Microreactor For Hydrogen Production Research Articles

A novel micro-reactor for hydrogen production from solid NaBH4 hydrolysis in a dual-cycle methodology

Hydrogen-based Fuel Cells (FCs) hold significant potential as energy conversion technologies. In a previous study, we presented a pump-based hydrogen generator (PHG) that utilizes a catalytic reaction between sodium borohydride (NaBH4) powder and water. The pump circulates the water solution through the powder chamber in a closed-loop reaction. The PHG demonstrated clear advantages over alternative hydrogen sources in terms of both safety and energy density. However, as operating time increases, the solution in the closed-loop PHG becomes saturated, causing the reaction rate to decline. This limitation can be overcome in cases where an external water source is available, such as marine vehicles, drones equipped with water recovery systems from their fuel cells, or systems located near pipelines. In such scenarios, introducing freshwater feeding and product emission offers intriguing possibilities for significantly enhancing the fuel's energy density and extending its effective operation time.Our current research introduces an innovative concept: a dual-cycle generator (DCG) that effectively overcomes the issue of solution saturation over time. It achieves this by combining solution circulation with freshwater feeding and product emission. Our study employed a DCG prototype to examine various operating modes and to demonstrate the effectiveness of this approach. The DCG achieved a calculated energy density for the fuel of 3868 Wh/kg, with 93% H2 extraction yield from the powder. Our findings reveal substantial improvements in terms of extended operation duration (81%), increased hydrogen flow rate (36%), enhanced energy density (33%), and improved H2 yield extraction from the powder (39%). This methodology holds promise for mobile applications or off-grid systems situated in proximity to a water source.

Application of metal-BDC-derived catalyst on cordierite honeycomb ceramic support in a microreactor for hydrogen production

Three metal-organic frameworks including Ce-BDC, In-BDC and In/Ce-BDC and corresponding derived CuO/ZnO/In2O3/CeO2 catalysts were prepared. The catalyst-loaded cordierite honeycomb ceramic supports were applied in a microreactor for hydrogen production via methanol steam reforming. The In/Ce-BDC-derived catalyst exhibited a methanol conversion rate of 100%, a hydrogen yield of 0.336 mol/h and an energy efficiency of 54% at 300 °C and an inlet methanol flow rate of 0.112 mol/h. Moreover, CO with content lower than 1.5% and catalytic stability of 30 h was recorded. The high specific surface area and superior redox property of the In/Ce-BDC-derived catalyst were characterized. The increased contents of oxygen vacancies and surface oxygen, in collaboration with the improved solid solubility of CuO and ZnO, were associated with the charge exchange induced by the strong interaction between In2O3 and CeO2, leading to the excellent catalytic performance of the In/Ce-BDC-derived catalyst.

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.

SIMULATION STUDY ON THE TUBULAR MICROREACTOR FOR HYDROGEN PRODUCTION BY STEAM REFORMING OF METHANOL

In order to reduce the carbon emissions of fuel vehicles, hydrogen has received extensive attention as a new clean energy. In this paper, a packed-bed microreactor for hydrogen production from methanol steam is designed for use in hydrogen fuel cells. By considering the heating gas velocity in the heating tubes, the inlet temperature of the microreactor, the size and number of heating tubes, inlet pressure, pellet porosity and thermal conductivity, parameters such as methanol conversion rates and hydrogen concentration were evaluated. First, the rate at which the gas is heated has a great influence on the reaction results. Choosing a larger heating gas velocity leads to an increase in the temperature inside the microreactor, thereby increasing the CH3OH conversion, resulting in a higher H2 concentration at the outlet. Changing the inlet temperature of the microreactor affects the reaction speed, but has little effect on the H2 concentration at the outlet. By studying the radius and number of heating tubes, we selected three different sets of data to compare the conversion rate of reactants and the concentration of products, and finally determined the optimal parameters as R = 4 mm and N = 8. Second, the inlet pressure has little effect on the H2 concentration at the outlet, but has a significant effect on the reaction speed. Particle porosity has no effect on the reaction results. Finally, the larger the thermal conductivity, the higher the temperature in the microreactor, which is more conducive to the reaction.

Performance and cold spot effect of methanol steam reforming for hydrogen production in micro-reactor

Catalytic hydrogen production by methanol steam reforming is considered to be an attractive hydrogen source option. However, performance of conventional packed beds for methanol steam reforming may be limited by heat transfer, which results in a low effective factor of the catalyst. In this work, CuO/ZnO/Al2O3 catalyst particles with diameter of 0.5 mm were filled in the micro-reactor for hydrogen production by methanol steam reforming. At steam to methanol ratio of 1.3, effects of inlet temperature, space velocity on reactor performance were investigated. The temperature distribution in the catalyst bed has also been studied. Results showed that methanol conversion decreased with space velocity and it increased with inlet temperature. Hydrogen production yield increased firstly and then decreased with space velocity. And it increased with the increasing of temperature. However, CO content in the product also increased with temperature, and it decreased with the increasing of inlet space velocity, especially at low temperature condition. Compared to conventional tubular fixed bed reactor, the micro-reactor presented a slightly better performance due to the fixed bed nature of catalyst, which is inefficiency in tubular reactor. Cold spot was observed at inlet of micro-reactor reaction chamber, and the highest temperature difference at cold spot area reached about 6 K. The maximum temperature difference throughout the catalyst bed reached 10 K in the micro-reactor.

Coupling exothermic and endothermic reactions in an ethanol microreformer for H2 production

The steam reforming of ethanol is carried out in a microreactor for hydrogen production. The heat for the endothermic reactions is supplied by means of ethanol combustion in air, which is carried out in contiguous microchannels. The same Pd-based catalyst is assumed to be coated on both reforming and combustion channels. By means of a 1D heterogeneous mathematical model, the influence of the feed temperatures of both streams on the reactor performance is analyzed. The results show that the degree of preheating of both streams has a strong influence on the hydrogen yields and maximum temperatures. The effect of the flowrate and composition of the fuel stream on the hydrogen yields is also studied.Fairly high hydrogen yields were obtained (2.6<ηH2<3.4) with low methane slips, within a feasible range of temperatures for the Pd catalyst (700<TMAX<770°C) to avoid catalyst deactivation. These maximum temperatures could still be further reduced by means of an optimal selection of the air flowrate and ethanol molar fraction on the fuel side, or using distributed feed of fuel along the reactor length.

Pore-scale simulation of coupled multiple physicochemical thermal processes in micro reactor for hydrogen production using lattice Boltzmann method

A general numerical scheme based on the lattice Boltzmann method (LBM) is established to investigate coupled multiple physicochemical thermal processes at the pore-scale, in which several sets of distribution functions are introduced to simulate fluid flow, mass transport, heat transfer and chemical reaction. Interactions among these processes are also considered. The scheme is then employed to study the reactive transport in a posted micro reactor. Specially, ammonia (NH3) decomposition, which can generate hydrogen (H2) for fuel of proton exchange membrane fuel cells (PEMFCs), is considered where the endothermic decomposition reaction takes place at the surface of posts covered with catalysts. Simulation results show that pore-scale phenomena are well captured and the coupled processes are clearly predicted. Effects of several operating and geometrical conditions including NH3 flow rate, operating temperature, post size, post insert position, post orientation, post arrangement and post orientation on the coupled physicochemical thermal processes are assessed in terms of NH3 conversion, temperature uniformity, H2 flow rate and subsequent current density generated in PEMFC.

Numerical Simulation of Transport Characteristics of Porous Metal Fiber Sintered Felts Used in Microreactor for Hydrogen Energy

The porous metal fiber sintered felt (PMFSF), a new catalyst support, was successfully used to construct a methanol steam reforming microreactor for hydrogen production. To study the transport characteristics of PMFSFs, a three-dimensional model with the cubic pore cell structure for PMFSFs was established. Using computational fluid dynamics fluent software, the velocity and pressure distribution when the fluid through the PMFSFs was investigated by changing the porosity of PMFSFs and inlet velocity of the fluid. In addition, fluid temperature distribution was analyzed under different inlet velocities by setting the temperature of fluid and wall. The result shows that the PMFSFs greatly enhance the transport characteristics because of its three-dimensional network structure and microchannel structure, it will become an ideal candidate for catalyst support material.

An Experimental Study on Micro Thixoforming Processing Parameters for Reaction Plate with Micro-Pin-Fin Arrays

Processing parameters of micro thixoforming, such as height-diameter ratio, die/punch temperature, billet temperature, and punch speed, have direct and complex impact on final quality of the workpiece, which is to be applied as the reaction plate of a microreactor for hydrogen production from methanol steam reforming. The micro/meso features of the workpiece, which is for catalyst loading, are micro-pin-fin arrays. Size of the surface area and uniformity of the pin-fins are quantified by average height (Ha) and relative standard deviation (RSD). An orthogonal experiment design is adopted to investigate the influence of the parameters on the semi-solid forming process. The results of the orthogonal experiment show that the optimum parameters are 150 °C for die/punch temperature, 576 °C for billet temperature, 0.14 for height-diameter ratio and 8.33 mm/s for punch speed. The experimental results validate that the optimized processing parameters can improve the quality of the reaction plate with micro-pin-fin arrays.

Effect of Catalytic Distribution on the Performance of Microreactor for Hydrogen Production through Methane Steam Reforming

The effect of catalyst coating distributing on the reactor performance for methane steam reforming(MSR) was numerically investigated. In calculation, the amount catalyst loaded on the microreactor wall was fixed but the catalyst active site density was distributed according to arithmetic progression along the flow direction. Results show that it is possible to get the higher conversion of CH4 and output of H2 due to the higher availability ratio of catalyst surface active sites at this distribution. And this distribution effect is more remarkable at higher space velocity or lower reaction temperature, however, there exists an optimal distribution which can reach the highest CH4 conversion and H2 production at 900K.

Using reverse micelles as microreactor for hydrogen production by coupled systems of Nostoc/R. palustris and Anabaena/R. palustris

Uptake hydrogenase negative mutants of bloom forming cyanobacteria (Nostoc and Anabaena) and the fermentative bacteria Rhodopseudomonas palustris P4 were used together for producing hydrogen within the reverse micelles fabricated by N-ethyl hexyl sodium sulfosuccinate (AOT) in isooctane and cetyl trimethyl ammonium bromide (CTAB) in benzene. The rate of H2 production in AOT/isooctane reverse micellar system was found to be more promising in comparison to the CTAB/Benzene reverse micellar entrapment. After mutagenesis in 2.0% (v/v) ethyl methane sulphonate (EMS) mutants of Nostoc and Anabaena were selected on BG-11 plates (containing 2% agar) and then used for analysis of produced hydrogen. In comparison to the unmutated Nostoc with R. palustris (within AOT/isooctane) the coupled system of mutated Nostoc and R. palustris produced H2 by 3.9-fold higher rate, which is 8.6 mmol H2/h/mg protein. Whereas, mutated Anabaena coupled with R. palustris produced 4.8 times higher hydrogen production within (AOT)/isooctane reverse micelles in comparison to the unmutated Anabaena with R. palustris. Effect of nitrogen to carbon ratio (N/C) on hydrogen production was studied and Anabaena/R. palustris and Nostoc/R. palustris systems were, respectively, found to generate 11.2 and 9.8 mmol H2/h/mg protein continuously for 3 days. Effects of temperature and light intensity were also investigated and we found that 32°C temperature and 1,000 Lux light intensity are the optimum values in these systems. Addition of sodium dithionite also resulted in further enhancement of the rate and duration of hydrogen production in both (mutated Nostoc/R. palustris and mutated Anabaena/R.␣palustris) systems.

A Microreactor for Hydrogen Production in Micro Fuel Cell Applications

A silicon-chip based microreactor has been successfully fabricated and tested for carrying out the reaction of methanol reforming for microscale hydrogen production. The developed microreactor in combination with a micro fuel cell is proposed as an alternative to conventional portable sources of electricity such as batteries due to its ability to provide an uninterrupted supply of electricity as long as a supply of methanol and water can be provided. The microreformer-fuel cell combination has the advantage of not requiring the tedious cycles needed by conventional rechargeable lithium-ion batteries. It also offers significantly higher energy storage densities, which translates into less frequent recharging through the refilling of methanol fuel. The microreactor consists of a network of catalyst-packed parallel microchannels of depths ranging from 200 to 400 /spl mu/m with a catalyst particle filter near the outlet fabricated using photolithography and deep-reactive ion etching (DRIE) on a silicon substrate. Issues related to microchannel and filter capping, on-chip heating and temperature sensing, introduction and trapping of catalyst particles in the microchannels, flow distribution, microfluidic interfacing, and thermal insulation have been addressed. Experimental runs have demonstrated a methanol to hydrogen molar conversion of at least 85% to 90% at flow rates enough to supply hydrogen to an 8- to 10-W fuel cell.