COUNTERCURRENT MULTISTAGE EXTRACTION
(using supercritical fluids)What for?
Separation of compounds,mostly liquid,
of similar volatility
Why supercritical fluids?
Low temperatureSolvent free products
Multistage countercurrent separationBetter and new products
Chapter 5
Example:
Separation of n-3 Fatty acids derived from fish oil
EPA C20 with 5 double bondsDHA C22 with 6 double bondsDPA C22 with 5 double bonds
EPA: Eicosapentanoic acid DPA: Docosapentanoic acid DHA: Docosahexanoic acid
COUNTERCURRENT MULTISTAGE EXTRACTION
Linoleic acid C17H31COOH, MW: 280,44
Linolenic acid C17H29COOH, MW: 278,42
Arachidonic acid C19H31COOH, MW: 304,46
Some Fatty Acids
Fatty acids in weight-percent Spezies -Linolenic acid EPA DPA DHA
C18:3 C20:5 C22:5 C22:6
Plants Flax 50 --- --- ---Soya 8 --- --- ---Thistle 9 --- --- ---
Algae Amphidinium carterri 0,1 7,4 0,6 25,4Dunaliella primolecta 10,4 9,7 3,9 ---Cryptomonas sp. 7,0 16,0 --- 10,0
Fish Mackerel 1,48 14,16 2,82 10,26Codfish 0,92 6,00 2,4 7,62Sardine --- 18,08 2,16 10,25Thuna fish --- 4,9 1,2 27,7Herring 1,15 4,28 0,74 4,06
Fatty Acid Content of Some Natural Materials
Component Feed Gas phase Liquid phase Ki Pseudo-
component[A-%] [A -%] [A -%] [-]
C14:0 7,22 12,21 6,91 1,770,13 0,22 0,12 1,830,19 0,31 0,19 1,630,48 0,70 0,47 1,49 C14
C16:4n-1 2,89 3,84 2,83 1,361,73 2,28 1,69 1,35
C16:1n-7 9,17 11,82 8,98 1,32C16:3n-3 1,12 1,45 1,10 1,32
0,38 0,48 0,38 1,26C16:0 16,13 19,81 15,85 1,25
0,41 0,49 0,41 1,200,21 0,24 0,20 1,200,17 0,19 0,17 1,120,41 0,43 0,40 1,08 C160,13 0,12 0,12 1,000,33 0,33 0,33 1,00
C18:4n-3 3,12 3,09 3,11 0,991,44 1,39 1,44 0,97
Analysis and Pseudo Components of Fish Oil FA I
C18:1n-9 10,12 9,62 10,11 0,95 3,05 2,86 3,05 0,940,44 0,40 0,43 0,930,12 0,10 0,12 0,83
C18-0 3,17 2,81 3,17 0,89 C18C20:4n-6 1,00 0,73 1,02 0,72C20:5n-3 18,07 13,51 18,30 0,74
0,24 0,13 0,23 0,57C20:4n-3 1,01 0,69 1,03 0,67
0,27 0,17 0,26 0,65C20:1n-11 0,69 0,46 0,69 0,67
0,30 0,20 0,31 0,650,23 0,15 0,17 0,88
C20:0 0,22 0,14 0,23 0,61C21:5n-3 0,74 0,49 0,76 0,64 C20
0,37 0,18 0,40 0,45C22:6n-3 10,26 5,81 10,52 0,55C22:4n-6 0,12 0,14C22:5n-3 2,17 1,19 2,23 0,53C22:1n-11 0,36 0,15 0,38 0,39C22:0 0,09 0,09C24:1 0,38 0,12 0,40 0,30 C22
99,08 99,31 98,74
Analysis and Pseudo Components of Fish Oil FA II
Triglycerides
P = Palmitic acid
O = Oleic acid
S = Stearic acid
Fatty Acids Glycerol Triglycerides
Triglycerides
s
Hydrolysis, Saponification
Glycerolysis
Methanolysis
Interesteri-
fication
Reduction
Transformation of Triglycerides
Countercurrent multistage processing
Characteristics:
Binary separation
Reflux
Enriching section
Stripping section
Supercritical solvent cycle
COMPOSITION OF PRODUCTS YIELD
FEED QUANTITY
COMPOSITION OF FEED
PHASE EQUILIBRIA: (EXPERIMENT; CORRELATING)
SEPARATION FACTORS
Definition of the separation problem
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
Definition of Task
Maximum concentration in a
countercurrent process
Limiting Phase Equilibrium
Phase equilibrium: PUFA - CO2
Separation PUFA - CO2-Propane
Se
pa
rati
on
fa
cto
r
Ethyl ester in gas [wt.-%]
14 MPa
333 K
Separation factor for FAEE in sc CO2
P,x - Diagramm PUFA- Feed - CO2
% C20:
EE1: 3.3
EE10: 91.6
EE 13: 9.5 +
90.5 % C 22
Density of Coexisting Phases
Equilibrium Calculations: Fundamental Equation
.lndR
R
1ln
,,
zVV
T
n
P
T
V
nVTii
ij
.
.;
.
Vi
Li
i
ii
i
LiL
ii
ViV
i
j
iij
x
yK
Px
f
Py
f
K
K
PT
V b
a T
V V bm
m
m
R ( )
( ),
.
or
1
,
5.0
5.0
5.0
1 1
ji
iijijjjiiij
ijjjiiij
N N
ijjim
xx
xkkaaa
kaaa
axxTa
Equilibrium Calculations: Cubic EOS (RK-type), Mixing Rule a
.15.0
with
1 1
ijjjiiij
N
i
N
jijjim
lbbb
bxxb
.min
,1
1
2calcexp2calcexp
N
iiiii yyxx
N
Equilibrium Calculations: Mixing Rule b,
0,0 0,2 0,4 0,6 0,8 1,01,0
1,1
1,2
1,3
1,4
1,5
1,6
1,7
1,8
1,9
2,0
T = 60 °C p = 12 MPa p = 14 MPa p = 16 MPa
[-
]
x (C14..C18) [wt.-fraction]
FA-ethyl esters - CO2
Riha 1996
Separation factor: Concentration Dependence
Design Methods For Number of Theoretical Stages
McCabe-Thiele Analysis
Ponchon-Savarit in a Jänecke-Diagram
Simulation
Mass balances:
Enthalpy balances:
Equilibrium relations:
Rate equations for mass transfer:
,0d
d
d
d
z
V
z
L ii ., VVLL ii
.0
d
d
d
d q
z
VH
z
LH Vi
.ii
i LL
VKV
,d
d iiiGi VVV
Pak
z
V
CC-GE: Basic Equations
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.
.f 11 xy
.11 112
1121 x
xy
.// 111111 pRnnnpppp VxRyVxVLyn
.// 111101111 0
pSppppVxLySxVLy
.111 FFF xFxLyV
Equilibrium
Mc- Cabe-Thiele Analysis
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.
.ipp
pipip L
L
VKV
,01,1, ippipiipip FVLVL
.andi
pippi
ip VVLL
,011 11
pFpVpLpVpLp qHFHVHLHVHLppppp
./ iii xyK
.,,,,,f jijii yyxxTPK
Scheme of Stage Calculations
Experimental Verfication in a Laboratory Plant
Van Gaver
PUFA - Separation: C16 - C18
Van Gaver
PUFA- Separation: C18: sat. / unsaturated
thnhHETP /
.
,d
,
Fak
VHTU
yy
yNTU
NTUHTUh
v
y
y
o
i
FA-ethyl esters - CO2
Riha 1996
HETP, HTU
C14..C18
Rücklauf
Fischöl-
esterfeed
C20 +C22
C24 + Rest
C20..C24 + Rest
CO2-Kreislauf
Rücklauf
Kolonnenschaltung zur Gewinnung einer PUFA-Fraktion
Feed
Distillation SFE-Countercurrent Extraction
AgNO3 Urea
EPA 44 wt.-%
DHA 42 wt.-%
EPA 73 wt.-%
DHA 85 wt.-%
EPA 92 wt.-%
DHA 90 wt.-%
Chromatographic Separation Processes, SFC
EPA > 95 wt.-% DPA > 95 wt.-% DHA > 95 wt.-%
Separation routes for n3 fatty acids (as esters)
Solexol - Process with near critical propane
IEC 41:280, 1949
Multistage cc separation of n3- FAEE
Krukonis 1988
Multistage cc separation of n3- FAEE
Krukonis 1988
THEORY
Krukonis 1988
THEORY
Multistage cc separation of n3- FAEE
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 ) ornumber 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
Summary and Design Procedure