Catalytic Steam Reforming Of Methane Research Articles

On the effects of surface waviness upon catalytic steam reforming of methane in micro-structured reactors - a computational study

The effects of wavy channels upon steam methane reforming in catalytic micro-structured reactors, using Nickle as the catalyst, are investigated numerically. Laminar, three-dimensional models of reacting flows, with heterogeneous chemistry, are developed and applied to micro-structured reactors with different wave patterns on their internal walls. It is observed that introduction of surface waves on the walls of reactor, can significantly alter production and consumption of H2 and CH4. This is shown to be due to large fluctuations in convective mass and heat transfer, induced by the surface waviness. In particular, it is shown that separation and reattachment of concentration and thermal boundary layers and the subsequent modifications in Sherwood and Nusselt number can significantly affect the catalytic processes over the walls of reactor. A major local intensification of catalytic processes is observed where Sherwood and Nusselt number are maximised. Similarly, the catalytic process becomes highly inefficient in places with minimal Sherwood (and Nusselt) number. The analyses further reveal that a strategic discrete coating of wavy walls with the catalyst can substantially improve the performance of microstructure. For example, by coating only 25% of the surface area of wavy walls, CH4 conversion rate and selectivity per coated surface area increase by 459% and 308% compared to those of an equivalent fully coated straight channel. This implies the possibility of developing highly efficient and cost-effective catalytic micro-reactors for production of hydrogen from methane.

Co-electrolysis of simulated coke oven gas using solid oxide electrolysis technology

Coke oven gas is a by-product of coke production for steelmaking and by volume typically consists of 55–60% hydrogen, 23–27% methane and impurities. An estimated 650 million tonnes of coke oven gas are produced worldwide, with up to 50% re-utilised within steelmaking. However, the rest is flared, contributing to carbon emissions and wasting valuable and useful gases. This study has investigated the co-electrolysis of simulated coke oven gas with steam using commercially available solid oxide electrolysis technology for the purposes of recovering hydrogen. The electrochemical performance of an anode supported button cell was characterised using open circuit potential measurements, current-voltage curves and electrochemical impedance spectroscopy. The product gas composition was analysed using quadrupole mass spectrometry. Co-electrolysis of simulated coke oven gas (30/70% methane/hydrogen) with 50% steam achieved a hydrogen amplification of 119% and a purity of 91.7% by volume, balanced mainly in carbon dioxide and carbon monoxide. Theoretically, this corresponds to a worldwide hydrogen production from coke oven gas of 87.6 million tonnes, which is in excess of the current global demand for hydrogen (70 million tonnes). Catalytic steam reforming of methane and the water-gas shift reaction increased the hydrogen content by 89% and a further 16% gain was due to electrochemical steam reduction. Co-electrolysing at high steam-to-carbon ratios was shown to increase hydrogen yield, improve cell performance, maximise methane and carbon monoxide conversion and inhibit carbon deposition. Studies into fuel variability effects show that greater methane contents gave higher hydrogen yields but decreased hydrogen purity and cell performance. Increasing the operating voltage increased the conversion of carbon dioxide into carbon monoxide via promotion of the reverse water-gas shift reaction. The work demonstrates the considerable potential to upgrade coke oven gas using solid oxide electrolysis technology, which could enable greater downstream recovery and purification of hydrogen from an under-utilised industrial waste resource.

Electro-catalytic steam reforming of methane over Ni-CeO2/γ-Al2O3-MgO catalyst

Catalytic steam reforming of methane with Ni-based catalysts is essential for industrial hydrogen production, but the high reforming temperature results in the catalyst deactivation by severe carbon deposition. In this work, a novel electro-catalytic protocol for steam reforming of methane was developed with aims of lowering the reforming temperature and prolonging the catalyst life. Three Ni-based catalysts, i.e., Ni/γ-Al2O3 (Ni/Al2O3), Ni/γ-Al2O3-MgO (Ni/AM) and Ni-CeO2/γ-Al2O3-MgO (Ni-CeO2/AM) were prepared for electro-catalysis to investigate the effects of current intensity, reforming temperature, and steam to carbon ratio on methane conversion, H2 yield and CO selectivity. Moreover, stability tests were performed on the three catalysts. The results indicated that the presence of electric current promoted the methane steam reforming at relatively low temperatures. Among the three catalysts, Ni-CeO2/AM showed the best performance on catalytic efficiency. Under conditions of 600 °C and current of 4.5A, CH4 conversion, H2 yield and CO selectivity achieved 96.4%, 75.3% and 40.1% respectively over Ni-CeO2/AM, which were comparable with those from conventional process at 700 °C. Moreover, after a 9-hour stability test, the CH4 conversion was maintained over 95% under Ni-CeO2/AM. Characterization results of the catalysts from the stability texts showed that the current could help generate more active centers for CH4 activation while inhibit the conversion of coke precursors into carbon on the catalyst surface.

Methane dissociative adsorption in catalytic steam reforming of methane over Pd/CeO2 in an electric field

To elucidate the reaction mechanism of catalytic steam reforming of methane in an electric field, operando–diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has been used to investigate methane dissociative adsorption at low temperatures using CH4, H2O, and their isotopes. Operando-analyses demonstrated that methane was adsorbed and converted into CO and CO2 more when CD4 and/or D2O was used instead of CH4 and/or H2O. This observed “inverse” kinetic isotope effect is based on the difference of CHH vibrational energy level at the transition state. Furthermore, CO2-methanation, which is the reverse reaction of steam reforming of methane, was irreversible with H2O in an electric field. These results demonstrate that the proton collision promoted methane activation irreversibly, even at low temperatures in an electric field.

A two-dimensional mathematical model for the catalytic steam reforming of methane in both conventional fixed-bed and fixed-bed membrane reactors for the Production of hydrogen

A modelling and simulation study of catalytic steam reforming of methane is presented in this paper. A two-dimensional pseudo-heterogeneous model is developed to simulate a conventional fixed-bed reactor (FBR) as well as a fixed-bed membrane reactor (FBMR) with sweep gas added in both co-current modes for the two reactor configurations. The developed model is based on mass and energy balance equations for the catalyst phase and the gas phase in both FBR and FBMR reactors. Firstly, a study is done for describing that the temperature profiles of gaseous and solid phases reach to stable state as well as the component distributions in the two FBR and FBMR reactors. The model covers the aspect of the partial pressure of hydrogen in the membrane reactor with the permeation of hydrogen across a Pd-based membrane. The conversion of methane is significantly enhanced by the partial removal of hydrogen as from the shell side as a result of diffusion through the Pd-based membrane. Simulation results demonstrated that methane conversion of 97.21% can be achieved in FBR at operating temperature of 1250 K relative to methane conversion of 99.79% to 923 K in FBMR. The yield of hydrogen achieved to level from 2.154 in FBR at operating temperature of 1250 K while the yield of hydrogen reached to level from 3.731 with a thickness from 1.7 μm in FBMR reactor.

Multi-scale approaches for gas-to-liquids process intensification: CFD modeling, process synthesis, and global optimization

This paper presents a multi-scale framework for the intensification of small scale gas-to-liquids (GTL) processes. As the process intensification tool, a radial microchannel reactor is used to facilitate the catalytic steam reforming of methane. Due to the endothermicity of this reaction, a microchannel reactor serves as a promising alternative because of its enhanced heat transfer characteristics. However, the underlying mathematical model for the microchannel reforming process is complex. Since our aim is to elucidate the optimal process topology from a plethora of alternatives through a global optimization framework, we built a surrogate mathematical model to bridge this gap. Through a rigorous model identification, parameter estimation, and cross-validation analysis we have developed an accurate mathematical model that can predict the microchannel reactor output within 0.43%. We then implemented this mathematical model into a process superstructure that considers several novel and competing process alternatives for the production of liquid fuels from natural gas. Across different case studies ranging from 500 to 5000 barrels per day of total production, we have observed that the microchannel process can improve break-even oil prices (BEOP) by as much as $10/bbl. Since the small scale GTL process aims to utilize stranded natural gas with almost zero value, a parametric analysis is performed to evaluate the BEOP at different feedstock prices. We have observed that the microchannel reforming alternative is the superior process at all the scales investigated when a natural gas price of $1/TSCF is considered. The topological findings suggest that process intensification through microchannel steam reforming is a viable approach to monetize stranded natural gas.

Porosity effect on ZrO2 hollow shells and hydrothermal stability for catalytic steam reforming of methane

This work reports the development of a Ni@yolk-ZrO2 catalyst, which could be a potential solution to tackling challenges in hydrogen production.

Thermodynamic analysis of hydrogen production via sorption-enhanced steam methane reforming in a new class of variable volume batch-membrane reactor

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO2 adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects.

Methane Steam Reforming over an Ni-YSZ Solid Oxide Fuel Cell Anode in Stack Configuration

The kinetics of catalytic steam reforming of methane over an Ni-YSZ anode of a solid oxide fuel cell (SOFC) have been investigated with the cell placed in a stack configuration. In order to decrease the degree of conversion, a single cell stack with reduced area was used. Measurements were performed in the temperature range 600–800°C and the partial pressures of all reactants and products were varied. The obtained rates could be well fitted with a power law expression (r ∝PCH40.7). A simple model is presented which is capable of predicting the methane conversion in a stack configuration from intrinsic kinetics of the anode support material. The predictions are compared with the stack measurements presented here, and good agreement is observed.

Methane Steam Reforming Kinetics on a Ni/Mg/K/Al2O3 Catalyst

The kinetics of methane steam reforming were studied on a Ni/Mg/K/Al2O3 catalyst that was developed for conditioning of biomass-derived syngas. Reactions were conducted in a packed-bed reactor while the concentrations of reactants (methane and steam) and products (hydrogen, carbon monoxide, and carbon dioxide) were varied at atmospheric pressure, with the effects of temperature (525–700 °C) and residence time also being investigated. A power law rate model was developed using nonlinear regression to provide a predictive capability for the rate of methane conversion over this catalyst, to be used for reactor design and technoeconomic analysis of process designs. In order to provide some mechanistic insight, and to compare this catalyst to other non-promoted Ni/Al2O3 catalysts reported in the literature, a reaction mechanism consisting of five elementary steps, using a Langmuir–Hinshelwood type approach, was also considered. These five steps included: (i) CH4 adsorption, (ii) H2O adsorption, (iii) surface reaction of adsorbed CH4 and H2O to form CO and H2, (iv) CO desorption, and (v) H2 desorption. Nonlinear regression was then used to fit each of the rate laws to the experimental data. From these results, the model that assumed CH4 adsorption to be the rate determining step provided the best fit of the experimental data. This finding is consistent with literature studies on non-promoted Ni/Al2O3 catalysts, in which methane adsorption has been proposed to be the rate determining step during catalytic methane steam reforming. Both the power rate laws and the rate law assuming CH4 adsorption to be the rate determining step can be used as predictive tools for determining methane conversion for a given set of process conditions. Additionally, a rate expression that assumed the rate was only a function of methane partial pressure was considered, namely, \(rate = k*P_{{CH_{4} }}\), where \(k = k_{0} *e^{{^{{ - {\text{Ea}}/{\text{RT}}}} }}\), with PCH4 in units of Torr. This first-order-methane rate expression fit the data well, yielding an apparent activation energy over this catalyst of Ea = 93 kJ/mol and the pre-exponential rate constant of k0 = 7.67 × 105 mol/(g-cat s Torr CH4).

Radial Microchannel Reactors (RMRs) for Efficient and Compact Steam Reforming of Methane: Experimental Demonstration and Design Simulations

This paper provides a first report of a novel radial microchannel reactor (RMR) architecture for catalytic steam reforming of methane to hydrogen and/or synthesis gas. A bench-scale RMR prototype with a channel width of 0.700 mm and wash-coated with 0.030 mm of a Ni-based catalyst is operated at 750 °C and 11 bar with feed composition of 25 mol % CH4, balance H2O. Results indicate that volumetric heat fluxes in excess of 150 W cm–3 are achievable at residence times of 6.8 ms, while volumetric heat fluxes in excess of 100 W cm–3 are observed at overall thermodynamic efficiencies >70%. Computational fluid dynamic (CFD) simulations of the RMR design are demonstrated for accurately predicting methane steam reformer performance and, subsequently, for rapidly investigating the influence of microchannel dimensions upon RMR performance. Design simulations predict that 20–100% improvements in volumetric heat-transfer rates may be achieved by reducing channel widths from 0.700 to 0.300 mm.

On the sol–gel synthesis and catalytic activity of Ce1−xAxO2−δ (A = Pr, Sm, Gd) SOFCs anode materials for reforming of methane

A sol–gel route to synthesize nanocrystalline praseodymium-, samarium- and gadolinium-doped ceria powders for solid oxides fuel Cells SOFCs is presented. The method involves metal nitrates with propionic acid (both as chelating ligand and solvent), gel formation, liquid nitrogen quenching, drying at 150 °C/24 h, and finally decomposition at 450 °C in nitrogen followed by calcination at 650 °C in air. TG–DTA, BET, XRD, FTIR, UV–vis and catalytic tests were used to characterize the samples. Ce0.8Pr0.2O2−δ sample exhibited the best catalytic performance in methane steam reforming under water deficient conditions, closely followed by Ce0.9Gd0.1O2−δ, Ce0.8Sm0.2O2−δ and Ce0.8Gd0.2O2−δ catalysts. The superior catalytic performance of Ce0.8Pr0.2O2−δ sample was attributed to the existence of praseodymium species (Pr4+/Pr3+) strongly interacting with ceria. The two systems act synergistically in the catalytic steam reforming of methane.

Low temperature hydrogen production by catalytic steam reforming of methane in an electric field

Catalytic steam reforming of methane in an electric field (electroreforming) at low temperatures such as 423 K was investigated. Pt catalysts supported on CeO2, CexZr1−xO2 solid solution and a physical mixture of CeO2 and other insulators (ZrO2, Al2O3 or SiO2) were used for electroreforming. Among these catalysts, Pt catalyst supported on CexZr1−xO2 solid solution showed the highest activity for electroreforming (CH4 conv. = 40.6% at 535.1 K). Results show that the interaction among the electrons, metal loading, and catalyst support was important for high catalytic activity on the electroreforming. Catalytic activity of the electroreforming increased in direct relation to the input current. Characterizations using X-ray diffraction (XRD), temperature programmed reduction with H2 (H2-TPR), and alternate current (AC) impedance measurement show that the catalyst structure is an important factor for activity of electroreforming.

Hydrogen production from catalytic steam reforming of methane: influence of catalyst composition

The effect of catalyst support (α-Al2O3, MgO and CaO) and catalyst metal (Ni and Ce) loading in the catalytic steam reforming of methane has been investigated. The catalysts were prepared via a wet impregnation method and examined at temperatures from 500 to 900°C. The results showed that the α-Al2O3 support gave the highest conversion of methane to hydrogen compared to the MgO and CaO supports. The H2 production and CH4 conversion increased at higher temperatures and with higher Ni metal loaded onto the support. There was no significant effect in terms of H2 production and CH4 conversion when >5 wt-% of Ni metal was present in the Ni/Ce/α-Al2O3 catalyst. However, H2 production decreased when the Ni content of the catalyst was >15 wt-%. The addition of Ce in the catalyst reduced the coke formation on the catalyst. The 5Ni/10Ce/α-Al2O3 catalyst was effective at high temperature (>900°C). The 5Ni/10Ce/α-Al2O3 catalyst was also found to be the most efficient catalyst in relation to the highest H2 production and CH4 conversion for the steam reforming of CH4 at 800°C.

Experimental design methodology for optimising catalytic performance of Ni/Ce/<I>α</I>-Al<SUB>2</SUB>O<SUB>3</SUB> catalyst for methane steam reforming

AbstractThe performance of a Ni/Ce/α-Al2O3 catalyst was optimised using a central composite design methodology to enhance hydrogen production and methane conversion in the catalytic steam reforming of methane. The influence of temperature, the presence of weight per cent Ni and Ce in the α-Al2O3 catalyst support and steam/methane ratio on CH4 conversion and H2 production were investigated. A 27 full factorial central composite experimental design was applied to determine the optimal levels for each of the significant variables. A second order polynomial was derived by multiple regression analysis on the experimental data. The CH4 conversion and H2 production increased significantly when the temperature was raised for the catalyst with a 10 wt-% content of Ni. Steam addition improved the CH4 conversion and H2 production; however, this required a higher operating temperature. Using this methodology, the optimum experimental values of 93·1%CH4 conversion and 73·5 vol.-%H2 were obtained using a catalyst with ...

Low temperature steam reforming of methane over metal catalyst supported on Ce xZr 1− xO 2 in an electric field

Catalytic steam reforming of methane in an electric field (named “electreforming”) was conducted over metal catalysts supported on CeO 2 or Ce x Zr 1− x O 2 at low temperatures such as 423 K where conventional catalytic reactions hardly proceeded. The conversion of methane was greatly increased by weak and effective application of an electric field to the catalyst bed. Use of Ce x Zr 1− x O 2 as a catalyst support promoted electreforming, the lattice oxygen of Ce x Zr 1− x O 2 playing an important role. Energy efficiency of electreforming, reaction mechanism, and the role of lattice oxygen were investigated and are discussed in this paper.

Catalytic steam reforming of methane under conditions of applicability with Pd membranes over supported Ru catalysts

Three Ru catalysts supported on SiO 2, ZrO 2–SiO 2 and ZrO 2–La 2O 3 have been prepared, characterized and tested in the methane steam reforming (SR) reaction, and for comparative purposes a Ni/SiO 2 catalyst has also been studied. Conditions of catalytic studies have been selected for the subsequent application in a hydrogen extraction Pd membrane reactor. That is, reaction temperatures in the range of 400–550 °C and with different amounts of catalyst in order to work under and/or close to the equilibrium conversion conditions. All the supported Ru samples exhibit high catalytic activity and similar CO and H 2 yields. Finally these catalysts are fully stable under reaction conditions at 550 °C for 15 h, while the Ni/SiO 2 sample suffers a significant deactivation. The main deactivation process affecting this latter catalyst is the carbon deposition of partially dehydrogenated intermediates as detected by Raman spectroscopy. Hence, these Ru catalysts appear to be suitable for application combined with metallic (Pd) membrane.

Potential for hydrogen generation from in situ combustion of Athabasca bitumen

The volume of heavy oil and bitumen in Alberta, Canada is estimated to be about 1.7 trillion barrels. The majority of the produced heavy oil and bitumen in Alberta is converted in surface upgraders to synthetic crude oil, a crude oil with API gravity typically between 31 and 33° API, which in turn can be converted to fuel, lubricant, and petrochemical products in standard refineries. To upgrade bitumen requires hydrogen. In current practice, much of this hydrogen is generated from catalytic steam reforming of methane together with the water–gas shift reaction. This means that heavy oil and bitumen upgrading, as is currently done, requires large amounts of natural gas to generate hydrogen. The potential for in situ generation of hydrogen by gasification of bitumen reservoirs offers an attractive alternative which can also have both economic and environmental benefits. For example, hydrogen generated from bitumen gasification can also be used for in situ upgrading as well as feedstock for ammonia and other chemicals. The water–gas shift reaction also generates carbon dioxide which could be potentially sequestered in an in situ gasification process so that emissions to the atmosphere are reduced. This technology provides a potential clean method to produce fuel and feedstock material from bitumen, a relatively “dirty” fuel and feedstock oil, in addition to more energy efficient ways of extracting in situ heavy oils. However, to design in situ bitumen gasification processes requires a reaction model that provides a reasonable representation of the gasification reactions. Here, a new kinetic model is developed to examine the potential for hydrogen generation from Athabasca bitumen. The kinetic model consists of thermal cracking, oxidation/combustion, hydrogen generation and hydrogen consumption reactions. A comparison of the simulation results and experimental data from the published literature reveal that the new model can predict hydrogen generation from gasification of methane, Athabasca bitumen, and coke.

Low temperature catalytic methane steam reforming over ceria–zirconia supported rhodium

This paper presents an experimental study of the catalytic steam reforming of methane over newly developed ceria–zirconia supported rhodium as an active candidate catalyst for low temperature sorption enhanced hydrogen production from methane. The kinetic experiments are performed in a tubular fixed bed reactor over a temperature range of 475–725 °C and a total pressure of 1.5 bar in the absence of mass transport limitations. The over all reaction orders in methane and steam are determined to be less than 1 from 475 to 625 °C. At low temperature, most of the gas product is composed of CO 2 and H 2 due to the pronounced influence of the water–gas shift reaction. At higher temperature and low steam/carbon ratio (S/C), this influence is diminished. Inhibitory effects of H 2, CO, and CO 2 on the methane conversion rates are detected. Temperature-programmed steam reforming experiments over ceria–zirconia support revealed insignificant methane adsorption on the surface from 550 to 725 °C. Catalyst deactivation and steady state stability over time were examined. A molecular reaction mechanism is proposed to qualitatively explain the kinetic observations. Two distinct sites are thought to be responsible for the dissociative adsorption of methane and steam on the catalyst and the support surfaces. Methane is dissociatively adsorbed on the rhodium active metal sites and steam is dissociatively adsorbed on the support surface. Surface reactions of carbon containing methane precursors on the interface between the active metal and the support are considered to be the rate determining steps.

Catalytic steam reforming of methane using Rh supported on Sr-substituted hexaaluminate

This paper reports the synthesis, characterization, and performance of steam-reforming catalysts based upon dispersed Rh particles on Sr-substituted hexaaluminate supports. As confirmed by electron microscopy and X-ray diffraction, the Sr-substituted hexaaluminate provides a plate-like support structure that resists sintering and occlusion of the Rh. The hexaaluminate is synthesized using an alumoxane process, with the cation substitution accomplished by exchange with metal acetylacetonates. The Rh is dispersed using impregnation with metal-nitrate salts. A stagnation-flow reactor is used to measure catalytic activity. In these experiments, the catalyst is applied to a flat surface that is held at a fixed temperature. Reactive gases (methane, steam, and diluent) impinge on the catalytic stagnation surface. Microprobe mass spectrometry is used to measure gas-phase species profiles in the boundary layer normal to the catalyst surface. The experiments are interpreted using a chemically reacting flow model, including an elementary heterogeneous chemical reaction mechanism. Results confirm that the Rh on Sr-substituted hexaaluminate is a highly stable and active reforming catalyst.