Lubricant Oil Base Stock Analysis by 1H and 13C NMR

During the course of lubricant property testing in the formulation of both diesel and gasoline lubricants certain base oil stocks have become associated with poor low temperature pumpability due to the formation of wax crystallization gels. Specific tests have been developed to identify these poor low temperature properties (mini-rotary viscometer (MRV)) which manifest themselves as large increases in viscosity and shear stress (the motivating force per unit area for fluid flow). The MRV test will be described later.

Two contrasting oils have been obtained:-

Oil A : readily passes the MRV test with an acceptable viscosity increase

(< 30,000 cP), and no measurable shear stress.

Oil B : fails the MRV test due to large viscosity increase (>400,000 cP) and

a large shear stress increase (300-500 Pa).

The reasons for the differences in low temperature crystallization behavior are not readily understandable from the basic physical and chemical tests which are performed on the base oils. Thus, a study has been undertaken to attempt to identify differences between the oils that might explain this behavior.

Differences in the paraffinic distribution are readily observed as are differences in aromatic character.