Startup and Transients in Millisecond Chemical Reactors

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

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.