1. Hierarchy of Decisions

2. LEVEL 3 :
purge
reactor
separator
products
feeds
Liquid ?
Liquid / Vapor ?
Vapor ?
Determined with
Flash calculation!

3. 1 ) If only liquid is present:
LEVEL 4 :
1 ) If only liquid is present:
LEVEL 3
reactor
liquid
separation
system
liquid
products
feeds
Liquid recycle

4. 2 ) If both liquid and vapor are present: Vapor Recovery system Phase
purge
LEVEL 4 :
2 ) If both liquid and vapor are present:
Vapor
Recovery
system
vapor
gas recycle
vapor
35C
Phase
Split
liq.
liq.
reactor
liquid
separation
system
liquid
products
feeds
Liq. recycle
LEVEL 3

5. 3 ) If only vapor is present: Vapor Recovery system Phase Split
purge
LEVEL 4 :
3 ) If only vapor is present:
Vapor
Recovery
system
vapor
gas recycle
35C
Phase
Split
liquid
liquid
vapor
reactor
liquid
separation
system
products
feeds
Liquid recycle
LEVEL 3

6. LOCATIONS OF VAPOR RECOVERY SYSTEM
Gas
Recycle
Purge 2 1 3
vapor from phase split
1 ) The purge stream
2 ) The gas-recycle stream
3) The flash vapor stream
4 ) None

7. RULES FOR PLACING THE VAPOR RECOVERY SYSTEM
1 ) Place the vapor recovery system on the purge stream if significant amounts
of valuable materials are being lost in the purge.
2 ) Place the vapor recovery system on the gas-recycle stream if materials that
are deleterious to the reactor operation (catalyst poisoning, etc.) are present
in this stream or if recycling of some components degrades the product
distribution.
3 ) Place the vapor recovery system on the flash vapor stream if both 1 ) and 2 )
are valid.
4 ) Do not use a vapor recovery system if neither 1 ) nor 2 ) are important.

8. TYPE OF VAPOR RECOVERY SYSTEM
1 ) Condensation - low. T and/or high P
2 ) Absorption
3 ) Adsorption
4 ) Membrane separation
5 ) Reaction
ADJUST MATERIAL BALANCE ?

9. Decisions in Synthesizing
Liquid Separation System
1. How should light ends be removed, if they might contaminate
the products?
2. What should be the destinations of light ends?
3. Do we recycle components that form azeotropes with reactants,
or do we split the azeotropes ?
4. What separations can be made by distillation ?
5. What sequence of columns do we use ?
6. How should we accomplish separations if distillation is not
feasible ?

10. Q1: Alternatives for Removing Light ends Phase Splitter — T and/or P
◆ Partial Condenser on Product Column (A)
◆ Pasteurization Section on Product Column (B)
◆ a Stabilizer Column before the Product Column (C)
Lower
cost
Higher
(A)
lights
(B)
(C)
lights
lights
product
product
product

11. 2 ) DESTINATIONS OF LIGHT ENDS
a ) vent or flare stacks - if light ends have very little value.
b ) fuel - if light ends are flammable.
c ) vapor recovery system - if light ends are valuable.
3 ) AZEOTROPES WITH REACTANTS
4 ) APPLICABILITY OF DISTILLATION
5 ) SEQUENCING OF SIMPLE COLUMNS
6 ) COMPLEX COLUMNS

12. Purge Compressor H2, CH4 Reactor Flash Toluene Benzene H2, CH4 Recycle
Product
Stablizer
Diphenyl

13. Run ASPEN PLUS to obtain M&E balance data !
Process Simulation
Run ASPEN PLUS to obtain M&E balance data !

14. ECONOMIC POTENTIAL AT LEVEL 4
EP4 = EP3 - annual purge loss - annualized distillation costs
- annualized vapor recovery costs
2106
1106
$/yr
-1106
-2106
-3106
0.2
0.4
0.6

15. 2 ) DESTINATION OF LIGHT ENDS
a ) vent or flare stacks - if light ends have very little value.
b ) fuel - if light ends are flammable.
c ) vapor recovery system - if light ends are valuable.
3 ) AZEOTROPES WITH REACTANTS
4 ) APPLICABILITY OF DISTILLATION
5 ) SEQUENCING OF SIMPLE COLUMNS
6 ) COMPLEX COLUMNS

16. A B C
Design 1 : Direct Sequence

17. A C B
Design 2 : Indirect Sequence

18. A B C
Design 3 : Side-stream rectifier

19. A B C
Design 4 : Side-stream Stripper

20. Prefractionator arrangement
A , B B
B , C C
Design 5
Prefractionator arrangement

21. A A B B C C
Design Design 7
side stream