• Goal (a) preparative work: to purify (or parti al purify) component (drugs, fuel, metal s, chemical feedstocks) 特特 : continuous operation; large in scal e, etc. (b) analytical goals: to generate informa tion about the mixture; to eliminate the interference component for measurement. Ch. 2 Basic concepts of separations Giddings, J.C.; Unified Separation Science, John Wiley & Sons, Inc, 1991.
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Goal (a) preparative work: to purify (or partial purify) component (drugs, fuel, metals, chemical feedstocks) 特徵 : continuous operation; large in scale,
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• Goal
(a) preparative work: to purify (or partial purify) component (drugs, fuel, metals, chemical feedstocks)
特徵 : continuous operation; large in scale, etc.
(b) analytical goals: to generate information about the mixture; to eliminate the interference component for measurement.
is the ratio of total amount (weight) of A in one phase to that in the 2nd phase
partition ratio :(capacity factor)
phase ratio:
ext
raff
W
W1
q
qk
1
2
raff
ext
V
V
V
V
kKD
(1) Partition coefficient
(2)
(3)
(4)
1
2
rafft
ext 1
solute
solute
V
V
q
qkKD
kKVCVC
VCq
D
1
1
1
1
raffraffextext
extext
111
raffext
raff
ext
ext
k
k
VKV
VK
VKV
Vq
D
D
raffD
D
D
Kkq
Kk
1
1
1
1
1
11
D
D
K
Kq
操作模式
(3) Multiple contact (countercurrent extraction)
(2) Multiple contact (crosscurrent extraction)
(1)Single contact
Multiple extraction
extracted left
0 0 0
1st extract q 1-q
2nd q(1-q) 1-q-q(1-q)=(1-q)2
.......
N q(1-q)n-1 (1-q)n
11
1raffext
raff ifK
K
VKV
VKq
n
D
D
n
D
Dn
A solute with a partition coefficient of 4.0 is extracted from 10 mL of phase 1 into phase 2. (a) What volume of phase 2 is needed to extract 99% of solution in one extraction? (b) What volume of phase 2 is needed to remove 99% of solution in three equal extractions instead?
Effect of pH value on extraction
KD ─→ D ( distribution coeff. )
H
K1K
K1
HKH
K1
H
K1
D
HA
AHK
HAHA
HAA1
HA
AHA
extractantinsoluteofformallofconc.
raffinateinsoluteofformallofconc.D
aD
D
a
D
a
a
aqo
aqaq
o
aqaq
HAo
org.
aq.
HAaq + H2O
H3O+ + A-
H
KHKD a
D
(b) at pH
D
a
2KD
KH
(a) very acid [H+] >>Ka D=KD
(c) [H+] <<Ka
D >>KD H
KKD a
D
Effect of pH value on extraction
KD ─→ D ( distribution coeff. )
Bo
org.
aq.
BH+
aq H+ + B
a
D
a
aqo
aqaq
o
aqaq
KK
1
H1
D
BH
BHK
BB
BB1
B
BB
extractantinsoluteofformallofconc.
raffinateinsoluteofformallofconc.D
DDaa KHKKK
HH
(b) at pH
2/KD
KH
D
a
(a) very acid [H+] >>Ka D >> KD
(c) [H+] <<Ka
DKD
a
a
K
K D
HKD
Suppose that the partition coefficient for an amine, B, is 0.33 and the acid dissociation constant of BH+ is Ka=1.0x10-9. If 50 mL of 0.010M aqueous amine is extracted with 100 mL of solvent. What will be the formal concentration remaining in the aqueous phase (a) at pH 10.0? (b) 8.0?
ApplicationExtraction of metal ions
H++HL
HL
+ Mn+ MLn
MLn
organic phase (ionic liquid)
aqueous phase
L-Ka
nL-Kf
加入 chelator (HL)
HL (aq) HL (o)
)(
)(
1aq
od HL
HLK (1)
HL (aq)+ H2O H3O+(aq) +L-
(aq)
aq
a HLLOH
K
3
(2)
Mn+(aq)+ nL-
(aq) MLn(aq)
)()(
)(
aqnaq
aqf LM
MLK (3)
MLn(o)MLn(aq)
)(
)(
2aqn
ond HL
HLK
(4)
→ HL, MLn在有機相中溶解度大,
1dK2dK >>1
→ [L-] is pH dependent
n(aq)
M
nML
n(aq)MLn(aq)
M
nML
aqCoCD
CL: orignal molar conc. of HL in organic phase mass balance