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