Solvent Cycle,

Methods for Solute Precipitation

Heat and Mass Transfer:

High Pressure chemical Engineering I (WS)

Chapter 7

Flow Scheme of a Solvent Cycle

Solvent Cycle Steps:

separate the extract from the solvent (1),

clean the solvent for reuse (2),

remove the solvent from raffinate (3),

adjust composition of solvent mixture (if applicable) (4).

Solvent Cycle

Single stage Multiple stage Counter- Chromato- (precipitation) current graphic

SFE Modes of Operation

Extraction From Solids

S t S / F

Essential oils (5 %) 20 < 1 > 20

Edible oils (2 %) 40 < 1 40

Coffee decaffeination (0.01 %) 200 5 40

Black tea decaff. (0.01 %) 230 1.5 150

Total amount of solvent S, kg/kgF

Extraction time t, h

Solvent to Feed Ratio S/F, kgS /(kgF h)

Basis:

Solvent: Carbon dioxide

10 - 30 MPa, 330 K

Solvent Cycle: Solvent to feed ratio of SFE processes

Countercurrent Separation

V/L v S / F

FAEE, FAME (5 %) 20 7.5 125

FFA (fatty acids) (2 %) 50 4.5 50

Squalene (1.5 %) 20 10 50

Tocopherol-Purif. (2.5 %) 35 20 45Solvent ratio V/L, kg/kg

Reflux ratio v, -

Solvent to feed ratio S/F, kgF /kgF

Basis:

Solvent: Carbon dioxide

10 - 30 MPa, 350 K

Solvent Cycle: Solvent to feed ratio of SFE processes

Chromatographic Separation

Pr tr S / F

DHA / DPA 1.5 15 900 x 103 EM

Phytol-isomers 10- 30 6 900 EM 200 SMB

Productivity Pr, gP /(kgStPh h)

Retention time, min

Solvent to feed ratio S/F, kgF /kgF

Basis:

Solvent: Carbon dioxide

10 - 30 MPa, 310 K

Solvent Cycle: Solvent to feed ratio of SFE processes

Reduction of pressure or density

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

......

Modes For Product Recovery

300 400 500 600 700 800 90010

100

1000

T = 313 K

T = 318 K

T = 333 KSol

ubili

ty [

mg/

kg C

O2]

Density [kg/m3]Birtigh, Brunner, Johannsen

Solubility of Caffeine in CO2

Gas Circuit in the Compressor Mode

Compressor Process, Throttling Sub-Critical

Compressor Process, Throttling Super- Critical

Pump Process

Pump Process, Throttling, Sub-Critical

Pump Process, Throttling Super- Critical

Extraction temperature: 313 K

Energy Consumption by Various Solvent Cycles

Mechanical EnergyThermal energy inThermal energy out

Pump with heat recovery

Pump without heat recovery

Compressor with heat recovery

Compressor without heat recovery

Ex

tra

cti

on

pre

ss

ure

[M

Pa

]

Energy [kJ/kg]

Energy needed for the gas cycle

70 kJ/kgCO2

95 kJ/kgCO2

for S/F 125 kg/kg:

8750 kJ/kgFeed

11875 kJ/kgFeed

Reduction of pressure or density (temperature)

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

Modes For Product Recovery

Brunner 1983

Solubility in a Gas With a Modifier (Entrainer)

Influence of temperature

Data by:Gährs 1984Ebeling, Franck 1984Johannsen, Brunner 1994

Solubility of Caffeine in CO2

Reduction of pressure or density

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

......

Modes For Product Recovery

Gährs 1984

Anti-Solvent: Solubility of Caffeine in CO2

Influence of nitrogen

Reduction of pressure or density

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

......

Modes For Product Recovery

PC

WT2

1

PC

P1

B1

RV3

PC

WT1 K1

RV1

RV2

M1

18 MPa323 K

P = 2 MPa

Coupling with a Membrane Unit

Solvent Cycle With Membrane Separation

GKSS-membrane (organic, active dense layer)

CO2

OC

Permeate

Retentate

1.86 wt.-%

< 0.06 wt.-%

p = 2.0 MPa

active dense layer

1.5 mole CO2

kg/(m2 h)

P = 18 MPa, T = 323 K

Separation by Membranes

Solvent Cycle in a T,s - Diagram

Extraction/separation

Precipitation athigh p

Precipitation atlow p

Compressor mode

Entropy

Te

mp

era

ture

CO 2

53 kJ/ kgCO2

21 kJ/ kgCO2

7.6 kJ/ kgCO2

1

2

3

Wie in 2Like in 2

Energy For Different Solvent Cycles

Pump-Cycle

Compressor-Cycle

Membrane-Cycle

Sartorelli 2001

Reduction of pressure or density

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

......

Modes For Product Recovery

0 100 200 300 400 500 600 700 800

Y [mg/kg CO 2]

0

0.1

0.2

0.3

0.4

0.5X

[k

g/kg

AC

]

T=318 KP=13 MPaP=20 MPaP=30 MPaP=13 MPa LangmuirP=20 MPa LangmuirP=30 MPa Langmuir

Adsorption of Caffeine on Activated Carbon

Silica with 52% loading,loaded by high pressure

adsorption

Silica with 50% loading, loaded by mixing,

conventional process

Recovery of Tocopherolacetate by Adsorption

200 250 300 350 400 450 500 550 600

40

45

50

55

60

autoclave: 333K, 20MPafixed bed adsorber: 353Kflow: 20g

solvent/min

feed in autoclave: TA ca. 97 wt.-% TA ca. 73 wt.-%

Load

ing

of a

dsor

bate

[wt.-

%]

Density CO

2

[kg/m3]

Recovery of Tocopherolacetate by Adsorption

Reduction of pressure or density

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

......

Modes For Product Recovery

100 1000 10000

10

100

1000

P = 19 MPa

T = 343,1 K

T = 323,1 K

P = 28 MPa

T = 343,1 K

Caf

fein

e Lo

adin

g in

SC

F P

hase

[mg/

kg]

Caffeine Loading in Water Phase [mg/kg]

Phase Equilibrium Caffeine - Water - CO2

Reduction of pressure or density

Anti solvent

Membrane separation

Adsorption

Absorption

De-Entrainment

......

Modes For Product Recovery

Brunner 1983

Solubility in a Gas With a Modifier (Entrainer)

Influence of temperature

0 0.05 0.1 0.15 0.2 0.25 0.3

mwater / mtotal

00.10.20.30.40.50.60.70.8

toco

chro

man

ol fr

actio

n

in fl

uid

phas

e [m

ass%

]

solubility tocochromanol in CO2

Figure 4:Tocochromanol fraction in SCF phase as function of the total water fraction

Birtigh

De-Entrainment

Generalization of Precipitation: Membership - Functions

Temperature at the Swimming Pool

T [oC] x25 35 450

1

(x)

„Hot“Not yet hot Too hot

(x): relative number of statements from people at the pool

0 1 2

0.1 0.5 0.9 0.2 0.9 1.6

1 4 7

Molar weight solute [kg/mol]

Loading

Reduced Pressure

Residence time [min]

fluid phase [wt%]

0.0

0.5

1.0

0.0

0.5

1.0

0 1 20.0

0.5

1.0

0.0

0.5

1.0

0.0

0.5

1.0

1 4 70.0

0.5

1.0

0.0 0.5 1.00.0

0.5

1.0

Inlet loading

Solubility in separator1 10 100

0.0

0.5

1.0

2

0 3 60.0

0.5

1.0

Inlet loading

Solubility in extractor

Birtigh

Membership Functions P Adsorption Membrane

Solubility of solute

Residence time

Solvent ratio

0.0 0.1 0.2

Absorbent

0.0 0.05 0.100.0

0.5

1.0

0.0 0.05 0.10.0

0.5

1.0

0.0

0.5

1.0

0.0 0.05 0.1

in water [g/g]

0.0

0.5

1.0

0.0 0.5 1.0

Inlet loadingSolubility in Separator

1 10 1000.0

0.5

1.0

21 10 1000.0

0.5

1.0

2 1 10 1000.0

0.5

1.0

2

TSeparator

TDecomposition

0.0

0.5

1.0

0.0 0.2 0.4

0 3 60.0

0.5

1.0

0 3 60.0

0.5

1.0

0 3 60.0

0.5

1.0

0 3 60.0

0.5

1.0

0.0

0.5

1.0

0.0 0.1 0.20.0

0.5

1.0

Reduced pressure

1 3 50.0

0.5

1.0 if only 1 phase in Extractor

0.0

0.5

1.0

0.0 0.2 0.4

[min]

if 2 phases in Extractor

Absorption De-Entrain T T

Birtigh

Membership Functions