Petroleum viscosity

Haney III, W. H., and Monticello, D. J., Microbial Process for Reduction of Petroleum Viscosity. Patent No. W09211343. 1992, July 09. 

The liquid dynamic viscosities at 100°F and 210°F are used to characterize petroleum fractions, notably the heavy fractions. 

The temperatures 100°F and 210°F (37.8°C, 98.9°C) have been selected because they were initially used in the ASTM procedure for calculating the viscosity index of petroleum cuts (ASTM D 2270). 

The molecular weight can be also estimated for petroleum fractions whose boiling point is not known precisely starting with a relation using the viscosities at 100 and 210°F ... 

Each petroleum cut obtained by mixing the TBP distilled fractions (and thus characterized by the TBP cut points) is described by a coiiection of properties including the viscosity at two temperatures. 

Liquid viscosity is one of the most difficult properties to calculate with accuracy, yet it has an important role in the calculation of heat transfer coefficients and pressure drop. No single method is satisfactory for all temperature and viscosity ranges. We will distinguish three cases for pure hydrocarbons and petroleum fractions ... 

Lubricants, Fuels, and Petroleum. The adipate and azelate diesters of through alcohols, as weU as those of tridecyl alcohol, are used as synthetic lubricants, hydrauHc fluids, and brake fluids. Phosphate esters are utilized as industrial and aviation functional fluids and to a smaH extent as additives in other lubricants. A number of alcohols, particularly the Cg materials, are employed to produce zinc dialkyldithiophosphates as lubricant antiwear additives. A smaH amount is used to make viscosity index improvers for lubricating oils. 2-Ethylhexyl nitrate [24247-96-7] serves as a cetane improver for diesel fuels and hexanol is used as an additive to fuel oil or other fuels (57). Various enhanced oil recovery processes utilize formulations containing hexanol or heptanol to displace oil from underground reservoirs (58) the alcohols and derivatives are also used as defoamers in oil production. 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

Low temperature filtration (qv) is a common final refining step to remove paraffin wax in order to lower the pour point of the oil (14). As an alternative to traditional filtration aided by a propane or methyl ethyl ketone solvent, catalytic hydrodewaxing cracks the wax molecules which are then removed as lower boiling products. Finished lubricating oils are then made by blending these refined stocks to the desired viscosity, followed by introducing additives needed to provide the required performance. Table 3 Usts properties of typical commercial petroleum oils. Methods for measuring these properties are available from the ASTM (10). 

Wide range of viscosity ia commercial petroleum oils is illustrated by the representative types listed ia Table 3. Despite this range, the largest proportion of oils are ia the 25-75 mm /s at 40°C viscosity range. Oils ia this range combine generally adequate hydrodynamic load capacity with low power loss, low volatiUty, and satisfactory low temperature properties. 

Fig. 8. Variation of viscosity with temperature for selected petroleum oils.

Although the viscosity index is useful for characterizing petroleum oils, other viscosity—temperature parameters are employed periodically. Viscosity temperature coefficients (VTCs) give the fractional drop in viscosity as temperature increases from 40 to 100°C and is useful in characterizing behavior of siHcones and some other synthetics. With petroleum base stocks, VTC tends to remain constant as increasing amounts of VI improvers are added. Constant B in equation 9, the slope of the line on the ASTM viscosity—temperature chart, also describes viscosity variation with temperature. 

Fig. 10. Viscosity—pressure curve for typical petroleum oils (—) paraffinic (-) aUcycHc and ( ) soHd. To convert MPa to atm, divide by 0.101.

Pour-Point Depressants. The pour point of alow viscosity paraffinic oil may be lowered by as much as 30—40°C by adding 1.0% or less of polymethacrylates, polymers formed by Eriedel-Crafts condensation of wax with alkylnaphthalene or phenols, or styrene esters (22). As wax crystallizes out of solution from the Hquid oil as it cools below its normal pour point, the additive molecules appear to adsorb on crystal faces so as to prevent growth of an interlocking wax network which would otherwise immobilize the oil. Pour-point depressants become less effective with nonparaffinic and higher viscosity petroleum oils where high viscosity plays a dominant role in immobilizing the oil in a pour-point test. 

Properties provided by the branched hydrocarbon chain stmcture of these PAO fluids include high viscosity index in the 130—150 range, pour points of —50 to —60° C for ISO 32 to 68 viscosity range (SAE lOW and SAE 20W, respectively), and high temperature stabifity superior to commercial petroleum products. In their use in automotive oils such as Mobil 1, some ester synthetic fluid is normally included in the formulation to provide sufficient solubihty for the approximately 20% additives now employed in many automotive oils. 

Poly(alkylene glycol)s have a number of characteristics that make them desirable as lubricants. Compared to petroleum lubricants, they have lower pour points, a higher viscosity index, and a wider range of solubilities including water, compatibility with elastomers, less tendency to form tar and sludge, and lower vapor pressure (35). 

Triaryl phosphates are produced by reaction of phosphoms oxychloride with phenoHc compounds at 100—200°C with magnesium or aluminum chloride catalyst. Past use of cresols and xylenols from coal tar or petroleum is replaced for lower toxicity and cost by synthetic phenoHcs, primarily isopropyl phenol, /-butyl phenol, and phenol itself A range of viscosities is achieved by selection and proportioning of the phenols and their isomers used for the starting material. 

Oils in Greases. Essentially the same type of oil is used in compounding a grease as would normally be selected for oil lubrication. Petroleum oils are used in about 99% of the grease produced and commonly are in the SAE 20—30 viscosity range with about 100 130 mm /s viscosity at 40°C. Such oils provide low volatiHty for long life at elevated temperatures (50) together with low torque down to subzero temperatures. 

The trend for increasing viscosity with increased dose is shown in Eigure 18 for several petroleum oils (72). Eor many lubricant appHcations, a dose that gives a 25% increase in 40°C viscosity can be taken as a tolerance limit. Lower radiation absorption seldom changes the lubricant sufficiently to... 

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