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Yong W.F.,National University of Singapore | Li F.Y.,National University of Singapore | Xiao Y.C.,Suzhou Faith and Hope Membrane Technology Co. | Chung T.S.,National University of Singapore | Tong Y.W.,National University of Singapore
Journal of Membrane Science | Year: 2013

Polymers of intrinsic microporosity (PIM-1) have received worldwide attention but most PIM-1 researches have been conducted on dense flat membranes. For the first time, we have fabricated PIM-1/Matrimid membranes in a useful form of hollow fibers with synergistic separation performance. The newly developed hollow fibers comprising 5-15wt% of highly permeable PIM-1 not only possess much higher gas-pair selectivity than PIM-1 but also have much greater permeance than pure Matrimid fibers. Data from positron annihilation lifetime spectroscopy (PALS), field emission scanning electron microscopy (FESEM) and apparent dense layer thickness indicate that the blend membranes have an ultrathin dense layer thickness of less than 70nm. PIM-1 and Matrimid are partially miscible. The effect of partial miscibility on dense selective layer was studied. Defect-free hollow fibers with gas pair selectivity more than 90% of the intrinsic value can be spun directly from dopes containing 5wt% PIM-1 with proper spinning conditions, while post annealing and additional silicone rubber coating are needed for membranes containing 10 and 15wt% PIM-1, respectively. Comparing to Matrimid, the CO2 permeance of as-spun fibers containing 5 and 10wt% PIM-1 increases 78% and 146%, respectively (e.g., from original 86.3GPU (1GPU=1×10-6cm3 (STP)/cm2scmHg=7.5005×10-12ms-1Pa-1) to 153.4GPU and 212.4GPU) without compromising CO2/CH4 selectivity. The CO2 permeance of the fiber containing 15wt% PIM-1 improves to 243.2GPU with a CO2/CH4 selectivity of 34.3 after silicon rubber coating. Under mixed gas tests of 50/50 CO2/CH4, this fiber shows a CO2 permeance of 188.9GPU and a CO2/CH4 selectivity of 28.8. The same fiber also has an impressive O2 permeance of 3.5 folds higher than the pristine Matrimid (e.g., from original 16.9GPU to 59.9GPU) with an O2/N2 selectivity of 6.1. The newly developed membranes may have great potential to be used for natural gas purification, air separation and CO2 capture. © 2013 Elsevier B.V.

Japip S.,National University of Singapore | Wang H.,National University of Singapore | Wang H.,Ngee Ann Polytechnic | Xiao Y.,Suzhou Faith and Hope Membrane Technology Ltd Co. | Chung T.S.,National University of Singapore
Journal of Membrane Science | Year: 2014

Zeolitic imidazolate framework (ZIF)-71 nano-particles have been demonstrated as potential inorganic fillers for fabricating high-performance membranes for gas separation. The newly synthesized ZIF-71 nano-particles with a particle size of less than 100nm were compatibly incorporated in 6FDA-Durene polyimide membranes as novel mixed matrix membranes (MMMs). No obvious agglomeration between ZIF-71 nano-particles and the 6FDA-Durene matrix was observed. The effect of ZIF-71 loading on gas separation performance was investigated for H2, O2, N2, CO2, CH4, C2H4, C2H6, C3H6 and C3H8. The incorporation of ZIF-71 nano-particles improves both gas permeation properties and membrane resistance against plasticization. With a 20wt% ZIF-71 addition, the pure CO2 permeability of the MMM is increased by 3-fold, while the ideal CO2/CH4 selectivity is reduced from 16.4 to 12.8. In addition, the CO2 plasticization pressure is increased from 16atm to 30atm. The MMM embedded with 20wt% ZIF-71 also displays a remarkable enhancement of C3H6 permeability from 57.6 Barrer to 371 Barrer without significantly compromising the ideal C3H6/C3H8 selectivity. The Positron Annihilation Lifetime Spectroscopy (PALS) and gas sorption characteristics further indicate that the permeability improvement is mainly due to the enhanced diffusivity and the molecular sieving effect of ZIF-71 nano-particles for separating C3H6/C3H8. © 2014 Elsevier B.V.

Chua M.L.,National University of Singapore | Xiao Y.C.,Suzhou Faith and Hope Membrane Technology Co. | Chung T.-S.,National University of Singapore
Chemical Engineering Science | Year: 2013

Thermal annealing is one of the feasible approaches to alter the molecular structure and enhance the gas separation performance of polyimide membranes for natural gas purification. In this study, annealing in air and incorporating β-CD and β-CD-ferrocene are employed to change the molecular structure and improve the CO2/CH4 gas-pair separation and stability of polyimide membranes. A 55% increment in CO2/CH4 selectivity at the expense of permeability are observed for the PI membrane annealed under air at 400°C compared to the as-cast membrane. A further twofold improvement in the permeability of the β-CD containing membrane annealed under air at 400°C is achieved. The CO2/CH4 selectivity also increases by 20%. With the inclusion of ferrocene, the membrane exhibits a decline in permeability with an improvement of CO2/CH4 selectivity to 47.3 when annealed in air at 400°C. The structural changes are elucidated by characterization techniques (TGA, XPS and gel content). The annealed membranes in air have shown improved resistance to CO2 plasticization and exhibit good mechanical strength. When subjected to a binary CO2/CH4 gas mixture, the gas separation performance remains almost unchanged compared to the pure gas tests. Membranes with high stability under binary gas tests, resistance to CO2 plasticization and strong mechanical strength are developed. © 2013 Elsevier Ltd.

Chua M.L.,National University of Singapore | Xiao Y.,Suzhou Faith and Hope Membrane Technology Co. | Chung T.-S.,National University of Singapore
Separation and Purification Technology | Year: 2014

Cross-linking polymer chains has proved to be one of the feasible ways to improve its gas separation performance and plasticization resistance, but often at the expense of permeability. In this study, an attempt to cross-link a polyimide (PI) without sacrificing the permeability of the membrane is made by employing an ionic thermally labile unit, iron (III) acetylacetonate (FeAc), coupled with low temperature annealing. Particularly, not only a cross-linked network is established, an increment of more than 88% in permeability is attained for the PI-6 wt% FeAc membrane as compared to pristine PI membrane. The permeability enhancement is resulted from increments in both solubility and diffusivity coefficients. The modified membranes also show improved resistance to CO2 plasticization in both pure CO2 and binary CO 2/CH4 gas tests. Various characterization techniques such as TGA, DSC, FTIR, gel content and density measurement were employed to elucidate the structural changes of the PI-FeAc membranes during the cross-linking and annealing processes. A moderate post thermally treated polyimide membranes blended with iron (III) acetylacetonate with enhanced gas separation performance, improved CO2 plasticization resistance and good stability under mixed gas has been developed. © 2014 Elsevier Ltd. All rights reserved.

Chua M.L.,National University of Singapore | Xiao Y.C.,Suzhou Faith and Hope Membrane Technology Co. | Chung T.-S.,National University of Singapore
Journal of Membrane Science | Year: 2012

Thermal annealing polymeric membranes consisting of thermally saccharide labile units have been proven to be a feasible approach to produce highly permeable gas separation membranes. In this work, thermal labile units with different molecular weights and structures, glucose (180g/mol), sucrose (342g/mol) and raffinose (504g/mol), are chosen to be grafted onto the side chains of a polyimide and the membranes are annealed to investigate the effects of thermally labile units on its properties. The gas separation performance of the membranes for various gases such as O 2, N 2, CO 2, CH 4, C 2H 6, C 3H 6 and C 3H 8 are examined. It is observed that when the grafted and annealed membranes are annealed from 200 to 400°C, a substantial increase in gas permeability is achieved with moderate gas-pair selectivity. It could be attributed to the formation of microvoids upon the degradation of the thermally labile unit. Depending on the thermally labile unit grafted, a four to eight-fold increase in gas permeability was seen. The variation of the gas separation performance with the thermally labile unit is elucidated by the thermal decomposition behavior of the thermally labile units and the interaction with the polymer matrix. The membrane resistance to CO 2 plasticization is also investigated. The annealed membranes show good flexibility with enhanced gas permeability and CO 2 plasticization resistance. The membranes exhibit excellent CO 2/C 2H 6 and C 3H 6/C 3H 8 separation performance. The selectivity for CO 2/C 2H 6 is over 34. The separation performance for O 2/N 2, CO 2/N 2 and CO 2/CH 4 gas pairs fall slightly below the upper bound. The CO 2 permeability of the membrane grafted with glucose declines slightly from 1389Barrers to 1339Barrers while maintaining the same CO 2/CH 4 selectivity of about 26.6 when subjected to a binary gas mixture. © 2012 Elsevier B.V.

Li F.Y.,National University of Singapore | Xiao Y.,Suzhou Faith and Hope Membrane Technology Co. | Chung T.-S.,National University of Singapore | Kawi S.,National University of Singapore
Macromolecules | Year: 2012

Novel thermally self-cross-linked polymers of intrinsic microporosity (PIM-1) membranes have been prepared by postmodification of PIM-1 at the elevated temperature for a period of 0.5-2 days. The occurrence of cross-linking reaction has been verified by thermogravimetric analysis (TGA), X-ray photoelectron spectrometer (XPS) and gel content analyses. TGA analyses indicate an increase in thermal stability of membranes after the thermal cross-linking treatment. There is also an obvious drop in the maximum decomposition rate comparing to the original PIM-1when membranes are thermally treated for an extended period of time. Both FTIR and XPS results suggest that the nitrile-containing PIM-1 membranes undergo a latent cross-linking reaction, and form stable bulky triazine rings. The resultant cross-linked polymeric membranes exhibit exceptional gas separation performance that surpasses the most recent upper bound of state-of-the-art polymeric membranes for the important gas separations, such as hydrogen purification, CO 2 capture and flue gas separation. In addition, both gas permeability (attributed to the contorted nature, rearrangement and pronounced inefficient packing of PIM polymer chains) and selectivity (attributed to the decrease of chain-to-chain spacing) increase diagonally with the upper bound line when thermal soaking time increases. PIM-1 thermally treated at 300 °C for 2 days has the CO 2 permeability of 4000 barrer with CO 2/CH 4 and CO 2/N 2 ideal selectivity of 54.8 and 41.7, respectively. The thermally cross-linked PIM-1 membranes will probably provide a promising alternative in industrial energy development. © 2012 American Chemical Society.

Li F.Y.,National University of Singapore | Xiao Y.,Suzhou Faith and Hope Membrane Technology Co. | Ong Y.K.,National University of Singapore | Chung T.-S.,National University of Singapore
Advanced Energy Materials | Year: 2012

Polymers of intrinsic microporosity (PIM-1) have been known for their super high permeability but average selectivity for medium-size gas pairs. They have unimpressive selectivity for H2 and CO2 separation (i.e., α (H2/CO2) = 0.6). For the first time, we have discovered that ultraviolet (UV)-rearranged polymers of PIM-1 membranes can be used for H2/CO2 separation with far superior separation performance to others in literatures. The PIM-1 membrane after UV radiation for 4 hours shows H2 permeability of 452 barrer with H 2/CO2 selectivity of 7.3. Experimental data and molecular simulation reveal that the polymer chains of PIM-1 undergo 1,2-migration reaction and transform to close-to-planar like rearranged structure after UV radiation. As a result, the UV-irradiated PIM-1 membrane shows considerable drops in both fractional free volume (FFV) and size of micro-pores. Positron annihilation lifetime (PAL) results have confirmed the chemical and structural changes, suggesting the FFV and pore size drops are mainly ascribed to the destructed spiro-carbon centre during UV radiation. Sorption and x-ray diffractor (XRD) analyses indicate that the impressive H2/CO 2 selectivity arises from the significantly enhanced diffusivity selectivity induced by UV radiation, followed by molecular rearrangement, conformation change and chain packing. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA.

Fu F.-J.,National University of Singapore | Zhang S.,National University of Singapore | Sun S.-P.,National University of Singapore | Wang K.-Y.,Suzhou Faith and Hope Membrane Technology Co. | Chung T.-S.,National University of Singapore
Journal of Membrane Science | Year: 2013

Novel mixed matrix hollow fiber membranes composed of a PBI/POSS outer layer and a PAN/PVP inner layer have been developed for forward osmosis and osmotic power generation. It is found that the incorporation of a small amount of POSS nanoparticles into the outer PBI dope has significant influence on both the morphology and the performance of the developed membranes. The addition of POSS and PVP into the outer PBI and inner PAN dopes respectively resulted in an integrally macrovoid-free and delamination-free dual-layer membrane. Increasing POSS concentration in the PBI dope enhances both water and salt permeability across the membranes. A POSS loading of 0.5wt% has been identified through NF and FO tests as the optimal concentration in this study. The membrane with this optimized concentration shows a maximum water flux 31.37LMH at room temperature using 2.0M MgCl2 as the draw solution in the FO process and a maximum power density of 2.47W/m2 in the PRO process at 7bar using 1.0M NaCl as the draw solution. With its unique fully hydrophilic structure, easy processability and cost-effective ultra-thin PBI outer-layer, this membrane may have wide applications in the future. © 2013 Elsevier B.V.

Shang G.,Shanghai JiaoTong University | Shen G.,Shanghai JiaoTong University | Liu L.,Shanghai JiaoTong University | Chen Q.,Anju Environmental Protection Technology Co. | Xu Z.,Suzhou Faith and Hope Membrane Technology Co.
Bioresource Technology | Year: 2013

Three different biochars as cost-effective substitutes for activated carbon (AC) were tested for their hydrogen sulfide (H2S) adsorption ability. The biochars were produced from camphor (SC), bamboo (SB), and rice hull (SR) at 400°C by oxygen-limited pyrolysis. The surface area (SA), pH, and Fourier transform infrared spectras of the biochars and AC were compared. The maximum removal rates and the saturation constants were obtained using the Michaelis-Menten-type equation. The three biochars were found to be alkaline, and the SAs of the biochars were much smaller than that of the AC. The H2S breakthrough capacity was related to the local pH within the pore system of the biochar. The order observed in terms of both biochar and AC adsorption capacity was SR>SB>SC>AC. SR efficiently removed H2S within the inlet concentration range of 10-50μL/L. Biochars derived from agricultural/forestry wastes are a promising H2S adsorbent with distinctive properties. © 2013 Elsevier Ltd.

Shao L.,Harbin Institute of Technology | Cheng X.Q.,Harbin Institute of Technology | Liu Y.,Harbin Institute of Technology | Quan S.,Harbin Institute of Technology | And 3 more authors.
Journal of Membrane Science | Year: 2013

In this study, new thin-film-composite (TFC) nanofiltration (NF) membranes were developed through interfacial polymerization (IP) on the lumen side of hollow fiber support membranes by exploring novel combinations of reacting monomers and optimizing the fabrication conditions. By varying the different combinations of reacting monomers, the molecular weight cut off (MWCO) of NF membranes in a hollow fiber module can be adjusted to approximately 300.0gmol-1 with a high pure water permeability of 3.1Lm-2h-1bar-1 at 3.0bar. These hollow fiber NF membranes demonstrated different rejections for different salts in the order of R(Na2SO4)>R(MgSO4)>R(NaCl)>R(MgCl2) and high pressure resistance. These membranes were further tested for the removal of typical dyes in aqueous solutions under varying conditions. For both the Safranin O and the Aniline blue dyes, the rejection was higher than 90% under the tested conditions, and the excellent performance of the NF membranes in the removal of dyes from wastewater was maintained over a wide pH range; the best performance was obtained at a pH of 11. Therefore, the novel NF membranes are promising for the removal of crucial dyes as a next-generation technology for industrial wastewater treatment. © 2012 Elsevier B.V.

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