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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. Source

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 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. Source

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. Source

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. Source

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. Source

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