and using the temperature differences given by Fig. 6, the TBP temperatures at 0 %,
10 %, 30 %, 50 %, 70 %, 90 %, and 100 % vol are obtained (Table 2).
Developing the Equilibrium Flash Vaporization Curve (EFV)
The Maxwell curves given as Fig. 7 are used to develop the equilibrium flash
vaporization curve (EFV) from the TBP. The EFV curve gives the temperature at
which a required volume of distillate will be vaporized. This distillate vapor is
always in equilibrium with its liquid residue. The development of the EFV curve is
always at atmospheric pressure. Other temperature- and pressure-related conditions
may be determined by using the vapor pressure curves or by constructing a phase
diagram.
The TBP reference line (DRL) is first drawn by a straight line through the 10 %
vol point and the 70 % vol point on the TBP curve. The slope of this line is
determined as temperature difference per volume percent. These data are then
used to determine the 50 % volume temperature of a flash reference line (FRL).
The curve in Fig. 7 relating Δt 50 (DRL–FRL) to DRL slope is used for this. Finally,
the curve on Fig. 7 relating the ratio of temperature differences between the FRL
and flash curve (EFV) from that for the TBP to DRL is applied to each percent
volume. From this the atmospheric EFV curve is drawn.
A sample calculation for the compilation of the EFV curve follows. Note that the
TBP curve is used to define product yields, while the EFV curve is used to define
temperature/pressure conditions in distillation. This example uses the TBP curve
developed above as a starting point (Table 3).
Calculating Vapor and Liquid Compositions from Equilibrium Flash
When a mixture of compounds vaporizes or condenses, there is a unique relationship between the composition of the mixture in the liquid phase and that in the
corresponding phase at any condition of temperature and pressure. This relationship
is termed the equilibrium flash vaporization for the mixture. An equilibrium flash
can be calculated using the procedure detailed in Appendix 1 of the current chapter.
Today these calculations are normally performed using process simulation
software; however, the principles are the same as the manual calculation method.
Table 2 Converting
ASTM to TBP distillation
ASTM (lab data)
TBP (from Fig. 6)
F
Δ
F
Δ
F
F
IBP
424
29
61
361
10 %vol
453
31
52
423
30 %vol
484
18
52
475
50 %vol
502
507
70 %vol
504
2
31
538
90 %vol
536
32
41
579
FBP
570
34
40
619
22
D.S.J. Jones
10 %, 30 %, 50 %, 70 %, 90 %, and 100 % vol are obtained (Table 2).
Developing the Equilibrium Flash Vaporization Curve (EFV)
The Maxwell curves given as Fig. 7 are used to develop the equilibrium flash
vaporization curve (EFV) from the TBP. The EFV curve gives the temperature at
which a required volume of distillate will be vaporized. This distillate vapor is
always in equilibrium with its liquid residue. The development of the EFV curve is
always at atmospheric pressure. Other temperature- and pressure-related conditions
may be determined by using the vapor pressure curves or by constructing a phase
diagram.
The TBP reference line (DRL) is first drawn by a straight line through the 10 %
vol point and the 70 % vol point on the TBP curve. The slope of this line is
determined as temperature difference per volume percent. These data are then
used to determine the 50 % volume temperature of a flash reference line (FRL).
The curve in Fig. 7 relating Δt 50 (DRL–FRL) to DRL slope is used for this. Finally,
the curve on Fig. 7 relating the ratio of temperature differences between the FRL
and flash curve (EFV) from that for the TBP to DRL is applied to each percent
volume. From this the atmospheric EFV curve is drawn.
A sample calculation for the compilation of the EFV curve follows. Note that the
TBP curve is used to define product yields, while the EFV curve is used to define
temperature/pressure conditions in distillation. This example uses the TBP curve
developed above as a starting point (Table 3).
Calculating Vapor and Liquid Compositions from Equilibrium Flash
When a mixture of compounds vaporizes or condenses, there is a unique relationship between the composition of the mixture in the liquid phase and that in the
corresponding phase at any condition of temperature and pressure. This relationship
is termed the equilibrium flash vaporization for the mixture. An equilibrium flash
can be calculated using the procedure detailed in Appendix 1 of the current chapter.
Today these calculations are normally performed using process simulation
software; however, the principles are the same as the manual calculation method.
Table 2 Converting
ASTM to TBP distillation
ASTM (lab data)
TBP (from Fig. 6)
F
Δ
F
Δ
F
F
IBP
424
29
61
361
10 %vol
453
31
52
423
30 %vol
484
18
52
475
50 %vol
502
507
70 %vol
504
2
31
538
90 %vol
536
32
41
579
FBP
570
34
40
619
22
D.S.J. Jones