TBP

This is the ASTM D 2892 test method and corresponds to a laboratory technique defined for a distillation column having 15 to 18 theoretical plates and operating with a 5 1 reflux ratio. The test is commonly known as the TBP for True Boiling Point. 

As stated above for the TBP distillation, petroleum cannot be heated above 340°C without its molecules starting to crack. Because of this, analytical distillation of heavy fractions is done according to the ASTM D 1160 method for petroleum materials that can be partially or completely vaporized at a maximum temperature of 400°C at pressures from 50 to 1 mm of mercury (6.55 to 0.133 kPa). 

D 2887, applies to products and petroleum fractions whose final boiling points are equal to or below 538°C (1000°F), and have boiling points above 38°C (100°F). The results obtained are equivalent to those obtained from the TBP distillation, ASTM D 2892. 

An example of the good correlation between TBP and simulated distillation is given in Figure 2.4, where it is shown that 71% of a Kuwait crude distils below 535T. 

True Boiling Point (TBP) jL Simulated distillation (gas chromatography) ... 

To extend the applicability of the characterization factor to the complex mixtures of hydrocarbons found in petroleum fractions, it was necessary to introduce the concept of a mean average boiling point temperature to a petroleum cut. This is calculated from the distillation curves, either ASTM or TBP. The volume average boiling point (VABP) is derived from the cut point temperatures for 10, 20, 50, 80 or 90% for the sample in question. In the above formula, VABP replaces the boiling point for the pure component. 

From the analytical results, it is possible to generate a model of the mixture consisting of an number of constituents that are either pure components or petroleum fractions, according to the schematic in Figure 4.1. The real or simulated results of the atmospheric TBP are an obligatory path between the experimental results and the generation of bases for calculation of thermodynamic and thermophysical properties for different cuts. 

Transformation of ASTM D 86 results into an atmospheric TBP, equation [4.19],... 

Transformation of ASTM D 1160 results into a TBP at 10 mmHg, equation [4.22]. 

The results can be converted into an atmospheric TBP by using an equation equivalent to that proposed by Riazi and published by the API ... 

Daubert has recently published a new method (Hydrocarbon Processing, September 1994, page 75) to convert D 86 data to TBP results using the following equations ... 

The results of the D 1160 distillation converted to 760 mmHg are not to be converted directly to an atmospheric TBP. The D 1160 results converted to 760 mmHg must be converted into the D 1160 equivalent at 10 mmHg, then these D 1160 results at 10 mmHg have to be transformed into a TBP at 10 mmHg and finally the TBP results at 10 mmHg are transformed into a TBP at 760 mmHg. 

For the fractions distilled at higher than 50%, the TBP and D 1160 curves are identical. 

Distillation simulated by gas chromatography is a reproducible method for analyzing a petroleum cut it is appiicabie for mixtures whose end point is less than 500°C and the boiling range is greater than 50°C. The results of this test are presented in the form of a curve showing temperature as a function of the weight per cent distilled equivalent to an atmospheric TBP. 

For paraffinic materials, the results are close to those of a TBP, the equipment being calibrated using n-paraffins. For aromatics, the differences are larger. 

Crude oil is generally characterized by a TBP analysis whose results are expressed as temperatures equivalent to atmospheric pressure as a function of the fraction of volume and weight distilled... 

Each petroleum cut obtained by mixing the TBP distilled fractions (and thus characterized by the TBP cut points) is described by a coiiection of properties including the viscosity at two temperatures. 

The normalized distillation curves, TBP, ASTM D 86, and ASTM D 1160, provide a way to judge the quality of a fractionation performed on petroleum cuts. 

Calculation of the atmospheric TBP is rapid if it can be assumed that this distillation is ideal (which is not always the case in reality). It is only necessary to arrange the components in order of increasing boiling points and to accumulate the volumes determined by using the standard specific gravity. 

This calculation starts from the TBP at atmospheric pressure. The API recommends a relation established by Riazi (1982) ( oj j... 

Table 4.16a Coeff exam dents for conver pie applied to a pt ting a TBP curve Hroleum cut (Riaz into an ASTM D 86 curve and an i s method). ...

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