Pour point lubricating base oils

Lubricating oil. A new process has been developed for the conversion of waste plastic and Fischer-Tropsch (FT) wax to lube range molecules that can be hydroisomerized to low pour point lube base oils of unconventional base oil (UCBO) quality. The process employs pyrolysis, a thermal, noncatalytic, low-pressure reaction where high-molecular-weight molecules are cracked to ones of lower molecular weight. The major by-product is diesel, with little production of C4- gas. The by-product liquids are highly olefinic and could be oligomerized to provide additional base oil. 

At low temperatures, grease hardens, leading to poor pumpability and rheological properties. Typically the pour point of base oil is considered the low-temperature limit of grease. Below this temperature, the base oil will not flow properly and therefore will not provide sufficient lubrication. 

Although lubricant base stocks have been subjected to dewaxing processes, they still contain large amounts of paraffins that result in a high pour point for the oil. In the paragraph on the cold behavior of diesel fuels, additives were mentioned that modify the paraffin crystalline system and oppose the precipitation of solids. 

Pour point is the lowest temperature at which an oil sample will flow by gravity alone. The oil is warmed and then cooled at a specified rate. The test jar is removed from the cooling bath at intervals to see if the sample is still mobile. The procedure is repeated until movement of the oil does not occur, ASTM D97/IP 15. The pour point is the last temperature before movement ceases, not the temperature at which solidification occurs. This is an important property of diesel fuels as well as lubricant base oils. High-viscosity oils may cease to flow at low temperatures because their viscosity becomes too high rather than because of wax formation. In these cases, the pour point will be higher than the cloud point. 

Lubricant base oils must meet minimum performance characteristics of viscosity, viscosity index, pour point and volatility, all of which must meet required standards. When dealing with re-refined base oils, additional characteristics such as colour and odour must also be considered. These properties, of dark colour and odour, are readily perceived by customers and consumers as representing deficiencies in quality. Many examples of re-refined base oils have a definite, characteristic, oxidised or cracked odour which may be totally unacceptable in some countries and markets. Table 15.2 gives quality guidelines for the acceptance of re-refined 150 and 500 base oils. 

Oil industry has a long history of application of NMR spectroscopy for characterization of crude oils, products and oil fractions. The methodology has been mainly ID proton- or carbon-detected experiments. Quantitative NMR and NMR experiments have been used in estimation of aromatic, olefin, naphtene and paraffin proportions in the samples. ° A more detailed characterization has been obtained using various ID carbon-detected experiments, like GASPE, CSE, QUAT and DEPT to obtain quantitative CH sub-spectra. " The goal of characterization of the oil fractions and quantification of certain structural features has been to find correlation between these features and the product properties (e.g. viscosity index, pour point). Due to environmental concerns oil companies are nowadays more interested in development of lubricant base oils that have low aromatic and olefin contents. Hydrogenation of unsaturated components also improves the stability of the base oils, which is an important property for the end-product. Quantitative analysis of a saturated oil fraction with NMR is a major challenge. When the oil fraction contains only aliphatic compounds, the spectrum width that contains the resonances narrows to ca. 1 ppm in the NMR spectrum and ca. 50 ppm in NMR spectrum. This causes excessive... 

PAO is a class of molecularly engineered base stock with optimized viscosity index, pour point, volatility, oxidative stability and other important lubricant base oil properties. Researchers at ExxonMobil have systematically synthesized polyalphaolefm oligomers of C30 to C40 by BF3 catalysis and compared their lubricant properties, as summarized in Table 2. °... 

Because the paraffin and mixed-base crudes yield lubricating oil fractions of high quality, means had to be devised in the early days of the petroleum industry to separate the wax from the oil. The removal of wax from petroleum fractions is one of the most important phases in the production of lubricating oils and fuel oils of low pour point, and has received the attention of many investigators. 

Pour point depressants The crystallization of paraffin wax in the base oil can lead to a gelation of the lubricant at low temperature. Pour point depressants cannot prevent crystallization but change the shape of the crystals from a needle-like to a densely packed, rounded one. This leads to a much better flow behavior. 

Lubricants are formulated products composed of a base stock, which is either a mineral or synthetic oil, and various specialty additives designed for specific performance needs. Additive levels in lubricants range from 1 to 25% depending on the application. Synthetic base stocks are oligomers of small molecules, synthesized to a defined molecular weight. Important performance indicators include viscosity index which measures the viscosity index behavior over a temperature range, oxidative stability, and pour point. The performance of synthetic and mineral oils (Morse, 1998 Shubkin, 1993) is summarized in Table 2.7. 

Extenders, Plasticizers, and Process Oils. Materials in this class can be prepared from the extracts obtained when narrow wax distillate cuts are solvent-refined— with furfural, for example— in the production of lubricating oils. These materials must have a low pour-point. Hydro-catalytic treatment over a mordenite-based catalyst removes residual n-paraflBnic wax with consequent reduction in pour-point of the product, which is obtained in good over-all yield. 

Paraffinic and naphthenic (cycloparaffinic) stocks may be used for the formulation of lubricating oils, each with favorable characteristics for particular uses. Paraffinic stocks are generally preferred for their superior lubricating power and oxidation resistance. Naphthenic stocks, on the other hand, have naturally lower pour points, i.e, they maintain flow characteristics at lower pour-points than paraffinics (Table 18.8) and are better solvents, features which are more important for applications such as heat transfer, metal working, and fire-resistant hydraulic fluids [33]. Any residual aromatics in the lubricating base stock will have been removed before formulation by solvent extraction, using N-methylpyrrolidone, furfural, or less frequently today, phenol (Eq. 18.39). 

In the majority of cases, chemical additives are used to enhance the properties of base oils to improve such characteristics as oxidation resistance (ASTM D-2893, ASTM D-4742,ASTM D-5846) change in viscosity (ASTM D-445, IP 71) with temperature, low-temperature flow properties as derived from the pour point (ASTM D-97, ASTM D-5853, ASTM D-5949, ASTM D-5950, ASTM D-5985, IP 15) and fluidity measurements (ASTM D-6351), emulsifying ability (ASTM D-2711), extreme pressure (ASTM D-2782, ASTM D-2783, ASTM D-3233, IP 240), antiwear and frictional properties (ASTM D-5183, ASTM D-6425), and corrosion resistance (ASTM D-4636). The selection of components for lubricating oil formulation requires knowledge of the most suitable crude sources for the base oils, the type of refining required, the types of additive necessary, and the possible effects of the interactions of these components on the properties of the finished lubricating oil. 

The yield of base oil after these processes depends on the amount of desirable components in the lubricant boiling range. Lubricant distillates from different crudes can have radically different properties. Table 1.2. Both the Forties and Arabian distillates have relatively high VI and high pour point because they are rich in alkanes and are examples of paraffinic cmde oils. Paraffinic crudes are preferred for manufacturing base oils where viscosity/temperature characteristics are important, e.g. for automotive lubricants for operation over a wide temperature range. However,... 

Naphthenics are made from a more limited range of crude oils than paraffinics, and in smaller quantities, at a restricted number of refineries. Important characteristics of naphthenic base oils are their naturally low pour points, because they are wax-free, and excellent solvency powers. Their viscosity/temperature characteristics are inferior to paraffinics, i.e. they have low/medium VI, but they are used in a wide range of applications where this is not a problem. Since naphthenic crudes are free of wax, no de-waxing step is needed but solvent extraction or hydrotreatment is often used now to reduce aromatic content and especially to remove polycyclic aromatics which may present a health hazard in untreated oils. The main producers of naphthenics are in North and South America because most of the world s supply of naphthenic lubricant crudes are found there. 

Hydraulic lubricants with particularly low pour points are formulated using naphthenic base oils which have poorer viscosity-temperature characteristics. But at higher pressures naphthenic oils have a significantly greater viscosity increase than paraffinic base oils. In consequence, these oils compensate or even exceed viscosity losses due to heating. 

Anti-wear additives are but one of a number of additive types formulated into base oils - there are also anti-oxidants. Chapter 4, and anti-acid, detergents anddis-persants. Chapter 7, lubricity, anti-wear, extreme pressure, pour point depressants, anti-rust and anti-foam additives. Chapter 6. Viscosity index improvers, VIIs, are high-molecular weight polymers which alter the temperature dependence of the base oil viscosity. Chapter 5. Taken altogether, the additive mass percentage of a formulated lubricant can be as high as 15-20%, a veritable chemical soup but one which is very carefully formulated and tested. The additives are often multi-functional, thus some VII compounds have a pour point depressant function. Chapters 5 and 6. Some anti-oxidants have anti-wear and also anti-acid functionality. Chapters 4, 6 and 3. Given these cross-interactions, formulation of a final lubricant product is a complex and skilled activity. Chapters 8-13. 

Viscosity index improvers. These make the oil a sufficiently low viscous fluid when cold (to facilitate starting) by lowering the pour point to between -45 and -45°C (depending on the oil), and to viscous fluid when hot (to prevent the contact between moving mechanical components). This class of additives are polymers which are introduced into a lubricating base to produce a relative greater increase in viscosity when hot than when cold. 

Still there are efforts to improve the performance of natural mineral oil-based lubricants by the synthesis of oligomeric hydrocarbons, which has been the subject of important research and development in the petroleum industry for many years and has led to commercialization of a number of synthetic lubricants. These materials are based on the oligomerization of a-olefins such as C6-C20 olefins. Industrial research effort on synthetic lubricants has generally focused on improved viscosity index, thermal and oxidative stability, and a pour point equal to or better than that of the corresponding mineral oil lubricants. 

Pour point and low temperature viscosities. Many S5mthetic base stocks have low pour points, -30 to -70°C, and superior low-temperature viscosities. Combination of low pour and superior low-temperature viscosity ensures oil flow to critical engine parts during cold starting, thus, offering better lubrication and protection. Conventional mineral oils typically have pour points in the range of 0 to -20°C. Below these temperatures, wax crystallization and oil gelation can occur, which prevent the flow of lubricant to critical machine parts. 

EO-based fluids are t5 ically waxy and have poor low temperature properties. They have high water miseibility and are typieally used to formulate water-based lubricants, especially fire-resistant hydraulie oil. PO-based fluids are excellent lubricant base stocks with high VI and low pour point. They have lower solubility in water than EO-based fluids but are not oil miscible. 

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