EXPERIMENTAL STUDIES OF PROPANE OXIDATION THROUGH THE NEGATIVE TEMPERATURE-COEFFICIENT REGION AT 10-ATMOSPHERE AND 15-ATMOSPHERE

A turbulent, high-pressure flow reactor has been used in conjunction w ith a novel,controlled cool-down (CCD) technique, in an experimental s tudy of the detailed product distribution from propane oxidation at 10 and 15 atm, 600 K < T < 900 K, and equivalence ratio of 0.4. The spec ies concentration profiles show the low-temperature hydrocarbon oxidat ion regime extending from approximately 680 to 770 K. They indicate pe ak species yields, corresponding to the maximum rate of reaction, occu rring at approximately 720-723 K. At higher temperatures, approximatel y 730-780 K, reactivity slows and practically stops. Above 780 K, incr easing species concentrations indicate the onset of intermediate tempe rature chemistry. Fundamental transitions in the reaction path and the dominant branching agent are shown by changes in the species yield pr ofiles. Specifically, below 690 K, CO2 is observed to be the major pro duct. Above 690 K, CO is the major product until approximately 740 K w here propylene becomes the major product. The temperatures at which th ese transitions occur change with pressure. The observed transitions i n the major products indicate shifts in the relative importance of the four chain branching mechanisms (i.e., branching via alkylhydroperoxi de decomposition, acetaldehyde decomposition, acylhydroperoxide decomp osition, and alkylhydroperoxy radical oxidation) brought about by both changes in temperature and pressure. The 'results of these experiment s present a unique challenge to modeling the chemical kinetics because of the mechanistic transitions due to range of temperatures investiga ted in a single experiment.