Low Temperature Ozonation of Canadian Athabasca Bitumen

Abstract

In this work, low temperature ozonation of Canadian Athabasca bitumen with ozone-enriched air in the temperature range of 140 to 160°C was investigated. Due to the resonance hybrid structure of ozone, it reacts directly and indirectly with the hydrocarbon molecules. Indirect ozone reaction mechanism involves free radical addition reactions similar to oxidation and leads to the observed increase in the viscosity and hardness of the ozonized bitumen. However, direct reaction mechanism of ozone involves possible ring-opening of cyclic hydrocarbons during ozonation. Of particular interest were the ring-cleavage reactions taking place during ozonation. A model compound ozonation study at 130°C showed that although ozonation of naphthenic-aromatic and heterocyclic compound classes present in oil sands bitumen resulted in moderate conversion of parent compounds to the ozonation products (except indene which had the highest ozonation conversion), these compound classes are primarily responsible for free radical addition reactions during ozonation. Ozonation of aromatic and acyclic paraffinic hydrocarbons resulted in relatively low ozonation conversion and no addition products were formed. Naphthenic and alkylaromatic compounds had relatively high ozonation conversion, and very low tendency to form addition reaction products. Ring-cleavage reaction products were formed during ozonation of aromatic, naphthenic-aromatic and heterocyclic compound classes. The aforementioned results of model compound classes ozonation could be applied to explain the bitumen ozonation results. A comparison between viscosity of ozonized and oxidized bitumen revealed that the increase in the bitumen viscosity and hardness in ozonation was relatively lower than oxidation using pure oxygen under the same reaction condition which might be due to the higher partial pressure of the oxidant leading to an increased rate of oxidation. In bitumen ozonation, ring-cleavage reactions happened as a result of direct reaction mechanism of ozone.