Catalysis of Propane Oxidation and Premixed Propane-Air Flames.

Abstract

Improvements in deriving energy from hydrocarbon fuels will have a large impact on our efforts to transition to sustainable and renewable energy resources. The hypothesis is that catalysis can extend the useful operating conditions for hydrocarbon oxidation and combustion, improve device efficiencies, and reduce pollutants. Catalysis of propane oxidation and premixed propane-air flames are examined experimentally, using a stagnation-flow reactor to identify the important physical and chemical mechanisms over a range of flow, catalyst, and temperature conditions. The propane oxidation studies consider five catalyst materials: platinum, palladium, SnO2, 90% SnO2 – 10% Pt (by mass), and quartz. The volume fractions of CO2, O2, C3H8, CO, NO and the electric power required to control the catalyst temperature quantify the activity of each catalyst for the equivalence ratios of 0.67, 1.00, and 1.50, and over the catalyst temperature range 23-800 oC. Quartz is used as a baseline and confirmed to be non-reactive at all conditions. 100% SnO2 has minimal reactivity. Platinum, palladium, and 90% SnO2 – 10% Pt show similar trends and have the highest catalytic activity for the fuel rich mixture. Palladium and 90% SnO2 – 10% Pt show an increasing catalyst-activation temperature (Tsa) for decreasing equivalence ratio, and platinum shows an approximately constant catalyst-activation temperature for decreasing equivalence ratio (Tsa = 310 oC). Of these the 90% SnO2 – 10% Pt catalyst shows the lowest Tsa, occurring for the fuel-rich mixture (Tsa = 250 oC). The studies of premixed propane-air flames consider platinum and quartz stagnation surfaces for fuel-mixture velocities from 0.6-1.6 m/s. Five flame structures are observed: cool core envelope, cone, envelope, disk, and ring flames. The lean-extinction limit, disk-to-ring flame transition mixture, and the disk-flame to stagnation-plane distance are reported. Platinum inhibits the ring flame structure. The lean-extinction limit and disk-flame to stagnation-plane separation distance are insensitive to the stagnation-plane material. The results set directions for development of improved catalyst systems, including the development of lean NOx catalysts with low light-off temperatures, methods to quantify catalyst aging and poisoning properties, and fundamental data to develop models of the catalyst chemistry for the design of novel energy generation techniques.