Kinetic enhancement of ammonia decomposition as a chemical hydrogen carrier in palladium membrane reactor
Kinetic enhancement of ammonia decomposition as a chemical hydrogen carrier in palladium membrane reactor
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DOI：
10.1016/j.cattod.2014.02.054
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发表时间：
2014-11-01
期刊：
影响因子：
5.3
通讯作者：
Sato, Takafumi
中科院分区：
文献类型：
--
作者：
Itoh, Naotsugu;Oshima, Atsushi;Sato, Takafumi
氨作为一种有前途的化学氢载体，在低温下使用钌负载催化剂进行分解，其中需要从氨中高效回收氢。在623 ~ 723k范围内，平衡转化率几乎达到100%，但分解仍然处于低转化率状态，因此现有催化剂的活性不足有待改进。本研究试图证明在钯膜反应器中可以增强这种动力学限制分解，而在大多数膜反应器应用中，通过选择性氢分离可以将平衡限制反应转移到产物侧。推导了Ru/SiO2催化剂分解氨的七种反应模型Langmuir-Hinshelwood型速率方程，并与实验结果进行了比较。结果表明，在623 ~ 723 K范围内，氮原子的联合脱附是反应速率的决定步骤。钯膜反应器的一维模型表明，根据反应模型（速率表达式），动力学增强有很大差异。采用200 pm厚钯管的膜反应器进行氨分解，转化率比常规填料反应器提高15%，723 K时氢气回收率可达60%。模拟结果表明，采用更薄的钯膜可以进一步增强性能。(C) 2014 Elsevier B.V.版权所有
Decomposition of ammonia as a promising chemical hydrogen carrier is carried out at low temperatures using a ruthenium supported catalyst, where a highly efficient hydrogen recovery from ammonia is being desired. The equilibrium conversion is almost 100% in the range of 623-723K but the decomposition remains in a low conversion, so that insufficient activity of present catalysts should be improved. This study attempts to prove that this kinetically limited decomposition can be enhanced in the palladium membrane reactor, while in most of membrane reactor applications the equilibrium limited reactions can be shifted to the product side by selective hydrogen separation.The Langmuir-Hinshelwood types of rate equations, seven reaction models, for ammonia decomposition using a Ru/SiO2 catalyst were derived and compared with experimental results. As the result, the combinative desorption of nitrogen atom was found to be the rate determining step in the range of 623-723 K. One dimensional model for a palladium membrane reactor could show that the kinetic enhancement differed considerably according to the reaction model (rate expression).In the ammonia decomposition employing a membrane reactor with a 200 pm-thick palladium tube, 15% increase in conversion compared with the conventional packed reactor and 60% of the hydrogen recovery at 723 K could be obtained. Simulation showed that further enhancement would be achievable by using thinner palladium membrane. (C) 2014 Elsevier B.V. All rights reserved.