Oxygen-permeable Membrane Reactor Research Articles

Exceptional performance of water splitting coupled with methane partial oxidation by oxygen-permeable membrane reactor

An oxygen-permeable membrane reactor, capable of high-performance water splitting and simultaneous methane conversion while maintaining the syngas ratio (H2/CO) close to 2, is reported in this study. Most coupling studies of water splitting and partial oxidation of methane (POM) using oxygen-conducting ceramic membranes have so far focused on the application in high-temperature (>900 °C) conditions that can accelerate the kinetics of surface exchange reactions. Considerable hydrogen production through the coupling reaction is possible below 800 °C by adopting Ruddlesden-Popper oxide for water reduction and a Ni/perovskite/fluorite composite for POM. The membrane composition was optimized to maximize the oxygen ionic conductivity and ensure the stability. Using a chemically stable dual-phase membrane with highly active coating layers, the production of 4.5 mL·cm−2·min−1 of hydrogen from water splitting and 14 mL·cm−2·min−1 of syngas from methane were stably secured at 800 °C. In addition, coupling reaction was confirmed to be possible even at 700 °C.

Barium Titanate as a Highly Stable Oxygen Permeable Membrane Reactor for Hydrogen Production from Thermal Water Splitting

Hydrogen production from water splitting by a mixed ionic-electronic conducting membrane is an efficient and promising technology; however, it is severely impeded by the poor reduction tolerance of the existing cobalt- or iron-containing membrane materials. In this work, a novel BaMg0.1Zr0.05Ti0.85O3−δ (BMZ-Ti) perovskite was synthesized by combining citric acid and ethylenediaminetetraacetic acid methods. The new membrane is characterized by its superior chemical stability in a wet H2 atmosphere as well as with environment-responsive mixed conductivity, generating from the mild reduction of Ti4+ at low oxygen partial pressure. Benefiting from these combined properties, the BMZ-Ti membrane showed an oxygen permeation flux larger than 0.3 mL min–1 cm–2 under a H2O/(CH4–CO2) gradient, more than 50 times larger than that under an air/He gradient, which was able to be used for coupling methane reforming with water dissociation to efficiently produce hydrogen with a production rate of 0.8 mL min–1 cm–2. Furthermore, no performance degradation was observed during an over 100 h test. These results highlight the potential of the BMZ-Ti membrane, with both environment-responsive mixed conductivity and excellent chemical stability, as a novel oxygen permeable membrane for hydrogen production from water.

One stone two birds: Simultaneous realization of partial oxidation of methane to syngas and N2 purification via robust ceramic oxygen-permeable membrane reactors

To obtain liquid fuel and high purity N2, extensive energy is consumed in converting methane to syngas (H2 + CO) and in separating N2 from air. Conventional studies were mainly focused on the partial oxidation of methane (POM) to syngas instead of the N2 purification. Here, we report a win-win scheme of POM to syngas and N2 purification using a high performance ceramic hollow membrane reactor. The mixed ionic and electronic conducting doped La0.8Ca0.2Fe0.95Ag0.05O3−δ (LCF-Ag) powder enduring harsh environment at high temperatures was synthesized and prepared into hollow fibre membranes. By using a self-designed injection device, the high-efficiency catalyst (Ni/LaNiO3/γ-Al2O3) was uniformly anchored on the inner surface of the hollow fiber along the whole length to guarantee the ideal reaction rate to achieve the desirable reaction efficiency, product selectivity and nitrogen purity. At 900 ℃, 99% methane conversion, 93% CO selectivity and syngas with suitable ratio of H2/CO were obtained by using both membrane modules containing one single or three hollow fiber membranes. Meanwhile, N2 with purity over 99.9% can be separated from gas mixture (synthetic air) due to the removal of oxygen which was consumed by POM. These results suggest that POM to syngas and N2 purification can be achieved using a high-performance ceramic hollow fiber membrane reactor toward green and energy-saving technology. This is a promising win-win scheme of catalytic reaction combining with gas separation.

Numerical Modeling of CO2 Splitting in High-Temperature Solar-Driven Oxygen Permeation Membrane Reactors

Abstract H2/CO production via H2O/CO2 splitting powered by concentrated solar energy is a promising pathway for energy conversion/storage. Oxygen permeable membrane reactor serves as an alternative reactor concept for realizing this chemical path with the advantages of continuous production, easy integration, and high product selectivity. In this paper, a mathematical model of steady-state mass and heat transfer coupled with reaction kinetics in the oxygen permeation membrane reactor was established. CO2 splitting in the ceria membrane reactor was simulated and the effects of various factors, including inert/CO2 flow configurations, reaction conditions, and geometric parameters of the membrane, on the CO2 conversion process, were studied. The increase of operating temperature could effectively improve the CO2 conversion ratio, and the effect of decreasing the oxygen pressure of the inert gas is very limited. The oxygen accumulation in the inert gas could lead to considerably high inert demand. Furthermore, conversion-limiting factors were studied under different conditions and there are two critical rate constants of reactions signifying a transition from a chemical kinetics limited conversion to oxygen diffusion limited conversion. This work helps guide reactor design and operate toward achieving the maximum CO2 conversion ratio.

Effect of Ru and Ni nanocatalysts on water splitting and hydrogen oxidation reactions in oxygen-permeable membrane reactors

Catalytic membrane reactors based on oxygen-permeable membranes, which coupling water splitting and hydrogen oxidation reactions and oxygen separation into a single unit, has been regarded as a promising route to produce high-purity hydrogen. Surface reactions including water splitting and hydrogen oxidation reactions play important roles in the hydrogen separation process. Catalysts with high catalytic activities towards these two reactions are highly desired. In this work, in-situ exsolved Ru and Ni nanocatalysts were prepared and tested for hydrogen separation in four membrane reactors. The Ru element incorporates into the lattice of Ce0.85Sm0.15O1.925 (SDC) support after being prepared in air but it is exsolved from the SDC lattice to form 3–5 nm nanoparticles after being reduced in hydrogen. The Ru nanoparticles prefer to stay at the step-faceting of the support. Meanwhile, the strong metal-support interactions (SMSI) between Ru and SDC support has been certified. The SMSI benefits the stabilization of Ru nanoparticles at elevated temperatures, thus the Ru/SDC catalyst shows high catalytic activity towards both hydrogen oxidation and water splitting reactions. A doubled hydrogen separation rate of 21.6 mL cm−2 min−1 was obtained at 900 °C when using the Ru/SDC catalyst compared with Ni-based catalysts. Experimental results show that the catalysts on both sides have great impacts on the hydrogen separation rate, indicating both the water splitting reaction and hydrogen oxidation reaction are potential rate determining steps.

Non-noble metal catalysts coated on oxygen-permeable membrane reactors for hydrogen separation

Catalytic membrane reactors for hydrogen separation based on oxygen-permeable membranes have attracted much attention. It is of great significance to develop effective non-noble metal catalysts for the membrane reactor. Fe, Co and Ni based catalysts are good alternatives due to their high abundance and low cost in practical applications. In this work, M/SDC (M = Fe, Co and Ni) catalysts are prepared for hydrogen separation. It was demonstrated that the catalytic activity increases in the order of Co/SDC < Fe/SDC < Ni/SDC. The hydrogen separation rate of the membrane reactor with the Ni/SDC catalyst is 1.5 times higher than that of with the Co/SDC catalyst under the same conditions. A model was used to estimate the resistances of surface reaction and bulk diffusion. It is concluded that the hydrogen separation process is jointly controlled by surface reactions and bulk diffusion even for the membrane reactors with the Ni/SDC catalyst.

Microstructural and Interfacial Designs of Oxygen-Permeable Membranes for Oxygen Separation and Reaction-Separation Coupling.

Mixed ionic-electronic conducting oxygen-permeable membranes can rapidly separate oxygen from air with 100% selectivity and low energy consumption. Combining reaction and separation in an oxygen-permeable membrane reactor significantly simplifies the technological scheme and reduces the process energy consumption. Recently, materials design and mechanism investigations have provided insight into the microstructural and interfacial effects. The microstructures of the membrane surfaces and bulk are closely related to the interfacial oxygen exchange kinetics and bulk diffusion kinetics. Therefore, the permeability and stability of oxygen-permeable membranes with a single-phase structure and a dual-phase structure can be adjusted through their microstructural and interfacial designs. Here, recent advances in the development of oxygen permeation models that provide a deep understanding of the microstructural and interfacial effects, and strategies to simultaneously improve the permeability and stability through microstructural and interfacial design are discussed in detail. Then, based on the developed high-performance membranes, highly effective membrane reactors for process intensification and new technology developments are highlighted. The new membrane reactors will trigger innovations in natural gas conversion, ammonia synthesis, and hydrogen-related clean energy technologies. Future opportunities and challenges in the development of oxygen-permeable membranes for oxygen separation and reaction-separation coupling are also explored.

Asymmetric dual-phase MIEC membrane reactor for energy-efficient coproduction of two kinds of synthesis gases

An asymmetric 75 wt% Sm0.15Ce0.85O1.925-25 wt% Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SDC-SSAF) dual-phase mixed ionic-electronic conducting (MIEC) oxygen-permeable membrane reactor was applied to coproduce ammonia synthesis gas (ASG, H2/N2 = 3) and liquid fuels synthesis gas (LFSG, H2/CO = 2). The effects of CH4 concentration, CH4 flow rate, steam flow rate and temperature on the performance of the membrane reactor were studied. The SDC-SSAF membrane reactor showed an excellent performance for the coproduction of ASG and LFSG. An ASG production rate of 20.7 mL cm−2 min−1, a LFSG production rate of 51.0 mL cm−2 min−1 and an oxygen permeation rate of 9.1 mL cm−2 min−1 were achieved at 925 °C. Compared with traditional industrial processes, the energy saving of this membrane reactor process is expected as high as 66.5%. The post-mortem of the membrane reactor using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) characterization revealed that the membrane has an excellent structural stability under operation condition.

Effects of membrane thickness and structural type on the hydrogen separation performance of oxygen-permeable membrane reactors

Membrane thickness and structural type, which are closely related to the species diffusion in the membrane bulk and reactions at the gas-solid interfaces, have important influences on the performance of a dense ceramic membrane. Recently, oxygen-permeable dense ceramic membrane reactors have been suggested for hydrogen purification at elevated temperatures. Mixed conducting composite with composition of 75 wt% Ce0.85Sm0.15O2-δ-25 wt% Sm0.6Sr0.4Al0.3Fe0.7O3-δ (SDC-SSAF) was fabricated into oxygen-permeable membranes with different thicknesses and structural types. The effects of membrane thickness and structural type on the hydrogen separation performance were tested under different hydrogen concentrations and flow rates on side I, different flow rates of steam/He mixed gas on side II as well as different temperatures. The effect of concentration polarization on hydrogen separation rate and the rate determining steps were discussed by comparing the performances of the symmetric membranes and the asymmetric membranes. The apparent activation energies of the membrane reactors for hydrogen separation were analyzed. This study will give some constructive guides to the subsequent work on how to effectively improve the hydrogen separation performance.

Simultaneous production of synthesis gases H2/N2 and H2/CO in a dual-phase mixed conducting membrane reactor

By respectively sending methane and the mixture of air and water to the opposite sides of Ce0.8Sm0.2O2-δ-Sr2Fe1.5Mo0.5O5+δ (CSO-SFMO) dual-phase oxygen-permeable membrane reactor, co-production of two synthesis gases H2/N2 and H2/CO were achieved in this work. A porous layer with the same material as the bulk membrane was deposited on the surface of CSO-SFMO membrane to catalyze surface reactions. It was found that CSO with fluorite structure and SFMO with perovskite structure show good chemical compatibility even after being sintered at high temperature. Moreover, the CSO-SFMO dual phase membrane with porous layer exhibits high oxygen permeability and good CO2 tolerance under harsh conditions. Using CSO-SFMO dual phase membrane as reactor, a suitable H2/N2 ratio of 3 and H2/CO ratio of 2 was obtained on the opposite sides of the membrane. Meanwhile, CO selectivity of 98%, CH4 conversion of 97% in the methane side and synthesis gas (H2+N2) production rate of 3.0cm3min−1cm−2 on the feed side were achieved at 900°C.

High‐rate hydrogen separation using an MIEC oxygen permeable membrane reactor

In this study, we propose using mixed ionic‐electronic conducting (MIEC) oxygen permeable membrane to separate hydrogen via the water splitting reaction. To do that, steam was fed to one side of the membrane (side I) and a low‐purity hydrogen was fed to the other side (side II). Oxygen from water splitting on side I permeates through the membrane driven by an oxygen chemical potential gradient across the membrane to react with the low‐purity hydrogen on side II. After condensation and drying, high‐purity hydrogen is acquired from side I. Thus, the hydrogen separation process is realized based on the fact that the low‐purity hydrogen is consumed and high‐purity hydrogen is acquired. We achieved a high hydrogen separation rate (13.5 mL cm−2 min−1) at 950°C in a reactor equipped with a 0.5‐mm‐thick Ba0.98Ce0.05Fe0.95O3‐δ membrane. This research proofed that it is feasible to upgrade hydrogen purity using an MIEC oxygen permeable membrane. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1278–1286, 2017

A polygeneration from a dual-gas partial catalytic oxidation coupling with an oxygen-permeable membrane reactor

Polygeneration system, typically involving chemicals/fuels and electricity co-production, is a promising technology for the sustainable development of energy andenvironment. In this study, a new polygeneration system based on coal and coke oven gas (COG) inputs for co-production of dimethyl ether (DME)/methanol and electricity is proposed. In the new system, an appropriate syngas for the synthesis of DME is from coal gasified gas (CGG) reforming of COG coupled with an oxygen-permeable membrane reactor, in which both COG and CGG reforming process and fuel combustion process are incorporated, which reduces exergy destruction in the whole reforming process. In order to obtain the best performance of CO2reduction, energy saving and economic benefit, the key operation parameters of the proposed process are analyzed and optimized. The new system is compared with the process based on CH4/CO2 dry reforming, in terms of exergy efficiency, exergy cost and CO2emissions. Through the new system, the exergy efficiency can be increased by 7.8%, the exergy cost can be reduced by 0.88USD/GJ and the CO2 emission can be reduced by 0.023kg/MJ. These results suggest that the polygeneration system from CGG and COG partial catalytic oxidation coupling with an oxygen-permeable membrane reactor (PL-PCO-OPMR) would be a more attractive way for highly efficient and clean use of CGG and COG.

Autothermal reforming of ethanol in dense oxygen permeation membrane reactor

Perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) material was synthesized by the combined EDTA–citric acid complexing method and the disk-type BSCF dense membrane reactor (DMR) was constructed for H2 production by ethanol oxidative steam reforming reaction. The autothermal reaction conditions in the DMR were obtained through optimizing the ethanol oxidative steam reforming reaction (EOSR). The results showed that the hydrogen yield decreases (3.5–3.2mol/molEtOH) with the net heat of reaction Q decreases from 0 to −257J/molEtOH because the oxygen permeation flux for the membrane increases with temperature. The hydrogen production is 3.5mol/molEtOH at autothermal temperature of 750°C and the oxygen permeation flux of the dense ceramic membrane reactor is 6.5ml(STP)/cm2min. The activation energy for oxygen permeation was 46.4kJ/mol under the air/Ar gradient, as compared to about 20.1kJ/mol under EOSR reaction, respectively. The BSCF DMR performed stably under the autothermal reaction condition was stable for at least 180h. These results indicate the BSCF membrane holding the high oxygen permeation flux, the excellent phase reversibility and the good stability under the highly reducing atmosphere, shows great application potential for H2 production via the autothermal reaction.

Influence of chromium in metallic components on oxygen permeability and microstructure of BaCo0.7Fe0.2Nb0.1O3−δ membrane

The influence of chromium in metal components on oxygen permeation and microstructure of BaCo0.7Fe0.2Nb0.1O3−δ(BCFNO) membrane was investigated under the condition of the oxygen-permeable membrane reactors. In the presence of chromia-forming metal components, the oxygen permeation flux decreased by about 2.4% and 10% when using dry air and humidified air (4% H2O) for 100h at 850°C, respectively. In the presence of chromia-forming alloys on the permeate side, the oxygen permeation flux decreased by 7% within 100h. Due to the deposition of volatile Cr species from chromia-forming alloys and formation of spinel phases of BaCrO4 and BaCr2O4 on the membrane surfaces, the performance of the membrane reactors deteriorated continuously as a function of time. Poisoning of chromium species is also a critical issue for the application of MIEC oxygen-permeable membrane reactors.

Thermodynamic study on solar thermochemical fuel production with oxygen permeation membrane reactors

Thermodynamic analysis is performed on a conceptual oxygen permeation membrane reactor driven by concentrated solar energy (heat) for isothermal H2O splitting for the purpose of solar fuel derivation. By way of a plug-flow reactor model, kinetic and thermodynamic factors responsible for conversion rate, reactor dimension, and solar-to-fuel efficiency are analyzed for the case of pump-assisted and methane-assisted scenarios. The pump-assisted case achieves the same solar-to-fuel efficiency (2.9% at 1500 degrees C) as isothermal solar thermochemical cycling, while the methane-assisted case attains much higher efficiencies at much lower temperatures, whose net solar-to-fuel efficiency reaches 63% at around 900 degrees C. The theoretical framework developed in this study can be applied to the solar thermochemical splitting of other gases such as CO2 and can be further extended to the co-splitting of H2O and CO2 for syngas production driven by solar energy only (i.e., without the participation of hydrocarbon fuels). Copyright (c) 2015 John Wiley & Sons, Ltd.

Investigation on the reforming reactions of coke-oven-gas to H2 and CO in oxygen-permeable membrane reactor

The reaction mechanisms for the reforming of coke oven gas (COG) and partial oxidation of methane (POM) to H2 and CO in Ba1.0Co0.7Fe0.2Nb0.1O3−δ (BCFNO) membrane reactor packed with NiO/MgO catalyst were investigated through designing experiments and test of oxygen permeation. The results indicated the direct partial oxidation mechanism was the dominant mechanism of POM process in BCFNO membrane reactor. The H2 in COG was proven to have an important effect on the oxygen permeation. The packing amount of catalysts in catalyst bed has little effect on oxygen permeation, while it has obvious effects on CO and H2 selectivity. Then the reaction mechanism was proposed. The H2 in COG adsorbs and reacts with the permeated oxygen to form H2O. Simultaneously the CH4 dissociates over Ni0 sites to form hydrogen and surface active carbon. The formed hydrogen reacts with oxygen to give H2O again. The remained CH4 was converted to H2 and CO by reforming with produced H2O in catalyst bed. Based on the reaction mechanism, the author had given a permeation-reforming tubular membrane reactor configuration for the COG conversion to hydrogen. The permeation-reforming reactor shows promise for scale-up of the reforming of COG.

Design of two-stage membrane reactor for the conversion of coke-oven gas to H2 and CO

The catalyst function was achieved in two regions in an oxygen permeation membrane reactor: H2 dissociated and reacted with lattice oxygen or oxygen ions to form H2O near the membrane surface. The H2O formed could react with the residual CH4 away from the membrane surface area.

Natural Gas to Fuels and Chemicals: Improved Methane Aromatization in an Oxygen-Permeable Membrane Reactor

Natural Gas to Fuels and Chemicals: Improved Methane Aromatization in an Oxygen-Permeable Membrane Reactor

A novel tubular oxygen-permeable membrane reactor for partial oxidation of CH4 in coke oven gas to syngas

Dense BaCo0.7Fe0.2Nb0.1O3−δ (BCFNO) membrane tubes were prepared by slip casting and readily brazed to 310S stainless steel supports using a silver-based alloy. A novel tubular membrane reactor was constructed by placing a cylindrical Ni-based monolithic catalyst coaxially around the tubular membrane and a conventional Ni-based catalyst-bed apart from the membrane tube. The novel membrane reactor was successfully applied to partial oxidation of CH4 in coke oven gas (COG). At 850 °C, 94% of CH4 conversion, 93% of H2 and as high as 11.3 cm3 cm−2 min−1 of oxygen permeation flux were obtained. The experimental H2 and CO selectivity and CH4 conversion were close to the thermodynamically predicated ones. There was a good match in the coefficient of thermal expansion (CTE) among BCFNO membrane, Ag-based alloy and 310S metal support. Long-term operation test results indicate that the novel tubular BCFNO membrane reactor exhibited not only high activity but also good stability for the partial oxidation of CH4 in COG to syngas.

Simulation of Fluidized Bed Oxygen Permeable Membrane Reactors for Hydrogen Production from Natural Gas

Hydrogen is an important chemical commodity. Fluidized bed oxygen permeable membrane reactor is a novel technology for hydrogen production from natural gas reforming. An Aspen model is built for this novel reactor. Influences of reaction pressure, oxygen to carbon ratio, and steam to carbon ratio on the hydrogen concentration in syn-gas, hydrogen yield, and reaction temperature and methane conversion are studied. The results are compared with the ordinary fluidized bed reactor. It shows that the fluidized bed oxygen permeable membrane reactor has a higher methane conversion and a hydrogen yield and a higher hydrogen concentration in the syngas, due to its in-situ oxygen separation from air.