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
COUNTERCURRENT MULTISTAGE EXTRACTION
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
Some Fatty Acids
Linoleic acid C17H31COOH, MW: 280,44
Linolenic acid C17H29COOH, MW: 278,42
Arachidonic acid C19H31COOH, MW: 304,46
Fatty Acid Content of Some Natural Materials
Spezies
Fatty acids in weight-percent
-Linolenic acid
EPA
C18:3
C20:5
DPA
C22:5
DHA
C22:6
Plants
Flax
Soya
Thistle
50
8
9
-------
-------
-------
Algae
Amphidinium carterri
Dunaliella primolecta
Cryptomonas sp.
0,1
10,4
7,0
7,4
9,7
16,0
0,6
3,9
---
25,4
--10,0
Fish
Mackerel
Codfish
Sardine
Thuna fish
Herring
1,48
0,92
----1,15
14,16
6,00
18,08
4,9
4,28
2,82
2,4
2,16
1,2
0,74
10,26
7,62
10,25
27,7
4,06
Analysis and Pseudo Components of Fish Oil FA I
Component
C14:0
C16:4n-1
C16:1n-7
C16:3n-3
C16:0
C18:4n-3
Feed
[A-%]
7,22
0,13
0,19
0,48
2,89
1,73
9,17
1,12
0,38
16,13
0,41
0,21
0,17
0,41
0,13
0,33
3,12
1,44
Gas phase
[A -%]
12,21
0,22
0,31
0,70
3,84
2,28
11,82
1,45
0,48
19,81
0,49
0,24
0,19
0,43
0,12
0,33
3,09
1,39
Liquid phase
[A -%]
6,91
0,12
0,19
0,47
2,83
1,69
8,98
1,10
0,38
15,85
0,41
0,20
0,17
0,40
0,12
0,33
3,11
1,44
Ki
[-]
1,77
1,83
1,63
1,49
1,36
1,35
1,32
1,32
1,26
1,25
1,20
1,20
1,12
1,08
1,00
1,00
0,99
0,97
Pseudocomponent
C14
C16
Analysis and Pseudo Components of Fish Oil FA II
C18:1n-9
C18-0
C20:4n-6
C20:5n-3
C20:4n-3
C20:1n-11
C20:0
C21:5n-3
C22:6n-3
C22:4n-6
C22:5n-3
C22:1n-11
C22:0
C24:1
10,12
3,05
0,44
0,12
3,17
1,00
18,07
0,24
1,01
0,27
0,69
0,30
0,23
0,22
0,74
0,37
10,26
0,12
2,17
0,36
0,09
0,38
99,08
9,62
2,86
0,40
0,10
2,81
0,73
13,51
0,13
0,69
0,17
0,46
0,20
0,15
0,14
0,49
0,18
5,81
1,19
0,15
0,12
99,31
10,11
3,05
0,43
0,12
3,17
1,02
18,30
0,23
1,03
0,26
0,69
0,31
0,17
0,23
0,76
0,40
10,52
0,14
2,23
0,38
0,09
0,40
98,74
0,95
0,94
0,93
0,83
0,89
0,72
0,74
0,57
0,67
0,65
0,67
0,65
0,88
0,61
0,64
0,45
0,55
C18
C20
0,53
0,39
0,30
C22
Triglycerides
P = Palmitic acid
O = Oleic acid
S = Stearic acid
Triglycerides
Fatty Acids Glycerol
Triglycerides
s
Transformation of Triglycerides
Hydrolysis,
Saponification
Glycerolysis
Methanolysis
Interesterification
Reduction
Countercurrent multistage processing
Characteristics:
Binary separation
Reflux
Enriching section
Stripping section
Supercritical solvent
cycle
Definition of the separation problem
COMPOSITION OF PRODUCTS
YIELD
FEED QUANTITY
COMPOSITION OF FEED
PHASE EQUILIBRIA:
(EXPERIMENT; CORRELATING)
SEPARATION FACTORS
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
Limiting Phase Equilibrium
Maximum concentration
in a
countercurrent process
Phase equilibrium: PUFA - CO2
Separation PUFA - CO2-Propane
Separation factor for FAEE in sc CO2
14 MPa
333 K
Ethyl ester in gas [wt.-%]
P,x - Diagramm PUFA- Feed - CO2
Density of Coexisting Phases
% C20:
EE1:
3.3
EE10: 91.6
EE 13: 9.5 +
90.5 % C 22
Equilibrium Calculations: Fundamental Equation
Ki
 ij 
.
Kj
V
L
fi
fi
L
 
; i 
.
yi P
xi P
V
i
yi  iL
Ki   V .
xi  i
1  P 
RT 




ln  i  

d V  ln z.



R T   ni T ,V ,n
V 
j i


V
Equilibrium Calculations: Cubic EOS (RK-type), Mixing Rule a
RT
am (T )
P

,
V  bm V (V  bm )
N
N

am T    xi x j aij
0.5

,
1
1
aij  aii a jj  1  kij 
0.5
or
a  aii a jj 

ij
0.5




x
i
k  k 
 .
ij
ij



x

x
j
i



Equilibrium Calculations: Mixing Rule b,
bm   xi x j bij 
N
N
i 1 j 1
with
bij  0.5bii  b jj 1  lij .

 

1 N exp
calc 2
exp
calc 2
   xi  xi
 yi  yi
,
N i 1
  min .
Separation factor: Concentration Dependence
FA-ethyl esters - CO2
2,0
1,9
T = 60 °C
p = 12 MPa
p = 14 MPa
p = 16 MPa
Riha 1996
1,8
1,7
 [-]
1,6
1,5
1,4
1,3
1,2
1,1
1,0
0,0
0,2
0,4
0,6
0,8
x (C14..C18) [wt.-fraction]
1,0
Design Methods For Number of Theoretical Stages
McCabe-Thiele
Analysis
Ponchon-Savarit in a
Jänecke-Diagram
Simulation
CC-GE: Basic Equations
Mass balances:
d Li d Vi

 0,
dz dz
Enthalpy balances:
Equilibrium relations:
L
i
 L,
V
d H i L  d H V V 

 q  0.
dz
dz
Ki V
Vi 
Li .
L

Rate equations for mass transfer:


dVi kG i a P

Vi  Vi ,
dz
V
i
V .
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.
Mc- Cabe-Thiele Analysis
Equilibrium
y1  f  x1 .
y1 
12 x1
.
1  12  1 x1


y1 p  Lp1 / Vp  x1 p1  Vn y1n  Rn x1R / Vp .
VF y1  LF x1  F x1 F .




y1 p  Lp 1 / Vp x1 p 1  S0 y1S  L1 x11 / Vp .




0

n
Minimum number of stages / mimimum reflux ratio
Limiting conditions
PUFA - separation: n-min, v-min
Jänecke - diagram for sc solvent
Countercurrent- Extraction in a Jänecke - Diagram
PUFA - separation: Jänecke analysis
Separation Analysis
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.
Scheme of Stage Calculations
Vip 
K ip V p
Lp
Lip .
Ki  yi / xi .
K i  f P, T , xi , x j , yi , y j .
Lip  Vip  Li , p 1  Vi , p 1  Fip  0,
 Lip  Lp
and
i
Vip  V p .
i
Lp H L  V p HV  Lp1 H L  V p1 HV  Fp H F  q p  0 ,
p
p
p 1
p1
p
Experimental Verfication in a Laboratory Plant
PUFA - Separation: C16 - C18
Van Gaver
PUFA- Separation: C18: sat. / unsaturated
Van Gaver
HETP, HTU
FA-ethyl esters - CO2
Riha 1996
HETP  h / nth
h  HTU  NTU ,
yo
NTU  
yi
dy
,

y y
Vv
HTU 
.
k aF
CO2-Kreislauf
C14..C18
Rücklauf
C20 +C22
Rücklauf
Fischölesterfeed
C20..C24 + Rest
C24 + Rest
Kolonnenschaltung zur Gewinnung einer PUFAFraktion
Separation routes for n3 fatty acids (as esters)
Feed
AgNO3
Distillation
Urea
SFE-Countercurrent Extraction
EPA 44 wt.-%
EPA 73 wt.-%
EPA 92 wt.-%
DHA 42 wt.-%
DHA 85 wt.-%
DHA 90 wt.-%
Chromatographic Separation Processes, SFC
EPA > 95 wt.-%
DPA > 95 wt.-%
DHA > 95 wt.-%
Solexol - Process with near critical propane
IEC 41:280, 1949
Multistage cc separation of n3- FAEE
Krukonis 1988
Multistage cc separation of n3- FAEE
THEORY
Krukonis 1988
Multistage cc separation of n3- FAEE
THEORY
Krukonis 1988
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)
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