Single Catalyst Pellet Performance in Exothermic Multiphase Reaction Systems

许多重要的商业化学品是由挥发性和非挥发性组分在负载催化剂上的反应产生的。这些作用的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氢化。这类反应是生产特种化学品（如苯胺和巴豆醛）和生物化学品（如氢化植物油和木糖）的重要步骤。除了本质上是多相反应外，这些反应通常是快速的（质量传递有限）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相汽化。在充满气体的孔隙中发生的气相催化反应可导致颗粒内温度和压力的大幅升高。总速率也可能由于相变和气相催化反应而大幅度增加。催化反应器内可能出现不希望出现的高温漂移（热点）。这些单球团现象使多相催化反应器的设计和控制复杂化。随着对这些系统的更好理解，可以开发新型多相反应堆的操作和设计，其中利用非等温现象的有益影响或避免有害影响。PI正在计划对放热多相反应系统中单个负载催化颗粒的行为进行基础实验和建模研究。单个颗粒甚至单个孔隙水平通常决定了整个反应器的行为。计划在负载钯球团上进行环己烯加氢的两个实验。在第一个实验中，球团悬浮在管中，由流动的液体膜和环形气流接触。随着各种散装条件的改变，将监测总体、速率、外部湿润程度、颗粒质量和颗粒温度。当相变发生时，将确定总体速率、温升和内外湿润程度对体积条件的依赖关系。在第二个实验中，将开发一个新的多相扩散和反应池，以更详细地研究颗粒内的温度分布。单个颗粒一面被液体浸湿，另一面被气体浸湿。充气和充液催化剂球团中温升的巨大差异为探测充气或充液孔的位置提供了一种手段。开发和数值解的几个相关模型的单一，部分润湿和填充的催化颗粒将进行。该研究将为多相反应器的最终设计提供基础数据。

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.