Gums, oxidation stability

The procedure most commonly employed (NF M 07-047 or ASTM D 2274) Is to age the diesel fuel for 16 hours while bubbling oxygen into it at 95°C. The gums and sediment obtained are recovered by filtration and weighed. There is no official French specification regarding oxidation stability however, in their own specifications, manufacturers have set a maximum value of 1.5 mg/100 ml. 

Another ASTM test method, Potential Gum (D873), combines the existent gum and the oxidation stability tests to measure potential gum. A sample of gasoline is subjected to the oxidation stability 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. 

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. 

For jet fuels, a visual rating of No. 1 or No. 2 is required at 260°C in the jet fuel thermal oxidation stability test (JFTOT-ASTM D 3241). Also, a pressure drop of less than 25 mm Hg is required in this test, As shown in Table XI, the 250°F+ product from hydrotreated Illinois H-Coal syncrude passes both parts of the JFTOT test, even when the jet fuel is not refined enough to pass three other specifications aromatic content, smoke point, and gum content. When jet fuels are prepared from coal-derived syncrudes, the smoke point appears to be the limiting specification. The gum content and end point specifications are met when the jet fuels are distilled at 600°F. 

The expected life of a diesel fuel is indicated by the oxidation stability test (ASTM D-2276). The test measures how much gum and sediment will be deposited after conditioning the fuel at 120°C in the presence of oxygen for 16 h. It roughly corresponds to a years storage at 25°C. A result of less than 20 mg/L of sediment and gum after the test is considered acceptable for normal diesel. 

It was established that catalysts present in CNTs also strongly affect thermal stability of CNTs in air. Active metal particles present in the nanotube samples catalyze carbon oxidation, so the amount of metal impurity in the sample can have a considerable influence on the thermal stability. For example, Zhou et al. (2001) found that if the oxidation of as-synthesized CNTs, which contained traces of catalyst (Fe), was quite rapid and homogeneous at 350 °C due to the catalytic effect, the purified CNTs had negligible weight loss, even after annealing at 460 °C. Furthermore, the presence of Fe obscured the dependence of oxidative stability on tube diameter as discussed earlier. After removing the Fe, all tubes were more appropriate for observing diameter-dependent oxidative stability. Li et al. (2011) have found that the presence of cobalt catalysts dramatically decreases the thermal stability of CNT/peroxide-curable methyl phenyl silicone gum composites as well. This means that the presence of uncontrolled impurities in CNTs can be one of the reasons for reduced reproducibility of sensor parameters. This conclusion is confirmed by results obtained by Boccaleri et al. (2006) and Zhou et al. (2001) (see Fig. 21.5). 

Oxidation of grease results in insoluble gum, sludge, and deposits and ultimately leads to decreased metal wettability, sluggish operation, reduced wear protection, and increased corrosion. Excessive temperatures result in accelerated oxidation or even carbonization, where grease hardens or forms a crust as a result of evaporation of base fluid and increased thickener concentration. Therefore, higher evaporation rates require more frequent relubrication. A number of studies have been reported on various aspects of thermo-oxidative stability [45, 46]. The oxidative stability of... 

Good Oxidation Stability. A good compressor oil must have high oxidation stability to minimize the formation of gum and carbon deposits. Such deposits can cause valve sticking. This can lead to very high temperature conditions, compressor malfunction, and fire or explosion of reciprocating compressors. 

Khouryieh H, Puli G, Williams K, Aramouni F. Effects of xanthan-locust bean gum mixtures on the physicochemical properties and oxidative stability of whey protein stabilised oil-in-water emulsions. Food Chem. 167 340-348,2015. 

Qiu, C., Zhao, M., Decker, E. A., McCltanents, D. J. (2015). Influence of anionic dietary fibers (xanthan gum and pectin) on oxidative stability and lipid digestibility of wheat protein-stabilized fish oil-in-water emulsion. Food Research International, 74, 131-139. 

Stability. Diesel fuel can undergo unwanted oxidation reactions leading to insoluble gums and also to highly colored by-products. Discoloration is beheved to be caused by oxidation of pyrroles, phenols, and thiophenols to form quiaoid stmctures (75). Eventually, these colored bodies may increase in molecular weight to form insoluble sludge. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Stabilization of Fuels and Lubricants. Gasoline and jet engine fuels contain unsaturated compounds that oxidize on storage, darken, and form gums and deposits. Radical scavengers such as 2,4-dimethyl-6-/ f2 butylphenol [1879-09-0] 2,6-di-/ f2 -butyl-/)-cresol (1), 2,6-di-/ f2 -butylphenol [128-39-2], and alkylated paraphenylene diamines ate used in concentrations of about 5—10 ppm as stabilizers. 

Carbon tetrachloride [56-23-5] (tetrachloromethane), CCl, at ordinary temperature and pressure is a heavy, colorless Hquid with a characteristic nonirritant odor it is nonflammable. Carbon tetrachloride contains 92 wt % chlorine. When in contact with a flame or very hot surface, the vapor decomposes to give toxic products, such as phosgene. It is the most toxic of the chloromethanes and the most unstable upon thermal oxidation. The commercial product frequendy contains added stabilizers. Carbon tetrachloride is miscible with many common organic Hquids and is a powerhil solvent for asphalt, benzyl resin (polymerized benzyl chloride), bitumens, chlorinated mbber, ethylceUulose, fats, gums, rosin, and waxes. 

It is possible to introduce this group selectively onto a primary alcohol in the presence of a secondary alcohol. The derivative is stable to KMn04, w-chloro-peroxybenzoic acid, LiAlH4, and Cr03 Pyr. Since this derivative is similar to the p-methoxyphenyl ether it should also be possible to remove it oxidatively. The GUM ethers are less stable than the MEM ethers in acid but have stability comparable to that of tlie SEM ethers. It is possible to remove the GUM ether in the presence of a MEM ether. 

Fluidized aqueous suspensions of 15% by weight or more of hydroxyethyl-cellulose, hydrophobically modified cellulose ether, hydrophobically modified hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, and polyethylene oxide are prepared by adding the polymer to a concentrated sodium formate solution containing xanthan gum as a stabilizer [278]. The xanthan gum is dissolved in water before sodium formate is added. Then the polymer is added to the solution to form a fluid suspension of the polymers. The polymer suspension can serve as an aqueous concentrate for further use. 

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