Method of analyzing high molecular weight dispersants in motor oils

Abstract

A method which involves the isolation, analysis and characterization of dispersants present in motor oils is disclosed. The method is particularly useful in connection with the characterization of high molecular weight polybutenyl succinimide dispersants present in finished motor oils so as to provide detailed information with respect to the starting material reactants needed to synthesize such dispersants. The method involves breaking down complexation present in the oil followed by the isolation of the dispersant from the oil via dialysis. The isolated dispersant in the form of a dialysis residue is then acidified and passed through an ion exchange chromatographic column to adsorb acid materials away from the dispersant. Dispersant content and total carbonyl content can then be determined. The dispersant is then subjected to saponification with sodium hydroxide to provide a hydrocarbyl sodium succinate and a polyamine. The saponified material is subjected to further dialysis to separate it from remaining oil and then further acidified. The acidification results in the formation of a corresponding succinic acid and a dialkyl ester derivative. Procedures such as GPC and VPO determinations can then be carried out. Model reactant components can then be prepared and reacted to determine if the reaction product obtained matches the original dispersant being analyzed.