Thin Film Composite Poly Research Articles

PH stable thin film composite poly(amine-urea) nanofiltration membranes with excellent rejection performance

pH stable nanofiltration membranes are highly desirable in treating acidic and alkali effluents and recovering the valuable byproducts. Efforts have been devoted to preparing nanofiltration membranes with good acid/alkali resistance but the separation performance is still to be improved. Poly(amine-urea) nanofiltration membranes with excellent rejection performances were prepared by the interfacial polymerization between polyethyleneimine with the mixed organic monomer of cyanuric chloride and 1, 4-phenylene diisocyanate. In comparison with pure polyamine and polyurea membranes, the optimal poly(amine-urea) membranes exhibit simultaneously improved membrane permeability and salt rejection, > 99% for MgSO4. The membrane morphology, pore structure and chemical properties of the membranes were thoroughly characterized, demonstrating that the poly(amine-urea) selective layer is thinner and denser compared with the polyamine/polyurea prepared with a single organic monomer. The underlying mechanisms for the synergistic effect between cyanuric chloride and 1, 4-phenylene diisocyanate were revealed. In addition, the poly(amine-urea) nanofiltration membranes maintain a high rejection for MgSO4, >96%, after exposure to 20 wt% HCl and 20 wt% NaOH aqueous solutions for 150 days, demonstrating excellent acid/alkali stability.

Nano/microstructure decorated thin film composite poly (arylene sulfide sulfone) membrane constructed by induced fouling in organic solvent ultrafiltration

In this study, novel thin film composite membranes with nano/macrostructure decorated surface were fabricated by deposition of poly (arylene sulfide sulfone) (PASS) polymer chains on oxidized poly (arylene sulfide sulfone) (O-PASS) support membrane during organic solvent ultrafiltration. Interestingly, the obtained membranes exhibited a rough surface structure composed of ordered arranged polymeric nodules with size ranging from nanoscale (100 nm) to macroscale (5 μm). Additionally, these membranes showed an improved, ultrahigh rejection of direct red 23, reactive blue 2, demonstrating their potential application for the reuse of dyes in wastewater. Furthermore, this novel synthesis approach of thin film composite membranes has great advantages in incorporating nanoparticles because of the facile process, the low consumption of nanoparticles and the high content of nanoparticles in the thin layer. During the whole thin layer synthesis process, only 2 mg of nanoparticles were used and thin layers with nanoparticles content of 20% were obtained. After the incorporation of candle soot, SiO2 and ZIF-8 in the separation layer, both the water permeation and rejection of direct red 23, reactive blue 2 and reactive orange 16 were greatly improved. Therefore, this study provides a novel and simple fabrication method for thin film composite membranes, which has advantages in incorporating nanoparticles in the thin separation layer to endow the membrane with an improved performance.

Regenerating Membrane Contactors for Solvent Absorption

Membrane contactors are a hybrid technology that incorporates the advantages of both solvent absorption and membrane separation. Porous and asymmetric composite membrane contactors have been studied for CO2 absorption, and both configurations are susceptible to pore wetting. This results in a significant reduction in the mass transfer efficiency. As such, regeneration methods to remove entrained liquids from the contactors are of interest. In this work, four regeneration protocols are trialled for a porous poly tetrafluoroethylene (PTFE) contactor and a thin film composite poly(1-trimethylsilyl)-1-propyne (PTMSP) contactor. It was found that air and vacuum drying at elevated temperatures increased the overall mass transfer coefficient of both contactors compared to the wetted state, but did not return either to their original performance. In addition, both contactors experienced rapid rewetting of the pores. Prewashing with methanol before air drying at elevated temperature produced the greatest improvement in overall mass transfer for the regenerated contactors. This was attributed to methanol miscibility with the water in the pores reducing the capillary pressure experienced during drying, as well as methanol swelling the PTMSP layer. However, original functionality was not achieved for either contactors and both continued to experience wetting over time, though at a slower rate than with non-methanol wash regeneration protocols.

Charge tunable thin-film composite membranes by gamma-ray triggered surface polymerization

Thin-film composite poly(amide) (PA) membranes have greatly diversified water supplies and food products. However, users would benefit from a control of the electrostatic interactions between the liquid and the net surface charge interface in order to benefit wider application. The ionic selectivity of the 100 nm PA semi-permeable layer is significantly affected by the pH of the solution. In this work, for the first time, a convenient route is presented to configure the surface charge of PA membranes by gamma ray induced surface grafting. This rapid and up-scalable method offers a versatile route for surface grafting by adjusting the irradiation total dose and the monomer concentration. Specifically, thin coatings obtained at low irradiation doses between 1 and 10 kGy and at low monomer concentration of 1 v/v% in methanol/water (1:1) solutions, dramatically altered the net surface charge of the pristine membranes from −25 mV to +45 mV, whilst the isoelectric point of the materials shifted from pH 3 to pH 7. This modification resulted in an improved water flux by over 55%, from 45.9 to up 70 L.m−2.h−1, whilst NaCl rejection was found to drop by only 1% compared to pristine membranes.

Enhanced both perm-selectivity and fouling resistance of poly(piperazine-amide) nanofiltration membrane by incorporating sericin as a co-reactant of aqueous phase

This study focuses on the fabrication of flat-sheet thin-film composite poly(piperazine-amide)-based nanofiltration membrane with enhanced both perm-selectivity and fouling resistance. Sericin was used as the co-reactant of piperazine (PIP) to form the selective skin layer through the interfacial reaction with trimesoyl chloride (TMC) on the surface of polysulfone porous support. Membranes prepared with different contents of sericin were rigorously characterized to investigate the effects of the incorporation of sericin on membrane physico-chemical and permeation properties. ATR-FTIR and EDX analyses confirmed the incorporation of sericin in the formed active layer, which was found to significantly enhance membrane water flux through enlarging membrane pore size and increasing surface hydrophilicity while maintaining Na2SO4 rejection through intensifying electrostatic repulsion effect. Membranes with both enhanced water permeability and solute selectivity could be prepared through controlling the content of sericin. For instance, by adding 0.06%(w/v) of sericin into the PIP-aqueous solution, the pure water permeability was enhanced by 36.7%, the Na2SO4 rejection was remained as high as 97.5% of the PIP-TMC membrane, and the selectivity to mixed NaCl/Na2SO4 solution was increased from 21.2 to 25.2. Moreover, the incorporation of sericin was also found to endow the membrane with improved fouling resistance to bovine serum albumin.

Zwitterions coated hollow fiber membranes with enhanced antifouling properties for osmotic power generation from municipal wastewater

Fouling on pressure-retarded osmosis (PRO) membranes leads to severe declines in water flux and power density because their porous substrates are facing the wastewater feed. Thus, inorganics, organics and microorganisms in the wastewater are prone to depositing on the substrate surface and even in its pores. In order to reduce the fouling propensity, coating the substrate surface of PRO membranes with zwitterionic materials proves to be an effective way. In this work, 2-methacryloyloxyethylphosphorylcholine (MPC), is modified and grafted onto the polydopamine (PDA) coated poly (ether sulfone) (PES) hollow fiber substrate. Both the synthesis and surface coating of MPC are easy and facile to be scaled up. Compared with the pristine PES and PES-PDA substrates, the MPC modified substrate (PES-PDA-MPC) exhibits high resistance to protein adsorption as well as bacteria adhesion. By using a state-of-the-art thin-film composite poly (ether sulfone) (TFC-PES) hollow fiber membrane as the control for power generation, the power density of the TFC-PES-PDA-MPC membrane can achieve as high as 7.7 W/m2 while the unmodified one has only 6.0 W/m2 after 3 h's PRO tests. In conclusion, the osmotic power generation of PRO membranes can be significantly sustained by modifying the membrane surface with zwitterions.

A study on the separation performance of zeolite filled thin film composite poly(dimethyl siloxane) membrane

In this study, ethanol/water was separated by means of pervaporation using a zeolite filled poly(dimethyl siloxane) (PDMS) non-porous membrane. Pristine and ZSM-5 type zeolite loaded membranes were prepared by means of solvent-free twin-screw compounding and subsequent compressing molding method. Effects of zeolite loading-level, feed temperature and concentration during separation were evaluated as experimental parameters. Hydrophobicity of the membranes was investigated by means of water contact angle. Mechanical properties were obtained through tensile tests. Morphologies of membranes were characterized by means of scanning electron microscopy (SEM). Pervaporation performance was evaluated in terms of flux, separation factor, and pervaporation separation index. Optimum zeolite loading level was determined as 30%by weight in terms of pervaporation and mechanical performance. At optimum concentration, separation factor and flux were determined as 4.95 and 0.246kg/m2h, respectively. It was demonstrated that flux drastically reduced from 0.246 to 0.03kg/m2h above 30wt.% ZSM-5.

Study on the thin film composite poly(piperazine-amide) nanofiltration membranes made of different polymeric substrates: Effect of operating conditions

Three composite nanofiltration (NF) membranes made of different substrate materials—polysulfone (PSf), polyethersulfone (PES) and polyetherimide (PEI)—were successfully prepared by interfacial polymerization technique. Prior to filtration tests, the composite NF membranes were characterized using field emission scanning electron microscope (FESEM), atomic force microscope (AFM) and X-ray photoelectron spectroscope (XPS). It was observed that the surface properties of composite NF membranes were obviously altered with the use of different substrate materials. The separation performance of the prepared composite NF membranes was further evaluated by varying operating conditions, which included feed salt concentration and operating temperature. Experimental results showed that the water flux of all TFC membranes tended to decrease with increasing Na2SO4 concentration in feed solution, due to the increase in feed osmotic pressure. Of the three TFC membranes studied, PSf-based membrane demonstrated the highest salt rejection but lowest water flux owing to its highest degree of polyamide cross-linking as shown in XPS data. With respect to thermal stability, PEI-based TFC membrane outperformed the rest, overcoming the trade-off effect between permeability and rejection when the feed solution temperature was gradually increased from 30 °C to 80 °C. In addition, the relatively smoother surface of hydrophilic PEI-based membrane when compared with PSf-based membrane was found to be less susceptible to BSA foulants, leading to lower flux decline. This is because smoother surface of polyamide layer would have minimum “valley clogging,” which improves membrane anti-fouling resistance.

Influence of silica nanospheres on the separation performance of thin film composite poly(piperazine-amide) nanofiltration membranes

A novel thin film nanocomposite nanofiltration (TFNN) membrane was fabricated by introducing silica nanospheres (ca. 235±11nm) in the interfacial polymerization process of trimesoyl chloride (TMC) and piperazine (PIP) over polysulfone (PS) support for investigating the effect of silica nanofiller on the separation performance (i.e., permeability and salt rejection) of conventional thin film composite poly(piperazine-amide) nanofiltration (TFCN) membrane. The physicochemical characterization results show that all of the silica nanospheres are uniformly embedded on the surface of TFNN membrane. The introduction of silica nanospheres improves the hydrophilicity of the TFCN membrane and also causes its isoelectric point shift to a lower pH value. Moreover, the active poly(piperazine-amide) barrier layer of TFNN membrane (60.8±2.3nm) is thinner than that of the pristine TFCN membrane (72.1±2.5nm) as a control sample. The separation performance tests reveal that the addition of silica nanospheres can obviously elevate the salt rejection of the pristine TFCN membrane from 87.58±0.15 to 94.81±0.17% under 2000ppm of MgSO4 solution and 0.5MPa operating pressure, simultaneously accompanied by the increases of permeate flux from 19.36±0.75 to 22.65±0.68L/m2h. Additionally, compared with pristine TFCN membrane, the fabricated TFNN membrane has relatively low salt rejection (43.20±0.27%) in 0.5MPa operating pressure for 500ppm of NaCl aqueous solution, which demonstrates that the introduction of silica nanospheres can dramatically promote the divalent-ionic separation selectivity. Furthermore, the experimental results suggest that the nanocomposite TFNN membrane possesses stable filtration performance in the softening process of MgSO4 aqueous solution. The separation performance improvement should be attributed to the optimizations of microstructures and surface features of active barrier layer of TFNN membrane, caused by the addition of silica nanospheres.

Novel CO2-Selective Cross-Linked Poly(vinyl alcohol)/Polyvinylpyrrolidone Blend Membrane Containing Amine Carrier for CO2–N2 Separation: Synthesis, Characterization, and Gas Permeation Study

This article reports structural characterizations and gas permeation properties of novel CO2-selective cross-linked thin-film composite poly(vinyl alcohol) (PVA)/polyvinylpyrrolidone (PVP) blend membranes doped with suitable amine carriers. The characterization of the active layer was carried out by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray diffraction. Gas streams containing 20% CO2 and 80% N2 by volume were used to study the transport properties of CO2 (CO2 and N2 flux, CO2 permeability, and CO2/N2 selectivity) across the membrane. The effects of active layer thickness (34–87 μm), feed absolute pressure (1.7–6.2 atm), temperature (90–125 °C), and sweep side water flow rate (0.02–0.075 cm3/min) on CO2 transport properties across the membrane were analyzed. The maximum CO2/N2 selectivity of 370 and a CO2 permeability of 1396 barrer were obtained for the composite membrane with 40 μm active layer thickness at 2.8 atm feed side absolute pressure and 100 °C.

Enhancing the permselectivity of thin-film composite poly(vinyl alcohol) (PVA) nanofiltration membrane by incorporating poly(sodium-p-styrene-sulfonate) (PSSNa)

Thin-film composite poly(vinyl alcohol) (PVA) nanofiltration membranes with improved permselectivity were prepared by incorporating poly(sodium-p-styrene-sulfonate) (PSSNa). Membranes were prepared through surface coating and in situ cross-linking procedure with porous polysulfone (PSf) membrane as support, PVA and PSSNa as coating materials, and glutaraldehyde as cross-linking agent. The effects of the incorporation of PSSNa on the membrane property and performance were investigated experimentally through ATR-FTIR spectroscopy, AFM analysis, streaming potential analysis, contact angle measurement and cross-flow permeation test. It was found that the incorporation of PSSNa resulted in increased membrane pore size, surface hydrophilicity and negative charge and thereby improved membrane permeability and solute selectivity. The PVA–PSf composite membrane exhibited a pure water flux of about 21.0l/m2h, NaCl rejection of 69.8% and Na2SO4 rejection of 96.5% when tested with 500mg/l electrolyte aqueous solution at neutral pH and 5.0bar, while the desired PSSNa/PVA–PSf composite membrane exhibited a higher pure water flux of 41.7l/m2h, lower NaCl rejection of 55.7% and higher Na2SO4 rejection of 98.3%. Moreover, compared with the PVA–PSf composite membrane, the PSSNa/PVA–PSf composite membrane possessed increased water flux and dye removal to anionic dye aqueous solution and improved fouling resistance to BSA aqueous solution.

CO2 separation using thermally stable crosslinked poly(vinyl alcohol) membrane blended with polyvinylpyrrolidone/polyethyleneimine/tetraethylenepentamine

This article reports structural characterizations and permeation of novel CO2-selective crosslinked thin film composite poly (vinyl alcohol) (PVA)/polyvinylpyrrolidone (PVP) blend membranes doped with suitable amine carriers. The characteristic properties of the active layer were examined by Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The effects of active layer thickness, feed pressure, temperature, and sweep side water flow rate on transport properties (CO2 and N2 flux, CO2 permeance, and CO2/N2 selectivity) were investigated with a mixed gas stream containing 20% CO2 and 80% N2 by volume. The temperature, feed pressure and sweep side water flow rate were varied from 90 to 125°C, 1.7 to 6.2atm and 0.02 to 0.075cm3/min, respectively. The selective dense layer containing amine carrier displays both high selectivity and permeance. The maximum CO2/N2 selectivity of 270 and a CO2 permeance of 29 GPU were obtained for the composite membrane with 45µm active layer thickness at 2.8atm feed side absolute pressure and 100°C temperature. Crosslinked-PVA–PVP with blended amines membrane also exhibited a good stability during a 300h test.

Study on ageing/fouling phenomena and the effect of upstream nanofiltration on in-situ product recovery of n-butanol through poly[1-(trimethylsilyl)-1-propyne] pervaporation membranes

Thin film composite poly[1-(trimethylsilyl)-1-propyne] – PTMSP – pervaporation membranes have been investigated for in-situ product recovery of n-butanol from a fermentation broth using a Clostridium acetobutylicum strain. For this specific application, a strong flux decline is observed which can be attributed to ageing and fouling phenomena in the membrane. In order to have a better understanding of these complex phenomena, X-ray photoelectron spectroscopy and infra-red spectroscopy have been used to monitor the ageing of the PTMSP membranes under different steady state conditions. The fouling effect of different components in the fermentation broth has been systematically investigated through off-line pervaporation tests on model mixtures with stepwise addition of fermentation by-products, revealing the negative impact of butyric acid and long chain fatty acids on the permeate flux. Additionally, long chain fatty acids, such as stearic acid, impact negatively the butanol/water separation factor. In order to remedy or at least decrease the impact of this fouling issue, the integration of an upstream nanofiltration step has been evaluated. This pre-treatment step has led to a drastic improvement of the flux through the filled PTMSP membrane (factor 4), while the butanol–water separation factor (27.5) remained much higher than the separation factor obtained with a commercial PDMS membrane (14.7).

Synthesis and characterization of crosslinked poly(vinyl alcohol)/poly(allylamine)/2-amino-2-hydroxymethyl-1,3-propanediol/polysulfone composite membrane for CO2/N2 separation

This study reports novel CO2-selective crosslinked thin film composite poly(vinyl alcohol) (PVA)/amine blend membranes, its structural characterizations and permeation studies. The characteristic properties of the active layer were examined with Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Effects of feed pressure, temperature, and sweep side water flow rate on transport properties (CO2 and N2 flux, CO2 permeability, and CO2/N2 selectivity) were investigated with a mixed gas stream containing 20% CO2 and 80% N2 by volume. The temperature, feed pressure and sweep side water flow rate were varied from 90 to 125°C, 1.7 to 6.2atm and 0.02 to 0.075cm3/min, respectively. The good miscibility properties, obtained from the blended amines with crosslinked PVA, allowed a thin selective dense layer to be formed on self-made porous PSf support, which displays both high selectivity and permeability. The maximum CO2/N2 selectivity of 260 and a CO2 permeability of 555 Barrer were obtained for the membrane with 14µm active layer thickness. Crosslinked PVA with blended amines membrane also exhibited a good stability during a 250h test.

Effect of amine salt surfactants on the performance of thin film composite poly(piperazine-amide) nanofiltration membranes

The role of amine salt surfactants on the performance of thin film composite nanofiltration (TFC NF) membranes is crucial for the development of advanced NF membranes, but the information is still not enough. This paper presents a systematic investigation of the effect of the types of amine salt surfactants on nanofiltration performance. Four types of amine salts with different molecular structures, molecular weights (MW) and charges, including tetraethylammonium chloride (TEAC), tetrabutylammonium bromide (TBAB), camphorsulfonic acid triethylamine salt (CAS-TEA), and 1-butyl-3-methylimidazolium chloride (BMMIC), were incorporated into piperazine (PIP) solution during interfacial polymerization(IP) with trimesoyl chloride (TMC). The formed thin film composite (TFC) piperazine–amide polymer was supported on a polyethersulfone (PES) ultrafiltration membrane (UF). The membrane surfaces were characterized by scanning electronic microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The flux and NaCl rejection were also evaluated. The addition of amine salt containing larger steric configuration cationic amine group in aqueous solution, resulted in a TFC membrane with better performance, and the amine salt would act as a surfactant and not adhere to the polymer layer at the end of polymerization.

Fabrication of thin film composite poly(amide)-carbon-nanotube supported membranes for enhanced performance in osmotically driven desalination systems

The search for lower energy consumption desalination systems has been driving research in the past decade towards the investigation of osmotically driven membrane processes, such as forward osmosis (FO) or osmotic distillation (OD). Despite similarities with reverse osmosis (RO) membranes, thin film composite (TFC) for FO membranes require careful design to reduce salt concentration polarization formation within the large pores composing the supporting layer. An investigation of a novel, highly stable, robust support made solely of carbon nanotubes (CNTs), which could find applications in both RO and FO was undertaken. TFC membranes were fabricated by interfacially polymerizing for the first time a dense poly(amide) (PA) layer on self-supporting bucky-papers (BPs) made of hydroxyl-functionalized entangled CNTs. These hydrophilic supports exhibited low contact angle with water (<20°), high water uptake capacity (17wt%), large porosity (>90%), making it a promising material when compared with poly(sulfone) (PSf), the traditional polymer used to fabricate TFC membrane supports in RO. In addition, the impact of the support hydrophilicity on the stability of the interfacially polymerized film and on water adsorption was investigated by oxygen-plasma treating various potential support materials, exhibiting similar geometrical properties. The morphology and salt diffusion of both CNT BP and PSf supports were investigated, and the novel BP–PA composite membranes were found to be superior to commercially available TFC membranes.

Developing thin film composite poly(piperazine-amide) and poly(vinyl-alcohol) nanofiltration membranes

In this work, two different thin film composite (TFC) nanofiltration (NF) membranes were fabricated for water softening: (i) poly(piperazine-amide) and (ii) poly(vinyl-alcohol) (PVA) nanofiltration membranes. The nanofiltration performance of membranes was evaluated by cross flow filtration using NaCl (1 g/l) and MgSO 4 (1 g/l) solution at 5 and 10 bar, 25 °C and 10 l/min. The morphological and hydrophilicity studies were carried out with scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle, respectively. Thin film composite poly(piperazine-amide) nanofiltration membrane was prepared by interfacial polymerization of piperazine (PIP) with trimesoyl chloride (TMC). The SEM and AFM studies indicated that a rough and dense film was formed on the polyethersulfone (PES) support membrane by interfacial polymerization. The water permeability of this membrane was 53 and 101 kg m − 2 h − 1 (during salt solution filtration), 57 and 126 kg m − 2 h − 1 (during pure water filtration) at 5 and 10 bar. Moreover, the rejection to the MgSO 4 as divalent salt (78 and 70%) was high compared to the NaCl as monovalent salt (44 and 35%). In second type, thin film composite poly(vinyl-alcohol) (PVA) nanofiltration membrane was prepared by dip coating and cross-linking with glutaraldehyde. In the case of PVA membrane, a thick and smooth film was formed. This membrane shows the water permeability of 60 and 109 kg m − 2 h − 1 (during salt solution filtration), 69 and 135 kg m − 2 h − 1 (during pure water filtration) and the rejection of 25 and 20% for NaCl and 72 and 63% for MgSO 4 at two different pressures. Moreover, these two NF membranes exhibited structural and performance stabilities. The calculated pore radius and thickness-to-porosity (Δ X / A K) ratio by the modified Nernst–Plank equation confirmed the obtained results of rejection data of the synthesized membranes.

Thin-film composite poly(esteramide)-based membranes

The permeation and chlorine tolerance of various thin-film composite poly(esteramide) membranes were investigated. The membranes were synthesized interfacially by reacting trimesoyl chloride with an aqueous phase containing m-phenylene diamine plus either m-aminophenol ( m-AP), bisphenol-A (Bis-A) or hydroquinone (HQ). The amount of ester groups actually incorporated in the membranes at various starting stoichiometric ratios was quantified. Membranes incorporating Bis-A or HQ gave complete sucrose rejection while the salt rejections decreased in the order: HQ > m-AP > Bis-A based systems. The HQ: m-PDA system showed permeation characteristics approaching those of polyamide membranes synthesized from m-PDA alone. The membrane chlorine tolerance was significantly increased by the incorporation of ester linkages.