Solventless Deasphalting: Selective Sulfonation Chemistry of Petroleum Asphaltenes and Resids

Asphaltenes are the lowest value component of petroleum. They are found in a variety of crude oils and in higher concentrations in resids and bitumens. Petroleum resid is the non-volatile fraction of crude oil or bitumen after distillation. Current disposition of the asphaltenes is high-temperature thermal chemistry to form higher value liquids and coke or as feedstock for asphalt. Asphaltenes are separated from a resid by a commercial process called solvent deasphalting. Deasphalting is accomplished by treating a resid with a hydrocarbon solvent (propane or butane commercially and pentane-heptane in the lab), and the asphaltenes precipitate out of solution. The rest of the resid is soluble, and this is called the deasphalted oil (DAO). The DAO is recovered by evaporation of the solvent. The DAO is higher value than the original resid, and it is used as residual sulfur fuel oil (RSFO) and, in some cases, as a feedstock for fluid catalytic cracking (FCC) to form higher value liquids. Asphaltenes are composed of highly polar molecules that are soluble to sparingly soluble in the resid. Deasphalting takes advantage of this by diluting the resid with a nonpolar solvent and making the surrounding medium less polar. The asphaltenes are no longer soluble, and they precipitate out of the mixture of resid and solvent. Recovery of the solvent from the DAO and solvent losses are major costs of deasphalting. The solvents are not as selective as would be desired, causing non-asphaltenic molecules to co-precipitate with the asphaltenes and some asphaltenic molecules to remain with the DAO fraction, making it less valuable. This paper summarizes initial research to replace solvent deasphalting with a selective chemical treatment. Initial studies focused on sulfonation. The chemistry relies on the selectivity of sulfur trioxide (SO3) to react with the larger polycyclic aromatics and heteroaromatics found in asphaltenes to form asphaltene sulfonic acids. The addition of a sulfonic acid function to the asphaltene molecule significantly increases its polarity and decreases its solubility, causing the sulfonated asphaltene to precipitate from the resid without the use of solvent. The value of this approach is in avoiding the use of liquid solvents, which are difficult to use and recover efficiently on a commercial scale.