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 Chapter 5
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COUNTERCURRENT MULTISTAGE EXTRACTION (using supercritical fluids) What for? Separation of compounds, mostly liquid, of similar volatility Why supercritical.
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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
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)