1. COUNTERCURRENT MULTISTAGE EXTRACTION
Chapter 5
COUNTERCURRENT MULTISTAGE EXTRACTION
(using supercritical fluids)
What for?
Separation of compounds,
mostly liquid,
of similar volatility
Why supercritical fluids?
Low temperature
Solvent free products
Multistage countercurrent separation
Better and new products

2. COUNTERCURRENT MULTISTAGE EXTRACTION Separation of n-3 Fatty acids
Example:
Separation of n-3 Fatty acids
derived from fish oil
EPA C20 with 5 double bonds
DHA C22 with 6 double bonds
DPA C22 with 5 double bonds
EPA: Eicosapentanoic acid
DPA: Docosapentanoic acid
DHA: Docosahexanoic acid

3. Some Fatty Acids Linoleic acid C17H31COOH, MW: 280,44
Linolenic acid C17H29COOH, MW: 278,42
Arachidonic acid C19H31COOH, MW: 304,46

4. Fatty Acid Content of Some Natural Materials
Fatty acids in weight-percent Spezies -Linolenic acid EPA DPA DHA
C18: C20: C22: C22:6
Plants Flax
Soya
Thistle
Algae Amphidinium carterri 0, , ,6 25,4
Dunaliella primolecta 10, , ,9 ---
Cryptomonas sp. 7, , ,0
Fish Mackerel 1, , ,82 10,26
Codfish 0, , ,4 7,62
Sardine , ,16 10,25
Thuna fish , ,2 27,7
Herring 1, , ,74 4,06

5. Analysis and Pseudo Components of Fish Oil FA I
Component Feed Gas phase Liquid phase Ki Pseudo component
[A-%] [A -%] [A -%] [-]
C14:0 7, ,21 6, ,77
0, , , ,83
0, ,31 0, ,63
0, ,70 0, , C14
C16:4n-1 2, ,84 2, ,36
1, ,28 1, ,35
C16:1n-7 9, ,82 8, ,32
C16:3n-3 1, ,45 1, ,32
0, ,48 0, ,26
C16:0 16, ,81 15, ,25
0, ,49 0, ,20
0, ,24 0, ,20
0, ,19 0, ,12
0, ,43 0, , C16
0, ,12 0, ,00
0, ,33 0, ,00
C18:4n-3 3, ,09 3, ,99
1, ,39 1, ,97

6. Analysis and Pseudo Components of Fish Oil FA II
C18:1n-9 10, ,62 10, ,95
3, ,86 3, ,94
0, ,40 0, ,93
0, ,10 0, ,83
C , ,81 3, ,89 C18
C20:4n-6 1, ,73 1, ,72
C20:5n-3 18, , , ,74
0, ,13 0, ,57
C20:4n-3 1, ,69 1, ,67
0, ,17 0, ,65
C20:1n-11 0, ,46 0, ,67
0, ,20 0, ,65
0, ,15 0, ,88
C20:0 0, ,14 0, ,61
C21:5n-3 0, ,49 0, ,64 C20
0, ,18 0, ,45
C22:6n-3 10, ,81 10, ,55
C22:4n-6 0,12 0,14
C22:5n-3 2, ,19 2, ,53
C22:1n-11 0, ,15 0, ,39
C22:0 0,09 0,09
C24:1 0, ,12 0, ,30 C22
99, ,31 98,74

7. Triglycerides
P = Palmitic acid
O = Oleic acid
S = Stearic acid

8. Fatty Acids Glycerol Triglycerides

9. Transformation of Triglycerides
Hydrolysis, Saponification
Glycerolysis
Methanolysis
Interesteri-
fication
Reduction

10. Countercurrent multistage processing
Characteristics:
Binary separation
Reflux
Enriching section
Stripping section
Supercritical solvent
cycle

11. COMPOSITION OF PRODUCTS YIELD FEED QUANTITY COMPOSITION OF FEED
Definition of the separation problem
COMPOSITION OF PRODUCTS
YIELD
FEED QUANTITY
COMPOSITION OF FEED
PHASE EQUILIBRIA:
(EXPERIMENT; CORRELATING)
SEPARATION FACTORS

12. COUNTERCURRENT MULTISTAGE EXTRACTION
Definition of Task
COUNTERCURRENT MULTISTAGE EXTRACTION
Determine:
Number of theoretical stages
(or number of transfer units).
Height (Size) of a separation device
Separation performance (Mass Transfer)
Capacity of a separation device
Throughput -----> diameter

13. Maximum concentration in a countercurrent process
Limiting Phase Equilibrium
Maximum concentration
in a
countercurrent process

14. Phase equilibrium: PUFA - CO2

15. Separation PUFA - CO2-Propane

16. Separation factor for FAEE in sc CO2
14 MPa
333 K
Separation factor 
Ethyl ester in gas [wt.-%]

17. P,x - Diagramm PUFA- Feed - CO2

18. Density of Coexisting Phases
EE1:
EE10: 91.6
EE 13: 9.5 +
90.5 % C 22

19. Equilibrium Calculations: Fundamental Equation

20. Equilibrium Calculations: Cubic EOS (RK-type), Mixing Rule a

21. Equilibrium Calculations: Mixing Rule b,

22. Separation factor: Concentration Dependence
FA-ethyl esters - CO2
Riha 1996

23. McCabe-Thiele Analysis
Design Methods For Number of Theoretical Stages
McCabe-Thiele Analysis
Ponchon-Savarit in a
Jänecke-Diagram
Simulation

24. CC-GE: Basic Equations
Mass balances:
Enthalpy balances:
Equilibrium relations:
Rate equations for mass transfer:

25. with:
z = axial coordinate in the separation device;
Li, Vi = flow of component i in the liquid and gaseous
phase;
L, V = total flow of liquid and gaseous phase;
HV, HL = enthalpy of gaseous and liquid phase;
kGi = mass transfer coefficient of component i, related
to the gaseous phase;
a = mass transfer area per volume of transfer
device;
P = total pressure;
Ki = equilibrium partition coefficient of component i
between gaseous and liquid phase;
Vi* = equilibrium concentration of component i in the
gaseous phase.

26. Mc- Cabe-Thiele Analysis
Equilibrium

27. Minimum number of stages / mimimum reflux ratio
Limiting conditions

28. PUFA - separation: n-min, v-min

29. Jänecke - diagram for sc solvent

30. Countercurrent- Extraction in a Jänecke - Diagram

31. PUFA - separation: Jänecke analysis

32. Separation Analysis

33. Simulation of the separation Select method: nth or NTU
Determine min. reflux, min. nth or NTU
Vary reflux-ratio;
Calculate separation as function of nth or NTU
Calculate nth or NTU as function of separation
Determine concentration profiles.

34. Scheme of Stage Calculations

35. Experimental Verfication in a Laboratory Plant

36. PUFA - Separation: C16 - C18
Van Gaver

37. PUFA- Separation: C18: sat. / unsaturated
Van Gaver

38. HETP, HTU
FA-ethyl esters - CO2
Riha 1996

39. Kolonnenschaltung zur Gewinnung einer PUFA-Fraktion

40. Separation routes for n3 fatty acids (as esters)
Feed
AgNO3
Urea
Distillation
SFE-Countercurrent Extraction
EPA 92 wt.-%
DHA 90 wt.-%
EPA 44 wt.-%
DHA 42 wt.-%
EPA 73 wt.-%
DHA 85 wt.-%
Chromatographic Separation Processes, SFC
EPA > 95 wt.-%
DPA > 95 wt.-%
DHA > 95 wt.-%

41. Solexol - Process with near critical propane
IEC 41:280, 1949

42. Multistage cc separation of n3- FAEE
Krukonis 1988

43. Multistage cc separation of n3- FAEE
THEORY
Krukonis 1988

44. Multistage cc separation of n3- FAEE
THEORY
Krukonis 1988

45. SOLVING A MULTICOMPONENT SEPARATION IN CC-GE Define the mixture:
Summary and Design Procedure
SOLVING A MULTICOMPONENT SEPARATION
IN CC-GE
Define the mixture:
components or pseudo-components
Define the separation:
identify key components,
purity and recovery rate
Determine separation performance:
(as a function of reflux ratio):
number of theoretical stages (n ) or
number of transfer units (NTU)

46. Determine efficiency of mass transfer equipment:
Summary and Design Procedure
Determine efficiency of mass transfer equipment:
tray efficiency, or HETP, or HTU
Determine limits for mass flow
of countercurrent streams:
maximum flow (entrainment, flooding)
minimum flow (for effective mass transfer)
Decide for a certain reflux ratio
Calculate separation performance
size of a column
for the chosen equipment and operating conditions