Process description for the A3 example simulation
- Last UpdatedJul 07, 2025
- 5 minute read
This simulation demonstrates the separation of a mixed IPA and water stream by using azeotropic distillation with a cyclohexane entrainer. IPA-water systems exhibit azeotropic behavior at lower concentrations of water. This hinders the separation in typical fractional distillation columns, since there's little difference between the vapor and liquid compositions at low water concentrations. The Binary1 Binary Phase Diagram in the simulation illustrates this behavior.
Figure 2: IPA-water azeotropic behavior
To break the azeotrope, we add a cyclohexane (CH) entrainer to the system before we send it to a fractional distillation column. The IPA-Water-CH mixture forms a lower-boiling azeotrope among two liquid phases. The addition of the CH entrainer modifies the activity coefficients of the IPA and water in the mixtures and pushes the IPA and water concentrations outside the binary azeotropic zone. This in turn provides better separation between IPA and water. The Ternary1 Ternary Phase Diagram in the simulation illustrates this behavior.
Figure 3: IPA-water-CH separation at 139 kPa
The process includes two fractional distillation towers (Columns) with a decanter (Separator) between the two towers. The first tower (T1) isolates IPA in the bottom product. The decanter (V1) separates the organic liquid phase from the aqueous liquid phase and recycles the organic phase to T1. The second tower (T2) isolates purified water in the bottom product and recycles a mixed distillate to T1.
We mix the recycle from T2 with fresh IPA-water feed before we feed it to T1. We mix the organic reflux from V1 with fresh make-up cyclohexane (CH) before we feed it to T1.
Because vapor-liquid-liquid equilibrium (VLLE) calculations can be computationally expensive, we use VLLE calculations only in the separation portion of the simulation. We know that CH breaks the azeotrope and no second liquid layer forms in T1. The second liquid phase forms only at the condenser operating conditions. Therefore, the liquid-liquid separation portion includes only the E1 heat exchanger and V1. We set the E1.PhasesSS and V1.Phases parameters to VLLE to override the phases selection from the fluid (VLEFluid) and perform VLLE calculations instead.
The following tables show the feed compositions, process conditions, and equipment configuration and sizes. The tables show only those values that differ from the default values for each model.
Table 1: Feed compositions
|
Component |
Composition |
|
|
Feed |
Makeup_CH |
|
|
WATER |
0.35 |
0 |
|
IPA |
0.65 |
0 |
|
CH |
0 |
1 |
Table 2: Process conditions
|
Variable |
Description |
Value |
UOM |
|---|---|---|---|
|
Feed.T |
Temperature of the fresh IPA-water mixture that enters the process. |
90 |
°C |
|
Feed.P |
Pressure of the fresh IPA-water mixture that enters the process. |
175 |
kPa |
|
Feed.F* |
Molar flowrate of the fresh IPA-water mixture that enters the process. |
100 |
kmol/h |
|
Makeup_CH.T |
Temperature of the fresh CH that enters the process. |
50 |
°C |
|
Makeup_CH.P |
Pressure of the fresh CH that enters the process. |
200 |
kPa |
|
E1.Tso |
Shell-side outlet temperature of the E1 heat exchanger. |
60 |
°C |
|
E1.Tti |
Tube-side inlet temperature of the E1 heat exchanger. |
29.85 |
°C |
|
E1.Tto |
Tube-side outlet temperature of the E1 heat exchanger. |
50 |
°C |
|
E1.DPs |
Shell-side pressure drop of the E1 heat exchanger. |
1 |
kPa |
|
E1.DPt |
Tube-side pressure drop of the E1 heat exchanger. |
1 |
kPa |
|
V1.T* |
Temperature of the decanter. |
45 |
°C |
|
T1.Ptop |
Pressure at the top stage of the first distillation tower. |
140 |
kPa |
|
T1.DPstage |
Pressure drop for each stage of the first distillation tower. |
2 |
kPa |
|
T1.DPreb |
Pressure drop for the reboiler of the first distillation tower. |
2 |
kPa |
|
T1.VFboilup |
Molar vapor fraction for the reboiler return of the first distillation tower. |
1 |
mol frac |
|
P1.W* |
Mass flowrate of the P1 Pump. |
12,270 |
kg/h |
|
P1.DP |
Pressure drop of the P1 Pump. |
100 |
kPa |
|
P2.P2* |
Outlet pressure of the P2 Pump. |
200 |
kPa |
|
E2.VFto* |
Tube-side outlet vapor fraction of the E2 heat exchanger. |
0.5 |
mol frac |
|
E2.DPt |
Tube-side pressure drop of the E2 heat exchanger. |
1 |
kPa |
|
T2.Ptop |
Pressure at the top stage of the second distillation tower. |
180 |
kPa |
|
T2.DPstage |
Pressure drop for each stage of the second distillation tower. |
1 |
kPa |
|
T2.DPcond |
Pressure drop for the condenser of the second distillation tower. |
0 |
kPa |
|
T2.DPreb |
Pressure drop for the reboiler of the second distillation tower. |
0 |
kPa |
|
T2.Lreflux* |
Liquid molar reflux rate of the second distillation tower. |
53.3 |
kmol/h |
|
T2.VFcond |
Condenser vapor fraction of the second distillation tower. |
0 |
mol frac |
|
E3.Tto* |
Tube-side outlet temperature of the E3 heat exchanger. |
88 |
°C |
|
E3.DPt |
Tube-side pressure drop of the E3 heat exchanger. |
1 |
kPa |
|
Pure_IPA.z[IPA]* |
Molar composition of IPA in the final IPA product that exits the process. |
0.999 |
mol frac |
|
SNK1.z[IPA]* |
Molar composition of IPA in the final water product that exits the process. |
0.001 |
mol frac |
* You must switch specifications to set these values. See Process mode for the A3 example simulation for more information.
Table 3: Equipment configuration and sizes
|
Variable or Parameter |
Description |
Value |
UOM |
|---|---|---|---|
|
T1.NStages |
Number of stages in the first distillation tower. |
19 |
- |
|
T1.FeedStage[S11] |
Stage at which the S11 stream enters the first distillation tower. |
3 |
- |
|
T1.FeedStage[Rflx] |
Stage at which the Rflx stream enters the first distillation tower. |
1 |
- |
|
T1.Condenser |
Configuration for the condenser of the first distillation tower. |
None |
- |
|
T1.Reboiler |
Configuration for the reboiler of the first distillation tower. |
Internal |
- |
|
T1.Contact |
Overall contact efficiency factor of the first distillation tower. |
1 |
fraction |
|
E1.PhasesSS |
Override for the phases selection in the fluid on the shell side of the heat exchanger. |
VLLE |
- |
|
V1.Phases |
Override for the phases selection in the fluid. |
VLLE |
- |
|
V1.L |
Horizontal length of the decanter. |
2 |
m |
|
V1.D |
Diameter of the decanter. |
1 |
m |
|
V1.Lboot |
Length of the boot of the decanter. |
0.5 |
m |
|
V1.Dboot |
Diameter of the boot of the decanter. |
0.5 |
m |
|
T2.NStages |
Number of stages in the first distillation tower. |
18 |
- |
|
T2.FeedStage[Rcy3] |
Stage at which the Rcy3 stream enters the second distillation tower. |
9 |
- |
|
T2.Condenser |
Configuration for the condenser of the second distillation tower. |
Internal |
- |
|
T2.Reboiler |
Configuration for the reboiler of the second distillation tower. |
Internal |
- |
|
T2.Contact |
Overall contact efficiency factor of the second distillation tower. |
1 |
fraction |