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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.

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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

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 25,4

Dunaliella primolecta 10,4 9,7 3,9 ---

Cryptomonas sp. 7,0 16,0 --- 10,0

Fish Mackerel 1,48 14,16 2,82 10,26

Codfish 0,92 6,00 2,4 7,62

Sardine --- 18,08 2,16 10,25

Thuna fish --- 4,9 1,2 27,7

Herring 1,15 4,28 0,74 4,06


Analysis and Pseudo Components of Fish Oil FA I

Component Feed Gas phase Liquid phase KiPseudo- component

[A-%] [A -%] [A -%] [-]

C14:0 7,22 12,21 6,91 1,77

0,13 0,22 0,12 1,83

0,19 0,31 0,19 1,63

0,48 0,70 0,47 1,49 C14

C16:4n-1 2,89 3,84 2,83 1,36

1,73 2,28 1,69 1,35

C16:1n-7 9,17 11,82 8,98 1,32

C16:3n-3 1,12 1,45 1,10 1,32

0,38 0,48 0,38 1,26

C16:0 16,13 19,81 15,85 1,25

0,41 0,49 0,41 1,20

0,21 0,24 0,20 1,20

0,17 0,19 0,17 1,12

0,41 0,43 0,40 1,08 C16

0,13 0,12 0,12 1,00

0,33 0,33 0,33 1,00

C18:4n-3 3,12 3,09 3,11 0,99

1,44 1,39 1,44 0,97


Analysis and Pseudo Components of Fish Oil FA II

C18:1n-9 10,12 9,62 10,11 0,95

3,05 2,86 3,05 0,94

0,44 0,40 0,43 0,93

0,12 0,10 0,12 0,83

C18-0 3,17 2,81 3,17 0,89 C18

C20:4n-6 1,00 0,73 1,02 0,72

C20:5n-3 18,07 13,51 18,30 0,74

0,24 0,13 0,23 0,57

C20:4n-3 1,01 0,69 1,03 0,67

0,27 0,17 0,26 0,65

C20:1n-11 0,69 0,46 0,69 0,67

0,30 0,20 0,31 0,65

0,23 0,15 0,17 0,88

C20:0 0,22 0,14 0,23 0,61

C21:5n-3 0,74 0,49 0,76 0,64 C20

0,37 0,18 0,40 0,45

C22:6n-3 10,26 5,81 10,52 0,55

C22:4n-6 0,12 0,14

C22:5n-3 2,17 1,19 2,23 0,53

C22:1n-11 0,36 0,15 0,38 0,39

C22:0 0,09 0,09

C24:1 0,38 0,12 0,40 0,30 C22

99,08 99,31 98,74


Triglycerides

P = Palmitic acid

O = Oleic acid

S = Stearic acid


Triglycerides

Fatty Acids Glycerol Triglycerides

s


Transformation of Triglycerides

Hydrolysis, Saponification

Glycerolysis

Methanolysis

Interesteri-

fication

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




    Separation factor for FAEE in sc CO2

    14 MPa

    333 K

    Separation factor 

    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





    Separation factor: Concentration Dependence

    FA-ethyl esters - CO2

    Riha 1996


    Design Methods For Number of Theoretical Stages

    McCabe-Thiele Analysis

    Ponchon-Savarit in a

    Jänecke-Diagram

    Simulation


    CC-GE: Basic Equations

    Mass balances:

    Enthalpy balances:

    Equilibrium relations:

    Rate equations for mass transfer:


    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.









    • 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.






    HETP, HTU

    FA-ethyl esters - CO2

    Riha 1996



    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.-%






    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


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