Lubricating oils, determination

Burdett, R.A., L.W. Taylor and L.C. Jones Jr (1955), Determination of aromatic hydrocarbons in lubricating oil fractions by far UV absorption spectroscopy , p. 30. In Molecular Spectroscopy Report Conf. Institute of Petroleum, London. 

Urea has the remarkable property of forming crystalline complexes or adducts with straight-chain organic compounds. These crystalline complexes consist of a hoUow channel, formed by the crystallized urea molecules, in which the hydrocarbon is completely occluded. Such compounds are known as clathrates. The type of hydrocarbon occluded, on the basis of its chain length, is determined by the temperature at which the clathrate is formed. This property of urea clathrates is widely used in the petroleum-refining industry for the production of jet aviation fuels (see Aviation and other gas-TURBINE fuels) and for dewaxing of lubricant oils (see also Petroleum, refinery processes). The clathrates are broken down by simply dissolving urea in water or in alcohol. 

Lubricating oil analysis, as the name implies, is an analysis technique that determines the condition of lubricating oils used in mechanical and electrical equipment. It is not a tool for determining the operating condition of machinery. Some forms of lubricating oil analysis will provide an accurate quantitative breakdown of individual chemical elements, both oil additive and contaminates, contained in the oil. A comparison of the amount of trace metals in successive oil samples can indicate wear patterns of oil wetted parts in plant equipment and will provide an indication of impending machine failure. 

Viscosity is one of the most important properties of lubricating oil. The actual viscosity of oil samples is compared to an unused sample to determine the thinning of thickening of the sample during use. Excessively low viscosity will reduce the oil film strength, weakening its ability to prevent metal-to-metal contact. 

Spectrographic analysis allows accurate, rapid measurements of many of the elements present in lubricating oil. These elements are generally classified as wear metals, contaminates, or additives. Some elements can be listed in more than one of these classifications. Standard lubricating oil analysis does not attempt to determine the specific failure modes of developing machine-train problems. Therefore, additional techniques must be used as part of a comprehensive predictive maintenance program. 

Wear particle analysis is related to oil analysis only in that the particles to be studied are collected through drawing a sample of lubricating oil. Where lubricating oil analysis determines the actual condition... 

SFC-FID is widely used for the analysis of (nonvolatile) textile finish components. An application of SFC in fuel product analysis is the determination of lubricating oil additives, which consist of complex mixtures of compounds such as zinc dialkylthiophosphates, organic sulfur compounds (e.g. nonylphenyl sulfides), hindered phenols (e.g. 2,6-di-f-butyl-4-methylphenol), hindered amines (e.g. dioctyldiphenylamines) and surfactants (sulfonic acid salts). Classical TLC, SEC and LC analysis are not satisfactory here because of the complexity of such mixtures of compounds, while their lability precludes GC determination. Both cSFC and pSFC enable analysis of most of these chemical classes [305]. Rather few examples have been reported of thermally unstable compounds analysed by SFC an example of thermally labile polymer additives are fire retardants [360]. pSFC has been used for the separation of a mixture of methylvinylsilicones and peroxides (thermally labile analytes) [361]. 

Table 8.23 collects together some typical ETAAS analyses of polymer formulations see also ref. [141a], GFAAS has also been applied for the determination of additive elements in lubricating oils [52]. Solidsampling GFAAS and NAA are preferred analytical tools for the analysis of mg samples, also in relation to RM production. 

Allan Walsh, in 1955, was the pioneer for the introduction of atomic absorption spectroscopy (AAS), which eventually proved to be one of the best-known-instrumental-techniques in the analytical armamentarium, that has since been exploited both intensively and extensively in carrying out the quantitative determination of trace metals in liquids of completely diversified nature, for instance blood serum-for Ca2+, Mg2+, Na+ and K+ edible oils-Ni2+ beer samples-Cu+ gasoline (petrol)-Pb2+ urine-Se4+ tap-water-Mg2+ Ca2+ lubricating oil-Vanadium (V). 

ASTM Method D3328-90 Water Petroleum oils such as distillate fuel, lubricating oil, and crude oil recovered from water or beaches. Identification of a recovered oil is determined by comparison with known oils, selected because of their possible relationship to the recovered oil. 

Thus, one test (ASTM D893) covers the determination of pentane- and toluene-insoluble constituents in used lubricating oils using pentane dilution and centrifugation as the method of separation. The other test (ASTM D4055) uses pentane dilution followed by membrane filtration to remove insoluble constituents larger than 0.8 p,m. 

Testing residual fuel oil does not suffer from the issues that are associated with sample volatility but the test methods are often sensitive to the presence of gas bubbles in the fuel oil. An air release test is available for application to lubricating oil (ASTM D3427 IP 313) and may be applied, with modification, to residual fuel oil. However, with dark-colored samples, it may be difficult to determine... 

The precipitation number is often equated to the asphaltene content, but there are several issues that remain obvious in its rejection for this purpose. For example, the method to determine the precipitation number (ASTM D91) advocates the use of naphtha for use with black oil or lubricating oil, and the amount... 

Optical examination of etched polished surfaces or small particles can often identify compounds or different minerals hy shape, color, optical properties, and the response to various etching attempts. A semi-quantitative elemental analysis can he used for elements with atomic number greater than four by SEM equipped with X-ray fluorescence and various electron detectors. The electron probe microanalyzer and Auer microprobe also provide elemental analysis of small areas. The secondary ion mass spectroscope, laser microprobe mass analyzer, and Raman microprobe analyzer can identify elements, compounds, and molecules. Electron diffraction patterns can be obtained with the TEM to determine which crystalline compounds are present. Ferrography is used for the identification of wear particles in lubricating oils. 

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