Dihydrolevoglucosenone (Cyrene™), a Bio-based Solvent for Liquid-Liquid Extraction Applications

Abstract

Dihydrolevoglycosenone, commercially known as Cyrene™, is a versatile bio-based solvent reported for various applications including being a medium of chemical reactions and membrane manufacture. In this work, application of Cyrene™ in liquid-liquid extractions has been investigated. Four ternary systems have been assessed at 298.15K, 323.15K and 348.15K, keeping CyreneTM and methylcyclohexane constant and changing the third compound to toluene, cyclohexanol, cyclohexanone and cyclopentyl methyl ether. Studying these selected ternary systems, yielded an indication of applicability of Cyrene™ in related industrial separation processes such as aromatic/aliphatic separations, and in separations of oxygenates in the cyclohexane oxidation process. Key factors are biphasic system formation, distribution coefficients and selectivity. All ternary systems showed type I liquid-liquid phase behavior with a selective extraction of ternary components from methylcyclohexane by Cyrene™. The highest selectivity at 298.15K was found for cyclohexanol with 61.4±4.33, followed by cyclohexanone with 44.1±8.63, while toluene and cyclopentyl methyl ether had a selectivity of respectively 12.0±0.89 and 6.4±0.08. Although CyreneTM is applicable in all four ternary systems, the miscibility gap is narrow for the oxygenated species, indicating a limited operation window for liquid-liquid extraction which will be more severe at higher temperatures. Overall, the studies showed that there are certainly application windows for Cyrene™. In the case of oxygenate extraction, a process with Cyrene™ appears energy-saving because the energy duty appears to be lower than when using water, the best alternative solvent, which is a low boiling solvent for this purpose.

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Dihydrolevoglucosenone (Cyrene), a Biobased Solvent for Liquid−
Liquid Extraction Applications
Thomas Brouwer and Boelo Schuur*
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sıSupporting Information
ABSTRACT: Dihydrolevoglycosenone, commercially known as Cyrene, is a versatile
biobased solvent reported for various applications including being a medium of chemical
reactions and membrane manufacture. In this work, application of Cyrene in liquid−
liquid extractions has been investigated. Four ternary systems have been assessed at
298.15 K, 323.15 K, and 348.15 K, keeping Cyrene and methylcyclohexane constant and
changing the third compound to toluene, cyclohexanol, cyclohexanone, and cyclopentyl
methyl ether. Studying these selected ternary systems yielded an indication of applicability
of Cyrene in related industrial separation processes such as aromatic/aliphatic separations
and in separations of oxygenates in the cyclohexane oxidation process. Key factors are
biphasic system formation, distribution coefficients, and selectivity. All ternary systems
showed type I liquid−liquid phase behavior with a selective extraction of ternary
components from methylcyclohexane by Cyrene. The highest selectivity at 298.15 K was
found for cyclohexanol with 61.4 ±4.33, followed by cyclohexanone with 44.1 ±8.63,
while toluene and cyclopentyl methyl ether had a selectivity of, respectively, 12.0 ±0.89 and 6.4 ±0.08. Although Cyrene is
applicable in all four ternary systems, the miscibility gap is narrow for the oxygenated species, indicating a limited operation window
for liquid−liquid extraction which will be more severe at higher temperatures. Overall, the studies showed that there are certainly
application windows for Cyrene. In the case of oxygenate extraction, a process with Cyrene appears energy-saving because the energy
duty appears to be lower than when using water, the best alternative solvent, which is a low boiling solvent for this purpose.
KEYWORDS: Dihydrolevoglucosenone, Cyrene, Biobased solvent, Liquid−liquid equilibrium, Liquid−liquid extraction
■INTRODUCTION
Insights in the liquid−liquid extraction (LLX) applicability of
dihydrolevoglycosenone, or Cyrene, were obtained by perform-
ing LLX in four different ternary systems. Cyrene, a biobased
polar solvent, attracted recent attention as being versatile for
various applications, e.g., as a medium to perform chemical
reactions
1−7
and to prepare membranes by phase inversion,
8
though no mention for LLX applications has been found as of
yet.
Cyrene can be an alternative aprotic dipolar solvent;
1,8
solvents of this class are typically used in a range of molecular
separations, from aromatic/aliphatic separation
9−11
to carbox-
ylic acid separation from water.
12
Industrially important
members of the solvent class of aprotic dipolar solvents include
N-methylpyrrolidone (NMP) and N,N-dimethylformamide
(DMF), which both are considered toxic solvents and subject
to restrictive legislation.
13−15
Cyrene is reported to have a much
lower toxicity,
16,17
and additionally since it is a biobased
product, it offers chances for the chemical industry to reduce the
consumption of fossil oil by replacing their toxic fossil oil-based
solvents for a much more benign biobased alternative.
18
In a
recent communication, the Circa Group announced a
production capacity of Cyrene of 1 kton per annum, which
signifies the mass production of this new biobased solvent.
19
Although bulk prices may not be publically available, Krishna et
al. state that the bulk price of Cyrene may be approximately 2
€/kg,
20
which is comparable with traditional solvents.
Two key classes of molecular separation processes using
solvents include extractive distillation (ED) and LLX. In another
article,
21
we showed the potential of Cyrene as an entrainer in
the ED of aromatic/aliphatic mixtures and paraffin/olefin
mixtures. Similarly, next to the already proven entrainer function
in extractive distillations, Cyrene may be useful for LLX as well.
In order to investigate the applicability of Cyrene in LLX
processes, we assessed the liquid−liquid equilibrium (LLE)
behavior of several ternary systems formed with Cyrene. The
investigated systems include (1) methylcyclohexane (MCH)
and toluene (TOL), (2) MCH and cyclohexanol (CHOH), (3)
MCH and cyclohexanone (CHO), and (4) MCH and
cyclopentyl methyl ether (CPME). The molecular structures
of all species used in this study are displayed in Figure 1.
Received: June 8, 2020
Revised: August 19, 2020
Published: August 31, 2020
Research Article
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These ternary mixtures have specifically been chosen to first
represent aromatics/aliphatics separations. These separations
using LLX have been the subject of study for a variety of model
compounds, including benzene, toluene, xylenes, (methyl)-
cyclohexane, and n-alkanes.
22−27
The model systems vary as the
related industrial mixture is complex.
28
The results in this study
on liquid−liquid equilibria with Cyrene, MCH, and TOL will be
compared to the elaborate work done in the past concerning
molecular solvents,
22−24
ionic liquids (ILs),
25,29,30
and deep
eutectic solvents (DESs).
31−33
The separation of alcohols and ketones from aliphatics was
chosen because the compounds possess either an alcohol or a
ketone functionality, and they are relevant industrial chemicals,
for example, in the industrial oxidation process of cyclohexane to
CHO and CHOH.
34,35
Kim et al. and Pei et al. investigated
similar systems with CHO and CHOH, though they used
cyclohexane as a hydrocarbon and studied dimethyl sulfoxide
(DMSO) and water as a solvent.
36,37
The last ternary mixture with MCH and CPME was chosen
for the CPME ether functionality. CPME also has the potential
of being a biobased solvent.
38−40
The extraction of CPME from
an aliphatic stream has not been studied yet.
Next to evaluation of the extraction performance of Cyrene
for each of the systems, the LLE was also correlated using the
UNIQUAC model. Last, by maintaining MCH as the constant,
it became possible to compare all the systems with each other
and investigate trends between different functional groups and
thus study the applicability of Cyrene for separating molecules
with these different functional groups.
■EXPERIMENTAL SECTION
Materials. Chemicals, if not otherwise specified, were used as
received without any additional purification. Cyclopentyl
methyl ether (≥99.9%), cyclohexanone (≥99.9%), and cyclo-
hexanol (99%) were obtained from Sigma-Aldrich, while
methylcylohexane (reagent grade, 99%) was purchased from
Honeywell. Toluene (ACS, reag.Ph.Eu) was procured from
VWR Chemicals, while analytical acetone (LiChrosolv) was
acquired from Merck. A 1 L bottle of dihydrolevoglucosenone,
or Cyrene (99.3%), was supplied by the Circa Group.
Liquid−Liquid Extraction Procedure. For the liquid−
liquid extraction experiments, closed 10 mL glass vials were
used. All compounds were weighed with an accuracy of 0.5 mg
on an analytical balance. Consecutively, a vortex mixer and a
temperature-controlled shaking bath were used in the
equilibration. The mixture was shaken at 200 rpm for at least
12 h at a constant temperature and subsequently settled for at
least 1 h prior to sample taking. The experiments were
conducted at 298.15 K, 323.15 K, or 348.15 K with a
temperature variation of 0.02K. A solvent to feed ratio on a
mass basis of 1 was maintained, and the total mass of each phase
was kept approximately at 3 g. A sample of 0.5−1.0 mL was taken
with a 2 mL syringe with an injection needle from both phases.
Both phases were analyzed following the analysis produced.
Analysis Procedure. A Thermo Scientific Trace 1300 gas
chromatograph with two parallel ovens and an autosampler
TriPlus for 100 liquid samples was used for the analyses. Each
system was analyzed using an Agilent DB-1MS column (60m ×
0.25 mm ×0.25 μm) with an injection volume of 1 μL diluted in
analytical acetone. The same instrumental method was used for
every system with a ramped temperature profile following the
program of initial temperature at 50 °C, followed by a direct
ramp of 10 °C/min to 200 °C. The second ramp, which was
directly initiated after reaching 200 °C, of 50 °C/min to 320 °C
finished the program, which lasted 20 min. The FID temperature
was 330 °C. A column flow of 2 mL/min with a split ratio of 5, an
airflow of 350 mL/min, a helium makeup flow of 40 mL/min,
and a hydrogen flow of 35 mL/min were used.
Fitting Procedure. Each ternary system was correlated for
all temperatures simultaneously with the UNIQUAC model.
This model predicts the activity coefficient as the summation of
the combinatorial (γi
c) and residual (γi
R) terms of the activity
coefficient, see eq 1.
41
γγ γ=+
l
nln ln
ii i
cR (1)
The combinatorial term, using the Guggenheim−Stavermann
approximation,
42
accounts for the influence of shape differences
between the molecules and the corresponding entropy effects.
This contribution of the activity coefficient is elaborated in eqs 2,
3, and 4.
γθθ
=Φ+−
Φ−Φ+−
Φ
i
k
j
j
j
j
j
y
{
z
z
z
z
z
i
k
j
j
j
j
j
i
k
j
j
j
j
j
y
{
z
z
z
z
z
y
{
z
z
z
z
z
xx
q
l
nln1 5ln1
i
i
i
i
ii
i
i
i
i
c
(2)
Φ=∑
xr
xr
i
ii
jjj (3)
θ=∑
xq
xq
i
ii
jjj(4)
where Φiis the volume fraction, θiis the surface area fraction, xi
is the molar fraction, riis the van der Waals volume, and qiis the
surface area of each component.
Figure 1. Structures of the molecules used in this study.
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The residual term, see eqs 5 and 6, is determined using the
same parameters and the additional empirical binary interaction
parameters τij. This value is fitted using the temperature
independent parameter (Aij) and temperature-dependent
parameter (Bij).
∑
γ
ττ
τ
=−
∑
∑−∑
i
k
j
j
j
j
j
j
j
j
i
k
j
j
j
j
j
j
j
y
{
z
z
z
z
z
z
z
y
{
z
z
z
z
z
z
z
z
q
qx
qx
qx
qx
l
n1ln
i
R
i
jjjji
jjjj
jjji
kkkkj (5)
τ
=+AB
T(K)
ij ij
ij
(6)
For the correlation, known van der Waals volumes and surface
areas were used, see Table 1. For Cyrene, the parameters were
not available in the literature and were estimated with Density
Functional Theory with a B3LYP 6-311+G** parametrization in
combination with the methodology of Banerjee et al.
43
■RESULTS AND DISCUSSION
The four ternary LLE systems that were investigated in this
study are presented in a subsection for each of the systems. All of
the systems showed type I phase behavior
46
for all temperatures
investigated. For each of the ternary systems, the selectivity (Sij)
of the solute (i), being toluene, cyclohexanol, cyclohexanone, or
CPME, over MCH (j) was examined (eq 8). This selectivity is
defined as the ratio of the distribution coefficients (KD,i) of each
of the solutes, which in turn is defined as the ratio of the
concentration of the solute, on a weight basis, in the solvent
([Xi]S) and the organic phase ([Xi]O)asineq 7.
=[]
[]
KX
X
i
i
i
D,
S
O(7)
=
S
K
K
ij
i
j
D,
D, (8)
All experimental results have been correlated using the
UNIQUAC model, which was checked on its thermodynamic
consistency using the Hessian matrix test. This information is
provided in the Supporting Information (SI),
47,48
as well as
tables with all the measured data and calculated distribution
coefficients and selectivities. This allows an approximate
description of the binodal curve and the tielines. After describing
the results for each of the ternary systems individually, in the last
subsection, all ternary systems are compared to enable a general
description of the affinities of Cyrene toward different moieties.
Additionally, rough short-cut calculations were performed of the
combined CHOH/MCH and CHO/MCH cases to assess the
potential of Cyrene in an LLX process.
Methylcyclohexane−Toluene−Cyrene. The results for
the MCH−toluene−Cyrene ternary system are displayed in
Figure 2. As can be seen from the binodal curves, a significant
miscibility region can be seen. For 298.15 K, only below ∼35 wt
% toluene is a biphasic system observed, which further reduces
with increasing temperatures. This is in line with our work on
extractive distillation at a temperature above 373 K, where no
phase splitting was observed for this system.
21
A selectivity of 11.99 ±0.89 was induced with a toluene
concentration of ∼0.74 wt % in the Cyrene phase at 298.15K.
This selectivity decreases to 6.76 ±0.65 and 4.91 ±0.58 at,
respectively, 353.15 K and 348.15 K for similar toluene
concentrations. This is due to a lower activity coefficient of
MCH in Cyrene, a consequence of a polarity decrease of the
solvent phase, which is a consequence of the higher hydrocarbon
(MCH and TOL) solubility at elevated temperatures, which in
turn is caused by the larger entropic contribution at higher
temperatures. The correlated UNIQUAC parameters are given
in Table 2.
The LLX performance of Cyrene has been put in perspective
by the comparison with other solvents, such as Sulfolane, n-
formylmorpholine,
26
methanol,
27
and various ILs, EMIM]-
[ESO4],
49
[HMIM][B(CN)4],
50
[BMIM][B(CN)4],
50
and
[BMIM][MSO4].
51
As can be seen in Figure 3, Sulfolane is outperforming Cyrene
regarding selectivity, and n-formylmorpholine
26
has a higher
selectivity at high toluene fractions in the solvent phase. Also,
both solvents have a more significant phase split than Cyrene.
Comparable performance was seen toward methanol,
27
though
Cyrene has a more significant phase split.
The ILs induce an almost complete immiscibility, due to
lower distribution coefficients compared to traditional solvents.
This immiscibility is due to their ionic nature, which does not
allow stabilization in the highly apolar hydrocarbon mixture.
Additionally, for low toluene fractions in the solvent phase, a
similar selectivity toward toluene is observed for the ILs
compared to Sulfolane. Although, at a higher toluene fraction,
the tetracyanoborate ILs
50
are able to retain a higher selectivity
compared to Sulfolane. A consequence of lower distribution
coefficients in ILs is however that a larger solvent quantity is
required for the LLX, and the equipment diameter will increase.
On the other hand, due to the larger selectivity, fewer stages are
required, reducing the equipment height. Higher selectivity
means that fewer aliphatics need to be boiled from the solvent in
the solvent regeneration, which is beneficial for the energy
requirement, which seems to be in favor for ILs. Overall, it is not
straightforward to decide which solvent is better, and a more
thorough process simulation including total annual cost
estimation is suggested but outside the scope of this paper.
Methylcyclohexane−Cyclopentyl Methyl Ether−Cy-
rene. As can be seen in Figure 4, Cyrene induces a selectivity
of 6.42 ±0.08, 4.55 ±0.41, and 3.91 ±0.31 at, respectively,
298.15 K, 323.15 K, and 348.15 K for ∼0.65 wt % of CPME in
the solvent phase.
The results indicate that Cyrene is selective toward the polar
ether moiety over the aliphatic MCH. A substantial miscibility
region at CPME contents over ∼35 wt % CPME is observed,
which resembles the LLX-application window of the MCH−
toluene case. In Table 3, the UNIQUAC parameters of the
correlation are displayed. This indicates that the dipolar
characteristics of the ether moiety induce similar intermolecular
interactions to those of the delocalized π-system of toluene.
Methylcyclohexane−Cyclohexanol−Cyrene. The re-
sults for the system MCH−CHOH−Cyrene are given in Figure
5. Cyrene induces a selectivity of 61.42 ±4.33, 32.8 ±5.83, and
Table 1. van der Waals Volumes and Surface Areas of All
Components
component riqi
methylcyclohexane
22
5.174 4.396
toluene
44
3.920 2.970
cyclohexanol
37
4.274 3.284
cyclohexanone
37
4.114 3.340
CPME
45
4.214 3.248
Cyrene 4.843 3.322
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16.6 ±2.26 at, respectively, 298.15 K, 323.15 K, and 348.15 K at
∼0.80 wt % of CHOH in the solvent phase. This is lower than
observed with DMSO
36
and water,
37
which have a selectivity of,
respectively, 155 and 1450, at low CHOH concentrations.
The lower selectivity of Cyrene can mainly be attributed to the
larger hydrocarbon backbone of Cyrene, compared to the small
DMSO and water molecules, which mitigates the multipole
interactions with the relatively unselective London dispersion
interactions.
52
Also in the ternary system MCH−CHOH−Cyrene, a large
miscibility region is observed, for concentrations above ∼25 wt
% cyclohexanol. Due to the large miscibility in the system, only a
small operation window is available for LLX, and the two phase
region decreases at increasing temperature. The larger
miscibility region indicates also that the capacity of Cyrene
(KD,CHOH = 4.64 at ∼0.80 wt % of CHOH in the solvent phase)
for CHOH is larger than that for water (KD,CHOH = 1.60I̵,
37
).
Cyrene would be preferred when high CHOH capacities are
required, while water is preferred when a larger immiscibility and
selectivity is required. DMSO has been shown to be quite toxic
53
and is for that reason not the preferred choice. The UNIQUAC
parameters for this system are present in Table 4.
Methylcyclohexane−Cyclohexanone−Cyrene. The re-
sults for the ternary system MCH−CHO−Cyrene are given in
Figure 6. Cyrene induces selectivities of 44.07 ±8.63, 32.14 ±
2.78, and 19.25 ±2.00 at, respectively, 298.15 K, 323.15 K, and
348.15 K for the lowest amount of CHO in the solvent phase
(∼0.60 wt %). Also in this case, the selectivity is lower than
reported for DMSO
36
and water,
37
which have been reported to
be 42.9 and 1202. Also in this case, a significant miscibility
region is observed at CHO contents higher than ∼23 wt %. The
single phase region is larger compared to the previous systems,
indicating a narrower LLX application window. This is due to
the mutual presence of ketone functionality in CHO and
Cyrene, resulting in a significant mutual solubility. Hence,
Cyrene has a larger capacity for CHO (KD,CHO = 4.47 at ∼0.60
wt % of CHO in the solvent phase) than water (KD,CHO =
Figure 2. Ternary diagrams of the LLE of toluene, MCH, and Cyrene with the tielines, feed compositions, and binodal curves at (a) 298.15 K, (b)
323.15 K, and (c) 348.15 K, and (d) the STOL,MCH of Cyrene at the same temperatures. The UNIQUAC fit is added throughout.
Table 2. Correlated UNIQUAC Parameter for the MCH−
Toluene−Cyrene System
component icomponent jA
ij Aji Bij Bji
MCH toluene 0 0 −191.0 171.5
Cyrene 4.587 −2.627 −1749 773.7
toluene 2.708 −4.999 −772.6 1463
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Figure 3. A comparison of (left) the LLE and (right) STOL,MCH at 298.15 K of several solvents: Cyrene, sulfolane, n-formylmorpholine,
26
methanol,
27
[EMIM][ESO4],
49
[HMIM][B(CN)4]*,
50
[BMIM][B(CN)4]*,
50
and [BMIM][MSO4].
51
*These systems were measured at 293.15 K.
Figure 4. Ternary diagrams of the LLE of CPME, MCH, and Cyrene with the tielines, feed compositions, and binodal curves at (a) 298.15 K, (b)
323.15 K, and (c) 348.15 K, and (d) the SCPME,MCH of Cyrene at the same temperatures. The UNIQUAC fit is added throughout.
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2.79I̵,
37
). Also for this case, Cyrene and water may be preferred
solvent choices, if either CHO capacity or immiscibly window
and selectivity are the selection criteria. As previously
mentioned, DMSO is toxic and is preferentially avoided. In
Table 5, the UNIQUAC parameters of the correlation are
displayed.
Comparative Study. By considering the combined data
from all ternary systems with toluene (TOL), cyclohexanol
(CHOH), cyclohexanone (CHO), and CPME, from MCH, the
performance of Cyrene toward particular moieties can be
evaluated. Cyrene is a bicyclic organic molecule in which a
double ether moiety, one in each ring, and a ketone functionality
are present. All moieties are aprotic and therefore can only act as
a hydrogen bond acceptor and will induce next to the
omnipresent London dispersion interactions also Keesom and
Debye interactions.
52
To see a comparison of the results, see
Table 6, and from Figures 2,4,5, and 6, it is concluded that
selectivity order is found to be mostly CHOH > CHO ≫TOL >
CPME. A larger temperature dependency is seen for CHOH,
likely due to intra- and intermolecular hydrogen bonding,
resulting in lower selectivity than CHO at higher temperatures.
CHOH and CHO are extracted with significantly higher
selectivity than toluene and CPME. This is due to respectively
the hydrogen bond donating character of CHOH and the
significant dipole moment of 2.75 D
54
of CHO, which induces
substantial Keesom and Debye interactions with Cyrene.
Toluene and CPME do not have hydrogen bonding donating
capabilities and have much lower dipole moments compared to
CHO, respectively, 0.37 D
55
and 1.27 D,
56
hence a lower
selectivity is induced. Toluene does however exhibit a significant
quadrupole moment,
57
which is responsible for more extensive
Keesom and Debye interactions, and therefore a larger
selectivity is induced compared to CPME.
When the CHO and CHOH cases are combined and their
extraction performances are compared, a measure of selectivity
toward both solutes may be estimated for the lowest weight
Table 3. Correlated UNIQUAC Parameter for the MCH−
CPME−Cyrene System
component icomponent jA
ij Aji Bij Bji
MCH CPME 0 0 −61.53 19.21
Cyrene 3.332 −2.020 −1356 588.3
CPME 2.319 −3.522 −661.0 899.1
Figure 5. Ternary diagrams of the LLE of cyclohexanol, MCH, and Cyrene with the tielines, feed compositions and binodal curves at (a) 298.15K, (b)
323.15K and (c) 348.15K, and (d) the SCHOH,MCH of Cyrene at the same temperatures. The UNIQUAC fit is added throughout.
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fractions of solute in the solvent phase. A selectivity ratio
(SCHOH,MCH/SCHO,MCH) of 1.42 and 1.21
37
is obtained for,
respectively, Cyrene and water. We speculate that Cyrene is a
slightly more selective solvent for the combined extraction of
CHO and CHOH than water, though this may be caused by the
different alkane used in both studies. A Cyrene-based LLX
process for this separation was further investigated by short-cut
energy calculations in the next section.
Process Considerations. Liquid−liquid equilibria are
cornerstones in an accurate description of liquid−liquid
Table 4. Correlated UNIQUAC parameter for the MCH−Cyclohexanol−Cyrene System
component icomponent jA
ij Aji Bij Bji
MCH cyclohexanol −0.1112 −0.1675 −435.6 239.5
Cyrene 1.738 −0.7045 −817.2 153.3
cyclohexanol 0 0 −128.7 12.05
Figure 6. Ternary diagrams of the LLE of cyclohexanone, MCH, and Cyrene with the tielines, feed compositions, and binodal curves at (a) 298.15 K,
(b) 323.15 K, and (c) 348.15 K, and (d) the SCHO,MCH of Cyrene at the same temperatures. The UNIQUAC fit is added throughout.
Table 5. Correlated UNIQUAC Parameter for the MCH−Cyclohexanone−Cyrene System
component icomponent jA
ij Aji Bij Bji
MCH cyclohexanone −1.090 −1.090 364.9 364.9
Cyrene 4.587 −2.627 −1749 773.7
cyclohexanone 2.507 −7.521 −531.6 2133
Table 6. A Comparison between the Distribution Coefficient and Selectivity Found for CHOH, CHO, TOL, and CPME at Similar
Low Weight Percentage in the Solvent Phase at 298.15 K, 323.15 K, and 348.15 K
component icomponent jcomponent jin solvent phase (wt %) distribution coefficient component j(−) selectivity (−)
(298.15 K/323.15 K/348.15 K)
MCH CHOH 0.80/0.65/0.51 4.64/2.94/1.64 61.4/32.8/16.6
CHO 0.87/0.60/0.56 4.47/3.15/2.20 44.1/32.1/19.3
TOL 0.74/0.82/0.72 0.98/0.54/0.51 12.0/5.80/5.32
CPME 0.83/0.63/0.57 0.30/0.40/0.40 5.15/4.27/3.54
ACS Sustainable Chemistry & Engineering pubs.acs.org/journal/ascecg Research Article
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ACS Sustainable Chem. Eng. 2020, 8, 14807−14817
14813

extractions (LLX) that arguably form the heart of LLX
processes. As solvents are rarely completely immiscible and
selective, several additional purification steps are required to
recover the solvent and obtain a pure product. An example is
given by de Graffet al.
58
where two distillation columns are used
to recover the solvent and pure products from an LLX column.
The raffinate can also be distilled to recover the solvent, though
for polar solvents the use of a water wash column to recover the
solvent can be applied to save energy. Subsequently, the water is
then evaporated from the solvent-rich water phase, and the
vapor is used to strip extracted solutes from the extract
stream.
59−61
To thoroughly compare Cyrene with all conven-
tional solvents for all studied applications, it will require rigorous
process simulations for all of these process steps, and even
consideration on which of the steps are required and preferred.
This is beyond the scope of this paper, in which the applicability
of Cyrene is explored, and a first indication of the usefulness of
the application is discussed on the basis of miscibility,
distribution coefficients, and selectivity. On the basis of a
short-cut calculation, an estimation of the required heat duty will
be given for the combined case of MCH/CHO and MCH/
CHOH. This case was chosen as being most interesting for
industrial application in the industrial oxidation process of
cyclohexane to CHO and CHOH.
34,35
The MCH-TOL case,
which certainly is also of industrial interest, was not simulated
because, on the basis of the liquid−liquid equilibrium data, it can
be seen that both Sulfolane and ILs are clearly superior over
Cyrene with regard to selectivity and immiscibility.
The most significant difference between water and Cyrene is
related to the recovery of the CHO and CHOH from the
solvent, which boil at respectively 429 and 433 K. Cyrene is a
high-boiling solvent (bp: 500 K
8
), whereas water is a low-boiling
solvent (bp: 373 K). Recovery of water thus implies that the
solvent has to be boiled offfrom the solutes, whereas the solutes
can be boiled offfrom the Cyrene. Cyrene has therefore a
significant advantage over water, due to the fact that the energy
penalty associated with the evaporation enthalpy of the solvent is
avoided in using the high-boiling Cyrene. Also, the capacity of
CHO and CHOH in water is lower compared to Cyrene. This
entails a larger amount of water being required to extract a
certain amount of CHO and/or CHOH than for Cyrene.
In order to estimate the magnitude of the energy advantage, a
set of rough calculations on the heat duty in the recovery
processes were performed. Using the LLE description by
UNIQUAC, the minimum solvent to feed (S:F) ratio (on mass
basis) was determined by simulation in ASPEN Plus of the LLX
process with 1000 equilibrium stages, a feed containing 90 wt %
MCH, and obtaining >99.9 wt % MCH purity. Afterward, for the
heat duty in the solvent recovery stage, a short-cut calculation
was applied. Assuming that most of the sensible heat may be
recoverable using heat exchangers, the latent heat of vapor-
ization (ΔHvap) of the most volatile compound was used as an
estimate. For water as solvent, a minimum S:F ratio of 1.8 was
obtained for CHOH and 7.3 for CHO. Since water for these
systems is a volatile solvent, evaporation of all the water resulted
in a heat duty of 41.3 MJ/kgCHOH and 166 MJ/kgCHO.
For Cyrene, a lower minimum S:F ratio was required, which is
a direct consequence from the larger capacity toward CHO and
CHOH, being 1.2 for CHOH and CHO. Furthermore, since
Cyrene in these systems is a high boiling solvent, the solutes
CHOH and CHO should be boiled off. Due to solvent leaching,
MCH should be boiled offfrom the raffinate to recover the
solvent, and the evaporation of MCH from the raffinate is
included in the calculations. This resulted for CHOH in a heat
duty of 3.86 MJ/kgCHOH and for CHO in 3.87 MJ/kgCHO. These
short-cut calculations show that extraction processes using
Cyrene instead of water may be 11 times more efficient for the
separation of CHOH from MCH and 43 times more efficient for
CHO from MCH. This is a rough heat duty estimate, and in an
accurate process simulation, the final heat duty may be less
beneficial. However, with the current figures, it shows high
potential for a significant advantage of the high boiling Cyrene
over the low boiling water. The fact that most energy savings
compared to water were accomplished by the higher boiling
point of the solvent suggests that for this application the use of
ionic liquids (ILs) might be interesting too, on the condition
that beneficial behavior is observed in LLE. However, no LLE
data have been found for MCH/CHOH or CHO with an IL.
The separation of CHO and CHOH may also be
accomplished with Cyrene due to the fact a larger selectivity is
observed toward CHOH than CHO. Although no phase
separation is expected and LLX is not possible, other separation
techniques may be used such as extractive distillation or perhaps
with an extractive divided wall configuration.
■CONCLUSION
Four biphasic ternary systems have been assessed in which
methylcyclohexane (MCH) and Cyrene were kept constant. As
a third compound, toluene, cyclohexanol, cyclohexanone, and
cyclopentyl methyl ether (CPME) were applied. For each
ternary system, a selective extraction was found at the three
studied temperatures of 298.15 K, 323.15 K, and 348.15 K.
Cyclohexanol (up to SCHOH,MCH =61.42±4.33) and
cyclohexanone (up to SCHO,MCH = 44.07 ±8.63) were most
selectively extracted, while toluene (up to STOL,MCH = 11.99 ±
0.89) and CPME (up to SCPME,MCH = 6.42 ±0.08) were
extracted with considerably lower selectivity. While Cyrene was
outperformed by Sulfolane and several ionic liquids in the
extraction of toluene, the potential of Cyrene in the cyclo-
hexanol/cyclohexanone systems was observed. Although a lower
selectivity was seen than with water, due to the high boiling point
of Cyrene, recovery can be much less costly. Overall, we
conclude that Cyrene can be applied as a biobased extraction
solvent for a variety of separations, although for several systems
the phase envelope is relatively narrow and narrower at higher
temperatures.
■ASSOCIATED CONTENT
*
sıSupporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acssuschemeng.0c04159.
Four tables with all experimental data for Figures 2,4,5
and 6, including weight percentages of all compounds in
each phase, the distribution coefficient of MCH and the
solute (being TOL, CHO, CHOH or CPME), and the
selectivity of that solute over MCH; the thermodynamic
consistency of all UNIQUAC correlations was checked
using the determinant of the Hessian matrix ap-
proach;
47,48
and the results displayed in four figures
(PDF)
■AUTHOR INFORMATION
Corresponding Author
Boelo Schuur −Sustainable Process Technology Group, Process
and Catalysis Engineering Cluster, Faculty of Science and
ACS Sustainable Chemistry & Engineering pubs.acs.org/journal/ascecg Research Article
https://dx.doi.org/10.1021/acssuschemeng.0c04159
ACS Sustainable Chem. Eng. 2020, 8, 14807−14817
14814

Technology, University of Twente, 7522 NB Enschede, The
Netherlands; orcid.org/0000-0001-5169-4311;
Phone: +31 53 489 2891; Email: b.schuur@utwente.nl
Author
Thomas Brouwer −Sustainable Process Technology Group,
Process and Catalysis Engineering Cluster, Faculty of Science and
Technology, University of Twente, 7522 NB Enschede, The
Netherlands; orcid.org/0000-0002-3975-4710
Complete contact information is available at:
https://pubs.acs.org/10.1021/acssuschemeng.0c04159
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
This has been an ISPT (Institute for Sustainable Process
Technology) project (TEEI314006/BL-20-07), cofunded by
the Topsector Energy by the Dutch Ministry of Economic
Affairs and Climate Policy. We would like to acknowledge the
Circa group for sending us 1 L of Cyrene to perform this
research.
■ABBREVIATIONS
[BMIM][B(CN)4] = 1-butyl-3-methylimidazolium tetracya-
noborate
[BMIM][MSO4] = 1-butyl-3-methylimidazolium methylsul-
fate
[EMIM][ESO4] = 1-ethyl-3-methylimidazolium ethylsulfate
[HMIM][B(CN)4] = 1-hexyl-3-methylimidazolium tetracya-
noborate
[Xi]O= Weight fraction of compound iin the organic phase
[Xi]S= Weight fraction of compound iin the solvent phase
Aij = Temperature independent UNIQUAC fit parameter
Bij = Temperature dependent UNIQUAC fit parameter
Bp = boiling point
CHO = Cyclohexanone
CHOH = Cyclohexanol
CPME = Cyclopentyl methyl ether
Cyrene = Dihydrolevoglycosenone
D = Debye
DMF = N,N-dimethylformamide
DMSO = Dimethyl sulfoxide
ED = Extractive distillation
KD,i= Distributation coefficient of solute i
LLE = Liquid−liquid equilibrium
LLX = Liquid−liquid extraction
MCH = Methylcyclohexane
NMP = N-methylpyrrolidone
qi= van der Waals surface area of solute i
ri= van der Waals volume of solute i
Sij = Selectivity of solute iover solute j
Sulfolane = Tetrahydrothiophene-1,1-dioxide
SI = Supporting Information
S:F ratio = Solvent to feed ratio (mass basis)
T(K) = Absolute temperature
TOL = Toluene
UNIQUAC = Universal quasichemical
yi= Activity coefficient of solute i
yi
C= Combinatorial term of the activity coefficient of solute i
yi
R= Residual term of activity coefficient of solute i
ΦI= Volume fraction
θI= Surface area fraction
τij = Binary interaction parameter between solutes iand j
I̵= Extrapolated from corresponding literature to similar
solute concentration in solvent phase.
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