Development of a robust and efficient biogas processor for hydrogen production. Part 1: Modelling and simulation

The present work deals with the modelling and simulation of a biogas Demo-processor for green hydrogen production via Autothermal reforming (ATR) process aimed at covering a wide span of potential applications, from fuel cells feed up to the production of pure hydrogen. The biogas ATR unit is composed of a structured catalyst support close coupled to a wall-flow filter that retain soot particles that can be formed during the ATR reaction. Modelling and simulation (CFD and FEM) were carried out to select the innovative catalyst support with promising results for the fuel processor. 3D digital sample reconstruction was performed for the selection of the appropriate porous structures commercially available for the soot filtration and furthermore, 2D CFD analysis was also used to examine flow uniformity issues due to soot trap integration downstream to the ATR. Moreover, the inherent flexibility of the model performed allowed its application in the assessment of the Demonstration plant operating in real conditions. Besides, Aspen simulation has demonstrated that the ATR process is the most promising process to hydrogen production compared to other types of reforming process.     

Self-sustained operation of a kWe-class kerosene-reforming processor for solid oxide fuel cells

In this paper, fuel-processing technologies are developed for application in residential power generation (RPG) in solid oxide fuel cells (SOFCs). Kerosene is selected as the fuel because of its high hydrogen density and because of the established infrastructure that already exists in South Korea. A kerosene fuel processor with two different reaction stages, autothermal reforming (ATR) and adsorptive desulfurization reactions, is developed for SOFC operations. ATR is suited to the reforming of liquid hydrocarbon fuels because oxygen-aided reactions can break the aromatics in the fuel and steam can suppress carbon deposition during the reforming reaction. ATR can also be implemented as a self-sustaining reactor due to the exothermicity of the reaction. The kW_e self-sustained kerosene fuel processor, including the desulfurizer, operates for about 250 h in this study. This fuel processor does not require a heat exchanger between the ATR reactor and the desulfurizer or electric equipment for heat supply and fuel or water vaporization because a suitable temperature of the ATR reformate is reached for H₂S adsorption on the ZnO catalyst beds in desulfurizer. Although the CH₄ concentration in the reformate gas of the fuel processor is higher due to the lower temperature of ATR tail gas, SOFCs can directly use CH₄ as a fuel with the addition of sufficient steam feeds (H₂O/CH₄ ≥ 1.5), in contrast to low-temperature fuel cells. The reforming efficiency of the fuel processor is about 60%, and the desulfurizer removed H₂S to a sufficient level to allow for the operation of SOFCs.     

Hydrogen-rich syngas production and carbon dioxide formation using aqueous urea solution in biogas steam reforming by thermodynamic analysis

Biogas is a renewable biofuel that contains a lot of CH₄ and CO₂. Biogas can be used to produce heat and electric power while reducing CH₄, one of greenhouse gas emissions. As a result, it has been getting increasing academic attention. There are some application ways of biogas; biogas can produce hydrogen to feed a fuel cell by reforming process. Urea is also a hydrogen carrier and could produce hydrogen by steam reforming. This study then employes steam reforming of biogas and compares hydrogen-rich syngas production and carbon dioxide with various methane concentrations using steam and aqueous urea solution (AUS) by Thermodynamic analysis. The results show that the utilization of AUS as a replacement for steam enriches the production of H₂ and CO and has a slight CO₂ rise compared with pure biogas steam reforming at a temperature higher than 800 °C. However, CO₂ formation is less than the initial CO₂ in biogas. At the reaction temperature of 700 °C, carbon formation does not occur in the reforming process for steam/biogas ratios higher than 2. These conditions led to the highest H₂, CO production, and reforming efficiency (about 125%). The results can be used as operation data for systems that combine biogas reforming and applied to solid oxide fuel cell (SOFC), which usually operates between 700 °C to 900 °C to generate electric power in the future.     

Performance of a PEMFC system integrated with a biogas chemical looping reforming processor: A theoretical analysis and comparison with other fuel processors (steam reforming,partial oxidation and auto-thermal reforming)

In this work, the performance of a PEMFC (proton exchange membrane fuel cell) system integrated with a biogas chemical looping reforming processor is analyzed. The global efficiency is investigated by means of a thermodynamic study and the application of a generalized steady-state electrochemical model. The theoretical analysis is carried out for the commercial fuel cell BCS 500W stack. From literature, chemical looping reforming (CLR) is described as an attractive process only if the system operates at high pressure. However, the present research shows that advantages of the CLR process can be obtained at atmospheric pressure if this technology is integrated with a PEMFC system. The performance of a complete fuel cell system employing a fuel processor based on CLR technology is compared with those achieved when conventional fuel processors (steam reforming (SR), partial oxidation (PO) and auto-thermal reforming (ATR)) are used. In the first part of this paper, the Gibbs energy minimization method is applied to the unit comprising the fuel- and air-reactors in CLR or to the reformer (SR, PO, ATR). The goal is to investigate the characteristics of these different types of reforming process to generate hydrogen from clean model biogas and identify the optimized operating conditions for each process. Then, in the second part of this research, material and energy balances are solved for the complete fuel cell system processing biogas, taking into account the optimized conditions found in the first part. The overall efficiency of the PEMFC stack integrated with the fuel processor is found to be dependent on the required power demand. At low loads, efficiency is around 45%, whereas, at higher power demands, efficiencies around 25% are calculated for all the fuel processors. Simulation results show that, to generate the same molar flow-rate of H₂ to operate the PEMFC stack at a given current, the global process involving SR reactor is by far much more energy demanding than the other technologies. In this case, biogas is burnt in a catalytic combustor to supply the energy required, and there is a concern with respect to CO₂ emissions. The use of fuel processors based on CLR, PO or ATR results in an auto-thermal global process. If CLR based fuel processor is employed, CO₂ can be easily recovered, since air is not mixed with the reformate. In addition, the highest values of voltage and power are achieved when the PEMFC stack is fed on the stream coming from SR and CLR fuel processors. When a H₂ mixture is produced by reforming biogas through PO and ATR technologies, the relative anode overpotential of a single cell is about 55 mV, whereas, with the use of CLR and SR processes, this value is reduced to ∼37 and 24 mV, respectively. In this way, CLR can be seen as an advantageous reforming technology, since it allows that the global process can be operated under auto-thermal conditions and, at the same time, it allows the PEMFC stack to achieve values of voltage and power closer to those obtained when SR fuel processors are used. Thus, efforts on the development of fuel processors based on CLR technology operating at atmospheric pressure can be considered by future researchers. In the case of biogas, the CO₂ captured can produce additional economical benefits in a ‘carbon market’.     

Biogas dry reforming over Ni-Al catalyst: Suppression of carbon deposition by catalyst preparation and activation

Biogas dry reforming is as an alternative renewable route for the hydrogen production. However, the major drawback of this process is the catalyst deactivation by carbon deposition and sintering. In this work, Ni-Al catalysts were studied aiming to suppress the carbon deposition in the dry reforming of biogas. The catalysts were prepared by coprecipitation and evaluated the washing step. The reactions were carried out with unreduced and reduced catalysts in a fixed bed tubular reactor using a synthetic biogas (60% CH₄ and 40% CO₂). The washing and activation steps influenced the characteristics of the catalysts and the catalytic properties in the biogas reforming. The unwashed sample resulted in an oxide containing potassium nickelate with high basicity and low surface area. Both washed samples, reduced and unreduced, showed a high amount of carbon formation, whereas no carbon formation was observed in the unwashed samples for the reactions in the temperature range of 500–750 °C. The unwashed and unreduced sample was the only one that maintained the activity during all the reaction time at 700 °C (40% CH₄ conversion and 75% CO₂ conversion), low coke amount and no evidence of sintering, which was confirmed by XRD, TPO, and SEM analyses. The carbon suppression was related to the nickelate phase and to the Ni carbide formation in the unwashed and unreduced catalyst. In summary, the carbon deposition in biogas dry reforming was completely controlled between 600 and 750 °C using the unwashed and unreduced Ni-Al catalyst.     

Combination of Langmuir-Hinshelwood-Hougen-Watson and microkinetic approaches for simulation of biogas dry reforming over a platinum-rhodium alumina catalyst

Dry reforming of CH₄ on a platinum-rhodium alumina catalyst is selected to numerically investigate biogas reforming process. Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expressions for dry reforming and reverse water-gas shift reactions are presented. Activation energies are estimated by combining microkinetics with the theory of unity bond index-quadratic exponential potential (UBI-QEP). Pre-exponential factors are initially obtained by using the transition state theory (TST) and optimised, later, by minimising errors between modelling and experimental data. Adsorption of CH₄ on the catalyst surface is found to be the rate determining step in the range of relatively low temperature (600–770 °C), while at relatively high temperature (770–950 °C) the thermal cracking of adsorbed CH₄ is the rate controlling step. Small effect of reverse water-gas shift reaction results in the ratio of H₂ to CO produced less than unity for all operating conditions. The simulation shows that the dry reforming process proceeds with reaction rate far from equilibrium state. The presented mechanism is capable of predicting the dependence of biogas dry reforming activities (e.g., reactant conversions, product formations, H₂ to CO ratio, and temperature profile inside the catalyst) on operating conditions (e.g., inlet temperature, heat supplied through the catalyst wall, and composition of biogas at inlet).     

H2S effect on dry reforming of biogas for syngas production

The effect of hydrogen sulfide (H₂S) on dry reforming of biogas for syngas production was studied both experimentally and theoretically. In the experimental work, the H₂S effect on Ni‐based catalyst activity was examined for reaction temperatures ranging from 600°C to 800°C. It was found that the presence of H₂S deactivated the Ni‐based catalysts significantly because of sulfur poisoning. Although bimetallic Pt‐Ni catalyst has better performance compared with monometallic Ni catalyst, deactivation was still found. The time‐on‐stream measured data also indicated that sulfur‐poisoned catalyst can be regenerated at high reaction temperatures. In the theoretical work, a thermodynamic equilibrium model was used to analyze the H₂S removal effect in dry reforming of H₂S‐contained biogas. Calcium oxide (CaO) and calcium carbonate (CaCO₃) were used as the H₂S sorbent. The results indicated that H₂S removal depends on the initial H₂S concentration and reaction temperature for both sorbents. Although CO₂ was also removed by CaO, the results from equilibrium analysis indicated that the dry reforming reaction in the presence of CaO was feasible similar to the sorption enhanced water‐gas shift and steam‐methane reforming reactions. The simulation results also indicated that CaO was a more preferable H₂S sorbent than CaCO₃ because syngas with an H₂/CO ratio closer to 2 can be produced and requires lower heat duty.     

Modeling and simulation of steam methane reforming and methane combustion over continuous and segmented catalyst beds in autothermal reactor

In this paper, a numerical analysis of the production of hydrogen via autothermal (ATR) steam methane reforming (SMR) is presented. The combustion reaction occurs over a Pt/Al₂O₃ catalyst, and the reforming reaction is operated using a Ni/Al₂O₃ catalyst inside the same cylindrical channel. A novel configuration with18 catalytic-bed macro-patterns alternately mounted, referred to as SDB, is designed and compared with the catalytic dual-bed reactor (conventional configuration), referred to as CDB, at the same operating temperature and pressure conditions of 900 °C and 14 bars, respectively. The results showed that hydrogen yield was improved by 4.5% compared to the conventional configuration, while a decrease of 67 °C of the highest temperature was noticed. Meanwhile, the methane conversion was 63.73% and 65.44% for the CDB and SDB configurations, respectively. Furthermore, the length of the reactor can be decreased by 27%, keeping the same hydrogen yield at the outlet of the conventional reactor, indicating a potential reduction in hydrogen cost.     

Hydrogen production from biogas reforming and the effect of H2S on CH4 conversion

Biogas produced during anaerobic decomposition of plant and animal wastes consists of high concentrations of methane (CH₄), carbon dioxide (CO₂) and traces of hydrogen sulfide (H₂S). The primary focus of this research was on investigating the effect of a major impurity (i.e., H₂S) on a commercial methane reforming catalyst during hydrogen production. The effect of temperature on CH₄ and CO₂ conversions was studied at three temperatures (650, 750 and 850 °C) during catalytic biogas reforming. The experimental CH₄ and CO₂ conversions thus obtained were found to follow a trend similar to the simulated conversions predicted using ASPEN plus. The gas compositions at thermodynamic equilibrium were estimated as a function of temperature to understand the intermediate reactions taking place during biogas dry reforming. The exit gas concentrations as a function of temperature during catalytic reforming also followed a trend similar to that predicted by the model. Finally, catalytic reforming experiments were carried out using three different H₂S concentrations (0.5, 1.0 and 1.5 mol%). The study found that even with the introduction of small amount of H₂S (0.5 mol%), the CH₄ and CO₂ conversions dropped to about 20% each as compared to 65% and 85%, respectively in the absence of H₂S.     

Autothermal reforming study of diesel for fuel cell application

Diesel is one of the best hydrogen storage systems, because of its very high hydrogen volumetric density (100 kg H₂ m⁻²) and gravimetric density (15% H₂). In this study, several catalysts were selected for diesel reforming. Three experimental catalysts (Pt on gadolinium-doped ceria, Rh and Ru on the same support) and two commercial catalysts (FCR-HC14 and FCR-HC35, Süd-Chemie, Inc.) were used to reform diesel. The effects of operating conditions, such as temperature, O₂/C16 and H₂O/C16 on autothermal reforming (ATR) were investigated. In addition, by analyzing the concentrations of products and the temperature profiles along the catalyst bed, we studied the reaction characteristics for a better understanding of the ATR reaction. The fuel delivery and heat transfer between the front exothermic part and the rear endothermic part of the catalyst bed were found to be significant. In this study, the characteristic differences between a surrogate fuel (C₁₆H₃₄) and commercial grade diesel for the ATR were also examined.     

Durability of a Ni based monolithic catalyst in the autothermal reforming of biogas

A Ni based catalyst supported on a cordierite monolithic substrate was applied to the autothermal reforming (ATR) of biogas to produce hydrogen. When the feed rates of oxygen and steam were constant, the Steam/CH₄ (S/CH₄) and O₂/CH₄ ratios changed because of an increase or decrease in the methane concentration of the biogas. The concentration of methane in the biogas fluctuates roughly between 35% and 65% according to factors such as the properties or amount of the waste. Therefore, the effect of S/CH₄ and O₂/CH₄ ratios on catalyst durability was confirmed by using actual biogas, which was produced by anaerobic fermentation of biomass at the biogasification bench-scale plant in Kyoto. Reforming reactions were carried out at ratios of S/CH₄ = 0–4, O₂/CH₄ = 0.5 and at S/CH₄ = 2, O₂/CH₄ = 0.6. The S/CH₄ range of 0–2.0 and the O₂/CH₄ range of 0.5–0.6 had no effect on the catalyst durability and a S/CH₄ ratio of more than 3.0 led to decreased catalytic performance.     

Syngas production by steam and oxy-steam reforming of biogas on monolith-supported CeO2-based catalysts

In this study, the syngas production by steam reforming (SR) and oxy-steam reforming (OSR) of clean biogas over cordierite monoliths (400 cpsi) lined with Ni, Rh, or Pt on CeO₂ catalyst was deeply investigated. Structured catalysts were prepared by using an alternative method to traditional washcoating based on the combination of the solution combustion synthesis (SCS) with the wetness impregnation (WI) technique. TEM and SEM analysis were used to study the morphology of the catalytic layer and to determine its thickness, while the quality of the coating in terms of adhesion on the monolith was evaluated by ultrasonic treatment in isopropyl alcohol solution. The performance and the stability of the structured catalysts were investigated at different process parameters, namely temperature (700–900 °C), steam-to-carbon (S/C = 1–5) and oxygen-to-carbon (O/C = 0.1–0.2) molar ratios, and weight space velocity (WSV = 30,000–250,000 NmL g_cat^?1 h^?1). The SCS + WI deposition method allowed obtaining a uniform and thin coated layer with high mechanical strength. The following order of activity was exploited: Rh > Pt > Ni for biogas SR and Rh > Pt ≈ Ni for biogas OSR. The Rh-based catalyst exhibited higher activity and long-lasting stability towards biogas SR and OSR reactions for syngas production.     

Membrane reformer module with Ni-foam catalyst for pure hydrogen production from methane: Experimental demonstration and modeling

Results of experiments and modeling of a compact (800 cm³) membrane reformer module for the production of 0.25–0.30 Nm³/h hydrogen by methane steam reforming are reported. The module consists of a two-sided composite membrane disc with a 50 μm PdAg layer and two adjacent 4 mm thick Ni foam discs (60 ppi). A nickel catalyst and a porous support were deposited on the foam discs to give the final composition of 10%Ni/10%MgO/Ni-foam. Membrane permeability by pure hydrogen was investigated, and coefficients of transverse hydrogen transport across the Ni foam to the membrane in the case of inlet binary N₂H₂ mixture were refined in order to account for concentration polarization effect into the model. Activity of the catalytic discs was measured in a differential laboratory scale reactor at a pressure of 1 bar and temperature of 400–600 °C. Modules were tested at a 8–13 bar pressure of the mixture in the reforming zone and at 1 bar of pure hydrogen under the membrane, H₂O/C = 2.5–3 and a module temperature of 550–680 °C (with and without hydrogen removal). Two modifications of the module were tested: consecutive (I-type) and parallel (II-type) flow of the reaction mixture around two sides of the membrane disc. In order to optimize construction of the module, calculations were made for revealing the effect of thickness of the PdAg membrane layer (5–50 μm), thickness of the Ni foam discs (0.5–8 mm) and temperature (600–700 °C) on the hydrogen output of the module. A comparison of the values obtained in our experiments (>1 MW/m³ and >0.7 kg(H₂)/h/m²) with the literature data reported by other authors showed that the developed modules are promising for practical application as components of a fuel processor section for mobile applications.     

Integrating chemical kinetics with CFD modeling for autothermal reforming of biogas

Using biogas for hydrogen production via autothermal reforming (ATR) can potentially increase the energy conversion efficiency and correspondingly reduce environmental impact. The present study aimed to investigate the performance and characteristics of biogas ATR. A two-dimensional numerical model was developed based on the integration of computational fluid dynamics (CFD) and chemical kinetics. The mass transport, chemical reactions and heat transfer can be analyzed simultaneously in the porous domain. The results show that the presence of CO₂ in the feedstock will reduce the performance of the biogas ATR. The effects of operating and feeding conditions were examined and the optimal conditions were identified. Operating the reformer with the steam-to-CH₄ ratio (S/CH₄) and air-to-CH₄ ratio (A/CH₄) equal to 0.5 and 2, respectively, can achieve high H₂ concentration, while operation with S/CH₄ and A/CH₄ equal to 4.5 and 2, respectively, can achieve high energy efficiency. The results also show that using either H₂ or O₂ membrane in the reformer can enhance the biogas autothermal reforming performance by producing high concentration of H₂ (40–65%) and solving the harmful hot spot problems.     

Comparative study of gasoline,diesel and biodiesel autothermal reforming over Rh-based FeCrAl-supported composite catalyst

Catalytic autothermal reforming (ATR) of a number of hydrocarbon fuels was studied over composite RhCZ-S catalyst (0.24 wt% Rh supported on structured Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl carrier). Iso-octane and n-hexadecane as model compounds of gasoline and diesel fuel, respectively, showed similar properties in ATR process, indicating weak influence of molecular weight and branching degree of liquid alkanes on catalyst performance. Biodiesel ATR characteristics were similar to those of n-hexadecane ATR, as the utilized biodiesel predominantly contained alkanes, being products of fatty acid tail fragments hydrogenation. Even in the case of gasoline ATR, sufficient amount of monoaromatics did not influence a lot on the catalyst performance. Diesel ATR showed rather different situation: the catalyst tended to lose activity due to coking, and incomplete fuel conversion was observed. Analysis of unreacted fuel revealed bi- and polyaromatic compounds (mainly naphtalenes and antracenes) were difficult to convert.     

Biogas reforming for hydrogen enrichment by ceria decorated over nickel catalyst supported on titania and alumina

Catalytic dry reforming of biogas for hydrogen enrichment was studied over cerium oxide promoted nickel catalysts supported on titanium dioxide and aluminium oxide. The catalysts were prepared by wet impregnation method and characterized by H₂-TPR, XRD, BET and FESEM techniques. Their catalytic performance in the biogas dry reforming reaction was studied at temperature ranges from 650 to 850 °C, with a CH₄/CO₂ ratio of 1.5:1. The H₂-TPR results revealed that 11 wt % Ni impregnation on TiO₂ support makes the catalyst with strong metal-support interaction which moderates the metal sintering. Also, the addition of CeO₂ effectively improved the CH₄ and CO₂ conversions as well as H₂ enrichment. At 850 °C, 11 wt % Ni/TiO₂ catalyst leads to 70.5% CH₄ conversion with 32.0% H₂ enrichment, whereas, Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) yielded high CH₄ conversion (84.9%) with 40.6% of H₂ enrichment. No significant change in the activity of the catalyst was observed with 8.8 wt % of carbon deposited on the Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) catalyst, after 7 h of continuous reforming. Moreover, under combined (dry and oxidative) reforming of biogas, the stoichiometric H₂/CO ratio (1.2) was observed at 0.47 O₂/CH₄ ratios with negligible carbon deposition. Thus, Ni_0·11/Ce_0.20 (Al₂O₃TiO₂) catalyst exhibited better activity and selectivity with high catalyst stability at 850 °C.     

Process simulation and techno-economic assessment of SER steam gasification for hydrogen production

In the SER (sorption enhanced reforming) gasification process a nitrogen-free, high calorific product gas can be produced. In addition, due to low gasification temperatures of 600–750 °C and the use of limestone as bed material, in-situ CO₂ capture is possible, leading to a hydrogen-rich and carbon-lean product gas. In this paper, results from a bubbling fluidised bed gasification model are compared to results of process demonstration tests in a 200 kW_th pilot plant.Based upon that, a concept for the hydrogen production via biomass SER gasification is studied in terms of efficiency and feasibility. Capital and operational expenditures as well as hydrogen production costs are calculated in a techno-economic assessment study. Furthermore, market framework conditions are discussed under which an economic hydrogen production via SER gasification is possible.     

Temperature and hydrogen flow rate controls of diesel autothermal reformer for 3.6 kW PEM fuel cell system with autoignition delay time analysis

In this paper catalyst temperature and hydrogen flow rate controls are an area of interest for autothermal reforming (ATR) of diesel fuel to provide continuous and necessary hydrogen flow to the on-board fuel cell vehicle system. ATR control system design is important to ensure proper and stable performance of fuel processor and fuel cell stack. Fast system response is required for varying load changes in the on-board fuel cell system. To cope with control objectives, a combination of PI and PID controllers are proposed to keep the controlled variables on their setpoints. ATR catalyst temperature is controlled with feedback PID controller through variable OCR (oxygen to carbon ratio) manipulation and kept to the setpoint value of 900 °C. Additionally diesel auto-ignition delay time is implemented through fuel flow rate delay to avoid complete oxidation of fuel. Hydrogen flow rate to the fuel cell stack is kept to setpoint of required hydrogen flow rate according to fuel cell load current using PI controller. An integrated dynamic model of fuel processor and fuel cell stack is also developed to check the fuel cell voltage. Product gas composition of 35, 18 and 4% is achieved for hydrogen, nitrogen, and carbon dioxide, respectively. The results show fast response capabilities of fuel processor following the fuel cell load change and successfully fulfills the control objectives.     

A 75-kW methanol reforming fuel cell system

A 75-kW methanol reforming fuel cell system, which consists of a fuel cell system and a methanol auto-thermal reforming fuel processor has been developed at Dalian Institute of Chemical Physics, Chinese Academy of Sciences (CAS). The core of the fuel cell system is a group of CO tolerant PEMFC stacks with a double layer composite structured anode. The fuel cell stacks show good CO tolerance even though 140 ppm CO was present in the reformate stream during transients. The auto-thermal reforming (ATR) fuel cell processor could adiabatically produce a suitable reformate without external energy consumption. The output of hydrogen-rich reformate was approximately 120 N m³ h⁻¹ with a H₂ content near 53% and the CO concentrations generally were under 30 ppm. The fuel cell system was integrated with the methanol reforming fuel processor and the peak power output of the fuel cell system exceeded 75 kW in testing. The hydrogen utilization approached 70% in the fuel cell system.     

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.