Detailed Study of Low-Temperature Oxidation of an Alaska Heavy Oil

In this work, low-temperature oxidation (LTO) of a heavy oil sample from Alaska has been investigated. Six isothermal and one non-isothermal experimental runs were conducted between 100 and 350 degrees C, where LTO dominates. The combustion data obtained from a thermogravimetric analyzer (TGA) was analyzed, and a comparison has been made between the kinetic parameters (reaction order, rate constant, and activation energy) from a first-order, general reaction rate and Segal and Fatu's approach. The temperature scan of the oxidation process revealed that there were four temperature intervals during which different modes dominated the LTO process. The first temperature interval, ranging from 100 to 150 degrees C, and the third interval, ranging from 200 to 250 degrees C, both had overall reactions that were endothermic. However, in the second zone from 150 and 200 degrees C and the fourth subzone from 250 to 350 degrees C, exothermic reactions were dominant. The peak LTO rate occurred during the fourth interval, from 250 to 350 degrees C, and exhibits a decreasing rate versus temperature: the greater the temperature, the lower the reaction rate. The results obtained from the isothermal runs reveal that the reaction rate constant, activation energy, and pre-exponential factor for each temperature (determined from the first-order rate model) are all higher than those measures obtained in the general reaction rate model. The results from the non-isothermal runs showed that the values of the reaction rate constant, activation energy, and pre-exponential factor obtained from the approach by Segal and Fatu are similar to those calculated from the general reaction rate model. This was particularly true for the LTO peak temperature. The analysis of the results yields the mean activation energy for the LTO peak equal to 1130.2 cal/mol for isothermal experiments.