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.     

Porous copper fiber sintered felts with surface microchannels for methanol steam reforming microreactor for hydrogen production

In this study, a laser micro-milling technique was introduced into the fabrication process of surface microchannels with different geometries and dimensions on the porous copper fiber sintered felts (PCFSFs). The PCFSFs with surface microchannels as catalyst supports were then used to construct a new type of laminated methanol steam reforming microreactor for hydrogen production. The microstructure morphology, pressure drop, velocity and permeability of PCFSF with surface microchannels were studied. The effect of surface microchannel shape (rectangular, stepped, and polyline) and catalyst loading amount on the reaction performance of methanol steam reforming microreactor for hydrogen production was further investigated. Our results show that the PCFSF with rectangular microchannels demonstrated a lower pressure drop, higher average velocity and higher permeability compared to the stepped and polyline microchannel. Furthermore, the PCFSF with rectangular microchannels also exhibited the highest methanol conversion and H₂ flow rate. The best reaction performance of methanol steam reforming microreactor for hydrogen production was obtained using PCFSF with rectangular microchannels when 0.5 g catalyst was loaded.     

Fabrication of porous metal by selective laser melting as catalyst support for hydrogen production microreactor

To improve the hydrogen production performance of microreactors, the selective laser melting method was proposed to fabricate the porous metals as catalyst supports with different pore structures, porosities, and materials. The influence of the porous structures on the molecule distribution after passing through the porous metals was analyzed by molecular dynamics simulation. The developed porous metals were then used as catalyst supports in a methanol steam reforming microreactor for hydrogen production. Our results show that the porosity of the porous metal had significantly influence on the catalyst infiltration and the reaction process of hydrogen production. A lower degree of catalyst infiltration of the porous metal was obtained with lower porosity. A copper layer-coated stainless-steel porous metal with a staggered structure and gradient porosity of 80%–60% exhibited much larger methanol conversion and H₂ flow rate due to its better heat and mass transfer characteristic. Methanol conversion and H₂ flow rates could reach 97% and 0.62 mol/h, respectively. Finally, it was found that the experimental results were in good agreement with the simulation results.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Design and performance evaluation of flexible tubular microreactor for methanol steam reforming reaction

To obtain the flexible microreactor for potential application in constrained space, a novel flexible tubular microreactor was designed by using a corrugated shell and a high porosity porous copper fiber rod (PCFR) as catalyst support. The effect of placement position, bending direction, and bending angle on reaction performance of flexible tubular microreactor was investigated. Then, the stability of flexible tubular microreactor was further evaluated. The experimental results showed that the placement position and bending direction had a significant influence on the reaction performance of flexible tubular microreactor. Methanol conversion of flexible tubular microreactor with the vertical placement was 6.67% higher than that with horizontal placement. Higher methanol conversion and H₂ flow rate were obtained when the microreactor bent along the vertical direction. The reaction performance of flexible tubular microreactor was found to decrease as the bending angle increased, and the methanol conversion decreased by around 14.07% with a bend of 90°. When the flexible tubular microreactor was horizontal placed with a bend of 60° in the vertical direction, the reaction performance of microreactor was not changed little after 20 cyclic bending. After continuous bending for 10 h, the methanol conversion and H₂ flow rate of flexible tubular microreactor were 70.58% and 0.88 mol/h, showing good reaction performance.     

K (Na)-promoted Ni,Al layered double hydroxide catalysts for the steam reforming of methanol

Production of hydrogen by methanol steam reforming has been studied over a series of Ni/Al layered double hydroxide catalysts prepared by the co-precipitation method, with the aim to develop a stable catalyst that can be used in a membrane-joint performer at temperatures greater than 300 °C. H₂, CO and CO₂ are generally the major products together with trace amounts of CH₄. The presence of potassium and/or sodium cations was found to improve the activity of methanol conversion. The selectivity for CO₂ rather than CO was better with K ions than Na ions, especially at higher temperatures (e.g. 390–400 °C). Methanol steam reforming over a K-promoted Ni/Al layered double hydroxide catalyst resulted in better activity and similar stability compared to a commercial Cu catalyst.     

Feasibility of preparing additive manufactured porous stainless steel felts with mathematical micro pore structure as novel catalyst support for hydrogen production via methanol steam reforming

In this paper, an additive manufacturing prepared porous stainless steel felt (AM-PSSF) is proposed as a novel catalyst support for hydrogen production via methanol steam reforming (MSR). In the method, 316 L stainless steel powder with diameter of 15–63 μm is processed by the additive manufacturing technology of selective laser melting (SLM). To accomplish the preparation, the reforming chamber where the AM-PSSF is embedded is firstly divided into an all-hexahedron mesh. Then, the triply periodic minimal surface (TPMS) unit with mathematical form, high interconnectivity and large specific surface area is mapped into the hexahedrons based on shape function, forming the fully connected three-dimensional (3D) micro pore structure of the AM-PSSF. By correlating the mathematical parameter and the porosity of the TPMS unit, and taking into account the SLM process, the porosity of the AM-PSSF is well controlled. Based on the designed 3D pore structure model, the AM-PSSF is produced using standard SLM process. The application of the AM-PSSF as catalyst support for hydrogen production through MSR indicates that: 1) both the naked and catalyst-coated AM-PSSF have the characteristics of high porosity, large specific surface area and high connectivity; 2) the MSR hydrogen production performance of the AM-PSSF is better than that of the commercial stainless steel fiber sintered felt. The feasibility of AM-PSSF as catalyst support for MSR hydrogen production may pave a better way to balance different requirements for catalyst support, thanks to the excellent controllability provided by AM on both the external shape and the internal pore structure, and to the produced rough surface morphology that benefits the catalyst adhesion strength. In addition, catalyst support with pore structures that are more accommodated with the flow field and the reaction rate of MSR reaction may be prepared in future, since the entire catalyst support structure, from macro scale to micro scale, is under control.     

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.     

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.     

One-step growth of CuO/ZnO/CeO2/ZrO2 nanoflowers catalyst by hydrothermal method on Al2O3 support for methanol steam reforming in a microreactor

CuO/ZnO/CeO₂/ZrO₂ nanoflowers catalyst was grown on an Al₂O₃ foam ceramic by a one-step hydrothermal process, while a naked Al₂O₃ foam ceramic and an Al₂O₃ foam ceramic grown with ZnO nanorods that directly impregnated into the catalyst precursor solution were also fabricated simultaneously. The morphology, composition, redox property and specific surface area of catalysts on the three ceramics were investigated in detail. The catalyst-loaded ceramics were used as catalyst supports in a microreactor to study the catalytic performance for methanol steam reforming. Results showed that the microreactor with Al₂O₃ support grown with nanoflowers catalyst achieved 99.8% methanol conversion rate, 0.16 mol/h H₂ flow rate at 310 °C, and an inlet methanol flow rate of 0.048 mol/h. Moreover, the microreactor exhibited 92% methanol conversion rate after 30 h continuous reaction.     

Hydrogen production employing Cu/Zn-BTC metal-organic framework on cordierite honeycomb ceramic support in methanol steam reforming process within a microreactor

Three metal-organic frameworks Cu-BTC, Zn-BTC, and Cu/Zn-BTC were prepared and impregnated in nitrate solutions to obtain the precursors. After calcination, three metal-BTC-derived CuO/ZnO/CeO₂/ZrO₂ catalysts were obtained. The samples were characterized and the catalyst-coated cordierite honeycomb ceramics were used in a microreactor for methanol steam reforming at different reaction conditions. Results showed that the Cu/Zn-BTC-derived catalyst exhibited the most fine and uniform particles, the best reducibility, the largest specific surface area, and the optimal surface elemental state due to the difference in the formation mechanisms, resulting in its remarkable catalytic performance. The ceramic support coated with Cu/Zn-BTC-derived catalyst could achieve 100% methanol conversion rate and 0.336 mol/h H₂ output at 260 °C in the microreactor. Stability tests demonstrated that the Cu/Zn-BTC-derived catalyst could maintain its excellent performance without deactivation within 30 h continuous reaction, which was connected with the Ce–Zr–O solid solution with high concentration of oxygen vacancies and surface oxygen.     

Hydrogen production in microreactor using porous SiC ceramic with a pore-in-pore hierarchical structure as catalyst support

Porous SiC ceramic as catalyst support with porous CuO/ZnO/CeO₂/ZrO₂ catalyst was fabricated via solution combustion method and used in a microreactor. A pore-in-pore hierarchical structure was formed on the support by using glycol as the fuel. The effects of fuel/nitrates molar ratio on the particle size, residual carbon, reducibility and structure of catalyst on the support were investigated. The optimal content of glycol was proposed and the catalytic performance of microreactor was further studied. Results showed that the catalyst loading amount was about 20% weight of the whole support and the loading intensity was strong. Moreover, the microreactor achieved a 100% methanol conversion rate at 280 °C and the conversion rate stayed around 95% after 30 h reaction by using the support over the optimal content of glycol, which exhibited excellent superiority in the methanol steam reforming process.     

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.