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Systematic Method for Screening Ionic Liquids as Extraction
Solvents Exemplified by Extractive Desulfurization Process
REFERENCES
ACKNOWLEDGEMENT
1. Eckert, F., Klamt, A. Fast solvent screening via quantum chemistry: COSMO‐RS approach. AIChE
Journal. 2002, 48(2): 369-385.
2. Song, Z., Zhou, T., Zhang, J., Cheng, H., Chen, L., Qi, Z. Screening of ionic liquids for solvent-sensitive
extraction–with deep desulfurization as an example. Chemical Engineering Science. 2015,129: 69-77.
3. Song, Z., Zhou, T., Qi, Z., Sundmacher, K. Systematic method for screening ionic liquids as extraction
solvents exemplified by an extractive desulfurization process. ACS Sustainable Chemistry &
Engineering, 2017, 5(4): 3382-3389.
National Natural Science Foundation of China (NSFC U1462123), Major State Basic Research
Development Program of China (973 Program 2012CB720502).
Deutsche Forschungsgemeinschaft (DFG) for the Collaborative Research Center SFB/TRR 63
"Integrated Chemical Processes in Liquid Multiphase Systems„.
MOTIVATION
IL SCREENING: STATE OF THE ART
x expensive and time-consuming
x limited to simple laboratory experiments
Ionic liquids (ILs) are highly promising alternatives for volatile organic solvents in
liquid-liquid extraction, gas absorption, extractive distillation, etc.
Application challenges
• huge number of ILs, various separation processes
• complex effects of IL molecular decision variables at different levels
Goal: develop systematic methods for screening practically attractive IL solvents
for separation processes.
Ab initio calculation x computationally expensive
NRTL, UNIQUAC, EoS (PC-SAFT) x require experimental data, molecule-specific,
x limited predictive ability for novel systems
UNIFAC-IL
x GC-based, limited group parameters available
COSMO-RS model independent of experiment, molecule/group σ-profile
virtually applicable to any system
good qualitative & acceptable quantitative prediction
1 i
1 1
E Rm m
1 2
1 2
E E
R R
m mS
m m
3
RSL m
γ∞ mole-based LLE mass-based LLE
β∞/β 28089 27584 3144
S∞/S 10349 11293 834
−/SL not considered 11265 831
Modified thermodynamic criteria
Physical property estimation by GC models [ref]
31 36
1 1
( ) 288.7m i ci j aj
i j
T K n t n t
20 67 20 67
1 1 1 1
ln 6.982 i i j j i i j j
i j i j
n a n a n b n b T
Step 1: Pre-screening by modified thermodynamic criteria
thermodynamic properties
LLE(mass-based β, S, SL)
physical properties
(Tm, η)
process performance
(operating conditions,
solvent/energy consumption)
COSMO-RS
GC methods
Aspen plus
conventional solvent
as benchmark
Tm < 298.15 K
η < 100 cP
acti
vit
y c
oeff
icie
nt m
odel
(NR
TL
)
Criteria derived from mass-based LLE are more reasonable and efficient.
Step 2: Further screening by Tm and η constraints
831 163 15 Tm < 298.15 K η < 100 cP
Top-ranked 4 IL candidates
Solvent β S SL Tm (K) η (cP)
IL1 2.66 104.03 2.14×10-6 281.14 88.55
IL2 2.31 119.58 2.56×10-5 253.01 64.73
IL3 2.27 77.34 2.85×10-5 286.08 71.31
IL4 3.02 134.94 3.02×10-5 268.80 53.95
sulfolane 2.10 71.15 9.09×10-3
All ILs have notably higher β and S, as well as lower SL than sulfolane.
Step 3: Final selection by process simulation
ILs defined as pseudo-component in Aspen Plus [ref]
MW, ρ, Tnb, critical properties
NRTL model as the thermodynamic model
parameters regressed from COSMO-RS data
B2
(Evap)
S1
Fresh IL
S2
Model fuel feed
10,000 kg/hr
S3
S4
Low-sulfur fuel product
S5
Sulfur-load IL
S6
Residual liquids
S7
Recycled IL
B1
(EC)
IL process
j iS
Process simulation of IL-based processes [ref]
Systematic IL screening
3 steps
decomposition
ILs: much lower energy and solvent consumption, higher fuel product recovery ratio
EDS case study: removal of trace aromatic sulfur compounds from fuel oils
m2
m3
m1
Specific global
composition
APPLICATION – EXTRACTIVE DESULFURIZATION
Current Methods
Experimental
Computational
Main Limitations of Previous Screening
Improved IL screening methods are highly desirable!
SYTEMATIC METHOD FOR IL SCREENING
β∞, S∞
Infinite dilution,
molar properties
Effect of molecular weights (MWs) of ILs, effect of practical condition
Melting point
Viscosity
β∞, S∞
Mixtures
to be separated
MW of ILs
Physical properties
Process performance
?
simulated by thiophene/n-octane mixture (sulfur content 100 ppm)
Sulfolane is employed as the benchmark solvent
(overall 36260 ILs combined from 370 cations and 98 anions in COSMOthermX database)
IL1 IL2 IL3 IL4
Sulfolane process requires 2 distillation columns.
more capital cost
Required S/F of all ILs is lower than sulfolane.
less solvent need
IL regeneration: different dependencies of the
operating pressure on the tempeature.
different energy cost
2 3 4 5 6 7 8 9 100.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Ma
ss r
ati
o o
f S
/F
Number of stages
IL1
IL2
IL3
IL4
Sulfolane
(a)
380 400 420 440 460 480 500 5200.0
0.2
0.4
0.6
0.8
1.0
Pre
ssu
re (
bar)
Temperature (K)
IL1 IL2 IL3 IL4
Extraction column
Evaporator
Z. Song1, T. Zhou1, Z. Qi2, K. Sundmacher1,3
1 Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstrasse 1, 39106 Magdeburg 2 Max Planck Partner Group at East China University of Science and Technology, Meilong Road 130, 200237 Shanghai 3 Otto-von-Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg
a list of top candidates