Mixed Gas Tests Research Articles

Fabrication and investigation of PEBAX/Fe-BTC, a high permeable and CO2 selective mixed matrix membrane

Mixed matrix membranes comprising commercial poly (ether-block-amid) or PEBAX® (1657) as continues phase and Fe-BTC metal organic framework as disperse phase are fabricated via phase inversion method. To investigate membrane structure various analysis including SEM, TGA, DLS and FTIR are performed. CO2 and CH4 permeability and Selectivity are measured for all membranes at 25°C and different pressures from 3 to 25bar. Moreover, mixed gas tests are implemented for 10/90 CO2/CH4 mixture. Cross section SEM images showed proper particles distribution and good interaction between polymer and particles. The replacement of various bounds in FTIR test confirmed the good compatibility of Fe-BTC with polymer matrix too. TGA results showed acceptable thermal resistance of all membranes. Membranes permeability increased with increase in particles loading percent due to high porosity of particles and also high adsorption capacity especially for CO2 molecules. The highest CO2 permeability was belong to PEBAX/Fe-BTC 40wt.% membrane which was 425.4 Barrer. Mixed matrix membranes showed selectivity enhancement too. However, PEBAX/Fe-BTC 20wt.% membrane had the best selectivity of 22.19, in membrane with higher loading percent particles agglomeration made interfacial voids which caused selectivity decrement specially in 40wt.% loading percent. All membranes showed permeability and selectivity growth till 7bar pressures however, selectivity decreased due to plasticization effect at higher pressures of 15 and 25bar. Membrane with 25wt.% loading percent showed 50% and 9% increase in CO2 permeability and selectivity at 7bar compare to base pressure of 3bar.

Effect of Ethylene Oxide Functional Groups in PEBA-CNT Membranes on CO2/CH4 Mixed Gas Separation

Poly (ether-block-amide) /poly (ethylene glycol)/ carbon nanotubes mixed matrix membranes have been successfully fabricated using solvent evaporation method to determine the effect of ethylene oxide groups on the performance of produced membranes. The effects of CNTs (2-8 wt%) and PEG (up to 50 wt%)were investigated in both single and mixed gas test setup in different temperature and pressure. Finally the membranes were structurally characterized using Scanning Electron Microscopy, X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, and Atomic Force Microscopy.Results showed that addition of carbon nanotubes enhanced the gas separation performance of membranes and presences of ether groups in poly ethylene glycol improved the CO2 permeability. Membrane containing 8 wt % carbon nanotubes and 50 wt % poly ethylene glycol showed the best performance with CO2/CH4 selectivity of 45 and CO2permeability of 302 at pressure of 14 bars. Also, mixed gas permeation experiments were carried out and results showed dramatic decrease in CO2 selectivity due to membrane plasticizing. The permeability of CO2 in mixed gas test for membrane containing 50 wt% pol ethylene glycol and 8 wt% was 193 with CO2/CH4 selectivity of 19 in room temperature. Furthermore, membranes produced by 6 and 8 wt% carbon nanotubes and 50 wt% poly ethylene glycol placed above Robeson’s trade-off line. The effect of temperature on performance of fabricated membrane was finally investigated. Results showed an increase in permeability and decrease in selectivity for all membranes.

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

Carbon capture and storage (CCS) using membranes for the separation of CO2 holds great promise for the reduction of atmospheric CO2 emissions from fuel combustion and industrial processes. Among the different process outlines, post-combustion CO2 capture could be easily implemented in existing power plants. However, for this technology to become viable, new membrane materials have to be developed. In this article we present the development of high performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer matrix. The CO2/N2 separation performance was evaluated by mixed gas tests (15CO2:85N2) at 25°C and 1–4bar transmembrane pressure difference. The CO2 membrane permeability was increased by the addition of the ZIF-94 particles, maintaining a constant CO2/N2 selectivity of ~22. The largest increase in CO2 permeability of ~ 200% was observed for 40wt% ZIF-94 loading, reaching the highest permeability (2310 Barrer) at similar selectivity among 6FDA-DAM MMMs reported in literature. For the first time, the ZIF-94 metal organic framework crystals with particle size smaller than 500nm were synthesized using nonhazardous solvent (tetrahydrofuran and methanol) instead of dimethylformamide (DMF) in a scalable process. Membranes were characterized by three non-invasive image techniques, i.e. SEM, AFM and nanoscale infrared imaging by scattering-type scanning near-field optical microscopy (s-SNOM). The combination of these techniques demonstrates a very good dispersion and interaction of the filler in the polymer layer, even at very high loadings.

Fabrication and operational considerations of hydrogen permeable Mo2C/V metal membranes and improvement with application of Pd

Mo2C has previously been demonstrated as an effective catalyst layer to enable stable H2 permeation through vanadium foils at high temperatures. In this study, this approach was extended to several group V metal foils (V, Nb, and Ta) as well as mixed gas testing. The best permeability was achieved with V, and an activation process was developed to recover the performance of V foils displaying evidence of oxidation. Nb foils yielded ~ 20% the permeability of V, while Ta was too brittle to operate effectively. Mo2C/V membranes were operated at feed conditions well above the ductile-to-brittle transition pressure without embrittlement; however, the H2 permeability of Mo2C/V membranes was significantly attenuated at lower temperatures (< 600°C). H2 permeation was also severely inhibited by the presence of N2 or CO2 in mixed gas environments due to strong competitive adsorption. The addition of a Pd catalyst layer on top of Mo2C improved mixed gas stability and increased H2 permeability to 2 × 10−8molm−1s−1Pa−0.5 at 500°C for V based membranes. As an interlayer, Mo2C was demonstrated to be a stable barrier preventing Pd-V interdiffusion at 500°C while simultaneously allowing significant H2 permeation.

Cardo-type random co-polyimide membranes for high pressure pure and mixed sour gas feed separations

A series of aromatic random co-polyimide membranes based on 6FDA-Durene/CARDO backbone with varying content of CARDO moiety (3:1; 1:1 and 1:3) were synthesized for enhanced acid gas separation performance. Gas transport properties of pure and mixed gas streams consisting of H2S, CO2, He, CH4, N2 and C2H6 through the dense films of the co-polyimide were studied. Mixed sweet gas tests were done with feeds containing no H2S up to 55bar, while mixed sour gas measurements were conducted with feeds containing H2S up to 34bar for 10% H2S and 20% H2S. The membranes exhibit very attractive pure gas transport properties, as CO2 permeability and CO2/CH4 selectivity are up to 323 barrer and 35 respectively. Furthermore, the transport properties of sour gas mixture consisting of five gases were also found attractive, as the CO2/CH4 and H2S/CH4 ideal selectivities are in the range of 18–23 and 19–21 respectively; while CO2 and H2S permeabilities are in the range of 38–51 and 40–47 barrers respectively for 20% H2S in the gas mixture. These values and separation performance exhibited by the co-polyimide are comparable and very competitive even, as compared to the values obtained in some of the high performance polymeric membranes that have been reported in the literature. The stability of the random co-polyimide 6FDA-Durene/CARDO membrane under these aggressive environments is quite remarkable.

Development of ethanolamine‐based ionic liquid membranes for efficient CO2/CH4 separation

ABSTRACTThis study is focused on the development of ionic liquids (ILs) based polymeric membranes for the separation of carbon dioxide (CO2) from methane (CH4). The advantage of ILs in selective CO2 absorption is that it enhances the CO2 selective separation for the ionic liquid membranes (ILMs). ILMs are developed and characterized with two different ILs using the solution‐casting method. Three different blend compositions of ILs and polysulfone (PSF) are selected for each ILMs 10, 20, and 30 wt %. Effect of the different types of ILs such as triethanolamine formate (TEAF) and triethanolamine acetate (TEAA) are investigated on PSF‐based ILMs. Field emission scanning electron microscopy analysis of the membranes showed reasonable homogeneity between the ILs and PSF. Thermogravimetric analysis showed that by increasing the ILs loading thermal stability of the membranes improved. Mechanical analysis on developed membranes showed that ILs phase reduced the amount of plastic flow of the PSF phase and therefore, fracture takes place at gradually lower strains with increasing ILs content. Gas permeation evaluation was carried out on the developed membranes for CO2/CH4 separation between 2 bar to 10 bar feed pressure. Results showed that CO2 permeance increases with the addition of ILs 10–30 wt % in ILMs. With 20–30 wt % TEAF‐ILMs and TEAA‐ILMs, the highest selectivity of a CO2/CH4 53.96 ± 0.3, 37.64 ± 0.2 and CO2 permeance 69.5 ± 0.6, 55.21 ± 0.3 is observed for treated membrane at 2–10 bar. The selectivity using mixed gas test at various CO2/CH4 compositions shows consistent results with the ideal gas selectivity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45395.

Boron-embedded hydrolyzed PIM-1 carbon membranes for synergistic ethylene/ethane purification

For the first time, boron embedded carbon membranes have shown superior C2H4 permeability and C2H4/C2H6 selectivity to the upper bound line under both pure and mixed gas tests. The precursors of the carbon membranes were prepared by incorporating various boron compounds with different molecular sizes into a hydrolyzed polymer of intrinsic microporosity (PIM-1) and then carbonized at 700°C. The increments in C2H4 permeability and C2H4/C2H6 selectivity followed the order of molecular size of the boron compounds. Both PALS results and CO2 adsorption isotherms confirmed the enlarged pore size and increased pore amount. The enhancements in C2H4 permeability and C2H4/C2H6 selectivity were mainly due to the higher C2H4 diffusivity and greater diffusion selectivity resulting from proper choices of boron additives and carbonization conditions. When 9,9-dihexylfluorene-2,7-diboronic acid (DHFDA) was embedded into the hydrolyzed PIM-1 and then carbonized at 700°C, the C2H4 permeability and C2H4/C2H6 selectivity of the carbonized membrane under mixed gas tests increased from 7.5 to 13.7 Barrer and from 9.3 to 9.7, respectively.

High-performance carbon molecular sieve membranes for ethylene/ethane separation derived from an intrinsically microporous polyimide

An intrinsically microporous polymer with hydroxyl functionalities, PIM-6FDA-OH, was used as a precursor for various types of carbon molecular sieve (CMS) membranes for ethylene/ethane separation. The pristine polyimide films were heated under controlled N2 atmosphere at different stages from 500 to 800°C. All CMS samples carbonized above 600°C surpassed the polymeric ethylene/ethane upper bound. Pure-gas selectivity reached 17.5 for the CMS carbonized at 800°C with an ethylene permeability of about 10Barrer at 2bar and 35°C, becoming the most selective CMS for ethylene/ethane separation reported to date. As expected, gravimetric sorption experiments showed that all CMS membranes had ethylene/ethane solubility selectivities close to one. The permselectivity increased with increasing pyrolysis temperature due to densification of the micropores in the CMS membranes, leading to enhanced diffusivity selectivity. Mixed-gas tests with a binary 50:50 v/v ethylene/ethane feed showed a decrease in selectivity from 14 to 8.3 as the total feed pressure was increased from 4 to 20bar. The selectivity drop under mixed-gas conditions was attributed to non-ideal effects: (i) competitive sorption that reduced the permeability of ethylene and (ii) dilation of the CMS that resulted in an increase in the ethane permeability.

Liberation of small molecules in polyimide membrane formation: An effect on gas separation properties

The ultra-micropores in polymeric membranes play a key role on the separation performance. This work demonstrates that liberation of small molecules in the membrane formation process is an effective approach to create ultra-micropores in a narrow size distribution in polymeric membranes. A crosslinkable Meldrum's acid derivative is used as the effective agent that liberates CO2 and acetone molecules in the polyimide (PI) membrane formation process and to chemically crosslink the PI-based membranes. Compared to the neat PI membrane, the modified membrane shows small ultra-micropores in a narrow size distribution measured with a positron annihilation lifetime spectroscopy. Consequently, the modified PI membranes become highly-selective toward H2 gas. With a small reduction of permeability (from 23.1 to 15.5 barrer), the ideal selectivity for H2/N2 (155) and H2/CO2 (5.3) of the modified PI membrane are about 3-fold of the values recorded with the neat PI membrane. In a binary mixed gas test at 20atm, the modified PI membrane shows a high H2 permeability of 24.5 barrer and a high H2/CO2 selectivity 14.1. The results demonstrate an effective and simple method to enhance the gas separation performance of polymeric membranes with modulation of the cavity sizes and size distribution of the membranes.

Microstructural Characterization and Mechanical Performance of Wafer-Level SLID Bonded Au-Sn and Cu-Sn Seal Rings for MEMS Encapsulation

Special applications, such as microelectromechanical systems (MEMS), often require hermetic sealing in order to achieve a desired operation. Solid–liquid interdiffusion (SLID) bonding is an attractive method for encapsulating MEMS devices at the wafer-level, providing, e.g., high re-melt temperatures and tolerance for topographical variations. Several different SLID bond solutions have been investigated; however, there are only a limited number of published reliability studies available. In this paper, wafer-level Au-Sn and Cu-Sn SLID seal rings were mechanically characterized with shear and tensile tests. The evolution of bond microstructures and consequent effects on mechanical reliability were evaluated with a mixed flow gas test, a high temperature storage test and a thermal shock (TS) test. Virgin samples showed high mechanical strength. The Au-Sn system, with a thin Ni layer between the TiW adhesion layer and the bond, demonstrated a shear strength of 170 MPa. Cu-Sn, with a Cu-Cu3Sn-Cu structure, exhibited a shear strength of 275 MPa. Statistically significant decreases in strength were identified after reliability tests. The shear strength of the Au-Sn bond with an (AuSn + Au5Sn)eut structure decreased 40% in a corrosive environment. After 3000 TS cycles, the tensile strength of the Cu-Sn bond reduced by 45%. Fracture surface analysis revealed through-bond failures that were not observed previously. In cross-sectional analysis, vertical cracks were observed, which may contribute to the decrease in tensile strength.

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.

Facilitated transport by amine-mediated poly(vinyl alcohol) membranes for CO2 removal from natural gas

The drive toward greater application of membrane has resulted in its rapid development in natural gas processing industry. In this work, amine-mediated membranes were tailored for CO2 removal from CO2/CH4 stream. The effects of various parameters such as amine concentration, microporous support, feed pressure and composition were examined to study the permeation behavior of pure and mixed gases. Generally, CO2 transport through the DEA-PVA membranes was higher than that of MEA-PVA membranes for approximately 70%. The membrane containing 15 wt% DEA and 35 wt% MEA revealed higher permselectivity. CO2 permeance enhancement of amine-PVA membranes in comparison with neat PVA membrane, confirmed that CO2-amine reaction was the dominant transport mechanism. Additionally, with increasing feed pressure, CO2/CH4 permselectivity decreased due to carrier saturation. However, lower partial pressure of CO2 was in favor of reaction mechanism in pure and mixed gas tests. On the other hand, CH4 is not significantly affected by feed pressure confirming that solutiondiffusion is the governing transport mechanism. Additionally, PTFE support with higher wettability showed better performance (18%) regardless of amine type, concentration and feed pressure. DEA-PVA membrane has exhibited good stability during 2 weeks, unlike MEA-impregnated membrane, which was probably due to carrier degradation over time. POLYM. ENG. SCI., 54:1268–1279, 2014. V C 2013 Society of Plastics Engineers

Physical aging, high temperature and water vapor permeation studies of UV-rearranged PIM-1 membranes for advanced hydrogen purification and production

Ultraviolet (UV)-rearranged PIM-1 membranes have been shown to exhibit superior gas separation performance for H2/CO2 separation. The long-term aging studies of up to 100 days were investigated and revealed that the UV-rearranged PIM-1 membranes are much more stable than the original PIM-1 membrane. By positron annihilation lifetime (PAL) analyses, a constant decrease of o-Ps lifetime during physical aging of all membranes was observed, while o-Ps intensity changed sparingly. Compared to pure gas tests, the UV-irradiated PIM-1 membrane shows considerably enhanced separation performance in mixed gas tests with and without CO under high temperatures. Although the UV-rearranged PIM-1 membranes reveal deteriorating gas separation performance under humid feed conditions due to the effect of water vapor induced plasticization, the overall gas separation performance still outperforms most literature data. The successful validation of the separation performance for the UV-rearranged PIM-1 membranes under similar industrial testing conditions may possibly suggest the great potential of this type of membrane for the purification and production of industrial hydrogen.

Natural gas purification and olefin/paraffin separation using thermal cross-linkable co-polyimide/ZIF-8 mixed matrix membranes

Using three 6FDA-based polyimides (6FDA-Durene, 6FDA-Durene/DABA (9/1), 6FDA-Durene/DABA (7/3)) and nano-size zeolitic imidazolate framework-8 (ZIF-8), we have fabricated mixed matrix membranes (MMMs) with uniform morphology comprising ZIF-8as high as 40wt% loading by directly mixing as-synthesized ZIF-8 suspension into the polymer solution. Permeability of all gases (CO2, CH4, C3H6, and C3H8) increases rapidly with an increase in ZIF-8 loading. However, the addition of ZIF-8 nano-particles into the polymer matrix increases the ideal CO2/CH4 selectivity of only 6.87%, while the ideal C3H6/C3H8 selectivity improves 134% from 11.68 to 27.38 for the MMM made of 6FDA-Durene/DABA (9/1) and 40wt% ZIF-8. Experimental data show that the plasticization resistance and gas pair selectivity of MMMs are strongly dependent on the amount of cross-linkable moiety and annealing temperature. MMMs made of 6FDA-Durene do not show considerable improvements on resistance against CO2-induced plasticization after annealing at 200–400°C, while MMMs synthesized from cross-linkable co-polyimides (6FDA-Durene/DABA (9/1) and 6FDA-Durene/DABA (7/3)) show significant enhancements in CO2/CH4 and C3H6/C3H8 selectivity as well as plasticization suppression characteristics up to a CO2 pressure of 30atm after annealing at 400°C due to the cross-linking reaction of the carboxyl acid (COOH) in the DABA moiety. The MMM made of 6FDA-Durene/DABA (9/1) and 40wt% ZIF-8 possess a notable ideal C3H6/C3H8 selectivity of 27.38 and a remarkable C3H6 permeability of 47.3 Barrer. After thermally annealed at 400°C, the MMM made of 6FDA-Durene/DABA (9/1) and 20wt% ZIF-8 shows a CO2/CH4 selectivity of 19.61 and an impressive CO2 permeability 728 Barrer in mixed gas tests. The newly developed MMMs may have great potential for industrial nature gas purification and C3H6/C3H8 separation.

High performance PIM-1/Matrimid hollow fiber membranes for CO2/CH4, O2/N2 and CO2/N2 separation

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.

Room-temperature synthesis of ZIF-90 nanocrystals and the derived nano-composite membranes for hydrogen separation

Nanocrystals of ZIF-90 have been synthesized at room temperature through a novel procedure and incorporated into PBI-based nano-composite membranes for hydrogen purification. The physical and chemical structures of the ZIF-90 nanoparticles have been examined via multiple advanced instrumental analyses including DLS, XRD, FESEM, NMR and FTIR. The nanocrystals show identical morphology, crystallinity and chemical structure but a significantly reduced particle size (around 100 nm) when compared with the ZIF-90 particles in previous studies. The derived ZIF-90–PBI nano-composite membranes exhibit homogeneous particle dispersion and fine particle–polymer adhesion, as well as excellent hydrogen purification performance at various testing conditions. The 45/55 (w/w) ZIF-90–PBI membrane with the highest ZIF-90 volume loading of up to 50.9 vol% possesses the best ideal H2–CO2 separation performance with a moderate H2 permeability of 24.5 Barrer and a high H2–CO2 selectivity of 25.0 in pure gas permeation tests at 35 °C. The membrane also shows promoted gas separation performance during mixed gas tests at 180 °C with an H2 permeability of 226.9 Barrer and an H2–CO2 separation factor of 13.3 that surpasses the latest Robeson upper bound for H2–CO2 separation. This work not only expands the field of nano-composite membrane fabrication, but also provides prospects for interdisciplinary research combining nano-science and chemical engineering for clean energy development.

Surface modification of polyimide membranes by diethylenetriamine (DETA) vapor for H2 purification and moisture effect on gas permeation

We have demonstrated the use of diethylenetriamine (DETA) for vapor-phase modification of 6FDA-polyimide membranes for improving H2/CO2 separation performance. The effectiveness of DETA as the crosslinker was compared using the conventional solution-phase and the new vapor-phase modification approaches. It is demonstrated that the latter approach is favored in view of the better membrane tensile properties, gas permeation properties and environmental friendliness. The effects of vapor-phase modification parameters, temperature and duration, on the effectiveness of H2/CO2 separation were investigated by evaluating the gas permeation properties in the resultant films using pure gas, dry-state and wet-state mixed gases. A series resistance model for a simplified reaction progression was applied to evaluate the intrinsic gas permeation properties of the modified layers attained from thick films. Much thinner films, however, provide an improved means of assessment. Compared to pure gas permeability, the H2 permeability decreases significantly while the CO2 permeability is almost not affected in dry-state mixed gas tests (H2:CO2=50:50vol%). In the wet-state mixed gas tests (relative humidity∼50%), the H2 permeability further drops in the modified films; the CO2 permeability drops in the unmodified films or films with a shorter modification duration (3min), owing to sorption competition with highly condensable water; whereas, the CO2 permeability increases unexpectedly in membranes with extended modifications (>6min), which is attributed to the water enhanced amine-induced sorption effect on transport when the modified membrane contains a large amount of amine groups. Overall, the DETA induced polyimide surface modification shows significant improvement for H2/CO2 separation but the performance decreases when a humid feed gas stream is used.

High performance ZIF-8/PBI nano-composite membranes for high temperature hydrogen separation consisting of carbon monoxide and water vapor

Two types of advanced nano-composite materials have been formed by incorporating as-synthesized wet-state zeolitic imidazolate frameworks-8 (ZIF-8) nano-particles into a polybenzimidazole (PBI) polymer. The loadings of ZIF-8 particles in the two membranes (i.e., 30/70 (w/w) ZIF-8/PBI and 60/40 (w/w) ZIF-8/PBI) are 38.2 vol % and 63.6 vol %, respectively. Due to different ZIF-8 loadings, variations in particle dispersion, membrane morphology and gas separation properties are observed. Gas permeation results suggest that intercalation occurs when the ZIF-8 loading reaches 63.6 vol %. The incorporation of ZIF-8 particles significantly enhances both solubility and diffusion coefficients but the enhancement in diffusion coefficient is much greater. Mixed gas tests for H2/CO2 separation were conducted from 35 to 230 °C, and both membranes exhibit remarkably high H2 permeability and H2/CO2 selectivity. The 30/70 (w/w) ZIF-8/PBI membrane has an H2/CO2 selectivity of 26.3 with an H2 permeability of 470.5 Barrer, while the 60/40 (w/w) ZIF-8/PBI membrane has an H2/CO2 selectivity of 12.3 with an H2 permeability of 2014.8 Barrer. Mixed gas data show that the presence of CO or water vapor impurity in the feed gas stream does not significantly influence the membrane performance at 230 °C. Thus, the newly developed H2-selective membranes may have bright prospects for hydrogen purification and CO2 capture in realistic industrial applications such as syngas processing, integrated gasification combined cycle (IGCC) power plant and hydrogen recovery.

Dense film polyimide membranes for aggressive sour gas feed separations

Dense film membranes of the copolyimide 6FDA-DAM:DABA (3:2) are studied for simultaneous removal of CO2 and H2S from sour natural gas streams. Pure and mixed gas permeation as well as pure gas sorption data are reported at 35°C and pressures up to 62bar. The H2S partial pressures used are representative of highly aggressive field operations. Penetrant-induced plasticization effects are evident at feed pressures below 1bar in pure H2S feeds; sub-Tg thermal annealing is used to effectively mitigate this effect, and these annealed films are used throughout the study. Surprisingly, H2S/CH4 selectivity nearly doubles for mixed gas testing in comparison to the pure component ideal selectivity values and approaches the level of a state-of-the-art glassy polymer, cellulose acetate (CA), at H2S partial pressures above 2bar. Furthermore, permeation experiments using a 9.95% H2S, 19.9% CO2, 70.15% CH4 mixture at low feed pressures give CO2/CH4 selectivity of up to 49—over 30% greater than the pure component selectivity for 6FDA-DAM:DABA (3:2). The overall sour gas separation performance of this polyimide is comparable to high-performance rubbery polymer membranes, which have been reported for only moderate H2S partial pressure feeds, and is superior to that for CA based on a practical combined acid gas separation efficiency metric that we introduce. Finally, methods for continued development of the current polyimide membrane material for aggressive sour gas separations are presented.

Separation of CO2 from CH4 using polysulfone/polyimide silica nanocomposite membranes

Mixed matrix membranes (MMMs) were developed by incorporating inorganic silica nanoparticles into blends of polysulfone/polyimide (PSF/PI) asymmetric membranes for gas separation using phase inversion technique. The membranes were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA). SEM results show different morphologies of surfaces and cross-sections of the membrane where agglomeration is observed at 20.1wt.% silica loading. TGA analysis indicates good thermal stability of the hybrid membranes. Permeation results show that CO2 permeance increased with the introduction of 5.2wt.% silica contents (73.7±0.2GPU) in PSF/PI-20% blend and it increased with the increase in silica contents. With 15.2wt.% silica contents, the highest permselectivity of αCO2/CH4=61.0±0.3–60.2±0.4 is observed for treated membrane at 2–10bar. The selectivity using mixed gas test at various CO2/CH4 compositions shows consistent results with the ideal gas selectivity.