Startup and Transients in Millisecond Chemical Reactors

短接触时间化学反应器在将轻烷烃转化为有用的化学品方面具有很大的前景，而且效率更高、成本更低、污染更少。该技术的重要应用是将天然气转化为液体燃料和将烷烃燃料转化为燃料电池所需的氢。该技术的实现需要对过程和机制进行表征。稳态行为已经被很好地理解，之前的研究描述了这些过程的性能和机制。然而，为了进一步了解短接触时间化学反应器中烷烃氧化的机理，必须对瞬态进行表征。我们有一个系统的程序来检验短接触时间化学反应器的瞬态行为。本研究有两个主要目标：(1)利用瞬态实验进一步表征这些过程的机制；(2)在小型燃料电池的燃料处理等应用中开发快速点火和瞬态方法。实验将包括质谱和温度测量对进料阶跃变化和同位素转换的响应。我们将通过流动气体滴定来检验催化剂上碳和氧的形成和去除。启动瞬态也将通过不同气体混合物的点火来检测，这些气体混合物催化或均质反应以获得快速加热到点火温度。其他实验将包括以不同频率周期性强迫成分，短接触时间内的气液反应，以及使用燃油喷射器的燃料闪蒸反应。我们还将开发在催化壁反应器中快速耦合放热和吸热过程的启动和终止中检查时间依赖性和分岔行为的能力。这些实验将通过计算流体动力学分析，使用基本阶跃模型来模拟启动和瞬态时的温度和覆盖范围。这将导致这些系统中更基本的基本阶跃模型和分岔行为的表征，这将对开发新的短接触时间化学过程至关重要。燃料电池将不再是实用的单元，燃料重整方法和快速轻量化策略的发展将是这些任务的关键组成部分。

Short contact time chemical reactors have great promise for conversion of light alkanes into useful chemicals with greater efficiency, lower cost, and less pollution. Important applications of this technology are conversion of natural gas to liquid fuels and reforming of alkane fuels to hydrogen for fuel cells. Implementation of this technology requires characterization of the processes and mechanisms. Steady state behavior is fairly well understood, and the previous grant characterized performance and mechanisms of these processes. However, transients must be characterized to develop lightoff protocols and to further understand the mechanisms of alkane oxidation in short contact time chemical reactors. We have a systematic program to examine the transient behavior of short contact time chemical reactors. This research has two major objectives: (1) use of transient experiments to further characterize the mechanisms of these processes and (2) the development of methods for fast lightoff and transients in applications such as fuel processing for small fuel cells. Experiments will involve mass spectrometric and temperature measurement of responses to step changes in feeds and isotope switching. We will examine carbon and oxygen formation and removal on the catalyst by titration with flowing gases. Startup transients will also be examined by ignition with different gas mixtures that react either catalytically or homogeneously to attain rapid heating to ignition temperatures. Other experiments will involve periodic forcing of composition at different frequencies, gas-liquid reactions at short contact time, and reactions involving flash vaporization of fuel using fuel injectors. We will also develop capabilities to examine time dependences and bifurcation behavior in startup and extinction of fast coupled exothermic and endothermic processes in the catalytic wall reactor. These experiments will be analyzed by computational fluid dynamics using elementary step models to simulate temperatures and coverages in startup and with transients. This will lead to more fundamental elementary step models and characterization of bifurcation behavior in these systems that will be essential in developing new short contact time chemical processes. Fuel cells will not be practical unit fuel reforming methods and fast lightoff strategies are developed, and this research will be a key ingredient in these tasks.