通过捏合制备的致密颗粒膏体的织构特性
Textural properties of dense granular pastes produced by kneading
AI总结：
本研究通过中试捏合实验探究捏合工艺参数对勃姆石膏体织构特性的影响，发现累积变形量和pH值分别在固定组成和固定变形条件下调控织构，并提出可综合二者作用的经验控制参数，为催化剂载体的系统设计提供依据。
摘要：
负载型催化剂的效率取决于其固体载体的多孔微观结构，该结构调控着传质、活性相暴露程度以及机械强度。本文聚焦于一种特定类型催化载体——γ-氧化铝挤出物——的捏合-挤出制备工艺。在该工艺中，首先将勃姆石粉末（γ-氧化铝的羟基氧化铝前驱体）与多种液体混合并随后捏合形成膏体，之后进行挤出。该工艺的关键步骤是捏合阶段，它可控制挤出物的织构和力学性能。本实验研究旨在测量捏合步骤对使用中试捏合机制备的勃姆石膏体的影响。膏体通过将勃姆石粉末与酸和碱溶液经两步工艺混合制得，该工艺被称为胶溶和中和。本研究在不同搅拌速度和持续时间下进行捏合，同时监测勃姆石膏体对捏合机桨叶施加的扭矩。此外，在捏合过程的不同阶段从中试捏合机中提取样品，并通过氮气吸附法和压汞法测定其织构特性。我们的研究结果表明，在固定组成下，勃姆石膏体的织构特性由捏合过程中累积的总变形量控制。相反，对于固定的累积变形量，pH值决定了织构特性。最后，我们确定了一个经验控制参数，该参数可捕捉pH值和累积变形量对勃姆石膏体关键织构属性的综合影响。这些结果为勃姆石基催化剂载体的系统设计方法奠定了基础。
英文摘要：
The efficiency of supported catalysts depends on the porous microstructure of their solid support, which regulates mass transfer, exposure to the active phase, and mechanical strength. Here, we focus on the manufacturing of a specific type of catalytic support, $γ$-alumina extrudates, by a kneading-extrusion process. In this process, a paste is initially formed by blending and subsequently kneading a boehmite powder, an aluminum oxide hydroxide precursor of $γ$-alumina, with various liquids before undergoing extrusion. The crucial step in this process is the kneading step, which allows control over the textural and mechanical properties of the extrudate. The present experimental study aims to measure the impact of the kneading step on boehmite pastes prepared using a pilot kneader. The pastes are obtained by mixing boehmite powder with an acid and a basic solution in a two-step process known as peptization and neutralization. In this study, kneading is conducted at various mixing speeds and durations while monitoring the torque exerted by the boehmite paste on the kneader blades. Moreover, samples are extracted from the pilot kneader at various stages of the kneading process, and their textural properties are determined by both nitrogen sorption and mercury intrusion porosimetry. Our findings show that, at fixed composition, the textural properties of boehmite pastes are controlled by the overall deformation accumulated during kneading. Conversely, for a fixed accumulated deformation, the pH sets the textural properties. Finally, we identify an empirical control parameter that captures the combined effects of pH and accumulated deformation on the key textural attributes of boehmite pastes. These results set the stage for a systematic design approach of boehmite-based catalyst supports.
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