Lube Crude Assay

A lube crude assay is a laboratory process to measure the lube processing response from crude to base oil. It is an important step in a manufacturer s lube crude selection. A crude assay will include process yields for desired base oils at their quality specifications. The manufacturer can use the assay data to predict the process response for their refinery and to assess the desirability of purchasing particular crude. The assay results may be used to calculate the impact on profitability. 

The convention now is to measure base stock viscosities at 40°C and 100°C. Waxy intermediates usually have their viscosities measured at 65°C instead of at 40°C, a temperature at which many of these will have solid wax present. These measurements are made according to ASTM D4456 or its equivalent, and when performed correctly give results that are sufficiently accurate to determine the viscosity index (VI)7 of the sample. Historically, particularly when viscosities were measured in SSU units, the temperatures employed were 100°F and 210°F. It should be mentioned that it is not uncommon to find that viscosities measured for other purposes (e.g., for vacuum gas oil fractions in crude assays) are not sufficiently accurate to provide good waxy Vis (which are useful for assessing crudes for lube use). 

In summary, the lube assay will characterize the potential of a crude to produce a specific Base stock (viscosity, viscosity index, saturates, wax, sulfur, basic nitrogen, etc) and to determine the expected yields from distillation, extraction and dewaxing. 

---