Gum in gasoline

The formation of additional gums in gasoline can be minimized by treating fuel with an antioxidant... 

Uses Antioxidant, heat stabilizer for syn. rug-backing, latex paints, rosin, ester gums, in gasoline and aviation fuels, insulating oils, paraffin wax Features Primary antioxidant provides better thermal stabilization of polyolefins and lower vapor pressure than common antioxidants Properties Gardner 12 clear liq. sol. in abs. ethanol, benzene, MEK,... 

Uses Primary antioxidant for syn. rug-backing, latex paints, rosin, ester gums, in gasoline and aviation fuels, insulating oils, paraffin wax, polymer stabilization... 

A number of laboratory tests are used to predict chemical stabihty. The amount of existent gum in a gasoline is determined by ASTM D381. This method involves evaporating a sample by a jet of heated air. The residue is weighed, solubles are extracted with / -heptane, and the sample is reweighed. 

Another ASTM test method. Potential Gum (D873), combines the existent gum and the oxidation stabihty tests to measure potential gum. A sample of gasoline is subjected to the oxidation stabihty test for 960 min, filtered to remove particulates, and then subjected to an existent gum test. The potential gum is expressed as the total (unwashed) gum in this test. 

Other tests to predict stabihty of gasoline have been developed and reported in the hterature. One, developed by the U.S. military, stores gasoline at elevated (43°C) temperatures for up to 12 weeks and measures existent gum at the end of that period (26). Another measures existent gum in the presence of copper. The copper catalyzes oxidation and may be a better estimator of the stabihty of gasoline at high temperature/low residence time conditions. 

Once gasoline is refined, chemicals ore added to reduce knocking and prevent the formation of gum in the engine. 

Uses Intermediate for dyes and antioxidants inhibits gum formation in gasoline corrosion inhibiter organic synthesis (preparation of p-phenylenediamine). 

Thermal and catalytically cracked gasoline fractions can contain significant concentrations of phenols, low-molecular-weight organic acids, and alkyl and aryl mercaptans. All of these compounds can initiate gum formation in gasoline. Caustic treatment readily removes these compounds. 

Fuel olefins have been implicated as the primary cause of deposits in gasoline fuel injectors and carburetors. High-boiling-point, high-molecular-weight aromatic components have also been shown to contribute to intake system deposit and gum formation. Once formed, other compounds in the fuel can adhere to these deposits to form an amorphous-type deposit. 

High gum level/ sediment in gasoline or diesel fuel... 

Ethylenedibromide. Ethyl enebromide or 1,2-Dibromoethane, BrCH2.CH2Br mw 187.88 colorless, nonflammable, poisonous liquid sp gr 2.180 at 20°/4°, ft p 10°, bp 131-7°, nD. 1.5357 at 25° si sol In w miscible with most solvents and thinners. It can be prepd by the action of bromine on ethylene gas used as scavenger for lead in gasoline as solvent for fats, oils, waxes, gums, etc and in prepn of celluloid. Avoid breathing vapor absorbs thru skin... 

Toluene is used as a high-octane blending stock in gasoline as a solvent for paints and coatings, gums, resins, oils, rubber and adhesives and as an intermediate in the preparation of many chemicals, dyes, pharmaceuticals, detergents and explosives (Lewis, 1993). 

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. 

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. 

The substituted phenols and cresols constitute about half the total volume of this group. Para-t-butylphenol is produced by the alkylation of phenol with isobutylene. The principal applications for this derivative are in the manufacture of modified phenolic resins for the rubber industry and in surface coatings. BHT is obtained from isobutylene and p-cresol. Technical-grade BHT is an antioxidant for plastics and elastomers, and is a gum inhibitor in gasoline. Food-grade BHT is an antioxidant in edible oils, preserves, and many other foods. 2,6-Di-t-butylphenol is used to produce a wide range of plastics additives, antioxidants, and gasoline additives. 

Table Z12 shows the typical analyses of a C5 gasoline and of aromatic cuts, obtained by naphtha steam ciaddng. As may be observed, these eShients contain non-ne gible amounts of diolefins and alkenylarcmiatics, which make those emfdqyed in the refinery (Cf fraction) unsuitable for direct use as a gasoline. These thenqally unstable components cause gumming in motors, and therefore must first be removed.

The other components are C5+ olefins and dienes and in particular cycto-pentadiene which easily dimerises to a Cio compound di-cyclo-pentadiene). As well as a strong odour, these materials readily polymerise to form gum in the gasoline and the raw pyrolysis gasoline is usually hydro-treated prior to use. In some cases, these C5 dienes are extracted and used to form low melting resins. One approach to upgrading the pyrolysis gasoline stream is shown in Figure 5.5 . 

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