and of Ag⁺ from binary mixtures of these cations with each of the cations listed was demonstrated using the emulsion membrane.     

Selective permeation through hydrophobic–hydrophilic membranes

Hydrophobic–hydrophilic composite membranes, containing polystyrene as the dispersed phase and polyacrylamide as the continuous phase, have been prepared by the concentrated emulsion polymerization method. They are highly absorptive for methyl chloride, benzene, and toluene, but poorly absorptive for cyclohexane. The absorption from toluene–cyclohexane mixtures was found to increse with increasing temperature and toluene concentration and to decrease with increasing fraction of polyacrylamide in the composite. The absorption is controlled by diffusion. The permeation rate through the membrane, which was determined by the pervaporation method, exhibits similar trends with respect to temperature, concentration, and fraction of polyacrylamide as absorption does. Higher permeation was obtained by increasing the temperature and by increasing the toluene concentration or by decreasing the fraction of polyacrylamide. The selectivity which was in the range of 4–8 varies inversely with the permeation rate through the membrane which was in the range of 2 × 10³?1.0 × 10⁴ g/m² h.     

Glycine Permeation through Na+, Ag+, and Cs+ Forms of Perfluorosulfonated Ion-Exchange Membranes

Abstract

We have studied the effect of counterions in perfluorosulfonated ion-exchange membranes on glycine permeation and found that counterions controlled permeation behavior. The Na⁺ form of the membrane exhibited saturation kinetics of the Michaelis-Menten type; that is, the flux rapidly increased with concentration and reached a limiting flux at a concentration of about 2 mol/L. The Cs⁺ form exhibited markedly lower fluxes which were nearly Fickian. For the Ag⁺ form, however, the fluxes increased rapidly and nonlinearly at low concentrations, but attained Fickian linearity at high concentrations. Ionizability of the sulfonate groups and hydration numbers of the counterions appeared to cause departure from Fickian behavior.     

Synthesis of ion‐imprinting chitosan/PVA crosslinked membrane for selective removal of Ag(I)

A novel ion‐imprinted membranes were synthesized for selective removal and preconentration for Ag(I) ions from aqueous solutions. The membranes were obtained via crosslinking of chitosan (CS), PVA, and blend chitosan/PVA using glutaraldehyde (GA) as crosslinker. The FTIR spectra were used to confirm the membrane formation. Comparing with the nonimprinted membranes, Ag(I)‐imprinted CS and CS/PVA has higher removal capacity and selectivity for Ag⁺ ions. An enhancement in the Ag⁺ removal capacity by ～ 20% (from 77.8 to 94.4 mg g^–1) and ～ 50% (from 83.9 to 125 mg g^–1) was found in the Ag(I)‐imprinted CS and Ag(I)‐imprinted CS/PVA membranes, respectively, when compared with the nonimprinted membranes. Removal equilibra was achieved in about 40 min for the non‐ and ion‐imprinted CS/PVA. The pH and temperature significantly affected the removal capacity of ion‐imprinted membrane. The relative selectivity coefficient values of Ag⁺/Cu²⁺ and Ag⁺/Ni²⁺ are 9 and 10.7 for ion‐imprinted CS membrane and 11.1 and 15 for ion‐imprinted CS/PVA membrane when compared with nonimprinted membranes. The imprinted membranes can be easily regenerated by 0.01M EDTA and therefore can be reused at least five times with only 15% loss of removal capacity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Factors Influencing Liquid Membrane Mass Transfer

Abstract

An improved design of a liquid membrane diffusion column was developed which enabled the measurement of a concentration difference of surfactant between liquid membranes and the solutions used to form them. The previously proposed model for liquid membrane diffusion which assumed that the films were of the order of a few molecules thick was not consistent with the data observed using a specially designed diffusion column. A bimodal droplet distribution was measured for a typical emulsion, and the influence of the liquid constituent of the membrane on the permeation rate was investigated. No statistically significant difference in permeation rates was noted when different liquids were used to form the membranes.     

Hybrid Cation Exchange Membranes with Lithium Ion‐Sieves for Highly Enhanced Li+ Permeation and Permselectivity

Cation exchange membranes (CEMs) hold promise for efficient and environment‐friendly lithium extraction from salt‐lake brine. However, development and practical application of CEMs are significantly hindered by the low Li⁺ permeation and permselectivity. Herein, novel hybrid CEMs are developed by dispersing lithium ion‐sieves (LMO) into sulfonated poly(ether ether ketone) matrix. Two kinds of LMOs are synthesized including acidified LMO (HMO) and its sulfonation compound (HMO‐S). The physicochemical property and separation performance of hybrid membranes are systematically investigated. The uniformly dispersed HMO and HMO‐S enhance the thermal, mechanical stability, and swelling resistance of hybrid membranes. Furthermore, these fillers obviously reduce the area resistance from 8.0 to less than 6.0 Ω cm^?2. Importantly, the unique Li⁺ transfer channels in HMO/HMO‐S efficiently elevate the Li⁺ permeation by up to 66%. While the “ion‐sieve effect” of the channels weakens the migration of Mg²⁺ and K⁺, thus notably rising Li⁺/Mg²⁺ and Li⁺/K⁺ permselectivities by ≈5 times, which is difficult to realize with conventional fillers. Comparing with HMO, HMO‐S shows higher improvement for permselectivity because of the reduced area resistance of the resultant hybrid membrane. This study paves a way to design and development of selective Li⁺ exchange membranes for transport and separation applications.     

Pervaporation membranes from natural rubber latex grafted with poly(2‐hydroxyethyl methacrylate) (NR‐g‐PHEMA) for the separation of water–acetone mixtures

NR‐graft‐PHEMA latexes were synthesized by the use of graft emulsion polymerization. By increasing the HEMA monomer concentration, we found that the grafting percentage (GP) also increased. In addition, GP increased significantly at low initiator concentrations before it leveled off at moderate concentrations, and a slight decrease was observed at high initiator concentrations. NR‐g‐PHEMA latexes were prepared as pervaporation membranes for the separation of water–acetone mixtures. From the equilibrium swelling, the nonideal behavior of membrane swelling in water–acetone mixtures was found such that there appeared the maximum swelling degree at a certain concentration of liquid mixtures. Moreover, the water concentration at maximum swelling shifted to high water concentration with increasing amount of graft‐PHEMA. The sorption study suggested the preferential sorption of water on the membranes. Also, the sorption isotherms implied that there was a coupling between water and acetone molecules. Pervaporation separation of water–acetone mixtures was studied with NR‐g‐PHEMA membranes. As the feed water concentration increased, the partial water fluxes increased in contrast to the partial fluxes of acetone. From the permeation ratio, θ_w, the strong coupling of acetone on the water transport was observed, particularly for the membrane with high graft‐PHEMA under acetone‐rich conditions. As the feed temperature increased, the total permeation across the membranes was enhanced. The partial fluxes of water and acetone as a function of temperature followed the Arrhenius relationship by which the activation energies for permeation were estimated as 3.53 kJ/mol for water and 21.95 kJ/mol for acetone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polysiloxaneimide membranes for removal of VOCs from water by pervaporation

For the separation of volatile organic compounds (VOCs) from water by pervaporation, three polysiloxaneimide (PSI) membranes were prepared by polycondensation of three aromatic dianhydrides of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic dianhydride (PMDA) with a siloxane‐containing diamine. The PSI membranes were characterized using ¹H‐NMR, ATR/IR, DSC, XRD, and a Rame‐Hart goniometer for contact angles. The degrees of sorption and sorption selectivity of the PSI membranes for pure organic compounds and organic aqueous solutions were investigated. The pervaporation properties of the PSI membrane were investigated in connection with the nature of organic aqueous solutions. The effects of feed concentration, feed temperature, permeate pressure, and membrane thickness on pervaporation performance were also investigated. The PSI membranes prepared have high pervaporation selectivity and permeation flux towards hydrophobic organic compounds. The PSI membranes with 150‐μm thickness exhibit a high pervaporation selectivity of 6000–9000 and a high permeation flux of 0.031–0.047 kg/m² h for 0.05 wt % of the toluene/water mixture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2691–2702, 2000     

Removal of Cu(II) from Aqueous Solution by Oil-Water Interfacial Emulsion Technique with Adsorbing Colloids

Abstract

Experimental investigations on the removal of Cu(II) from an aqueous solution were carried out by an interfacial emulsion technique with an adsorbing colloid (Al(OH)₃, FE(OH)₃), Cu(II) from the aqueous solution was segregated into a compact emulsion between water and a water-immiscible oil phase by an interfacial emulsion technique that uses the adsorptive power of the oil-water interface. Trimethylamine was effective as a surfactant for the removal of Cu(II), and the optimum pH for the removal of Cu(II) was found at 9.0 when using Fe(OH)₃ and at 10.0 when using Al(OH)₃ as an adsorbing colloid, respectively. The effects of pH, mixing time, initial surfactant concentration, initial Fe(III) concentration, and foreign ions (Na⁺, Ca²⁺, CI^?, NO₃ ^?, HPO₄ ^2?) on the removal efficiency were investigated. The adsorption and separation mechanisms for the removal of Cu(II) by the interfacial emulsion technique of adsorbing colloids were observed.     

Selective Separation of Toluene/n‐Heptane by Supported Ionic Liquid Membranes with [Bmim][BF4]

Room‐temperature ionic liquids serve as alternative solvents for volatile organic compounds in liquid‐liquid extraction and liquid membrane separation. 1‐Butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF₄]) was applied for extraction and supported ionic liquid membranes (SILMs) to separate toluene and n‐heptane. A high separation factor of toluene was achieved due to the strong interaction between ionic liquid cations and toluene. The mass transfer performance of the SILM process was enhanced by higher operating temperature. With the increase of initial toluene concentration in the feed phase, the mass transfer flux and removal efficiency of the SILM process were improved, while the separation factor decreased. The mass transfer flux was growing with the increase of flow rate at both sides. The SILM process was stable over a long time period due to the high viscosity and low volatility of [Bmim][BF₄].     

Effect of polyvinylpyrrolidone molecular weights on morphology,oil/water separation,mechanical and thermal properties of polyetherimide/polyvinylpyrrolidone hollow fiber membranes

We prepared polyetherimide (PEI) hollow fiber membranes using polyvinylpyrrolidones (PVP) with different molecular weights (PVP 10,000, PVP 40,000, and PVP 1,300,000) as additives for oil/water separation. Asymmetric hollow fiber membranes were fabricated by wet phase inversion technique from 25 wt % or 30 wt % solids of 20 : 5 : 75 or 20 : 10 : 70 (weight ratio) PEI/PVP/N‐metyl‐2‐pyrrolidone (NMP) solutions and a 95 : 5 NMP/water solution was used as bore fluid to eliminate resistance on the internal surface. Effects of PVP molecular weights on morphology, oil‐surfactant‐water separation characteristics, mechanical, and thermal properties of PEI/PVP hollow fiber membranes were investigated. It was found that an increase in PVP molecular weight and percentage in PEI/PVP dope solution resulted in the membrane morphology change from the finger‐like structure to the spongy structure. Without sodium hypochlorite posttreatment, hollow fiber membranes with higher PVP molecular weights had a higher rejection but with a lower water flux. For oil‐surfactant‐water emulsion systems (1600 ppm surfactant of sodium dodecylbenzenesulfonate and 2500 ppm oil of n‐decane), experimental results illustrated that the rejection rates for surfactant, total organic carbon, and oil were 76.1 ≈ 79.8%, 91.0 ≈ 93.0%, and more than 99%, respectively. Based on the glass transition temperature values, PVP existed in hollow fiber membranes and resulted in the hydrophilicity of membranes. In addition, using NaOCl as a posttreatment agent for membranes showed a significant improvement in membrane permeability for PVP with a molecular weight of 1300 K, whereas the elongation at break of the treated hollow fiber membranes decreased significantly. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2220–2233, 1999     

Physicochemical investigation of radiation‐grafted poly(acrylic acid)‐graft‐poly(tetrafluoroethylene–ethylene) copolymer membranes and their use in metal recovery from aqueous solution

ET‐g‐PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene–ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K⁺, Ag⁺, Hg²⁺, Co²⁺, and Cu²⁺ in a mixed aqueous solution. The ion‐exchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg²⁺ ion content of the membrane was more than that of either the K⁺ or Ag⁺ ions. The presence of metal ions in the membranes was studied by infrared and energy‐dispersive spectroscopy measurements. Scanning electron microscopy of the grafted and metal‐treated grafted membranes showed modification of the morphology of the surface due to the adsorption of K⁺ and Ag⁺ ions. No change was observed for the surface of the membrane that was treated with Hg²⁺ ions. The thermal stability of different membranes was improved more with Ag⁺ and Hg²⁺ ions than with K⁺ ions. It was found that the modified grafted membranes possessed good hydrophilicity, which may make them promising candidates for practical applications, such as for cation‐exchange membranes in the recovery of metals from an aqueous solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2692–2698, 2002     

Synthesis of highly selective copolymer membranes and their application for the dehydration of tetrahydrofuran by pervaporation

Acrylonitrile was copolymerized with 2‐hydroxyethyl methacrylate (HEMA) at three different copolymer compositions by emulsion polymerization to produce polyacrylonitrile–2‐hydroxyethyl methacrylate (PANHEMA) copolymer membranes containing increasing amounts of HEMA from PANHEMA‐1 to PANHEMA‐3. The dehydration of tetrahydrofuran (THF) over a concentration range of 0–14 wt % water in the feed was studied by pervaporation with these three copolymer membranes. The permeate water flux and separation factor for water was measured over the same concentration range at 30, 40, and 50°C. Among the copolymer membranes, PANHEMA‐1 exhibited a reasonable water flux (34.9 g m^?2 h^?1) with a very high water selectivity (264), whereas PANHEMA‐3 showed a higher water flux (52 g m^?2 h^?1) but a lower water selectivity (176.5) for highly concentrated THF (0.56 wt % water in the feed) at 30°C. The permeation factors of water for all of the membranes were much greater than unity, which signified a strong positive coupling effect of THF on water permeation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 728–737, 2007     

Role of silane grafting in the development of a superhydrophobic clay-alumina composite membrane for separation of water in oil emulsion

Hydrophobic composite kaolin-coated clay-alumina membranes are unique choices for water in oil emulsion separation. In this work, a membrane fabrication approach is presented using kaolin clay coating in the clay-alumina tubular composite support tube and subsequently grafting by different concentrations of fluoroalkyl silane (FAS: 1H, 1H, 2H, 2H, -Perfluorooctyltriethoxysilane) on the membrane surface. Different concentrations of fluoroalkyl silane formed distinctive hierarchical structures which exhibited hydrophobicity of the membrane surface. The pore property, surface roughness properties, and thermogravimetric properties can be suitably tailored by tuning the silane concentration in the grafting solution. The surfaces of comparatively higher silane content grafted (M50 and M100) composite membranes were found to be superhydrophobic. Comparably, our optimal composite membrane (M100) displayed a moderate steady flux rate of 80-100LMH (Lm^?2h ^?1) and excellent water rejection (>99%) properties during the separation of water in hexane and toluene emulsion at a cross-flow transmembrane pressure of 1 bar. The role of silane concentration on permeated hexane and toluene flux rate, water rejection rate, surface wettability, microstructure, and hydrophobic stability reveals new distinguishing insights into the hydrophobic clay-alumina composite membrane fabrication.     

Separation of cadmium(II) from spent nickel/cadmium battery by emulsion liquid membrane

Experiments were conducted to investigate the separation of cadmium(II) from spent nickel/cadmium battery by emulsion liquid membrane. Liquid membrane mainly consisted of a diluent (kerosene), a surfactant (Span 80), a carrier (di(2‐ethylhexyl) phosphoric acid, D2EHPA) and an internal phase (sulfuric acid). Main research effort was focused on the identification of optimal parameters affecting the separation process, such as D2EHPA (4.4 vol%), Span 80 (6.6 vol%), pH in the external phase (3.0), treat ratio (0.4), agitation time (10 min), and sulfuric acid concentration (1500 mol / m³). With the selected emulsion liquid membrane to separate cadmium(II) from the leaching solution of spent nickel/cadmium battery, the fraction extracted of cadmium(II) ions (0.963) was much more than that of nickel(II) ions (0.026). The organic membrane phase after demulsification was re‐mulsification and recycled up to eight times.     

A Star-Shaped Anionic Surfactant: Synthesis,Alkalinity Resistance,Interfacial Tension and Emulsification Properties at the Crude Oil–Water Interface

In this research, a star‐shaped surfactant was synthesized through the chlorination reaction, alkylation reaction and sulfonation reaction of triethanolamine, which is composed of three hydrophobic chains and three sulfonate hydrophilic groups. The critical micelle concentration (CMC) of the surfactant was measured by the surface tension method, and the results showed that it had high surface activity with CMC of 5.53 × 10^?5 mol/L. The surfactant was superior in surface active properties to the reference surfactants SDBS and DADS‐C₁₂. The interfacial tension (IFT) of the studied crude oil–water system (surfactant concentration 0.1 g/L, NaOH concentration 0.5 g/L, and experimental temperature 50 °C) dropped to 1.1 × 10^?4 mN/m, which can fulfil the requirement of surfactants for oil displacement. An aqueous solution of the surfactant and crude oil was emulsified by shaking, which formed a highly stable oil‐in‐water (O/W) emulsion with particle size of 5–20 μm. The oil displacement effect was almost 12%.