Formulation and morphology of kaolin-filled rubber composites

In the present work the formulation and morphology of novel kaolin-filled rubber composites were investigated. The kaolin-filled rubber composites were obtained by filling rubbers such as natural rubber (NR), styrene–butadiene rubber (SBR), polybutadiene rubber (ER), nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), chloroprene rubber (CR) and methyl vinyl silicon rubber (MVQ). The best formulation of filled rubbers was determined by determining the mechanical and thermal properties of the composites. Structural characterization was carried out by using infrared spectroscopy (IR) and a polarizing light microscope (PLM). The kaolin/rubber composites have outstanding mechanical and thermal properties except elongation at break, and good compatibility. The best formulation of kaolin filled rubbers is respectively 40 parts per hundred rubber (phr), 40 phr, 50 phr, 40 phr, 50 phr, and 50 phr for NR, SBR, BR, NBR, EPDM and CR. Kaolin can replace silica in the specific rubber products, and is suitable to reinforce more steric rigid rubber.     

Preparation and characterization of polyvinylchloride based mixed matrix membrane filled with multi walled carbon nano tubes for carbon dioxide separation

Poly vinyl chloride/multi wall carbon nano tubes (PVC/MWCNTs) mixed matrix membranes (MMMs) were prepared for gas separation. Raw and functionalized MWCNTs (R-MWCNTs and C-MWCNTs) were utilized in membranes preparation. The C-MWCNT shows better performance compared to raw ones. Membrane (CO₂/CH₄) selectivity was increased from 39.21 to 52.18 at 2 bar pressure by MWCNT loading ratio. The modified membranes with styrene butadiene rubber (SBR-MMMs) showed 63.52 and 34.70 selectivity for (CO₂/CH₄) and (CO₂/N₂) at 2 bar pressure. Mechanical properties analysis exhibited tensile module improvement utilizing blending modification. Increase of feed pressure led to membrane gas permeability decreasing. But gas pair selectivity follows a nearly constant behavior for MMMs and increasing behavior for blend MMMs.     

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.     

Fabrication and modification of cellulose acetate based mixed matrix membrane: Gas separation and physical properties

[Cellulose acetate (CA)-blend-multi walled carbon nano tubes (MWCNTs)] mixed matrix membranes (MMMs), [CA/polyethylene glycol (PEG)/MWCNTs] and [CA/styrene butadiene rubber (SBR)/MWCNTs] blend MMMs were prepared by solution casting method for gas separation applications using Tetrahydrofuran (THF) as solvent. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxylic-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas separation performance of prepared membranes were investigated for pure He, N₂, CH₄ and CO₂ gases. Results indicated that utilizing C-MWCNT instead of R-MWCNTs in membrane fabrication has better performance and (CO₂/CH₄) and (CO₂/N₂) selectivity reached to 21.81 and 13.74 from 13.41 and 9.33 at 0.65 wt% of MWCNTs loading respectively. The effects of PEG and SBR on the gas transport performance and mechanical properties were also investigated. The highest CO₂/CH₄ selectivity at 2 bar pressure was reached to 53.98 for [CA/PEG/C-MWCNT] and 43.91 for [CA/SBR/C-MWCNT] blend MMMs at 0.5 wt% and 2 wt% MWCNTs loading ratio respectively. Moreover, increase of feed pressure led to membrane gas permeability and gas pair selectivity improvement for almost all prepared membranes. The mechanical properties analysis exhibited tensile modules improvement with increasing MWCNTs loading ratio and utilizing polymer blending.     

Removal of pyridine from water by pervaporation using filled SBR Membranes

Styrene butadiene rubber (SBR) was efficiently cured (crosslinked) by using sulfur to accelerator ratio less than unity. This cured SBR was further compounded with carbon black filler (grade N330) with three different doses i.e., 5, 10, and 20 wt % of filler to form three different filled and crosslinked membranes, i.e., SBR5, SBR10, and SBR20. These filled rubber membranes and one unfilled but efficiently cured membrane, i.e. SBR0, were used for pervaporative removal of pyridine from its mixtures with water. The filled membranes were found to show better selectivity and mechanical properties but lower flux than the unfilled membrane. All of these membranes showed reasonably good range of flux and pyridine selectivity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ceramic membrane synthesis based on alkali activated blast furnace slag for separation of water from ethanol

The main purpose of this research is synthesis of zeolite ceramic membranes based on alkali activated blast furnace slag for pervaporation separation of ethanol/water mixture (90 wt%). A new and simple method was applied to fabricate these ceramic membranes. In addition, gross waste of steel industry (blast furnace slag) was firstly used as the main starting material for making the membranes. In this study, for making the zeolite ceramic membranes, some experiments were conducted with water levels of 38, 40, 42 and 44 wt% of the blast furnace slag and NaOH levels of 4, 4.2, 4.4 and 4.6 wt% of the blast furnace slag. At first, for making the membranes, a primary geopolymer gel was prepared. Afterward the membranes were cast at 25 °C for 24 h. In order to form the zeolite layer, the membranes after geopolymerization process were kept at 90 °C for 24 h. The maximum value of selectivity (2579.48) was obtained for separation of water from ethanol using the synthesized membrane with 42 wt% water and 4 wt% NaOH.     

Carbon molecular sieve dense film membranes derived from Matrimid® for ethylene/ethane separation

Development of dense film carbon molecular sieve (CMS) membranes for ethylene/ethane (C₂H₄/C₂H₆) separation is reported. A commercial polyimide, Matrimid®, was pyrolyzed under vacuum and inert argon atmosphere, and the resultant CMS films were characterized using pure C₂H₄ and C₂H₆ permeation at 35 °C, 50 psia feed pressure. The effects on C₂H₄/C₂H₆ separation caused by different final vacuum pyrolysis temperatures from 500 to 800 °C are reported. For all pyrolysis temperatures separation surpassed the estimated ‘upper bound’ solution processable polymer line for C₂H₄ permeability vs. C₂H₄/C₂H₆ selectivity. C₂H₄ permeability decreased and selectivity increased with increasing pyrolysis temperature until 650–675 °C where an optimum combination of C₂H₄ permeability ～14–15 Barrer with C₂H₄/C₂H₆ selectivity ～12 was observed. A modified heating rate protocol for 675 °C showed further increase in permeability with no selectivity loss. CMS films produced from argon pyrolysis showed results comparable to vacuum pyrolysis. Further, mixed gas (63.2 mol% C₂H₄ + 36.8 mol% C₂H₆) permeation showed a slightly lower C₂H₄ permeability with C₂H₄/C₂H₆ selectivity increase rather than a decrease that is often seen with polymers. The high selectivity of these membranes was shown to arise from a high ‘entropic selection’ indicating that the ‘slimmer’ ethylene molecule has significant advantage over ethane in passing through the rigid ‘slit-shaped’ CMS pore structure.     

Role of critical concentration of PEI in NMP solutions on gas permeation characteristics of PEI gas separation membranes

In preparation of polymeric gas separation membranes by phase inversion method, polymer concentration is one of the most important variables which can change membrane morphology and behavior. In this research, critical concentration of the polyetherimide (PEI) solutions in N-methyl-2-pyrrolidone (NMP) as a solvent was determined by viscometric method. The influence of temperature on critical concentration was studied. Three asymmetric PDMS/PEI membranes with different concentrations of PEI were prepared and characterized for H₂/CH₄ separation. The results showed that the membranes with higher concentrations than critical concentration were more suitable for gas separation. In addition, the viscosity data were fitted by appropriate equations and the densities were satisfactorily correlated by a simple first-order polynomial with respect to temperature and the PEI mass fraction. The prepared membrane showed the selectivity of 26 for H₂/CH₄ separation at 1 bar and 25 °C for pure gas and 24.8 for mixed gas. The influence of the pressure on the H₂ and CH₄ permeance and the selectivity for a mixed binary gas showed that the permeance of both gases declined by pressure enhancement and the selectivity increased.     

UV curable sulfonated hybrid materials and their performance as proton exchange membranes

In this study 2-acrylamido-2-methylpropanesulfonic acid (AMPS) containing UV curable nanocomposite membranes were prepared by using the sol–gel method. Tetraethylorthosilicate (TEOS), and 3-(methacryloyloxy)propyl trimethoxysilane (MAPTMS) were used, respectively as an inorganic precursor and coupling agent. Cross linking agents such as poly(ethylene glycol diacrylate) (PEGMA) and ethylene glycol dimethacrylate (EGDMA) were used to arrange the mechanical and physical properties of the resulting hybrid membrane. The hybrid formulation polymerized under UV irradiation and the gel percentage, water uptake of the membranes were calculated. The polymerization conversion of the organic part was investigated by using photo-differential scanning calorimetry (photo-DSC). The thermal and mechanical properties of the membranes indicated good stability. The morphological structure of membranes was investigated by scanning electron microscopy (SEM). In addition proton conductivity and methanol selectivity measurements were performed. The proton conductivity of the AMPS20–SOLGEL30 nanocomposite membrane is about 0.138 S cm^?1 at 50 °C. Selectivity toward methanol for the same membrane is very low with a selectivity factor of α = 0.032, which satisfies the requirements for DMFC applications.     

Carbon molecular sieve gas separation membranes based on an intrinsically microporous polyimide precursor

We report the physical characteristics and gas transport properties for a series of pyrolyzed membranes derived from an intrinsically microporous polyimide containing spiro-centers (PIM-6FDA-OH) by step-wise heat treatment to 440, 530, 600, 630 and 800 °C, respectively. At 440 °C, the PIM-6FDA-OH was converted to a polybenzoxazole and exhibited a 3-fold increase in CO₂ permeability (from 251 to 683 Barrer) with a 50% reduction in selectivity over CH₄ (from 28 to 14). At 530 °C, a distinct intermediate amorphous carbon structure with superior gas separation properties was formed. A 56% increase in CO₂-probed surface area accompanied a 16-fold increase in CO₂ permeability (4110 Barrer) over the pristine polymer. The graphitic carbon membrane, obtained by heat treatment at 600 °C, exhibited excellent gas separation properties, including a remarkable CO₂ permeability of 5040 Barrer with a high selectivity over CH₄ of 38. Above 600 °C, the strong emergence of ultramicroporosity (<7 Å) as evidenced by WAXD and CO₂ adsorption studies elicits a prominent molecular sieving effect, yielding gas separation performance well above the permeability-selectivity trade-off curves of polymeric membranes.     

Heterogeneous membranes based on a composite of a hypercrosslinked microparticle adsorbent and polyimide binder

This paper deals with the preparation and characterization of heterogeneous membranes based on microparticle hypercrosslinked polymeric adsorbents with a polyimide binder. The polyimide based membrane extension is hindered by their low permeability. We enhanced the permeability of polyimide membranes by changed chemical structure and by adding of the new type fillers. Hypercrosslinked polystyrene microparticles of diameter 1–5 μm were prepared by SnCl₄-catalyzed Friedel–Crafts reaction of polystyrene with chloromethyl methyl ether in 1,2-dichlorethane solution. The precursor polyamic acid (PAA) was synthesized by the reaction of equimolar amounts of 4,4′-oxy(bis(phthalic anhydride)) (ODPA) and bis(4,4′-oxydianiline) (ODA) or 4,4′-[(1,4-phenylene)dipropane-2,2-diyl]dianiline (BIS P) in N-methylpyrrolidone (content 10 wt.%). A PAA solution in N-methylpyrrolidone with the adsorbent was spread onto a glass substrate and kept at 60–240 °C for 12 h. Heterogeneous membranes were characterized by thermal, mechanical and separation measurements. The permeability for membrane ODPA–BIS P filled with 10 wt.% of hypercrosslinked adsorbent was 3.5 × 10⁻¹¹ cm³(STP) cm cm⁻² s⁻¹ cmHg⁻¹ for nitrogen and 4 × 10⁻⁹ cm³(STP) cm cm⁻² s⁻¹ cmHg⁻¹ for hydrogen. The permeability of homogeneous polyimide membranes is up to one order of magnitude lower. The diffusion coefficient of heterogeneous membranes increased in the order CH₄ < N₂ < O₂ < CO₂ < H₂. The selectivity of hydrogen–nitrogen separation with the amount of adsorbent decreased from 164 to 69. The prepared membranes are intended for separation of gases and low organic molecules even at enhanced temperature. The present paper aims at giving information on the influence of hypercrosslinked adsorbents and polyimide binding materials on the gas separation properties of membranes.     

Separation of gas and organic/water mixtures by MFI type zeolite membranes synthesized in a flow system

MFI type zeolite membranes were synthesized in a recirculating flow system at 95 °C where the synthesis solution was flown over the tubular α-alumina supports. The performance of the membranes for the separation of binary gas mixtures and alcohol/water liquid mixtures was investigated. A membrane synthesized by two consecutive synthesis steps had a separation selectivity of 15 and 11 for equimolar mixtures of n-C₄H₁₀/CH₄ and n-C₄H₁₀/N₂ at 200 °C, respectively. The membrane selectively permeated large n-C₄H₁₀ over small CH₄ and N₂, suggesting that the separation is essentially adsorption-based and the membrane has few nonselective intercrystalline pores. The selectivities in the pervaporation separation of 5% ethanol/95% water mixture were 43 and 23 with permeate fluxes of 0.2 and 1.9 kg/m² h at 25 and 85 °C, respectively. The separation performance of membranes showed that MFI type membranes prepared in a recirculating flow system can be used both in the separation of gas and liquid mixtures.     

Effect of impurities in the recovery of 1-(5-bromo-fur-2-il)-2-bromo-2-nitroethane using nanofiltration

The recovery of the active pharmaceutical ingredient 1-(5-bromo-fur-2-il)-2-bromo-2-nitroethane (denoted as G-1) from residual ethanol produced during the purification of G-1 was studied by using solvent resistant nanofiltration. The effect of the impurities pyridine, acetic anhydride and bromine on the process performance was studied.Four commercial nanofiltration membranes were studied in a stirred dead-end filtration module, i.e. NF 90, NF 270, Duramem 150 and BW30XLE, supplied by Evonik Industries and Filmtec (Dow). The membranes Duramem 150 and NF 90 showed the best performance, allowing a recovery of G-1 of above 60% in one stage. The separation factor of pyridine/G-1 for Duramem 150 and NF 90 was found to be higher than 2 for synthetic mixtures containing 26.75 g/L of G-1, 5.35 g/L of pyridine, 0.149 g/L of bromine and 0.105 g/L of acetic anhydride in ethanol. It was found that when using dead-end filtration, the recovery of G-1 is low when a high purity is required; both parameters cannot be optimized together. However, it is shown that with a sequence of filtrations, the recovery can be significantly improved at a given purity of G-1. These results indicate that the application of organic solvent nanofiltration for the recycling of valuable pharmaceutical compounds is feasible in realistic conditions.     

Effects of hypochlorite exposure on flux through polyethersulphone ultrafiltration membranes

Polyethersulphone ultrafiltration membranes with a nominal molecular weight cut off of 10 kDa were degraded in solutions of sodium hypochlorite over a range of pH values at 55 °C to achieve exposure measured in ppm-days of chlorine exposure. The degraded membranes were tested, using an ÄKTAcrossflow? system, for clean water flux, demineralised whey flux and protein rejection. The water fluxes for three membranes (new, 10,000 ppm-day pH 12, and 10,000 ppm-day pH 9) were found to be about 100, 200 and 400 L m^?2 h^?1, respectively with cross flow at 1 bar transmembrane pressure. However whey fluxes were about 23, 5, and 6 L m^?2 h^?1 for the same three membranes. Size exclusion chromatography of the permeates showed significant permeation of α-lactalbumin and β-lactoglobulin through membranes degraded at pH 9 for 20,000 ppm-days, while almost no permeation was found for degradation at pH 12.These results show that hypochlorite degradation affected fluxes by at least two mechanisms. It was likely that membrane pitting increased the pore size causing increased water flux and reduced protein rejection. However hypochlorite also seemed to alter the membrane surface properties, causing the protein to form a less permeable layer that reduced the flux of whey.     

Preparation and characterization of novel ceramic membranes for micro-filtration applications

Porous microfiltration range ceramic membranes were prepared using kaolin and other suitable materials like feldspar, quartz, boric acid, activated carbon, sodium metasilicate and titanium dioxide following standard paste casting route. The membranes were casted as circular disks of 40 mm ID and 5 mm thickness. They were characterized using thermo gravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD) and scanning electron microscope (SEM) to evaluate the effect of maximum sintering temperature on the structure, porosity and mechanical integrity. The prepared membranes were initially dried at 120 °C and 250 °C for 24 h each and finally sintered at 850 °C, 900 °C and 950 °C for 6 h. Morphological parameters viz. pore size distribution, porosity, average pore size of the prepared membranes were determined and the membrane performance were evaluated by carrying out the permeation experiment with pure water. Results show that the average pore size of the membranes increases from 1.59 µm to 2.56 µm and porosity of the membrane supports decreases from 18.88% to 5.59% with increase in sintering temperature from 850 °C to 950 °C. The membrane corrosion resistance was also tested using acid and base and it is observed that there is no significant weight loss in the process. Based on market price of the inorganic precursors, the membrane cost was estimated to be $92/m² which can be considered low cost in the microfiltration range for industrial applications.     

Preparation and characterization of polysulfone mixed matrix membrane incorporated with palladium nanoparticles in the inversed microemulsion for hydrogen separation

Polysulfone (PSf) membrane shows acceptable gas separation performance, but its application is limited by the “trade-off” between selectivity and permeability. In this study, PSf mixed matrix membranes (MMMs) incorporated with palladium (Pd) nanoparticles in the inversed microemulsion were proposed for hydrogen (H₂) separation. Pd nanoparticles can be kinetically stabilized and dispersed using electrostatic and/or steric forces of a stabilizer which is typically introduced during the formation of Pd nanoparticles in the inversed microemulsion. Pd nanoparticles were synthesized by loading (PdCl₂) into the polymeric matrix, polyethylene glycol (PEG) which acts as reducing agent and stabilizer. The dry–wet phase inversion method was applied for the preparation of asymmetric PSf MMMs. The effects of Pd (0–4 wt%) on the membrane characteristics and separation performance were studied. Experimental findings verified that the MMMs are able to achieved a high H₂/N₂ selectivity of 21.69 and a satisfactory H₂ permeance of 46.24 GPU due to the changes in membrane structure from fully developed finger-like structure to closed cell structure besides the growth of dense layer. However, the selectivity of H₂/CO₂ decreased due to the addition of PEG.     

Preparation and characterization of PVC based heterogeneous ion exchange membrane coated with Ag nanoparticles by (thermal-plasma) treatment assisted surface modification

PVC based heterogeneous cation exchange membranes were prepared by solution casting technique. Ag nanoparticles were also utilized as surface modifier by plasma treatment. Thermal treatment was used to improve the Ag nanoparticles stability on membrane surface. The effect of treating temperature on separation characteristics of coated membranes was studied. SEM images showed membrane rugosity increasing by the increase of treating temperature. Transport number, selectivity and permeability were enhanced initially by increase of treating temperature up to 80 °C and then showed decreasing trend. Conversely membrane resistance showed opposite trend. Modified membrane at 80 °C showed better performance compared to others.     

Porous membrane based on chitosan–SiO2 for coin cell proton battery

Porous chitosan–SiO₂ membranes were prepared by ultrasonic mixing solution-cast and porogen removal method at different SiO₂ weight ratios. To remove SiO₂ from chitosan membranes, NaOH solution was used to dissolve SiO₂. Porous chitosan:SiO₂ membrane with the weight ratio 1:2 produced optimum average pore size (8.5 μm) with an amorphous structure and the highest water uptake (257.1%). Further soaking of this membrane in NH₄CH₃COO electrolyte solution for two days produced the highest conductivity (3.6×10⁻³ S cm⁻¹) and optimum breakdown voltage (1.8 V). Fabrication of coin cell proton battery displayed an open circuit potential of 1.5 V for 7 days, maximum power density (6.7 mW cm⁻²) and small current resistance (0.03 Ω). The specific discharge capacities obtained from discharge profile of 39.7 mA h g⁻¹ (0.5 mA) and 43.8 mA h g⁻¹ (1.0 mA) increased as the discharge currents were increased. These results showed that a porous chitosan–SiO₂ membrane is suitable membrane for the proton batteries.     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Selective separation of low concentration CO2 using hydrogel immobilized CA enzyme based hollow fiber membrane reactors

This paper reported the results of developing a novel hollow fiber membrane reactor contained immobilized enzyme for selective separation of low concentration CO₂ from mixed gas streams. In the reactor, two bundles of poly(vinylidene fluoride) (PVDF) hollow fiber membranes were aligned staggered parallel in a tube module, and lab-made poly(acrylic acid-co-acrylamide)/hydrotalcite (PAA-AAm/HT) nanocomposite hydrogel was filled between fibers, in which carbonic anhydrase (CA enzyme) was immobilized. The effects of CA concentration, buffer concentration, the flow rate of sweep gas, operational temperature, and CO₂ concentration on separation performance were investigated in detail. The results showed that the transport resistance was mainly from the hydrogel layer, and decreased greatly with immobilization of carbonic anhydrase in hydrogel. Moreover, immobilized CA could retain over 76% enzymatic activity and thermal stability was also improved. The data showed that this enzyme-based membrane reactor could effectively separate CO₂ at low concentration from mixed gas streams. For the feed with 0.1% (v/v) of CO₂, the selectivity of CO₂/N₂ was 820, CO₂/O₂ was 330, and CO₂ permeance was 1.65×10^?8 mol/m² s Pa. Prolonged runs lasting 30 h showed that separation performances of the membrane reactor were quite stable.