Types of Distillation Curve
1- True Boiling point(TBP) Distillation
2- ASTM Distillation
3- Semi-fractionating Distillation
4- Equilibrium Flash Vaporization(EFV)
1) TBP: This type of distillation is commonly used due to the accuracy of the results obtained
by this method which is very close to that obtained via real distillation or industrial
distillation. In this distillation, there is a fractionation column located between the condenser
and the flask. In general, this type of distillation is carried out by two steps: firstly, under
atmospheric pressure until 300°C (1% distilled very 2 min), secondly under vacuum pressure
(to prevent cracking process and to reduce the boiling point) at 40mmHg (1% distilled every
3-5 min). In this process, the vapor press. temp. is plotted vs. distilled(%) to get TBP curve.
2) ASTM: In this type of distillation there is on fractionation column located between the
condenser and the flask. On the other hand, the raised vapor will not be fractionated in this
process. This distillation is used with fractions having short range of the boiling point.
3) Semi-fractionating distillation: In this type of distillation, their will be some
fractionating process on the raised vapor via package located between the condenser and the
flask.
4) Equilibrium Flash Vaporization (EFV): Is a single stage separation technique. A liquid
mixture feed is pumped through a heater to raise the temperature and enthalpy of the mixture.
It then flows through a valve and the pressure is reduced, causing the liquid to partially
vaporize. Because the vapor and liquid are in such close contact up until the "flash" occurs,
the product liquid and vapor phases approach equilibrium.
Fig. 5. TBP cut point versus ASTM end point
Fig. 6. Crude distillation curve
Fig. 7. TBP and gravity-mid-percent curves
Average Boiling Point
1- Volume Average Boiling Point (VABP)
T20% T50% T80%
VABP
3
Ti% = Temp. at i vol. % distilled
For short cut Boiling Point (having short B.P)
VABP T50%
2- Weight Average Boiling Point (WABP)
T10% T20% T30% ..........T90%
WABP
9
Ti% = Temp. at i weight. % distilled
3- Molal Average Boiling Point (MABP)
Tx1 Tx 2 Tx 3 ..........
MABP
x1 x 2 x3 ................
Tix = Temp. at i mol. x distilled, x is the no. of mole
MABP VABP T
4) Slope of Distillation Curve
T70% T10%
Slope
60
If the slope 2 Short Cut (T50% ) VABP WABP MABP
Fig. 10 is used to convert Distillation Curve from any type to any type.
Figure 11 is used to find T50% for EFV ( y axix T50%( ASTM or TBP) T50%( EFV ) )
Fig. 8. Molal average boiling point of petroleum fractions
Fig.9. Mean average boiling point of petroleum fractions
Also, Differential (Δ) can be estimated from the following eq.
Fig. 10. Relationships between the slopes of various distillation curves
Fig. 11. Relationships between distillation temperatures at 50% vaporized and the flash
(E.F.V.) Temp. at 50%
Ex) Find T100% and T0% for EFV if T 50%(TBP) = 570 and Slope = 9.4.
Sol.: From Fig.10, the slope of EFV curve = 6.6 (at 9.4 TBP)
From Fig. 11, ΔT = 65 (at T50%(TBP) = 570)
T50%( EFV ) T50%( ASTM or TBP) T 570 65 505
y T100% 505
slope 6.6 T100% 835
x 50 0
y 505 T0%
Slope 6.6 T0% 175
x 100 50
Fig. 12. Sulfur content of products from Middle East crude oils
Home work
For a given crude oil; 1- Draw a TBP curve, 2- Evaluate the crude, 3- Find the value of Kw if
API=43, 4- Draw a EFV on the same Figure, 5- Find the vol. dis. At 1100F if CCR= 1.8%
then draw it, and 6- Find the vol. of the distilled at 1000F.
Vol. Distilled 0 10 20 30 40 50 60 70 80
Temp. (F) 160 270 335 400 480 560 610 680 820 1100
Sp.gr 0 0.72 0.75 0.78 0.80 0.82 0.835 0.85 0.87
