Abstract
Short chain alkenyl succinimides (ASIs) were synthesized and used as high purity chemical models to investigate the autoxidative degradation at 170 °C of polyisobutenyl succinimide dispersants (PIBSIs), a significant additive in automotive engine lubricants. Degradation products were characterized by gas chromatography–electron ionization mass spectrometry and quantified by gas chromatography-flame ionization detection. The rate of autoxidation of ASIs in a model lubricant, squalane, was also investigated. Although this is a complex molecule containing many possible sites of radical attack, all of the autoxidation products identified result from attack at the double bond or the adjacent allylic hydrogen atoms, which indicates the controlling influence of the double bond in the degradation of alkenyl succinimides, and therefore of commercial polyisobutenyl succinimide dispersants. The observed site-selective cleavage of the ASI structure, and by analogy PIBSI dispersants, would yield products that both reduce dispersancy and promote the formation of insoluble products that could have a detrimental effect on lubricant performance.
Highlights
Lubricants for modern internal combustion engines require a precisely formulated additive package to improve the performance of the lubricant and the engine; through cleaning, cooling, and protecting the engine, equipment lifetime and emissions can be improved
N-butyl alkenyl succinimides (ASIs) (Figure 3, R = n-butyl) was the main dispersant analogue studied for this work because of its favorable gas chromatography (GC) retention time as it did not overlap with the model base oil or squalane autoxidation products
A cluster of four peaks and a single peak (10 and 11, Figure 5) with a higher retention time than N-butyl ASI were characterized as oxygenated ASI products
Summary
Lubricants for modern internal combustion engines require a precisely formulated additive package to improve the performance of the lubricant and the engine; through cleaning, cooling, and protecting the engine, equipment lifetime and emissions can be improved. Polar products can impede lubricant flow, increasing mechanical wear and lubricant viscosity.. A fully formulated engine oil lubricant comprises an additive package and a viscosity index improver dissolved in a base oil; liquid hydrocarbons either produced synthetically or refined from crude oil. Constituting around 90% (w/w) of the lubricant oil, the mechanisms of base oil autoxidation have been investigated in detail through the use of model hydrocarbons.− Smaller hydrocarbons− and fatty acid methyl esters have been investigated to determine fuel degradation mechanisms and higher mass ester base oils used for lubricant degradation studies. There has been little research in this area. The effect of autoxidation on polyisobutenyl succinimide (PIBSI) dispersants is reported here
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