Catalytic Autothermal Reforming Research Articles

Heterogeneous numerical modelling for the auto thermal reforming of crude glycerol in a fixed bed reactor

A mathematical model for the catalytic autothermal reforming (ATR) reaction of synthetic crude glycerol to hydrogen in a fixed bed tubular reactor (FBTR) and over an in-house developed metal oxide catalyst is presented in this work. The heterogeneous model equations account for a two-phase system of solid catalyst and bulk feed gas. Also, the ATR of crude glycerol reaction scheme and intrinsic kinetic rate model over an active, selective, and stable nickel-based catalyst were integrated in the developed model. Also, the model was validated using experimental data generated in our labs for the ATR of synthetic crude glycerol. The modelling results adequately described the detailed gas product composition and distribution, temperature profiles, and conversion propagation in the axial direction of the fixed bed reactor over a wide range of reaction temperature (773–923 K) and mass-time (12.71–158.23 g cat·min·(mol C) −1 ). The crude glycerol conversion predicted with the model showing a close resemblance to those obtained experimentally with an average absolute deviation (AAD) of less than 8%. The maximum crude glycerol conversion and hydrogen yield were found to be 92% and 3 mol hydrogen/mol crude glycerol, respectively. Also, the gas product concentration profile in the reactor was adequately described (90%) accuracy with a hydrogen concentration of 39 vol%.

Optimization of hydrogen production via catalytic autothermal reforming of crude glycerol using response surface methodology and artificial neural network

In this work, the central composite design of the response surface methodology (RSM) and artificial neural network (ANN) were deployed to investigate process variables and optimize hydrogen gas production via autothermal reforming of crude glycerol using 5%Ni/CeZrCa catalyst in a packed bed tubular reactor. The input variables studied are reaction temperature, feed flow rate, steam to carbon ratio (S/C), oxygen to carbon ratio (O/C), and catalyst weight. The neural network analysis of these input variables measured their individual significance and contribution in the autothermal reforming process prior to the development of a quadratic polynomial model with RSM for predicting hydrogen yield as well as optimization. Statistical analyses showed that the mathematical model developed excellently represents the data with high model adequacy and no significant lack of fit. The results of the neural network input variable significance ranking approach showed that the reaction temperature contributed more than any other independent variable at a ranking weight of 53% while the O/C ratio showed the least impact at 3%. The results of the optimization gave the optimum parameters for hydrogen gas yield as follows; Temperature: 650°C, crude glycerol flow rate: 3.3 mmol C/min, S/C: 2.34, O/C: 0.052, and catalyst weight of 0.15 g with a maximum feed conversion of approximately 92% and 97% H2 yield. ANN provided a better regression with excellent statistical test values as follows R2: 0.999, MSE: 10−8, AAD: 0.34%, and RMSE: 3.5 × 10−4%. It is clear from the results of the model adequacy and error calculations that ANN is superior and has shown a better model fit than the RSM.

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al2O3 catalytic layer and patterned Pt/Al2O3 catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.

Simulation of diesel autothermal reforming over Rh/Ce0.75Zr0.25O2-δ-η-Al2O3/FeCrAl wire mesh honeycomb catalytic module

The study was dedicated to the mathematical modeling of the catalytic autothermal reforming (ATR) of diesel fuel – effective method for hydrogen production. The structured wire mesh Rh/Ce0.75Zr0.25O2-δ-η-Al2O3/FeCrAl catalyst was tested in pilot scale reactor and showed high efficiency in studied diesel autothermal reaction conditions. The process simulation was carried out by commercial software COMSOL Multiphysics in 2D axisymmetric geometry. The catalyst module was simulated as homogeneous porous medium. Reaction model included diesel oxidation, diesel steam reforming, water-gas shift reaction, CO methanation, CO oxidation and hydrogen oxidation. Fitting the experimental results including product distribution and temperature profile allowed to define the kinetic parameters corresponding to the best fit. The suggested simple quasi-homogeneous model describes experimental results (module temperature and outlet gas composition) with a good accuracy and could be used for process optimization and up-scaling.

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 Ce0.75Zr0.25O2-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.

Design, scale-up, and operation of a Rh/Ce0.75Zr0.25O2-δ-ƞ-Al2O3/FeCrAl alloy wire mesh honeycomb catalytic module in diesel autothermal reforming

Catalytic autothermal reforming is considered as one of the most effective methods for production of hydrogen from heavy hydrocarbon fuels for solid oxide fuel cells (SOFC). Diesel is an attractive fuel because of its high energy density, widespread use and well – developed infrastructure. Catalysts supported on structured carriers (e.g. FeCrAl modules) provide controlled reaction conditions throughout the reactor volume that favorably compete, for example, with fixed bed reactors. The use of structured catalysts provides efficient heat and mass transfer, low gas dynamic resistance, and high catalyst performance that facilitates the reduction of catalyst quantity per unit volume of the reactor. The ability to perform the process under controlled optimum conditions leads to increased selectivity and minimizes undesirable side reactions, such as coke formation. In the present work, the active component Rh/Ce0.75Zr0.25O2-δ was supported on FeCrAl metal meshes using Al2O3 as a binding structural component. The obtained catalysts Rh/Ce0.75Zr0.25O2-δ-ƞ-Al2O3/FeCrAl were tested in laboratory and pilot scale reactors in n-hexadecane and diesel autothermal reaction conditions. Winter grade diesel used in the experiments contained up to 31% of aromatics. Operating conditions were found to provide a 100% conversion of n-hexadecane and diesel and stable catalyst activity for a long time-on-stream exposure. The catalysts provided equilibrium product distribution and a maximum syngas (CO + H2) productivity of 3 m3Lcat−1h−1 (STP) at the studied experimental conditions. The produced syngas can be supplied as a fuel for power generation units based on high-temperature solid oxide fuel cells.

Robust model predictive control of a catalytic autothermal methane reformer for fuel cell applications

Model uncertainty is an inseparable part of a methane reforming process since many of its main parameters describe microscale behavior. A robust control approach for a catalytic fuel reformer is presented to guarantee performance constraints are met even in the presence of model uncertainty. The control strategy is based on a recently developed sampling-based robust model predictive control (RMPC) with a new approach to capturing the uncertainty. Particular features of the control strategy is the use of a metric for coking susceptibility as a constraint on the inlet gas composition, a cost based metric for evaluating decisions on controller commands, and the ability to meet constraints on reactor temperature, outlet gas energy content, and hydrogen to carbon monoxide ratio. Simulation results carried out in MATLAB on random plants show the constraints are met regardless the model uncertainty and measurement noise.

Packed bed reactor modeling of the catalytic auto-thermal reforming of synthetic crude glycerol

Modeling and simulation studies of synthetic crude glycerol auto-thermal reforming were performed in a catalytic packed bed reactor over a 5wt% Ni/CeZrCa catalyst. The numerical model comprised of two-dimensional material and energy balance equations and an in-house developed power law kinetic rate model. The model was validated against experimental data and a close agreement between the predicted and experimentally measured values was obtained with an average absolute deviation of <9%. Also, it was found that for the set of conditions and reactor dimensions used for this study, the effect of the axial dispersion term on the glycerol conversion was negligible. This effect is expected to be more pronounced at a larger scale and under actual operating conditions and therefore should not be neglected.

Hydrogen production via catalytic autothermal reforming of desulfurized Jet-A fuel

On-board hydrogen production via catalytic autothermal reforming is beneficial to vehicles using fuel cells as auxiliary power unit because it eliminates the challenges of hydrogen storage. As the primary fuel for both civilian and military air flight application, Jet-A fuel (after desulfurization) was reformed for making hydrogen-rich fuels in this study using an in-house-made Rh/NiO/K-La-Ce-Al-OX catalyst under various operating conditions. Based on the preliminary thermodynamic analysis of reaction equilibrium, important parameters such as ratios of H2O/C and O2/C were selected, in the range of 1.1–2.5 and 0.5–1.0, respectively. The optimal operating conditions were experimentally obtained at the reactor's temperature of 696 °C, which gave H2O/C = 2.5 and O2/C = 0.5, and the obtained fuel conversion percentage, hydrogen yield, and energy efficiency were 0.89, 1.44, and 0.65, respectively. In addition, a discussion of the molar fraction variation of CO and CO2 at different H2O/C, as well as the analysis of fuel conversion profile, leads to the finding of effective approaches for suppression of coke formation.

Numerical investigation on the transient characteristics of hydrogen production from catalytic autothermal reforming of methane in a micro combustor with multiple cylinders

The transient characteristics of autothermal reforming of methane in a cube micro combustor with multiple cylinders are numerically investigated. The effects of mixture gas composition, catalytic wall temperature and inlet velocity of the mixture feed gas on autothermal reforming of methane are thoroughly discussed. The results demonstrate that the yield of hydrogen decreases and the time to steady state slightly decreases with the increasing of steam content at a constant O2/CH4 molar ratio, while the yield of hydrogen decreases and the time to steady state slightly increases with the increasing of oxygen content at a constant H2O/CH4 molar ratio. Methane conversion significantly increases with the increasing of catalytic wall temperature, meanwhile, the reaction time to steady state sharply decreases, which are 61ms and 29ms at 790 K and 1190 K, respectively. The flow velocity has a determined influence on autothermal reforming of methane. As the velocity decreases from 0.5 m/s to 0.05 m/s, methane conversion increases from 62.60% to 98.88% and the yield of hydrogen increases from 56.21% to 90.48%. Higher inlet velocity leads to short residence time, which may not be sufficient to complete the reaction.

Fuel cell feed system based on H2 production by a compact multi-fuel catalytic ATR reactor

Hydrogen fuel cells seem the most viable solution to the pollution reduction and the energy growing demand. Very compact and small size production plant for distribute H2 production may reduce hydrogen transport and storage difficulties. Due to the high reactor compactness and thermal self-sustainability, the auto-thermal reforming (ATR) reaction of gaseous and liquid hydrocarbons can be the optimal solution. Fossil hydrocarbons like methane, gasoline and diesel still remain the favourite feed for catalytic auto-thermal reformer, due to the widespread existing delivery pipelines and the high energy density. Unfortunately, due to the different characteristics of liquid and gaseous fuels, it's very difficult to realize a multi-fuel processor characterized by high performances in terms of thermal efficiency and hydrogen yield, and, up to now, very low number of papers dealing with multi-fuel reformers is present in the literature.In this work, a catalytic reactor for the auto-thermal reforming of gaseous and liquid hydrocarbons was developed. An high pressure feed system, based on the “common rail” technology, was adopted for liquid fuel, allowing the formation of micro-droplets, assuring a very quick liquid fuel vaporization, an uniform mixing with other reactants, avoiding the coke formation, and improving the hydrogen yield and thermal efficiency. A commercial monolith structured catalysts was used and the influence of catalyst configuration was analysed. In order to obtain a total self-sustainable process and a very compact system, a heat exchanger was integrated in the reactor to preheat water and air streams by exploiting the heat from exhaust stream. The process is monitored by following temperatures and compositions along the catalytic bed.Preliminary tests showed high thermal system efficiency, with a good hydrocarbon conversion at different operating conditions. The low start-up times make the system extremely versatile, and suitable for batch operations.

Monolith and foam catalysts performances in ATR of liquid and gaseous fuels

Hydrogen fuel cells seem the most viable solution to the pollution reduction and the energy growing demand. Very compact and small size production plant for distribute production may reduce hydrogen transport and storage difficulties. Due to the high reactor compactness and thermal self-sustainability, the auto-thermal reforming (ATR) reaction of gaseous and liquid hydrocarbons can be the optimal solution. Fossil hydrocarbons like methane, gasoline and diesel still remain the favourite feed for catalytic auto-thermal reformer, due to the widespread existing delivery pipelines and the high energy density. Unfortunately, due to the different characteristics of liquid and gaseous fuels, it is very difficult to realize a multi-fuel processor characterized by high performances in terms of thermal efficiency and hydrogen yield, and, up to now, very low number of papers dealing with multi-fuel reformers is present in the literature.In this work, a catalytic reactor for the auto-thermal reforming of gaseous and liquid hydrocarbons was developed. An high pressure feed system, based on the “common rail” technology was adopted for liquid fuel, allowing the formation of micro-droplets, assuring a very quick liquid fuel vaporization, an uniform mixing with other reactants, avoiding the coke formation, and improving the hydrogen yield and thermal efficiency. A commercial monolith structured catalysts was used: the influence of catalyst configuration was analysed. In order to obtain a total self-sustainable process and a very compact system, a heat exchanger was integrated in the reactor to preheat water and air streams by exploiting the heat from exhaust stream. Process control is assured by monitoring temperatures and composition in up to 6 point along the catalytic bed.Preliminary tests showed high thermal system efficiency, with a good hydrocarbon conversion at different operating conditions. The low start-up times makes the system extremely versatile, and suitable for batch operations.

Modelling and simulation of a catalytic autothermal methane reformer with Rh catalyst

A model of a ATR fixed bed reactor with Rh catalyst has been developed and validated on the basis of experimental results. Experiments have been conducted in a small scale reactor and solid temperature profiles have been measured with IR camera. Temperature profiles present high peak temperature at reactor entrance as consequence of the partial separation in space of the reforming and oxidation reactions. Thus, the kinetic model for Rh catalyst refers to an indirect scheme including a shift factor which is crucial for good predictive capabilities of the reactor model. The model validation has been conducted by comparing solid temperature profiles with those obtained experimentally at different feed compositions, total flow rate and preheating temperatures. The model well describes the experimental results in all the investigated operating conditions. The validated model has been then used to analyze the effect of thermal conductivity and of the flow rate on overall reactor performances.

Nickel phosphide catalyst for autothermal reforming of surrogate gasoline fuel

AbstractAn investigation into the catalytic autothermal reforming (ATR) of a mixture of n‐octane and naphthalene (6 wt %), designed as a surrogate gasoline, is undertaken. Carbon deposition on the metallic Ni catalyst has been aware of the main hurdle for the catalytic reforming of hydrocarbons especially those with high carbon numbers. This work develops NixPy crystallites on a CeO2 powder support by electroless nickel plating and calcination. The catalyst exhibits nil coking extent after reforming the surrogate fuel. The NixPy crystallites are determined by XRD and its Ni‐P bonding is confirmed by XPS, where the Ni carries slightly higher negative charge than the Ni0 as usually observed. The XPS investigation also divulges the presence of Ce3+ species in the CeO2 support on which the NixPy crystallites are distributed, indicating that the support contains oxygen vacancies. These two subtle structural differences are proposed to provide the catalyst with resistance to coking. © 2011 American Institute of Chemical Engineers AIChE J, 2011

A microreactor modeling, analysis and optimization for methane autothermal reforming in fuel cell applications

Hydrogen production through autothermal reforming (ATR) of hydrocarbons, such as methane, is an attractive option for mobile applications of hydrogen fuel cells. In the present study, a numerical investigation of catalytic autothermal reforming of methane in a surface microreactor is presented. The microreactor is intended for use in a micro-fuel processor device for a low-power PEM fuel cell in a mobile application. A three-dimensional ATR reactor model is developed to simulate the flow and surface reactions in a microchannel of square cross-section. A four-reaction mechanism is implemented to simulate the surface reactions on a Ni/Al2O3 catalyst, and a global mechanism is used to model gas-phase methane oxidation. The governing equations in the model include conservations of mass, momentum, energy and chemical species. The simulation results reveal the dependency of hydrogen yield on space velocity (SV), air/fuel molar ratio (A/F), water/fuel molar ratio (W/F), and the feed gas temperature. The optimum conditions for the highest hydrogen yield were obtained in our simulations as: space velocity of 50,000h−1, A/F of 1.0, W/F of 3.0 and feed gas temperature of 600°C. The carbon monoxide production at these conditions is small enough to make the generated synthesis gas suitable for fuel cell applications after further treatment downstream of the ATR microreactor.

Influence of Temperature and Pressure on the Non-Catalytic Partial Oxidation of Natural Gas

The influence of temperature and pressure on the non-catalytic partial oxidation and reforming of natural gas in an entrained-flow reactor under non-equilibrium conditions has been investigated experimentally in pilot scale.As thermochemical equilibrium suggests, the methane conversion increases drastically with temperature, but does not reach equilibrium in the investigated range of parameters (Tmax = 1450 °C; 30 bar (3 MPa) &lt; p(g) &lt; 100 bar (10 MPa), 5 s &lt; ? &lt; 20 s). A practical method to describe the non-equilibrium state of a partial oxidation product gas at high temperatures due to kinetic limitations and/or mixing conditions within a reactor is by calculating apparent equilibrium temperatures Teq,ap for the main global kinetic reactions from the measured concentrations of the gas. The temperature difference between Teq,ap and the measured reactor outlet temperature Tex results in the temperature differental approach (?TApp = Teq,ap - Tex).In this paper, typical parameters influencing ?TApp for the methane reforming reaction (temperature T, pressure p, residence time ?) were examined. ?TApp was found in the range between -300 K and -50 K in non-catalytic partial oxidation. Its absolute value decreases with increasing pressure and decreasing ratio of steam to fuel carbon H2O : Cf , but is just weakly dependent on the reactor temperature Tex in a range from 1100-1450 °C. The results were used for the evaluation and further development of a model combining kinetics and residence time behaviour of the non-catalytic partial oxidation and reforming of natural gas.For comparison, results from catalytic autothermal reforming of natural gas and non-catalytic partial oxidation of liquid hydrocarbons are also presented.

Kinetic modeling of high pressure autothermal reforming

Previously a lab scale catalytic autothermal reformer (ATR) capable of operating at pressures from 6 to 50 bar was constructed and tested. The objective of the experimental program was to maximize H 2 production per mole of O 2 supplied (H 2(out)/O 2(in)). In this companion paper a 1-D, heterogeneous, numerical model is developed and tested for simulating the high pressure ATR. The effects of molar steam to carbon (S/C) and oxygen to carbon (O 2/C) ratios are studied and optimal operating conditions are identified for three system operating pressures; 6, 28 and 50 bar. Experimental optimal conditions and model results are compared and found to be in close agreement. The optimal conditions, however, predicted by the model at pressures of 28 and 50 bar have higher S/C ratios and produce higher H 2(out)/O 2(in) yields than the experimentally determined optimums. A sensitivity analysis consisting of 9 model parameters is also performed. The model is most sensitive to the activation energy of the two steam reforming reactions used in the model and the operating parameter O 2/C.

High pressure autothermal reforming in low oxygen environments

Abstract Recent interest in fuel cells has led to the conceptual design of an ocean floor, fuel cell-based, power generating station fueled by methane from natural gas seeps or from the controlled decomposition of methane hydrates. Because the dissolved oxygen concentration in deep ocean water is too low to provide adequate supplies to a fuel processor and fuel cell, oxygen must be stored onboard the generating station. A lab scale catalytic autothermal reformer capable of operating at pressures of 6–50 bar was constructed and tested. The objective of the experimental program was to maximize H2 production per mole of O2 supplied (H2(out)/O2(in)). Optimization, using oxygen-to-carbon (O2/C) and water-to-carbon (S/C) ratios as independent variables, was conducted at three pressures using bottled O2. Surface response methodology was employed using a 22 factorial design. Optimal points were validated using H2O2 as both a stored oxidizer and steam source. The optimal experimental conditions for maximizing the moles of H2(out)/O2(in) occurred at a S/C ratio of 3.00–3.35 and an O2/C ratio of 0.44–0.48. When using H2O2 as the oxidizer, the moles of H2(out)/O2(in) increased ≤14%. An equilibrium model was also used to compare experimental and theoretical results.

Catalytic autothermal reforming of propane over the noble metal-doped hydrotalcite-type catalysts

This study examined the propane reforming performance of noble metal-doped hydrotalcite-type catalysts in a continuous flow fixed-bed catalytic reactor for autothermal reforming. Hydrotalcite-type catalysts were prepared by co-precipitation and were modified by the addition of noble metals, such as Pt, Pd, and Ru. The noble metal-doped hydrotalcite-type catalysts showed better propane reforming performances than the Ni/MgAl catalyst due to the more abundant distribution of Ni catalyst particles and the lower level of carbon deposition. In the case of the hydrotalcite-type catalyst prepared using a mixed solvent of water and alcohol, the reforming activity increased due to an increase in the degree of dispersion and better thermal stability. Propane autothermal reforming over the noble metal-doped hydrotalcite-type catalysts showed higher reforming performance, better stability and less carbon deposition, which highlights their feasibility for hydrogen production from hydrocarbons.

Reactor temperature profile during autothermal methane reforming on Rh/Al 2O 3 catalyst by IR imaging

Catalytic autothermal reforming of methane was studied over a commercial rhodium catalyst as a function of feed flow rate, feed composition and oven temperature. The process is carried out in a catalytic fixed bed reactor inserted in a tubular oven. Temperature profile of the catalyst bed was measured by IR thermography and product composition was measured with a continuous gas analyzer. The effect of water addition at fixed flow rate on catalyst temperature profile was investigated in two ways. In one case, upon water addition, an equivalent amount of nitrogen was removed from the feed in order to keep oxygen and methane concentrations constant. With this protocol nitrogen to oxygen ratio varies as a function of amount of water in the feed. In the other case, upon water addition, nitrogen, oxygen and methane were all reduced to keep total flow rate constant, thus keeping both oxygen to methane and nitrogen to oxygen ratios constant. The effect of water addition on product composition was investigated as a function of reactor thermal level, regulated by acting on oven temperature.