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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)