Characteristics and Properties of Coke Formed by Low-Temperature Oxidation and Thermal Pyrolysis during in Situ Combustion
Yibo Li, Chen Luo, Xiang Lin, Kai Li, Zun-Rong Xiao, Zhiqiang Wang, Wanfen Pu
Abstract
In order to understand the mechanism of in situ combustion, many studies have investigated the characteristics and properties of oxidized coke and pyrolyzed coke. However, in earlier research, the influence of light hydrocarbon and other compounds always led to a calculation error in the activation energy. In the work described here, we produced and separated oxidized coke and pyrolyzed coke, respectively, first to eliminate the influence of impurity and, second, to examine their properties by means of the TG-DSC equipment. The kinetic parameters were calculated by the Ozawa–Flynn–Wall model. The results showed that the crude oil achieved two major mass losses in the 300–400 and 500–600 °C temperature ranges, while the oxidized coke and the pyrolyzed coke released more heat than crude oil in the same conditions. At 300 and 350 °C, the high temperature can cause the thermal pyrolysis of the crude oil because the generation of coke requires more energy. These temperature levels cannot trigger the generation of coke and thus the pyrolyzed products stayed in one phase. At 400 °C, the pyrolyzed product cracked into two products: light oil and coke. The generated coke could only achieve major mass loss over 500 °C, releasing more heat than both oxidized oil and crude oil. According to the Ozawa–Flynn–Wall model, the crude oil achieved higher instantaneous activation energy at each conversion rate compared to results for oxidized coke and pyrolyzed coke. With the increase in conversion rate, the activation energy of oxidized coke rose while that of pyrolyzed coke decreased slightly.