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     

Design of mixed conducting ceramic membranes/reactors for the partial oxidation of methane to syngas

The performance of mixed conducting ceramic membrane reactors for the partial oxidation of methane (POM) to syngas has been analyzed through a two‐dimensional mathematical model, in which the material balance, the heat balance and the momentum balance for both the shell and the tube phase are taken into account. The modeling results indicate that the membrane reactors have many advantages over the conventional fixed bed reactors such as the higher CO selectivity and yield, the lower heating point and the lower pressure drop as well. When the methane feed is converted completely into product in the membrane reactors, temperature flying can take place, which may be restrained by increasing the feed flow rate or by lowering the operation temperature. The reaction capacity of the membrane reactor is mainly determined by the oxygen permeation rate rather than by the POM reaction rate on the catalyst. In order to improve the membrane reactor performance, reduction of mass transfer resistance in the catalyst bed is necessary. Using the smaller membrane tubes is an effective way to achieve a higher reaction capacity, but the pressure drop is a severe problem to be faced. The methane feed velocity for the operation of mixed conducting membrane reactors should be carefully regulated so as to obtain the maximum syngas yield, which can be estimated from their oxygen permeability. The mathematical model and the kinetic parameters have been validated by comparing modeling results with the experimental data for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐α (LSCF) membrane reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

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     

Oxygen selective ceramic hollow fiber membranes for partial oxidation of methane

A BaCo_xFe_yZr_zO_3?δ (BCFZ) perovskite hollow fiber membrane was used to construct reactors for the partial oxidation of methane (POM) to syngas. The performance of the BCFZ fibers in the POM was studied (i) without any catalyst, (ii) with catalyst‐coated fibers, and (iii) with catalyst packed around the fibers. In addition to the performance in the POM, the stability of the BCFZ hollow fiber membranes was investigated for the different catalyst arrangements. Best stability of the BCFZ hollow fiber membrane reactor in the POM could be obtained if the reforming catalyst is placed behind the oxygen permeation zone. It was found that a direct contact of the catalyst and the fiber must be avoided which could be achieved by coating the fiber with a gold film. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Mathematical Modeling and Optimization of Combined Steam and Dry Reforming of Methane Process in Catalytic Fluidized Bed Membrane Reactor

Mathematical modeling of the methane-combined reforming process (steam methane reforming–dry reforming methane) was performed in a fluidized bed membrane reactor. The model characterizes multiple phases and regions considering low-density phase, high-density phase, membrane, and free board regions that allow study of reactor performance. It is demonstrated that the combined effect of membrane and reaction coupling provides opportunities to overcome equilibrium limits and helps to achieve higher conversion. Additionally, the influence of key parameters on reactor performance including reactor temperature, reactor pressure, steam to methane feed ratio (S/C), and carbon dioxide to methane feed ratio (CO₂/C) were investigated in the multi-objective genetic algorithm to find the optimal operating conditions. Finally, the process of steam reforming was simulated in selected optimal conditions and the results are compared to those of the combined reforming process. Comparison reveals the superiority of the combined reforming process in terms of methane conversion, catalyst activity, and outlet H₂/CO ratio in the syngas product in being close to unity.     

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.     

Comparative study between fluidized bed and fixed bed reactors in methane reforming combined with methane combustion for the internal heat supply under pressurized condition

The effect of catalyst fluidization on the conversion of methane to syngas in methane reforming with CO₂ and H₂O in the presence of O₂ under pressurized conditions was investigated over Ni and Pt catalysts. Methane and CO₂ conversion in the fluidized bed reactor was higher than those in the fixed bed reactor over Ni_0.15Mg_0.85O catalyst under 1.0 MPa. This reactor effect was dependent on the catalyst properties. Conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that this phenomenon is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor. Although serious carbon deposition was observed on Ni_0.15Mg_0.85O in the fixed bed reactor, it was inhibited in the fluidized bed reactor.     

A novel porous‐dense dual‐layer composite membrane reactor with long‐term stability

A porous‐dense dual‐layer composite membrane reactor was proposed. The dual‐layer composite membrane composed of dense 0.5 wt % Nb₂O₅‐doped SrCo_0.8Fe_0.2O_3‐δ (SCFNb) layer and porous Ba_0.3Sr_0.7Fe_0.9Mo_0.1O_3‐δ (BSFM) layer was prepared. The stability of SCFNb membrane reactor was improved significantly by the porous‐dense dual‐layer design philosophy. The porous BSFM surface‐coating layer can effectively reduce the corrosion of the reducing atmosphere to the membrane, whereas the dense SCFNb layer permeated oxygen effectively. Compared with single‐layer dense SCFNb membrane reactor, no degradation of performance was observed in the dual‐layer membrane reactor under partial oxidation of methane during continuously operating for 1500 h at 850°C. At 900°C, oxygen flux of 18.6 mL (STP: Standard Temperature and Pressure) cm^?2 min^?1, hydrogen production of 53.67 mL (STP) cm^?2 min^?1, CH₄ conversion of 99.34% and CO selectivity of about 94% were achieved. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4355–4363, 2013     

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.     

Computational fluid dynamics modeling of hydrogen production in an autothermal reactor: Effect of different thermal conditions

A numerical model was developed and validated to simulate and improve the reforming efficiency of methane to syngas (CO+H₂) in an autothermal reactor. This work was undertaken in a 0.8 cm diameter and 30 cm length quartz tubular reactor. The exhaust gas from combustion at the bottom of reactor was passed over a Ru/γ-Al₂O₃ catalyst bed. The Eddy Dissipation Concept (EDC) model for turbulence-chemistry interaction in combination with a modified standard k-? model for turbulence and a reaction mechanism with 23 species and 39 elementary reactions were considered in the combustion model. The pre-exponential factors and activation energy values for the catalyst (Ru) were obtained by using the experimental results. The percentage of difference between the predicted and measured mole fractions of the major species in the exhaust gas from combustion and catalyst bed zones was less than 5.02% and 7.73%, respectively. In addition, the results showed that the reforming efficiency, based on hydrogen yield, was increased with increase in catalyst bed’s thermal conductivity. Moreover, an enhancement of 4.34% in the reforming efficiency was obtained with increase in the catalyst bed wall heat flux from 0.5 to 2.0 kW/m².     

Partial oxidation of methane in BaCe0.1Co0.4Fe0.5O3−δ membrane reactor

A new perovskite material, BaCe_0.1Co_0.4Fe_0.5O_3?δ used as dense oxygen permeable membrane for partial oxidation of methane (POM) reaction was investigated. In order to improve the synergetic effects between membrane and catalyst, LiLaNiO/γ-Al₂O₃ catalyst was directly packed onto the surface of the membrane to carry out POM. In BaCe_0.1Co_0.4Fe_0.5O_3?δ membrane reactor, high oxygen permeation flux, high CH₄ conversion and CO selectivity were obtained. At 950 °C, oxygen flux of 9.5 ml cm^?2 min^?1, CH₄ conversion of 99% and CO selectivity of 93% were achieved with a membrane thickness of 1.0 mm. There was an induction process at the initial stage of POM, which was related to the reduction of NiO to Ni⁰ in LiLaNiO/γ-Al₂O₃ catalyst. Experiments illustrated that higher reaction temperature would shorten the induction time. During continuously operating for 1000 h at 875 °C, no degradation of performance of the membrane reaction was observed. SEM characterization also demonstrated that the membrane disc maintained an integral structure without any cracks after long-term operation.     

Investigation on the partial oxidation of methane to syngas in a tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane reactor

A perovskite material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), with both electronic and ionic conductivity, was synthesized by a combined citrate–EDTA complexing method. The dense membrane tube made of BSCF was fabricated using the plastic extrusion method. The partial oxidation of methane (POM) to syngas was performed in the tubular BSCF membrane reactor packed with a LiLaNiO/γ–Al₂O₃ catalyst. The reaction performance of the membrane reactor was investigated as functions of temperature, air flow rate in the shell side and methane concentration in the tube side. The mechanism of POM in the membrane reactor was discussed in detail. It was found that in the tubular membrane reactor, combustion reaction of methane with permeated oxygen took place in the reaction zone close to the surface of the membrane, then followed by steam and CO₂ reforming of methane in the middle zone of the tube side. The membrane tube can be operated steadily for 500 h in pure methane with 94% methane conversion and higher than 95% CO selectivity, and higher than 8.0 ml/cm² min oxygen permeation flux.     

N2O Decomposition Catalysed by Transition Metal Ions

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al₂O₃), reduced nickel catalyst (Ni⁰/Al₂O₃), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al₂O₃) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH₄/O₂ reaction, even with a pre-reduced nickel catalyst, and Ni⁰ is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni⁰ is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.     

Development and Application of Oxygen Permeable Membrane in Selective Oxidation of Light Alkanes

In this paper, oxygen permeable membrane used in membrane reactor for selective oxidation of alkanes will be discussed in detail. The recent developments for the membrane materials will be presented, and the strategy for the selection of the membrane materials will be outlined. The main applications of oxygen permeable membrane in selective oxidation of light alkanes will be summarized, which includes partial oxidation of methane (POM) to syngas and partial oxidation of heptane (POH) to produce H₂, oxidative coupling of methane (OCM) to C₂, oxidative dehydrogenation of ethane (ODE) to ethylene and oxidative dehydrogenation of propane (ODP) to propylene. Achievements for the membrane material developments and selective oxidation of light alkanes in membrane reactor in our group are highlighted.     

Ultra-rapid synthesis of syngas by the catalytic reforming of methane enhanced byin-situ heat supply through combustion

Development in highly active catalysts for the reforming of methane with CO₂ and partial oxidation of methane was conducted to produce hydrogen and carbon monoxide with high reaction rates. An Ni-based four-components catalyst, Ni-Ce₂O₃-Pt-Rh, supported on an alumina wash-coated ceramic fiber in a plate shape was suitable for the objective reaction. By combining the catalytic combustion of ethane or propane, methane conversion was markedly enhanced, and a high space-time yield of syngas, 25,000 mol/l·h was obtained at a catalyst temperature of 700 ‡C or furnace temperature of 500 ‡C. The extraordinary high space-time yield of syngas was also confirmed even under the very rapid flow rate conditions as a contact time of 3 m-sec by using a monolithic shape of catalyst bed without back pressure.     

Temperature profile in a two-stage fixed bed reactor for catalytic partial oxidation of methane to syngas

Detailed axial temperature distribution has been studied in a two-stage process for catalytic partial oxidation of methane to syngas, which consists of two consecutive fixed bed reactors with oxygen or air separately introduced. The first stage of the reactor, packed with a combustion catalyst, is used for catalytic combustion of methane at low initial temperature. While the second stage, filled with a partial oxidation catalyst, is used for the partial oxidation of methane to syngas. A pilot-scale reactor packed with up to 80 g combustion catalyst and 80 g partial oxidation catalyst was employed. The effects of oxygen distribution in the two sections, and gas hourly space velocity (GHSV) on the catalyst bed temperature profile, as well as conversion of methane and selectivities to syngas were investigated under atmospheric pressure. It is found that both oxygen splitting ratio and GHSV have significant influence on the temperature profile in the reactor, which can be explained by the synergetic effects of the fast exothermic oxidation reactions and the slow endothermic (steam and CO₂) reforming reactions. Almost no change in activity and selectivity was observed after a stability experiment for 300 h.     

High-Throughput Screening for the Promoters of Alumina Supported Ni Catalysts in Autothermal Reforming of Methane

The conversion of natural gas(methane) to syngas (reforming reaction) is regarded as alternative routes for production of great value compounds, such as synthetic liquid fuels and oxygenated compounds. The aim of this work is to investigate the highest activity catalyst among 30 catalyst candidates which consists of Ni-M [M (promoter) = Co, Fe, Ce] on γ-Al₂O₃, by combinatorial method for autothermal reforming. The catalyst candidates with different M/Ni molar ratio were prepared by the impregnation method. The consistent results were found between 32 channel reactors and single fixed bed reactor. It was found that the best catalyst is 5.54 wt%Ni-13.3wt% Ce/γ-Al₂O₃.     

Catalytic partial oxidation of methane to syngas in a fixed-bed reactor with an O2-distributor: The axial temperature profile and species profile study

Catalytic partial oxidation of methane (CPOM) to syngas has been investigated in a fixed-bed reactor with an O₂-distributor (FR-OD). The axial temperature profile and species profile along the Ni or Rh-based catalyst bed have been measured at different conditions. As the O₂ was distributed radially into the catalyst bed through several rows of holes arranged at the special zone of the OD, a microenvironment maintaining a low O₂/CH₄ ratio (0.10–0.22) was provided in the catalyst bed. The hotspot phenomena appeared at the entrance of the catalyst bed have been effectively controlled. A more uniform temperature profile along the catalyst bed has been given, which is beneficial to the stability of catalyst and the safety of reactor operation.     

Partial oxidation of methane to synthesis gas over corundum supported mixed oxides: One channel studies

Catalytic partial oxidation of methane (POM) over the monolithic catalyst LaNiO_x/CeO₂–ZrO₂/α-Al₂O₃ has been studied. Experiments were conducted with one channel of a monolith at a varied channel length, contact time (1–6 ms) and temperature using the diluted gas mixture (1% CH₄ + 0.5% O₂ in He). At increasing temperature and contact time, CO selectivity rises within the whole temperature range whereas the contact time dependence of H₂/CO ratio varies with the temperature. These results support the POM reaction scheme including primary formation of CO and H₂ followed by their oxidation in the presence of gas-phase O₂. Steam and dry methane reforming reactions occur in the part of monolithic channel where oxygen is absent, thus increasing syngas yield.     

Effective methane reforming with CO2 and O2 under pressurized condition using NiO–MgO and fluidized bed reactor

Circulation of Ni_0.15Mg_0.85O catalyst particles in the fluidized bed reactor gave much higher CH₄ conversion in methane reforming with CO₂ and O₂ under pressurized condition than the case of the catalyst without moving in the fixed bed reactor. In addition, circulation of the catalyst particles in the fluidized bed reactor inhibited carbon deposition which is the serious problem in methane reforming.