Lubricating oil fractions

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. 

The crystallization of wax from lubricating oil fractions makes better oil. This is done by adding a solvent (often a mixture of benzene and methyl ethyl ketone) to the oil at a temperature of about -5 F. The benzene keeps the oil in solution and maintains fluidity at low temperature the methyl ethyl ketone acts to precipitate the wax. Rotary filters deposit the wax crystals on a sp woven cloth stretched over a perforated cylindrical drum. A vacuum in the drum draws the oil through the perforations. The wax crystals are removed from the cloth by metal scrapers and ol vent-washed to remove oil followed by solvent distillation to remove oil for reuse. 

Middle distillate one of the distillates obtained between kerosene and lubricating oil fractions in the refining processes. These include light fuel oils and diesel fuels. 

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. 

The asphaltenes are nonvolatile and remain in the residue when the crude is subjected to distillation. The resins are partially volatile and therefore may be present in the lubricating oil fractions of higher boiling point as well as in the residue. Among the many methods employed for the separation of these materials from the oil fractions are distillation, adsorption, chemical treatment, and precipitation by special solvents. 

A number of special vacuum distillation processes have been developed, whereby thermal decomposition of the oil is kept to a minimum. One of these employs thin film vaporization, in which mercury vapor is employed as an indirect heating medium (89, 71). Another employs a carrier other than steam—for example, kerosene—in the vaporization of the heavy lubricating oil fractions (16). These processes are being operated on a commercial scale, but apparently because of their special nature they have not been widely adopted by the petroleum industry. 

A whole lubricating oil fraction consists of four major classes of hydrocarbons—namely (a) asphalts and resins, (b) aromatics, (c) naphthenes and branched paraffins, and (d) paraffin wax. Sulfuric acid is remarkably effective for removing undesirable constituents a and b by a combination of reaction and extraction and has little or no effect on wax (which must be removed by other means) or the naphthenic-type materials which comprise a good lubricating oil. 

The source of paraffin wax is the lighter lubricating oil fractions after distillation from the crudes. The wax content of these is commonly 10 zfc 5% (103). These oils set to gels due to crystallization of the wax and therefore wax removal is a necessity for lubricating-oil manufacture. Wax is a true by-product, yet one of such great value that at times it is prepared as a primary product and the oils are cracked. 

Lillard, Jones, and Anderson (29) in 1951, relating to the types of hydrocarbons in the lubricating oil fraction of a mid-continent and a Gulf Coast petroleum... 

Middle distillate distillate boiling between the kerosene and lubricating oil fractions. 

Mild hydrogenation of lubricating-oil fractions can also be used to improve the color, odor, acid value, carbon residue, and sulfur content and to lessen the tendency to emulsify. A commercial application of such a... 

The development of vacuum distillation provided the means of separating lubricating oil fractions with predetermined viscosity ranges and removed the hmit on the maximum viscosity that might be obtained in distillate oil. Vacuum distillation prevented residual asphaltic material from contaminating lubricating oils but did not remove other undesirable materials such as acidic components or components that caused the oil to thicken excessively when cold and become very thin when hot. 

Asphalt is a dark-brown to black solid or semisolid consisting of carbon, hydrogen, oxygen, sulfur, and sometimes nitrogen. It is made up of three components (1) asphaltene, a hard, friable, infusible powder, (2) resin, a semisolid to solid ductile and adhesive material, and (3) oil, which is structurally similar to the lubricating oil fraction from which it is derived. 

Petroleum ceresins and petrolatum wax are isolated from residues. Paraffin wax, on the other hand, is almost invariably isolated from distillates by solvent extraction or precipitation followed by sweating or emulsion de-oiling. According to Sachanen (77), the wax content of lubricating oil fractions is commonly 10% =b 5%. 

Rossini, Hill, and others have pointed out the great difficulties which will be encountered in isolating and identifying the hydrocarbon in the gas oil, lubricating oil fraction, and wax cut of the crude. Hill, in his paper (55), lists the following means at our disposal for tackling this problem ... 

The next method is the crystallization method. This method is very frequently used by crude oil chemists for the classification of lubricating oil fractions. This method is based on difference in the crystallization temperatures of the compounds in the sample. The samples which are analyzed by this method are usually highly viscous. This makes it difficult to separate the crystallized substances from the sample. Consequently, the sample is usually dissolved in a special solvent. Examples of such solvents are liquefied propane, ethyl ether, and a mixture of acetone and toluene. 

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