Film Boiling with Chemical Reaction: catalytic decomposition and hydrogen production in a self-assembled reactor

Cornell University, Ithaca NY

Investigators

Abstract

Film Boiling with Chemical Reaction: Catalytic decomposition and hydrogen production in a self-assembled reactor PI: C. Thomas Avedisian, Cornell University Co-PI: Wing Tsang, National Institute of Standards and Technology Abstract The proposal was received as an unsolicited submission to the Chemical and Transport Systems Division and was subsequently transferred to the Thermal Transport and Thermal Processing Program. This research concerns developing a new type of chemical reactor for studying catalytic decomposition of organic liquids. The reactor concept is based on high temperature catalytic reaction in a subcooled liquid in which film boiling is established on a heated, catalyst-coated, surface such as a horizontal tube that is our baseline configuration. The reactor volume is the vapor film surrounding the tube surface, and it is self-assembled in the sense of forming naturally as a consequence of establishing the film-boiling regime by heat transfer from the tube to the surrounding liquid. Control variables for creating the reactor are the tube wall temperature and tube diameter, both of which also effect product yields. The research will demonstrate operation of the reactor with conversion of methanol to hydrogen and carbon monoxide on a catalyst-coated tube immersed in a pool of sub-cooled methanol. A catalyst is required to drive the reaction at operational temperatures. The reactor will operate as follows. In film boiling, liquid will evaporate and diffuse across the film to the tube surface where reactant molecules are adsorbed and react, and vapor is simultaneously transported around the tube and combines with products that diffuse from the tube surface into the vapor film. The gas mixture containing product and reactant vapors will be expelled from the system in the form of bubbles that percolate from the top of the tube. The intellectual merit of the study is found in the development of the enabling technology for film boiling with chemical reaction. Film boiling has not previously been used in a process to deliberately promote chemical reaction for a useful purpose, as a means to produce hydrogen, as a process to evaluate catalyst performance, or to measure rate constants associated with performance. The research of this project will examine this potential. A test cell will be fabricated to contain a submerged tube coated with a catalyst (e.g., platinum black for methanol conversion) and be designed to measure product yields. The data will be used in an analysis of film boiling with chemical reaction to extract kinetic rate data from product yield measurements. The research team consists of two PIs with experience in phase change processes and chemical kinetics. The broader impacts of the project relate to the variations and multiple functions envisioned for the film boiling reactor concept. These include as a tool to study reaction engineering and as a portable means to produce hydrogen from organic liquids including biomass-derived fuels. The geometry selected for study is a horizontal tube coated with a catalyst because it is amenable to modeling and extending film boiling theory to chemical reaction; other physical configurations for a film boiling reactor are envisioned, including flat plates, tube arrays and scale-down to include a lab-on-a-chip concept. With film boiling on the outside of a tube, the catalyst can be visually observed throughout reaction which contrasts with other reactor designs where the high temperature reaction zone is visually inaccessible and performance is measured by knowing only what went in and what came out. As a means to produce hydrogen, the intent will be to show that hydrogen can be produced from the comparatively small physical volume of the vapor film surrounding the tube in the film boiling regime. With the tube surface being hot to drive surface reactions and the liquid/vapor interface cold, the problem of high temperature containment of reactant usually associated with other reactor concepts (e.g., packed bed reactor) is eliminated.