Desulfurization of petroleum residues and their carbonization properties

The desulfurization of petroleum residues of high sulfur content was carried out using three kinds of Lewis acids under a nitrogen flow of atmospheric pressure at 150–330°C. Considerable amounts of sulfur were eliminated from the residue as hydrogen sulfide with the aid of aluminum chloride at 150°C or higher temperatures. Ferric or zinc chloride was found also to eliminate sulfur from the residue in the form of the corresponding metal sulfides at 330°C without the evolution of hydrogen sulfide.Effects of such desulfurization on the coking properties were observed by means of optical microscopy and X-ray diffraction. Although the original residues gave cokes with a mosaic arrangement of anisotropic domains, benzene-soluble fractions of the desulfurized residue gave a graphitizable needle coke. The desulfurized residues were further analyzed by chemical techniques to study the structural change brought about by acidic desulfurization. This kind of desulfurization was revealed to be carried out without decreasing the aromaticity of the residue, being different from the hydrodesulfurization with cobalt-molybdena catalysts.