The literature of the past thirty years shows that the low-temperature oxidation (LTO) of hydrocarbon liquids generally results in a more viscous end product. The In Situ Combustion Research Group at The University of Calgary has found, however, that upgrading can occur during LTO in the presence of caustic additives. Because it was believed that caustic inhibits oxidation reactions as evidenced by a reduction in or absence of coke formation, and allows the oil to upgrade by thermal cracking via a free radical mechanism, a systematic study was undertaken to investigate the effect of caustic on the LTO of heavy oil.

To date, nearly 200 LTO tests have been performed on Athabasca bitumen. These experiments were carried out by varying caustic concentrations, temperatures, oxygen partial pressures, total cell pressures, and run times. All effleunt gases were analyzed using gas chromatography, the pH of free water was measured, and hydrocarbon products underwent determination of coke and asphaltene contents, viscosity, and density. CHN and S analyses were carried out on the whole oil, and coke and asphaltene fractions.

Several instances of upgrading were observed. Optimum conditions occurred at lower caustic concentrations, lower temperatures, lower oxygen partial pressures, and longer run times. The amount of oxygen reacted appears to be the most critical parameter affecting the system. The presence of caustic apparently did not inhibit the oxidation reactions from taking place, but, rather, modified the process by impeding the asphaltene fraction from converting to coke.

You can access this article if you purchase or spend a download.