Lube Basestock Manufacturing Technology and Engine Oil Pumpability 940098
The trouble-free operation of an engine during and after starting at low temperatures is achieved by an uninterrupted supply of oil to points of friction, i.e., by the oil's pumpability. A key parameter in pumpability is wax, and in particular its composition, concentration and morphology. Wax or paraffin compositions of engine oils are dependent upon the basestocks used in the formulation. The hydrocarbon compositions of lube basestocks and the carbon number distribution for each hydrocarbon class (n-paraffins,isoparaffins, cycloparaffins, aromatics) depend upon the crude oil's source and more importantly on the manufacturing technology used. In North America, there are essentially four process pathways used to produce lubricant basestocks: solvent extraction or hydrocracking, followed by solvent dewaxing or catalytic dewaxing. Each process pathway can produce basestocks with similar physical properties (viscosity, viscosity index, pour point), but these basestocks may have markedly different paraffin compositions (concentration, carbon number distribution and paraffin type), which impart different low temperature pumpability properties to engine oils formulated with these basestocks. In contrast, basestocks produced at different refineries via the same pathway have similar paraffin (wax) compositions and thus, similar pumpability properties. In pumpability tests on three SAE 10W-40 oils (ASTM D 4684 at -25°C) formulated with basestocks produced via three different pathways, the oils exhibited different pumpability properties.
The non-conventional, mineral typed, basestocks are manufactured by these same processes, except that the severity of the process technology has been increased. These non-conventional basestocks have good pumpability properties because the wax crystals that formed have a poorly defined structure and are easily sheared.