Alkylation of Asphaltenes

Abstract

This work investigated different acid catalysts and olefinic alkylating agents for the alkylation of an industrial asphaltenes feed. The working hypothesis was that alkylation would change the solubility parameter and increase the H/C ratio of asphaltenes sufficiently to cause some asphaltenes to maltenes conversion. The acid catalysts that were investigated were phosphoric acid, aluminium chloride, hydrochloric acid and amorphous silica alumina (Siral40). The olefins employed for alkylation were ethylene, propylene and hexene. These model olefins were used for experimental convenience; industrial applications would typically employ olefins in cracked naphtha. The products from reaction were characterized by determining the n-pentane precipitated asphaltenes content, H/C ratio, aliphatic/aromatic hydrogen ratio, micro-carbon residue and infrared spectroscopy. The most successful combination of catalyst and olefin for alkylating asphaltenes was the amorphous silica-alumina catalyst (Siral40) and propylene. Propylene reacted with asphaltenes over Siral40 to generate an increase in maltenes content. It was postulated that success of alkylation of asphaltenes by propylene over Siral40 could be attributed to the ability to cause scission of bridging carbon-sulfur bonds. This was further investigated by model compound reactions. It was found that Siral40 in combination with propylene resulted in complete conversion of dibenzyl sulfide and benzyl phenyl sulfide, as well as near complete desulfurization of the reaction products from dibenzyl sulfide. It was also determined that 40 % of the sulfur of the industrial asphaltenes feed was aliphatic sulfur, of which at least some would be present in bridging sulfide (thioether) groups. Conversion of asphaltenes with propylene over Siral40 at 325 ºC resulted in ~20% asphaltenes into maltenes conversion.