Hydrogen production from methane under the interaction of catalytic partial oxidation,water gas shift reaction and heat recovery

Hydrogen production from the combination of catalytic partial oxidation of methane (CPOM) and water gas shift reaction (WGSR), viz. the two-stage reaction, in a Swiss-roll reactor is investigated numerically. Particular emphasis is placed on the interaction among the reaction of CPOM, the cooling effect due to steam injection and the excess enthalpy recovery with heat recirculation. A rhodium (Rh) catalyst bed sitting at the center of the reactor is used to trigger CPOM, and two different WGSRs, with the aids of a high-temperature (Fe–Cr-based) shift catalyst and a low-temperature (Cu–Zn-based) shift catalyst, are excited. Two important parameters, including the oxygen/methane (O/C) ratio and the steam/methane (S/C) ratio, affecting the efficiencies of methane conversion and hydrogen production are taken into account. The predictions indicate that the O/C ratio of 1.2 provides the best production of H₂ from the two-stage reaction. For a fixed O/C ratio, the H₂ yield is relatively low at a lower S/C ratio, stemming from the lower performance of WGSR, even though the cooling effect of steam is lower. On the contrary, the cooling effect becomes pronounced as the S/C ratio is high to a certain extent and the lessened CPOM leads to a lower H₂ yield. As a result, with the condition of gas hourly space velocity (GHSV) of 10,000 h⁻¹, the optimal operation for hydrogen production in the Swiss-roll reactor is suggested at O/C = 1.2 and S/C = 4–6.     

Mathematical simulation of hydrogen production via methanol steam reforming using double-jacketed membrane reactor

The hydrogen production and purification via methanol reforming reaction was studied in a double-jacketed Pd membrane reactor using a 1-D, non-isothermal mathematical model. Both mass and heat transfer behavior were evaluated simultaneously in three parts of the reactor, annular side, permeation tube and the oxidation side. The simulation results exhibited that increasing the volumetric flow rate of hydrogen in permeation side could enhance hydrogen permeation rate across the membrane. The optimum velocity ratio between permeation and annular sides is 10. However, hydrogen removal could lower the temperature in the reformer. The hydrogen production rate increases as temperature increases at a given Damköhler number, but the methanol conversion and hydrogen recovery yield decrease. In addition, the optimum molar ratio of air and methanol was 1.3 with three air inlet temperatures. The performance of a double-jacketed membrane reactor was compared with an autothermal reactor by judging against methanol conversion, hydrogen recovery yield and production rate. Under the same reaction conditions, the double-jacketed reactor can convert more methanol at a given reactor volume than that of an autothermal reactor.     

Hydrogen production by glycerol reforming in a two-fixed-bed reactor

A two-stage fixed bed system was used in the hydrogen production from glycerol reforming. The calcined dolomite catalyst was used in the first fixed bed, and the Nickel-based catalyst was used in the second fixed bed to produce hydrogen from the glycerol steam reforming. The results showed that the hydrogen yield and carbon conversion gradually increased with the temperature increasing. When the temperature exceeded 800 °C, the growth rate of hydrogen yield and carbon conversion decreased. As the space velocity increased, the hydrogen yield and carbon conversion gradually decreased. When the space velocity was greater than 2 h^?1, the decline rate of hydrogen yield and carbon conversion decreased rapidly. As the water-to-carbon ratio (S/C) increased, the hydrogen yield and carbon conversion gradually increased. The growth rate of hydrogen yield and carbon conversion became smaller when the S/C was more than 5. Compared with the single-stage fixed-bed reactor, the utilization of two-stage fixed-bed catalytic reaction system can not only increase the hydrogen yield and carbon conversion, but extend the life of the Nickel-based catalyst. Under the optimal reaction conditions, the hydrogen yield is as high as 84.3%, and the carbon conversion is as high as 88.23%.     

Hydrogen production via catalytic pulsed plasma conversion of methane: Effect of Ni–K2O/Al2O3 loading,applied voltage,and argon flow rate

Despite industrial application of methane as an energy source and raw material for chemical manufacturing, it is a potent heat absorber and a strong greenhouse gas. Evidently reduction of methane emission especially in the natural gas sector is essential. Methane to hydrogen conversion through non-thermal plasma technologies has received increasing attention. In this paper, catalytic methane conversion into hydrogen is experimentally studied via nano-second pulsed DBD plasma reactor. The effect of carrier gas flow, applied voltage, and commercial Ni–K₂O/Al₂O₃ catalyst loading on methane conversion, hydrogen production, hydrogen selectivity, discharge power, and energy efficiency are studied. The results showed that in the plasma alone system, the highest methane conversion and hydrogen production occurs at argon flow rate of 70 mL/min. Increase in the applied voltage increases the methane conversion and hydrogen production while it decreases the energy efficiency. Presence of 1 g Ni–K₂O/Al₂O₃ catalyst shifts the optimum voltage for methane conversion and hydrogen production to 8 kV, reduces the required power, and increases the energy efficiency of the process. Finally in the catalytic plasma mode the optimum process condition occurs at the argon flow rate of 70 mL/min, applied voltage of 8 kV, and catalyst loading of 6 g. Compared with the optimum condition in the absence of catalyst, presence of 6 g Ni–K₂O/Al₂O₃ catalyst increased the methane conversion, hydrogen production, hydrogen selectivity and energy efficiency by 15.7, 22.5, 7.1, and 40% respectively.     

Enhancement effect of heat recovery on hydrogen production from catalytic partial oxidation of methane

The effect of heat recovery on hydrogen production from catalytic partial oxidation of methane (CPOM) and its reaction characteristics in a reactor are investigated using numerical simulations. The reactor is featured by a Swiss-roll structure in which a rhodium (Rh) catalyst bed is embedded at the center of the reactor. By recovering the waste heat from the product gas to preheat the reactants, it is found that the combustion, steam reforming and dry reforming of methane in the catalyst bed are enhanced to a great extent. As a result, the methane conversion and hydrogen yield are improved more than 10%. Considering the operation conditions, a high performance of hydrogen production from CPOM can be achieved if the number of turns in the reactor is increased or the gas hourly space velocity (GHSV) of the reactants in the catalyst bed is lower. However, with the condition of heat recovery, the flow direction of the reactants in the reactor almost plays no part in affecting the performance of CPOM. In summary, the predictions reveal that the reactor with a Swiss-roll structure can be applied for implementing CPOM with high yield of hydrogen.     

Plasma reforming for hydrogen production: Pathways,reactors and storage

Hydrogen is an energy carrier with a very high energy density (>119 MJ/kg). Pure hydrogen is barely available; thus, it requires extraction from its compounds. Steam reforming and water electrolysis are commercially viable technologies for hydrogen production from water, alcohols, methane, and other hydrocarbons; however, both processes are energy-intensive. Current study aims at understanding the methane and ethanol-water mixture pathway to generate hydrogen molecules. The various intermediate species (like CH_X, CH₂O, CH₃CHO) are generated before decomposing methane/ethanol into hydrogen radicals, which later combine to form hydrogen molecules. The study further discusses the various operating parameters involved in plasma reforming reactors. All the reactors work on the same principle, generating plasma to excite electrons for collision. The dielectric barrier discharge reactor can be operated with or without a catalyst; however, feed flow rate and discharge power are the most influencing parameters. In a pulsed plasma reactor, feed flow rate, electrode velocity, and gap are the main factors that can raise methane conversion (40–60%). While the gliding arc plasma reactor can generate up to 50% hydrogen yield at optimized values of oxygen/carbon ratio and residence time, the hydrogen yield in the microwave plasma reactor is affected by flow rate and feed concentration. Therefore, all the reactors have the potential to generate hydrogen at lower energy demand.     

Characteristics of hydrogen production by a plasma–catalyst hybrid converter with energy saving schemes under atmospheric pressure

This paper investigated the production of hydrogen from methane under atmospheric pressure using a plasma–catalyst hybrid converter with emphasis on energy conservation. A spark discharge was used to ionize the hydrocarbon fuel and air mixture with a catalyst to enhance hydrogen production using two energy saving schemes, namely, heat recycling and heat insulation. The experimental results showed that higher methane feeding rate resulted in higher reformate gas temperature and a corresponding increase in methane conversion efficiency. The energy saving systems also enabled the oxygen/carbon ratio to be decreased to reduce oxidation of hydrogen and carbon monoxide and thereby improving the concentrations of hydrogen and carbon monoxide. By heat recycling, a lower methane feeding rate showed an 8.7% improvement in methane conversion efficiency whilst improvement was not apparent with higher methane supply rates due to the already high conversion efficiency. Moreover, it was shown that hydrogen production increased significantly with the reaction from water–gas shifting under the same operation parameters but with high methane selectivity. The best combination resulting in a total thermal efficiency of 77.11% was 10 L/min methane feeding rate and 0.8 O₂/C ratio. With water–gas shifting (S/C ratio=0.5), an 86.26% hydrogen yield, equating to 17.25 L/min hydrogen production rate could be achieved. The equilibrium production rate was calculated using the commercialized HSC Chemistry software (^©ChemSW Software, Inc.). Good correlation was obtained between the calculations and the experimental results.     

Experimental study on partial oxidation of methane to produce hydrogen using low‐temperature plasma in AC Glidarc discharge

A reformer using low‐temperature plasma was designed and developed for hydrogen production. The reformer has three electrodes and uses AC gliding arc discharge. A reference condition, which is the highest hydrogen production, has a O₂/C ratio of 0.45, input flow rate of 4.9 l min^?1 and power supply of 1 kW. And the methane conversion rate, the high hydrogen selectivity and the reformer efficiency were 69.2, 77.8 and 35.2%, respectively. To investigate reforming characteristics, parametric studies were achieved for the gas components ratio, a gas flow rate, a reactor temperature, an input electric power and catalyst addition effect. The results are as follows: The gas components ratio was an important factor, which had maximum value. When the gas flow rate, the reactor temperature and the electric power were increased, the methane conversion rate and the hydrogen concentration also increased. Copyright © 2008 John Wiley & Sons, Ltd.     

Production of hydrogen by partial oxidation with thermal plasma

The purpose of this paper is to investigate the characteristics and optimum operating conditions of the plasmatron-assisted CH₄ reforming reaction for the hydrogen-rich gas production. In order to increase the hydrogen production and the methane conversion rate, parametric screening study was conducted at various CH₄ flow ratio and steam flow ratio and with and without adding catalyst in the reactor. High-temperature plasma flame was made with air and arc discharge, and the air flow rate and the input power were set to 5.1  L/min and 6.4 kW, respectively.When the steam flow ratio was 30.2%, the hydrogen production was maximized and the optimal methane conversion rate was 99.7%. Under these optimal conditions, the following syngas concentrations were determined: H₂, 50.4%; CO, 5.7%; CO₂, 13.8%; and C₂H₂, 1.1%. H₂/CO ratio was 9.7 and the hydrogen yield was 93.7%.     

Design and testing of a novel catalytic reactor to generate hydrogen

A catalytic reactor to generate hydrogen with a large conversion efficiency and a stable rate of generation is based on a π-shaped design that decreases the effect of hydrogen on the catalyst surface so as to increase the opportunities for contact between sodium borohydride (NaBH₄) and the catalyst. This novel design is tested in terms of the effect of its rate of volumetric flow, position of catalyst, angle of flow channel, ratio of areas of gas channel and flow channel, and ratio of widths of gas channel and flow channel, on the efficiency of chemical conversion and the stability of hydrogen generation. We compare this efficiency and stability with the corresponding properties of a conventional reactor. The results indicate that placing the catalyst at the back of the flow channel provided uninterrupted space for liquid and gas at the front end, thereby improving the sustainability of the sodium borohydride for the catalytic reaction. An increased angle of the flow channel improved the capability of bubbles to escape from the surface of the catalyst, which, when appropriately designed, increased the efficiency by 13.4%. The increased rate of volume flow of sodium borohydride resulted in a decreased duration of contact between sodium borohydride and the catalyst, thereby decreasing the conversion efficiency. When the rate of volume flow of sodium borohydride was 0.5–2.0 mL/min, the effect of ratios of area and widths of gas channel to flow channel on the overall conversion efficiency followed no significant pattern. A comprehensive comparison between a conventional reactor and this new gas-flow channel-based reactor showed that, when appropriately designed, the new reactors can increase the efficiency of chemical conversion from 69.7% to 90.2%, with a decreased amplitude of hydrogen generation from 250% to 42.9%.     

Thermal behavior and hydrogen production of methanol steam reforming and autothermal reforming with spiral preheating

The present study aims to investigate the thermal behavior and hydrogen production characteristics from methanol steam reforming (MSR) and autothermal reforming (ATR) under the effects of a Cu-Zn-based catalyst and spiral preheating. Two different reaction temperatures of 250 and 300 °C are taken into account. Meanwhile, the O/C ratio (i.e. the molar ratio between O₂ and methanol) and S/C ratio (i.e. the molar ratio between steam and methanol) are controlled in the ranges of 0-0.5 and 1-2, respectively. The condition of O/C = 0 represents the reaction of MSR. By monitoring the supplied power into the reactor with a fixed gas hourly space velocity (GHSV) of 72,000 h⁻¹, the experimental results indicate that an exothermic reaction from ATR can be attained once the O/C ratio is as high as 0.125. Increasing O/C ratio causes more heat released from the reaction, this results in the decrease in the frequency of supplied power, especially at O/C = 0.5. It is noted that the concentration of CO in the product gas is quite low compared to that of CO₂. An increase in O/C ratio abates the concentration of H₂ from the consumption of per mol methanol; however, the H₂ yield in terms of thermodynamic analysis is increased. On account of the utilization of spiral preheating on the reactants, within the investigated operating conditions the methanol conversion and hydrogen yield were always higher than 95 and 90%, respectively. A comparison suggests that the methanol conversion from ATR of methanol with spiral preheating is superior to those of other studies.     

Enhancement of hydrogen reaction in a micro-channel by catalyst segmentation

The paper addresses the combustion characteristics of multi-segment catalysts in a micro-reactor by numerical simulation with detailed heterogeneous and homogeneous chemistries. The effect of multi-segment catalyst is delineated in terms of different catalyst dispositions, different flow conditions and different reactor properties. With a fixed total catalyst length (1 cm), multi-segment catalyst reveals better performance than single catalyst. The space between catalyst segments reduces the inhibition of homogeneous reactions by catalyst and promotes homogeneous reactions in this region since the neighboring catalysts help to maintain a high wall temperature. Therefore, homogeneous combustion can shift upstream with the multi-segment catalyst. The results of different catalyst dispositions show that more catalyst segments has better performance but the catalyst space distance has no obvious effects due to the fast reaction rate of hydrogen. For different flow conditions, the results indicate multi-segment catalyst disposition has better conversion ratio even though there is no homogeneous combustion in the fluid region for fuel-lean condition. The results for different inlet velocities show that multi-segment catalyst has no obvious benefit on lower inlet velocity. However, it can extend the blowout velocity. Finally different reactor dimension and wall material are simulated. Although heterogeneous reactions strengthen in small channel, multi-segment catalyst still has obvious benefit. The results of different wall thermal conductivity do not have obvious difference for multi-segment catalyst. These results can be used in the design of a catalytic micro-reactor for hydrogen/air reactions.     

二甲醚水蒸气重整制氢的模型建立和数值模拟

为研究二甲醚的水蒸气重整制氢过程,设计了一种带有隔热套、瓦片式加热通道和催化反应床的重整反应器。建立了反应器的数学模型,并利用COMSOL软件对其仿真。试验研究了反应气体温度、水蒸气与二甲醚的物质的量比和反应器结构参数对二甲醚转化率、氢产率的影响。模拟结果显示了二甲醚水蒸气重整制氢过程中的各组分质量分布及不同温度、不同水醚物质的量比下二甲醚转化率和制氢率情况,给重整器的研究提供了参考。通过试验验证了模型的可行性,获得了微型催化重整床反应器的设计数据。结果显示较高的进口温度可以提升反应速率,从而提高二甲醚转化率;水醚物质的量比的提高促进了正反应,加快了二甲醚的消耗,提高了二甲醚的转化率和氢产率。     

Methanol steam reforming reaction in a Pd–Ag membrane reactor for CO-free hydrogen production

A dense tubular Pd–Ag membrane reactor was used to carry out the methanol steam reforming reaction for producing a CO-free hydrogen stream. A Cu/Zn/Mg-based catalyst was packed in the lumen side of the membrane reactor and the experimental tests were performed at a reaction temperature of 300 °C and at a H₂O/methanol feed molar ratio of 3/1. The effects of the different flow configurations, as well as the sweep factor and the reaction pressure were analysed. Experimental results in terms of CO-free hydrogen recovery, hydrogen yield, CO-free hydrogen yield and hydrogen selectivity are presented. Moreover, a comparison between the performances of the membrane reactor and a traditional reactor working at the same operative conditions is proposed and discussed.     

Hydrogen production using integrated methanol‐steam reforming reactor with various reformer designs for PEM fuel cells

A 95 mm × 40 mm × 15 mm compact reactor for hydrogen production from methanol‐steam reforming (MSR) is constructed by integrating a vaporizer, reformer, and combustor into a single unit. CuO/ZnO/Al₂O₃ is used as the catalyst for the MSR while the required heat is provided using Platinum (Pt) ‐catalytic methanol combustion. The reactor performance is measured using three reformer designs: patterned micro‐channel; inserted catalyst layer placed in a single plain channel; and catalyst coated directly on the bottom wall of single plain channel. Because of longer reactant residence time and more effective heat transfer, slightly higher methanol conversion can be obtained from the reformer with patterned microchannels. The experimental results show that there is no significant reactor performance difference in methanol conversion, hydrogen (H₂) production rate, and carbon monoxide (CO) composition among these three reformer designs. These results indicated that the flow and heat transfer may not play important roles in compact size reactors. The reformer design with inserted catalyst layer provides convenience in replacing the aged catalyst, which may be attractive in practical applications compared with the conventional packed bed and wall‐coated reformers. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental and theoretical analysis of a monolith type auto-thermal reforming reactor

In this study, the effects of inlet conditions on the performance of a natural gas autothermal reforming reactor loaded with a commercial monolith catalyst are investigated. The reactor has a hydrogen production capacity of 1.5 kW and, is a part of a fuel processor, applicable in a residential-scale fuel cell system. Experimental, kinetic and equilibrium results are all presented. The experimental data were input into commercial software, Aspen HYSYS (ver.8.8). Equilibrium state calculations are based on the maximization of entropy. Monolith catalyst performance is consistent with thermodynamics, especially for lower oxygen feeding. The kinetic is also run into HYSYS and the results are in harmony with the experimental findings. The effects of the operating parameters, namely the oxygen-to-carbon ratio, the steam-to-carbon ratio and the reactor inlet temperature, on the hydrogen yield, fuel conversion, efficiency, and compositions are discussed experimentally and theoretically. The main impact among the parameters that affect the monolith performance is determined as the oxygen-to-carbon ratio. The favourable operating conditions are determined as inlet temperatures of 400 °C–550 °C, the steam-to-carbon ratio of 3.0, and the oxygen-to-carbon ratio of 0.5 with the hydrogen yield of 2.32–2.46, fuel conversion of 90%–96.5% and the efficiency of 67–72%.     

Numerical and experimental study on hydrogen production via dimethyl ether steam reforming

This work presents the characteristics of catalytic dimethyl ether (DME)/steam reforming based on a Cu–Zn/γ-Al₂O₃ catalyst for hydrogen production. A kinetic model for a reformer that operates at low temperature (200 °C–500 °C) is simulated using COMSOL 5.2 software. Experimental verification is performed to examine the critical parameters for the reforming process. During the experiment, superior Cu–Zn/γ-Al₂O₃catalysts are manufactured using the sol-gel method, and ceramic honeycombs coated with this catalyst (1.77 g on each honeycomb, five honeycombs in the reactor) are utilized as catalyst bed in the reformer to enhance performance. The steam, DME mass ratio is stabilized at 3:1 using a mass flow controller (MFC) and a generator. The hydrogen production rate can be significantly affected depending on the reactant's mass flow rate and temperature. And the maximum hydrogen yield can reach 90% at 400 °C. Maximum 8% error for the hydrogen yield is achieved between modeling and experimental results. These experiments can be further explored for directly feeding hydrogen to proton exchange membrane fuel cell (PEMFC) under the load variations.     

Simulation of a fuel reforming system based on catalytic partial oxidation

Catalytic partial oxidation (CPO) has potential for producing hydrogen that can be fed to a fuel cell for portable power generation. In order to be used for this purpose, catalytic partial oxidation must be combined with other processes, such as water-gas shift and preferential oxidation, to produce hydrogen with minimal carbon monoxide. This paper evaluates the use of catalytic partial oxidation in an integrated system for conversion of a military logistic fuel, JP-8, to high-purity hydrogen. A fuel processing system using CPO as the first processing step is simulated to understand the trade-offs involved in using CPO. The effects of water flow rate, CPO reactor temperature, carbon to oxygen ratio in the CPO reactor, temperature of preferential oxidation, oxygen to carbon ratio in the preferential oxidation reactor, and temperature for the water-gas shift reaction are evaluated. The possibility of recycling water from the fuel cell for use in fuel processing is evaluated. Finally, heat integration options are explored. A process efficiency, defined as the ratio of the lower heating value of hydrogen to that of JP-8, of around 53% is possible with a carbon to oxygen ratio of 0.7. Higher efficiencies are possible (up to 71%) when higher C/O ratios are used, provided that olefin production can be minimized in the CPO reactor.     

CO-free hydrogen production by steam reforming of acetic acid carried out in a Pd–Ag membrane reactor: The effect of co-current and counter-current mode

In this experimental work, a dense tubular Pd–Ag membrane reactor is used for carrying out the acetic acid steam reforming reaction for producing a CO-free hydrogen stream. The influence of the different flow configurations, as well as the sweep factor and the reaction pressure is analysed. A Ni-based commercial catalyst was packed in the lumen side of the membrane reactor and the experimental tests were performed at a reaction temperature of 400 °C and at a H₂O/acetic acid feed molar ratio of 10/1. Results in terms of CO-free hydrogen recovery, hydrogen yield and products selectivities are proposed. Moreover, a comparison between the performances of the membrane reactor and a traditional reactor working at the same operative conditions is illustrated and discussed.     

A study of methanol steam reforming on distributed catalyst bed

Heterogeneous catalytic fixed bed usually suffers from severe limitations of mass and heat transfer. These disadvantages limit reformers to a low efficiency of catalyst utilization. Three catalyst activity distributions have been applied to force the reactor temperature profile to be near isothermal operation for maximization of methanol conversion. A plate-type reactor has been developed to investigate the influence of catalyst activity distribution on methanol steam reforming. Cold spot temperature gradients are observed in the temperature profile along the reactor axis. It has been experimentally verified that reducing cold spot temperature gradients contributes to the improvement of the catalytic hydrogen production. The lowest cold spot temperature gradient of 3 K is obtained on gradient catalyst distribution type A. This is attributed to good characteristics of local thermal effect. Low activity at the reactor inlet with gradual rise along with the reactor flow channel forms the optimal activity distribution. Hydrogen production rate of 161.3 L/h is obtained at the methanol conversion of 93.1% for the gradient distribution type A when the inlet temperature is 543 K.