Degradation of lubricants

Zeman, A., Stuwe, R., and Koch, K. 1984. The DSC Cell A Versatile Tool to Study Thermal-Oxidative Degradation of Lubricants and Related Problems. Thermochim. Acta, 80,1-9. 

Lubricants used in car engines are formulated by blending a base oil with additives to yield a mixture with the desirable physical attributes. In this problem, ctudents examine the degradation of lubricants by oxidation and design an improved lubricant system. The design should include the lubricant system s physical and chemical characteristics, as well as an explanation as to how it is applied to automobiles. Focus automotive industry, petroleum industry. 

Degradation of lubricants by oxidative mechanisms is potentially a very serious problem. Although the formulated lubricant may have many desirable properties when new, oxidation can lead to a dramatic loss of performance in service by reactions such as ... 

The use of additives to control lubricant degradation requires a focus on alkyl radicals (R), alkylperoxy radicals (ROO) and hydroperoxides (ROOH). Primary alkoxy radicals (RCH2O) and hydroxy radicals (HO) rapidly abstract hydrogen from the substrate. It is therefore very unlikely that they can be deactivated by natural or synthetic antioxidants. In practice, three additive types have proven to be successful in controlling the degradation of lubricating oils ... 

Organophosphorus compounds Phosphites are the main organophosphorus compounds used to control oxidative degradation of lubricants. They eliminate hydroperoxides, peroxy and alkoxy radicals, retard the darkening of lubricants over time and also limit photodegradation. These performance characteristics may be of importance for polyalphaolefins, hydrocracked or severely hydrotreated base stocks and white oils. 

The environmental degradation of lubricating oils is less easily demonstrated. One of the problems is the complex and varied nature of the used material. Materials other than hydrocarbons can inhibit or influence the rate of degradation, which is of greatest interest. Once released into the environment, there is a finite time before the waste lubricant is bound up in sediments or soils. Once there, due to the hydrophobic nature of the material, water is excluded and conditions are essentially anoxic. Anaerobic degradation of oils does not readily occur in nature - much to the relief of the oil exploration and refining industry. However, waste lubricant on the road or in soil or sediments is not locked in place in the same way as crude oil in rock formations. Heavy rain can wash surfaces, churn up river beds and release sediments, whilst the action of animals and plant can oxygenate soils. One means of... 

The thermal degradation of lubricant base oils is known to occur at high temperature and to result in the formation of several carbonyl and hydroxy species (lactones, peroxy esters, peroxy acids, esters, ketones, etc.), which are formed by a free radical-initiated chain reaction [33]. 

Vegetable and seed oils as well as some synthetic base stocks present a new class of biodegradable base stocks. These fluids (10) have excellent biodegradation properties as measured by criteria developed by the Environmental Protection Agency (EPA) or Organization of Economic Cooperation and Development (OECD). OECD 301 and EPA 560/6-82-003 measure the biodegradation of lubricants. These tests were developed to measure the degradation of oil, especially two-cycle ok, on waterways. Aquatic toxicity criteria toward fish is also found to be acceptable for this class of fluids as measured by EPA 560/6-82-002 and OECD 203 1-12. 

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reaction can cause degradation of the mechanical, aesthetic, and electrical properties of polymers loss of flavor and development of rancidity ia foods and an iacrease ia the viscosity, acidity, and formation of iasolubles ia lubricants. The need for antioxidants depends upon the chemical composition of the substrate and the conditions of exposure. Relatively high concentrations of antioxidants are used to stabilize polymers such as natural mbber and polyunsaturated oils. Saturated polymers have greater oxidative stabiUty and require relatively low concentrations of stabilizers. Specialized antioxidants which have been commercialized meet the needs of the iadustry by extending the useflil Hves of the many substrates produced under anticipated conditions of exposure. The sales of antioxidants ia the United States were approximately 730 million ia 1990 (1,2). 

The rod drop monitor is recommended for all non-lubricated compressor applications, because there is no lubricant to act as a buffer to prevent piston-to-cylinder contact on the loss of the wear band. Lubricated com pressors handling gases with traces of water or gas components that can degrade the local lubricant are candidates. Hydrogen compressors should be considered for monitors because hydrogen is a difficult gas in it sc It and may contain trace quantities of water. While sweet gas compressor-, as are found in pipeline service, would normally not be considered a problem, the rod drop monitor may be used to signal a loss of lubricant anti the compressor can be shutdown before damage can occur. 

Many impurities are present in commercial caprolactam which pass into the liquid wastes from PCA manufacture from which caprolactam monomer may be recovered. Also, the products of die thermal degradation of PCA, dyes, lubricants, and other PCA fillers may be contained in the regenerated CL. Identification of die contaminants by IR spectroscopy has led to the detection of lower carboxylic acids, secondary amines, ketones, and esters. Aldehydes and hydroperoxides have been identified by polarography and thin-layer chromatography. 

In summary, the degradation of the PFPE lubricants is a complex process involving several mechanisms, including thermal decomposition, catalytic decomposition, tribo-chemical reactions activated by exoelectron emission, and mechanical scission, which comes into the play simultaneously. 

Autoxidation. Self-catalyzed oxidation in the presence of air. Autoxidation can be initiated by heat, light, or a catalyst. The commercial production of phenol and acetone from cumene is autoxidation. Other examples include the degradation of polymers exposed to sunlight for long periods of time gum formation in lubricating oils and gasoline and the spoilage of fats. 

Primary organics are emitted to the atmosphere by industrial sources (oil refineries, chemical plants, producers and users of solvents and plasticizers), vehicles (as a result of incomplete fuel combustion, oxygenated degradation products of lubricating oil, polymers from tires), and agricultural activities (use of pesticides). An exhaustive literature survey is beyond the scope of this section, but can be found in Air Quaiity Criteria for Particulate Matter many useful references are also available. 

Hindered phenol and phenylenediamine (PDA) compounds are commonly used and quite effective at preventing free-radical oxidative degradation of fuel. They can be used in gasoline, kerosene, jet fuel, and certain distillates and lubricants. Often, a synergistic effect can be obtained by using a combination of a hindered phenol and a phenylenediamine antioxidant in the same application. 

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