Exploring the chemical reactivity of asphaltenes

Most of the hydrocarbon derivatives from petroleum are used to produce energy by combustion, but very few percent are converted to industrially useful compounds by controlled reactions with oxygen or chlorine. The hydrocarbons have high C/H ratio and are inert to attack by most of the chemical reagents and reacts with oxygen and halogens only under the special conditions of radical initiated reactions. One of the major constituents of the heavy residual oils and asphalts is the asphaltenes. Asphaltenes are composed of condensed aromatic structures units bearing alicyclic sites substituted and connected to aliphatic chains with or without heteroatoms. The objective of this study was to investigate the reacting behavior of asphaltenes to understand the structural, chemical and molecular nature of asphaltenes. Relatively little is known about the effect of chlorination on asphaltene chemistry and structure. In an effort to increase this understanding, the reaction of asphaltenes with sulfuryl chloride (SO2Cl2) alone and in presence of an initiator, 2.2'-azobis-(-methylpropionitrile), commonly named as AIBN (azoisobutylnitrile), was carried out. Asphaltenes contain predominantly C and H atoms in the form of aromatic and aliphatic structures. Both can be reactive and that the aromatic structures may affect the reaction pathway. All reactions began with the formation of free radical from SO2Cl2 followed by the abstraction of H atom which provided reactive radical intermediates. The IR spectra clearly show the addition of Cl groups in aliphatic as well as in aromatic structure of asphaltenes. The compositional data generated by this work will enhance the understanding of asphaltene structure.