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.     

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.     

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.     

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.     

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.     

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.     

Experimental investigation on hydrogen production by methanol steam reforming in a novel multichannel micro packed bed reformer

A novel multichannel micro packed bed reactor with bifurcation inlet manifold and rectangular outlet manifold was developed to improve the methanol steam reforming performance in this study. The commercial CuO/ZnO/Al₂O₃ catalyst particles were directly packed in the reactor. The flow distribution uniformity in the reactor was optimized numerically. Experiments were conducted to study the influences of steam to carbon molar ratio (S/C), weight hourly space velocity (WHSV), reactor operating temperature (T) and catalyst particle size on the methanol conversion rate, H₂ production rate, CO concentration in the reformate, and CO₂ selectivity. The results show that increase of the S/C and T, as well as decrease of the WHSV and catalyst particle size, both enhance the methanol conversion. The CO concentration decreases as the S/C and WHSV increase as well as the T and catalyst particle size decrease. Moreover, T plays a more important role on the methanol steam reforming performance than WHSV and S/C. The impacts on CO concentration become insignificant when the S/C is higher than 1.3, WHSV is larger than 1.34 h⁻¹ and T is lower than 275 °C. A long term stability test of this reactor was also performed for 36 h and achieved high methanol conversion rate above 94.04% and low CO concentration less than 1.05% under specific operating conditions.     

Microwave-activated methanol steam reforming for hydrogen production

Methanol steam reforming (MSR) was carried out in a catalytic packed bed reactor under electrical and microwave heating using the two most common catalysts for this process-CuZnO/Al₂O₃ and PdZnO/Al₂O₃. Significant two-dimensional temperature gradients were found, especially in the latter case. Our results show that for the same average bed temperature, methanol conversion is higher under microwave heating (>10%). On the other hand, the product distribution is not affected by the heating mode. We demonstrate that even in cases where the maximum temperature along the entire height of the bed is significantly higher under electrical heating, conversion is either higher in the microwave case or approximately the same between the two heating modes. Finally, our experimental data indicate that a given methanol conversion can be achieved with lower net heat input to the reactor under microwave heating. This does not mean lower total energy consumption in the microwave process due to the limitations in the magnetron efficiency and the reflected power. However, it may be an implicit indication of higher temperature at metal sites than in bulk phase (microscale hot spot formation) due to the selective heating principle.     

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.     

Numerical analysis of methanol steam reforming reactor heated by catalytic combustion for hydrogen production

Thermal coupling of endothermic and exothermic reactions is an important pathway for integrated thermal management within a methanol steam reforming reactor heated by methanol catalytic combustion. In this study, a numerical model is developed for heat and mass transfer calculations, methanol steam reforming and catalytic combustion reactions, which is used to explore the effects of design parameters on compact parallel channel reactor performance. Efficiency of the integrated reactor is optimized by the coupling of endothermic and exothermic reactions using conventional wall material. Temperature uniformity is improved by the adjustment of the flow arrangement and the catalyst distribution. This work provides an effective energy management strategy and tool which can be adopted in the design of portable hydrogen generation systems.     

Recent trends in the development of reactor systems for hydrogen production via methanol steam reforming

Hydrogen is currently receiving significant attention as an alternative energy resource, and among the various methods for producing hydrogen, methanol steam reforming (MSR) has attracted great attention because of its economy and practicality. Because the MSR reaction is inherently activated over catalytic materials, studies have focused on the development of noble metal-based catalysts and the improvement of existing catalysts with respect to performance and stability. However, less attention has been paid to the modification and development of innovative MSR reactors to improve their performance and efficiency. Therefore, in this review paper, we summarize the trends in the development of MSR reactor systems, including microreactors and membrane reactors, as well as the various structured catalyst materials appropriate for application in complex reactors. In addition, other engineering approaches to achieve highly efficient MSR reactors for the production of hydrogen are discussed.     

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.     

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.     

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.     

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.     

RuRh based catalysts for hydrogen production via methanol steam reforming in conventional and membrane reactors

Results of hydrogen production study in methanol steam reforming (MSR) process with the use of Ru_0.5–Rh_0.5 catalysts supported on different carbon materials: synthetic graphite-like material Sibunit, carbon black Ketjenblack EC600DJ, detonation nanodiamonds (DND) and ZrO₂-based material with fluorite structure, doped with ceria, have been described. The samples have been tested in conventional flow reactor and membrane (MR) reactor, containing Pd-based membranes with different composition, thickness and surface architecture. It has been shown that the catalytic activity of the composites depends on the support nature. The RuRh/DND catalyst exhibits the highest activity, whereas RuRh/Ce_0.1Zr_0.9O_2–δ is the most selective. The use of PdAg (23%) foil with the surface modified by palladium black showed great advantages comparing to the smooth dense membrane. The use of the MR with the PdAg membrane improves the MSR reaction and provides almost 50% increase in the hydrogen yield. The hydrogen produced with the use of the MR is ultra pure.     

Robust multi-objective optimization of methanol steam reforming for boosting hydrogen production

Methanol steam reforming (MSR) has been considered as a promising method for producing pure hydrogen in recent decades. A comprehensive two-dimensional steady-state mathematical model was developed to analyze the MSR reactor. To improving high purity hydrogen production, a triple-objective optimization of the MSR reactor is performed. Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is employed as a robust optimization approach to maximize the three objectives, termed as, methanol conversion, CO selectivity, and H₂ selectivity. The Pareto optimal frontier has also been provided and the ultimate solution of the Pareto front has been found by the three decision-making methods (TOPSIS, LINMAP, and Shannon's Entropy). Among the three distinct decision-making approaches, LINMAP presents better results according to the deviation index parameter. It has been shown that a perfect agreement is available between the plant and simulation data. Operating under the optimum values based on the LINMAP method confirms an almost 47.04% enhancement of H₂ mass fraction compared to the conventional industrial MSR reactor. The predicted results advocate that the key superiority of the optimized-industrial reactor is the remarkable higher production rate of hydrogen compared to the conventional MSR reactor which makes optimized-industrial reactor both feasible and beneficial.     

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.