Separation Properties Of Membranes Research Articles

Towards improved separation performance using porous FO membranes: The critical roles of membrane separation properties and draw solution

The use of porous membranes for forward osmosis (FO) applications has been recently reported in the literature. In the current study, a series of porous-FO membranes were fabricated to systematically study the role of membrane separation properties on the FO performance of porous membranes. In addition, two types of draw solutes, a polyelectrolye poly(sodium 4-styrene-sulfonate) (PSS) and a neutral linear polymer polyethylene glycols (PEGs), were evaluated as the draw solutes. The effect of draw solution properties (type of draw solutes, their molecular weight, and concentration) on the FO performance was investigated. Membrane post-treatment at higher annealing temperature was found to increase solute rejection and decrease water permeability. As a result, reverse solute diffusion (RDS) became less severe at higher annealing temperature. The FO water flux of the porous membranes was affected by RDS in addition to the water permeability of the porous FO membranes, both of which had a strong dependence on the annealing temperature. Compared to neutral PEG, the polyelectrolyte PSS was a much better choice for draw solutes with higher FO water flux and lower RDS. The better performance of PSS can be attributed to its higher rejection by the porous FO membranes and its high osmotic pressure compared to PEG at same weight concentration. Implications for the design of porous FO membranes and draw solution are discussed.

Propylene/Propane Mixture Separation Characteristics and Stability of Carbon Molecular Sieve Membranes

Propylene/propane mixture separation properties of high quality carbon molecular sieve (CMS) membranes prepared on mesoporous γ-alumina supports were studied at different feed pressures (up to 100 psia), feed compositions, and permeation temperatures. The membrane exhibits a mixture propylene/propane selectivity of above 30 under the studied conditions, with no plasticization effect observed at feed pressures up to 100 psia (∼700 kPa). Temperature dependences of the permeance and selectivity suggest a diffusion dominated mechanism for the permeation and separation of propylene/propane through the CMS membrane. The propylene/propane separation characteristics tend to stabilize after a decline in gas permeance and an increase in propylene/propane selectivity while on stream of propylene/propane mixture for 10 days. The initial changes in separation properties of the CMS membrane are due to the reduction in the effective pore size caused by oxygen chemisorption and physical aging of the pore structure. CMS m...

Degradation of PVDF-based composite membrane and its impacts on membrane intrinsic and separation properties

Abstract In this work, an attempt was made to evaluate the effects of ultraviolet (UV) irradiation period on the intrinsic and separation properties of composite membrane composed of organic polyvinylidene fluoride and inorganic titanium dioxide (TiO2) nanoparticles by exposing the membrane to UV-A light for up to 250 h. The changes on membrane structural morphologies and chemical characteristics upon UV exposure were studied by field-emission scanning electron microscope and Fourier transform infrared, respectively. It was observed that some cracks and fractures were formed on the membrane outer surface when it was exposed to 120-h UV light. Further increase in UV irradiation time to 250 h had caused membrane structure to collapse, turning it into powder form. Filtration experiments showed that the permeate flux of irradiated membrane was significantly increased from 10.89 L/m2 h to 21.84 L/m2 h (>100% flux increment) while oil rejection decreased with increasing UV exposure time from 0 h to 120 h. Furthermore, the mechanical strength and thermal stability of irradiated membrane were also reported to decrease with increasing UV exposure time, suggesting the negative impacts of UV light on the membrane overall stability. This research is of particular importance to evaluate the suitability and sustainability of polymeric membrane, which is widely considered as the host for photocatalyts and used for wastewater treatment process under UV irradiation.

Separations of binary mixtures of CO2/CH4 and CO2/N2 with mixed-matrix membranes containing Zn(pyrz)2(SiF6) metal-organic framework

In this work, mixed-matrix membranes comprising Zn(pyrz)2(SiF6) (or SIFSIX-3-Zn) metal-organic framework were fabricated for potential applications in biogas upgrading and post-combustion CO2 capture. First, submicron-sized Zn(pyrz)2(SiF6) crystals that selectively adsorb and transport CO2 over CH4 and N2 were synthesized by a facile sonochemical method. Then, high-quality mixed-matrix membranes free of filler/polymer interfacial voids were succesfully fabricated by employing crosslinked polyethylene oxide as a polymer matrix. CO2/CH4 and CO2/N2 mixture gas permeation tests revealed that the separation properties of mixed-matrix membranes, especially selectivities, were significantly improved compared to those of pure polymeric membrane owing to the selective CO2 uptake and transport in Zn(pyrz)2(SiF6) crystals.

A study on the stability of polyethersulfone ultrafiltration membranes in a photocatalytic membrane reactor

To date no information about the stability of the polymer membranes in photocatalytic membrane reactors (PMRs) has been published. In order to implement this technology into the full scale the lifespan of the membranes should be assessed. In this paper the investigations on the influence of membrane properties, type of a TiO2 photocatalyst (P25, ST-01, A700, and A800), a presence of oxidative species and the process parameters such as feed cross flow velocity and transmembrane pressure (TMP) on the stability of commercial polyethersulfone ultrafiltration membranes with different cut-off in a PMR are presented. Under the conditions prevailing in the PMR all the tested membranes lost their separation properties towards dextrans. The membrane characterized by the finest pores and thus the most delicate skin layer was damaged to the highest extent. The small angular-shaped particles of ST-01 caused a more severe damage of the membrane surface than the large round-edge shaped particles of A800. The deterioration of the membrane separation properties was less severe at low (1bar) TMP value compared to that at TMP of 3bar. The loss of the separation properties of the membranes was caused to a greater extent by the abrasion of their surface by the photocatalyst particles than by the action of oxidative species.

Design of poly(ether block amide)/polyacrylonitrile composite membrane for carbon dioxide capture

In this study, poly(ether block amide) was used as coating material to develop a novel composite polymer membrane for CO 2 capture. Polyacrylonitrile (PAN) ultrafiltration membrane was applied as substrate. Between them, a gutter layer prepared from cross-linked polydimethylsiloxane (PDMS) blending with amino silicone was introduced to improve separation performance of the composite membrane. The separation properties of resultant triple layer composite membrane was characterized using pure CO 2 and N 2 gases. It was found that the crosslinking degree of the gutter layer had great influence on membrane performance, which could be significantly improved with the help of amino-PDMS gutter layer compared with that of the membrane having Pebax coating directly onto PAN substrate. Using 2 wt.% Pebax coating solution and properly cross-linked gutter layer, the designed Pebax/amino-PDMS/PAN composite membrane showed CO 2 permeance of 147 GPU and CO 2/ N 2 selectivity of 62.

Behaviour of RO90 membrane on the removal of 4-nitrophenol and 4-nitroaniline by low pressure reverse osmosis

Industrial and groundwater wastewater contains organic compounds that cause a serious environmental problem, specifically, 4-nitrophenol (4NP) and 4-nitroaniline (4NA) have been listed as major priority contaminants by the US environmental protection agency (EPA).This paper makes a comparative study on the removal of two organic compounds, 4NP and 4NA, from aqueous solutions by low pressure reverse osmosis using a RO90 polyamide membrane, analyzing the effect of different experimental conditions such as feed organic compound concentration, applied pressure and pH. The loss of efficiency of RO90 membrane after a long period of use and the effect of ultrasound cleaning treatment on that efficiency have also been studied.Different rejection behavior is observed for the two compounds at pH higher than 6, 4NA shows a rejection decrease and 4NP shows an important rejection increase as pH increases. Ultrasound treatment on the used membrane leads to a partial membrane regeneration, but it is far from regenerating the initial membrane separation properties.

Pervaporative desulfurization of gasoline – separation of thiophene/n-heptane mixture / Perwaporacyjne odsiarczanie benzyny – separacja mieszanin tiofen/n-heptan

Abstract This paper presents the recent advances in pervaporative reduction of sulfur content in gasoline. Methods of preliminary selection of membrane active layer material are presented. Interactions between gasoline components (typical hydrocarbon and sulfur species) and membranes are showed. Influence of pervaporation process parameters i.e. feed temperature, downstream pressure and feed flow rate on the separation efficiency is discussed. Investigations of the influence of sulfur concentration in fluid catalytic cracking (FCC) gasoline on membrane performance have been conducted. A series of PV tests was carried out to investigate the separation properties of the commercial composite membrane with an active layer made of poly(dimethylsiloxane) and to determine the efficiency of organic sulphur compound (thiophene) removal from model thiophene/n-heptane mixture depending on its concentration.

Enhanced CO2/CH4 separation properties of asymmetric mixed matrix membrane by incorporating nano-porous ZSM-5 and MIL-53 particles into Matrimid®5218

Asymmetric Matrimid/fillers mixed matrix membranes, composed of a metal organic framework (MIL-53; with CO2 sorption properties) and a zeolite (ZSM-5; with size selective properties) as porous fillers, were used in CO2/CH4 separation. Cross-sectional SEM images of membranes showed a complete porous structure with finger-like pores. The presence of 6 wt. % of ZSM-5 in membrane matrix led to the CO2/CH4 selectivity enhancement. Conversely, results obtained from gas permeance tests (i.e., pure and mixed gas test) conducted over those membranes which contain higher loading percentage, showed the increase of permeation along with selectivity decline. Creation of interfacial voids between polymer and particles at higher loading of ZSM-5 caused the performance failure of membrane and selectivity was decreased, too. Alternatively, those membranes incorporated with MIL-53 particles, compared to pure Matrimid, showed significant enhancement in permeance of gases and CO2/CH4 selectivity. Organic linkers of MIL-53 improve the quality of polymer–filler interfaces and decrease the probability of the formation of interfacial voids as much as possible, which resulted in membrane performance enhancement. In pure permeation, CO2 permeance showed 270% growth and CO2/CH4 selectivity increased from 14.8 to 23.6 in membranes containing 15 wt. % MIL-53 compared to pure asymmetric Matrimid. MMMs filled with MIL-53 particles were suggested more proper separation factor compared to those embedded by ZSM-5 particles. The superior performance of Matrimid/MIL-53 MMM was attributed to the quality of polymer/filler interfaces as well as selective CO2 adsorption with embedded MIL-53. The best CO2 permeance and CO2/CH4 selectivity gained by Matrimide/MIL-53 at 3 bar were 46 GPU and 23.6 respectively; where Matrimid/ZSM-5 exhibited a CO2 permeance of 14.5 GPU and CO2/CH4 selectivity of 15.6. As the feed pressure increased from 3 to 12 bar, the permeance of both gases in MMMs decreased and CO2/CH4 selectivity increased, too. The increase of operating temperature from 35 to 65 °C resulted in enhancement of gas permeance, while CO2/CH4 selectivity decreased. Various permeation models (i.e., Maxwell, Bruggeman and Lewis–Nielsen) were used to predict mixed matrix membranes' separation properties. All models showed appropriate compatibility with experimental data at lower particles loading.

Poly(ether-b-amide)/Tween20 Gel Membranes for CO2/N2 Separation

Poly(ether-b-amide) (PEBA)/Tween20 gel membranes containing from 0 wt% to 65 wt% of Tween20 in PEBA2533, PEBA3533, and PEBA4033 were prepared by solvent casting method for CO2/N2 separation. The gas separation properties of the polymeric gel membranes were tested for single gases of CO2 and N2 at 25°C with the feed pressure of 0.6 atm. For all pure PEBA membranes, CO2 and N2 permeability decreased as the amount of polyamide block increased, but CO2/N2 selectivity increased. For PEBA/Tween20 gel membranes, both the CO2 permeability and CO2/N2 selectivity were greatly enhanced with the increase of Tween20 content. For the membrane of PEBA4033/Tween20-65, CO2/N2 selectivity, and CO2 permeability reached 54 and 146 Barrer, respectively, which is very interesting for potential application in CO2 removal from flue gas.

Molecular layer-by-layer assembled forward osmosis membranes

A recently devised, molecular layer-by-layer (mLbL) approach based on the alternative cross-linking of monomers was employed to fabricate high-performance thin film composite (TFC) forward osmosis (FO) membranes with excellent rejection toward monovalent NaCl salt. An ultrathin and highly dense polyamide (PA) selective layer with a precisely controlled structure was created on a tailored porous support via mLbL. The intrinsic separation properties of the mLbL-assembled TFC membranes were tuned by adjusting the mLbL cycle number to optimize the FO performance. The best FO performance was achieved at 10 mLbL cycles (mLbL-10), where the permeability and selectivity were properly balanced. Importantly, the mLbL-10 membrane exhibited superior FO performance compared to the commercial HTI FO membranes as well as hand-cast TFC membranes prepared by the conventional interfacial polymerization: the mLbL-10 membrane showed ~3.5 times higher water flux, ~60% lower reverse salt flux and ~85% lower specific salt flux compared to the cellulose triacetate HTI membrane, with 0.5M NaCl draw solution and DI water feed solution in FO mode. The stability and the associated membrane performance of the mLbL-assembled membrane depending on the ionic strength of the environment were explained by the swelling behavior of the polyelectrolyte-assembled interlayer adhered underneath the PA selective layer.

High flux, positively charged loose nanofiltration membrane by blending with poly (ionic liquid) brushes grafted silica spheres

Silica spheres modified by poly (ionic liquid) brushes, a novel positively charged nanomaterial is prepared by atom transfer radical polymerization (ATRP). A high flux positively charged loose nanofiltration membrane is fabricated via “blending-phase inversion” method. The morphology structures, hydrophilicity, thermal and mechanical properties, permeation performance of these membranes are investigated in detail. The results reveal that the hybrid membranes have enhanced surface hydrophilicity, water permeability, thermal stability, and mechanical properties. Characterization of membrane separation properties shows that the hybrid membranes possess higher salt permeability and relatively higher rejection for reactive dyes, which may open opportunities for the recycling of reactive dyes wastewater. Moreover, such hybrid membranes have an outstanding operational stability and salts concentration showed little effect on the separation properties.

Enhancement of the gas separation properties of polyurethane membranes by alumina nanoparticles

In this work, polyurethane (PU) nanocomposite membranes were prepared using different concentrations of alumina (Al2O3) nanoparticles (0, 2.5, 5, 10, 20, and 30wt%). The main objective of this work is to evaluate the permeability of CO2, CH4, O2, and N2 gases in the polyurethane hybrid membranes at various Al2O3 contents and with two different chain extenders. Polyurethane was synthesized by bulk two-step polymerization based on polytetramethylene glycol (PTMG) and hexamethylene diisocyanate (HMDI). 1,4-butanediol (BDO) and 2-methyl-1,3-propanediol (MPD) were used as chain extenders to complete the conversion of the prepolymers to the final polyurethanes. The prepared polyurethane–Al2O3 membranes were characterized using Fourier Attenuated Total Reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscope (SEM), wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) analyses. The results show a reduction in the gas permeability, but a significant enhancement in the CO2/N2, CO2/CH4, and O2/N2 selectivities with alumina content. The separation performances of the membranes were compared with Robeson׳s upper bound limit. The new modified Higuchi model was applied to predict the permeability of polyurethane–alumina hybrid membranes.

Enhanced separation and antifouling properties of PVDF ultrafiltration membranes with surface covalent self-assembly of polyethylene glycol

A branched PEG layer on a PVDF membrane surface exhibited exclusion capability to pollutants.

Polypropylene membranes with the double sensitivity effect

ABSTRACTThis article describes the modification of polypropylene membranes leading to the preparation of thermo‐ and pH‐sensitive structures. Poly(N‐isopropylacrylamide), poly(acrylic acid), or copolymer poly(N‐isopropylacrylamide‐co‐acrylic acid) was grafted on to the membranes' surface activated by dielectric barrier discharge plasma. The properties of the modified membranes were evaluated by means of infrared spectroscopy and contact angle measurements. The effect of modification was monitored by the determination of water flux at two temperatures (20 and 45°C) and at various pH values (2.8–8.0). The membrane separation properties were investigated for the solutions of o‐bromocresol purple. It was found that membranes grafted with copolymer were responsive to both stimuli and they could be used for separation purpose. The separation performance was tailored by alteration of pH and temperature of feed solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41763.

PVDF hollow fiber formation via modified NIPS method: Evolution elucidation of phase separation mechanism, structure and properties of membrane with coagulation strength varied

In this work, hollow fiber membrane was prepared from poly(vinylidene fluoride) (PVDF)/triethyl phosphate (TEP)/water systems by modified non-solvent induced phase separation technique (mNIPS), which was characterized in the process with relative high polymer content of 30 wt% in spinning dope. The ternary phase diagram and precipitation rate were determined to elucidate the various membrane formation mechanisms, and the membranes morphologies were observed by field emission scanning electronic microscopy (FESEM). It was indicated that the phase separation mechanism was found to heavily depend on the bath strength. Although the solid-liquid demixing process initiated the precipitation process, by changing the bath gradually from pure water to 40% TEP, the liquid-liquid demixing occurred earlier and earlier. Accordingly the top surface morphologies evolved from a dense skin (asymmetric membrane) to a totally porous morphology (symmetric membrane). In addition, the permeability, maximum stress at break, medium pore size and porosity of hollow fiber membranes were also investigated. In conclusion, the successful application of modified non-solvent induced phase separation (mNIPS) may provide an effective route to improve the membrane structure modulation.

Preparation and investigation of the gas separation properties of polyurethane-TiO2 nanocomposite membranes

The effect of TiO2 nanoparticles on the gas separation properties of polyurethane has been investigated. Polyurethane was synthesized using hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) as hard segment and poly(tetramethylene glycol) (PTMG, 2,000 g/mol) as soft segment. The synthesized polymer was in a 1: 2: 1 molar ratio of polyol:diisocyanate:chain extender through bulk two-step polymerization. PU membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), X-ray diffraction and Fourier Transform Infrared (FTIR) analyses characterized the prepared membranes. FTIR and SEM results indicate the good interaction between particles and polymer matrix and also the nanoscale dispersion of TiO2 particles in polymer matrix. Gas permeation properties of PU-TiO2 nanocomposite membranes with TiO2 contents up to 30 wt% were studied for N2, O2, CH4 and CO2 gases at 10 bar and 25 °C. Results suggest a decrease in permeability of studied gases and increase in gas selectivities as TiO2 content increases.

A facile modification approach for polyacrylonitrile-based UF hollow fiber membrane utilizing polyacrylonitrile-g-poly(vinyl alcohol) graft copolymer

Facile blending approach utilizing amphiphilic copolymers has received enormous attention from researchers owing to their unique self-organizing behaviour that can improve membrane structure and separation properties. This paper discusses the effect of the amount of acrylonitrile (AN) monomer added during polyacrylonitrile-g-polyvinyl alcohol (PAN-g-PVA) copolymer synthesis and its relationship to the properties and performance of PAN-based ultrafiltration (UF) hollow fiber membrane. The hollow fiber membranes were characterized using atomic force microscope, scanning electron microscope, X-ray photoelectron spectroscope and contact angle goniometer, in addition to performance evaluation with respect to protein rejection and antifouling resistance. As for the UF experiments, the membrane incorporated with copolymer of highest monomer composition achieved the highest pure water flux (178.76 L/m2.hr) coupled with good rejection of bovine serum albumin (BSA) and albumin from chicken egg (at least 83 %) when tested at 1 bar. The promising results are mainly due to the changes in the membrane morphological properties, surface roughness, surface chemical composition and hydrophilicity upon the addition of the copolymer. In terms of anti-fouling performance, generally, blend membrane prepared from copolymer of lowest amount of monomer produced good flux recovery for all proteins (74 %, 67 % and 62 % during BSA, albumin from chicken egg and trypsin) filtration due to the enrichment of PVA on membrane surface and its low surface roughness. The experimental results offer an important insight into the relationship between amount of monomer added during graft copolymer synthesis and membrane properties and performance, providing valuable information for high performance UF membrane for fouling mitigation especially in the area involving proteinaceous solution.

Preparation and separation properties of porous norbornane-bridged silica membrane

Bis(trimethoxysilyl)norbornane (BTMSN) bearing a highly rigid norbornane bridge was employed as a new silica membrane precursor. The membrane prepared by subjecting BTMSN to the sol–gel process was examined for gas and water separation, and the results were compared with those of ethylene- and ethenylene-bridged silica membranes reported previously. Interestingly, the gas permeability of the BTMSN silica membrane was higher than that of the ethylene- and ethenylene-bridged silica membranes, whereas the water permeability was rather suppressed. The moderately high H2/SF6 permeance ratio of 1,160 and the NaCl rejection of 95 % (2,000 ppm aqueous NaCl) obtained for the BTMSN silica membrane clearly indicate its potential application to gas and water separation.

Silylated Mesoporous Silica Membranes on Polymeric Hollow Fiber Supports: Synthesis and Permeation Properties

We report the synthesis and organic/water separation properties of mesoporous silica membranes, supported on low-cost and scalable polymeric (polyamide-imide) hollow fibers, and modified by trimethylsilylation with hexamethyldisilazane. Thin (∼1 μm) defect-free membranes are prepared, with high room-temperature gas permeances (e.g., 20,000 GPU for N2). The membrane morphology is characterized by multiple techniques, including SEM, TEM, XRD, and FT-ATR spectroscopy. Silylation leads to capping of the surface silanol groups in the mesopores with trimethylsilyl groups, and does not affect the integrity of the mesoporous silica structure and the underlying hollow fiber. The silylated membranes are evaluated for pervaporative separation of ethanol (EtOH), methylethyl ketone (MEK), ethyl acetate (EA), iso-butanol (i-BuOH), and n-butanol (n-BuOH) from their dilute (5 wt %) aqueous solutions. The membranes show separation factors in the range of 4-90 and high organic fluxes in the range of 0.18-2.15 kg m(-2) h(-1) at 303 K. The intrinsic selectivities (organic/water permeability ratios) of the silylated membranes at 303 K are 0.33 (EtOH/water), 0.5 (MEK/water), 0.25 (EA/water), 1.25 (i-BuOH/water), and 1.67 (n-BuOH/water) respectively, in comparison to 0.05, 0.015, 0.005, 0.08, and 0.14 for the unmodified membranes. The silylated membranes allow upgradation of water/organics feeds to permeate streams with considerably higher organics content. The selective and high-flux separation is attributed to both the organophilic nature of the modified mesopores and the large effective pore size. Comparison with other organics/water separation membranes reveals that the present membranes show promise due to high flux, use of scalable and low-cost supports, and good separation factors that can be further enhanced by tailoring the mesopore silylation chemistry.