Peroxide Formation in Low Sulfur Automotive Diesel Fuels

The requirement by the U.S. EPA that highway diesel fuel be limited to no more than 500 parts per million by mass of sulfur after October 1993, will require an increase in hydrotreating severity to achieve the needed sulfur reduction. It is known that severe hydrotreating can produce problems with the performance of the fuel, one being the increased susceptibility of the fuel to oxidize during storage in the presence of air. Formation of high levels of peroxides in the fuel can lead to incompatibility with fuel system elastomers.

To determine the potential for increased oxidation tendency with future highway fuels, Products Research Division of Exxon Research & Engineering Company undertook a study comparing current diesel fuels with prototype low sulfur blends. The indications from the study are that low sulfur fuels have an increased tendency for peroxide formation.

Results with anti-oxidant additives are shown and prospects for additives to control the problem are discussed.