A strategy to overcome the thermodynamic limitation in CO2 conversion using ionic liquids and urea

Article abstract of DOI:10.1039/c4gc02199a

Enhancing the equilibrium conversion of thermodynamically unfavorable reactions is a very interesting and challenging topic for chemists. The unique properties of ionic liquids (ILs) provide new opportunities to solve this problem. Herein a strategy is proposed to circumvent the thermodynamic limitation of chemical reactions using the designable and non-volatile nature of ILs. In this approach a reactant first reacts with a functional IL to form a high energy IL intermediate, which can further react with other reactants to yield products and regenerate the IL. To verify the feasibility of this strategy, the syntheses of dimethyl carbonate (DMC) and methyl formate (MF) via urea, which are very important reactions used to convert CO₂ but are thermodynamically unfavorable, were conducted with the aid of a diol IL. It was found that the equilibrium yields of DMC and MF obtained by this methodology could be 64 times and 9 times higher, respectively, than those of the conventional methods. This journal is

Full text of DOI:10.1039/c4gc02199a

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ARTICLE TYPE
A Strategy to Overcome the Thermodynamic Limitation in CO2
Conversion by Using Ionic Liquid and Urea
Zhaofu Zhang,* Congyi Wu, Jun Ma, Jinliang Song, Honglei Fan, Jinli Liu, Qinggong Zhu and Buxing
Han*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Enhancing the equilibrium conversion of thermodynamically unfavorable reactions is a very interesting
and challenging topic for chemists. The unique properties of ionic liquids (ILs) provide new opportunities
to solve the problem. Herein a strategy is proposed to circumvent the thermodynamic limitation of
10 chemical reactions using the designable and nonꢀvolatile natures of ILs. In this approach a reactant first
reacts with a functional IL to form a high energy IL intermediate, which can further react with other
reactants to yield products and the IL is regenerated. To verify the feasibility of this strategy, the
syntheses of dimethyl carbonate (DMC) and methyl formate (MF) via urea, which are very important
reactions to convert CO2 but are thermodynamically unfavorable, were conducted with the aid of a diol
15 IL. It was found that the equilibrium yields of DMC and MF obtained by this methodology could be
respectively 64 times and 9 times higher than those of the conventional methods.
work, we proposed a strategy to enhance the equilibrium
conversion of thermodynamically unfavorable reactions using the
nonꢀvolatile and designable natures of ILs. As examples, the
50 conversion of CO2 to dimethyl carbonate (DMC) and methyl
formate (MF) via urea, which are both very important but
thermodynamically unfavorable reactions, were studied to verify
the feasibility of the strategy. It was demonstrated that the
methodology was very successful to circumvent the
55 thermodynamic limitation of the reactions.
Introduction
Many important chemical reactions are thermodynamically
unfavorable with low or very low equilibrium conversion, which
20 limits their industrial application. Exploration of effective
protocols to shift the reaction equilibrium to desired direction has
been a very interesting and challenging topic in chemical
community.
Carbon dioxide (CO2) is the major greenhouse gas, and it is
25 also an abundant, renewable, nontoxic, nonꢀflammable, easily
available carbon resource. Utilization of CO2 as a feedstock to
produce valueꢀadded chemicals and fuels benefits the sustainable
development of our society, which has attracted extensively
attention. CO2 has been used as a feedstock to synthesize various
30 chemicals,1 such as cyclic carbonates,2 methanol,3 formic acid,4
nitrogen containing chemicals,5 and polymers.6 However, CO2 is
the highest oxidation state of carbon, the low energy level of CO2
blocks its conversion to chemicals and fuels. Finding a way to
overcome thermodynamic limitation is crucial for extending
35 range of CO2 utilization.
Results and discussion
Principle of the strategy.
We discuss the principle using an equilibrium reaction expressed
by eqn (1), in which A reacts with B to form C and D, and C is
60 volatile. In order to overcome the thermodynamic limitation of
the reaction, reactant A first reacts with a functional IL to form
product C and an IL intermediate I that is a high energy substance
(eqn (2)), and the reaction is also thermodynamically
unfavorable. However, the thermodynamic problem can be
65 solved by removing the C (e.g. ammonia in this work) produced
continuously in the reaction process, which can be easily realized
as C is volatile, while the IL and IL intermediate I are nonꢀ
volatile. In the second step, the IL intermediate I reacts with
reactant B to form product D (eqn (3)), and the IL is regenerated
70 at the same time. Therefore, by using the designable nature and
nonꢀvolatility of ILs, we can overcome the thermodynamic
limitation of the reactions that meet the conditions discussed
above.
Ionic liquids (ILs) are organic salts with low melting point
(e.g. below 100 C). ILs have some unusual properties, such as
o
negligible vapor pressure, wide liquidꢀtemperature range, high
thermal stability, excellent solvents for both organic and
40 inorganic substances, and their structures can be designed for
desired functions.7 Applications of ILs in different fields have
been studied extensively in recent years, including chemical
reactions,8 adsorption of CO2 and SO2 from gas streams,9
extraction and fractionation,10 and so on.11
45
The unique properties of ILs provide new opportunities to
solve the challenging problems in chemical reactions. In this
C + D
A + B
(1)
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according to the procedures reported in literature,21 with urea to
form the cycle carbonate IL intermediate (2) and ammonia.
During the reaction the ammonia produced is removed
continuously by blowing an inert gas (CO2 was utilized in this
55 work), so that the thermodynamically unfavorable reaction (Step
1 in Scheme 1) can proceed smoothly. Because the IL (1), the IL
intermediate (2), urea and the catalyst are nonꢀvolatile at the
experimental condition, only ammonia is carried out by the CO2
flow. The ammonia and CO2 can be converted into urea by the
60 widely used process. The second step (Step 2 in Scheme 1)
involves the transesterification of the high energy level IL
intermediate (2) with methanol to yield the desired product DMC,
and the diol IL (1) is regenerated at the same time, and the diol IL
(1) can be reused. In this way, the nonvolatile and designable
65 natures of ILs are used elegantly to overcome the thermodynamic
limitation of the reaction shown in eqn (5).
C + I
A + IL
I + B
(2)
(3)
D + IL
Synthesis of DMC.
DMC is a very useful and environmentally benign chemical due
to its negligible toxicity and good biodegradability. It can be used
as a green solvent, precursor of polycarbonate resins, methylating
and carbonylating agent which can substitute for some toxic
substances such as dimethyl sulphate, phosgene, and methyl
chloroformate.12 It can also be used as gasoline octane
5
10 enhancer.13 DMC can be produced by different ways, such as
reaction of phosgene with methanol,14 oxidative carbonylation of
methanol,15 oxidative reaction of carbon monoxide and methyl
nitrite,16 transesterification of methanol with cyclic carbonates
which are produced from epoxides.17 However, these routes have
15 some inevitable shortcomings such as toxic, corrosive, explosive
reactants are used. DMC can be synthesized by direct reaction of
CO2 and methanol as shown in eqn (4). This route is attractive
because both reactants are very cheap. The equilibrium
conversion of this reaction is very low due to thermodynamic
20 limitation.18 To enhance the equilibrium conversion, dehydrating
agents have been used,19 which increases the cost because of the
consumption of dehydrating agents and causes separation
problem.
CO2
O
O
HO
IL
OH
Step 1
O
O
2NH
+
3
+
H2N
NH2
2
IL
1
Step 2
2CH3OH
Alcoholysis of urea can form alkyl carbonates including
25 DMC,20 as shown in eqn (5). Meanwhile, the ammonia liberated
can be recycled and only CO2 and alcohol are consumed in the
process because urea is produced from CO2 and ammonia in
industry.20a The obvious advantage of this route is that simple and
cheap catalyst can be used to accelerate the reaction and the
30 reaction can be conducted at ambient pressure.20 However, this
reaction is also thermodynamically unfavorable, and the
equilibrium conversion is very low even large excess of methanol
is used. Removal of ammonia continuously from the reaction
system can shift the reaction equilibrium to DMC side, and this
35 can be realized by coupling of the reaction and condensing
process.20cꢀ20e In this route, methanol and DMC vaporized are
condensed in condenser and return back to the reactor.
Obviously, the evaporatingꢀcondensing of the methanol and the
product occurs repeatedly in the reaction process, which leads to
40 high energy consumption and low efficiency. The equilibrium
can be shifted by neutralizing the ammonia produced,20f but this
need postꢀtreatment.
HO
IL
OH
O
Reuse
N
+
O
N
O
O
N
S
OH
O
:
:
S
1
S
CF3
O
OH
O
F3C
O
O
N
N
N
S
O
O
S
2
S
CF3
F3C
O
O
O
Scheme 1 The reactions of the diol IL (1) with urea to form the IL
intermediate (2) and ammonia (Step 1), and IL intermediate (2) reacts
70 with methanol to produce DMC and the diol IL (1) is regenerated at the
same time (Step 2). Structures of the diol IL (1) and the IL intermediate
(2) are provided at the bottom.
To synthesize IL intermediate (2), some simple and
commonly used catalysts22 for the reaction of urea with hydroxyl
75 groups to produce cycle carbonates were tested for the reaction of
the diol IL (1) with urea (Step 1 in Scheme 1), and the results are
shown in Fig. 1. Obviously, the metal oxides and metal chlorides
could promote the reaction effectively, and ZnO exhibited the
highest activity among them. Therefore, the reaction conditions
80 were further optimized using ZnO as the catalyst.
O
CO2
+
2CH3OH
+ H2O
O
O
(4)
O
O
+
2CH3OH
+ 2NH3
O
O
H2N
NH2
CO2
(5)
45
In this work, the new strategy was used to overcome the
thermodynamic limitation to produce DMC from urea and
methanol. Two steps are involved, as shown schematically in
Scheme 1. The first step is the reaction of a diol IL (1), 1ꢀ(6’,7’ꢀ
dihydroxylꢀ4’ꢀthiaheptyl)ꢀ3ꢀmethylimidazolium
50 bis((trifluoromethyl)ꢀsulfonyl)ꢀimide which was synthesized
2
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60
40
20
a
b
60
40
20
0
45
30
15
0
0
120
140
160
C
0
1
2
3
Temperatureo
(
)
ZnO (wt%)
100
d
c
80
60
40
20
0
90
80
70
ZnCl2 ZnO Bu2SnO MgO
SnCl2
Sweeping with CO 2
Closed system
Fig. 1 The performance of various catalysts on the synthesis of IL
intermediate (2) (step 1 in Scheme 1). Diol IL (1) 1.02 g, urea 0.12 g,
catalysts 0.2 mmol, CO2 flow rate 5 mL/min, 150 oC, 2 hrs.
1.0
1.1
1.2
1.3
1.4
0
2
6
8
10
4Time (h)
Mole Ratio (Urea/IL)
5
The effects of ZnO amount and temperature on the yield of IL
intermediate (2) are presented in Fig. 2a and 2b, respectively. As
shown in Fig. 2a, the yield increased with increasing amount of
the catalyst, and increased slowly as the amount of ZnO exceeded
1.6 wt% (IL basis). Fig. 2b demonstrates that the yield was very
45 Fig. 2 Effects of reaction conditions on yield of the IL intermediate (2)
[IL(1) basis]. (a) Effect of amount of ZnO (wt% in ILꢀZnO mixture), IL
(1) 1.02 g, molar ratio of urea:IL 1:1, CO2 flow rate 5 mL/min, 150 oC, 2
hrs; (b) Effect of temperature, IL(1) 1.02 g, molar ratio of urea:IL 1:1, 1.6
wt% ZnO in ILꢀZnO mixture, CO2 flow rate 5 mL/min, 2 hrs; (c) Effect
50 of reaction time, IL(1) 1.02 g, molar ratio of urea:IL 1:1, 1.6 wt% ZnO in
o
10 low at lower temperature, and increased dramatically in the range
of 140 oC to 150 oC, and then decreased slightly with further
increasing temperature. The main reason for this phenomenon
may be that urea decomposes considerably at the higher
temperature.23
ILꢀZnO mixture, CO2 flow rate 5 mL/min if used, 150 C; (d) Effect of
molar ratio of urea:IL, IL(1) 1.02 g, 1.6 wt% ZnO in ILꢀZnO mixture,
CO2 flow rate 5 mL/min, 150 oC, 8 hrs.
Transesterification of cycle carbonates and alcohols to
55 produce linear alkyl carbonates is a class of well established
15
The effect of reaction time on the yield of the IL intermediate
(2) is illustrated in Fig. 2c. The yield increased with time at the
beginning, and was independent of time after 8 hrs. The
maximum yield was 87% at the urea:diol IL (1) molar ratio of 1:1.
The maximum yield was less than the theoretical value (100%),
24
reactions, and bases can catalyze the reaction effectively.
Therefore, DMC can be produced by the transesterification of the
IL intermediate (2) and methanol (Step 2 in Scheme 1), and the
catalyst ZnO used in Step
1 can also catalyzed the
60 transesterification reaction due to its basic nature. It can be
known from Scheme 1 that stoichiometrically two moles of
methanol react with one mole of IL intermediate (2) to produce
one mole of DMC. In this work, the yields of DMC at the
methanol:IL intermediate (2) feeding molar ratios of 10:1, 30:1,
65 and 100:1 were studied, and the results are presented in Fig. 3.
The yield of DMC increased with reaction time at beginning, and
then became independent of time because transesterification
reactions are also reversible. The maximum yields at the feeding
ratios of 10:1, 30:1, and 100:1 were 73%, 82%, and 87%,
70 respectively. For comparison, the yield of DMC by the
conventional route （eqn (5)) without removing the NH3 released
20 which resulted from the decomposition and loss of urea during
the reaction. For comparison, we also carried out the experiments
in the reactor without removing the ammonia produced in the
reaction. The maximum yield of the IL intermediate (2) was only
3%, as shown in Fig. 2c. When CO2 is sealed in cell to enhance
25 the yield of DMC,20f the effection is limited. This indicates that
removal of the ammonia formed in the reaction process was the
key to reach high yield. We also used N2 as the blowing gas to
remove the ammonia at the reaction condition of Fig. 2c, and the
results were nearly the same with that when CO2 was utilized,
30 indicating that the only function of CO2 was to remove the
ammonia produced to shift the reaction equilibrium. However,
CO2 is preferable in practical application because CO2 is required
in the conversion of ammonia back into urea. In this way, the
ammonia acts as a bridge for the reaction of CO2 and the diol IL
35 (1) to form the IL intermediate (2).
The effect of the urea:diol IL (1) molar ratio in the feed on
the maximum yield of the IL intermediate (2) was also
investigated. The yield increased as the urea:diol IL (1) molar
ratio was increased, as can be known from Fig. 2d. At the feed
40 molar ratio of 1.4:1, the yield of the IL intermediate (2)
was >99%, indicating that nearly all of the diol IL (1) was
converted into the IL intermediate (2) at this condition.
o
was also determined at 150 C and different feeding molar ratios
of methanol and urea using ZnO as catalyst, and the results are
given in Fig. 3. The equilibrium yields of DMC at the
75 methanol:urea feed molar ratios of 10:1 and 100:1 were 1% and
2%, respectively. The yields were very low due to the
thermodynamic limitation,20cꢀ20e which is consistent with the
results reported in the literature for this reaction.25 It can be easily
known from the results in Fig. 2 and 3 that the novel strategy
80 proposed in this work is very efficient to overcome the
thermodynamic limitation of the reaction. For example, using this
strategy, one mole of urea could produce 0.87 mole of IL
intermediate (2) at the urea:IL(1) feeding molar ratio of 1:1 (Fig.
2c). Therefore, one mole of urea could produce about 0.64 mole
85 of DMC at the methanol:IL intermediate (2) feeding molar ratio
of 10:1 because one mole of IL intermediate (2) could generate
0.73 mole of DMC (Fig. 3). By the direct reaction of urea with
methanol without removing NH3, one mole of urea could only
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CO2
produce 0.01 mole of DMC at the methanol:urea feeding molar
ratio of 10:1 (Fig. 3). Therefore, the yield obtained by the present
protocol can be 64 times higher than that of the conventional
method.
O
C
O
C
HO
IL
OH
Step 1
O
O
2NH
+
3
100
80
60
40
20
0
+
H2N
NH2
2
IL
1
CH3OH
CO2 H2
Step 2
HO
IL
OH
O
C
0
1
2
3
4
Time (h)
5
X
Reuse
+
Fig. 3 The yields of DMC by the transesterification reaction of the IL
intermediate (2) with methanol (step 2 in Scheme 1) [IL intermediate (2)
basis] and by the alcoholysis reaction of urea and methanol shown in eq 5
H
O
Scheme 1 The reactions of the diol IL (1) with urea to form the IL
intermediate (2) and ammonia (Step 1), and the IL intermediate (2) reacts
with CO2, H2 and methanol to produce MF and the diol IL (1) is
40 regenerated at the same time (Step 2).
（Urea basis） at the same reaction condition. IL intermediate (2) or urea
o
10 2.0 mmol, 150 C, ZnO 16 mg, □ methanol:IL intermediate (2) 10:1, ◆
methanol:IL intermediate (2) 30:1, ● methanol:IL intermediate (2) 100:1,
▲ methanol: urea 10:1, ■ methanol:urea 100:1.
HCOOCH3 + H2O
+ H2 + CH3OH
CO2
(6)
Synthesis of MF.
O
MF can be used as insecticide, solvent, and can also be used to
15 synthesize pharmaceuticals, formamide, dimethylformamide, and
formic acid.26 In industry, MF is mainly produced by the
carbonylation of methanol with CO catalyzed by strong base
(such as sodium methoxide). MF can be synthesized from CO2,
H2 and methanol as shown is eqn (6), this is an attractive reaction
20 and has attracted considerable attention.26,27 However, this
reaction is also a thermodynamic unfavorable, and the low
conversion blocks its application in industry. If water is removed
from the reaction system, equilibrium will shift to the right side
and yield of MF will be enhanced. The strategy proposed in this
25 work was also used to synthesize MF from urea, H2 and methanol,
as shown schematically in Scheme 2.
HO OH
O
O
+ H2O
+ CO2
IL
IL
(7)
(8)
O
O
HO OH
O
O
+ H2 + CH3OH
+
H
O
IL
IL
RuCl3 and 1,8ꢀdiazabicyclo[5,4,0]undecꢀ7ꢀene (DBU) was
45 used as catalysts for step 2. The RuCl3 catalyzes the generation of
formic acid and DBU promotes the reaction of formic acid and
methanol to yield MF.27d The dependence of the yield of MF on
reaction time is presented in Fig. 4. The yield of MF increased at
beginning and became independent of time after 16 hrs,
50 indicating that the equilibrium of the reactions has been reached.
The maximum yield was 38% in 16 hrs under the reaction
condition in this work. For comparison, the yield of MF by the
conventional route eqn (6) without IL intermediate (2) was also
determined at the same condition, and the results are also given in
55 Fig. 4. The equilibrium yield of MF was only 4.2% due to the
thermodynamic limitation.26,27 It can be known from the results
that the yield of MF by the present protocol can be 9 times higher
than that of the route reported.26,27 So the novel strategy proposed
in this work is also very efficient to overcome the thermodynamic
60 limitation in synthesis of MF.
Step 1 in the MF synthesis is the same as that in DMC
synthesis, in which IL intermediate (2) is formed. Step 2 consists
of two reactions. One is the reaction of CO2, H2 and methanol to
30 produced MF and water as shown in eqn (6).26,27 The other is the
reaction of the IL intermediate (2) reacts with water to shift the
reaction and it is converted to diol IL (1) and CO2 as shown in
eqn (7). In other words, the IL intermediate (2) acts as a
dehydration agent, which is changed back into the diol IL in the
35 reaction. Combining eq (6) with (7) gets the overall eqn (8).
40
35
30
IL Intermediate
No IL
25
20
15
10
5
0
0
4
8
12
16
20
24
Time (h)
Fig. 4 The yields of MF on time for the reaction of methanol and CO2, H2
with and without IL intermediate (2). Methanol 10 mmol, RuCl3•2H2O 6
mg, DBU 0.6 mmol, total pressure of H2 and CO2 10 MPa (H2 5 MPa),
4
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o
150 C, methanol and carbonate IL (2) (if used) feeding molar ratio was
1:1.
Experimental section
50 Generals
The reusability of the diol IL(1)/ZnO.
3ꢀAllylꢀ1ꢀmethylimidazolium bromide ([amim]Br) with a purity
of > 99% was supplied by Centre for Green Chemistry and
Catalysis, LICP, CAS. 1ꢀThioglycerol (>95%) and 2,2ꢀ
The reusability of the diol IL(1)/ZnO catalytic system was
studied in synthesis of DMC, and the results are given in Fig. 5.
In the experiments, urea first reacted with the diol IL(1) to
produce the carbonate IL (2) at the condition of Fig. 2d with a
urea:diol IL(1) molar ratio of 1.4:1, and the yield of IL
intermediate (2) was determined (step 1 in Scheme 1). Then IL
10 intermediate (2) reacted with methanol to produce DMC by the
transesterification reaction at the condition of Fig. 3 at methanol:
IL intermediate (2) molar ratio of 100:1 with a reaction time of 2
hrs. After reaction, the reactor was cooled to 50 oC, and the DMC
and methanol in the reactor were carried out by CO2 flow and
15 were absorbed in a cold trap with DMF as absorbent. The IL/ZnO
catalytic system was reused directly for the next run at the same
condition. It can be known from Fig. 5 that the yields of the IL
intermediate (2) and DMC were almost same in the three cycles,
indicating that the IL/ZnO catalytic system had excellent
20 reusability.
5
dimethoxyꢀ2ꢀphenylacetophenone
(DMPA,
>98%)
were
55 analytical grade and purchased from TCI Co., Ltd. ZnO, ZnCl2,
Bu2SnO, MgO, and SnCl2 were all analytical grade and were
provided by Sinopharm Chemical Reagent Co., Ltd. CO2 with a
purity of 99.99% and H2 with a purity of 99.999% were obtained
from Beijing Analytical Instrument Factory. All reagents were
60 used as received.
The diol IL (1) 1ꢀ(6’,7’ꢀdihydroxylꢀ4’ꢀthiaheptyl)ꢀ3ꢀ
methylimidazolium bis((trifluoromethyl)ꢀsulfonyl)ꢀimide was
synthesized from [amim]Br and 1ꢀthioglycero initiated by DMPA
according to the procedures described in the literature1. 1H
65 NMR(400 MHz, Bruker Avance 400, CD3CN): δ=8.43 (s, 1H);
7.38 (br s, 1H); 7.33 (br s, 1H); 4.22ꢀ4.28 (br, 2H); 3.83 (br, 3H);
3.65ꢀ3.72 (br, 1H); 3.49ꢀ3.56 (br, 1H); 3.42ꢀ3.48 (br, 1H); 3.08ꢀ
3.14 (br, 1H); 2.80ꢀ2.86 (br, 1H); 2.63ꢀ2.70 (br, 1H); 2.50ꢀ2.61
(br, 3H); 2.08ꢀ2.16 (br, 2H).
2
100
75
50
25
0
DMC
70
Cycle carbonate IL (2): 1H NMR (400 MHz, CD3CN): δ=8.43
(s, 1H); 7.38 (br s, 1H); 7.33 (br s, 1H); 4.88ꢀ4.97 (br, 1H); 4.54ꢀ
4.60 (br, 1H); 4.19ꢀ4.26 (br, 3H); 3.83 (br, 3H); 2.88ꢀ2.93 (br,
2H); 2.58ꢀ2.64 (br, 2H); 2.08ꢀ2.16 (br, 2H).
Typical procedures for the reactions
75 The procedures for the reactions are as follow. In a typical
experiment to produce the IL intermediate (2) (Step 1 in Scheme
1), 1.02 g diol IL(1), desired amounts of urea, and catalyst were
added into a stainless steel reactor of 10 mL with a magnetic
stirrer, which was the similar to that used previously.28 The
80 reactor was heated to desired temperature after the air was
removed, then the stirrer was started and CO2 blowed through the
reactor to remove the ammonia produced in the reaction
continuously. The reactor was cooled in water to stop the reaction
after a certain reaction time, and the yield of the IL intermediate
85 (2) was determined by 1H NMR. In synthesis of DMC (Step 2 in
Scheme 1), a known amount of methanol was added into the
reactor above. After reacted at 150 oC for desired time, the reactor
was cooled to 50 oC quickly. The product and methanol were
removed by CO2 flow and were absorbed in a cold trap with
1
2
3
Cycle
Fig. 5 Reuse of the diol IL (1)/ZnO. Reaction condition for producing the
IL intermediate (2): diol IL (1) 1.02 g, ZnO 1.6 wt% ZnO in ILꢀZnO
mixture, molar ratio of diol IL (1):urea 1:1.4, CO2 flow rate 5 mL/min,
25 150 oC, 8 hrs; reaction condition for the transesterification of the IL
intermediate (2) and methanol to produce DMC: methanol:IL
intermediate (2) 100:1, 150 oC, 2 hrs.
Conclusions
In summary, we have proposed a strategy to enhance the
30 equilibrium conversion of thermodynamically unfavorable
chemical reactions using the unique properties of ILs. The
methodology has been successfully used for the transformation of
CO2 to DMC and MF via urea. In these reactions, urea first reacts 90 DMF as absorbent. The amount of DMC was determined by GC
with a diol IL to form a cycle carbonate IL that has high energy
35 level by removing the ammonia released continuously. Then
DMC is produced by the reaction of methanol with the high
energy level cycle carbonate IL, and the IL is regenerated at the
(Agilent 4890 D) equipped with a flameꢀionized detector using
ethylbenzene as internal standard. In reuse experiments of the
diol IL/ZnO system, the diol IL/ZnO catalytic system was utilized
directly for the next run after the product and methanol were
same time and can be reused. It is found that by using this 95 removed by CO2 flow. In synthesis of methyl formate (step 2 in
principle, the equilibrium yield of DMC can be 64 times larger
40 than that obtained by traditional route. Using this protocol, the
equilibrium yield of MF from the reaction of CO2, H2 and
methanol can be 9 times higher than that of the conventional
Scheme 2), a known amount of methanol, RuCl3•2H2O and DBU
were added into the reactor above. The reactor was heated up to
150 oC for desired time. Hydrogen was introduced into the cell to
5 MPa, and then CO2 was introduced into the cell up to 10 MPa.
methods. We believe that the highly efficient routes to produce 100 The reaction mixture was stirred and the reactor was cooled to 50
DMC and MF have great potential of application, and the novel
45 idea of using a functional IL as a reactive and renewable
intermediate in chemical reactions opens a promising way to
solve the challenging chemical problems and to explore new
reactions.
oC quickly. The quantitative determination of MF produced was
the same as that of DMC analysis.
Acknowledgements
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

Green Chemistry
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View Article Online
DOI: 10.1039/C4GC02199A
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The authors thank the Ministry of Science and Technology of
China (2011CB808603), the National Natural Science
Foundation of China (21173239, 21133009, 21303224,
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| Journal Name, [year], [vol], 00–00
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Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C4GC02199A
TOC
A strategy is proposed to overcome the thermodynamic limitation
5 nofonc-hveomlaitcialel rneaatcutrieosnosf(ICLOs. conversion) using the designable and
2