Experimental study on coking behavior of heavy oils in low temperature oxidation process

Key words:  heavy oil  air injection  low-temperature oxidation  coking temperature  thermogravimetric analysis  differential thermal analysis

Abstract:

The behaviors of oxidation and coking of heavy oil samples in the presence of air and nitrogen were investigated using different methods, including thermogravimetry analysis (TGA), differential scanning calorimeter (DSC) and a high temperature and high pressure reactor. The effect of low-temperature oxidation on the critical coking temperature of heavy oils at different reaction conditions was studied. The experimental results show that low temperature oxidation can reduce the critical coking temperature of heavy oils. The critical coking temperature of the heavy oil studied in the presence of nitrogen is over 400 ℃ but it reduces to 280 ℃ in the presence of air. The reduction of the coking temperature can be attributed to the thermal effect and the formation of oxygenated oil components in the low temperature oxidation process. It is speculated that the stability of the colloidal structure of heavy oil components can be reduced at the oxygenated condition, which can cause phase separation to accelerate the aggregation of complex asphaltene and resin molecules, leading to chemical copolymerization and coke formation.