Syngas production in a novel perovskite membrane reactor with co-feed of CO2

Partial oxidation of methane（POM） co-fed with CO₂ to syngas in a novel catalytic BaCo_0.6Fe_0.2Ta_0.2O_3-δ oxygen permeable membrane reactor was successfully reported.Adding CO₂ to the partial oxidation of methane reaction not only alters the ratio of CO/H₂,but also increases the oxygen permeation flux and CH₄ conversion.Around 96%CH₄ conversion with more than 93%CO₂ conversion and 100%CO selectivity is achieved,which shows an excellent reaction performance.A steady oxygen permeation flux of 15 mL/（cm² min） is obtained during the 100-h operation,which shows good stability as well.     

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

Dense planar and tubular oxygen separation membranes of La_0.5Sr_0.5FeO_{3 −  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.     

La1-xSrxFeO3钙钛矿型氧化物中的晶格氧用于甲烷部分氧化制合成气

采用燃烧法制备了Sr掺杂钙钛矿型氧化物La_1-xSr_xFeO₃（x=0,0.3,0.5,0.9）载氧体,对载氧体分别进行X射线衍射、扫描电镜和H₂程序升温还原反应表征,在热重循环装置和固定床反应装置上考察甲烷与载氧体晶格氧的部分氧化反应.结果表明,La_1-xSr_xFeO₃氧化物中的晶格氧适用于甲烷部分氧化制合成气,晶格氧的得失是一个可逆过程,Sr的掺杂提高了载氧体的供氧能力,5次循环后载氧体得失晶格氧的能力没有明显的衰减.从甲烷转化率、n（H₂）/n（CO）比以及H₂和CO的选择性等方面来考虑,x=0.3-0.5比较理想,甲烷转化率维持在70%左右,气体产物中n（H₂）/n（CO）约为2,CH₄没有发生明显的裂解.     

A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄-H₂O-O₂ reaction in membrane reactor and the reaction close to CH₄ + 0.35O₂ + 1.3H₂O → CO₂ + 3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C₂ selectivity up to 40–70% was achieved, albeit that conversion rate were low, typically 0.5–3.5% at 800–900°C with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/γ-Al₂O₃ with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH₄ conversion, 93.0% CO selectivity and 10.45 ml/cm² min oxygen permeation flux were achieved under steady state at 850°C. Methane conversion and oxygen permeation flux increased with increasing temperature. No fracture of the membrane reactor was observed during syngas production. However, H₂-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875°C for more than 500 h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm² min.     

Combination of CO2 reforming and partial oxidation of CH4 over Ni/Al2O3 catalysts using fluidized bed reactor

The effects of the Ni loading, total feed flow rate, prereduction temperature, reaction temperature and feed gas ratio for combination of CO₂ reforming and partial oxidation of CH₄ over Ni/Al₂O₃ were investigated using a fluidized bed reactor. Methane conversion to syngas was drastically enhanced using a fluidized bed reactor over Ni/Al₂O₃ catalyst calcined at high temperature. The fluidized bed and the fixed bed reactor were compared and a promoting mechanism of the fluidized bed reactor was proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

NiO-CaO materials as promising catalysts for hydrogen production through carbon dioxide capture and subsequent dry methane reforming

In this work, CaO-NiO mixed oxide powders were evaluated as consecutive CO_2 chemisorbents and catalytic materials for hydrogen production thought the CH_4 reforming process. Between the NiO impregnated CaO and CaO-NiO mechanical composite, the first one presented better chemical behaviors during the CO_2 capture and CH_4 reforming processes, obtaining syngas(H_2+ CO) as final product. Results showed that syngas was produced at two different temperature ranges, between 400 and 600 °C and at T 800 °C, where the first temperature range corresponds to the CH_4 reforming process but the second temperature range was attributed to a different catalytic reaction process: CH_4 partial oxidation. These results were confirmed through different isothermal and cyclic experiments as well as by XRD analysis of the final catalytic products, where the nickel reduction was evidenced. Moreover, when a CO-O_2 flow was used during the carbonation process a triple process was achieved:(i) CO oxidation,(ii) CO_2 chemisorption and(iii) CH_4 reforming. Using this gas flow the hydrogen production was always higher than that obtained with CO_2.     

The oxidative stream reforming of methane to syngas in a thin tubular mixed-conducting membrane reactor

The oxidative stream reforming of methane (OSRM) to syngas, involving coupling of exothermic partial oxidation of methane (POM) and endothermic steam reforming of methane (SRM) processes, was studied in a thin tubular Al₂O₃-doped SrCo_0.8Fe_0.2O_3−δ membrane reactor packed with a Ni/γ-Al₂O₃ catalyst. The influences of the temperature and feed concentration on the membrane reaction performances were investigated in detail. The methane and steam conversions increased with increasing the temperature and high conversions were obtained in 850–900 °C. Different from the POM reaction, in the OSRM reaction the temperature and H₂O/CH₄ profoundly influenced the CO selectivity, H₂/CO and heat of the reaction. The CO selectivity increased with increasing the temperature or decreasing the H₂O/CH₄ ratio in the feed owing to the water gas shift reaction (H₂O + CO → CO₂ + H₂). And the H₂ selectivity based on methane conversion was always 100% because the net steam conversion was greater than zero. The H₂/CO in product could be tuned from 1.9 to 2.8 by adjusting the reaction temperature or H₂O/CH₄. Depending on the temperature or H₂O/CH₄, furthermore, the OSRM process could be performed auto-thermally with idealized reaction condition.     

Planar and tubular perovskite-type membrane reactors for the partial oxidation of methane to syngas

Dense planar and tubular oxygen separation membranes of La_0.6Ca_0.4Fe_0.75Co_0.25O_3– were investigated as reactors for the partial oxidation (POX) of methane to syngas. Their permeation properties were measured in an air/argon pO₂ gradient as a function of temperature. At 900 °C, the oxygen flux through a 1.26-mm-thick membrane was 0.075 mol/cm²·s and through a 0.25-mm-thick tube, 0.24 mol/cm²·s.For the POX measurements, a catalyst was added to the membrane and methane was introduced on the argon side. This resulted in a gradual increase of the oxygen flux with increasing concentration of methane, reaching 2 mol/cm²·s at 900 °C with pure methane. For the planar reactor, the CO selectivity reached 99% and the CH₄ conversion 75% at 918 °C with pure methane. For the tubular reactor, the CO selectivity and CH₄ conversion were 83 and 99%, respectively, under the same conditions. After 1,400 h of operation in a tubular POX reactor, the membrane was examined revealing phase demixing and local decomposition.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

化学循环重整甲烷制合成气LaBO3钙钛矿型氧载体研究

采用溶胶-凝胶法制备了不同B位可变价离子的La-B-O复合氧载体(B=Cr、Ni),采用XRD、BET、FT-IR、H2-TPR及CH4-TPSR等进行了表征,并用于化学循环重整(CLR)CH4反应中.结果表明,LaNiO3氧化物更易于与CH4发生深度氧化和选择氧化,LaCrO3氧化物则利于CH4裂解,其氧物种氧化CH4的能力较弱.在连续流动CLR反应中,LaNiO3具有较高的供氧量和持续供氧能力,能将CH4选择氧化为H2/CO=1.45的合成气,其CH4转化率和CO选择性分别达到23.4%和86.9%,且其结构保持了较高的稳定性.     

Tap study of the impact of the oxidation state of Pt/PrCeZrO and Pt/GdCeZrO catalysts on their reactivity in the partial/deep oxidation of methane

The temporal analysis of products (TAP) technique coupled with the oxygen TPD was used to elucidate the effects of the Pt-supported fluorite-like doped ceria–zirconia oxide chemical composition and the type of pretreatment on their oxygen bonding strength, mobility, and reactivity as related to catalytic properties in the partial oxidation of methane into synthesis gas. A rapid evolution of hydrogen under CH₄ pulse observed for oxidized catalysts agrees with the direct route of the methane selective oxidation into syngas. This route is favored by the Pt-support interaction and a moderate bonding strength of surface oxygen species along with a high lattice oxygen mobility.     

Pyrolysis and Oxidation of Methane in a RF Plasma Reactor

The chemical kinetic effects of RF plasma on the pyrolysis and oxidation of methane were studied experimentally and computationally in a laminar flow reactor at 100 Torr and 373 K with and without oxygen addition into He/CH₄ mixtures. The formation of excited species as well as intermediate species and products in the RF plasma reactor was measured with optical emission spectrometer and Gas Chromatography and the data were used to validate the kinetic model. The kinetic analysis was performed to understand the key reaction pathways. The experimental results showed that H₂, C₂ and C₃ hydrocarbon formation was the major pathways for plasma assisted pyrolysis of methane. In contrast, with oxygen addition, C₂ and C₃ formation dramatically decreased, and syngas (H₂ and CO) became the major products. The above results revealed oxygen addition significantly modified the chemistry of plasma assisted fuel pyrolysis in a RF discharge. Moreover, an increase of E/n was found to be more beneficial for the formation of higher hydrocarbons while a small amount of oxygen was presented in a He/CH₄ mixture. A reaction path flux analysis showed that in a RF plasma, the formation of active species such as CH₃, CH₂, CH, H, O and O (¹D) via the electron impact dissociation reactions played a critical role in the subsequent processes of radical chain propagating and products formation. The results showed that the electronically excitation, ionization, and dissociation processes as well as the products formation were selective and strongly dependent on the reduced electric field.     

A Highly Efficient Sandwich‐Like Symmetrical Dual‐Phase Oxygen‐Transporting Membrane Reactor for Hydrogen Production by Water Splitting

Water splitting coupled with partial oxidation of methane (POM) using an oxygen‐transporting membrane (OTM) would be a potentially ideal way to produce high‐purity hydrogen as well as syngas. Over the past decades, substantial efforts have been devoted to the development of supported membranes with appropriate configurations to achieve considerable performance improvements. Herein, we describe the design of a novel symmetrical membrane reactor with a sandwich‐like structure, whereby a largescale production (>10 mL min^?1 cm^?2) of hydrogen and syngas can be obtained simultaneously on opposite sides of the OTM. Furthermore, this special membrane reactor could regenerate the coke‐deactivated catalyst in situ by water steam in a single unit. These results represent an important first step in the development of membrane separation technologies for the integration of multiple chemical processes.     

Mixed ionic–electronic conducting (MIEC) ceramic-based membranes for oxygen separation

Although Nernst observed ionic conduction of zirconia–yttria solutions in 1899, the field of oxygen separation research remained dormant. In the last 30 years, research efforts by the scientific community intensified significantly, stemming from the pioneering work of Takahashi and co-workers, with the initial development of mixed ionic–electronic conducting (MIEC) oxides. A large number of MIEC compounds have been synthesized and characterized since then, mainly based on perovskites (ABO_3−δ and A₂BO_4±δ) and fluorites (A_δB_1−δO_2−δ and A_2δB_2−2δO₃), or dual-phases by the introduction of metal or ceramic elements. These compounds form dense ceramic membranes, which exhibit significant oxygen ionic and electronic conductivity at elevated temperatures. In turn, this process allows for the ionic transport of oxygen from air due to the differential partial pressure of oxygen across the membrane, providing the driving force for oxygen ion transport. As a result, defect-free synthesized membranes deliver 100% pure oxygen. Electrons involved in the electrochemical oxidation and reduction of oxygen ions and oxygen molecules respectively are transported in the opposite direction, thus ensuring overall electrical neutrality. Notably, the fundamental application of the defect theory was deduced to a plethora of MIEC materials over the last 30 years, providing the understanding of electronic and ionic transport, in particular when dopants are introduced to the compound of interest. As a consequence, there are many special cases of ionic oxygen transport limitation accompanied by phase changes, depending upon the temperature and oxygen partial pressure operating conditions. This paper aims at reviewing all the significant and relevant contribution of the research community in this area in the last three decades in conjunction with theoretical principles.     

A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄?H₂O?O₂ reaction in membrane reactor and the reaction close to CH₄+0.35O₂+1.3H₂O→CO₂+3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

Applications of catalytic inorganic membrane reactors to refinery products

Catalytic membrane reactors are reviewed as applied to opportunities and applications within petroleum refineries. Since so many inorganic membranes take advantage of H₂ permselectivity and H₂ demands are increasing in a refinery, there are a number of interesting process applications being considered. H₂ production can be enhanced by using Pd based membranes for dehydrogenation, oxydehydrogenation, and decomposition reactions. Permselective H₂ membranes could be used for carrying out selective hydrogenations of organic substrates and coupled reactions. These membranes have been also considered for enhancing steam reforming reactions for the production of bulk H₂, the water gas shift reaction, and the conversion of natural gas to syngas and liquid fuels. Dense oxide membranes are also being developed for the selective oxidation of CH₄ to syngas. For many of these processes, the formation of carbon during steam reforming or dehydrogenation reactions will always be a huge hurdle towards any successful commercial application of Pd membranes to such processes. In any of these applications one has to understand production problems associated with the metal membranes, the refinery demands for high purity H₂, and the reactor fabrication hurdles; these will be evaluated with recent examples. For all these applications, the critical issues that need to be resolved for the commercial use of catalytic membrane reactors will be discussed.     

Effect of oxygen addition on the hydrogen production from ethanol steam reforming in a Pd–Ag membrane reactor

In this communication, a porous stainless steel (PSS) tube was electrolessly plated into Pd–Ag membrane reactor which was used for separating hydrogen produced in an ethanol steam reforming reaction with the addition of oxygen, which has not been reported before. Palladium and silver were deposited on porous stainless steel tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. Ethanol–water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with MDC-3. The reaction temperatures were set at 593–723 K and the pressures 3–10 atm. The effect of oxygen addition plays a vital role on the ethanol steam reforming reaction, especially for the Pd–Ag membrane reactor in which a higher flux of hydrogen is required. If oxygen in the feed is not sufficient, it would be possible that steam reforming reaction prevails. Inversely, high O₂ addition will shift the reaction scenario to be partial oxidation dominating, and selectivity of CO₂ increases with increasing oxygen feed. At high pressure, autothermal reaction of ethanol would be easily reached.     

Photoassisted Selective Steam and Dry Reforming of Methane to Syngas Catalyzed by Rhodium–Vanadium Bimetallic Oxide Cluster Anions at Room Temperature

Photoassisted steam reforming and dry (CO₂) reforming of methane (SRM and DRM) at room temperature with high syngas selectivity have been achieved in the gas-phase catalysis for the first time. The catalysts used are bimetallic rhodium–vanadium oxide cluster anions of Rh₂VO_1–3⁻. Both the oxidation of methane and reduction of H₂O/CO₂ can take place efficiently in the dark while the pivotal step to govern syngas selectivity is photo-excitation of the reaction intermediates Rh₂VO_2,3CH₂⁻ to specific electronically excited states that can selectively produce CO and H₂. Electronic excitation over Rh₂VO_2,3CH₂⁻ to control the syngas selectivity is further confirmed from the comparison with the thermal excitation of Rh₂VO_2,3CH₂⁻, which leads to diversity of products. The atomic-level mechanism obtained from the well-controlled cluster reactions provides insight into the process of selective syngas production from the photocatalytic SRM and DRM reactions over supported metal oxide catalysts.     

TG measurement of reactivity of candidate oxygen carrier materials

This study examined several candidate raw materials for use as the reactive agents in developing new oxygen carriers for chemical looping combustion. A thermogravimetric analyzer, Mettler TGA/DSC1, was used to measure oxygen capacity and relative reaction rates during oxidation and reduction cycles. The reactive gases used were 4 % hydrogen in inert gas for the reduction cycle and air for the oxidation cycle, with a nitrogen purge between reduction and oxidation cycles. Samples were typically tested for at least ten cycles to study any change in reactivity or oxygen capacity. Reaction temperatures tested ranged from 700 to 900 °C. Materials tested included an iron oxide ore, iron-based tailings from a metals extraction process, a nickel oxide supported on nickel aluminate and a copper oxide plus inert material system. The materials varied in their oxygen capacity, reactivity and the change in properties with repeat cycles. Of the samples tested, the NiO–NiAl₂O₄ oxygen carrier demonstrated the fastest reaction in reduction and oxidation and had stable properties over ten cycles. The iron oxide ore sample performance declined significantly with repeat cycles. The performance of the iron-based tailings declined slightly over the ten cycles. The addition of inert second phase materials to CuO improved the performance by inhibiting sintering of the oxide at the operating temperature. Although the reactivity of the tailings and iron hydroxide samples was not as high as the NiO based oxygen carrier, they are promising carrier materials due to their low cost and lower toxicity relative to nickel. Future experiments will look at CO and CH₄ reduction reactions using the TG, surface characterization using SEM, XRD, and cyclic testing in a batch fluidized bed reactor.     

Partial oxidation of ethane to syngas in an oxygen-permeable membrane reactor

A perovskite-type oxide of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) with mixed electronic and oxygen ionic conductivity at high temperatures was used as an oxygen-permeable membrane. A tubular membrane of BSCFO made by extrusion method has been used in the membrane reactor to exclusively transport oxygen for the partial oxidation of ethane (POE) to syngas with catalyst of LiLaNiO/γ-Al₂O₃ at temperatures of 800–900 °C. After only 30 min POE reaction in the membrane reactor, the oxygen permeation flux reached at 8.2 ml cm⁻² min⁻¹. After that, the oxygen permeation flux increased slowly and it took 12 h to reach at 11.0 ml cm⁻² min⁻¹. SEM and EDS analysis showed that Sr and Ba segregations occurred on the used membrane surface exposed to air while Co slightly enriched on the membrane surface exposed to ethane. The oxygen permeation flux increased with increasing of concentration of C₂H₆, which was attributed to increasing of the driving force resulting from the more reducing conditions produced with an increase of concentration of C₂H₆ in the feed gas. The tubular membrane reactor was successfully operated for POE reaction at 875 °C for more than 100 h without failure, with ethane conversion of ∼100%, CO selectivity of >91% and oxygen permeation fluxes of 10–11 ml cm⁻² min⁻¹.