Gasoline sludge formation

Hydrocarbon oxidation may also be considered a free radical chain-type reaction. At elevated temperatures, hydrocarbon free radicals (R) are formed which react with oxygen lo form peroxy radicals (R(X These, in turn, take up a hydrogen atom from the hydrocarbon to form a hydroperoxide (ROOH) and another hydrocarbon free radical. The cycle repeals itself with the addition of oxygen. The unstable hydroperoxides remaining are the major points for degradation and lead to rancidity and color development in oils, fats, and waxes decomposition and gum formation in gasolines sludging in lubricants and breakdown of plastics and rubber products. Antioxidants, such as amines and phenols, are often introduced into hydrocarbon systems in order lo prevent this free radical oxidation sequence. 

Early workers found that small amounts of rubber dissolved into mineral oil substantially raised VI however, high levels of unsaturation in the polymer led to oxidation and sludge formation. This was overcome by using a synthetic polymer prepared from gasoline light ends [1], and similar behaviour was later described for... 

Can. —When cans are to be used, they must have seams that have been soldered on the exterior surfiices with a flux of rosin in a suitable solvent. Such a flux is easily removed with gasoline, whereas many others are very difficult to remove. Minute traces of flux may contaminate the sample so that results obtained on tests such as dielectric strength, oxidation resistance, and sludge formation may be erroneous. Internal epoxy lined cans may have residual contamination and precautions should be taken to ensure its removal. Practice D4306 should be used when taking samples for aviation fuels. 

The early workers in the field of lubricants observed that small amoimts of rubber dissolved in a mineral oil raised the VI substantially. However, high unsaturation in the polymer led to oxidation and sludge formation. Otto et al. [3] discovered that this could be overcome through the use of a synthetic polymer prepared from the light ends of the gasoline. Similar observations were later made for polymethacrylates by Rohm and Haas Co. [4,5] and for polyisobutylenes by Farbenindustrie AG [6,7]. Because these materials were initially used mainly to increase the VI, they became known as the viscosity index improvers. 

Stability—In petroleum products, the resistance to chemical change. Gum stability in gasoline means resistance to gum formation while in storage. Oxidation stability in lubricating oils and other products means resistance to oxidation to form sludge or gum in use. 

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