Mineral-based oils

The mineral-based oils are produced from heavy-end crude oil distillates. Distillate sneams may be treated in several ways, such as vacuum-, solvent-, acid-, or hydrotreated, to produce oils with commercial properties. Hydrocarbon types ranging from C15 to C50 are found in the various types of oils, with the heavier distillates having higher percentages of the higher-carbon-number compounds. 

The WTD is a cumulative rating based on observation of deposits in the groove and land areas of the piston and lacquer on piston skirts which have been weighted and calculated in accordance with the test procedure. The evalated lubricating oils also contained, where required, conventional viscosity improver, a metal detergent and ZDDP in mineral base oil. The WTD ratings were as follows ... 

Crankcase oil or motor oil may be either mineral-based or synthetic. The mineral-based oils are more widely used than the synthetic oils and may be used in automotive engines, railroad and truck diesel engines, marine equipment, jet and other aircraft engines, and most small 2- and 4-stroke engines. 

Abstract The source, composition and suitability of crude oils for base oil production are reviewed. The physical and chemical properties of alkanes, naphthenes and aromatics and their characteristics for lubricant applications are examined. Properties and applications of various base oils are defined and specified. Production of conventional mineral oils is described, including the various processes to remove wax and other deleterious substances, followed by increasingly severe hydrogenation to produce base oils of increased quality and performance. The API categorization of mineral base oils, either direct from the refinery or after hydrotreatment of increasing severity, is described, together with sub-categories. 

Traditionally, synthetic PAOs have had significant performance advantages over equiviscous mineral base oils by their higher viscosity index, lower pour point, reduced volatility and improved oxidation stability in the presence of antioxidants. GTL base oils now challenge PAOs in performance and can be very cost competitive with the relatively expensive synthetics. A review in 2006 described performance comparisons of base oils with a viscosity of 4 cSt at 100°C [37]. It is suggested that the GTL fluids can match the PAOs in Noack volatility, oxidation resistance and thermal stability, whereas the PAOs retain some superiority in their extreme low-temperature fluidity. 

The Ui method permits a better understanding of the interactions observed between ZDDP (zinc dialkyldithiophosphates) additives and various mineral base oils [17]. This applies for the anti-wear (AW), extreme pressure (EP) and antioxidant functions of ZDDP. The viscosity of base oils was shown to be a factor controlling these relationships. The o method has also been found useful in showing the directions of the relationships. For the case when an observed change should be considered as a complex one, the influence of the tested medium on it may be expressed as a sum as follows ... 

For industrial gears where the conditions of tooth engagement are not excessively severe, and the danger of scuffing is small, mineral base oils may be used. The choice of oil viscosity depends on the transmitted power and pinion speed, Fig. 8.7. In general, the lubricant viscosity required decreases as the speed increases, and... 

Process oils are not typical lubricants and are mostly used as processing aids in manufacture. They are generally additive-free mixtures of crude oil hydrocarbons and include products such as (i) medicinal white oils, (ii) technical white oils, (iii) bright process oils and (iv) dark process oils. Medicinal white oils are composed exclusively of isoparaffins and alkylnaphthenes. Technical white oils are less refined products than medicinal white oils and are composed of saturated hydrocarbons, though they may also contain a slight amount of aromatic compounds. Bright process oils include both yellow raffinates and brown distillates. Dark process oils are extracts from solvent refining of mineral base oils. 

Hydrocarbon-based hydraulic fluids can be subdivided into two categories those with a mineral base oil which were introduced to overcome the poor low-temperature properties and instability of the castor oil-based hydraulic fluids and those with a polyalphaolefin (PAO) base oil. Both are used extensively in military aircraft. 

Complex processes are required to deal with the wide range of contaminants and additives present in waste lubricants from multiple sources. The objective is to recycle waste lubricants to produce base oils that can then be used as substitutes or alternatives to virgin mineral base oils. The main re-refining processes are summarised in the sub-sections below most are continuous rather than batch processes and rely on receiving a reasonably homogenous used lubricant feedstock if the products are to be consistent. 

Base oils produced by the acid/clay process usually have a dark colour, have a burnt odour and are inferior to virgin mineral base oils. 

Sulphur Content This is seen as an index of inherent anti-oxidant capacity in virgin mineral base oils. For re-refined base oils, those hydrocarbons that were inherently oxidatively unstable would have been oxidised during previous use. The function of the sulphur content of a re-refined base oil is not clear and more work is required to determine the need or the concentration of sulphur required to meet minimum performance requirements. 

Both quality and process control should be able to produce a product of known and consistent quality, suitable for use as a lubricant base stock. In past practice, however, oils that can meet the required performance characteristics have tended not to be readily available and have historically been expensive. For these reasons, the use of re-refined oils as a lubricant base oil was not considered to represent a viable alternative to virgin mineral base oils of consistent quality when these are readily available. More recently, the quality of re-refined base oils has increased to a high level, for some cases up to Gp. II quality, and in volume quantity. In addition, the substantially increased price of crude oil, and its associated products, has made re-refining of used lubricant much more economically viable. The alternative route of using the used lubricant as a fuel directly or as a fuel extender is now much more restricted and controlled by environmental legislative authorisations and is also much less viable economically. 

To meet enhanced lubricant performance and service interval life, base oils are already moving upwards, away from Gp.I towards the more highly treated and refined mineral base oils of Gps.II and III and also the synthetic base oils of PAOs and esters. Their relative costs and benefits will determine the base oil mix. Chapters 1 and 2. 

S. K. Sahoo, D. C. Pandey, and I. D. Singh, Studies on the Optimal Hydrocarbon Structure in Next Generation Mineral Base Oils, Proceedings of the International Symposium on Fuels and Lubricants, New Delhi, pp. 273-278 (2000). 

Measurements of a mineral, base oil (Figure 3) show significant shear thickening properties at stress levels above 10 kPa (17). Viscosity did Increase with a factor of about 4, when shear stress was raised to 1 MPa. The spread of the measured points from a continuous flow curve... 

Figure 3 A mineral, base oil. Significant shear thickening effect is found above 10 kPa shear stress. The spread of the measuring points may Indicate a minor change from liquid state. L/D =1, 25 C, Pressure s. 1 MPa.

Figure 6.16 shows friction vs. sliding velocity for a mineral oil with and without nano-boric acid powders. As is clear, the friction coefficient is much lower for oil containing nano-boric acid. Note that the difference is particularly significant at low sliding velocities, where much severe metal-to-metal contact occurs. Overall, the addition of nanometer-sized boric acid powders significantly reduces the friction coefficients of both PAO and mineral base oils. 

Samples of difatty amidoamines (Varisoft 510, AA(H), 100% A.I. Varisoft 511, AA(S), 100% A.I. and Varisoft 512, AA(S), 90% active in isopropanol) were obtained from Goldschmidt Chemical Corporation. The Aim used was 90% active 4,5-dihydro-l-methyl-2-nortaUow alkyl-(2-tallow amidoethyl) imidazolin-ium methyl sulfate by Akzo-Nobel. Quatemized triethanolamine diester methyl sulfate (DEQ Tetranyl AT-75 85%) sample was obtained from Kao Corporation Japan. DEQ (H) (100% hydrogenated diesterquat) sample was obtained from High Point Chemical Corporation. Armeen DMHTD, H-tallow dimethyl amine was obtained from Akzo Chemical Company. BP-7050 polymer was obtained from BP Chemical Limited, United Kingdom. This polymer is acrylamide/qua-temary ammonium acrylate (50%) in solvent refined mineral base oil. 

Features Compat. with mineral base oils, wh. oils, syn. base stocks... 

Uses Detergent, rust Inhibitor, and boundary lubricant for hydraulic fluids, stationary diesel lubricants, soluble oils, cutting fluids, and mst preventive oils Features Exhibits a low level of reactivily In formulations compat. with mineral base oils, white oils, and synthetic base slocks Properties Sp.gr. 0.960 (15 C) vise. 55 cSf (100 C) flash pt. (COC) 220 C Use Level 0.5-10% by wt Storage Store 60-80 C Calcium Caseinate R [DMV Infl.]... 

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