Effect of calcite and dolomite on crude oil combustion characterized by TG-FTIR

Abstract

This study is aimed at studying the influence of calcite and dolomite on crude oil combustion using TG-FTIR technique. According to the TG-DTG curves and the released gaseous products, the entire combustion process of crude oil can be divided into three regions: low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The presence of calcite or dolomite significantly promoted the continuity of reactions, thus resulting in a smooth transition from LTO to FD, and further to HTO. Specifically, the explicit boundary between LTO and FD disappeared, the reaction of fuel formation started in the later stage of LTO, and the FD process was also partly merged with HTO reaction into one reaction region, even the simultaneous occurrence of FD and HTO reactions was observed for calcite. In general, calcite and dolomite have distinct catalytic effects on crude oil combustion. Their existence made fuel deposition and its combustion easier by significantly reducing the activation energy (mainly in FD stage and the beginning of HTO stage) from about 250 to 450 kJ/mol to 150–225 kJ/mol, which thus leads to a more continuous FD-HTO process. Calcite has a superior catalytic effect than dolomite as it achieved lower values of activation energy with smaller fluctuation (maximum 175 and 225 kJ/mol for calcite and dolomite, respectively). These results indicate that the presence of calcite and dolomite (especially calcite) is favourable for accelerating crude oil combustion reaction in in-situ combustion (ISC) process.