Oxidation of Oils and Bitumen at Various O2 Concentrations

This paper describes the effects of various amounts of oxygen on the oxidation of conventional oils and Athabasca bitumen and their coke-forming tendency. At any given oxygen concentration, the weight loss profile with an increasing temperature up to 500 degrees C during simultaneous thermal analysis (STA) shows the presence of two distinct regions: one below 400 degrees C, showing distillation/bond breaking and low-temperature oxidation, and the other beyond 400 degrees C, depicting fuel deposition combined with high-temperature oxidation and combustion of hydrocarbons. Heat-flow changes during oxidation show that exothermicity of the reaction is dependent upon the oxygen concentration as well as the heating rate. The activation energy of the oxidation step was calculated for each oxygen concentration using the Coats- Redfern method. The data showed a decrease in the activation energy with an increase in the oxygen concentration, showing dominance of different reactions under different O-2 concentrations. The activation energy value for oxidation above 400 degrees C decreased from 72 kJ/mol in the presence of N-2 to 30 kJ/mol in the presence of 21% O-2. The effect of oxidation on the coke-forming tendency during pyrolysis for some oil fractions shows that, for a fixed sample amount, coke-forming propensity may increase or decrease depending upon the O-2 concentration in the atmosphere above the sample. The extent of increase or decrease in coke-forming tendency varies for different petroleum oils. A Fourier transform infrared (FTIR) spectroscopy study of the sample before and after heating in inert or oxidative atmospheres shows that the presence of small amounts of O-2 affect these samples to varying levels depending upon their chemical composition. Results also give proof of oxidative addition reactions taking place in the presence of O-2 within the whole evaluated temperature range, spanning from about 300 to 500 degrees C.