Single Catalyst Pellet Performance in Exothermic Multiphase Reaction Systems

许多具有重要商业价值的化学品是由挥发性成分和非挥发性成分在负载型催化剂上反应产生的。其中很大一部分是有机化合物在贵金属和镍催化剂上的氧化和加氢反应。这种反应是生产特种化学品(例如，苯胺和巴豆醛)和生物化学品(例如氢化植物油和木糖)的重要步骤。除了性质上的多相反应外，这些反应通常是快速的(质量传输有限)和相当放热的。反应热可导致催化剂颗粒孔内和外表面的液态汽化。在充满气体的气孔中发生的气相催化反应会导致颗粒内温度和压力的大幅上升。由于相变和气相催化反应，总速率也可能大幅增加。催化反应器内可能会出现不受欢迎的高温漂移(热点)。这些单粒现象使多相催化反应器的设计和控制变得复杂。随着对这些系统的更好的了解，可以开发新类型的多相反应堆操作和设计，其中利用了非等温现象的有利影响或避免了不利影响。该研究所正在计划对放热多相反应系统中单个负载型催化颗粒的行为进行基本的实验和模型研究。单颗粒甚至单孔水平通常决定了整个反应堆的行为。计划在负载型钯颗粒上进行环己烯加氢反应的两个实验。在第一个实验中，颗粒悬浮在管子中，通过流动的液膜和环状气体流动接触。随着各种散装条件的改变，将监测总体、速度、外部润湿程度、球团质量和球团温度。随着相变的发生，整体速率、温升和内外润湿程度对整体条件的依赖程度将被确定。在第二个实验中，将开发一种新的多相扩散和反应池，以更详细地研究粒子内的温度分布。单个颗粒在一个面上被液体润湿，在另一个面上被气体润湿。充气和充液催化剂颗粒的温升相差很大，为探测充气或充液气孔的位置提供了一种方法。对单一、部分润湿和填充的催化颗粒的几个相关模型进行了开发和数值求解。这项研究应提供最终用于多相反应堆设计的基础数据。

Many commercially important chemicals are produced by the reaction of a volatile and a nonvolatile component on a supported catalyst. A large fraction of these actions are oxidations and hydrogenations of organic compounds over precious metal and nickel catalysts. Such reactions are an important step in the production of specialty chemicals (for example aniline and crotonaldehyde) and biochemicals (for example hydrogenated vegetable oils and xylose). In addition to being multiphase in nature, these reactions are typically fast (mass transport limited) and quite exothermic. The reaction heat can lead to liquid-phase vaporization both within the catalyst pellet pores and on the external surface. The gas-phase catalytic reaction occurring in the gas-filled pores can result in a large rise in the intraparticle temperature and pressure. The overall rate may also increase substantially as a result of the phase change and gas-phase catalytic reaction. Undesirable high temperature excursions (hot spots) within a catalytic reactor may result. These single pellet phenomena complicate the design and control of multiphase catalytic reactors. With a better understanding of these systems new types of multiphase reactor operations and designs can be developed in which the beneficial influence of the nonisothermal phenomena is exploited or the detrimental impact is avoided. The PI is planning a fundamental experimental and modelling study of the behavior of a single supported catalytic pellet in an exothermic multiphase reaction system. The single pellet or even single pore level often dictates the overall reactor behavior. Two experiments involving cyclohexene hydrogenation on a supported palladium pellet are planned. In the first experiment the pellet is suspended in a tube and contacted by a flowing liquid film and annular gas flow. The overall, rate, degree of external wetting, pellet mass, and the pellet temperature will be monitored as various bulk conditions are changed. The dependence of the overall rate, temperature rise, and the degree of internal and external wetting on the bulk conditions will be determined as phase change occurs. In the second experiment a novel multiphase diffusion and reaction cell will be developed to study in more detail the intraparticle temperature profile. The single pellet is wetted on one face by the liquid and on the other by the gas. The large differences of temperature rise in gas- and liquid-filled catalyst pellets provides a means of probing the location of gas- or liquid-fill pores. Development and numerical solution of several pertinent models of the single, partially wetted and filled catalytic pellet will be carried out. The research should provide fundamental data to be ultimately used in multiphase reactor design.