Mathematical Modeling of Methane Air Conversion on a Structured Porous Metal Catalyst

A one-dimensional two-phase mathematical model of an ideal plug-flow reactor for methane air conversion on a Ni–MgO monolith catalyst on porous nickel was proposed. The model describes the methane air conversion as the result of three simultaneous reaction stages: methane deep oxidation, methane steam reforming, and reverse shift reaction. The effect of the external gas–solid mass transfer is taken into account in two variants: (i) independent diffusion and (ii) multicomponent diffusion for all mixture components. The results of modeling were used to analyze the experimental data (obtained in our previous work) on the dependence of the temperature of the front layer of the catalyst on the pressure and excess air coefficient. The best agreement between the calculation and experiment was obtained under conditions of complete external diffusion control of the exothermic stage for oxygen and the transition (between the kinetic and external diffusion) region of the endothermic stage, the kinetic effect of the endothermic stage being further limited by internal pore-diffusion resistance of the rate of this stage for methane.     

Self-oscillations on a partially wetted catalyst pellet in α-methylstyrene hydrogenation: Experiment and mathematical modeling

Self-oscillation modes on an irrigated porous catalyst pellet in exothermic hydrogenation accompanied by liquid evaporation is studied. By NMR tomography (magnetic resonance microimaging), images of the liquid-phase distribution within the porous object are obtained and the liquid-phase redistribution is monitored immediately during the process without destroying the object and without introducing any probes or molecular labels.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 1, 2005, pp. 27–38.Original Russian Text Copyright © 2005 by Kirillov, Koptyug, Kulikov, Kuzin, Lysova, Shigarov, Parmon.     

Thermally Coupled Catalytic Reactor for Steam Reforming of Methane and Liquid Hydrocarbons: Experiment and Mathematical Modeling

An energy-efficient catalytic reactor for producing synthesis gas from methane and liquid hydrocarbons is proposed that is based on the coupling of an endothermic reaction (steam reforming of methane, hexane, or isooctane) and an exothermic reaction (hydrogen oxidation by atmospheric oxygen) in a single cocurrent apparatus. To describe the processes in such an apparatus, a two-dimensional two-temperature mathematical model is developed. It was revealed experimentally and by mathematical modeling that the heat- and mass-transfer coefficients of the gas flow in contact with the catalytically active wall in the exothermic reaction zone considerably affect the thermal conditions in the reactor.     

Experimental study of vaporization effect on steady state and dynamic behavior of catalytic pellets

The impact of the combined evaporation of the liquid phase and reaction on single catalyst pellet performance has been studied experimentally. The exothermic, catalyzed hydrogenation of -methylstyrene (AMS) to cumene has been employed as a model reaction. Steady state and dynamic experiments have been performed in a single catalytic pellet reactor using five catalytic pellets of different porous structures, thermal conductivity, apparent catalytic activity and distribution of catalyst in the pellet. Gas-phase temperature, concentration of AMS in the gas phase and the liquid flow rates have been varied. The measured center and surface temperatures of each pellet reveal the existence of two significantly different steady states in the range of liquid flow rate. The range of the liquid flow rate over which the two steady states were observed, the pellet temperature and the pellet dynamics depend strongly on the amount of AMS vapor in the gas phase and the catalyst properties. The obtained experimental data are helpful to elucidate the mechanism of hot-spot formation and runaway in multiphase fixed-bed reactors.     

Development of a catalytic heating system for external combustion engines

A catalytic heater design was proposed for an external combustion engine. This design is based on the partial oxidation or autothermal conversion of hydrocarbon fuel to syngas and its further oxidation with heat generation in a radial catalytic reactor integrated with a tubular heat exchanger. The theoretical analysis of operational regimes for a catalytic heater with a thermal power of 25–50 kW was performed with regard to the distribution of gas and the mathematical modeling of processes in a catalyst bed integrated with a heat exchanger, and some estimates were given for the performance of an external combustion engine. The conditions providing a uniform distribution of gas along the length of a radial reactor with suction of a reaction mixture into the catalyst bed were determined. A design of catalytic heating system elements was developed, and some layout solutions that provide a rational mutual arrangement of system components were created.     

Biofuels as a promising source of hydrogen for fuel cell power plants

The state of the art in biomass conversion into liquid hydrocarbon biofuels aimed at obtaining synthesis gas and hydrogen for duel elements is analyzed. The most promising liquid hydrocarbon and oxygencontaining fuels for synthesis gas production are vegetable oils, diesel fuel, and biodiesel. Mathematical models are developed for the autothermal reforming, steam reforming and pre-reforming of biodiesel into synthesis gas and for the steam reforming of pre-reforming products integrated with the membrane separation of hydrogen. The results of calculations are verified against experimental data. The solution suggested here ensures 93.5% efficiency of the membrane separation of hydrogen from the reaction mixture and a theoretical hydrogen yield of 128 mol per kilogram of biodiesel.     

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.     

Experimental and theoretical study of associated petroleum gas processing into normalized gas by soft steam reforming

The article presents the results of experimental investigation and mathematical modeling of a new technology for converting associated petroleum gas to a normalized combustible gas that can be used in gas turbine and gas reciprocator power plants or, after removing part of the СО₂, can be pipelined. The essence of the new technology is that the C2+ hydrocarbons contained in associated petroleum gas are converted by soft steam reforming into a gaseous fuel that consists mainly of methane and contains carbon dioxide and a small amount of hydrogen. This process increases the volume of the gas mixture and normalizes its heating value and Wobbe index to the standard characteristics of commercial natural gas (purified from СО₂). The soft steam reforming technology has been tested on laboratory, pilot, and pre-commercial scales. A mathematical model has been developed for the process. A numerical analysis based on this model has demonstrated that, using this technology, it is possible to process associated petroleum gases varying widely in methane homologue concentrations in one tubular catalytic reactor.