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.     

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.     

Preparing a novel gradient porous metal fiber sintered felt with better manufacturability for hydrogen production via methanol steam reforming

The porous copper fiber sintered felts with gradient porosity structure (gradient PCFSFs) as catalyst supports is beneficial for heat and mass transfer for methanol steam reforming (MSR). However, the previously developed gradient PCFSF based on the velocity distribution introduces curved interface between different porosity portions, making the mold pressing method for its preparation more sensitive to tiny process changes. To improve its manufacturability, a novel gradient PCFSF with planar interface (PCFSF-SLR) is proposed in this paper by fabrication with multi-step mold pressing and solid phase sintering method using cutting copper fibers. Furthermore, MSR experiments under different gas hourly space velocities and reaction temperatures are conducted to verify the characteristics of PCFSF-SLR loaded with Cu/Zn/Al/Zr catalyst. The results have shown that the reaction characteristics of the PCFSF-SLR were similar to those with curved interfaces, and PCFSF-SLRs with a middle portion porosity of 0.9 have better hydrogen production performance and lower carbon monoxide concentration. More importantly, the results indicated that the methanol conversion and hydrogen flow rate of the gradient PCFSF with planar interface and porosity of 0.7-0.9-0.8 were close or even almost the same with that of the best gradient PCFSFs with curved interface and porosities of 0.7-0.9-0.8 and 0.8-0.9-0.7. Therefore, the proposed PCFSF-SLR provides a superior alternative to gradient PCFSFs with better manufacturability.     

Structural design and performance research of methanol steam reforming microchannel for hydrogen production based on mixing effect

To improve hydrogen production performance of reforming, a plate-type microchannel carrier plate with a ridge structure was designed based on the mixing effect. The mixing effect of the ridge structure on the hydrogen production performance of reforming was analyzed. Then the effects of geometric parameters (shape, size, spacing, and tilt angle) of the ridge structure on heat, mass transfer, and the hydrogen production performance of the reforming process were modelled and simulated. Finally, data analysis and structural optimisation of microchannels with the ridge structure were conducted via methanol steam reforming hydrogen production experiments. The experimental results show that the trapezoidal ridge structure microchannel (T-type0) achieved the best hydrogen production performance, whose methanol conversion rate was 60.8%, under the gas hourly space velocity of 48,757 mL/(g&h). Especially compared with the ordinary rectangular microchannel structure (O-type0), the methanol conversion rate of the trapezoidal ridge structure microchannel increased by 25.2%. Moreover, the pressure drop of this microchannel did not increase significantly, indicating that the structure did not significantly increase the pressure drop loss while enhancing the heat and mass transfer. Therefore, the ridge structure proposed in this paper can effectively improve heat and mass transfer performance and the hydrogen production efficiency of the microchannel.     

Laser micro-milling of microchannel on copper sheet as catalyst support used in microreactor for hydrogen production

Microchannel structure as catalyst support has been widely used to construct numerous microreactors for hydrogen production. In this work, the laser micro-milling technique was introduced into the fabrication process of microchannels with different geometry and dimensions. The effects of varying scanning speed, laser output power and number of scans on the surface morphology and geometrical dimension of microchannels have been investigated based on SEM observations. It is found that the change of scanning speed and laser output power significantly affected the surface morphology of microchannel. Moreover, the depth of microchannel was increased when the laser output power and number of scans were increased. Subsequently, the microchannels on copper sheet fabricated by the laser micro-milling technique were used as catalyst support to conduct the methanol steam reforming reaction. The better reaction performance of methanol steam reforming in microchannels indicates that laser micro-milling process is probably suitable to fabricate the microchannel reactor for the commercial application.     

Hydrogen production from cylindrical methanol steam reforming microreactor with porous Cu-Al fiber sintered felt

In this study, the porous Cu-Al fiber sintered felt (PCAFSF) was fabricated by low temperature solid-phase sintering method. The laminated PCAFSF as the catalyst support was used for cylindrical methanol steam reforming microreactor for hydrogen production. The two-layer impregnation method was employed to coat the Cu/Zn/Al/Zr catalyst on the PCAFSF. The material composition, specific surface area and catalyst loading of PCAFSF were also measured. The effect of the fiber material, surface morphology and porosity on the reaction performance of methanol steam reforming microreactor for hydrogen production was further investigated. Our results show that the PCAFSF demonstrated much higher methanol conversion and H₂ flow rate compared to the porous Cu fiber sintered felt (PCFSF) and porous Al fiber sintered felt (PAFSF) having the same porosity. Furthermore, the rough PCAFSF showed much higher methanol conversion and H₂ flow rate compared to the smooth PCAFSF. In case of the PCAFSF, the methanol conversion and H₂ flow rate were increased with the decrease of Cu fiber weight and the increase of Al fiber weight. The best reaction performance of microreactor for hydrogen production was obtained using the three layer PCAFSFs with 80% porosity and 1.12 g Cu fiber/1.02 g Al fiber.     

Numerical modeling of microchannel reactors with gradient porous surfaces for hydrogen production based on fractal geometry

A microchannel reactor with a porous surface catalyst support has been applied to methanol steam reforming (MSR) for hydrogen production. The fluid flow, heat transfer, and hydrogen production efficiency of the microchannel reactor are significantly affected by the fabricated porous surface support, such as the pore sizes and their distributions. This paper presents a novel microchannel reactor with a gradient porous surface as the reaction substrate to enhance the performance of the microreactor for hydrogen production. Numerical modeling of the gradient porous surface is developed based on fractal geometry, and three different types of porous surfaces as the catalyst supports (two gradient porous surfaces and one uniform pore-size surface) are investigated. The fluid flow and heat transfer characteristics of these three types of microchannel reactors are studied numerically, and the results showed that the microreactor with a positive gradient pore sized surface exhibited relatively better overall performance. Experimental setups and tests were performed and the results validate that the microchannel reactor with a positive gradient porous surface can increase the heat transfer performance by up to 18% and can decrease the pressure drop by up to 8% when compared to a microreactor with a uniform pore sized surface. Hydrogen production experiments demonstrated that the microreactor with positive gradient pore sizes has the highest methanol conversion rate of 56.3%, and this rate is determined to be 6% and 9% higher than that of microreactors with reverse gradient porous surfaces and uniform pore sized surface, respectively.     

Qualitative investigation on effects of manifold shape on methanol steam reforming for hydrogen production

Fluid velocity distribution among microchannels plays important role on the reaction performances. In this work, the velocity distribution among microchannels with two different manifold structures is compared by a three-dimensional CFD model under two situations respectively, no reaction and methanol steam reforming occurs. Then the performances of methanol steam reforming in both plates are experimentally investigated, and the effect of manifold shape on the hydrogen production performances is qualitatively analyzed by the combination of simulation results of velocity distribution. It is found that the microchannel plate with right-angle manifold enables narrow velocity distributions under different entrance velocities and reaction temperatures, whether no reaction occurs or methanol steam reforming is progressing, which can be the critical element results in better conversion rate and selectivity of process than that of the microchannel plate with oblique-angle manifold. Optimizing the structural parameters to facilitate a relatively uniform velocity distribution to increase the hydrogen production performances may be a key factor to be considered.     

Methanol steam reforming microreactor with novel 3D-Printed porous stainless steel support as catalyst support

In order to study the methanol steam reforming performance of the 3D-printed porous support for hydrogen production, three dimensional (3D) printing technology was proposed to fabricate porous stainless steel supports with body-centered cubic structure (BCCS) and face-centered cubic structure (FCCS). Catalyst loading strength of the 3D-printed porous stainless steel supports was studied. Moreover, methanol steam reforming performance of different 3D-printed porous supports for hydrogen production was experimentally investigated by changing reaction parameters. The results show that the 3D-printed porous stainless steel supports with BCCS and FCCS exhibit better catalyst loading strength, and can be used in the microreactor for methanol steam reforming for hydrogen production. Compared with 90 pores per inch (PPI) Fe-based foam support, 3D-printed porous stainless steel supports with FCCS and BCCS show the similar methanol steam reforming performance for hydrogen production in the condition of 6500 mL/(g·h) gas hourly space velocity (GHSV) with 360 °C reaction temperature. This work provides a new idea for the structural design and fabrication of the porous support for methanol steam reforming microreactor for hydrogen production.     

Stacked etched aluminum flow-through membranes for methanol steam reforming

Electrochemical etching has been used to obtain aluminum foil with high surface area for use as electrodes in electrolytic capacitors. In this approach, direct current etching first generates straight penetrating microchannels, and then a second etching step enlarges the microchannel diameter. In the present work, we developed catalyst supports using aluminum etched with microchannels as a microreactor. The metal aluminum foil catalyst support obtained by etching contained microchannels with a diameter of 1.0–3.0 μm (10,000–15,000 microchannels/mm²). We stacked membrane layers and evaluated their performance in methanol steam reforming. The performance of the reactors containing stacked membranes improved as the layer number increased. The microchannels in this catalytic membrane could be used as reaction channels, were easy to fabricate at low cost, and could be mass-produced continuously. This novel catalytic membrane support opens up new possibilities for practical fabrication of industrial materials.     

Development of methanol steam reforming microreactor based on stacked wave sheets and copper foam for hydrogen production

Methanol steam reforming has been used for in-situ hydrogen production and supply for proton exchange membrane fuel cell (PEMFC), while its power density and energy efficiency still needs to be improved. Herein, we present a novel methanol steam reforming microreactor based on the stacked wave sheets and copper foam for highly efficient hydrogen production. The structural of stacked wave sheets and copper foam, and their roles in the microreactor are described, methanol catalytic combustion is adopted to supply heat for methanol steam reforming reaction and enables the microreactor to work automatically. For catalyst carrier, a fractal body-centered cubic model is established to study the flow characteristics and chemical reaction performances of the copper foam with coated catalyst layer. Both simulation and experimental results showed that the reformate flowrate increases with the increasing of microreactor layers and methanol solution flowrate, the discrepancies of methanol conversion between simulation and experimental tests are less than 7%. Experimental results demonstrated that the reformate flowrate of 1.0 SLM can be achieved with methanol conversion rate of 65%, the output power of the microreactor is 159 W and power density is 395 W/L. The results obtained in this study indicates that stacked wave sheets and copper foam can uniform the reactant flow and improve the hydrogen production performances.     

Structural design of self-thermal methanol steam reforming microreactor with porous combustion reaction support for hydrogen production

To replace the traditional electric heating mode and increase methanol steam reforming reaction performance in hydrogen production, methanol catalytic combustion was proposed as heat-supply mode for methanol steam reforming microreactor. In this study, the methanol catalytic combustion microreactor and self-thermal methanol steam reforming microreactor for hydrogen production were developed. Furthermore, the catalytic combustion reaction supports with different structures were designed. It was found that the developed self-thermal methanol steam reforming microreactor had better reaction performance. Compared with A-type, the △T_max of C-type porous reaction support was decreased by 24.4 °C under 1.3 mL/min methanol injection rate. Moreover, methanol conversion and H₂ flow rate of the self-thermal methanol steam reforming microreactor with C-type porous reaction support were increased by 15.2% under 10 mL/h methanol-water mixture injection rate and 340 °C self-thermal temperature. Meanwhile, the CO selectivity was decreased by 4.1%. This work provides a new structural design of the self-thermal methanol steam reforming microreactor for hydrogen production for the fuel cell.     

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.     

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.     

Autothermal generation of hydrogen from ethanol in a microreactor

A two-side platelet microreactor was designed, modeled, and tested for the generation of hydrogen from ethanol under autothermal regime. The microchannels of one side of the platelet microreactor were coated with Co/ZnO catalyst for conducting the ethanol steam reforming reaction for producing hydrogen at low temperature, whereas the microchannels of the other side of the platelet were coated with _CuMnOx${\mathrm{CuMnO}}_x$ catalyst for the complete oxidation of ethanol. The heat released during ethanol combustion was used for maintaining the heat demand for the endothermic steam reforming side of the microreactor. Several preparation methods were used and compared for the deposition of catalysts in the microchannels in order to guarantee homogeneous deposition and stability. An amount of 3.67 mol of hydrogen per mol of total ethanol consumed in both sides of the microreactor was obtained at 733 K. The overall efficiency of the microreactor was 71%.     

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.     

Fabrication of high aspect ratio ceramic micro-channel in diamond wire sawing as catalyst support used in micro-reactor for hydrogen production

Ceramic is an ideal material for preparing micro-channel catalyst supports with their characteristics of high temperature resistance, corrosion resistance and mechanical strength. High aspect ratio micro-channel structure has the advantages of large specific surface area, strong mass and heat transfer performance and high material utilization. However, ceramic materials are hard and brittle, and it is difficult to fabricate micro-channel structures with aspect ratio more than 1.5:1 by traditional processing methods. In this paper, a cutting method of large diameter diamond wire sawing was proposed. The micro-channels with width of 520 μm and aspect ratio of more than 4:1 was successfully fabricated by this method. Furthermore, the integrity of the micro-channel structure processed by diamond wire sawing was analyzed. And than the effect of surface morphology in different processing parameters on the catalyst loading performance were studied. The catalyst loading strength of ceramic slices with different surface morphology was tested. Finally, the ceramic micro-channel array was used as the catalyst support in micro-reactor for hydrogen production via methanol steam reforming (MSR). The methanol conversion rate and H₂ production rate could reach 87.8% and 74.6 mmol/h, respectively under GHSV 12600 ml/g·h at 300 °C. The experimental results show that the large-diameter diamond wire sawing technology can be used to process ceramic microchannels with high aspect ratio; using ceramic microchannel arrays as catalyst supports in hydrogen production can obtain better reaction performance; the feasibility of ceramic materials were broadened as microchannel catalyst supports.     

Autothermal hydrogen generation from methanol in a ceramic microchannel network

In this paper, the authors present the first demonstration of a new class of integrated ceramic microchannel reactors for all-in-one reforming of hydrocarbon fuels. The reactor concept employs precision-machined metal distributors capable of realizing complex flow distribution patterns with extruded ceramic microchannel networks for cost-effective thermal integration of multiple chemical processes. The presently reported reactor is comprised of five methanol steam reforming channels packed with CuO/γ-Al₂O₃, interspersed with four methanol combustion channels washcoated with Pt/γ-Al₂O₃, for autothermal hydrogen production (i.e., without external heating). Results demonstrate the capability of this new device for integrating combustion and steam reforming of methanol for autothermal production of hydrogen, owing to the axially self-insulating nature of distributor-packaged ceramic microchannels. In the absence of any external insulation, stable reforming of methanol to hydrogen at conversions >90% and hydrogen yields >70% was achieved at a maximum reactor temperature of 400 °C, while simultaneously maintaining a packaging temperature <50 °C.     

Feasibility investigations on multi-cutter milling process: A novel fabrication method for microreactors with multiple microchannels

A novel multi-cutter milling process for multiple parallel microchannels with manifolds is proposed to address the challenge of mass manufacture as required for cost-effective commercial applications. Several slotting cutters are stacked together to form a composite tool for machining microchannels simultaneously. The feasibility of this new fabrication process is experimentally investigated under different machining conditions and reaction characteristics of methanol steam reforming for hydrogen production. The influences of cutting parameters and the composite tool on the microchannel qualities and burr formation are analyzed. Experimental results indicate that larger cutting speed, smaller feed rate and cutting depth are in favor of obtaining relatively good microchannel qualities and small burrs. Of all the cutting parameters considered in these experiments, 94.2 m min⁻¹ cutting speed, 23.5 mm min⁻¹ feed rate and 0.5 mm cutting depth are found to be the optimum value. According to the comparisons of experimental results of multi-cutter milling process and estimated one of other alternative methods, it is found that multi-cutter milling process shows much shorter machining time and higher work removal rate than that of other alternative methods. Reaction characteristics of methanol steam reforming in microchannels also indicate that multi-cutter milling process is probably suitable for a commercial application.     

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%.