A HIGHLY SENSITIVE DETECTION METHOD FOR TEMPERATURE PROGRAMMED OXIDATION OF COKE DEPOSITS - METHANATION OF CO2 IN THE PRESENCE OF O2

Temperature programmed oxidation is the most widely used technique in the study of coked catalysts. This technique provides useful information about coke distribution and coke type on the catalyst surfaces. A new detection method, which gives continuous monitoring of coke oxidation rate, has been applied to this technique. The new detection method is simple and highly sensitive. It consists of a methanator and a flame ionization detector. It involves the conversion of C02, an FID insensitive gas, to an FID sensitive gas, CH4, in the presence of an oxygen-containing carrier gas. It has been found that the conversion efficiency of the methanator strongly depends on oxygen concentration, its flow rate, and the temperature of the methanator. At temperature below 673 K and at <3% O2, the incomplete conversion of C02 to CH4 is mainly due to kinetic limitations brought about by the excess water produced in the methanator from the oxygen in the carrier gas. At higher temperatures and OZ concentrations, equilibrium limits the conversion of C02 to a low level. Complete conversion of C02 to CH4 is realized when O2 < 3%, carrier gas at 20-60 cc/min, and methanator at 673 K. © 1992.