Preparation of C/CMS composite membranes derived from Poly(furfuryl alcohol) polymerized by iodine catalyst

C/CMS composite membranes derived from poly(furfuryl alcohol) (PFA) polymerized by iodine catalyst were prepared. Gas separation performance was investigated by molecular probe study with pure gases (H₂, CO₂, O₂, N₂, and CH₄) at 25 °C. The pyrolysis behaviour of PFA was studied by TG and DTG. The surface morphology of C/CMS composite membranes was observed by SEM and HRTEM. The results show a C/CMS composite membrane with uniform and defect-free thin top layer can be prepared by the PFA liquid in only one coating step. The C/CMS composite membranes have excellent gas separation properties for the gas pairs such as H₂/N₂, CO₂/N₂, O₂/N₂ and CO₂/CH₄, the permselectivities for above gas pairs in same sequence were 124.72, 12.74, 9.12 and 15.91 respectively. Compared to carbon membranes derived from PFA polymerized by acid catalyst, the carbon membranes obtained from PFA polymerized by iodine catalyst have slightly lower permselectivity, but higher permeance.     

Uniformity control and ultra-micropore development of tubular carbon membrane for light gas separation

Tubular carbon molecular sieve (CMS) membranes have been recognized as a potential module for commercial application due to its high mechanical strength and large surface area. However, the carbon layer uniformity was restricted by substrate texture and dope fluidity when the dip-coating method was used. This study evaluated the influence of various parameters of dip-coating with an integrated vacuum-assisted system, including solvent vaporization rates, vertical immersion/withdrawal velocity, vacuum degree, dope composition, coating cycles on the microstructure, and gas separation performance of CMS membranes. Using vacuum assistance and a low-vaporization solvent minimized the influence of viscosity and gravity on dope fluidity as a result of fast phase inversion. The as-prepared tubular CMS membranes showed enhanced perm-selectivity according to a H₂/N₂ gas selectivity of 8.8, a CO₂/N₂ gas selectivity of 6.7, a H₂ permeability of 464 barrer, and a CO₂ permeability of 356 barrer.     

Preparation of polyethyleneglycol (PEG) and cellulose acetate (CA) blend membranes and their gas permeabilities

Miscible blend membranes containing 10 wt % PEG of low molecular weight 200, 600, 2000, and 6000, and 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, and 60 wt % of molecular weight 20,000 were prepared to investigate the effect of PEG on gas permeabilities and selectivities for CO₂ over N₂ and CH₄. The permeabilities of CO₂, H₂, O₂, CH₄, and N₂ were measured at temperatures from 30 to 80°C and pressures from 20 cmHg to 76 cmHg using a manometric permeation apparatus. It was determined that the blend membrane, which contained 10% PEG 20,000, exhibited higher permeability for CO₂ and higher permselectivity for CO₂ over N₂ and CH₄ than those of the membranes that contained 10% PEG of the molecular weight ranging from 200 to 6000. The high PEG 20,000 content blend membranes showed remarkable permeation properties such that the permeability coefficients of CO₂ and the ideal separation factors for CO₂ over N₂ reached above 200 barrer and 22, respectively, at 70°C and 20 cmHg. Based on the data of gas permeability coefficients, time lags, and characterization of the membranes, it is proposed that the apparent solubility coefficients of all CA and PEG blend membranes for CO₂ were lower than those of the CA membrane. However, almost all of the blend membranes containing PEG 20,000 showed higher apparent diffusivity coefficients for CO₂, resulting in higher permeability coefficients of CO₂ than those of the CA membrane. It is attributed to the high diffusivity selectivities of CA and PEG 20,000 blend membranes that their ideal separation factors for CO₂ over N₂ were higher than those of the CA membrane in the temperature range from 50 to 80°C, even though the ideal separation factors of all CA and PEG blend membranes for CO₂ over CH₄ became lower than those of the CA membrane over nearly the full temperature range from 30 to 80°C. © 1995 John Wiley & Sons, Inc.     

Modeling and optimization of gas transport characteristics of carbon molecular sieve membranes through statistical analysis

This study aims to propose the importance of employing statistical analysis and modeling for investigation on the design and optimization of CMS membranes for gas separation. The factorial methodology is used to optimize permeability and selectivity through implementing the general factorial design considering the three main parameters such as choice of precursor materials, blend composition and the final pyrolysis temperature. Findings by statistical analysis showed that the linear and quadric terms of these three variables had significant effects. The optimal conditions are the Matrimid, blend composition 70%, and pyrolysis temperature at 800°C. Under these conditions, the model estimated a CO₂/CH₄, H₂/CO₂, and O₂/N₂ selectivity of 120.2, 8.39, and 8.06, respectively. Employed statistical technique and developed models can be used as a useful tool for design and optimization of appropriate gas separation membranes with effective performance for various industrial applications. POLYM. ENG. SCI., 54:147–157, 2014. © 2013 Society of Plastics Engineers     

Ultra-thin skin carbon hollow fiber membranes for sustainable molecular separations

A transformative platform is reported to derive ultra-thin carbon molecular sieve (CMS) hollow fiber membranes from dual-layer precursor hollow fibers with independently tuned skin layer and substrate properties. These ultra-thin CMS hollow fiber membranes show attractive CO₂/CH₄ separation factors and excellent CO₂ permeances up to ~1,400% higher than state-of-the-art asymmetric CMS hollow fiber membranes. They provide a unique combination of permeance and selectivity competitive with zeolite membranes, but with much higher membrane packing density and potentially much lower costs.     

A paradoxical flame-retardant effect of nitrates in ATH-filled ethylene–vinyl acetate copolymer

In the course of a study of metal salts as flame retardants, it was surprisingly found that metal nitrates reduced the flammability of ATH-filled ethylene–vinyl acetate copolymer (EVA). The limiting oxygen index (LOI) of ATH-filled EVA was increased by the nitrates in the order of Cu(NO₃)₂·3H₂O > (NH₄)₂Ce(NO₃)₆ > Zn(NO₃)₂·6H₂O > Fe(NO₃)₃·9H₂O > Al(NO₃)₃·9H₂O > NaNO₃. The effects were not caused by the water of hydration. All metal nitrates except NaNO₃ reached a UL 94 V-2 rating at 3 phr. Based on TGA, DSC, FTIR, and gas detection, the proposed mechanism of the flame-retardant effect of nitrates is the oxidative degradation of the polymer to produce noncombustible products (CO₂ and nitrogen oxides) at a rate sufficient to interfere with the normal combustion process despite the exothermicity of the oxidative degradation. It is possible that surface carboxylic acid structures also contribute to the flame-retardant effect. © 1995 John Wiley & Sons, Inc.     

Adsorption separation of vinyl chloride and acetylene on activated carbon modified by metal ions

This work mainly involved the adsorption separation of vinyl chloride and acetylene on modified activated carbons. Six metal ions with different hardness were loaded on activated carbon respectively. The effect of metal ions on the adsorption separation performance of vinyl chloride and acetylene was investigated. The experimental results shown that the separation factor of C₂H₃Cl to C₂H₂ over modified activated carbon followed the order: Al(III)/AC > Mg(II)/AC > Fe(III)/AC > AC > Zn(II)/AC ≈ Cu(II)/AC > Ag(I)/AC. The effect of the hardness of metal ions on the adsorption capacity of C₂H₂ was more remarkable than that of C₂H₃Cl, thus the separation factor of C₂H₃Cl to C₂H₂ increased with the rising of absolute hardness of the metal ions.     

Gas permeability and permselectivity of plasma‐treated polyethylene membranes

The effects of NH₃‐plasma and N₂‐plasma treatments on rubbery polyethylene (PE) membranes on the permeation behavior for carbon dioxide (CO₂), O₂, and N₂ were investigated with permeability measurements. The NH₃‐plasma and N₂‐plasma treatments on PE membranes increased both the permeation coefficient for CO₂ and the ideal separation factor for CO₂ with respect to N₂. For O₂ transport, both the permeation coefficient for O₂ and the ideal separation factor for O₂ with respect to N₂ were increased. NH₃‐plasma and N₂‐plasma treatments on polymer membranes possibly bring about an augmentation of permeability and permselectivity simultaneously. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 383–387, 2006     

Gas permeabilities of cellulose nitrate/poly(ethylene glycol) blend membranes

The permeability (P) of cellulose nitrate (CN)/poly(ethylene glycol) (PEG) blend membranes for N₂, O₂, and CO₂ has been measured as a function of film composition. The system CN/PEG-300 showed excellent miscibility, and films of the composition from 100/0 to 50/50 could be used for permeability measurements. P for each gas has been found to be almost constant or rather slightly lowered up to ca. 20 wt % PEG-300 content and then increased appreciably with increasing fraction of PEG. The increment of permeability was most remarkable for CO₂, and hence the permselectivity for CO₂ was considerably enhanced. Such a behavior of P has been found to be attributable to the plasticizing effect of PEG molecule lowering the glass transition temperature of the blend polymers. The effect of the molecular weight of PEG and that of closed voids generated in glassy blend membranes fabricated from acetone cast on gas permeabilities have been also discussed.     

Preparation and properties of microporous cellulose membranes from novel cellulose/aqueous sodium hydroxide solutions

Microporous cellulose membranes were prepared from novel cellulose/aqueous sodium hydroxide solutions by coagulation with aqueous H₂SO₄ solutions. The free and glass‐contacting surface morphology of the microporous cellulose membranes showed an asymmetric porous structure. The morphological structure, tensile properties, and permeability of the microporous cellulose membranes could be controlled by changes in the coagulation conditions such as the coagulant concentration and the coagulation time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 920–926, 2006     

Permselectivity of cellulose acetate membranes; separation of H2/CO mixtures and the effect of added transition metals

Cellulose acetate membranes permit permeation of H₂ and CO₂ but are relatively impervious to CO and N₂. Permselectivity was demonstrated by effective separation of H₂ from its mixtures with CO. The presence of RuCl₃ in the membrane does not result in any appreciable change in permselectivity. The exposure of RuCl₃- and RhCl₃-modified membranes to H₂/CO mixtures results in the formation of RuCl₂(CO)_x and [RhCl(CO)₂]₂, respectively. However, these complexes are not covalently anchored to the cellulose acetate matrix and apparently function only as additives that block access to the press and channels in the cellulose acetate membrane.     

A high CO2 permselective mesoporous silica/carbon composite membrane for CO2 separation

Ordered mesoporous silica/carbon composite membranes with a high CO₂ permeability and selectivity were designed and prepared by incorporating SBA-15 or MCM-48 particles into polymeric precursors followed by heat treatment. The as-made composite membranes were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and N₂ adsorption, of which the gas separation performance in terms of gas permeability and selectivity were evaluated using the single gas (CO₂, N₂, CH₄) and gas mixtures (CO₂/N₂ and CO₂/CH₄, 50/50 mol.%). In comparison to the pure carbon membranes and microporous zeolite/C composite membranes, the as-made mesoporous silica/C composite membranes, and the MCM-48/C composite membrane in particular, exhibit an outstanding CO₂ gas permeability and selectivity for the separation of CO₂/CH₄ and CO₂/N₂ gas pairs owing to the smaller gas diffusive resistance through the membrane and additional gas permeation channels created by the incorporation of mesoporous silicas in carbon membrane matrix. The channel shape and dimension of mesoporous silicas are key parameters for governing the gas permeability of the as-made composite membranes. The gas separation mechanism and the functions of porous materials incorporated inside the composite membranes are addressed.     

Gas permeability and permselectivity of plasma‐treated polypropylene membranes

The effects of NH₃‐plasma and N₂‐plasma treatment on rubbery polypropylene (PP) membrane upon permeation behavior for CO₂, O₂, and N₂ were investigated from their permeability measurements. The NH₃‐plasma and N₂‐plasma treatment on PP membranes could increase both the permeability coefficient for CO₂ and the ideal separation factor for CO₂ relative to N₂. For O₂ transport, both the permeability coefficient for O₂ and the ideal separation factor for O₂ relative to N₂ also increased. NH₃‐plasma and N₂‐plasma treatment on PP membranes possibly brings about an augmentation of permeability for CO₂ and permselectivity of CO₂ relative to N₂ simultaneously, but unfortunately the plasma‐treated PP membrane does not reach the level of CO₂ separation membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Crossflow filtration of iron(III), copper(II), and cadmium(II) aqueous solutions with alginic acid/cellulose composite membranes

The removal of Fe(III), Cu(II), and Cd(II) ions from aqueous solutions was investigated with a crossflow filtration technique. Alginic acid (AA)/cellulose composite membranes were used for retention. In the filtration of Fe(III) solutions, the effects of the crossflow velocity, applied pressure, AA content of the membranes, and pH on the retention percentage and the permeate flux were examined. The maximum retention percentage was found to be 89% for a 1 × 10^?4M Fe(III) solution at the flow velocity of 100 mL/min and the pressure of 60 kPa with 0.50% (w/v) AA/cellulose composite membranes at pH 3. Aqueous solutions of Cu(II) and Cd(II) were filtered at the flow velocity of 100 mL/min and pressure of 10 kPa. The effects of the AA content of the membranes and pH of the waste medium on the retention percentage and the permeate flux were determined. For 1 × 10^?4M Cu(II) and Cd(II) solutions, the maximum retention percentages were found to be 94 and 75%, respectively, at pH 7 with 0.50% (w/v) AA/cellulose composite membranes. When metal‐ion mixtures were used, the retention percentages of Fe(III), Cu(II), and Cd(II) were found to be 89, 48, and 10%, respectively, at pH 3 with 0.50% (w/v) AA/cellulose composite membranes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Catalytic oxidation of toluene and m-xylene by activated carbon fiber impregnated with transition metals

The catalytic oxidation of volatile organic compounds (VOCs) into mainly CO₂ and H₂O appears promising in the context of the abatement of atmospheric gaseous pollutants and is the subject of this paper. The catalytic oxidation of toluene and m-xylene was carried out in a tubular reactor on a phenolic resin based activated carbon fiber (ACF) impregnated with nitrates of Co, Cr, Ni, and Cu at the reaction temperatures below 300 °C. The extent of the removal (i.e. conversion) of toluene and m-xylene was examined through the breakthrough curves and was found to strongly depend on the types and loading of the metal precursors. The experimental results showed that the reaction rate was significantly affected by O₂ concentration below 3% (v/v). The performance of the ACFs impregnated with 5% (w/w) of Ni oxide was found to be superior to that of other metal oxides at reaction temperature between 170 and 290 °C. A surface kinetic mechanism for the catalytic oxidation of volatile organic compound was proposed and incorporated in a transport model developed to explain the experimental breakthrough data.     

Screening of Catalysts for Acrylonitrile Decomposition

The catalytic decomposition of acrylonitrile over various metal components (Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, and Pt) supported on several metal oxides (Al₂O₃, SiO₂, TiO₂, ZrO₂, and MgO) and ZSM-5 was studied. The most promising catalyst was Cu-ZSM-5, which exhibited 100% conversion and at least 80% N₂ selectivity above 350 °C.     

Asymmetric structure and enhanced gas separation performance induced by in situ growth of silver nanoparticles in carbon membranes

Ion-exchanged sulfonated poly(aryl ether ketone), SPAEK with different counter-ions (H⁺, Na⁺ and Ag⁺) have been utilized as polymeric precursors to fabricate carbon membranes. The effects of the substituted metal ions in polymeric precursors on the separation properties of resultant carbon membranes were investigated. X-ray diffraction analysis reveals that the polymer chain packing is improved by the substituted metal ions. The silver doped SPAEK membrane demonstrates the smallest d-spacing due to the strong interactions between the silver ions and the polar groups within the polymeric matrix. The carbon membrane derived from Ag-SPAEK exhibits a more porous structure compared to that from ion-exchanged SPAEK membranes. The silver doping enhances the ideal gas permeability of carbonized membranes by 100 fold. On top of this, the H₂/N₂ selectivity increases from 100 to 220 while the CO₂/CH₄ selectivity jumps from 25 to 67. An interesting phenomenon was observed, which is the migration of silver nanoparticles and the subsequent accumulation in the bulk of membrane after carbonization. A possible mechanism to explain for this particle relocation is the Ostwald ripening. The special directional dispersion of metal nanoparticles in carbonaceous materials was investigated and discussed.     

In Situ Hydrogenation of CO2 by Al/Fe and Zn/Cu Alloy Catalysts under Mild Conditions

The development of efficient metal catalysts for in situ hydrogenation of CO₂ in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO₂ was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions.     

Mathematical modeling and optimization of gas transport through carbon molecular sieve membrane and determining the model parameters using genetic algorithm

Permeation of N₂, CH₄, O₂ and CO₂ molecules through a carbon molecular sieve (CMS) was studied over a wide range of pressures using the transport mechanism. For proper utilization of carbon molecular sieve membrane in gas separation processes, prediction of behavior and recognition of proper gas transport mechanism as well as finding effective permeation parameters are necessary. A mathematical model of the gas transfer through a CMS membrane was developed using genetic algorithm (GA). Numerous types of mechanisms have been proposed so far for gas transport through capillaries, namely: Knudsen, slip and viscous flow. Moreover, surface flow usually occurs in parallel with other transport mechanisms such as Knudsen or viscous flow. The experimental data of gas permeation in CMS membranes and an appropriate genetic algorithm-based optimization method were used to establish the transport parameters. A GA, an optimization procedure based on the theory of evolution, was compared with non-linear regression for the ability of these two algorithms to fit the coefficients of Poultry growth models. It was found that GA approach could be more capable to define the parameters of permeation equation than non-linear regression. The model in most cases showed a good agreement between the predicted and measured values of the permeability.     

Quest for high performance carbon capture membranes: Fabrication of SAPO-34 and CNTs-doped polyethersulfone-based mixed-matrix membranes

Gas separation process is an effective method for capturing and removing CO₂ from post-combustion flue gases. Due to their various essential properties such as ability to improve process efficiency, polymeric membranes are known to dominate the market. Trade-off between gas permeability and selectivity through membranes limits their separation performance. In this study, solution casting cum phase separation method was utilized to create polyethersulfone-based composite membranes doped with carbon nanotubes (CNTs) and silico aluminophosphate (SAPO-34) as nanofiller materials. Membrane properties were then examined by performing gas permeation test, chemical structural analysis and optical microscopy. While enhancing membranes CO₂ permeance, SAPO-34 and CNTs mixture improved their CO₂/N₂ selectivity. By carefully adjusting membrane casting factors such as filler loadings. Using Taguchi statistical analysis, their carbon capture efficiency was improved. The improved mixed-matrix membrane with loading of 5 wt% CNTs and 10 wt% SAPO-34 in PES showed highly promising separation performance with a CO₂ permeability of 319 Barrer and an ideal CO₂/N₂ selectivity of 12, both of which are within the 2008 Robeson upper bound. A better mixed-matrix membrane with outstanding CO₂/N₂ selectivity and CO₂ permeability was produced as a result of the synergistic effect of adding two types of fillers in optimized loading.