Thin-film Composite Hollow Fiber Membranes Research Articles

Preparation, characterization and performance evaluations of thin film composite hollow fiber membrane for energy generation

This article analyzes the different types of thin film composite hollow fiber (TFC-HF) membranes and their performance of pressure retarded osmosis (PRO) for power generation. Pressure retarded osmosis (PRO) is an osmotically-driven membrane process that can be used to harvest salinity-gradient power. For the first time, the potential of using different types of TFC-HF membranes for PRO has been explored. Several types of TFC-HF membranes with well-designed substrate structures were prepared. This study systematically investigates the effects of operating conditions and effect of membrane preparation/fabrication conditions such as concentration of monomers like m-phenylenediamine (MPD) and trimesoyl chloride (TMC), effect of reaction times, effect of pressures on the membrane performance using KIER manufactured polyethersulfone (PES) HF membranes as a substrate. The TFC-HF membranes show reasonably high water fluxes under the PRO mode using 0.6M NaCl as the draw solution and deionized water as the feed solution. Moreover, the surface and skin morphology of the substrate may play an essential role in the formation of the polyamide layer as well as in its perfectness and PRO performance. The implications of the results for power generation by PRO are evaluated and discussed. Our results provide significant implications for PRO scaling control.

Thin-film composite P84 co-polyimide hollow fiber membranes for osmotic power generation

A series of well-designed thin-film composite (TFC) hollow fiber membranes via dual-layer co-extrusion technology for pressure retarded osmosis (PRO) applications is reported in this work. By controlling the phase inversion process during spinning, we have molecularly engineered hollow fiber membranes with various structures, dimensions, pore characteristics, and mechanical properties as supports for the synthesis of TFC membranes. Under hydraulic tests, these hollow fiber membrane supports possess high burst pressures from 13 to 24bar. The TFC membranes fabricated by interfacial polymerization on the inner surface of the hollow fiber supports not only exhibit relatively high power densities of 5–12Wm−2 but also display a superior tolerance to high pressures up to 21bar. The TFC membrane synthesized on a small dimensional hollow fiber support, which was spun from a P84 co-polyimide/ethylene glycol (EG)/N-methyl-2-pyrrolidinone (NMP) dope solution with a bore fluid of a water/EG/NMP mixture, shows the most impressive PRO performance (i.e., 12Wm−2 at 21bar using water and 1M NaCl as feeds). Experimental results also suggest that inner-selective TFC hollow fiber membranes made from small dimensional fiber supports by means of delayed demixing during the fiber spinning are preferential for high pressure PRO processes. In addition, it was found that the flow rate of brine solutions plays a crucial effect on TFC membrane performance for osmotic power generation. By investigating the pressure drop as a function of flow rate, one may be able to choose appropriate PRO operation conditions to further ensure the sustainability of hollow fiber membranes for power generation.

Outer-Selective Pressure-Retarded Osmosis Hollow Fiber Membranes from Vacuum-Assisted Interfacial Polymerization for Osmotic Power Generation

In this paper, we report the technical breakthroughs to synthesize outer-selective thin-film composite (TFC) hollow fiber membranes, which is in an urgent need for osmotic power generation with the pressure-retarded osmosis (PRO) process. In the first step, a defect-free thin-film composite membrane module is achieved by vacuum-assisted interfacial polymerization. The PRO performance is further enhanced by optimizing the support in terms of pore size and mechanical strength and the TFC layer with polydopamine coating and molecular engineering of the interfacial polymerization solution. The newly developed membranes can stand over 20 bar with a peak power density of 7.63 W/m(2), which is equivalent to 13.72 W/m(2) of its inner-selective hollow fiber counterpart with the same module size, packing density, and fiber dimensions. The study may provide insightful guidelines for optimizing the interfacial polymerization procedures and scaling up of the outer-selective TFC hollow fiber membrane modules for PRO power generation.

Fabrication and use of hollow fiber thin film composite membranes for ethanol dehydration

In this study, the development of thin film composite (TFC) pervaporation hollow fiber membranes for biofuel dehydration at high fluxes is presented. The novel membranes consist of a thin selective polyamide layer formed by interfacial polymerization onto a porous polyethersulfone (PES) hollow fiber support that is free of macrovoids. This membrane support was fabricated using the dual-layer co-extrusion technology to design and effectively control the phase inversion during the membrane formation. The macrovoid-free and highly porous morphology of the membrane support is desirable. Not only does it provide excellent membrane strength, but also minimize the mass transfer resistance encountered during the pervaporation process, thus enhancing the total flux. The effects of key fabrication parameters such as drying methods of hollow fiber supports, interfacial polymerization conditions including heat treatment, different alcohols and water as cleaning solvents on membrane formation, membrane morphology and pervaporation performance of the resultant TFC membranes are systematically investigated and elucidated. The surface modification of the TFC membranes with polydopamine or silicone rubber coatings is proposed to simply and effectively enhance the membrane selectivity. The polydopamine-coated and silicone rubber-coated TFC membranes exhibit water separation factors of up to 51 and 60, with substantial high fluxes of 6.6 and 7.5kgm−2h−1, respectively. The newly developed TFC hollow fiber membranes possess reasonably good selectivity/separation factors and superior permeation fluxes in comparison with most polymeric membranes that have been reported in the open literature.

Robust and High performance hollow fiber membranes for energy harvesting from salinity gradients by pressure retarded osmosis

Pressure retarded osmosis (PRO) is a promising membrane process to harvest the vast amount of free energy from the mixing of fresh and salty waters without adverse environmental impacts. A competent membrane for PRO should possess the features of high water permeability to allow water permeation, excellent salt rejection to maintain the osmotic driving force, low structure parameter to minimize the internal concentration polarization (ICP), and robust strength to withstand the required hydraulic pressure. In this work, we have developed a novel hollow fiber membrane by balancing these competing factors based on our prior experience in the thin-film composite (TFC) membranes. The newly developed TFC hollow fiber membrane can achieve a power density of 20.9W/m2 at a pressure of 15bar, using synthetic seawater brine (1.0M NaCl) as the draw solution and synthetic river water (1mM NaCl) as the feed water, respectively. The simultaneous specific reverse salt flux was found to be 0.03mol/L, which is much lower than reported flat-sheet membranes, as the self-supported hollow fiber membrane can eliminate the deformation-enhanced reverse salt diffusion that is typical for flat-sheet membranes. However it was observed that the water permeability and structure parameter of the TFC hollow fiber membrane varied noticeably corresponding to the change in the hydraulic pressure imposed in the fiber lumen. Over a certain range (ΔP<15bar), such variations of increasing A value and decreasing S value proved to have positive impacts, as they facilitate the water permeation and reduce the ICP in the PRO process.

The Preparation of Polyamide/Polyacrylonitrile Composite Hollow Fiber Membranes for Pervaporation

This paper prepared polyamide (PA)/polyacrylonitrile (PAN) thin-film composite hollow fiber membranes via interfacial polymerization by using triethylenetetramine (TETA) and trimesoyl chloride (TMC) as the monomers and asymmetric PAN hollow fiber membrane as the substrate. The effect of hydrolysis of asymmetric PAN hollow fiber membranes on the chemical properties was investigated. The results showed that the chemical properties of PAN hollow fiber membranes were affected by hydrolysis. Moreover, the effects of PA thin film polymerized onto the inner and outer surface of asymmetric PAN hollow fiber membranes on pervaporation performances were also investigated. The results also revealed that the interfacial polymerized PA/PAN composite hollow fiber membranes that were polymerized onto the outer surface of asymmetric PAN hollow fiber membranes can be used in the pervaporation of aqueous alcohol solution.

Application of thin-film composite hollow fiber membrane to submerged nanofiltration of anionic dye aqueous solutions

Submerged nanofiltration of anionic dye aqueous solution by laboratory-fabricated sodium carboxymethyl cellulose (CMCNa)/polypropylene (PP) thin-film composite hollow fiber membrane was investigated in this paper. The CMCNa/PP thin-film composite membranes were prepared through dip-coating CMCNa skin layer on the outer surface of polypropylene microporous hollow fibers followed by cross-linking with FeCl3. The molecular weight cut-off (MWCO) and surface zeta potential of the tailor fabricated membrane were estimated through permeation tests using different PEG solutions and measurements of surface steaming potential, respectively. Submerged nanofiltration tests were then performed with anionic dye solutions under different conditions. It was found that, at neutral pH, the negatively charged CMCNa/PP composite hollow fiber membrane with a MWCO of about 700Da could effectively remove anionic dyes (Congo red and Methyl blue) from aqueous solution with good long-term performance stability and anti-fouling property through submerged nanofiltration. The dye retention and water permeability was affected by the trans-membrane pressure, the dye concentration as well as the presence of salt in the solution. The dye retention, water permeability and salt rejection rate to aqueous solution containing 2000mg/l Congo red and 10,000mg/l NaCl were 99.8%, 7.0l/m2hbar, and lower than 2.0%, respectively.

Thin-film composite hollow fiber membranes for pressure retarded osmosis (PRO) process with high power density

For the first time, a specially designed pressure retarded osmosis (PRO) hollow fiber membrane has been successfully developed and applied in the PRO process to demonstrate its potential for power generation. The membrane fabrication method is similar to that used for making thin-film composite (TFC) forward osmosis hollow fiber membranes, but further optimization and improvement have led to a new type of TFC hollow fiber membranes with much greater mechanical strength in addition to its excellent separation property and high water flux. The TFC PRO hollow fiber membranes have a water permeability ( A) of 9.22 × 10 −12 m/(s Pa), salt permeability ( B) of 3.86 × 10 −8 m/s and structural parameter ( S) of 4.6 × 10 −4 m. It can withstand hydrostatic pressure as high as 9 bar with its relatively large dimension of 0.98 mm lumen diameter. This PRO hollow fiber membrane is superior to all other PRO membranes reported in the open literature in terms of power density. A power density as high as 10.6 W/m 2 can be achieved using seawater brine (1.0 M NaCl) and wastewater brine (40 mM NaCl), which suggests that the newly developed PRO hollow fiber membrane has great potential to be applied in PRO processes to harvest salinity gradient energy. A higher pressure is preferred as it allows generation of higher power density (pressures of 12 bar may be optimal for seawater as the high salinity stream), and this can be realized by reduced fiber dimension. Further optimization of the membrane structure will be performed.

Interfacially polymerized thin film composite membranes on microporous polypropylene supports for solvent-resistant nanofiltration

Interfacial polymerization (IP) is a powerful technique for fabrication of thin film composite (TFC) membranes. The polymers used most often as support are polysulfone (PS) or polyethersulfone (PES). These supports have limited stability in organic solvents. In this work, microporous polypropylene (PP) flat film and hollow fiber membranes were used as a support to fabricate TFC membranes for nanofiltration by the IP technique. Porous polypropylene membranes can provide substantial chemical, pH, and solvent resistance and are therefore suitable as supports for fabricating TFC membranes functioning as solvent-stable nanofiltration membranes. The surface and the pore interior of polypropylene flat sheet and hollow fiber membranes were hydrophilized first by pre-wetting with acetone followed by oxidation with chromic acid solution. A standard procedure to successfully coat the hydrophilized flat film and hollow fiber membranes was developed next. The monomeric system chosen for IP was poly(ethyleneimine) and isophthaloyl dichloride. The TFC hollow fiber membranes were characterized by nanofiltration of safranin O (MW 351) and brilliant blue R (MW 826) dyes in methanol. Rejection values of 88% and 43% were achieved for brilliant blue R and safranin O, respectively at a transmembrane pressure of 413 kPa in the TFC hollow fiber membranes. Pressure dependences of the solvent flux and solute rejection of the TFC membranes were studied using the modified flat sheet membranes up to a pressure of 965–1241 kPa. Solvent flux increased linearly with an increase in the transmembrane pressure. Solute rejection also increased with an increase in the transmembrane pressure. All modified membranes were also characterized using scanning electron microscopy. Extended-term solvent stability of the fabricated membranes was studied in toluene; the membranes demonstrated substantial solvent stability in toluene.

Development of thin-film composite hollow-fiber membranes from modified polyphenylene oxide for gas separation applications

The effect of sulfonation and bromination-sulfonation on the gas transport properties of polyphenylene oxide has been investigated. These high-performance modified polymers have been studied in the form of TFC membranes by solution coating on the skin side of polyetherimide hollow fibers. TFC membrane modules prepared from sulfonated-brominated polyphenylene oxide as the active layer coated on polyetherimide hollow fibers. Stability of the TFC membranes was greatly improved when a wet feed stream was used instead of a dry one. Water vapor in the feed stream most likely prevented the active layer from stress cracking on drying. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 275–282, 2001