Effects of kaolinite and its thermal transformation on oxidation of heavy oil

Kaolinite is a common 1:1 layered clay mineral in oil reservoirs and also a natural solid acid catalyst. Some studies have shown that kaolinite has a catalytic effect on the oxidation of heavy oil. Its catalytic effect depends on the type and amount of acid sites and is closely related to its thermal transformation, particularly the dehydroxylation process. The effects of kaolinite and its thermal transformation on the oxidation of heavy oil were investigated with thermal analysis and the Ozawa-Flynn-Wall isoconversional method. The results revealed that kaolinite had significant effects on the High-temperature oxidation (HTO) and Fuel deposition (FD) stages of heavy oil oxidation, but its effect on the Low-temperature oxidation (LTO) stage was small. In the HTO stage, the temperature at which the CO2 release rate peaked decreased dramatically, whereas the temperature at which the H2O release rate peaked increased remarkably. With the increase in the content of added kaolinite, the maximum activation energy in the FD stage of the oxidation reaction of heavy oil and the average activation energy in the HTO stage gradually decreased. It was noteworthy that the transformation of kaolinite upon thermal treatment, especially the dehydroxylation process above 400 °C, resulted in a progressive decline in the peak temperature in the HTO stage of heavy oil, but had little influence on that in the LTO stage of heavy oil oxidation.