UNS: Earth Abundant Membrane Reactors for Efficient Chemical Processing

膜反应器将反应和分离集成到一个单元操作中，其中产品被连续去除，推动反应完成，同时执行产品提纯。这类反应器中的关键元件是膜，膜通常是浸渍了催化剂的金属。这种膜反应器由对氢具有选择性的致密金属膜组成，在许多应用中具有巨大的潜力，例如天然气的水蒸气重整生产氢气(然后可以用于替代能源系统，如燃料电池)。钯(Pd)及其合金是使用最广泛的氢膜材料，因为它们既有解离氢气的能力，又因为它们在广泛的温度范围内对氢气具有高的渗透性。但是，对于实际应用来说，这样的膜太昂贵了。该项目的目的是寻找在这种工艺中更便宜但可用的替代膜材料。地球上丰富的体心立方(BCC)金属，如Nb(Nb)、Ta(Ta)和V(V)及其相关合金具有必要的氢渗透性，但它们缺乏Pd的催化活性。PIS计划使用纳米结构的过渡金属碳化物薄膜作为有效和稳定的催化层，使BCC膜反应器能够在各种实际的化学过程中使用。他们计划测试他们的氨(NH3)分解和合成的反应器。在这个项目中，PIS将开发用于膜反应器的BCC金属膜。在致密的金属膜中，氢被分解成原子氢，它们将利用这种试剂尚未开发的化学潜力来进行氢化化学，如氨合成，这通常需要非常高的压力。将使用不对称膜，即具有不同催化层的bcc金属箔，应用于进料和渗透侧。首先，不对称结构将被用来识别和量化控制氢气通过体心立方复合膜渗透的步骤。体心立方金属的一个关键材料挑战是，当氢的溶解度超过临界值时，它们容易失去延展性。将采用非对称设计概念，在高压进料侧浇注氢气通量，并将其从渗透表面快速释放。这样的设计将在不牺牲机械完整性的情况下最大限度地提高透气性。最后，具有独特的反应物分解和产物形成催化剂的不对称膜将被用来最大限度地发挥膜反应器用于化学合成的潜力。甲烷的水蒸气重整可以在膜反应器中完成，同时将操作温度从900℃降低到500℃，这比仅在美国的传统工艺每年可以节省2×10^14BTU。PIS将把以膜反应器分解NH3为基础的实验模块纳入高级运输和反应堆工程课程。他们计划让本科生研究人员参与这项研究。此外，还将与丹佛大都会的男孩和女孩俱乐部合作举办两项年度活动。这些活动将汇集低收入的K-12学生和本科生，从事以工程和化学为主题的动手科学活动。

Wolden, 1512172Membrane reactors integrate reaction and separation into a single unit operation where product is removed continuously, driving the reaction to completion while simultaneously performing product purification. The critical element in such reactors is the membrane, which is often a metal impregnated with a catalyst. Such membrane reactors, comprised of dense metal membranes that are selective to hydrogen, have great potential in numerous applications such as steam reforming of natural gas to produce hydrogen (which can then be used in alternate energy systems such as fuel cells). Palladium (Pd) and its alloys are the most widely used hydrogen membrane materials due to their ability to both dissociate hydrogen and because they have a high permeability to hydrogen across a wide range of temperatures. But, such membranes are too costly for practical applications. This project is aimed at finding replacement membrane materials that are cheaper yet usable in such processes. Earth abundant body centered cubic (BCC) metals such as Niobium (Nb), Tantalum (Ta), and Vanadium (V) and related alloys have the necessary hydrogen permeability but they lack the catalytic activity of Pd. The PIs plan to use nanostructured transition metal carbide thin films as effective and stable catalyst layers to enable the use of BCC membrane reactors in various practical chemical processes. They plan to test their reactor for both ammonia (NH3) decomposition and synthesis.Intellectual MeritIn this project the PIs will develop BCC metal membranes for use in membrane reactors. In dense metal membranes hydrogen is dissociated into atomic hydrogen, and they will exploit the untapped chemical potential of this reagent to enable hydrogenation chemistries such as ammonia synthesis, which normally requires very high pressure. Asymmetric membranes, BCC metal foils with different catalyst layers, applied to the feed and permeate side, will be used. First, asymmetric structures will be used to discern and quantify the steps that control H2 permeation through BCC composite membranes. A critical materials challenge with the BCC metals is their proclivity to lose ductility when the hydrogen solubility exceeds a critical value. Asymmetric design concepts will be employed to gate the H2 flux at the high pressure feed side and quickly release it from the permeate surface. Such designs will be engineered to maximize permeance without sacrificing mechanical integrity. Lastly, asymmetric membranes with unique catalysts designed for reactant decomposition and product formation will be used to maximize the potential of membrane reactors for chemical synthesis.Broader ImpactsMembrane reactors have potential to impact a range of industrially important processes from steam reforming to various de/hydrogenation chemistries. Steam reforming of methane can be driven to completion in a membrane reactor while simultaneously reducing operating temperatures from 900 to 500 °C, which could save 2 x 10^14 BTU/year over conventional processing in the US alone. The PIs will integrate an experimental module based on membrane reactor decomposition of NH3 into the senior transport and reactor engineering curricula. They plan to engage undergraduate researchers in this research. In addition two annual events will be held in partnership with the Boys and Girls Clubs of Metro Denver. These events will bring together low-income K - 12 students and undergraduates to engage in hands-on science activities with the themes of engineering and chemistry.