Kinetics of Low-Temperature Oxidation of Light Crude Oil

The in situ combustion (ISC) process has drawn a lot of attention in the field of heavy oils. However, in the case of a light crude oil reservoir, in which low-temperature oxidation (LTO) is dominant, it is still less well-understood, especially for its reaction mechanism. In this paper, ramped temperature oxidation (RTO) experiments with different temperature intervals are used to investigate the oxidation reaction behaviors on various distillation pseudo-components from Dagang light crude oil. Both RTO and isothermal experiments are conducted on the whole crude oil and the sand mixture to obtain the LTO kinetic behaviors. The results indicate that oxygen addition reaction of the crude oil occurs to a great extent in the low-temperature region of 120-200 degrees C. Because the LTO reaction incorporates an oxygen atom into petroleum molecules rather than forming high-temperature oxidation (HTO) products (i.e., CO2, CO, and H2O), CO2 production is minor during the LTO process. The acid number of the crude oil increases with an increasing reaction time and temperature during the LTO as a result of the formation of organic acids. Two pseudo-component distillates were subjected to major oxygen additions as evidenced by oxygen uptake and increases of the acid numbers of oxidation products. The apparent activation energy (E-a) of the crude oil that derived from the results of RTO tests (at different temperature ranges) accompanied by the isoconversional method present the Ea values varying from 160 to 350 kJ/mol as the temperature changes from 205 to 230 degrees C. The E-a value obtained through the isothermal experiment shows a decreasing trend from 200 to 33 kJ/mol as the temperature increases from 148 to 235 degrees C.