多通道钯膜反应器中钯纳米晶/陶瓷复合材料的研制及其CFD模拟研究

Natural gas steam reforming in Pd membrane reactors becomes a hot research topic as it combines the separation and reaction in one unit and thus greatly lowers the investment and production cost compared to conventional natural gas steam reforming process for H2 production. However, the stability issue appears as the main obstacle for its industrial applications. The novel design of highly stable Pd composite membranes and the structural optimization of Pd membrane reactors are critical in order to overcome such an issue. Therefore, in this study, novel composite materials of Pd nanocrystals/ceramics is proposed, which can effectively suppress Pd lattice expansion due to much higher surface H concentration than interior H concentration, and simultaneously avoid the contact/interactions between reforming catalyst and Pd membrane surface. In addition, methane steam reforming is carried out within highly-efficient multi-channel Pd membrane reactors for the first time, which in combination with CFD (computational fluid dynamics) simulation can significantly improve the stability via structural optimization of membrane reactors. This study mainly revolves around the fabrication, optimization and stability investigation of Pd nanocrystals/ceramics composite materials, as well as experimental study, CFD simulation, structural optimization and stability investigation of methane steam reforming Pd membrane reactor, which show great promise to overcome the challenge of poor stability of methane steam reforming Pd membrane reactor and thus push forward a novel technical route for cheap hydrogen production.

与传统过程相比，甲烷水蒸气重整钯膜反应器制氢能实现反应和分离一体化，显著降低装置投资和生产成本，因此成为当前的研究热点。但甲烷水蒸气重整钯膜反应器的稳定性较差，尚达不到工业应用的要求。开发高稳定性的钯复合膜材料新体系并进行钯膜反应器结构的优化设计是实现其商业应用的关键。为此，本项目创造性地提出钯纳米晶/陶瓷复合材料的新体系，借助于钯纳米晶表面氢吸附量大于体相氢吸附量的特点抑制钯晶格膨胀，同时避免催化剂与钯膜的相互作用；另外，首次开发高效多通道钯膜反应器及其CFD模拟技术，通过优化反应器结构，增强传热传质效率以提高其稳定性。本项目将围绕钯纳米晶/陶瓷复合材料的制备、优化设计及稳定性考察，钯膜反应器制氢实验研究、CFD模拟、结构优化及稳定性考察等方面开展研究，这对于解决钯膜反应器稳定性差的关键问题，开辟廉价的钯膜反应器制氢技术路线具有重要的研究意义。

目前世界上90%的氢气是由天然气重整过程制得，该过程包含多个步骤而且重整需要在约850 ℃的高温下进行，而与钯膜相结合后，能使反应步骤缩短为一步进行，实现氢气的原位分离，并能将反应温度降低到550 ℃，具有显著的经济前景。目前亟待提高重整钯膜反应器的稳定性和效率，其关键是开发高稳定性的钯复合膜材料新体系并进行钯膜反应器结构的创新设计。.为此本课题开展了如下研究：.采用循环化学镀方法在19通道及7通道陶瓷内表面制备金属钯膜，选择性能达到50000以上，氢气渗透速率大于5 Nm3/h.bar，实现高性能多通道钯膜的制备。.将钯纳米粒子以化学镀的方式嵌入多孔膜孔道内，得到致密无缺陷的钯纳米粒子/陶瓷透氢膜复合材料，开发出钯复合膜新制备方法。对钯纳米晶/α-Al2O3/γ-Al2O3/ZrO2进行表面形貌和横截面形貌及EDS分析, 可以看到复合材料表面密集分布着钯纳米晶，钯纳米晶/ZrO2致密复合层的厚度约为3 μm。.制备Pd-Mn/CeO2, Ni/MoC, Ni/γ-Al2O3催化剂并在400-850 ℃下进行甲烷水蒸气重整反应器的性能测试。其中Ni/MoC和Pd-Mn/CeO2在550 ℃下的转化率为44%和57%，低于Ni/γ-Al2O3 (转化率61%)。Ni/MoC和Pd-Mn/CeO2在400 ℃下的转化率分别达到12%和16%，有一定的低温活性。.开展多通道钯膜氢气渗透的2D CFD模拟，模拟气氛为50%H2/N2混合气，测试温度为400 ℃，pfeed/pperm=10/3 bar, 总流速为0.6-2 L/min。合作搭建甲烷重整膜反应器CFD模型，和意大利合作方进行深入探讨，包括钯膜反应器传质影响，催化剂动力学等。.针对目前缺乏孔口直径表征方法的难题，我们发明了“改进”的液-液排除法用于测量多孔材料孔口直径分布。发明了将溶胶凝胶与悬浮粒子烧结相结合的方法，得到平整、光滑、无缺陷的修饰层，特别适合钯膜的制备。.研发单通道不锈钢负载钯复合膜Pd/MnO2/stainless steel，透氢速率达到1.8E-6 mol/m2.s.Pa, 透氢选择性达到77,038，好于目前文献报道的水平。.首次提出了钯复合膜原位“自动”修复的新路线，在合成气工作气氛下缺陷的原位“自动修复”，能将钯复合膜的选择性从4000提高到40000，具有良好的重复性。