ASTM D86 Conversion to TBP 760

All assay distillation curves must be converted to a 760 mm Hg TBP basis before use in determining the pseudocomponent normal boiling points. All four methods may be used to convert ASTM D86 test data. Note that the data are corrected for laboratory pressures different from 760 mm Hg and for cracking (if requested) prior to conversion to a TBP. See API Cracking Equation and ASTM D86 Pressure Correction for further details.

API 1994

This is the method detailed in the 1994 API Technical Data Book which was developed by Daubert, T.E.. This method uses an approach similiar to that of the API 1963 procedure, which always produces a monotonic TBP curve.

Reference: Daubert, T.E., Hydrocarbon Processing, September - 1994, pp 74-78.

API 1987

This is the method published in the 1987 API Technical Data Book which was developed by Riazi and Daubert. The following equation is used to convert each D86 temperature to a TBP temperature:

where:

a, b = constants for each standard volume percent and TBP and D86 are Deg R.

Note: This method is reputed to be more accurate than older methods by statistical comparisons. However it is important to note that the point by point approach does not guarantee that the TBP curve produced will be monotonic, especially for narrow boiling stocks. Should a non-monotonic curve be predicted for a stock, it is recommended that one of the other conversion methods be used.

Reference: Riazi M.R. and Daubert, T.E., Oil and Gas Journal, August 25, 1986, pp 50-57.

API 1963

This method is taken from the API Technical Data Book prior to the 1987 Edition and uses a procedure developed by W.C. Edmister, et.al., which is presented as Figure 3A1.1. This technique provides a curve relating the D86 50 percent distilled point to the TBP 50 percent distilled point. A series of curves are also provided to convert the D86 temperature differences to TBP temperature differences. Curves are provided for: IBP - 10 %, 10 - 30%, 30 - 50%, 50 - 70%, 70 - 90%, and 90% - EP. The TBP temperature differences are applied to the TBP 50 percent distilled point to generate the complete TBP curve. Generally, the newer API methods are preferred to this option.

Note: This method was used exclusively in the SimSci Process Simulation Program for all versions prior to Version 3.01 and always produces a monotonic TBP curve.

Edmister-Okamoto

This is an earlier version of the API 1963 method. Application is identical to that described above for API 1963.

Reference: Edmister, W.C. and Okamoto, G.G., "Equilibrium Flash Vaporization Correlation for Petroleum Fractions", Petroleum Refiner, Vol.38, No.8, p 117 (1959).

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