TBP, ASTM, and EFV Compared

The TBP, ASTM, and EFV distillation methods achieve different levels of separation for a given sample, as related to the different techniques used in these analyses. Figure 4.10 shows TBP, ASTM, and EFV curves for a middle distillate fraction crude oil, showing significant differences in IBP and EP of the three curves [6]. Note that three curves converge near 50% volume distilled. TBP distillation achieves a higher degree of separation than ASTM and ASTM achieves better separation than EFV, as can be seen in the curves in Figure 4.10. Empirical correlations have been developed to convert one set of distillation data to another [7].

Figure 4.10: TBP, ASTM, and EFV curves for a middle distillate fraction crude oil.

Each distillation method discussed in this section has an application in petroleum refining. TBP distillation is used to characterize crude oils and constitute a significant component of crude essay. ASTM methods are usually used for refinery products and property calculations and correlations for distillate fractions. EFV provides useful data for flashing operations in the refinery.

There are no standard methods for TBP distillation, but ASTM D-2892 method is used to approximate the TBP distillation. This method is also referred to as 15-5 distillation, because of 15 theoretical plates and a reflux ratio of 5 used in the distillation. A simulated distillation method described in ASTM D2887 may also be used to obtain TBP data for crude oils.