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Extraction Technology

Extraction Process

Figure 8.1 Typical liquid-liquid extraction process.

Typical Extractor Heavy Phase

In

Heavy Phase Out

Light Phase Out

Light Phase In

Heavy Phase Out

Light Phase OutHeavy Phase

In

Light Phase In

Light Phase Dispersed Heavy Phase Dispersed

Typical Extractor

Feed In

Raffinate Out

Extract Out

Solvent In

Light Phase Dispersed

Liquid-liquid Equilibrium

Ii

IIi

IIi

Ii

IIii

Iii

IIi

vapii

Ii

vapii

IIi

Ii

xx

xx

PxPx

ff

Phase I

Phase II

Design MethodsTheoretical Trays

Hunter – Nash graphical methodAspen

Packed Tower Height Seibert et al.

Sieve Tray Efficiency Seibert et al.

Hunter – Nash Graphical Method

Blender Material Balance

M = F + S = RNp+ E1

M xM = F xF + S yS = RNp xNp + E1y1

Hunter – Nash Graphical Method

Figure 8.14 Location of product point.

“P” Point10 lbs

12 lbs

9 lbs

100 lbs

90 lbs

78 lbs

69 lbs 150 lbs

159 lbs

171 lbs

181 lbs = 81 lbs

= 81 lbs

= 81 lbs

= 81 lbs

Hunter – Nash Graphical Method

Figure 8.15 Location of operating point.

Hunter – Nash Graphical Method

Figure 8.18 Determination of minimum solvent to feed ratio.

Hunter – Nash Graphical Method

Figure 8.17 Determination of the number of equilibrium stages.

Graphical Method ExampleIn a continuous counter-current train of mixer settlers, 100 kg/hr of a 40 wt % acetone / 60 wt % water

solution is to be reduced to 10 wt % acetone by extraction with pure 1,1,2 trichloroethane (TCE) at 25 C.

Find: 1. The minimum solvent rate2. At 1.8 times the minimum solvent rate, find the number of mixer settlers required.

C2H3Cl3 Water Acetone C2H3Cl3 Water Acetone

0.73 82.23 17.04 73.76 1.10 25.14

1.02 72.06 26.92 59.21 2.27 38.52

1.17 67.95 30.88 53.92 3.11 42.97

1.60 62.67 35.73 47.53 4.26 48.21

2.10 57.00 40.90 40.00 6.05 53.95

3.75 50.20 46.05 33.70 8.90 57.40

6.52 41.70 51.78 26.26 13.40 60.34

Water Phase ( wt %) TCE Phase ( wt %)

s

F

RNp

E1min

Mmin

TCE

Acetone

Water

s

F

RNp

E1

M

Acetone

TCE Water

10 Minute ProblemA feed stream “C” of 100 kg/min containing 30 mass percent solute “A” is being contacted in a single stage stirred contactor with 50 kg/min of pure solvent “S” (equilibrium figure below). Determine the composition and amount of the resulting raffinate and extract streams.

Photo of Sieve tray

Extractor Sieve Tray

Trayed Extractor Efficiency(Treybal Empirical Model)

42.05.012.3

c

dto U

UHE

Where: Ht = tray spacing (ft)Ud = superficial dispersed phase velocity Uc = superficial continuous phase velocity = interfacial tension (dyne/cm)

Interfacial Tension

Trayed Extractor Efficiency(Seibert Model)

c

dcd

dVS

drod

o

VS

o

fod

dVS

drod

o

VS

o

fod

MDMD

o UmU

UdhzK

dd

UK

UdhzK

dd

UK

EEE

,2

,

,,

34.01

64.4

ln11ln

Kod,f

Kod,r

Seibert, A.F. and Fair, J.R., “Mass-Transfer Efficiency of a Large-scale Sieve Tray Extractor,” Ind. Eng. Chem. Res., 32 (10): 2213-19 (1993).

Trayed Extractor Efficiency

c

d

d

c

d

SrddSrd

ABc

cc

c

VSSccdcc

VS

ABrc

rc

dc

rd

rod

ScUkScUk

DScdUSc

dDk

km

k

K

16

1

00375.06023.0

Re1Re698.011

5.0

,5.0

,

4.05.0,

,,

,

Correction of k d,r from Seibert Table VI Equation 16

cddcwhereg

d

dNQU

Q

dNDk

Dk

km

k

K

VS

oo

do

d

VSo

ff

dABfd

f

cABfc

fc

dc

fd

fod

4.10.1:5.1

4

63.13.11

1

2/1

2

32/1

,,

2/1

,,

,,

,

Trayed Extractor Efficiency

dVS

dsos

d

cdso

dd

c

socVS

Wc

WVS

C

c

UUUU

UUdN

HHPNHH

PN

cPPgdHg

P

92.1exp

192.1exp

3.59857.042.33.59857.094.0

9.03

4

Re

441.0149.0Re757.0

149.0Re

149.014.02

4

32

Trayed Extractor Efficiency

gdgd

gU

UdgUh

o

downc

d

doo

od

2.02

02

2

2

2.347.2log

71.0150.0

Trayed Extractor Hydraulics

h

Structured

IMTP

Pall Rings

Packed Liquid-liquid Extraction

Packed Extractor Design (Hydraulics)

3.59857.042.33.59857.094.0

9.03

4

4.10.1:15.1

441.0149.0Re757.0

149.0Re

149.014.02

4

32

2/1

HHPNHH

PN

cPPgdHg

P

cddcwhereg

d

Wc

WVS

C

c

VS

Seibert, A.F., Reeves, B.E., and Fair, J.R., “Performance of a Large-scale Packed Liquid-Liquid Extractor,” Ind. Eng. Chem. Res. 29 (9); 1901-07 (1990).

Packed Extractor Design (Hydraulics)

2

,

,

,

2

Re

8cos925.0163.51

18cos1

8cos92.1exp

192.1exp

8cos

VSp

floodc

floodd

sofloodc

d

cVSpVSpdsos

d

cdso

VSpd

dc

socVS

daUU

UU

UdadaUU

UU

daU

UdN

Packed Extractor Design (Mass Transfer)

c

d

d

c

d

SrddSd

ABc

cc

c

VSSccdcc

VS

ABc

cddcoc

VS

dw

woc

cocococ

ScUkScUk

DScdUSc

dDk

kkmK

dawhere

aKUHTUNTUHTUZ

16

1

00375.06023.0

Re1Re698.0111

6*

5.0

,5.0

4.05.0

Extraction Equipment Selection

Depends on:

- solvent recovery economics- viscosities, interfacial tension, solids- product/solvent value- flowrates- risk assessment- operation experience

Static Columns

Column interface

Large-diameterElgin head

Light liquid out

Heavy liquid in

Light-phase distributor

Heavy liquid out

Light liquid in

Ragremoval

Light liquid out

Heavy liquid in

Light liquid in

Heavy liquid out

Interface

Packing

Redistributor

(a)

Spray Tower

Packed Tower

Static ColumnsLight liquid out

Heavy liquid in

Light liquid in

Heavy liquid out

Operatinginterface

Perforatedplate

Downcomer

Coalesceddispersed

Sieve Tray

Oldshue-Rushston Column

Light liquid out

Heavy liquid in

Light liquid in

Heavy liquid out

Interface

Stator Ring

Stirrer

• Develop in 1950s• Many commercial installations• Solids handling• Viscosities to 500 cP• Differential contactor

Reciprocating Plate Extractor (Karr)

Heavy liquid in

Heavy liquid out

Light liquid in

Light liquid out

Interface

• Developed in 1959• Many commercial installations• V. High Volumetric Efficiency• Vary tray amplitude and frequency• Caution at low interfacial tensions• Tray movement can clean walls• Differential contactor• Scale-up to the 0.38 power on diameter• Other variations (e.g. VPE)

Podbielniak• Horizontal centrifugal extractor• High efficiency• Short residence time• Minimum inventory

Heavy phase in

Heavy phase out

Light phase out Light phase in

Mixer-Settler

• Wide range of designs• Handle wide range of flow ratios• Easy start-up• Easy to clean/inspect• Batch operations• Larger equipment• Handles solids• Low headroom• Occupy much floor space• Can add stages• Interstage pumping often required• High solvent inventory

Hollow Fiber Extractor

• Developed in 1980s• Modified in 1990s• Stage contactor• Low organic solvent to aqueous feed ratios• Few commercial extraction applications• Many commercial gas/liquid applications

Solvent InSolvent Out

Feed OutFeed In

M/S

RTLQVF-RZE

(agitated cell)

Kühni

Pulsed:packed plate

Karr

RDC

Packed

Sieve Tray

Stichlmair (1980)