Oxidizing inhibitors

Oxidation inhibitors Oxidation methods Oxidation reactions Oxidation resistance Oxidations... 

Two undesirable aspects of FCC naphtha quaUty are that it may contain unacceptably high amounts of foul smelling mercaptans, and that its thermal stabiUty may be too low. Mercaptans are usually found in the light FCC naphtha and may be removed or converted to sulfides and disulfides by a sweetening process such as Merox, developed by UOP. Thermal stabiUty is improved in sweetening processes through removal of cresyUc and naphthenic acids. It may be further improved by clay treating and by addition of oxidation inhibitors such as phenylene diamine. 

Caloria HT43. Caloria HT 43, manufactured by Exxon Co., is a paraffinic-based oil that is compounded with an oxidation inhibitor. 

Practically all lubricating oils contain at least one additive some oils contain several. The amount of additive that is used varies from < 0.01 to 30% or more. Additives can have detrimental side effects, especially if the dosage is excessive or if interactions with other additives occur. Some additives are multifimctional, eg, certain VI improvers also function as pour-point depressants or dispersants. The additives most commonly used in hydrautic fluids include pour-point depressants, viscosity index improvers, defoamers, oxidation inhibitors, mst and corrosion inhibitors, and antiwear compounds. 

Oxidation Inhibitors. When oil is heated in the presence of air, oxidation occurs. As a result of this oxidation, the oil viscosity and the... 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

Almost all premium lubricants are so-called paraffinic oils composed primarily of both paraffinic and aUcycUc stmctures, with only a minor portion of aromatics. When stabilized with an oxidation inhibitor and fortified with other appropriate additives, these paraffinic—aUcycUc compositions provide nonsludging oils that are satisfactory for almost any type of service. 

R, mst inhibitor O, oxidation inhibitor D, detergent—dispersant VI, viscosity-index improver P, pour-point depressant W, antiwear EP, extreme pressure F, antifoam and M, friction modifier. 

Oxidation inhibitors function by intermpting the hydroperoxide chain reaction. At temperatures up to ca 120°C, di-Z fZ-butyl- -cresol, 2-naphthol,... 

Zinc dialkyl dithiophosphates are the primary oxidation inhibitors in combining these functions with antiwear properties in automotive oils and high pressure hydrauhc fluids. Their production volume is followed by aromatic amines, sulfurized olefins, and phenols (22). 

Ester fluids are modified with additives in much the same manner as petroleum oils. They are stabili2ed with an oxidation inhibitor, eg, 0.5 wt % phenothia2ine. Improved load capacity for gears and rolling bearings in aircraft engines is provided by 1—5% tricresyl phosphate. Zinc... 

Nickel dialkyldithiocarbamates stabili2e vulcani2ates of epichlorhydrinethylene oxide against heat aging (178). Nickel dibutyldithiocarbamate [56377-13-0] is used as an oxidation inhibitor in synthetic elastomers. Nickel chelates of substituted acetylacetonates are flame retardants for epoxy resins (179). Nickel dicycloalkyldithiophosphinates have been proposed as flame-retardant additives for polystyrene (180—182) (see Flame retardants Heat stabilizers). 

Eor antioxidant activity, the reaction of aminyl radicals with peroxy radicals is very beneficial. The nitroxyl radicals formed in this reaction are extremely effective oxidation inhibitors. Nitroxides function by trapping chain-propagating alkyl radicals to give hydroxylamine ethers. These ethers, in turn, quench chain propagating peroxy radicals and in the process regenerate the original nitroxides. The cycHc nature of this process accounts for the superlative antioxidant activity of nitroxides (see Antioxidants). Thus, antioxidant activity improves with an increase in stabiUty of the aminyl and nitroxyl radicals. Consequendy, commercial DPA antioxidants are alkylated in the ortho and para positions to prevent undesirable coupling reactions. 

ButylatedPhenols and Cresols. Butylated phenols and cresols, used primarily as oxidation inhibitors and chain terrninators, are manufactured by direct alkylation of the phenol using a wide variety of conditions and acid catalysts, including sulfuric acid, -toluenesulfonic acid, and sulfonic acid ion-exchange resins (110,111). By use of a small amount of catalyst and short residence times, the first-formed, ortho-alkylated products can be made to predominate. Eor the preparation of the 2,6-substituted products, aluminum phenoxides generated in situ from the phenol being alkylated are used as catalyst. Reaction conditions are controlled to minimise formation of the thermodynamically favored 4-substituted products (see Alkylphenols). The most commonly used is -/ fZ-butylphenol [98-54-4] for manufacture of phenoHc resins. The tert-huty group leaves only two rather than three active sites for condensation with formaldehyde and thus modifies the characteristics of the resin. 

ButylatedHydroxyAnisole (BHA). This material is an oxidation inhibitor and has been accepted for use in foods where the use of butylated hydroxytoluene (BHT) is restricted (see Food additives). It is manufactured by the alkylation of 4-hydroxyanisole [150-76-5] with isobutylene that yields a mixture of 2- and S-Z fZ-butyl isomers as products (124). 

The best oxidation inhibitors are not usually the best antio2onants (qv). A disubstituted i ra-phenylenediamine such as AJ-isopropyl-AT-phenyl- -phenylenediamine is often selected for that purpose. -Phenylenediamine derivatives iaterfere with cure chemistry and scorchiness, and can stain objects ia contact with the vulcani2ate (114). On balance, /V-(1,3-dimethy1buty1)-/V-phenyl- -phenylenediamine and phenyl /to1y1- -pheny1enediamines have the best combination of properties. They are less scorchy and provide excellent o2one and heat resistance. Additional protection is gained ia blends with a small amount of EPDM mbber (126). 

The per pass ethylene conversion in the primary reactors is maintained at 20—30% in order to ensure catalyst selectivities of 70—80%. Vapor-phase oxidation inhibitors such as ethylene dichloride or vinyl chloride or other halogenated compounds are added to the inlet of the reactors in ppm concentrations to retard carbon dioxide formation (107,120,121). The process stream exiting the reactor may contain 1—3 mol % ethylene oxide. This hot effluent gas is then cooled ia a shell-and-tube heat exchanger to around 35—40°C by usiag the cold recycle reactor feed stream gas from the primary absorber. The cooled cmde product gas is then compressed ia a centrifugal blower before entering the primary absorber. 

Universal at 100° F) and a viscosity index of 95. They contain necessary oxidation inhibitors and antiwear agents, as the same oil is used for bearings and gear lubrication. Oils tend to retain water, either from steam condensation or from condensation that occurs in the tanks. The presence of water is detrimental as it encourages the for-... 

Besides the use of anodic polarization with impressed current to achieve passivation, raising the cathodic partial current density by special alloying elements and the use of oxidizing inhibitors (and/or passivators) to assist the formation of passive films can be included in the anodic protection method [1-3]. 

A turbine oil with rust and oxidation inhibitors is preferred. This oil must be kept clean, cooled, and have the correct viscosity. Synthetic oils should not be used without the manufacturer s approval. 

Several techniques can be used to separate phenol. Solvent extraction using gas oil or lube oil (process MSAs Sj and S2, respectively) is a potential option. Besides the purification of wastewater, the transfer of phenol to gas oil and lube oil is a useful process for the oils. Phenol tends to act as an oxidation inhibitor and serves to improve color stability and reduce sediment formation. The data for the waste streams and the process MSAs are given in Tables 3.4 and 3.5, respectively. 

The extent to which changes occur in different liquids depends on the type of liquid, type of refining, and whether it has been treated to provide further resistance to oxidation. The stability of liquids can be improved by the addition of oxidation inhibitors. Inhibitors selected to improve stability must be compatible with the other required properties of the liquid. 

Oxidation of lubricating oil can result in lacquer deposits, metal corrosion, or thickening of the oil. Most lubricants contain oxidation inhibitors. However when additives are used up, oxidation of the oil itself begins. The quantity of oxidation in an oil sample is measured by differential infrared analysis. 

In the USA, there is the ASTM standards and the well-known General Electric requirements. The total useful life of turbine oil is its most important characteristic. ASTM method D943 (IP 157) measures the life indirectly by assessing the useful life of the oxidation inhibitor contained in the formulation and are often referred to as the TOST life of the oil. Rust prevention is generally assessed by the ASTM D665 (IP 135) method. 

The important commercial feature of these juices, especially significant with blackcurrant and tomato juices, is their ascorbic acid (or vitamin C) content, of which loss by oxidation is known to be accelerated both by heat and by metal (particularly copper) contamination. The effect of copper has been carefully investigated for pure ascorbic acid", and more recently ascorbic acid in blackcurrant juice and model systems. There are, however, oxidation inhibitors of different kinds (which may themselves be heat-sensitive) present in various fruits, which give differing results. The presence of metals will also affect flavours", may cause discoloration, and may give rise to clouding effects, as in apple juice. ... 

Oxidation inhibitor To increase oxidation reistance Oil-soluble amine and phenol... 

Thus, effectiveness of basic (alkaline) additives has been greatly improved by increasing their solubility in base stocks, by exploiting synergistic action between two similar additive types and by the use of a third additive to enhance (catalyse) the performance of the other two. Similar principles have been used to augment the performance of oxidation inhibitors. 

A temperature of 30-40 C and a moderate pressure are enough to cause a violent polymerisation, which can increase the pressure in the reactor to 1000 -1200 bar. In storage, a low polymerisation can also be dangerous for a different reason. In this case, polymer precipitates in the form of flakes causing the volume to rise, which can eventually cause the storage tanks to detonate. Butadiene can only be stored if it contains a poiymerisation inhibitor, which also plays the role of an oxidation inhibitor. Tert-butylcatechol concentrated at 0.2% is perfect for this use, but rust and water can damage the inhibitor. 

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