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%.     

Methanol steam reforming in a microchannel reactor by Zn-, Ce- and Zr- modified mesoporous Cu/SBA-15 nanocatalyst

Hydrogen production by steam reforming of methanol was studied over several Cu/SAB-15-based nanocatalysts in a parallel-type microchannel reactor. The catalysts were prepared through impregnation method and XRD, BET, FT-IR, FE-SEM, TEM, H₂-TPR and TGA techniques were used to characterize surface and structural properties of the synthesized catalysts. The effects of reaction temperature, WHSV and S/C molar ratio on the methanol conversion and selectivities of the gaseous products were studied. Then, effects of the metallic promoters were investigated to improve performance of the catalysts. It was revealed that ZnO and CeO₂ promoters have positive effects on decreasing CO selectivity and ZrO₂ promotes methanol conversion. Furthermore, ZrO₂ and CeO₂ were declared to improve stability of the catalyst. Among the evaluated catalysts, Cu/ZnO/CeO₂/ZrO₂/SBA-15 can provide optimal methanol conversion with low CO concentration in the gaseous products. For this catalyst, the methanol conversion and hydrogen selectivity reached 95.2% and 94.6%, 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.     

High H2 selectivity with low coke formation for methanol steam reforming over Cu/Y1.5Ce0.84Ru0.04O4 catalyst in a microchannel plate reactor

The synthesized novel metal oxides Y_xCe_yRu_zO₄ (x = 1.5, y = 0.84, z = 0.04) which was produced by the sol-gel method was used as a support for Cu active metal on the surface of a microchannel plate reactor in the methanol steam reforming (MSR) process. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area analysis (S_BET), energy-dispersive X-ray analysis (EDX), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed desorption (NH₃-TPD), and temperature-programmed reduction (H₂-TPR). High methanol conversion (99.5%) and H₂ selectivity (98.7%) and low CO selectivity (1.4%) were achieved for Cu/Y_xCe_yRu_zO₄ coated microchannel reactor at 250 °C. FE-SEM images and TGA curve of the spent catalyst displayed no coke formation on the surface of the catalyst after 32 h on stream at 300 °C. The low reduction temperature of Cu, high BET surface area, and high pore volume of the catalyst are considered imperative factors that cause a better dispersion of copper on the Y_1.5Ce_0.84Ru_0.04O₄ support.     

Evaluation of silica membrane reactor performance for hydrogen production via methanol steam reforming: Modeling study

The aim of this work is to analyze the potential application of microporous silica membrane reactor carrying out methanol steam reforming reaction for hydrogen production. As a further study, a comparison with dense Pd–Ag membrane reactor and a traditional reactor, working at the same operating conditions of silica membrane reactor, is realized.     

Modeling and analysis of flow distribution in an A-type microchannel reactor

Flow distribution among microchannels is a fatal factor affecting the performance of laminated microchannel reactors for hydrogen production. Homogeneous flow strongly depends on the structural design of the microchannel reactor. The present work concentrates on improving the flow distribution in microchannel reactors for hydrogen production by optimization of the structural design. An innovative A-type microchannel reactor for hydrogen production with one inlet/two outlets was developed and analyzed. The equivalent electrical resistance network model was used to calculate the flow distribution in the microchannel reactor which was validated by computational fluid dynamics (CFD). The influences of structural parameters on flow distribution in the A-type were investigated quantitatively. The calculated results showed that longer microchannels with a higher aspect ratio and a small side length in the manifolds were beneficial for attaining uniform flow distribution in the A-type microchannel reactor. Furthermore, it was found that flow distributions among the microchannels in the A-type were much more uniform than those in the conventional Z-type microchannel reactor with one inlet/one outlet. Finally, an optimization strategy was proposed to optimize the manifold geometries to obtain a comparatively even flow distribution among microchannels.     

Theoretical evaluation of various configurations of silica membrane reactor in methanol steam reforming using CFD method

The main purposes of this work was to evaluate from a theoretical point of view the performance of silica membrane reactors (MRs) in various configurations for generating hydrogen via methanol steam reforming (MSR) reaction using a two dimensional computational fluid dynamic (CFD) method, presenting details about molar fractions of gas species, velocity and pressure distributions at the simulated conditions. The CFD model was firstly validated and, then, used for the simulations, achieving an acceptable agreement between numerical outcomes and experimental data. The simulations were realized for MSR reaction carried out in three types of silica MRs, namely: 1) silica MR with cocurrent flow pattern (MR1); 2) silica MR with countercurrent flow pattern (MR2); 3) silica MR with countercurrent flow pattern including a water gas shift (WGS) reaction stage in the permeate side (MR3), meanwhile comparing the results with a traditional reactor (TR). The influence of several operating parameters (reaction temperature and pressure, and feed flow rate) on the performance of the aforementioned silica MRs in terms of methanol conversion, hydrogen yield and CO-selectivity was evaluated and the results compared with an equivalent TR. The simulations via CFD method indicated the MR3 results to be the best solution over the other MR proposed configurations and the TR as well, presenting the best simulation results at 10 bar of transmembrane pressure, 513 K, SF = 6, GHSV = 6000 h⁻¹ and feed molar ratio = 3/1 with CO selectivity ≤0.04%, methanol conversion and hydrogen yield >90%.     

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.     

A transient study of double-jacketed membrane reactor via methanol steam reforming

A non-isothermal unsteady-state model was established to simulate methanol steam reforming using a double-jacketed Pd membrane reactor. At steady state, a self-sustained membrane reactor was achieved by the oxidation of residual methanol and hydrogen from reformer for endothermic steam reforming. The molar fractions of species and reformer temperature were analyzed under co-current operation between oxidation and reformer sides. The start-up of reformer was simulated under two conditions: (1) The catalyst temperature was lower than the influent temperature and (2) The catalyst temperature was higher than influent temperature. Condition 1 yielded higher methanol conversion and reformer temperature than condition 2 at steady state. Moreover, the instability of species can be minimized on condition 1 during start-up. The fluctuation of membrane reactor at steady state was also studied. Two strategies were compared to analyze the reformer response when temporary extra hydrogen was required. The results showed that increasing inlet methanol outperformed increasing reformer temperature.     

H2 production in silica membrane reactor via methanol steam reforming: Modeling and HAZOP analysis

The main aim of this work is the presentation of both qualitative safety and quantitative operating analyses of silica membrane reactor (MR) for carrying out methanol steam reforming (MSR) reaction to produce hydrogen. To perform the safety analysis, HAZOP method is used. Before the HAZOP analysis, a comprehensive investigation of most important operating parameters effects on silica MR performance is required. Therefore, for a quantitative analysis, a 1-dimensional and isothermal model is developed for evaluating the reaction temperature, reaction pressure, feed molar ratio (steam/methanol) and feed flow rate effects on silica MR performance in terms of methanol conversion and hydrogen recovery. The model validation results show good agreement with experimental data from literature. As a consequence, simulation results indicate that the reaction pressure and feed molar ratio have dual effect on silica MR performance. In particular, it is found that methanol conversion is decreased by increasing the reaction pressure from 1.5 to 4.0 bar, whereas over 4.0 bar, it is improved. Moreover, the hydrogen recovery is decreased by increasing the feed molar ratio from 1 to 5, while over 5, it was approximately constant. After the evaluation of modeling results, the HAZOP analysis for silica MR is carried out during MSR reaction. The analysed operating parameters in the modeling study have been considered as key parameters in the HAZOP analysis. The safety assessment results are presented in tables as check list. By considering the HAZOP results, safety pretreatment works are recommended before or during the experimental tests of MSR reaction in silica MR. According to different parameters consequences, reaction temperature is the most critical parameter in MSR reaction for the silica MR studied in this work. In particular, to avoid the consequences of temperature deviation, it is recommended to use a PID temperature controller in the silica MR for MSR reaction.     

Development of the integrated methanol fuel processor using micro-channel patterned devices and its performance for steam reforming of methanol

A plate-type integrated fuel processor consisting of three different micro-structured modules was developed for hydrogen production in a 150 W PEMFC system. This system includes a reformer with combustor, two heat exchangers, and an evaporator with a combustor. Methanol steam reforming was chosen as a means to produce hydrogen for the PEMFC system. This system could be operated without any external heat supply. Hydrogen was used as the initial combustion fuel during startup, while methanol was used later. Cu/Zn/Al₂O₃ and Pt/Al₂O₃ catalysts were chosen for the steam reforming of methanol and the combustion, respectively, and coated on microchannel-patterned stainless steel sheets.

The integrated system was operated consistently with 80% of methanol conversion at for 20 h without deactivation of the catalysts. The production rate on dry basis and the composition of hydrogen was and ca 70%, respectively. Overall the thermal efficiency of this fuel processor based on the LHV was 56.7%.     

Design of a solar-driven methanol steam reforming receiver/reactor with a thermal storage medium and its performance analysis

A novel method of triple line focused on solar-powered receiver/reactor with a thermal storage medium for methanol steam reforming (MSR) hydrogen production is proposed in this paper. The photo-thermal-chemical energy conversion and coupling equations of the receiver/reactor are established, and the dynamic regularity between solar radiation and the hydrogen production characteristics is obtained by numerical simulation. The results show that a high solar radiation intensity helps to stabilize the duration of the reaction. For every 100 W m⁻² increase in the solar radiation intensity, the duration of the reaction maintained at the phase change point temperature of the phase change material (PCM) increases by approximately 11%. The daily hydrogen production performance of the system in Kunming (102°43′E and 25°02′N) during typical solar days is studied. The average annual total hydrogen production per unit of the lighting area is approximately 1300 m³. This research can guide similar issues related to solar thermochemical technology.     

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.     

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.     

Comparison between 1D and 2D numerical models of a multi-tubular packed-bed reactor for methanol steam reforming

The hydrogen-rich gas produced in-situ by methanol steam reforming (MSR) reactions significantly affects the performance and endurance of the high-temperature polymer electrolyte membrane (HT-PEM) fuel cell stack. A numerical study of MSR reactions over a commercial CuO/ZnO/Al₂O₃ catalyst coupling with the heat and mass transfer phenomena in a co-current packed-bed reactor is conducted. The simulation results of a 1D and a 2D pseudo-homogeneous reactor model are compared, which indicates the importance of radial gradients in the catalyst bed. The effects of geometry and operating parameters on the steady-state performance of the reactor are investigated. The simulation results show that the increases in the inlet temperature of burner gas and the tube diameter significantly increase the non-uniformity of radial temperature distributions in reformer tubes. Hot spots are formed near the tube wall in the entrance region. The hot-spot temperature in the catalyst bed rises with the increase in the inlet temperature of burner gas. Moreover, the difference in simulation results between the 1D and 2D models is shown to be primarily influenced by the tube diameter. With a methanol conversion approaching 100% or a relatively small tube diameter, the simplified 1D model can be used instead of the 2D model to estimate the reactor performance.     

Co-current and counter-current modes for methanol steam reforming membrane reactor

In this simulation study, methanol steam reforming reaction to produce synthesis gas has been studied in a membrane reactor when shell side and lumen side streams are in co-current mode or in counter-current mode. The simulation results for both co-current and counter-current modes are presented in terms of methanol conversion and molar fraction versus temperature, pressure, _H2O/_CH3OH${\mathrm{H}}_2\mathrm{O}/{\mathrm{CH}}_3\mathrm{OH}$ molar feed flow rate ratio and axial co-ordinate.     

Stacked etched aluminum flow-through membranes for methanol steam reforming

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

Numerical investigation of a multichannel reactor for syngas production by methanol steam reforming at various operating conditions

A novel multichannel reactor with a bifurcation inlet manifold, a rectangular outlet manifold, and sixteen parallel minichannels with commercial CuO/ZnO/Al₂O₃ catalyst for methanol steam reforming was numerically investigated in this paper. A three-dimensional numerical model was established to study the heat and mass transfer characteristics as well as the chemical reaction rates. The numerical model adopted the triple rate kinetic model of methanol steam reforming which can accurately calculate the consumption and generation of each species in the reactor. The effects of steam to carbon molar ratio, weight hourly space velocity, operating temperature and catalyst layer thickness on the methanol steam reforming performance were evaluated and discussed. The distributions of temperature, velocity, species concentration, and reaction rates in the reactor were obtained and analyzed to explain the mechanisms of different effects. It is suggested that the operating temperature of 548 K, steam to carbon ratio of 1.3, and weight hourly space velocity of 0.67 h⁻¹ are recommended operating conditions for methanol steam reforming by the novel multichannel reactor with catalyst fully packed in the parallel minichannels.     

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.