Oxy‐fuel combustion for CO2 capture using a CO2‐tolerant oxygen transporting membrane

CO₂ capture via an oxy‐fuel route through the U‐shaped (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) hollow fiber membrane with 100% CH₄ conversion and 100% CO₂ selectivity for 450 h has been explored for the first time. X‐ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy characterizations of the spent hollow fiber membrane have also been investigated. All these results indicate that PLNCG hollow fiber membrane shows excellent reaction performance and good stability under oxy‐fuel reaction conditions, which will be a potential rounte for reducing CO₂ emissions worldwide. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3856–3862, 2013     

Oxygen separation through U‐shaped hollow fiber membrane using pure CO2 as sweep gas

A number of U‐shaped K₂NiF₄‐type oxide hollow fiber membranes based on (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) were successfully prepared by a phase inversion spinning process. The PLNCG hollow fiber membranes were then used to investigate the effect of CO₂ concentration in both the sweep gas and the feed air on the oxygen permeation flux. With pure CO₂ as the sweep gas and even 10% CO₂ in the feed air, a steady oxygen permeation flux of 0.9 mL/min^·cm² (STP) is obtained at 975°C during 310 h, and no decline of the oxygen permeation flux is observed. XRD, SEM and EDS characterizations show the spent membrane still maintains the intact microstructure and perfect K₂NiF₄‐type phase structure without carbonate, which indicates that the U‐shaped PLNCG hollow fiber membrane is a very stable membrane under CO₂ atmosphere and has great potential for the practical application in oxyfuel techniques for CO₂ capture and storage.©2011 American Institute of Chemical Engineers AIChE J, 2012     

A robust mixed‐conducting multichannel hollow fiber membrane reactor

To accelerate the commercial application of mixed‐conducting membrane reactor for catalytic reaction processes, a robust mixed‐conducting multichannel hollow fiber (MCMHF) membrane reactor was constructed and characterized in this work. The MCMHF membrane based on reduction‐tolerant and CO₂‐stable SrFe_0.8Nb_0.2O_3‐δ (SFN) oxide not only possesses a good mechanical strength but also has a high oxygen permeation flux under air/He gradient, which is about four times that of SFN disk membrane. When partial oxidation of methane (POM) was performed in the MCMHF membrane reactor, excellent reaction performance (oxygen flux of 19.2 mL min^?1 cm^?2, hydrogen production rate of 54.7 mL min^?1 cm^?2, methane conversion of 94.6% and the CO selectivity of 99%) was achieved at 1173 K. And also, the MCMHF membrane reactor for POM reaction was operated stably for 120 h without obvious degradation of reaction performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2592–2599, 2015     

A CO2‐stable hollow‐fiber membrane with high hydrogen permeation flux

A Mo‐substituted lanthanum tungstate mixed proton‐electron conductor, La_5.5W_0.6Mo_0.4O_11.25?δ (LWM04), was synthesized using solid state reactions. Dense U‐shaped LWM04 hollow‐fiber membranes were successfully prepared using wet‐spinning phase‐inversion and sintering. The stability of LWM04 in a CO₂‐containing atmosphere and the permeation of hydrogen through the LWM04 hollow‐fiber membrane were investigated in detail. A high hydrogen permeation flux of 1.36 mL/min cm² was obtained for the U‐shaped LWM04 hollow‐fiber membranes at 975°C when a mixture of 80% H₂?20% He was used as the feed gas and the sweep side was humidified. Moreover, the hydrogen permeation flux did not significantly decrease over 70 h of operation when fed with a mixture containing 25% CO₂, 50% H₂, and 25% He, indicating that the LWM04 hollow‐fiber membrane has good stability under a CO₂‐containing atmosphere. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1997–2007, 2015     

Preparation of polyvinylamine/polysulfone composite hollow‐fiber membranes and their CO2/CH4 separation performance

Fixed‐carrier composite hollow‐fiber membranes were prepared with polyvinylamine (PVAm) as the selective layer and a polysulfone ultrafiltration membrane as the substrate. The effects of the PVAm concentration in the coating solution, the number of coatings, and the crosslinking of glutaraldehyde and sulfuric acid on the CO₂ permeation rate and CO₂/CH₄ selectivity of the composite membranes were investigated. As the PVAm concentration and the number of coatings increased, the CO₂/CH₄ selectivity increased, but the CO₂ permeation rate decreased. The membranes crosslinked by glutaraldehyde or sulfuric acid possessed higher CO₂/CH₄ selectivities but lower CO₂ permeation rates. For the pure feed gas, a composite hollow‐fiber membrane coated with a 2 wt % PVAm solution two times and then crosslinked with glutaraldehyde and an acid solution in sequence had a CO₂ permeation rate of 3.99 × 10^?6 cm³ cm^?2 s^?1 cmHg^?1 and an ideal CO₂/CH₄ selectivity of 206 at a feed gas pressure of 96 cmHg and 298 K. The effect of time on the performance of the membranes was also investigated. The performance stability of the membranes was good during 6 days of testing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1885–1891, 2006     

Carbon dioxide separation and dry reforming of methane for synthesis of syngas by a dual‐phase membrane reactor

High‐temperature CO₂ selective membranes offer potential for use to separate flue gas and produce a warm, pure CO₂ stream as a chemical feedstock. The coupling of separation of CO₂ by a ceramic–carbonate dual‐phase membrane with dry reforming of CH₄ to produce syngas is reported. CO₂ permeation and the dry reforming reaction performance of the membrane reactor were experimentally studied with a CO₂–N₂ mixture as the feed and CH₄ as the sweep gas passing through either an empty permeation chamber or one that was packed with a solid catalyst. CO₂ permeation flux through the membrane matches the rate of dry reforming of methane using a 10% Ni/γ‐alumina catalyst at temperatures above 750°C. At 850°C under the reaction conditions, the membrane reactor gives a CO₂ permeation flux of 0.17 mL min^?1 cm^?2, hydrogen production rate of 0.3 mL min^?1 cm^?2 with a H₂ to CO formation ratio of about 1, and conversion of CO₂ and CH₄, respectively, of 88.5 and 8.1%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2207–2218, 2013     

Performance of Ba0.5Sr0.5Co0.8Fe0.2O3 + δ membrane after laser ablation for methane conversion

A cross-shaped pattern was formed on the surface of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ oxygen permeation membrane by laser ablation. A membrane reactor made from this membrane was operated for partial oxidation of methane to syngas in the presence of Ni/ZrO₂ catalyst. The CH₄ conversion and CO selectivity of the membrane reactor were 98.8% and 91.5%, respectively, and the oxygen permeation flux through the membrane was 11.0 ml/cm² min at 850 °C. The effects of space velocity (SV) on CH₄ conversion and CO selectivity in such reactor were discussed. The mechanism of POM in such membrane reactor may follow the combustion and reforming mechanism.     

La0.6Sr0.4Co0.8Ga0.2O3‐δ (LSCG) hollow fiber membrane reactor: Partial oxidation of methane at medium temperature

In this study, La_0.6Sr_0.4Co_0.8Ga_0.2O_3‐δ (LSCG) hollow fiber membrane reactor was integrated with Ni/LaAlO₃‐Al₂O₃ catalyst for the catalytic partial oxidation of methane (POM) reaction. The process was successfully carried out in the medium temperature range (600–800°C) for reaction of blank POM with bare membrane, catalytic POM reaction and swept with H₂:CO gas mixture. For the catalytic POM reaction, enhancement in selectivity to H₂ and CO is obtained between 650–750°C when O₂:CH₄ <1. High CH₄ conversion of 97% is achieved at 750°C with corresponding H₂ and CO selectivity of about 74 and 91%. The oxygen flux of the membranes also increased with the increase in oxygen partial pressure gradient across the membrane. The postreacted membranes were tested via XRD and FESEM‐EDX for their crystallinity and surface morphology. XPS analysis was further used to investigate the O1s, Co 2p and Sr 3d binding energies of the segregated elements from the reducing reaction environment. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3874–3885, 2013     

Oxygen permeation through a CO2‐tolerant mixed conducting oxide (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ

A novel K₂NiF₄‐type oxide based on (Pr_0.9La_0.1)₂(Ni_0.74Cu_0.21Ga_0.05)O_4+δ (PLNCG) dense mixed conducting ceramic membrane was successfully prepared through a sol–gel route. The oxygen permeation flux through the membrane swept by pure CO₂ was comparative to that swept by He. The oxygen permeation and the stability of PLNCG under pure CO₂ were investigated in detail. A membrane with a thickness of 0.8 mm was steadily operated for 230 h with a constant oxygen permeation flux of 0.32 mL/(min cm²) at 975^°C using pure CO₂ as sweep gas. X‐ray diffraction shows that PLNCG can maintain its fluorite phase, and no carbonates were observed, even when it was exposed to pure CO₂ for a long time. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2473–2478, 2012     

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

Composite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N₂ adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO₂ permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO₂/N₂ and CO₂/CH₄ also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO₂ preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO₂ solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44999.     

Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow‐fiber membranes

Permeation properties of pure H₂, N₂, CH₄, C₂H₆, and C₃H₈ through asymmetric polyetherimide (PEI) hollow‐fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow‐fiber membrane was spun from a N‐methyl‐2‐pyrrolidone/ethanol solvent system via a dry‐wet phase‐inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H₂/N₂ selectivity >50 at 25°C). H₂ permeation through the PEI hollow fiber was dominated by the solution‐diffusion mechanism in the nonporous part. For CH₄ and N₂, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H₂, CH₄, and N₂. For C₂H₆ and C₃H₈, however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H₂ permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N₂ and CH₄, whereas the permeability of C₂H₆ and C₃H₈ decreased with increasing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 698–702, 2002     

Enhancing co‐production of H2 and syngas via water splitting and POM on surface‐modified oxygen permeable membranes

In this article, we report a detailed study on co‐production of H₂ and syngas on La_0.9Ca_0.1FeO_3?δ (LCF‐91) membranes via water splitting and partial oxidation of methane, respectively. A permeation model shows that the surface reaction on the sweep side is the rate limiting step for this process on a 0.9 mm‐thick dense membrane at 990°C. Hence, sweep side surface modifications such as adding a porous layer and nickel catalysts were applied; the hydrogen production rate from water thermolysis is enhanced by two orders of magnitude to 0.37 μmol/cm²?s compared with the results on the unmodified membrane. At the sweep side exit, syngas (H₂/CO = 2) is produced and negligible solid carbon is found. Yet near the membrane surface on the sweep side, methane can decompose into solid carbon and hydrogen at the surface, or it may be oxidized into CO and CO₂, depending on the oxygen permeation flux. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4427–4435, 2016     

Gas permeation performance of cellulose hollow fiber membranes made from the cellulose/N‐methylmorpholine‐N‐oxide/H2O system

Cellulose hollow fiber membranes (CHFM) were prepared using a spinning solution containing N‐methylmorpholine‐N‐oxide as solvent and water as a nonsolvent additive. Water was also used as both the internal and external coagulant. It was demonstrated that the phase separation mechanism of this system was delayed demixing. The CHFM was revealed to be homogeneously dense structure after desiccation. The gas permeation properties of CO₂, N₂, CH₄, and H₂ through CHFM were investigated as a function of membrane water content and operation pressure. The water content of CHFM had crucial influence on gas permeation performance, and the permeation rates of all gases increased sharply with the increase of membrane water content. The permeation rate of CO₂ increased with the increase of operation pressure, which has no significant effect on N₂, H₂, and CH₄. At the end of this article a detailed comparison of gas permeation performance and mechanism between the CHFM and cellulose acetate flat membrane was given. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1873–1880, 2004     

CO2‐facilitated transport through poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate)/polysulfone composite membranes

Poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate) (VSA–SA)/polysulfone (PS) composite membranes were prepared for the separation of CO₂. VSA–SA contained secondary amines and carboxylate ions that could act as carriers for CO₂. At 20°C and 1.06 atm of feed pressure, a VSA–SA/PS composite membrane displayed a pure CO₂ permeation rate of 6.12 × 10^?6 cm³(STP)/cm² s cmHg and a CO₂/CH₄ ideal selectivity of 524.5. In experiments with a mixed gas of 50 vol % CO₂ and 50 vol % CH₄, at 20°C and 1.04 atm of feed pressure, the CO₂ permeation rate was 9.2 × 10^?6 cm³ (STP)/cm² s cmHg, and the selectivity of CO₂/CH₄ was 46.8. Crosslinkages with metal ions were effective for increasing the selectivity. Both the selectivity of CO₂ over CH₄ and the CO₂ permeation rate had a maximum against the carrier concentration. The high CO₂ permeation rate originated from the facilitated transport mechanism, which was confirmed by Fourier transform infrared with attenuated total reflectance techniques. The performance of the membranes prepared in this work had good stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 275–282, 2006     

The effect of ethane on the performance of commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes in CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation applications

Impurities such as hydrogen sulfide, water vapor and heavy hydrocarbons in natural gas have considerable effects on the membrane performance. Small amounts of condensable and polymer soluble components in the feed gas cause swelling or plasticization of glassy membranes, leading to a reduction in membrane selectivity. In the present research the influence of ethane was investigated on the permeance and selectivity of two commercially available hollow fiber membranes, namely Cardo-type polyimide and PPO hollow fibers for CO₂/CH₄ separations. It was concluded that the gas mixture permeation rate was increased in the presence of C₂H₆. However, the CO₂/CH₄ separation factors remained almost the same in the presence and absence of the C₂H₆.     

Improving the POM performance of YBa2Cu3O7−δ membrane reactor by Co doping

The performance of Co doped YBa₂Cu₃O_7−δ (YBCO) membrane reactor have been investigated in a process of the partial oxidation of methane (POM) to syngas. The results shows that doping YBCO membrane with a little Co can enhance its oxygen permeation flux and improve its stability in reducing atmosphere noticeably. At 900 °C, with feed flow at 50 ml/min, CH₄ 6.0 v%, SV = 12,000 h⁻¹, and Ni/ZrO₂ catalyst, CH₄ conversion rate, CO selectivity, and oxygen permeation flux can reach to 98%, 92% and 1.41 ml min⁻¹ cm⁻² respectively.     

Effect of gas permeation temperature and annealing procedure on the performance of binary and ternary mixed matrix membranes of polyethersulfone,SAPO‐34, and 2‐hydroxy 5‐methyl aniline

This study investigated the effect of annealing time and temperature on gas separation performance of mixed matrix membranes (MMMs) prepared from polyethersulfone (PES), SAPO‐34, and 2‐hydroxy 5‐methyl aniline (HMA). A postannealing period at 120°C for a week extensively increased the reproducibility and stability of MMMs, but for pure PES membranes no post‐annealing was necessary for stable and reproducible performance. The effect of operation temperature was also investigated. The permeabilities of H₂, CO₂, and CH₄ increased with increasing permeation temperature from 35°C to 120°C, yet CO₂/CH₄ and H₂/CH₄ selectivities decreased. PES/SAPO‐34/HMA ternary and PES/SAPO‐34 binary MMMs exhibited the highest ideal selectivity and permeability values at all temperatures, respectively. For H₂/CO₂ pair, when temperature increased from 35°C to 120°C, selectivity increased from 3.2 to 4.6 and H₂ permeability increased from 8 to 26.5 Barrer for ternary MMM, demonstrating the advantage of using this membrane at high temperatures. The activation energies were in the order of CH₄ > H₂ > CO₂ for all membranes. PES/SAPO‐34/HMA membrane had activation energies higher than that of PES/SAPO‐34 membrane, suggesting that HMA acts as a compatibilizer between the two phases. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40679.     

Preparation and oxygen permeation of U‐shaped perovskite hollow‐fiber membranes

The oxygen permeation of dense U‐shaped perovskite hollow‐fiber membranes based on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ prepared by a phase inversion spinning process is reported. The perovskite hollow fibers with totally dense wall were obtained with the outer diameter of 1.147 mm and the inner diameter of 0.691 mm. The dependences of the oxygen permeation on the air flow rate on the shell side, the helium flow rate on the core side, the oxygen partial pressures, and the operating temperatures were experimentally investigated. According to the Wagner theory, it follows that the oxygen transport through the U‐shaped hollow‐fiber membrane is controlled by both surface reaction and bulk diffusion at the temperature ranges of 750–950°C. High oxygen permeation flux of 3.0 ml/(min cm²) was kept for about 250 h at 950°C under the conditions of the air feed flow rate of 150 ml/min and the helium flow rate of 50 ml/min. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Performance of an oxygen-permeable membrane reactor for partial oxidation of methane in coke oven gas to syngas

Perovskite-type oxygen-permeable membrane reactors of BaCo_0.7Fe_0.2Nb_0.1O_3−δ packed with Ni-based catalyst had high oxygen permeability and could be used for syngas production by partial oxidation of methane in coke oven gas (COG). The BCFNO membrane itself had a poor catalytic activity to partial oxidation of CH₄ in COG. After the catalyst was packed on the membrane surface, 92% of methane conversion, 90% of H₂ selectivity, 104% of CO selectivity and as high as 15 ml/cm²/min of oxygen permeation flux were obtained at 1148 K. During continuously operating for 550 h at 1148 K, no degradation of performance of the BCFNO membrane reactor was observed under the condition of hydrogen-rich COG. The possible reaction pathways were proposed to be an oxidation-reforming process. The oxidation of H₂ in COG with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and H₂O reacts with CH₄ by reforming reactions to form H₂ and CO.     

Effect of reaction conditions on supercritical hexanes mediated higher alcohol synthesis over a CuCoZn catalyst

Higher alcohol synthesis (HAS) from syngas over a Cu?Co based catalyst was investigated under supercritical hexanes conditions. The effects of hexanes/syngas molar ratio, H₂/CO molar ratio, and gas hourly space velocity (GHSV) on gas‐phase HAS and supercritical hexanes‐phase HAS (SC‐HAS) were investigated. The CO conversion remained relatively constant with increases in the hexanes/syngas molar ratio, whereas the CH₄ selectivity decreased. Higher alcohol productivity was found to increase monotonically with an increase in the hexanes/syngas molar ratio. Productivity of higher alcohols increased with an increase in the H₂/CO ratio under the gas‐phase conditions. An opposite trend in higher alcohol productivity with H₂/CO was observed in SC‐HAS. Further experiments were performed using argon as the reaction medium for comparison with the supercritical hexanes medium results. The enhanced higher alcohol productivity observed in this system can be attributed to improved extraction of alcohol products from the catalyst pores under the supercritical conditions. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1786–1796, 2014