Synthesis gas production using steam hydrogasification and steam reforming

Experimental work has been carried out on the mixed reforming reaction, i.e., simultaneous steam and CO₂ reforming of methane under a wide range of feed compositions and four different reaction temperatures from 700 °C to 850 °C using a commercial steam reforming catalyst. The experiments were conducted for a CO₂/CH₄ ratio from 0 to 2 and a steam to methane ratio from 3 to 5. The effect of CO₂/CH₄ ratio on the exit H₂/CO ratio and the conversions of the reactants indicate that the dry reforming reaction is dominant under increased carbon dioxide in the feed. Steam reforming of typical steam hydrogasification product gas consisting of CO, H₂ and CO₂ in addition to steam and methane has also been investigated. The H₂/CO ratio of the product synthesis gas varies from 4.3 to 3.7 and from 4.8 to 4.1 depending on the feed composition and reaction temperature. The CO/CO₂ ratios of the synthesis gas varied from 1.9 to 2.9 and 2.0 to 3.3. The results are compared with simulation results obtained through the Aspen Plus process simulation tool. The results demonstrate that a coupled steam hydrogasification and reforming process can generate a synthesis gas with a flexible H₂/CO ratio from carbon-containing feedstocks.     

CO2 reforming of CH4 in coke oven gas to syngas over coal char catalyst

The CO₂ reforming of methane (in coke oven gas) on the coal char catalyst was performed in a fixed bed reactor at temperatures between 800 and 1200 °C under normal pressure. The effects of the coal char catalyst pretreatment and the ratio of CO₂/CH₄ were studied. Experimental results showed that the coal char was an effective catalyst for production of syngas, and addition of CO₂ did not enhance the CH₄ reforming to H₂. It was also found that the product gas ratio of H₂/CO is strongly influenced by the feed ratio of CO₂/CH₄. The modified coal char catalyst was more active during the CO₂–CH₄ reforming than the coal char catalyst based on the catalyst volume, furthermore the modified catalyst exhibited high activity in CO₂–CH₄ reforming to syngas. The conversion of methane can be divided into two stages. In the first stage, the conversion of CH₄ gradually decreased. In the second stage, the conversion of methane maintained nearly constant. The conversion of CO₂ decreased slightly during the overall reactions in CO₂–CH₄ reforming. The coal char catalyst is a highly promising catalyst for the CO₂ reforming of methane to syngas.     

Catalytic syngas production from greenhouse gasses: Performance comparison of Ru-Al2O3 and Rh-CeO2 catalysts

In this work, 3% Ru-Al₂O₃ and 2% Rh-CeO₂ catalysts were synthesized and tested for CH₄-CO₂ reforming activity using either CO₂-rich or CO₂-lean model biogas feed. Low carbon deposition was observed on both catalysts, which negligibly influenced catalytic activity. Catalyst deactivation during temperature programmed reaction was observed only with Ru-Al₂O₃, which was caused by metallic cluster sintering. Both catalysts exhibited good stability during the 70 h exposure to undiluted equimolar CH₄/CO₂ gas stream at 750 °C. By varying residence time in the reactor during CH₄-CO₂ reforming, very similar quantities of H₂ were consumed for water formation. Reverse water-gas shift (RWGS) reaction occurred to a very similar extent either with low or high WHSV values over both catalysts, revealing that product gas mixture contained near RWGS equilibrium composition, confirming the dominance of WGS reaction and showing that shortening the contact time would actually decrease the H₂/CO ratio in the syngas produced by CH₄-CO₂ reforming, as long as RWGS is quasi equilibrated. H₂/CO molar ratio in the produced syngas can be increased either by operating at higher temperatures, or by using a feed stream with CH₄/CO₂ ratio well above 1.     

Thermodynamic analysis of dry autothermal reforming of glycerol

Dry autothermal reforming of glycerol uses a combination of dry (CO₂) reforming and partial oxidation reactions to produce syngas rich product stream. Thermodynamic equilibrium data for dry autothermal reforming of glycerol was generated for temperature range 600-1000 K, 1 bar pressure, OCGR [feed O₂/C (C of glycerol only) ratio] 0.1 to 0.5 and CGR [feed CO₂/glycerol ratio] 1 to 5 and analyzed. The objective of the paper is to identify the thermodynamic domain of the process operation, study the variation of product distribution pattern and describe the optimum conditions to maximize yield of the desired product and minimize the undesired product formation. Higher OCGR and higher CGR yielded a syngas ratio (∼ 1), with lower carbon and methane formation, while lower CGR and lower OCGR yielded good hydrogen and total hydrogen, with low water and CO₂ production. The best thermoneutral condition for DATR of glycerol operation was seen at a temperature of 926.31 K at 1 bar pressure, OCGR = 0.3 and CGR = 1 that gave 2.67 mol of hydrogen, 4.8 mol of total hydrogen with negligible methane and carbon formations.     

Simultaneous oxidative conversion and CO2 or steam reforming of methane to syngas over CoO–NiO–MgO catalyst

CO₂ reforming, oxidative conversion and simultaneous oxidative conversion and CO₂ or steam reforming of methane to syngas (CO and H₂) over NiO–CoO–MgO (Co: Ni: Mg=0·5: 0·5:1·0) solid solution at 700–850°C and high space velocity (5·1×10⁵ cm³ g⁻¹ h⁻¹ for oxidative conversion and 4·5×10⁴ cm³ g⁻¹ h⁻¹ for oxy-steam or oxy-CO₂ reforming) for different CH₄/O₂ (1·8–8·0) and CH₄/CO₂ or H₂O (1·5–8·4) ratios have been thoroughly investigated. Because of the replacement of 50 mol% of the NiO by CoO in NiO–MgO (Ni/Mg=1·0), the performance of the catalyst in the methane to syngas conversion process is improved; the carbon formation on the catalyst is drastically reduced. The CoO–NiO–MgO catalyst shows high methane conversion activity (methane conversion >80%) and high selectivity for both CO and H₂ in the oxy-CO₂ reforming and oxy-steam reforming processes at ⩾800°C. The oxy-steam or CO₂ reforming process involves the coupling of the exothermic oxidative conversion and endothermic CO₂ or steam reforming reactions, making these processes highly energy efficient and also safe to operate. These processes can be made thermoneutral or mildly exothermic or mildly endothermic by manipulating the process conditions (viz. temperature and/or CH₄/O₂ ratio in the feed). © 1998 Society of Chemistry Industry     

直流电弧等离子体甲烷二氧化碳重整反应

采用一种简单结构的直流电弧反应器,在无催化剂存在的条件下,高效率地实现了毫秒级甲烷二氧化碳的重整反应,产物选择性好,并且在反应过程中几乎没有积炭生成。在恒定输入功率(170W)的条件下考察了气体总流量和二氧化碳/甲烷摩尔比对反应结果的影响。提高反应气体的输入能量密度可以提高甲烷和二氧化碳的转化率,并且能够有效地抑制副产物的生成。当二氧化碳/甲烷摩尔比为1时,二氧化碳转化率为89.8%,甲烷转化率为96.3%,氢气和一氧化碳的选择性分别为99.6%和99.3%。二氧化碳过量可显著促进甲烷的转化以及同时获得合成气的高选择性。采用比能耗对该过程的能量利用效率进行了分析,以期指导反应条件优化以提高过程的能量利用效率。     

Effects of preparation methods on the properties of cobalt/carbon catalyst for methane reforming with carbon dioxide to syngas

The effect of different preparation methods on the physicochemical property, reforming reactivity, stability and carbon deposition resistance of cobalt/carbon catalyst was investigated through fixed bed flow reaction. The catalysts were prepared by the impregnation and characterized by the XRD and scanning electron microscopy (SEM). The result indicated that the active components of cobalt/carbon catalyst prepared by using ultrasonic wave distributed evenly, activity was high and the loading time was short. The Co/Carbon catalyst prepared by incipient-wetness impregnation, 10 wt% loading and 300 °C calcination, achieved the best activity. Furthermore, the effect of reaction temperature, air speed and CH₄/CO₂ ratio on the catalyst activity and CO/H₂ ratio in products was investigated. It was found that the conversion of CO₂ and CH₄ increased with the increasing of reaction temperature. However, the conversion of CO₂ and CH₄ increased first and then decreased with the increasing of air speed. With the increasing of CH₄/CO₂ in feed gas, both the catalyst activity and the CO/H₂ ratio in products decreased.     

Thermodynamic investigation into carbon deposition and sulfur evolution in a Ca-based chemical-looping combustion system

Chemical-looping combustion is a promising technology that concentrates CO₂ and separates it during combustion. In this study, both the carbon deposition and sulfur evolution in the reduction of a calcium sulfate (CaSO₄) oxygen carrier with a typical syngas were investigated using thermodynamic simulations. The effects of reaction temperature, operating pressure and the oxygen ratio number (defined in this paper) on the amount of deposited carbon and released sulfurous gases are discussed. A reaction temperature from 750 to 950 °C, an operating pressure from 1 to 15 bars and an oxygen ratio number between 0.4 and 0.8 were determined to be the most favorable operating conditions. In addition, the amounts of released sulfurous gases were found to be largely dependent on the partial pressures of H₂ and CO based on the thermo-gravimetric analyzer (TGA) tests. When the partial pressure of H₂ or CO was above 40 kPa, the release of sulfurous gases could be prevented in the reaction between CaSO₄ and syngas, even if the reaction temperature was as high as 1000 °C. The XRD profiles of the products also demonstrated that the mole fraction of CaS in the products increased gradually with an increasing partial pressure of H₂ or CO, until the products were almost pure CaS.     

Methane reforming of syngas produced by co-gasification of coal and wastes. Effect of catalysts and of experimental conditions

Syngas obtained by co-gasification of coal and wastes was hot cleaned in two catalytic reactors, which allowed destroying tar and gaseous hydrocarbons with more than one carbon atom. H₂S and NH₃ contents were also significantly reduced, but CH₄ concentrations varying between 2% and 10% and small amounts of H₂S (below 100 ppmv) were still found in syngas, depending on coal type and waste composition. This paper studies the effect of experimental conditions on CH₄ destruction by reforming reactions in absence and in presence of catalysts. The effect of experimental conditions (temperature, steam flow rate and syngas composition) on CH₄ destruction and on CO conversion into CO₂ in the absence of catalyst was studied first, using the Equilibrium Reactor model from CHEMKIN modelling software. The selected experimental conditions were then tested in a fixed bed reactor with and without catalyst and the results obtained were consistent with CHEMKIN Equilibrium Reactor model predictions. Commercial Ni-based catalysts were tested (G-90 B5 and G 56B from C&CS). These catalysts were capable of significantly reducing CH₄ content, by promoting reforming reactions. At the experimental conditions used and in absence of steam, G 56B seems to be more effective in CH₄ conversion, as lower CH₄ contents were obtained. In presence of steam both catalysts were capable of completely destroying CH₄. Both catalysts also promoted WGS (water gas shift) reaction to some extent, though they are not specific catalysts for this reaction. Thus, a high increase in H₂ content was observed, due to its formation by both reforming and WGS reactions. For a complete conversion of CO into CO₂ and H₂ a specific catalyst for WGS reaction is still needed.     

Effect of three processes on CO2 and O2 simultaneously reforming of coke oven gas to syngas

CO₂ and O₂ simultaneously reforming of coke oven gas (COG) in three processes including non-catalytic process (NCP), catalytic process (CP), and two-stage process (TSP) was investigated under two important operating conditions, CO₂/CH₄ and O₂/CH₄, over Ni-based catalyst in a fixed bed reactor. It was found that the technical indexes depend strongly on CO₂/CH₄ and O₂/CH₄ in different processes. CO₂ can adjust H₂/CO ratio in a wider range (0.52–3.83) in the presence of O₂. The conversions of CH₄ increase in overall COG reforming processes by adding O₂. Also, a little O₂ promotes CO₂ conversions in NCP and restrains CO₂ conversions in CP and TSP. The addition of O₂ can also adjust H₂/CO ratio of syngas, which is actually at the cost of H₂ consumption by oxidation rather than reverse water gas shift (RWGS) reaction. In addition, H₂ combustion in the first-stage of TSP provides heat to drive the endothermic CH₄ reforming reactions and RWGS reaction in the second-stage of TSP to achieve higher CH₄ and CO₂ conversions. Therefore, TSP precedes significantly NCP and CP in the reforming of COG. When H₂/CO ratio is 2.10, the conversions of CH₄ and CO₂ are 98.96 and 62.32% respectively; and, oxygen consumption is 0.13 m³ per COG m³ at gas hour space velocity 9256 h⁻¹ in TSP.     

Enhanced stability of a direct-methane and carbon dioxide protonic ceramic fuel cell with a PrCrO3 based reforming layer

Dry reforming of methane (CH₄ + CO₂ = 2CO + 2H₂) is a very interesting approach both to reduce the overall carbon footprint of the increasing worldwide fossil-based methane consumption as well as to cut emission greenhouse gas of CO₂. Utilizing the produced syngas as fuel directly in protonic ceramic fuel cell can further kill two birds with one stone: obtain power output and high purity CO. However, the drawback of the coking deposition limits the process of the above strategy. Here, we synthesis a Ni-based catalyst with high conversion rates (∼88% for CO₂ and ∼89% for CH₄) and excellent stability (>160 h at 700 °C) proceeded by Ce doping, and further employ it as reforming layer on solid oxide fuel cell. The results demonstrate that the Ce substitution plays an important role for homogenous Ni nanoparticles exsolution, benefiting for the coking resistance of the catalyst then the stability of the cell using CH₄ and CO₂ as fuel directly.     

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.     

Conversion of methane to syngas in a solid oxide fuel cell with Ni-SDC anode and LSGM electrolyte

A solid oxide fuel cell constructed from Ni-SDC anode and LSGM electrolyte was applied to the partial oxidation of methane to syngas (CO+H₂) at 700-800 °C with the merits of co-generation of electricity and controllable O₂ supply. It was found that the co-generated syngas at H₂/CO ratio of 1.4-2.0 varied with applied current densities, CH₄ flow rates and operating temperatures. The cell voltage at 100 mA cm⁻² and 800 °C was 0.90 V, i.e. about 90 mW cm⁻² power density could be obtained. The cell operating at 50 mA cm⁻² for 24 h almost showed no degradation of the cell performance. The observed carbon deposition seemed mainly taking place by CH₄ cracking reaction.     

Catalytic test of supported Ni catalysts with core/shell structure for dry reforming of methane

Supported nickel catalysts with core/shell structures of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ were synthesized under multi-bubble sonoluminescence (MBSL) conditions and tested for dry reforming of methane (DRM) to produce hydrogen and carbon monoxide. A supported Ni catalyst made of 10% Ni loading on Al₂O₃ and MgO-Al₂O₃, which performed best in the steam reforming of methane (97% methane conversion at 750 °C) and in the partial oxidation of methane (96% methane conversion at 800 °C), showed also good performance in DRM and excellent thermal stability for the first 150 h. The supported Ni catalysts Ni/Al₂O₃ and Ni/MgO-Al₂O₃ yielded methane conversions of 92% and 92.5%, respectively and CO₂ conversions of 95.0% and 91.8%, respectively, at a reaction temperature of 800 °C with a molar ratio of CH₄/CO₂ = 1. Those were near thermodynamic equilibrium values.     

Partial oxidation of methane to synthesis gas over Rh/α-Al2O3 at high temperatures

The partial oxidation of methane to synthesis gas has been studied in a continuous flow reactor using a Rh/α-Al₂O₃ catalyst under conditions as close as possible to those industrially relevant: pressures up to 800 kPa and temperatures higher than 1274 K in order to avoid the formation of carbon and to obtain high equilibrium selectivities to CO and H₂. Intrinsic kinetic data were obtained when the feed was diluted with helium. Gas-phase reactions were found to occur at 500 kPa when the feed was not diluted. A reaction network has been derived from experimental results in which oxygen conversions range from 0 to 1. CO₂, C₂H₆ and H₂O are the primary products. C₂H₄ is formed by oxidative dehydrogenation of C₂H₆. CO and H₂ are formed by reforming of CH₄ by CO₂ and H₂O; an additional direct route to CO and H₂ at low oxygen conversions cannot be excluded. The catalyst appears to be present in two states, the transition being at an oxygen conversion of 0.4 under the conditions used. The support probably enhances oxidation reactions by reverse spillover of oxygen or hydroxyl species onto rhodium. The support as such behaves similarly to the catalyst at low oxygen conversions, but shows no reforming activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Carbon Dioxide Reforming of Methane with Pt Catalysts Using Microwave Dielectric Heating

Microwave heating was applied to the catalytic reforming reaction of methane with carbon dioxide over platinum catalysts. It was found that CO₂ and CH₄ conversions and the product selectivity (H₂/CO) were generally higher under microwave conditions than that obtained with conventional heating at the same measured temperature. The effect of microwave heating was attributed to the formation of hot spots with higher temperature than that measured in the bulk catalyst bed.     

Coupling and reforming of methane by means of low pressure radio-frequency plasmas

Non-oxidative coupling of CH₄/H₂ mixtures was carried out by means of radio frequency (rf) glow discharges for the first time. A central composite design was employed to determine the best experimental conditions for methane transformation into higher hydrocarbons and to fit the experimental data. rf power was the factor showing the highest effect on the results while CH₄/H₂ mole ratio showed the lowest. Conversion was 46.4% at 100 W, 0.07 mbar and CH₄/H₂ mole ratio of 1/2. Selectivity was 56.9% for C₂, 6.9% for C₃, and 36.2% for C₄ hydrocarbons. Least squares fits of quadratic equations yielded approximating functions permitting to predict results of random experiments with errors of about 5%. The same rf system was used for the reforming of methane with CO₂, O₂, and steam plasmas, respectively. The highest oxidation was observed with oxygen whilst steam plasma produced the best results. H₂/CO mole ratio was adjusted by setting specific experimental parameters of the latter. CO₂ free synthesis gas was produced at higher H₂O and CH₄ flow rates, i.e. 0.8 mmol/h and higher power, i.e. 100 W. CO₂ and CO free H₂ was produced at 0.3 and 0.6 mmol/h flow rates of H₂O and CH₄, respectively, and 50 W.     

Effect of methane concentration on reaction behavior in direct-methane solid oxide fuel cells with (Ce,Gd)O2−x-impregnated FeCr layer for fuel processing

A solid oxide fuel cell (SOFC) with a Ni-yttria-stabilized zirconia anode of 1 cm² area was set up with a porous disk of gadolinia-doped ceria-impregnated FeCr as a gas diffusion layer (GDL) under direct-methane feeding. In this setup of SOFC plus GDL, the tests at 800 °C and ambient pressure show that the current density, the methane conversion rate, the product formation rates, and the CO₂ selectivity increased with increasing methane concentration. The major reaction in the GDL is CO₂ reforming of methane to produce the syngas (CO plus H₂). The anodic electrochemical oxidation of CO from GDL results in an overall rate of CO₂ formation being much larger than that of CO formation. There is a synergy between the rate of reaction in the GDL and that over the anode.     

Thermodynamic study of combining chemical looping combustion and combined reforming of propane

Existing energy generation technologies emit CO₂ gas and are posing a serious problem of global warming and climate change. The thermodynamic feasibility of a new process scheme combining chemical looping combustion (CLC) and combined reforming (CR) of propane (LPG) is studied in this paper. The study of CLC of propane with CaSO₄ as oxygen carrier shows thermodynamic feasibility in temperature range (400-782.95 °C) at 1 bar pressure. The CO₂ generated in the CLC can be used for combined reforming of propane in an autothermal way within the temperature range (400-1000 °C) at 1 bar pressure to generate syngas of ratio 3.0 (above 600 °C) which is extremely desirable for petrochemical manufacture. The process scheme generates (a) huge thermal energy in CLC that can be used for various processes, (b) pure N₂ and syngas rich streams can be used for petrochemical manufacture and (c) takes care of the expensive CO₂ separation from flue gas stream and CO₂ sequestration. The thermoneutral temperature (TNP) of 702.12 °C yielding maximum syngas of 5.98 mol per mole propane fed, of syngas ratio 1.73 with negligible methane and carbon formation was identified as the best condition for the CR reactor operation. The process can be used for different fuels and oxygen carriers.     

Carbon dioxide reforming of methane with a free energy minimization approach

Carbon dioxide reforming of methane to syngas is one of the primary technologies of the new poly-generation energy system on the basis of gasification gas and coke oven gas. A free energy minimization is applied to study the influence of operating parameters (temperature, pressure and methane-to-carbon dioxide ratio) on methane conversion, products distribution, and energy coupling between methane oxidation and carbon dioxide reforming methane. The results show that the methane conversion increases with temperature and decreases with pressure. When the methane-to-carbon dioxide ratio increases, the methane conversion drops but the H₂/CO ratio increases. By the introduction of oxygen, an energy balance in the process of the carbon dioxide reforming methane and oxidation can be realized, and the CO/H₂ ratio can be adjusted as well without water-gas shift reaction for Fischer-Tropsch or methanol synthesis. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.