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.     

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.     

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.     

反应机理分布对甲醇蒸汽重整制氢过程的影响

为强化微通道中甲醇蒸汽重整过程,考察了反应机理分布对制氢的影响。利用计算流体力学软件FLUENT中的通用有限速率模型对该过程进行了数值研究。计算表明,在相同反应条件下,采用贵金属催化剂所对应的反应机理的甲醇转化率较高,但其成本相应高。通过对催化表面上催化剂的分段布置,可以提高甲醇转化率,且在低温和高进口速度时更有效。在铜基和贵金属催化剂用量相等和温度453 K、进口速度0.4 m.-s1时甲醇转化率提高2.7%。     

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%.     

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.     

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.     

Trapezoidal cavity for high reforming temperature performance of auto-thermal methanol steam reforming micro-reactor for hydrogen production

To realize high reforming temperature performance of auto-thermal methanol steam reforming micro-reactor (ATMSRM) for hydrogen production (HP) and enhance its long-term HP performance, a trapezoidal cavity on methanol steam reforming (MSR) chamber plate is proposed. A numerical simulation model of the ATMSRM for HP is built. The influence of different geometric sizes of the trapezoidal cavity on reforming temperature performance of ATMSRM is investigated by the numerical simulation model. The reforming temperature performance and HP performance of ATMSRMs using the optimal trapezoidal cavity, the combustion reaction support (CRS) with optimal multiple micro-channels and the non-optimization are compared. The reforming temperature performance and HP performance of the size-enlarged ATMSRM with the optimal trapezoidal cavity are also studied. The results show that compared to other trapezoidal cavities, reforming temperature difference per 1 °C (△TA) of the ATMSRM using the F-type trapezoidal cavity with 50 mm length, 76 mm width, 0.4 mm front end depth and 0.2 mm back end depth is smaller, which is 0.01709 °C °C^?1 under 0.9 mL/min combustion methanol injection rate and 4 mL/h reforming methanol-water mixture injection rate. Compared with ATMSRMs using the CRS with optimal multiple micro-channels and the non-optimization, ATMSRM using F-type trapezoidal cavity has a better comprehensive HP performance. Compared with non-enlarged ATMSRM using F-type trapezoidal cavity, size-enlarged ATMSRM using F-type trapezoidal cavity has bigger △TA, larger reforming methanol conversion rate, higher hydrogen yield and more carbon monoxide selectivity. This research work offers a new method for enhancing reforming temperature performance of ATMSRM for HP.     

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.     

A high-performance PdZn alloy catalyst obtained from metal-organic framework for methanol steam reforming hydrogen production

Methanol steam reforming (MSR) is deemed to be an effective way for hydrogen production and Pd/ZnO catalyst were found to exhibit high activity in this reaction. However, their activities are strongly related to the preparations methods. In most cases, these catalysts are synthesized by impregnation or co-precipitation methods, aiming to change the dispersion and stability of Pd nanoparticle to get better performance. Here we report an efficient Pd/ZnO catalyst that was synthesized with zeolitic imidazolate framework-8 (ZIF-8) as the precursor, on which Pd ions was supported after NaHB₄ reduction. Typically, when the catalyst reduced at 300 °C for 2 h, the methanol conversion could reach 97–98% and the CO₂ selectivity is around 86.3% under the reaction condition of 0.1 MPa, water/CH₃OH = 1.2:1 (mol ratio), WHSV_methanol = 43152ml/g_cat*h, catalyst = 0.1 g, our catalyst was found to show much better performance than other Pd@ZnO catalysts prepared by other methods, especially in terms of selectivity which is particularly important for hydrogen fuel cell application considering that Pt electrode could be poisoned by even trace amount of CO. It turned out that the large surface area, enough holes, evenly distributed PdZn alloy activity sites and abundant oxygen vacancies lead to the overall excellent performance of our catalyst.     

Underwater vehicle hydrogen production from methanol steam reforming using hydrogen peroxide

Methanol steam reforming (MSR) can supply hydrogen (H₂) to underwater vehicles equipped with a fuel cell. Low reaction temperatures ensure the composition of the reformed gas suitable for the H₂ purification unit and increase the design freedom of a reforming plant. However, such temperatures decrease the catalyst activity and thereby the methanol (MeOH) conversion and H₂ production. Herein, hydrogen peroxide (H₂O₂) was supplied with MeOH and water (H₂O) to ensure sufficient MeOH conversion and H₂ production at low temperatures. A tube reactor loaded with a commercial Cu/Zn catalyst was installed in an electric furnace maintained at 200–250 °C, and MeOH and 0 wt%, 11.88 wt%, 22.51 wt%, and 32.07 wt% H₂O₂ were supplied. When the furnace temperature was 200 °C, the MeOH conversion was 49.3% at 0 wt% H₂O₂ but 93.5% at 32.07 wt% H₂O₂. The effect of adding H₂O₂ was greater under the temperature conditions where the MeOH conversion was 100% or less. To analyze the effect of H₂O₂ addition on catalyst durability, the furnace was maintained at 200 °C, and the reactor was continuously operated for 110 h with 0 wt% and 32.07 wt% H₂O₂. The addition of H₂O₂ did not significantly decrease the Cu/Zn catalyst durability.     

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.     

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.     

Zinc oxide nanorods based catalysts for hydrogen production by steam reforming of methanol

Zinc oxide (ZnO) nanorods were epitaxially grown on porous cordierite support by a hydrothermal process and utilized for catalyzing methanol steam reforming (MSR) reaction. Catalytic activity of ZnO nanorods for MSR process was correlated to the terminated surfaces of ZnO crystallites. Copper (Cu), palladium (Pd) and gold (Au) nanoparticles infused ZnO nanorods were prepared by in-situ precipitation of the metals on the nanorods. 28% hydrogen selectivity was observed with Cu/ZnO nanorods (Cu/10Zn), while Pd/ZnO nanorods and (Pd/10Zn) showed slightly lower activity. Higher catalytic activity of copper and palladium impregnated ZnO nanorods can be attributed to the synergistic combination of bimetallic oxides. In contrast, Au/ZnO nanorods (Au/10Zn) showed very high activity for methanol dehydrogenation and higher than 97% methanol conversion was achieved for operating temperatures as low as 200 °C.     

Copper zinc oxide nanocatalysts grown on cordierite substrate for hydrogen production using methanol steam reforming

Hydrogen production from methanol rather than the traditional source, methane, is considered to be advantageous in ease of transportation and storage. However, the current copper-based catalysts utilized in methanol steam reforming are associated with challenges of sintering at high temperature and production of CO which could poison fuel cells. In addressing these challenges, ZnO nanorods were grown hydrothermally on the surface of cordierite and impregnated with Cu to produce catalysts for methanol steam reforming. The catalysts were characterized using SEM, XRD, FTIR, XPS, BET and Raman Spectroscopy. A fixed-bed reactor was used for testing the catalysts while the reaction products were characterized using a GC fitted with FID and TCD. The effects of temperature, methanol concentration and particle size of catalysts on methanol steam reforming were investigated. The experiments were carried out between 180 and 350 °C. CO selectivity of 0% was observed for temperatures between 180 and 230 °C for 0.8 MeOH:1H₂O with an average H₂ selectivity of 98% for that temperature range. XPS showed that the catalyst was relatively unchanged after reaction while Raman spectroscopy revealed coke formation on the catalyst surface for reactions carried out above 300 °C. This shows that the catalyst is active and selective for the reaction.     

Effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat

This paper reports the effects of particle sizes on methanol steam reforming for hydrogen production in a reactor heated by waste heat. The unsteady model was set up, which has been applied to investigate the effects of particle sizes (1.77 mm–14.60 mm) on particle temperature, heat transfer quantity, overall coefficient of heat-transfer, etc. The heat transfer performance of waste heat recovery heat exchanger is improved when the particle size increases, which is conducive to increase hydrogen production. The particle temperature change rate, the specific enthalpy change rate, the moving velocity of the maximum heat release rate particle, the contribution rate of solid phases, the heat release rate and the overall coefficient of heat-transfer increase, but the effective time of heat transfer decreases. When the particle size increases from 1.77 mm to 14.60 mm, the solid phase average contribution rate increases from 89.43% to 94.03%, the overall coefficient of heat-transfer increases from 1.39 W m⁻² K⁻¹ to 13.41 W m⁻² K⁻¹, the heat release rate increases from 48.9% to 99.9% and the effective time of heat transfer reduces from 48 h to 6.7 h.     

Morphology effect of ceria on the performance of CuO/CeO2 catalysts for hydrogen production by methanol steam reforming

Nano-rod(R), nano-particle(P) and sponginess(S) of ceria samples were used to study catalytic performance of hydrogen production by methanol steam reforming. The samples were prepared by hydrothermal method, precipitation method, and sol-gel method, respectively, and the CuO was supported on the different morpholopy of CeO₂ samples by wet impregnation. SEM, TEM, XRD, XRF, BET, H₂-TPR, XPS and N₂O titration methods were used to study correlation between the structure and the catalytic performance for methanol steam reforming. The results showed that the morphology of the prepared CeO₂ support dramatically influenced the performance of catalysts. Due to the stronger interaction between copper oxide and ceria support, the CuO/CeO₂-R catalyst had exhibited the better catalytic activity than those of the CuO/CeO₂P and CuO/CeO₂S catalysts. Moreover, higher Cu dispersion, lower reduction temperature of CuO, and higher content of active species Cu⁺ were also advantageous to raising catalytic effects. Besides, with the highest content of surface Ce³⁺, the CuO/CeO₂-R had estimated the content of oxygen vacancy on the surface of the catalyst. The existence of surface oxygen vacancy had a positive effect on the methanol steam reforming.     

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.