ASTM D2887 data are quick and inexpensive to generate, since they are based upon analysis using a chromatograph. D2887 data must be converted to a 760 mmHg TBP curve before being used to determine pseudo-component normal boiling points.
The two methods of particular relevance when using D2887 data are the API 1994 and the API 1987 options. The API94 option is the default conversion method in PRO/II . In keyword input, this is the CONVERSION=API94 option on the ASSAY statement of COMPONENT DATA input. From the Input menu of the Graphical User Interface, select Assay Characterization ... to display the SIMSCI - Assay Cutpoints and Characterization dialog. Click the Characterization options ... button to display the Assay Data - Characterization Options dialog. The Distillation Curve Interconversions: drop-down list box provides several options, with API 1994 being the default selection.
Refer PRO/II Reference Manual Volume I, Chapter 1, Assay Processing: Interconversion of Distillation Curves for a more complete discussion of all the interconversion options.
API 1994 Conversion Method
The 1994 API Technical Data book recommends procedure 3A3.1 as the preferred interconversion method. Starting with version 8.1 of PRO/II, this is the default method used to convert D2887 to TBP 760. This method converts D2887 data directly to a TBP curve. A basic assumption is that TBP(50), the true boiling point at 50 volume percent distilled, is equal to SD(50), the simulated distillation (D2887) temperature at 50 weight percent:
TBP(50) = SD(50) (1)
A second equation relates the temperature difference of TBP cut points directly to the temperature difference of corresponding ASTM D2887 cut points:
Wi = C ViD (2)
where:
Wi is the TBP temperature difference (F) between two cut points (i)
Vi is the Simulated Distillation (D2887) temperature difference (F) between the same two cut points (i)
C and D are constants for various cut point ranges, and
i is the identifier of the cut point range.
A third set of equations (not presented here) relates the TBP of cut points at 5, 10, 30, 70, 90, 95, and 100 percent to the TBP at 50 percent by using the temperature differences from equation (2). See PRO/II Reference Manual Volume I, Chapter 2, Assay Processing, Interconversion of Distillation Curves, Conversion of D2887 Curves, for a presentation of all the equations.
The steps in the procedure include:
(1) Use equation 1 to compute the TBP at the 50% distilled point.
(2) Use equation 2 to calculate the necessary TBP differences.
(3) Use the third set of equations to calculate the desired TBP temperatures
API 1987 Conversion Method
This is a two-step method that:
(1) Converts the D2887 data to a D86 curve (See ASTM D2887 to ASTMD86 Conversion )
(2) Converts the intermediate D86 curve to the final TBP curve (See ASTM D86 to TBP Curve Interconversion).
Additional Information
Assay Processing Reference Help