Membrane Reactor For Partial Oxidation Research Articles

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Status of CO<sub>2</sub>-stable dual-phase mixed conductor oxygen permeable membrane materials

Dense ceramic mixed ionic-electronic conducting membranes (MIECMs) are renowned for their rich and varied properties as admirable candidates in energy industries, such as oxygen separation from air, cathode materials for solid fuel oxide cells (SOFCs) or membrane reactors for partial oxidation of light hydrocarbons. Especially, the MIECMs integrated oxy-fuel combustion is considered to be a promising cost-effective and efficient method for CO2 capture and sequestration. During the oxy-fuel process, high purity oxygen production has been put forward to use OTMs technology instead of the conventional cryogenic technique, which can benefit from low costs and energy consumption and high efficiency. According to the phase numbers, the OTMs can be classified into single phase and composite OTMs. Extensive research activities have been directed towards the single phase perovskite-type oxides due to their high oxygen permeability. However, their industrial practical application was limited since they suffer from deactivation in the presence of CO2 due to alkaline earth carbonates forming on their surfaces. In order to overcome these issues, focus has shifted to the development of dual-phase membranes consisting of an oxygen ion conducting phase and an electron ion conducting phase, which benefit from the contribution of each phase and overcome the limitations of perovskite materials. Dual-phase OTM typically composed of an oxygen conducting phase (OCP) and an electronic conducting phase (ECP), which displays a better structural and mechanical stability comparing with the single phase OTM under reducing atmosphere due to the incorporation of fluorite phase. The first generation dual-phase OTMs are usually made from the fluorite oxides and noble metals, where fluorite oxides are used as the OCP and noble metals are adopted as the ECP. However, the noble metal-containing dual-phase OTM is too expensive. In order to lower the costs, researchers have developd the second generation dual-phase OTMs, which are consisted of fluorite oxides and perovskite oxides. Although the costs have been reduced, reactions between two phases were usually observed in the second generation dual-phase OTMs. Based on the previous findings and driven by the demands for oxy-fuel combustion for CO2 capture, research put forwards to the new CO2-stable dual-phase OTMs without noble metals and alkaline earth elements. Until now, already a large number of CO2-stable dual-phase membrane materials have been explored. However, their CO2 stabilities have been enhanced, but most of their oxygen permeabilities are too low for practical applications. Therefore, continues research efforts have to be made since most of available OTMs materials can′t satisfy the practical applications. In order to enhance the oxygen permeability and/or improve material thermochemical stability of dual-phase OTMs, the large majority of studies focused on tuning the composition through doping, synthesized temperatures, modified the membrane surfaces with coating or development of new synthesis methods. Meanwhile, considerable theoretical efforts have been put into the dual-phase OTMs, a number of models for permeation process such as Bouwmeester model, Xu-Thomson model, and Zhu model et al. are proposed. Up to now, countless publications has been produced in this field. In order to give the guidelines for the development of the dual-phase OTM materials and promote the process of industrialization of the OTMs technology in the oxy-fuel process, we summarize the status of CO2-stable dual-phase mixed conductor oxygen permeable membrane materials. In this review, the oxygen permeability mechanism and research progress of the dual-phase OTM materials are briefly introduced firstly. Subsequently, the influence of the preparation methods, sintering temperatures, ratios of two phases and the composition of the two phases on the oxygen permeability and stability are analyzed systematically. Next, the applications of dual phase MIECM reactor in partial oxidation of methane to syngas (POM), coupling reactions, water decomposition and oxy-fuel combustion are introduced and analyzed. Finally, the existing scientific problems and the possible research directions have been pointed out.

Oxygen nonstoichiometry and defect equilibria in La0.49Sr0.5–xBaxFeO3–δ

High level of mixed-conductivity and good stability of oxide La0.5Sr0.5FeO3–δ make it promising for the development of functional materials for such energy-related applications as solid oxide fuel cells and membrane reactors for partial oxidation of methane. The oxygen content in La0.49Sr0.5−xBaxFeO3–δ (x = 0, 0.25, 0.5) was measured by means of coulometric titration in the interval of partial oxygen pressure between 10−20 and 0.5 atm at temperatures 750–950 °C. The obtained results were employed for defect structure analysis of oxides. An ideal solution model enabled satisfactory simulation of experimental data for barium-free oxide. A reasonable data description for barium-containing oxides was achieved in the model, assuming that some of the oxygen vacancies are unavailable for oxygen ions. Partial substitution of barium for strontium was found to decrease the oxidation reaction constant of iron ions, resulting in a raised concentration of n-type electronic charge carriers and a reduced concentration of p-type carriers.

Low temperature partial oxidation of methane via BaBi0.05Co0.8Nb0.15O3−δ-Ni phyllosilicate catalytic hollow fiber membrane reactor

BaBi0.05Co0.8Nb0.15O3−δ (BBCN) hollow fiber membrane and Ni phyllosilicate catalyst were integrated to form a remarkable catalytic membrane reactor for partial oxidation of methane (POM) reaction at low temperature (650–750°C). This catalytic membrane reactor demonstrates a good catalytic-separation performance, achieving excellent hydrogen production rate of 33ml/min, high oxygen permeation flux through BBCN membrane of 15ml/min/cm2, good methane conversion of 80% and CO selectivity of 85% under low temperature (730°C), high reactant feeding rate (FCH4=25ml/min) and small amount of catalyst (20mg) during 100h of stability test. Several characterization techniques such as in situ high temperature XRD, SEM-EDX, TPR, TGA, BET and XPS were performed to further analyze and explain this remarkable performance. The good stability results reveal that the high oxygen permeation rate through BBCN hollow fiber membranes could prevent the hollow fiber membrane from breaking under high reducing gas concentration. Moreover, there is an optimum ratio of oxygen permeation flux to methane feeding rate to achieve high hydrogen production yield. If the oxygen permeation flux is higher than this optimum ratio, the excess oxygen will lead to deep oxidation of methane and loss of hydrogen selectivity.

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.

Functional LSM–ScSZ/NiO–ScSZ dual-layer hollow fibres for partial oxidation of methane

In this study, a functional La 0.80Sr 0.20MnO 3−δ (LSM)–Scandia-Stabilized-Zirconia (ScSZ)/NiO–ScSZ dual-layer hollow fibre has been developed using a single-step co-extrusion and co-sintering process, and has been employed as a dual-layer hollow fibre membrane reactor for partial oxidation of methane. Oxygen permeation rate between 0.49 and 1.82 ml/min and methane conversion between 53.55% and 98.78% have been achieved when operating temperature is elevated from 920 to 1060 °C, together with a significant reduction in coke-deposition. Oxygen permeation through the outer LSM–ScSZ permeation layer (approximately 109.2 μm in thickness) is found to be the controlling step to methane conversion at the operating temperature below 990 °C, above which the excessive oxygen permeation results in formation of CO 2 and H 2O as by-products. The experimental results further suggest that the amount of NiO in the inner NiO–ScSZ layer should be optimised based on the factors such as catalytic activity/stability, porosity and mechanical strength in addition to the sintering behaviour which has to be matched to the outer LSM–ScSZ layer.

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 CH 4 in COG. After the catalyst was packed on the membrane surface, 92% of methane conversion, 90% of H 2 selectivity, 104% of CO selectivity and as high as 15 ml/cm 2/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 H 2 in COG with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and H 2O reacts with CH 4 by reforming reactions to form H 2 and CO.

Catalytic partial oxidation of coke oven gas to syngas in an oxygen permeation membrane reactor combined with NiO/MgO catalyst

A high oxygen permeability and sufficient chemical and mechanical stability mixed ion and electron conductivity membrane to withstand the hash strong oxidation and reduction working conditions is significant for the membrane reactor to commercial-scale plant. In this paper, a disk-shaped Ba 1.0Co 0.7Fe 0.2Nb 0.1O 3−δ membrane was applied to a membrane reactor for the partial oxidation of methane in coke oven gas (COG) to syngas. The reaction was carried out using NiO/MgO solid solution catalyst by feeding COG. The reforming process was performed successfully; 95% CH 4 conversion, 80% H 2 selectivity, 106% CO selectivity and 16.3 ml cm −2 min −1 oxygen permeation flux were achieved at 1148 K. The reaction has been steadily carried out for more than 100 h. The NiO/MgO catalyst used in the membrane reactor exhibited good catalytic activity and resistance to coking in the COG atmosphere. Characterization of the membrane surface by SEM and XRD after long life test showed that both the surface exposed to the air side and reaction side still preserved the Perovskite structure which is implied that the practical application of this membrane as membrane reactor for partial oxidation of COG is promising.

Performance of a tubular oxygen-permeable membrane reactor for partial oxidation of CH 4 in coke oven gas to syngas

A gas-tight BaCo 0.7Fe 0.2Nb 0.1O 3-δ (BCFNO) tubular membrane was fabricated by hot pressure casting. And a membrane reactor with BCFNO tubular membrane and Ag-based sealant was readily constructed and applied to partial oxidation of CH 4 in coke oven gas. At 875 °C, 95% of methane conversion, 91% of H 2 and as high as 10 ml·cm −2 ·min −1 of oxygen permeation flux were obtained. There was a good match in the coefficient of thermal expansion between Ag-based alloy and BCFNO membrane materials. The tubular BCFNO membrane reactor packed with Ni-based catalysts exhibited not only high activity but also good stability in hydrogen-enriched coke oven gas (COG) atmosphere.

One Component Membrane Reactor for Partial Oxidation of Methane Using Asymmetric Membranes

Abstract Oxygen permeable asymmetric membranes of Ca0.8Sr0.2Ti0.7Fe0.3O3−δ were applied to a one-component membrane reactor (OCMR) for the partial oxidation of methane. CH4 conversion and oxygen flux of OCMR with a 43-μm dense layer at 1173 K reached 71% and 1.7 mL min−1 cm−2, respectively. These values are 2.5 times greater than that of a 500-μm self-supported membrane.

Evaluation of La0.5Sr0.5FeO3 − δ membrane reactors for partial oxidation of methane

Dense planar and tubular oxygen separation membranes of La0.5Sr0.5FeO3 − δ were studied in the partial oxidation of methane to syngas process. The oxygen permeation properties were obtained from the analysis of the outlet gas and compared with the data calculated from conductivity measurements. For the planar reactor, the selectivity achieved 95% and the CH4 conversion was 95–99% at 900 °C with pure methane. For the tubular reactor, the CO selectivity and CH4 conversion were 90% and 100%, respectively, under the same conditions. In both cases, the H2/CO ratio was 1.6–1.9. No degradation of membranes was observed after 250 h of operation.

Asymmetric Tubular Oxygen-Permeable Ceramic Membrane Reactor for Partial Oxidation of Methane

We report a successful paradigm of implementing the nickel catalyst for partial oxidation of methane (POM) in an oxygen-permeable ceramic membrane reactor (OPCMR). With using air feed, the OPCM (or the cathode of O2 reaction) was completely gastight but presented a desirable oxygen anion flux, which is required by POM in the anodic side. An almost 100% of CH4 conversion with high selectivity of CO and H2 was achieved in the anode, which was initially a composite of YSZ and NiO. It is also found that a mutual diffusion of Ni2+ and Zr4+ ions happens between the YSZ and NiO phases, which affected performance of POM. Besides experimental work, a new activation pathway was proposed to describe cleavage of the first C−H bond of methane. This activation pathway was simulated using the density function-theory and the computed activation energy for breaking up the first C−H bond falls in the experimental measurement range.

Re-evaluation of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ perovskite as oxygen semi-permeable membrane

Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF), a mixed oxygen ionic and electronic conducting ceramic derived from SrCo 0.8Fe 0.2O 3− δ (SCF), was re-evaluated for its possible application as an oxygen semi-permeable membrane and membrane reactor for partial oxidation of light hydrocarbons. The partial substitution of Sr 2+ with Ba 2+ in SCF led to an increase in the phase stability of the cubic perovskite structure. Both BSCF and SCF were found to have high oxygen nonstoichiometry. However, BSCF possessed a higher oxygen nonstoichiometry than SCF at room temperature, but a similar value at high temperatures. This resulted in the lower chemical expansion for BSCF than SCF. The doping of Ba 2+ in SCF led to the decrease of the electronic conductivity, but an increase in the oxygen ionic conductivity. The oxygen permeation study of the BSCF membrane demonstrated that the permeation rate was mainly rate-determined by the slow surface exchange kinetics at the oxygen lean side (or reaction side) membrane surface. The high ionic conductivity and the slow surface exchange kinetics resulted in the surface oxygen partial pressure at the reaction side membrane surface to be much higher than the surrounded atmosphere, therefore protecting the BSCF membrane from reduction.

Catalytic Membrane Reactors for Partial Oxidation Using Perovskite Hollow Fiber Membranes and for Partial Hydrogenation Using a Catalytic Membrane Contactor

Two consecutive model reactions of the type A - B→ C are studied in two kinds of catalytic membrane reactors. The partial oxidation of methane to synthesis gas due to CH 4 + 1/ 2 0 2 → CO + 2H 2 was investigated in a novel type of permselective membrane reactor using perovskite hollow fibers for the selective separation of oxygen from air. Partial hydrogenations were studied in a pore-through-flow membrane reactor as a special type of a catalytic membrane contactor. The catalytically functionalized pores of the membrane provide a medium with defined contact times for the cofeed of hydrogen and an unsaturated hydrocarbon, and the attempts of the scale-up of the successful laboratory experiments to the pilot scale are reported.

Reaction and oxygen permeation studies in Sm 0.4Ba 0.6Fe 0.8Co 0.2O 3 − δ membrane reactor for partial oxidation of methane to syngas

A disk-type Sm 0.4Ba 0.6Co 0.2Fe 0.8O 3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H 2). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH 4 diluted with Ar. While CH 4 conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH 4 conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH 4 compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH 4 was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H 2 was fed. It is implied that the oxidation of CO and H 2 with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO 2 and H 2O react with CH 4 by reforming reactions to form syngas.

Effect of reactor dimensions on the performance of an O [formula omitted] pump integrated partial oxidation reformer—a modelling approach

This paper describes a two-dimensional model of an oxygen permeable membrane reactor for partial oxidation of methane (POM). The model covers all aspects of major chemical kinetics, heat and mass transfer phenomena in the tubular reactor with oxygen permeation in radial direction through an ion-conducting membrane. The temperature and concentrations of the major species in the membrane tube were calculated. Results showed that the overall performance of the reactor was strongly dependent on the reactor dimensions and operating conditions. A reactor with smaller diameter ( D) and greater length-to-diameter ratio ( L/ D) gives better performance in terms of high methane (CH 4 ) conversion and high hydrogen (H 2 ) concentration. Under inlet gas temperature of 900 K and space velocity of 15,000 h - 1 , the CH 4 conversion and dry H 2 concentration can reach 98% and 64%, respectively, in the reactor with diameter D around 10 mm and L/D > 25 .

Partial oxidation of CH4 to synthesis gas using Ni-catalyst/Au|YSZ|Ag electrochemical membrane reactor

Spc-Ni/MgAl (spc-: solid phase crystallization method) catalyst has been prepared from Mg–Al hydrotalcite-like compounds containing Ni at the Mg site as the precursors and successfully used as a catalyst on an electrochemical membrane reactor for partial oxidation of CH4 at 1173K. The precursors based on [Mg2+A1−xl3+(OH)2x]x+(CO3−)x·mH2O, in which a ratio of Mg/Al varied and a part of Mg2+ ions were replaced by Ni2+ ions, were prepared by co-precipitation method, thermally decomposed, calcined and reduced to spc-Ni/MgAl catalyst. The electrochemical reactor, using yttria-stabilized zirconia (YSZ) as a solid electrolyte, has been employed as an oxygen permeable membrane reactor. The Ni catalyst coupled with Au paste was used as the catalyst-anode, while Ag paste was used as the cathode of the electrochemical cell. The reaction was carried out over the catalyst-anode film under oxygen pumping through the YSZ, and the results were compared with those obtained by various supported Ni catalysts prepared by impregnation (imp-) method. Spc-Ni/MgAl catalysts showed higher activity than imp-Ni catalysts and the best composition of metals in the catalyst was spc-Ni0.5/Mg2.5Al. This catalyst showed the CH4 conversion following the thermodynamic equilibrium between 1023 and 1173K, while the other catalysts of different compositions or imp-Ni catalysts showed a clear decrease in the CH4 conversion with decreasing temperature. Moreover, spc-Ni0.5/Mg2.5Al catalyst showed stable activity during the reaction for 40h. It is concluded that the high and stable activity for the partial oxidation of CH4 is due to highly dispersed and stable Ni metal particles formed on spc-Ni0.5/Mg2.5Al catalyst film.

Novel and ideal zirconium-based dense membrane reactors for partial oxidation of methane to syngas

A novel and ideal dense catalytic membrane reactor for the reaction of partial oxidation of methane to syngas (POM) was constructed from the stable mixed conducting perovskite material of BaCo0.4Fe0.4Zr0.2O3−δ and the catalyst of LiLaNiO/γ-Al2O3. The POM reaction was performed successfully. Not only was a short induction period of 2 h obtained, but also a high catalytic performance of 96–98% CH4 conversion, 98–99% CO selectivity and an oxygen permeation flux of 5.4–5.8 ml cm−2 min−1 (1.9–2.0 μmol m−2 S−1 Pa−1) at 850 °C were achieved. Moreover, the reaction has been steadily carried out for more than 2200 h, and no interaction between the membrane material and the catalyst took place.

Experimental and simulation study on a catalyst packed tubular dense membrane reactor for partial oxidation of methane to syngas

Experimental and simulation study on a catalyst packed tubular dense membrane reactor for partial oxidation of methane to syngas

An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas

Today only a small percentage of methane is used as a chemical feedstock to produce syngas that is a valuable feedstock for the production of higher hydrocarbons or methanol. Currently, the process extensively used in industry for the production of syngas is the steam reforming of methane in large furnaces. The reaction is industrially operated under strong conditions resulting in several undesirable consequences: sintering of the catalyst, danger of explosion, very high carbon deposition and the use of high-temperature resisting materials. A potential alternative technique to steam reforming processes for producing syngas is the partial oxidation of methane with oxygen, having over steam reforming the disadvantage that pure oxygen is required. Utilisation of air instead of pure oxygen is beneficial only if it can be performed by using a membrane reactor in which the membrane is permselective to oxygen. Another route to produce syngas using the partial oxidation of methane is offered by membrane reactors, i.e. engineering systems that combine the separation properties of membrane with the typical characteristics of catalytic reactions. It is well known that the use of dense palladium as membrane enables hydrogen product to permeate out through the membrane, shifting thereby conversions towards the values higher than thermodynamic equilibrium ones and providing pure hydrogen product. In fact, only hydrogen is allowed to permeate through dense palladium membranes. In this work five reactors are investigated with respect to the partial oxidation of methane. In particular, the performance of a traditional reactor (TR), three composite ceramic palladium membrane reactors (MRa, MRb and MRc), and a dense palladium membrane Reactor (PMR), all having the same geometrical dimensions and using the same Ni-based catalyst, are evaluated in terms of experimental results of methane conversion to syngas and in terms of hydrogen selectivity. A comparison between methane conversion at various temperatures and data in literature is also presented.