A performance study of methanol steam reforming microreactor with porous copper fiber sintered felt as catalyst support for fuel cells

A porous copper fiber sintered felt (PCFSF) as catalyst support is used to construct a methanol steam reforming microreactor for hydrogen production. The PCFSF has been produced by solid-state sintering of copper fibers which is fabricated using the cutting method. The impregnation method is employed to coat Cu/Zn/Al/Zr catalyst on the PCFSF. In this study, the effect of the porosity and manufacturing parameters for the PCFSF on the performance of methanol steam reforming microreactor is studied by varying the gas hourly space velocity (GHSV) and reaction temperature. When the 80% porosity PCFSF sintered at 800 °C in the reduction atmosphere is used as catalyst support, it is found that the microreactor shows remarkable superiority in the methanol conversion and H₂ flow rate in comparison to the ones fabricated under other manufacturing parameters. Moreover, the microreactor with this catalyst-coated PCFSF also demonstrates the excellent stability of catalytic reaction in the methanol steam reforming process.     

Factors influencing methanol steam reforming inside the oriented linear copper fiber sintered felt

A kind of oriented linear copper fiber sintered felt as a catalyst support for methanol steam reforming is briefly introduced in this work. The sintered felt porosity, sintered felt length and manifold shape as three fundamental influencing factors are experimental investigated their effects on the performances of methanol steam reforming. Experimental results indicate that the sintered felt with moderate porosity and long sintered felt length can effectively enhance the reaction performances of methanol steam reforming. The sintered felt with symmetric triangle manifold can achieve better reaction performances than the one with oblique triangle manifold. However, it is also found that the structural parameters of sintered felt and manifold shape show little influence on the methanol steam reforming at low GHSVs and reaction temperatures. Among these influencing factors, the sintered felt length showed much more influences on the performances of methanol steam reforming than the sintered felt porosity and manifold shape at high reaction temperature.     

Numerical study of flow distribution uniformity for the optimization of gradient porosity configuration of porous copper fiber sintered felt for hydrogen production through methanol steam reforming micro-reactor

A macroscopic numerical method is proposed to study the flow distribution uniformity of a novel porous copper fiber sintered felt (PCFSF), which has gradient porosities and was developed as the methanol steam reforming micro-reactor catalyst support for hydrogen production for fuel cell applications. The macroscopic porous media developed by the ANSYS/FLUENT software is used to represent the PCFSF. Our results indicate that the gradient porosity can reshape the flow distribution of PCFSFs greatly, thus producing significant influence on their performance. It is further revealed that, for a PCFSF with a determined gradient porosity configuration but different reactant feed directions, the velocity uniformity can be used as a quantitative criterion to evaluate the performance of hydrogen production. Furthermore, new gradient PCFSFs are produced according to the flow distribution of original gradient PCFSFs. The preliminary experimental results of the new gradient PCFSFs of 0.8-0.9-0.7 and 0.7-0.9-0.8 exhibit better methanol conversion and H₂ flow rate. This indicates that the numerical method can be used for the optimization of PCFSFs' gradient porosity configuration, which consists of the shape and position of the interfaces between different porosity portions, the number of interfaces and the porosity distribution in different portions.     

Oriented linear cutting fiber sintered felt as an innovative catalyst support for methanol steam reforming

A kind of oriented linear cutting fiber sintered felt as an innovative catalyst support for methanol steam reforming was proposed. Multiple long copper fibers fabricated by cutting method were arranged in parallel and then sintered together in a mold pressing equipment under the condition of high temperature and protective gas atmosphere. The characteristics of oriented linear cutting fiber sintered felt coated with Cu/Zn/Al/Zr catalyst for methanol steam reforming were experimental investigated under different GHSVs and reaction temperatures. Results indicated that the structure of sintered felt was the key influencing factor for the reaction performances on the condition of low GHSV or reaction temperature whereas the structure of sintered felt showed little influences with high GHSV or reaction temperature. By the analysis of SEM image and ultrasonic vibration testing method, it was found that the coarse surface pattern of cutting fiber could effectively enhance the adhesion intensity between the catalyst and the copper fibers, as well as present relatively large specific surface area in the microchannels. And hence the oriented linear cutting fiber sintered felt present better performances of methanol steam reforming than the oriented linear copper wire sintered felt on the condition of low GHSV or reaction temperature.     

Methanol steam reforming in a planar wash coated microreactor integrated with a micro-combustor

A numerical simulation of methanol steam reforming in a microreactor integrated with a methanol micro-combustor is presented. Typical Cu/ZnO/Al₂O₃ and Pt catalysts are considered for the steam reforming and combustor channels respectively. The channel widths are considered at 700 μm in the baseline case, and the reactor length is taken at 20 mm. Effects of Cu/ZnO catalyst thickness, gas hourly space velocities of both steam reforming and combustion channels, reactor geometry, separating substrate properties, as well as inlet composition of the steam reforming channel are investigated. Results indicate that increasing catalyst thickness will enhance hydrogen production by about 68% when the catalyst thickness is increased from 10 μm to 100 μm. Gas space velocity of the steam reforming channel shows an optimum value of 3000 h⁻¹ for hydrogen yield, and the optimum value for the space velocity of the combustor channel is calculated at 24,000 h⁻¹. Effects of inlet steam to carbon ratio on hydrogen yield, methanol conversion, and CO generation are also examined. In addition, effects of the separating substrate thickness and material are examined. Higher methanol conversion and hydrogen yield are obtained by choosing a thinner substrate, while no significant change is seen by changing the substrate material from steel to aluminum with considerably different thermal conductivities. The produced hydrogen from an assembly of such microreactor at optimal conditions will be sufficient to operate a low-power, portable fuel cell.     

Experiments on hydrogen production from methanol steam reforming in the microchannel reactor

The entire experiments were conducted for microchannel methanol steam reforming, by which, the selection of catalyst, the operating parameters and the configuration of microchannels were discussed thoroughly. It was found that the higher the Cu concentration is, the more the corresponding active surface area of Cu will be, thereby improving the catalytic activity. The Cu-to-Zn ratio in Cu/ZnO/Al₂O₃ catalyst should be set at 1:1. The impacts of reaction temperature, feed flow rate, mixture temperature, and H₂O-to-CH₃OH molar ratio on the methanol conversion rate were also revealed and discussed. Characteristics of micro-reactors with various microchannels, including that 20 mm and 50 mm in length, as well as non-parallel microchannels, were investigated. It was found that the increase of microchannel length can improve the methanol conversion rate significantly. Besides, non-parallel microchannels help to maintain flow and temperature distribution uniformity, which can improve the performance of micro-reactor. In the present experiments, the presence of CO was under the condition that the methanol conversion rate was above 70%.     

Experiments on hydrogen production from methanol steam reforming in fluidized bed reactor

A novel approach for the hydrogen production which integrated methanol steam reforming and fluidized bed reactor (FBR) was proposed. The reaction was carried out over Cu/ZnO/Al₂O₃ catalysts. The critical fluidized velocities under different catalyst particle sizes and masses were obtained. The influences of the operating parameters, including that of H₂O-to-CH₃OH molar ratio, feed flow rate, reaction temperature, and catalyst mass on the performance of methanol steam reforming were investigated in FBR to obtain the optimum experimental conditions. More uniform temperature distribution, larger surface volume ratio and longer contacting time can be achieved in FBR than that in fixed bed reactor. The results indicate that the methanol conversion rate in FBR can be as high as 91.95% while the reaction temperatures is 330 °C, steam-to-carbon molar ratio is 1.3, and feed flow rate is 540 ml/h under the present experiments, which is much higher than that in the fixed bed.     

A novel thermally autonomous methanol steam reforming microreactor using SiC honeycomb ceramic as catalyst support for hydrogen production

Methanol steam reforming (MSR) is an attractive option for in-situ hydrogen production and to supply for transportation and industrial applications. This paper presents a novel thermally autonomous MSR microreactor that uses silicon carbide (SiC) honeycomb ceramic as a catalyst support to enhance energy conversion efficiency and hydrogen production. The structural design and working principle of the MSR microreactor are described along with the development of a 3D numerical model to study the heat transfer and fluid flow characteristics. The simulation results indicate that the proposed microreactor has a significantly low drop in pressure and more uniform temperature distribution in the SiC ceramic support. Further, the microreactor was developed and an experimental setup was conducted to test its hydrogen production performance. The experimental results show that the developed microreactor can be operated as thermally autonomous to reach its target working temperature within 9 min. The maximum energy efficiency of the microreactor is 67.85% and a hydrogen production of 316.37 ml/min can be achieved at an inlet methanol flow rate of 360 μl/min. The obtained results demonstrate that SiC honeycomb ceramic with high thermal conductivity can serve as an effective catalyst support for the development of MSR microreactors for high volume and efficient hydrogen production.     

Hydrogen production and thermal behavior of methanol autothermal reforming and steam reforming triggered by microwave heating

Hydrogen production and thermal behavior of methanol autothermal reforming (ATR) triggered by microwave heating are studied. Methanol steam reforming (MSR) is also investigated for comparison. A commercial Cu–Zn-based catalyst is used. The gas hourly space velocity (GHSV) is fixed at 72,000 h⁻¹, and the reaction temperature and the oxygen/methanol molar ratio (i.e. O₂/C ratio) are in the ranges of 250–300 °C and 0–0.5, respectively. The results suggest that an increase in O₂/C ratio or reaction temperature diminishes the supplied energy for microwave irradiation, as a result of more oxidative reactions involved. However, the performance of methanol ATR at 300 °C is lower than that at 250 °C. The methanol conversion of ATR is beyond 90% at O₂/C = 0.125 and 0.5, whereas it is relatively low (56–67%) at O₂/C = 0.25, presumably due to the weakened microwave irradiation and insufficient heat release. The spectrum analysis of supplied power using the fast Fourier transform (FFT) algorithm indicates that the supplied power characteristics of endothermic reactions are different from those of exothermic reactions.     

A performance study of methanol steam reforming in an A-type microchannel reactor

The methanol steam reforming (MSR) performance in a microchannel reactor is directly related to the flow pattern design of the microchannel reactor. Hydrogen production improvements can be achieved by optimal design of the flow pattern. In this study, an A-type microchannel reactor with a flow pattern design of one inlet and two outlets was applied to conduct the MSR for hydrogen production. The MSR performance of the A-type microchannel reactor was investigated through numerical analysis by establishing a three-dimensional simulation model and compared with that of the conventional Z-type microchannel reactor. Experiments were also conducted to test the MSR performance and validate the accuracy of the simulation model. The results showed that compared with the conventional Z-type microchannel reactor, the species distributions in the A-type microchannel reactor were more homogeneous. In addition, compared with the Z-type microchannel reactor, the A-type microchannel reactor was shown to effectively increase the methanol conversion rate by up to 8% and decrease the pressure drop by about 20%, regardless of a slightly higher CO mole fraction. It was also noted that with various quantities of microchannels and microchannel cross sections, the A-type microchannel reactor was still more competitive in terms of a higher methanol conversion rate and a lower pressure drop.     

Performance assessment and evaluation of catalytic membrane reactor for pure hydrogen production via steam reforming of methanol

The steam reforming of methanol was investigated in a catalytic Pd–Ag membrane reactor at different operating conditions on a commercial Cu/ZnO/Al₂O₃ catalyst. A comprehensive two-dimensional non-isothermal stationary mathematical model has been developed. The present model takes into account the main chemical reactions, heat and mass transfer phenomena in the membrane reactor with hydrogen permeation across the PdAg membrane in radial direction. Model validation revealed that the predicted results satisfy the experimental data reasonably well under the different operating conditions. Also the impact of different operating parameters including temperature, pressure, sweep ratio and steam ratio on the performance of reactor has been examined in terms of methanol conversion and hydrogen recovery. The modeling results have indicated the high performance of the membrane reactor which is related to continuous removal of hydrogen from retentate side through the membrane to shift the reaction equilibrium towards formation of hydrogen. The obtained results have confirmed that increasing the temperature improves the kinetic properties of the catalyst and increase in the membrane's H₂ permeance, which results in higher methanol conversion and hydrogen production. Also it is inferred that the hydrogen recovery is favored at higher temperature, pressure, sweep ratio and steam ratio. The model prediction revealed that at 573 K, 2 bar and sweep ratio of 1, the maximum hydrogen recovery improves from 64% to 100% with increasing the steam ratio from 1 to 4.     

Methanol steam reforming in microreactor with constructal tree-shaped network

The construcal tree-shaped network is introduced into the design of a methanol steam microreactor in the context of optimization of the flow configuration. A three-dimensional model for methanol steam reaction in this designed microreactor is developed and numerically analyzed. The methanol conversion, CO concentration in the product and the total pressure drop of the gases in the microreactor with constructal tree-shaped network are evaluated and compared with those in the serpentine reactor. It is found that the reaction of methanol steam reforming is enhanced in the constructal tree-shaped microreactor, since the tree-shaped reactor configuration, which acts an optimizer for the reactant distribution, provides a reaction space with larger surface-to-volume ratio and the reduction of reactant velocities in the branches. Compared with the serpentine microreactor, the constructal reactor possesses a higher methanol conversion rate accompanied with a higher CO concentration. The conversion rate of the constructal microreactor is more than 10% over that of serpentine reactor. More particularly, the reduction of flow distance makes the constructal microreactor still possess almost the same pressure drop as the corresponding serpentine reactor, despite that the bifurcations induce extra local pressure loss, and the reduction of channel size in branches also causes pressure losses.     

H2 production in silica membrane reactor via methanol steam reforming: Modeling and HAZOP analysis

The main aim of this work is the presentation of both qualitative safety and quantitative operating analyses of silica membrane reactor (MR) for carrying out methanol steam reforming (MSR) reaction to produce hydrogen. To perform the safety analysis, HAZOP method is used. Before the HAZOP analysis, a comprehensive investigation of most important operating parameters effects on silica MR performance is required. Therefore, for a quantitative analysis, a 1-dimensional and isothermal model is developed for evaluating the reaction temperature, reaction pressure, feed molar ratio (steam/methanol) and feed flow rate effects on silica MR performance in terms of methanol conversion and hydrogen recovery. The model validation results show good agreement with experimental data from literature. As a consequence, simulation results indicate that the reaction pressure and feed molar ratio have dual effect on silica MR performance. In particular, it is found that methanol conversion is decreased by increasing the reaction pressure from 1.5 to 4.0 bar, whereas over 4.0 bar, it is improved. Moreover, the hydrogen recovery is decreased by increasing the feed molar ratio from 1 to 5, while over 5, it was approximately constant. After the evaluation of modeling results, the HAZOP analysis for silica MR is carried out during MSR reaction. The analysed operating parameters in the modeling study have been considered as key parameters in the HAZOP analysis. The safety assessment results are presented in tables as check list. By considering the HAZOP results, safety pretreatment works are recommended before or during the experimental tests of MSR reaction in silica MR. According to different parameters consequences, reaction temperature is the most critical parameter in MSR reaction for the silica MR studied in this work. In particular, to avoid the consequences of temperature deviation, it is recommended to use a PID temperature controller in the silica MR for MSR reaction.     

Hydrogen production with a low carbon monoxide content via methanol steam reforming over CuxCeyMgz/Al2O3 catalysts: Optimization and stability

Catalytic activities of Ce–Mg promoted Cu/Al₂O₃ catalysts via methanol steam reforming was investigated in terms of the methanol conversion level, carbon monoxide selectivity and hydrogen yield. The factors chosen were the reaction temperature, copper content, Mg/(Ce + Mg) weight-percentage and steam to carbon ratios. The catalysts were prepared by co-precipitation and characterized by means of XRD, BET, H₂-TPR, and FESEM. The Ce–Mg bi-promoter catalysts gave higher performance due to magnesium penetration into the cerium structure causing oxygen vacancy defects on the ceria. A response-surface-model was then designed to optimize the condition at a 95% confidence interval for complete methanol conversion to a high H₂ yield with a low CO content, and revealed an optimal copper level of 46–50 wt%, Mg/(Ce + Mg) of 16.2–18.0%, temperature of 245–250 °C and S/C ratio of 1.74–1.80. No deactivation of the Cu_0.5Ce_0.25Mg_0.05/Al catalyst was observed during a 72-h stability test.     

Feasibility study of porous copper fiber sintered felt: A novel porous flow field in proton exchange membrane fuel cells

A novel porous flow field made of the porous copper fiber sintered felt (PCFSF) is developed for proton exchange membrane (PEM) fuel cells. The feasibility of this material is systematically investigated involving fabrication, characterization and application. The experimental results reveal that a lower cutting speed helps prevent the fibers from formation failure and morphological defects. A lower feed rate and a smaller back-cutting depth both reduce the equivalent diameter of the copper fibers. The sintering temperature, time and pressure combine to affect the formation quality of the PCFSF which has three-dimensional network structure with open pores distributed stochastically. The wettability tests show that the PCFSF is hydrophobic and the contact angle increases with the increase of porosity. The corrosion behaviors of the PCFSF in simulated PEM fuel cell environment prove that the PCFSF without any coating and alloying treatment is not quite competent, although the Cu corrosion does not critically happen in the tested fuel cell. The resistance tests demonstrate that the combined total electrical resistance of the composite bipolar plate is smaller than the graphite plate. The single-cell tests show that the performance of the fuel cell with the PCFSF flow field is acceptable. The effects of the operating parameters such as the anode operating pressure and cathode air flow rate are also explored.     

Hydrogen production from ethanol steam reforming in a micro-channel reactor

Ethanol steam reforming was studied over a supported Ir/CeO₂ catalyst in a micro-channel structured reactor. The catalyst coating was deposited on the channel walls and showed a remarkably high homogeneity and an excellent adherence to the stainless steel substrate, leading to stable performance during long-term runs. Hydrogen yields exceeding 40 L_H2 g_cat⁻¹ h⁻¹ were achieved during testing with partial ethanol conversion of 65% and a residence time in the order of a few milliseconds. This hydrogen productivity was found significantly higher than in a comparable conventional fixed-bed reactor hence being extremely promising for hydrogen production in micro fuel cell applications.     

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.     

Ethanol steam reforming reaction in a porous stainless steel supported palladium membrane reactor

In this experimental work, the ethanol steam reforming reaction is performed in a porous stainless steel supported palladium membrane reactor with the aim of investigating the influence of the membrane characteristics as well as of the reaction pressure. The membrane is prepared by electroless plating technique with the palladium layer around 25 μm deposited onto a stainless steel tubular macroporous support. The experimental campaign is directed both towards permeation and reaction tests. Firstly, pure He and H₂ are supplied separately between 350 and 400 °C in the MR in permeator modality for calculating the ideal selectivity αH₂/He. Thus, the MR is packed with 3 g of a commercial Co/Al₂O₃ catalyst and reaction tests are performed at 400 °C, by varying the reaction pressure from 3.0 to 8.0 bar. Experimental results in terms of ethanol conversions as well as recovery and purity of hydrogen are given and compared with some results in the same research field from the open literature.As best result of this work, 100% ethanol conversion is reached at 400 °C and 8 bar, recovering a hydrogen-rich stream consisting of more than 50% over the total hydrogen produced from reaction, having a purity around 65%.     

Numerical analysis of performance enhancement and non-isothermal reactant transport of a cylindrical methanol reformer wrapped with a porous sheath under steam reforming

This paper accomplished a three-dimensional computational analysis of the methanol reformer with steam reforming by the Arrhenius form of reaction model and SIMPLE-C algorithm. The performance enhancement and non-isothermal reactant transport of the cylindrical reformer wrapped with a porous sheath were investigated. The parameters, including temperature of internal heater (T_H), porosity (ε), and thickness of porous sheath (R_P), on methanol conversion, hydrogen, carbon monoxide, carbon dioxide productions, temperature and velocity fields with the same inlet conditions have been investigated. The results present that higher methanol conversion and richer hydrogen production occur as temperature of heater, porosity, and porous sheath thickness increase. As temperature of internal heater is equal to 250 °C, employing a porous sheath with ε = 0.9 and R_P = 10 mm to wrap a reformer results in the maximum enhancements of 35.71% in methanol conversion and 21.18% in hydrogen production. Besides, a porous sheath with ε = 0.5 and R_P = 10 mm leads to the maximum reduction of 2.23% in carbon monoxide produced from the reformer at T_H = 300 °C.