Chemistry of hydrocarbon compounds – Product blend – e.g. – composition – etc. – or blending process... – Component of indefinite molecular weight greater than 150
Patent
1997-02-27
2000-07-25
Howard, Jacqueline V.
Chemistry of hydrocarbon compounds
Product blend, e.g., composition, etc., or blending process...
Component of indefinite molecular weight greater than 150
C10M12702
Patent
active
060938617
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to lubricating oil compositions, especially engine oils.
When two metal surfaces move over each other, considerable heat is evolved due to friction. The function of a lubricant is to separate the two rubbing surfaces by a film thereby greatly reducing the coefficient of friction. If this film fails, the frictional heat produced may melt the surfaces causing them to weld together or seize. When conditions are such that a continuous thick (>0.001 in.) film of lubricant separates the solid surfaces at all points, then frictional resistance is controlled by the viscosity of the lubricant. This is referred to as "hydrodynamic lubrication". Under conditions of high speed or high load, thick lubricant films may be absent or incomplete and lubrication of the parts is effected by layers of adsorbed polar molecules. This situation is referred to as "boundary lubrication". Metal surfaces, which are covered by films of metal oxides, are highly polar and hence are not readily "wetted" by non polar hydrocarbon oils. Used alone, hydrocarbon oils are therefore poor lubricants in these circumstances. Lubricants therefore contain additives which either react with metal surfaces or are adsorbed on the surfaces thereby allowing oil to wet the surface or provide boundary lubrication, thus preventing direct metal to metal contact.
Apart from certain speciality products and synthetic oils, the vast bulk of lubricants are based upon hydrocarbons derived from petroleum.
Crude oils contain a number of broad classes of hydrocarbons, the proportions of which vary greatly from oil to oil. derivates of isoprene such as phytane and pristane and degradation products from molecules such as carotene. These compounds have low melting points and so confer low pour points on lubricating oils. They are also stable to degradation by heat and oxygen and have high viscosity indexes, so this iso-paraffin group is the preferred feedstock for lube oil manufacture. except that, due to their higher melting points, they raise the pour point of a lube oil. rings with alkyl side chains. They lower the pour point of an oil but they have a low viscosity index. fused ring systems with alkyl side chains. This group has a low viscosity index and poor thermal stability. crudes, especially those from parts of the Middle East. It has similar properties to aromatics, but are usually even less stable.
In order to prepare a suitable lube oil base stock, a manufacturer will select feeds which have appropriate molecular weight ranges and are rich in the desired classes of hydrocarbons (iso-paraffins), and low in aromatics, ONS compounds, and paraffins so that production costs can be kept low. Crudes such as those from Pennyslvania which are ideal for lube oil manufacture are being depleted, so now most manufacturers use a feed stock mix which is carefully selected to meet the product mix required by the market. Some manufacturers upgrade their feedstock by using a severe hydrogenation/hydrogenolysis process called hydrocracking to remove sulphur, aromatics, and to open rings and crack larger molecules.
The residue from the primary distillation of selected crude oils which are rich in iso-paraffins is distilled at reduced pressure (a few mm of Hg) in the presence of steam. Most usually, three fractions are obtained: two distillate cuts and the residue or bottoms. Typical cuts are shown in the table below.
______________________________________ Lubricating Oil Fractions
Molecular
Boiling Range .degree. C.
Fraction No. of C atoms Weight (Plant conditions)
______________________________________
Light 22-36 300-500 370-500
(Low viscosity)
Medium 29-45 400-600 450-550
(medium viscosity)
Heavy 43 600 >500(residue)
(high viscosity)
______________________________________
The desired oily alkane material is extracted from the viscous bottoms product from the vacuum tower using liquid propane (high pressure, 65.degree. C.) in a propane de-asphalting plant. The more polar, high molecular weight polycyclic
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