The conversion of petroleum residues to asphalt by air oxidation

Abstract

The known chemistry of asphalts is reviewed, including the concepts of the colloidal state, the proposed structures for the resin and asphaltene molecules, and the oxidation reactions taking place in asphalts on air blowing and on weathering. Experiments on the blowing of Lloydminster reduced crude with nitrogen, air and oxygen are reported. Results of the fractionation of the asphalt residues obtained into oils, resins and asphaltenes are recorded. The oxygen content of these three fractions for each of the blown residues is reported. From these investigations, evidence is presented to show that with the blowing conditions used, the primary oxidation reaction is one resulting in dehydrogenation of the asphalt molecules. An increase in asphaltene content on blowing at the expense of the oils and resins is observed. The oxygen determinations indicate that the asphalt increases in oxygen content. Of the three fractions, the resins are the only bodies to increase in oxygen content, the oil and asphaltene content remaining essentially constant. This is regarded as indicating instability of oxidized oil molecules, and the formation of asphaltene molecules containing oxygen in the same proportion as the original asphaltenes. Based on the comparison of the observed oxidation characteristics to the oxidation characteristics of pure hydrocarbons, the suggestion is made that the molecules undergoing oxidation are polynuclear aromatic or aromatic naphthenic compounds. Suggestions for further investigations following this method of attack on the study of this oxidation reaction are outlined.