Mixed Reforming Research Articles

Introduction to the modeling of complex chemical reaction equilibrium using gPROMS® and GAMS®

AbstractIn the present paper several aspects of the simulation of complex chemical equilibrium are discussed, using two research and educational software: gPROMS® and GAMS®. All computations are performed to boost the understanding of chemical engineering students, undergraduate, and graduate, of the complex concepts behind both thermo‐chemical processes and optimization techniques. Four case studies with varying levels of difficulty illustrate the proposed methodology and robustness of the modeling systems: Catalytic steam reforming of bio‐ethanol at high temperatures. Partial oxidation of naphthalene using either air or pure oxygen. Supercritical water gasification of Microalga Spirulina. Dry and mixed reforming of glucose.Our results indicate that the use of optimization tools offered bygPROMS® and GAMS®software are useful and efficient tools to calculate the chemical and phase equilibrium by minimizing the Gibbs energy, provided that adequate initial guesses are used. Furthermore, the computational time spent in the calculations was generally quite short. The obtained equilibrium compositions are benchmarked using the ubiquitous process simulators: ASPEN‐Plus® and/or ASPEN‐Hysys® as well as data available from the open literature. We obtained excellent agreement between our results and their counterpart obtained using ASPEN‐Plus®. In the last part of this manuscript, authors share their experience in supervising senior term projects on the subject. A questionnaire was used to collect qualitative and quantitative feedback from the nine students involved in the projects. Their responses to a questionnaire focused on the chemical engineering thermodynamics theory as well as software usage during their investigations. This questionnaire demonstrates that students can overcome mathematical complexity by either using mathematical software or equivalent modeling systems (e.g., Matlab®, Mathematica©, gPROMS®, and GAMS®).

Mixed reforming of methane over Ni–K/CeO2–Al2O3: Study of catalyst performance and reaction kinetics

Syngas can be effectively produced by mixed reforming of methane (MRM). In this work, the performance of Ni–K/CeO2–Al2O3 catalyst in this process was investigated in a fixed-bed reactor in the 923–1073 K range. Both potassium and ceria are renowned for improving the performance of Ni catalyst in the reforming process. The influence of reaction conditions (viz. temperature, space time, feed composition and time-on-stream) on the conversion of two reactants CH4 and CO2, yield of the products H2 and CO and the H2/CO ratio in syngas were studied. At T = 1073 K and W/Q0 = 0.17 g-h/L (here, W and Q0 denote catalyst mass and volumetric flow rate of feed), conversions of CH4 and CO2 were 91.2 and 80.1%. When S/C ratio (or steam-to-carbon ratio) in feed increased from 0.2 to 0.5 mol/mol, H2/CO ratio at T = 1073 K changed from 1.32 to 2.14 mol/mol. The catalyst performed stably for 50 h of time-on-stream. Reaction kinetics was studied between 973 and 1073 K and power law kinetic model was suggested. The apparent activation energy values for consumption of CH4 and CO2 were found to be 33.3 and 45.5 kJ/mol, respectively. This work is expected to aid catalyst development and reactor design for the MRM process.

Process design and simulation study: CO2 utilization through mixed reforming of methane for methanol synthesis

A case study is performed using Aspen HYSYS to investigate CO2 utilization for methanol synthesis. The base case is a conventional steam methane reforming process for methanol production. Two modified cases (mixed reforming with/without CO2 capture after the reformer) are developed with the aim to increase CO2 utilization. Simulation results revealed that both stoichiometric number and CO/CO2 ratio played an important role on syngas reactivity, which led to an overall increase in methanol yield. As a result, the volume of unreacted gas in the synthesis loop was reduced and allowed for a smaller reactor design. In terms of overall CO2 intensity, no significant improvements can be observed since the base case had a large volume of H2 rich purged gas sent to the reformer furnace. When the purged gas was not used as a reformer fuel, the CO2 intensity of the other cases became 50% less than the base case.

Efficient removal of the carbon deposits formed during the mixed methane reforming over Ni/Al2O3

This work investigates the process of elimination of carbon deposits formed during the mixed reforming of methane mixture. The mixed reforming of methane to synthesis gas was studied over Ni/Al2O3 catalyst in the 650–750°C. The amount of carbon deposit on the surface of catalyst varied from 2.8 to 5.9%, depending on the reaction temperature. The reactivity of carbon species was evaluated in the oxygen, hydrogen, carbon dioxide, and water mixtures. The obtained results revealed the presence of highly active carbon form (etched at a temperature below 200 °C) and inactive form (gasification at a temperature above 500 °C). The SEM and Raman analyses confirmed the presence of carbon in the form of filaments. Among all investigated gasification agents, water vapor was found to be the most efficient in removing the carbon deposit due to better adsorption of water on the surface of aluminum oxide. The overall mechanism of mixed methane reforming along with carbon gasification was shown.

CO2-utilization in the synthesis of methanol: Potential analysis and exergetic assessment

Carbon capture and utilization represents a major strategy to reduce anthropogenic CO2-emissions by valorization to chemical and petrochemical products. The integration of CO2 is not only aimed at abating emissions, but also at a partial substitution of raw materials, most of which are fossil fuels. In this context, Gas-to-Liquid processes are of great importance, in particular the production of methanol from its predominating feedstock natural gas. In the present study the CO2-utilization potential and impact of CO2-integration measures in methanol synthesis routes are investigated and assessed from a thermodynamic point of view. Sensitivity analyses for an estimation of the CO2-integration potential by dry reforming and direct hydrogenation are carried out. In a dry-reforming process, a carbon dioxide-to-methane mole ratio of one results from tradeoffs among the CH4-conversion, the desired syngas composition, and the heat demand.Regarding the direct hydrogenation, a CO2 inlet fraction of 10 mol-% is recommended for a pareto-optimal operation with a high product yield and a large conversion rate for CO2. The CO2-integration measures are implemented into three processes to evaluate and assess their effects on the overall systems by means of an exergetic analysis. The processes mainly differ in regard to the reforming technology and use conventional steam reforming, dry reforming by CO2, and mixed reforming. Compared to a conventional production process, the natural gas feed is successfully decreased by 38.7 t/h, 50.3 t/h and 61.4 t/h, while an amount of 191.5 kgCO2, 89.3 kgCO2, 425.8 kgCO2 per MWh total exergy of product can be abated, respectively. The process with mixed reforming exhibits a large exergetic efficiency of 48.6%, resulting from a careful integration of CO2 in conjunction with further syngas conditioning units. The processes with steam reforming and dry reforming have, however, lower efficiencies (31.1% and 39.8%, respectively) due to large irreversibilities within the furnace and the steam cycle, which result from the required large amounts for high-temperature process heat. The analyses show that the CO2 stream must be integrated carefully to the plant in order to avoid an excessive increase of the irreversibilities.

Techno-economic and environmental analyses of a novel, sustainable process for production of liquid fuels using helium heat transfer

In this paper, several new processes are proposed which co-generate electricity and liquid fuels (such as diesel, gasoline, or dimethyl ether) from biomass, natural gas and heat from a high temperature gas-cooled reactor. This carbonless heat provides the required energy to drive an endothermic steam methane reforming process, which yields H2-rich syngas (H2/CO > 6) with lower greenhouse gas emissions than traditional steam methane reforming processes. Since downstream Fischer-Tropsch, methanol, or dimethyl ether synthesis processes require an H2/CO ratio of around 2, biomass gasification is integrated into the process. Biomass-derived syngas is sufficiently H2-lean such that blending it with the steam methane reforming derived syngas yields a syngas of the appropriate H2/CO ratio of around 2. In a prior work, we also demonstrated that integrating carbonless heat with combined steam and CO2 reforming of methane is a promising option to produce a syngas with proper H2/CO ratio for Fischer-Tropsch and methanol/dimethyl ether applications. In this study, we presented another novel design called gas-nuclear-to-liquids process which can be applied for liquid fuel production without needing H2/CO adjustment. Chemical process simulations of several candidate processes were developed, which used the rigorous multi-scale, two-dimensional, heterogeneous models for the carbonless-heat-powered steam methane reforming and mixed reforming of methane processes developed in prior works in gPROMS. In addition, 1D process models within Aspen Plus were also used (Aspen Plus simulation and gPROMS models are provided to the reader). The performance of the presented systems was compared with a biomass-gas-to-liquids plant where heat from gasification drives the steam methane reforming instead of the high temperature gas-cooled reactor. Techno-economic analyses and greenhouse gas life cycle analyses of each case were completed to investigate the economic and environmental impacts of the proposed processes. Optional carbon capture and sequestration technology is also considered. The analysis demonstrates that carbonless heat integration leads to thermal efficiencies of up to 55% (high heating value based) as well as suitable profits in the right market conditions. It is also found that net negative life cycle greenhouse gas emissions of the final products can be achieved owing to use of biomass, carbonless heat, and carbon capture and sequestration. Even without carbon capture and sequestration, the life cycle greenhouse gas emissions of the proposed process are 25–57% lower than traditional natural gas-to-dimethyl ether and coal-to- dimethyl ether processes.

Using multi-criteria and thermodynamic analysis to optimize process parameters for mixed reforming of biogas

Syngas is a gas mixture that can be obtained from a variety of raw materials and used as source of hydrogen. Biogas is an interesting raw material from which to produce syngas via thermo-catalytic reforming because it is abundant, can be obtained from low-cost feedstock, and is potentially carbon-neutral. However, difficulties arise because biogas composition changes from source to source, the reforming process can be quite energy-intensive and there is associated catalyst deactivation through carbon deposition. Mixed reforming of biogas with steam and/or air shows benefits in terms of carbon deposition and energy requirements, but the reaction network is complicated and finding the optimal operating conditions is not trivial. Although several analytical techniques have been used in the literature to find the optimal process conditions, a direct comparison is difficult due to the different criteria and/or boundaries considered. This paper aims to develop a novel and comprehensive methodology for identifying the optimal thermodynamic operating conditions (temperature and feed ratios) for mixed reforming of biogas with air and steam, based on equilibrium data manipulated via two multi-criteria decision making (MCDM) techniques in series, namely the entropy and the TOPSIS methods. The optimal scenario is when biogas made of 50–60% CH4 in CO2 is reacted in the reforming reactor at CH4/CO2/O2/H2O = 1/1–0.67/0–0.1/3–2.4 and 790-735 °C, resulting in a product stream composed of 66–65% H2, 0.8–1% CO and 33-28% CO2 on a dry basis after the water-gas shift section. At these conditions the hydrogen yield and the conversion of methane in the biogas can be simultaneously maximized, while the yield of solid carbon and the net energy requirement of the overall process can be minimized. In conjunction with the numerical results, the main outcome of this paper is the development of a novel method based on MCDM techniques for the optimization of the operating conditions in a network of reactions.

Thermodynamic analysis of a new chemical looping process for syngas production with simultaneous CO2 capture and utilization

Since typical CO2 capture technologies lack the consideration of a reliable CO2 storage method or integration with CO2 utilization, this study proposes a new chemical looping reforming process for syngas production with simultaneous CO2 capture and utilization. It integrates chemical looping, mixed reforming (i.e. CO2 reforming and partial oxidation) and calcium looping using CO2 carriers (CCs) and oxygen carriers (OCs). This novel process implements energy-efficient operation, attains flexible H2/CO ratio, and captures CO2 with immediate CO2 conversion. Through thermodynamic screening, Fe- and Cu-based metal/metal oxides and CaO and MnO are identified as the potential OCs and CCs. For process characteristics, almost full CO2 capture is achieved, CH4 conversion rate is over 92.11%, maximum CO2 utilization rate is 99.18%, H2/CO ratio is close to 2, and energy consumption is reduced by 40.74% and 68.62% compared to that of conventional mixed reforming and tri-reforming processes, respectively. Steam addition, low pressure and high temperature are benefit to enhance system performance. From experiment results, gas product distribution, solid reactivity and crystalline phases for solid demonstrate the feasibility of this novel process. More importantly, this process provides a new route to achieve integrated CO2 capture and conversion with the clean usages of carbonaceous energy sources.

Supported Ru−Ni Catalysts for Biogas and Biohydrogen Conversion into Syngas

Catalytic properties of monometallic Ni and bimetallic Ru–Ni supported on Al2O3, CaO–Al2O3, and MgO–Al2O3 have been studied in mixed reforming of methane. Physicochemical properties of the catalytic systems have been studied by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscope and temperature-programmed reduction by hydrogen. It has been shown that, of all the studied samples, the highest conversion of methane and carbon dioxide is achieved in the presence of the Ru−Ni/MgO–Al2O3 bimetallic catalyst. Temperature-programmed reduction has confirmed the effect of hydrogen spillower from ruthenium to NiO. The formation of Ru–Ni alloy has also been found.

Carbon Deposits Formed on the Surface of Ru–Ni Catalysts During the Mixed Reforming of Methane Process

Monometallic nickel and bimetallic ruthenium–nickel catalysts supported onto aluminum oxide without additives and aluminum oxide modified with MgO and CaO were prepared by an impregnation method. The catalysts were tested in the process of the mixed reforming of methane, and their properties were characterized by thermogravimetry, scanning electron microscopy, and X-ray diffractometry. The total organic carbon content of the catalysts was also measured. The promoting effect of ruthenium and structural promoters on the catalytic activity of Ni/Al2O3 was confirmed. The Ru–Ni/MgO–Al2O3 catalyst exhibited the highest stability and activity; this fact can be explained by the increased adsorption of methane on the surface of ruthenium–nickel clusters.

Dynamic Modeling of Integrated Mixed Reforming and Carbonless Heat Systems

In the previous study, a dynamic and two-dimensional model for a steam methane reforming process integrated with nuclear heat production was developed. It was shown that the integrated high temperature gas-cooled reactor (HTGR)/steam methane reforming (SMR) is an efficient process for applications such as hydrogen production. In this study, it is demonstrated that combining nuclear heat with the mix of steam and dry reforming process can be a promising option to achieve certain desired H2/CO ratios for Fischer–Tropsch or other downstream energy conversion processes. The model developed in the previous study is extended to the combined steam and dry reforming process. The resulting model was validated using reported experimental data at nonequilibrium and equilibrium conditions. The dynamic and steady state performance of the integrated mixed reforming of methane and nuclear heat system was studied, and it was found that in addition to desired H2/CO ratios, higher methane conversion and lower CO2 emissions...

Carbon dioxide reforming of methane over Ni/Mg0.4Al0.4-La0.1Zr0.1(O) catalyst prepared by recombination sol–gel method

Based on several catalysts preparation methods, we developed a new sol–gel method and produce a series of quaternary catalysts Ni/MgxAlx-La0.5-xZr0.5-x(O) (x = 0, 0.13, 0.25, 0.33, 0.4, 0.43, 0.5) using different ratios of binary metallic oxide (MgAl(O) to LaZr(O)). The synthesized samples were employed in the dry reforming of methane (DRM) and mixed reforming of hydrocarbons (CH4 & C2H6) (MRH) to evaluate their performances at 800 °C under atmospheric pressure. The experimental result indicates that the catalytic activity was mainly dependent on the interaction between active component (NiO particle) and support, and Ni/Mg0.4Al0.4-La0.1Zr0.1(O) exhibited the highest activity (CH4 96.1% & CO2 95.9%) during DRM. The physicochemical properties of these catalysts were analyzed by N2 adsorption–desorption, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), H2 temperature-programmed reduction (H2-TPR) and thermogravimetric analysis (TGA). The TPR analysis result illustrated that strong interaction between Ni active species and support was observed on catalysis Ni/Mg0.4Al0.4-La0.1Zr0.1(O), increasing the stability of Ni and thus enhanced both abilities of anti-sintering and anti-coking during the reaction. The XRD characterization of fresh and used Mg0.4Al0.4-La0.1Zr0.1(O) witnessed that the active component Ni was well dispersed on the support, and the minimal carbon deposition was detected on the used Ni/Mg0.4Al0.4-La0.1Zr0.1(O) by TGA and SEM compared with other catalysts. The 80 h activity test confirmed that the Mg0.4Al0.4-La0.1Zr0.1(O) can still perform high conversions (both CH4 & CO2 > 95% after 80 h) and stability after a long time DRM reaction. Moreover, the quaternary Ni/Mg0.4Al0.4-La0.1Zr0.1(O) is also suitable for mixed hydrocarbons reforming to produce syngas, which showed its excellent performance (CH4 94%, CO2 96% and C2H6 100%) during the reaction and may be widely used in the future.

On the dry and mixed reforming of methane over Ni/Al2O3 – Influence of reaction variables on syngas production

Dry and mixed reforming of methane (DRM and MRM) are candidate routes for the production of synthesis gas. By this way, two Greenhouse gases CH4 and CO2 can be effectively valorised. In the present work, activity trials were performed in a fixed bed reactor using commercial Ni/Al2O3 catalyst. The reaction variables were so varied: temperature 773–1073 K, space time 0.08–0.33 g h/L, CO2/CH4 0.5–2 mol/mol (for DRM) and steam/carbon ratio 0.2–0.5 mol/mol (for MRM). The dependency of CH4 and CO2 conversions, H2 and CO yields and syngas ratio on the reaction conditions was studied. The best conditions for stoichiometric feed composition were 0.25 g h/L space time at 1073 K temperature, wherein CH4 and CO2 conversions were 90 and 85.7% for DRM and 83 and 78.2% for MRM. After 10 h time-on-stream, the carbon deposition rate over Ni/Al2O3 was 22.7 and 20.4 mg/gcat/h for DRM and MRM correspondingly. The role of secondary reactions in the DRM and MRM process was elucidated.

Efficient utilization of carbon dioxide in a gas-to-methanol process composed of CO2/steam–mixed reforming and methanol synthesis

Two process models for a carbon-dioxide-utilized gas-to-methanol (GTM) process (CGTM) that primarily produces methanol were developed using the process simulation software Aspen Plus. Both models comprised a reforming unit, a methanol synthesis unit and a recycling unit, with the feeding point of the fresh feed CO2 as the principal configurational difference. In the reforming unit, CO2/Steam–mixed reforming was performed to generate the targeted syngas in flexible compositions. Meanwhile, CO2 hydrogenation was conducted over a Cu-based catalysts in the methanol synthesis unit to directly produce the targeted product, methanol. After methanol synthesis, the unreacted syngas was recycled to the methanol synthesis and reforming units to enhance energy efficiency. The simulation results revealed that both CGTM options can favorably improve the energy efficiency and significantly reduce the total CO2 emissions, compared to a conventional GTM process. The energy efficiency was shown to be highly affected by the recycle ratio and a higher recycle ratio seemed to favorably improve CO2 conversion, enhance energy efficiency, and reduce CO2 emissions. However, the split ratio (recycle-to-reforming unit/total recycle) seems to have little effect on the energy efficiency, and the optimum recycle to the reforming unit was determined to be none.

Kinetics for Steam and CO2 Reforming of Methane Over Ni/La/Al2O3 Catalyst.

Kinetic studies of mixed (steam and dry) reforming of methane on Ni/La/Al2O3 and Ni/La-Co (1, 3 wt%)/Al2O3 catalysts were performed in an atmospheric fixed-bed reactor. Kinetic parameters for the mixed reforming over these catalysts were obtained under reaction conditions free from heat and mass transfer limitations. Variables for the mixed reforming were the reaction temperature and partial pressure of reactants. The fitting of the experimental data for the rate of methane conversion, rCH4, using the power law rate equation rCH4 = k(PrCH4)α(PCO2)β(PH2O)γ showed that the reaction orders α, β, and γ are steady and obtained values equal to α = 1, β = 0, and γ = 0. In other words, among CH4, CO2, H2O, and H2, only CH4 reaction orders were not zero and they were affected by the promoters. The apparent activation energy on catalysts Ni/La/Al2O3, Ni/La-Co (1)/Al2O3 and Ni/La-Co (3)/Al2O3 is 85.2, 93.8, and 99.4 kJ/mol, respectively. The addition of Co to Ni/La/Al2O3 was increased the apparent activation energy of the mixed reforming reaction. And the Ni/La-Co (3 wt%)/Al2O3 catalyst showed the highest reforming activity and apparent activation energy. The Co promoters can increase the apparent activation energy of mixed reforming of methane.

Solar-to-Fuel Energy Conversion Analysis of Solarised Mixed Reforming of Methane

Abstract An energetic upgrade factor has been defined as the ratio of the lower heating value (LHV) of the syngas (H 2 plus CO) produced plus unreacted feedstock to that of the feedstock processed. It is used to evaluate the thermal performance of the steam reforming of methane,mixed reforming of methane with steam and carbon dioxide, and carbon dioxide reforming of methane based on the calculated equilibrium product compositions. A non-stoichiometric equilibrium model was developed using FactSage 6.3 software to conduct the thermodynamic calculations for production of syngas. The results show that increasing temperature or decreasing pressure can enhance the energetic upgrade factor of all three reforming processes. The ratio of the feedstock components has an effect on the energetic upgrade factor for the three reforming processes. There is an optimum ratio exisitng that provides the highest energetic upgrade factor for each of the three reforming processes. Replacement of H 2 O by CO 2 can enhance the energetic upgrade factor, particularly at high temperatures with no carbon formation. The analysis also identifies operating regimes where carbon formation is thermodynamically possible as well as discusses the undesirable effect that this carbon formation has on the energetic upgrade factor.

Thermodynamic analysis of carbon dioxide reforming of methane and its practical relevance

Thermodynamic equilibrium analysis of reforming of methane with carbon dioxide (dry reforming) and in combination with steam reforming (mixed reforming) was performed using constrained Gibbs free energy minimization method. The results were compared with that of a commercial plant reactor and our experimental data over Ni/MgO catalysts tested in a fixed-bed quartz reactor. It was concluded equilibrium values are good measures of reaction performance and could be used for prediction of reaction performance and coke formation studies. Numerical values 1.02 and 1.96 were obtained for approach to equilibrium of carbon dioxide reforming and steam reforming reactions, respectively, at 850 °C and space velocity of 530 ml/h.gcat. These values illustrated that, during dry reforming; first carbon dioxide reforming equilibrates, and then steam reforming reaction approaches to equilibrium in the reverse direction.

Modeling and analysis of a methanol synthesis process using a mixed reforming reactor: Perspective on methanol production and CO2 utilization

In this study, kinetic models were developed for the mixed reforming and synthesis of methanol (MeOH). The effectiveness of the reforming model in our previous work was proven in an experimental study using a bench-scale reactor, while the intrinsic rate model and effectiveness factors were developed to represent the MeOH synthesis. For a 10-ton-per-day production of MeOH, the rate model was used to determine the size of a reforming reactor so that the supplied heat could be used exclusively to engage the reaction (not for the heat-up of the reactant), while the MeOH reactor was specified using the reported values. The process model was then used to evaluate various effects of the following factors on the MeOH production rate: (1) reaction temperature, (2) CO2 fraction in the feed, and (3) the recycle route of the unreacted gas either to the feed or to the MeOH reactor. Additionally, an analysis was conducted with respect to both the overall and local CO2 conversions in each reactor, and it was shown that a trade-off existed between the maximum MeOH production rate and the maximum CO2 utilization, regardless of the existence of a recycle stream.

Modeling and optimization of the mixed reforming of methane: Maximizing CO2 utilization for non-equilibrated reaction

In the present study, a reactor model for mixed reforming over Ni-based catalyst was developed to investigate non-equilibrium behavior and reactions. Kinetic parameters were estimated by fitting experimental data for CH4 and CO2 conversions and H2/CO ratios under a variety of conditions, and the CO2 consumption rate was shown to be significantly affected by operating conditions due to the different characteristics of each reaction: dry reforming (DRM), steam reforming for the production of CO (SRM1) and CO2 (SRM2), and the water–gas shift (WGS) reaction. For optimization study, a reactor composed of three sections with different inert fractions and wall temperatures was considered, and optimization was conducted using various weighting factors on the CO productivity and the CO2 consumption per unit CO productivity; when maximum CO2 consumption per CO productivity was achieved, inert fraction of the first part of the reactor was lowered and wall temperature for the third part of the reactor was decreased, compared to maximum CO productivity case. Further analysis of instantaneous reaction rates showed that, in the case of maximum CO2 consumption, one third of the later part of the reactor could be obviated, resulting in an increase in CO productivity per unit volume, that is, the efficiency of the reactor. As a result, the strategy in the present study was successfully applied in the design of a mixed reforming reaction process providing maximum CO2 conversion as well as minimum CO2 emissions while reducing energy costs.

Optimized mixed reforming of biogas with O2 addition in spark-discharge plasma

Adding O2 into biogas to achieve partial oxidation and CO2 mixed reforming can not only increase H2 þ CO concentration, but also reduce energy cost for H2 production. In this study, optimized mixed reforming of biogas with O2 addition in spark-discharge plasma was pursued in combination with thermodynamic-equilibrium calculation. With respect to mixed reforming of biogas with O2 addition in spark-discharge plasma, combination coefficients of independent reactions were given to quantitatively evaluate the mixed extent at various O2/(CH4eCO2) ratios. Compared thermodynamic-equilibrium with experimental results, it can be concluded that the optimal O2/(CH4eCO2) ratio for optimized mixed reforming of biogas in spark-discharge plasma was about 0.7. When total-carbon conversion was relatively high (>75%), H2 þ CO concentration on wet basis was the highest and energy cost for H2 production was the lowest at O2/(CH4eCO2) ¼ 0.7, and their experimental results were closest to their thermodynamic-equilibrium values.