用于甲醇蒸汽重整制氢的钯合金膜反应器的研究与进展

Research and Development of Palladium Alloy Membrane Reactor for Hydrogen Production by Steam Reforming of Methanol

氢气的储运安全与成本问题限制了氢的规模使用。利用甲醇蒸汽重整(MSR)可以实施现场规模化制氢且反应条件温和,可避免以上限制。其中在钯合金膜反应器进行MSR制氢工艺流程简单、制氢效率高和能耗低,应用前景广阔。但在MSR制氢过程中,反应中间体和催化剂以及CO等多种杂质气体共存时会严重降低钯合金膜的透氢性能和抗毒化性能,大大降低了钯合金膜反应器的制氢效率和寿命。介绍了在MSR反应中操作条件和钯合金膜性能对膜反应器性能和寿命的影响。阐述了钯合金膜常用的基体和制备方法,并从钯合金膜透氢性和抗毒化性两方面进行讨论和比较。此外,综述了在MSR反应下常用的Pd-Ag, Pd-Cu和Pd-Au二元钯合金膜在膜反应器中氢渗透和抗杂质气体毒化方面的研究进展,分析了存在的问题和可能的解决方法。最后对钯合金膜应用在MSR制氢膜反应器未来研究方向进行了展望。

With the deterioration of energy crisis and environmental pollution, the development and utilization of abundant, clean and safe renewable energy becomes an urgent need for the rapid development of society. The production process of hydrogen is relatively mature. As a carrier of clean energy, hydrogen only emits water after combustion, and it has better combustion characteristics in traditional combustion systems. In recent years, it has attracted much attention in fields such as fuel cells. Among them, the proton exchange membrane fuel cell(PEMFC) has the advantages of low pollution, high power density and fast start-up, and has become the most potential fuel cell at this stage. However, the safety and cost of hydrogen storage and transportation limit the large-scale application of hydrogen. Methanol, liquid ammonia and other hydrogen storage media are liquid at normal temperature and pressure, with high hydrogen storage density, good safety, mature technology and low cost, which can meet the application of hydrogen in many aspects. Among them, the H/C ratio(molratio) of methanol is high, and the methanol steam reforming(MSR) reaction temperature is low(200~350 ℃), which can realize large-scale hydrogen production. The traditional methanol reforming hydrogen production process has the disadvantages of large volume and high energy consumption, and it is difficult to apply in small scale hydrogen production. As a new type of hydrogen production device, membrane reactor has the advantages of high selectivity, high energy efficiency and small size, and can be used in small hydrogen production devices. Palladium and its alloy membranes have complete hydrogen selectivity and are promising for membrane reactors. However, under MSR reaction conditions, the coexistence of intermediates, catalysts and various impurity gases such as CO affects the hydrogen permeability and poisoning resistance of palladium alloy membranes, which limits the wide application of membrane reactors. This paper introduced the research status and existing problems of commonly used membrane reactors, as well as the effects of palladium alloy membrane properties and operating conditions on the performance and life of membrane reactors in MSR reactions. The packed bed membrane reactor had a simple structure and could be expanded in a multi-tube membrane reactor, but the packed bed membrane reactor had the disadvantages of concentration polarization, excessive internal pressure drops and temperature difficult to control. The fluidized bed membrane reactor had good mass transfer and heat transfer properties, but the violent movement of particles generated by the bed bubbles in the fluidized bed membrane reactor led to the internal degradation of the reactor and catalyst loss, reducing the life of the membrane reactor. In addition, reasonable operating conditions and palladium alloy membranes with high hydrogen permeability and high resistance to impurity gas poisoning could improve hydrogen production efficiency and membrane reactor life. Among them, the performance of palladium alloy membrane was affected by the choice of membrane substrate and preparation method. The commonly used substrates and preparation methods of palladium alloy membranes were expounded, and the stability and hydrogen permeability of palladium alloy membranes were discussed and compared. The high surface roughness of the porous ceramic matrix and the existence of macropores were not conducive to the preparation of dense and thin palladium alloy membranes. The porous metal matrix and palladium were prone to interdiffusion at high temperatures, which would destroy the integrity of the membrane. Therefore, to prepare a complete, continuous and dense thin palladium alloy film, the surface treatment of the substrate was necessary. However, the substrate itself needed to have a small pore size(50~100 nm) and be uniform or select an appropriate modification process for surface treatment. In addition, the research progress of Pd-Ag, Pd-Cu and PdAu binary palladium alloy membranes commonly used in MSR reactions in membrane reactors was reviewed, and the problems and possible solutions in membrane reactors were analyzed. In methanol reforming hydrogen production membrane reactors, Pd-Ag, Pd-Cu and Pd-Au binary palladium alloy membranes were commonly used. Pd-Ag alloy film had good hydrogen permeability, but it was more sensitive to CO and has poor resistance to poisoning. Pd-Cu alloy film had good poisoning resistance to impurity gases, high stability, high mechanical strength and low cost;however, precise composition control was required in the preparation process, and Pd-Cu alloy had a mixed interstitial phase of face-centered cubic(fcc) and body-centered cubic(bcc). The heat treatment process was difficult to control, which would result in uneven composition of the prepared Pd-Cu alloy films, which also limited the wide application of Pd-Cu alloy films. Pd-Au alloy film had good poisoning resistance and wide reasonable composition range, and could replace Pd-Cu alloy film in membrane reactors, but Au had high cost and was easy to segregate to the surface of the film, reducing hydrogen permeability. It was difficult to achieve uniform composition of Pd-Au alloys during heat treatment. Finally, the future research direction of palladium alloy membrane application in methanol reforming hydrogen production membrane reactor was prospected.