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NCHU-SF : Ch. 2-1
SUPERCRITICAL FLUIDS
FOR
SEPARATION
NCHU-SF : Ch. 2-2
What for
do we need phase equilibrium?
Design of solvent cycle (process)
Objectives
NCHU-SF : Ch. 2-3
Solubility of the compounds
Change of solubility with process conditions
Capacity of the solvent
Solubility of solvent in condensed phase
Distribution of compounds between the phases (separation factor, selectivity)
Two-phase area
What do we need to know about phase equilibrium?
Objectives
NCHU-SF : Ch. 2-4
For what type of systems (chemical compounds) do we need phase
equilibrium?
CO2, C3H8, H2O, .... (gases)
Paraffins, glycerides, vitamins, ...
Terpenes, sesquiterpenes, mono-, di-, tri-
....
....
Objectives
NCHU-SF : Ch. 2-5
Extraction with Supercritical Fluids
The need for phase equilibria:
Solubility, K-factor, Separation factor, Two-phase region
Flow scheme of gas extraction (SFE)
NCHU-SF : Ch. 2-6
Kennedy 1950
Solubility of quartz in water
NCHU-SF : Ch. 2-7
Poynting-effect
Vapor pressure enhancement E.U. Franck 1956____ 25 oC, ------ 500 oC
.d
d 0
G
L
TV
V
P
P
,ln 0102
01
PPRT
V
P
P L P02/P01 VL
NCHU-SF : Ch. 2-8
Poynting-Factor
System: Ethanol - Water, 343 K
Ethanol Water
kPa
10 1.0022 1.00061000 1.022 1.006510000 1.2425 1.0667
01
02
PP
NCHU-SF : Ch. 2-9
Density CO2 (calc. Bender EOS)
NCHU-SF : Ch. 2-10
Silan, Vapor Curve
1,E-05
1,E-04
1,E-03
1,E-02
1,E-01
1,E+00
1,E+01
1,E+02
75 125 175 225 275
Temperature, K
Pre
ssu
re, b
ar
Vapour Pressure vs. Temperature
NCHU-SF : Ch. 2-11
Density of supoercritical Fluid responsible for solvent power
(increasing with pressure, decreasing with temperature)
Hydrostatic pressure enhances effective vapour pressure
(Poynting effect, small)
Temperature increases vapour pressure
(exponentially, big effect)
Influences on Solute Concentration in Gaseous Phase
NCHU-SF : Ch. 2-12
Solubility of Caffeine in CO2
Gährs 1984Ebeling, Franck 1984Johannsen, Brunner 1994
NCHU-SF : Ch. 2-13
Tsekhanskaja 1964
So
lub
ility
[g
/l]
Solubility of Naphthalene in Ethylene
NCHU-SF : Ch. 2-14
Brunner 1978
Oleic acid - ethylene
NCHU-SF : Ch. 2-15
Solubility of oleic acid in various gases
Brunner 1978
NCHU-SF : Ch. 2-16
Solubility of Triglycerides in sc Gases
Triglycerides of palm oil
Brunner 1978
NCHU-SF : Ch. 2-17
Solubility in sc CO2
NCHU-SF : Ch. 2-18
Solubility of Xanthines in dry sc CO2
Johannsen and Brunner 1994
NCHU-SF : Ch. 2-19
P,T,x-diagram of a binary system
NCHU-SF : Ch. 2-20
P,x-diagram ethane - heptane
Kay 1938
NCHU-SF : Ch. 2-21
Kay 1938
T,x-diagram ethane - heptane
NCHU-SF : Ch. 2-22
Melting point temperature of B higher than critical temperature of A
Phase equilibria of a binary system
NCHU-SF : Ch. 2-23
Phase equilibrium in a binary system
Melting point temperature of B higher than critical temperature of A;Interrupted critical curve.
NCHU-SF : Ch. 2-24
P,T- projections of phase boundary lines
NCHU-SF : Ch. 2-25
Phase behaviour of a ternary system
Temperature dependence
Pressure dependence
NCHU-SF : Ch. 2-26
CO2 - benzene - oleic acid
NCHU-SF : Ch. 2-27
Ethylene - DMF - C18 fatty acids
NCHU-SF : Ch. 2-28
Solubility Enhancement by a Modifier
NCHU-SF : Ch. 2-29
Sch
mitt
198
4Solubility Enhancement by Entrainer (Modifier)
NCHU-SF : Ch. 2-30
Gährs 1984
Solubility of Caffeine in CO2
Influence of nitrogen
NCHU-SF : Ch. 2-31
Influence of propane
Prausnitz, Joshi 1984
Solubility of Phenanthrene in CO2
NCHU-SF : Ch. 2-32
Phase Equilibrium in a Ternary System
Brunner 1983
NCHU-SF : Ch. 2-33
Brunner 1983
Solubility in a gas with a modifier
Influence of temperature
NCHU-SF : Ch. 2-34
Brunner 1983
Separation Factor
Influence of entrainer
NCHU-SF : Ch. 2-35
Influence of concentration
Brunner 1983
Separation Factor
NCHU-SF : Ch. 2-36
Three Phase Equilibrium
NCHU-SF : Ch. 2-37
P,T-diagrams of Complex Mixtures
NCHU-SF : Ch. 2-38
Measuring Phase Equilibrium
NCHU-SF : Ch. 2-39
Measuring Phase Equilibrium
NCHU-SF : Ch. 2-40
Modeling of Phase Equilibrium with EOS
HPW modification of RK-EOS
NCHU-SF : Ch. 2-41
Gas-Liquid Phase Equilibrium
Two different ways:
A
= standard fugacity i = activity coefficient: gE-models)
B
= fugacity coefficient: Equations of state
LVii ff
0iiii fxf
0if
Pxf iii
i
Thermodynamic Equilibrium
NCHU-SF : Ch. 2-42
VLE-Calculation:
With the simplification:
since
:
LVii ff
Pyfx iiiiiV0
Pyfx iiSATiii
V
SATi
SATi
SATi Pf PyPx iii
SATSATiii
V
Calculation of Phase Equilibrium
NCHU-SF : Ch. 2-43
Low pressure High pressure
.0iiiii pxPyp
.0
P
pK iii
0
0
jj
iiij p
p
.0iiiii pxPy
.i
ioi
i P
pK
.0
0
ijj
jiiij p
p
Phase Equilibrium: Non Ideal Solutions
NCHU-SF : Ch. 2-44
P = 101 kPa
Methanol - water Chloroform - acetone
= 1
= 1
Concentration dependence of separation factor
NCHU-SF : Ch. 2-45
Concentration dependence of separation factor
NCHU-SF : Ch. 2-46
1lim
1
TPT
TfK
si
sireines
si
ixi
P
H
P
fK
vi
isvi
iii
xi
,,
0
0lim
T = const.
VLE
T = const.
VLE
xsf = const.
xsf = solvent free concentrations in liquid phase
Limiting values of the partition coefficient K
Phase Equilibrium
NCHU-SF : Ch. 2-47
jr
vjs
ijjr
vj
vireines
si
si
ijx H
TPf
TPT
i
,
0
,
1lim
jr
si
ijx H
P
i
lim1
0,
0
0 ,,
,,lim
jsfl
j
sfvvj
vi
iiij
x fxvT
yvTf
i
s
s
x P
P
2
1112
0lim
1
Limiting values of separation factor
Binary system i-j in a multicomponent system At low pressure
s
s
sf
s
x P
P
H
P
22
1112
1lim
1
Binär:
Phase Equilibrium
NCHU-SF : Ch. 2-48
Murphy´s Law of Thermodynamics
THINGS GET WORSE
UNDER PRESSURE