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Calculation of Phase Equilibria ofIonic Liquids and CO2 using GC-NLF EoS
Korea University
Chemical & Biological Engineering
Kim, Yong-soo
Thermodynamics & Properties Laboratory
What Are Ionic Liquids?
Organic salts composed of cations and anions
Usually liquid state in near room temp.
Reprinted from Seddon et al., Pure Appl. Chem., 72, 2275-2287, 2000
Thermodynamics & Properties Laboratory
Characteristics of Ionic Liquids
Negligible vapor pressure– No fugitive emissions
Wide liquidus range : 300 to 400℃
Good sovents – Dissolving both polar and nonpolar species
Modification of physical and chemical properties– The substituents on the cations (alkyl groups)
– The choice of anion
Thermodynamics & Properties Laboratory
Applications of Ionic Liquids Ⅰ
Reactions– Hydrogenation, hydroformylation, isomerization,
alkylation, Diels-Alder reaction, etc…– Good or better reaction rates and selectivities
Electrolyte/fuel cells– Wide electrochemical window, high conductivity,
and a low dielectric constant
Lubricants– High thermal stability and large liquidus range
Thermodynamics & Properties Laboratory
Applications of Ionic Liquids Ⅱ
Combining of Ionic liquids and SCF CO2
– Recovery of organic solute from ionic liquids using SCF CO2
No contamination in SCF phase
– Continuous catalytic processes using SCR CO2
as mobile phase
Liquid-Liquid extraction
Gas separations– The solubility of CO2 in [bmim][PF6] is about
0.6-0.7 mole fraction at 100 bar.
Thermodynamics & Properties Laboratory
Motive
Studies on ionic liquids– Focused on the synthesis of ionic liquids and
the application of catalytic reaction as solvents
– Very few measurements and no modeling of the phase equilibria relating ionic liquids
This work– Modeling of phase equilibria for ionic liquids
and carbon dioxide
– Application of group-contribution NLF theory
Thermodynamics & Properties Laboratory
NLF-HB Theory
Nonrandom Lattice Fluid Hydrogen BondingTheory– NLF EOS by You et al. [1994 a, b]
– Expansion to associating system using Veytsman statistics[1990] by Yeom et al. [1999]
– A normalization of Veytsman statistics by Lee et al. [2001]
– Application of amino acids using extended Veytsman statistics by Park et al. [2002, 2003]
Thermodynamics & Properties Laboratory
GC-NLF Theory
Calculations of parameters for group contribution– Connectivity relation :
– Group size parameters :
– Group energy parameters :
)1(2)2( Gq
Gq
Gq lzrzq −+−=
=
=G
j
Gjiji rvr
1
= =
= =
= =
== G
k
G
l
Gl
Gkjlik
G
k
G
l
Gkl
Gl
GkjlikG
k
G
l
Gkl
Gjl
Gikij
qqvv
qqvv
1 1
1 1
1 1
εεθθε
Thermodynamics & Properties Laboratory
GC-NLF Theory
The temperature dependency of size and energy parameters proposed by Kehiaian
– Group size parameters
– Group energy parameters
( )( )ooGjo
Gj
Gj
Gj TTTTTcTThwr −++−+= ln)(
( )( )ooGijo
Gij
Gij
Gij TTTTTdTTba −++−+= ln)(ε
Thermodynamics & Properties Laboratory
Groups of Ionic Liquids
Cations Anions
– [BF4]- , [PF6]
- , [(CF3SO2)2N]-
NNCH2 CH3
CH2CH2
CH3
+
Thermodynamics & Properties Laboratory
Determination of Group Parameters
Methyl and ethyl group : from Kang’s data
Ionic liquids : Imidazolium and anions– Liquid density
– Assuming that its vapor pressure is less than 10-5 bar.
Carbon dioxide– Using PVT data
– Conversion of values of You et al. [1994]
Carbon dioxide and other groups– VLE data
Thermodynamics & Properties Laboratory
Group size parameters
Thermodynamics & Properties Laboratory
Group interaction parameters Ⅰ
Thermodynamics & Properties Laboratory
Group interaction parameters Ⅱ
Thermodynamics & Properties Laboratory
Result – Density of Ionic Liquids
The comparions of experimental and calculated densitiesof ionic liquids at various temperatures
Temperature [K]
290 300 310 320 330 340 350
Den
sity
of i
onic
liqu
ids [
g/cm
3 ]
0.6
0.8
1.0
1.2
1.4
[bmim][PF6] (Gu et al., 2002)[c8mim][PF6] (Gu et al., 2002)[emim][BF4] (Noda et al., 2001)[c8mim][BF4] (Gu et al., 2002)GC-NLF EoS Experimental accuracy ± 0.60 %
Average deviation with experimental data is ± 0.55 %
Thermodynamics & Properties Laboratory
Result – Low Pressure for [bmim][BF4]
Average deviation with experimental data is ± 2.6 %
Experimental accuracy ± 1.0 % in mole fraction
The solubility of carbon dioxide in [bmim][BF4] [Husson-Borg et al., 2003]
Pressure [bar]
0.0 0.2 0.4 0.6 0.8 1.0
Mol
e fr
actio
n of
CO
2 in
[bm
im][
BF 4]
0.000
0.005
0.010
0.015
303.7 K313.9 K324.1 K 334.4 K344.5 KGC-NLF EoS
Thermodynamics & Properties Laboratory
Result – Medium Pressure for [bmim][PF6]
The solubility of carbon dioxide in [bmim][PF6] [Anthony et al. 2002]
Pressure (bar)
0 2 4 6 8 10 12
Mol
e fr
actio
n of
CO
2 in
[bm
im][
PF6]
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35283.15 K298.15 K323.15 KCalculation at 283.15 KCalculation at 298.15 KCalculation at 313.15 K
Average deviation with experimental data is ±0.0079 in mole fraction.
Thermodynamics & Properties Laboratory
Result – High Pressure for [bmim][PF6]
The solubility of carbon dioxide in [bmim][PF6] [Kamps et al. 2003]
Pressure / bar
0 20 40 60 80 100
CO
2 mol
e fr
actio
n in
[bm
im][
PF6]
0.0
0.1
0.2
0.3
0.4
0.5
0.6
293.15 K313.15 K333.15 K353.15 K373.15 K393.15 KGC-NLF EoS
Average deviation with experimental data is ±0.017 in mole fraction.
Thermodynamics & Properties Laboratory
Result – Length of Alkyl Chains
The solubility of carbon dioxide in [Cxmim][BF4] at 298.15 K
Pressure (bar)
0 2 4 6 8 10
Mol
e fr
actio
n of
CO
2 in
[Cxm
im][
BF 4]
0.00
0.05
0.10
0.15
0.20
[c6mim][BF4][emim][BF4]GC-NLF EoS The solubility of CO2 increase with
length of alkyl chain substituted on imidazolium ring.
Thermodynamics & Properties Laboratory
Conclusions
GC-NLF equation of state was found to be effective to predict the phase equilibria of carbon dioxide and ionic liquids.
– For wide range of pressure and temperature
– The effect of the length of alkyl chain in imidazolium ring on the solubility of carbon dioxide in ionic liquids
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