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.     

Development of three-electrode type micro-electrochemical reactor on anodized aluminum with photon rupture and electrochemistry

Photon rupture with a focused single pulse of pulsed YAG-laser irradiation was used to fabricate an aluminum electrochemical micro-reactor. Porous type anodic oxide film formed on aluminum specimens was irradiated in solutions with a pulsed Nd-YAG laser beam through a convex lens to fabricate micro-channels, micro-electrode, and through holes (for reference electrode, solution inlet, and outlet). During irradiation, specimens were moved by a computer controlled XYZ stage. After irradiation, the surface of the micro-channel and through hole were again treated to form anodic oxide film and the surface of the micro-electrode was treated electrochemically to provide an Au layer. The calculated volume of the micro-reactor including micro-channel and through holes is about 1.5 μl. The cyclic voltammogram of the micro-electrochemical cell was measured in K₃Fe(CN)₆/K₄Fe(CN)₆ with both static and flowing solution at different scanning rates. The anodic and cathodic peak currents were measured and the values depended on scanning rate and ion concentration when the solution was static. With the flowing solution, limiting currents were observed and the anodic limiting current was increased with the cubic root of the solution flow rate.     

Effects of structural parameters on the performance of a micro-reactor with micro-pin-fin arrays (MPFAR) for hydrogen production

To enhance the energy conversion efficiency of the micro-reactor with micro-pin-fin arrays (MPFAR) for hydrogen production, the effect of structural parameters (the height of the micro-pin-fin, the transverse and longitudinal center distance between two adjacent micro-pin-fins) on the performance of the MPFAR for hydrogen production is investigated. Based on the geometrical parameters, a theoretical model of material balance for hydrogen production in the MPFAR is established. The calculated results show that with the increase of the micro-pin-fin height or the decrease of the distance between two adjacent micro-pin-fins, the methanol conversion rate and the CO molar fraction increase. The methanol conversion rate increases by about 10% when the height of micro-pin-fin increases from 0.2 to 1 mm or the center distance between the two adjacent micro-pin-fins increases from 1.2 to 2.6 mm. The comparisons between the experimental and calculated results validate the theoretical model of material balance utilized in this study. Finally, a better geometrical structure of micro-pin-fin arrays is obtained, in which the height of the micro-pin-fin, the transverse and longitudinal center distances between two adjacent micro-pin-fins are 1.0 mm, 1.2 mm and 1.2 mm, respectively. The hydrogen yield in the MPFAR can reach about 8.3 ml/min under the condition that the methanol conversion rate is above 90%.     

CFD simulation with detailed chemistry of steam reforming of methane for hydrogen production in an integrated micro-reactor

micro-reactor has drawn more and more attention in recent years due to the process intensification on basic transport phenomena in micro-channels, which would often lead to the improved reactor performance. Steam reforming of methane (SRM) in micro-reactor has great potential to realize a low-cost, compact process for hydrogen production via an evident shortening of reaction time from seconds to milliseconds. This work focuses on the detailed modeling and simulation of a micro-reactor design for SRM reaction with the integration of a micro-channel for Rh-catalyzed endothermic reaction, a micro-channel for Pt-catalyzed exothermic reaction and a wall in between with Rh or Pt-catalyst coated layer. The elementary reaction kinetics for SRM process is adopted in the CFD model, while the combustion channel is described by global reaction kinetics. The model predictions were quantitatively validated by the experimental data in the literature. For the extremely fast reactions in both channels, the simulations indicated the significance of the heat conduction ability of the reactor wall as well as the interplay between the exothermic and endothermic reactions (e.g., the flow rate ratio of fuel gas to reforming gas). The characteristic width of 0.5 mm is considered to be a suitable channel size to balance the trade-off between the heat transfer behavior in micro-channels and the easy fabrication of micro-channels.     

Hydrogen production by steam reforming of dimethyl ether and CO-PrOx in a metal foam micro-reactor

A bi-function catalyst containing CuZnAlCr and HZSM-5 was used to generate hydrogen by stream reforming of dimethyl ether (SRD) in a metal foam micro-reactor and a fix-bed reactor. Dimethyl ether conversion of 99% and hydrogen yield of >95% was reached with HZSM-5/CuZnAlCr (mass ratio of 1:1) in the micro-reactor. A suitable balance between the dimethyl ether hydrolysis and methanol reforming steps requires the proper acidity and the metal sites. The CuZnAlCr/HZSM-5 properties, effect of CuZnAlCr to HZSM-5 mass ratio were investigated in the metal foam micro-reactor. Moreover, CO was removed from hydrogen-rich gas by preferential oxidation reaction (CO-PrOx) with PtFe/γ-Al₂O₃ catalyst in a similar metal foam micro-reactor follows the SRD stage. With the optimized O₂/CO ratio and reaction temperature, the CO concentration dropped to <10 ppm and hydrogen yield of ∼90% were achieved in the new-type SRD-COPrOx system. The SRD-COPrOx system provide a constant hydrogen production with CO concentration lower than 10 ppm during 20 h. The results indicate that metal foam micro-reactor has the great potential in the DME steam reforming to supply hydrogen for low-temperature fuel cells.     

Enhancement of hydrogen reaction in a micro-channel by catalyst segmentation

The paper addresses the combustion characteristics of multi-segment catalysts in a micro-reactor by numerical simulation with detailed heterogeneous and homogeneous chemistries. The effect of multi-segment catalyst is delineated in terms of different catalyst dispositions, different flow conditions and different reactor properties. With a fixed total catalyst length (1 cm), multi-segment catalyst reveals better performance than single catalyst. The space between catalyst segments reduces the inhibition of homogeneous reactions by catalyst and promotes homogeneous reactions in this region since the neighboring catalysts help to maintain a high wall temperature. Therefore, homogeneous combustion can shift upstream with the multi-segment catalyst. The results of different catalyst dispositions show that more catalyst segments has better performance but the catalyst space distance has no obvious effects due to the fast reaction rate of hydrogen. For different flow conditions, the results indicate multi-segment catalyst disposition has better conversion ratio even though there is no homogeneous combustion in the fluid region for fuel-lean condition. The results for different inlet velocities show that multi-segment catalyst has no obvious benefit on lower inlet velocity. However, it can extend the blowout velocity. Finally different reactor dimension and wall material are simulated. Although heterogeneous reactions strengthen in small channel, multi-segment catalyst still has obvious benefit. The results of different wall thermal conductivity do not have obvious difference for multi-segment catalyst. These results can be used in the design of a catalytic micro-reactor for hydrogen/air reactions.     

气液微反应器研究及展望

气液微反应器具有效率高,速度快,操作灵活,易于装卸和运输的特点,是作为实现过程强化、满足绿色化工生产的重要设备之一。对各种新型气液微反应器进行了介绍,阐述了气液微反应器内流动特性和传质特性,最后对其未来进行了展望。     

Accelerated biogas production without leachate recycle

The economics of biogas production remain marginal, even on ‘free’ substrates such as wastes. However, new insights into the fundamental processes of solid-state digestion promise a much faster and more predictable process. This holds the future prospect of profitable biogas production from anaerobic composters fed with a range of solid substrates, including food industry wastes and biomass crops.A novel process model proposes that reaction occurs at a well-defined but mobile interface between raw and depleted wastes, forming the boundary of an independent expanding micro-reactor. Very small seed particles cannot establish such micro-reactors. The present paper explores the implications for seeding practice. Leachate recycle might do no more than compensate for erratic seeding, by transporting nutrients into well-seeded zones. Inoculating the waste with well-distributed seed particles of viable size could be more effective — and a great deal simpler and cheaper.     

长链烯烃-苯烷基化反应性能影响因素的研究

通过多种渠道对自行研制的固体酸催化剂的烷基化反应进行了考察。由于烷基化反应是厌水反应 ,故在反应中对催化剂中所含的物理及化学吸附水要严格的脱除。主要针对这方面的问题在工艺操作过程中分别对催化剂的活化方式、降温方式、进料温度以及不同排气速度等进行了考察 ,最后确定了活化方式为柱内活化 ,降温方式为快速降温 ,进料温度不大于 80℃ ,排气速度为 30mL/h。实验的最佳条件 :反应温度为 2 0 0～ 2 80℃、反应压力为 35～ 5 0MPa、苯烯摩尔比为 (8～ 1 0 )∶1。     

Effect of enhanced mixing on partial oxidation of methane in a novel micro-reactor

A miniaturised hydrogen generator is being developed for small mobile/onboard fuel cell applications based on the concept of partial oxidation of methane (POM). The generator comprises several hundred micro-reactors each in the shape of a tubular vessel fitted with a multi-holed baffle-plate for mixing enhancement. Experiments were conducted on 1:1 scale replicas of the reactor over a range of temperatures between 300 and 1000 °C under both catalytic and non-catalytic conditions. Results indicate that the application of the multi-holed baffle-plate considerably improves the conversion rates of reactants and the selectivity of desired products (i.e. H₂) especially when rhodium is used as a catalyst. To the contrary, increasing pressure led to the formation of undesirable soot residues, a reduction in methane conversion and a deterioration of the hydrogen selectivity.