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