Loss Percent Residue Distillation

(EP)

note: Percent recovery = 97.5; percent residue = 1.0; percent loss convert degrees Fahrenheit to degrees Celsius, °C = (°F - 32)/1.8.

1.5. To note: Percent recovery = 97.5; percent residue = 1.0; percent loss convert degrees Fahrenheit to degrees Celsius, °C = (°F - 32)/1.8.

Distillation Curve Butane

FIG. 13-82 Representative ASTM D 86 distillation curves.

20 40 60 80 Volume percent vaporized

FIG. 13-82 Representative ASTM D 86 distillation curves.

Data from a true-boiling-point (TBP) distillation test provides a much better theoretical basis for characterization. If the sample contains compounds that have moderate differences in boiling points such as in a light gasoline containing light hydrocarbons (e.g., isobutane, n-butane, isopentane, etc.), a plot of overhead-vapor-distillate temperature versus percent distilled in a TBP test would appear in the form of steps as in Fig. 13-83. However, if the sample has a higher average boiling range when the number of close-boiling isomers increases, the steps become indistinct and a TBP curve such as that in Fig. 13-84 results. Because the degree of separation for a TBP distillation test is much higher than for an ASTM distillation test, the IBP is lower and the EP is higher for the TBP method as compared with the ASTM method, as shown in Fig. 13-84.

A standard TBP laboratory-distillation-test method has not been well accepted. Instead, as discussed by Nelson (op. cit., pp. 95-99),

FIG. 13-83 Variation of boiling temperature with percent distilled in true-boiling-point distillation of light hydrocarbons.

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