Carbon dioxide capture and use: Organic synthesis using carbon dioxide from exhaust gas

Article abstract of DOI:10.1002/anie.201308341

A carbon capture and use (CCU) strategy was applied to organic synthesis. Carbon dioxide (CO₂) captured directly from exhaust gas was used for organic transformations as efficiently as hyper-pure CO₂ gas from a commercial source, even for highly air- and moisture-sensitive reactions. The CO₂ capturing aqueous ethanolamine solution could be recycled continuously without any diminished reaction efficiency. Exhaust gas is good enough! Carbon dioxide captured directly from exhaust gas was used for organic syntheses (see picture) as efficiently as hyper-pure CO₂ gas from a commercial source, even for highly air- and moisture-sensitive reactions. The CO₂ capturing aqueous ethanolamine solution could be recycled continuously without any diminished reaction efficiency. Copyright

Full text of DOI:10.1002/anie.201308341

Angewandte
Chemie
DOI: 10.1002/anie.201308341
Sustainable Chemistry
Carbon Dioxide Capture and Use: Organic Synthesis Using Carbon
Dioxide from Exhaust Gas**
Seung Hyo Kim, Kwang Hee Kim, and Soon Hyeok Hong*
Dedicated to Professor Robert H. Grubbs
Abstract: A carbon capture and use (CCU) strategy was
applied to organic synthesis. Carbon dioxide (CO2) captured
directly from exhaust gas was used for organic transformations
as efficiently as hyper-pure CO2 gas from a commercial source,
even for highly air- and moisture-sensitive reactions. The CO2
capturing aqueous ethanolamine solution could be recycled
continuously without any diminished reaction efficiency.
R
ecycling carbon dioxide (CO2) as a renewable and environ-
ment-friendly source of carbon is one of the most attractive
solutions to reduce our dependence on petrochemicals. One
of the main approaches to recycle CO2 is its capture and use
(CCU);[1] this approach has the potential to afford value-
added products from the sustainable C1 feedstock and to
make large-scale cuts in atmospheric CO2 emissions by
capturing anthropogenic CO2 without restructuring or closing
the industrial plants.
Figure 1. Carbon dioxide capture and use for organic synthesis.
Therefore, it is highly desirable to use the environment-
friendly raw material, CO2, as a C1 source for synthesizing
fine chemicals. Urea has already been synthesized on an
industrial scale using CO2.[6] Moreover, catalytic syntheses of
polycarbonates[7] and cyclic carbonates[8] have recently been
commercially used. Significant amounts of academic research
have been conducted to transform CO2 into fine chemi-
cals.[9,10] Inspired by the overall CCU concept, we envisioned
that the CO2 from exhaust gas rather than commercial CO2
gas can be used for usual organic syntheses. Herein, we report
an unprecedented strategy for using CO2 that is captured
from combustion sources for organic syntheses (Figure 1).
We devised our strategy as follows: 1) selective capturing
of CO2 generated from fossil fuel combustion using an
alkanolamine solution[11] and then 2) conduct organic reac-
tions with CO2 released from the captured material
(Figure 1). The alkanolamine solution used in the process
can be recycled for subsequent capture and release processes.
To test this idea, previously reported silver-catalyzed carbox-
ylation of alkynes[12] was chosen as the model reaction to
confirm if the amount and purity of CO2 released from the
captured materials are sufficient to carry out an organic
reaction (Table 1).[13] When hyper-pure CO2 (> 99.999%)
obtained from a commercial supplier was directly applied to
the reaction mixture under atmospheric pressure, the carbox-
ylation of acetylene afforded the corresponding product in
83% yield (Table 1, entry 1).[12]
Currently, amine scrubbing technology is used for captur-
ing CO2 in industry,[2] while the development of advanced
CO2 capture materials such as ionic liquids and metal–organic
framework materials is underway.[3] In the amine-based CO2
capture process, alkanolamines selectively react with CO2 in
flue gas to form the corresponding carbamates (Figure 1).[4]
The alkanolamines can be recovered by stripping CO2 with
water vapor at 100–1208C and recycled back to the beginning
of the process. After the water is condensed from the stripper
vapor, the CO2 is compressed to 100–150 bar. The condensed
CO2 is then transported using pipeline or ship for geologic
sequestration, and only a small portion of it is used as a C1
source for chemical synthesis.[5] A high cost is paid for the
transportation and sequestration.
[*] S. H. Kim, K. H. Kim, Prof. Dr. S. H. Hong
Center for Nanoparticle Research
Institute for Basic Science (IBS), Seoul 151-742 (Republic of Korea)
and
Department of Chemistry, College of Natural Sciences
Seoul National University, Seoul 151-747 (Republic of Korea)
and
Korea Carbon Capture Sequestration R&D Center (KCRC)
Daejeon 305-303 (Republic of Korea)
E-mail: soonhong@snu.ac.kr
Several alkanolamine solutions either in DMF or water
(e.g., 7 molality (m), about 30% ethanolamine (MEA) by
weight, the most used concentration and CO2 capture
material in industry, respectively) have been tested as CO2
capture and release materials.[11] To optimize the reaction
conditions, hyper-pure CO2 gas was introduced into the
alkanolamine solution for 15 min, and the saturated CO2
Homepage: http://gomc.snu.ac.kr
[**] This work was supported by the Korea CCS R&D Center (grant
number NRF-2013M1A8A1035844) and Institute for Basic Science
(IBS), funded by the Korea government (Ministry of Science, ICT &
Future Planning).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201308341.
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Table 1: Alkyne carboxylation reaction to test efficiencies of CO2 captur-
release capability and low costs, which also account for it
being the most popularly used in industry.[16]
ing solutions.[a]
Encouraged by the initial results, the strategy to use CO2
from exhaust gas was further applied to the carboxylation of
various alkynes (Table 2).[12] A burning candle, a mixture of
C20–C40 hydrocarbons, was selected as the combustion source.
An aqueous MEA solution (7 m, 25 mL of H2O) in a reaction
tube was chosen to capture CO2 from the combustion source
and then release CO2 for the target reaction. The recycled
solution was used for all the experiments listed in Tables 2 and
4. Photographs of the reaction set up following the design in
Figure 1 are presented in the Supporting Information (Fig-
ures 1S and 2S in the Supporting Information). Although
some soot was produced due to incomplete combustion, to
our delight, the carboxylation reactions with released CO2,
which was captured by the MEA solution from the combus-
Entry
Amine[b]
Solvent
Volume [mL][c]
Yields[d]
1[e]
2
Pure CO2 (>99.999%)
–
–
83%
82%
67%
73%
H2O
H2O
DMF
25
5
3
4
5
5
6
7
H2O
DMF
H2O
5
5
5
73%
59%
8%
Table 2: Alkyne carboxylation using CO2 from combustion.[a]
8
9
DMF
H2O
5
5
67%
19%
10
H2O
5
69%
[a] Reaction conditions: phenylacetylene (1.0 mmol, 1.0 equiv), AgI
(2.5 mol%), Cs2CO3 (1.5 equiv), CO2 (ambient pressure) from an amine
solution, DMF (10 mL), 258C, 16 h. [b] Pure CO2 was captured by the
amine solution for 15 minutes. [c] Volume of solvent, and molality of
amine solutions: 7 m. [d] Yield of isolated products. [e] The reaction was
performed with hyper-pure CO2 gas.
Entry
Substrates
Recycle
times
Yields [%]
1
2
1
55
3
–
–
82
80
81
0
3[c]
4[d]
5[e]
39
6
2
84
78
80
88
81
solution was used as the CO2 source for the model reactions.
Most of the tested alkanolamine solutions were suitable to be
used as CO2 capture and release material (Table 1). Both
DMFand water worked well as the solvent for MEA (Table 1,
entries 2–4).[2] For our reaction scale (1 mmol), about 35 mL
of aqueous MEA solution (7 m, 25 mL of the solvent) was
enough to show activity comparable to that obtained using
commercial hyper-pure CO2 gas (Table 1, entries 1 and 2). In
the case of diethanolamine, a secondary amine, the reaction
afforded better yield of the product in water than in DMF
(Table 1, entries 5 and 6). The use of diisopropanolamine
afforded a poor yield (8%) of the product in water; however,
a moderate yield (67%) was obtained in DMF (Table 1,
entries 7 and 8).[14] Because tertiary N-methyldiethanolamine
(no acidic H present) cannot react with CO2, its solution in
DMF could not be used to capture CO2 and no reaction
occurred.[15] However, its aqueous solution afforded 19%
yield of the product (Table 1, entry 9). This is because N-
methyldiethanolamine acts as a base and promotes CO2
hydrolysis to afford carbonates that can produce CO2 upon
heating.[15] Sterically hindered 2-amino-2-methyl-1-propanol
that was used to prevent degradation at high temperature
afforded the product in good yields (69%, Table 1,
entry 10).[15] Among the alkanolamine solutions tested, the
aqueous MEA solution was chosen as the optimum CO2-
capturing solution because of excellent CO2 capture and
7
24
26
14
32
8
9
10[f]
11
12
30
21
85
90
13[f]
14[f]
15[f]
20
18
12
89
67
65
[a] Reaction conditions: alkynes (1.0 mmol, 1.0 equiv), AgI (2.5 mol%),
Cs2CO3 (1.5 equiv), CO2 (ambient pressure) from an aqueous MEA
solution (7 m, 25 mL of H2O), DMF (10 mL), 258C, 16 h. [b] A candle
was burned for 3 h, and the CO2 from the exhaust gas was captured in
the MEA solution. [c] CO2 was generated by methanol combustion.
[d] Exhaust gas was directly introduced to the reaction mixture for 7 h.
[e] Dry ice was directly added to the reaction mixture. [f] 508C, 24 h.
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Table 3: Cyclic carbonate synthesis using CO2 from combustion.[a]
tion of the candle, were as efficient as that with hyper-pure
CO2 gas (80–82% yields, Table 2, entries 1–3). Furthermore,
even after recycling the MEA solution 55 times, the reaction
yield did not reduce significantly (80% yield, Table 2,
entry 2). When another combustion source, methanol, was
used for CO2 generation, the reaction efficiency was not
affected either (81% yield, Table 2, entry 3). However, no
reaction occurred when the exhaust gas from the combustion
of candle was directly introduced into the reaction medium
(Table 2, entry 4), which showed that it was essential to use
the MEA solution to increase the CO2 concentration and
purity of the combustion gas. Dry ice, a general source of CO2
in organic chemistry, was directly introduced into the
reaction; however, the yield (39%) was low, presumably
due to the reaction being sensitive to air and water (Table 2,
entry 5). The substrate scope was expanded using the recycled
aqueous MEA solution (Table 2). All the reactions were run
twice, and proceeded smoothly exhibiting comparable reac-
tion yields with previously reported studies using hyper-pure
CO2 gas.[12] The reaction yields were consistent regardless of
the number of times that the aqueous MEA solution was
recycled.
Next, CO2 was incorporated into epoxides to form cyclic
carbonates to check for the applicability of this method to
other reactions.[8] There is an increasing demand for cyclic
carbonates in both industry and academia.[8,17] Carbonates are
used as monomers to synthesize polycarbonates and polyur-
ethanes.[7] Furthermore, the hydrogenation of cyclic carbo-
nates is a promising route to convert CO2 to methanol, an
excellent alternative fuel.[18] Therefore, the syntheses of
carbonates using CO2 gas from combustion sources are an
attractive route for carbon recycling. The incorporation of
CO2 into epoxides to synthesize carbonates is usually
performed at pressures higher than 1 atm.[8] Very recently,
Shi and co-workers reported a carbonate synthesis under
atmospheric pressure using commercially available N-heter-
ocyclic carbene (NHC) and ZnBr2 as the catalyst.[19] We
applied our strategy to evaluate this reaction. Although the
reactions involving NHC are usually air and moisture
sensitive, all the product were obtained in excellent yields
using the released CO2 that was captured by the MEA
solution from the combustion source (90–93%, Table 3).
Therefore, the quality of CO2 captured using the MEA
solution was sufficient to conduct even air and moisture
sensitive reactions using NHC-based transition metal cata-
lysts.
Entry
1
Substrate
Yields [%][c]
90
Entry
3
Substrate
Yields [%][c]
93
2
91%
4
92
[a] Reaction conditions: epoxides (2.0 mmol 1.0 equiv), ZnBr2 (2 mol%),
K2CO3 (2 mol%), 1,3-bis-(2,6-diisopropylphenyl)imidazolinium chloride
(2 mol%), CO2 (ambient pressure) from the captured material, DMSO
(1 mL), 24 h, 808C. [b] A candle was burned for 5 h, and the CO2 from the
exhaust gas was captured in the MEA (aq) solution (70 mL, 7 m).
[c] Yield of isolated products.
comparable to that of the reaction with dry ice (96%, Table 4,
entry 2). The reaction could also be applied to other Grignard
reagents performing carboxylations in high yields (89–99%,
Table 4, entries 3–4). Notably, the use of 54-times-recycled
MEA solution did not diminish the reaction efficiency
(Table 4, entry 4).
In conclusion, an unprecedented organic synthesis strat-
egy using CO2 from exhaust gas was demonstrated. We have
validated that the CO2 generated from several combustion
sources could be used in organic syntheses as efficiently as
Table 4: Grignard reaction with CO2 from combustion.[a]
Finally, we applied our strategy to one of the most widely
used organic reactions, Grignard reaction.[20] The reaction of
Grignard reagents with CO2 using dry ice is a well-known
synthetic route to obtain carboxylic acids. We conducted
Grignard reactions to confirm the quality of CO2 captured
using the recycled aqueous MEA solution that had been used
for alkyne carboxylation. Grignard reagents are very sensitive
to moisture, as it causes protonation, and to O2 in air, as it
forms peroxides.[20] Therefore, it would be good to verify if
this strategy can be applied to highly moisture and oxygen
sensitive reactions. The incorporation of CO2 into phenyl
magnesium bromide using our set-up afforded benzoic acid in
excellent yield (98% yield, Table 4, entry 1), which was
Entry Substrate
1
Yields [%][c] Entry Substrate
Yields [%][c]
89
98
96
3
4
2[d]
99
[a] Reaction conditions: Grignard reagents (1.0 mmol), THF (1 mL), CO2
(ambient pressure) from the recycled captured material, 258C, 1 h. [b] A
candle was burned for 3 h, and the CO2 from the exhaust gas was
captured in the aqueous MEA solution (7 m, 25 mL of H2O). [c] Yield of
isolated products. [d] Dry ice was directly added into the reaction tube as
the CO2 source.
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a Schlenk flask. To capture CO2, the exhaust gas from the combustion
of a candle was bubbled through the MEA solution for 3 h at room
temperature. The CO2-saturated solution could be stored at room
temperature for more than a week and used when needed. The flask
with the solution was connected to a reflux condenser. The top end of
the reflux condenser was connected to a dry column linked to
a bubbler. The MEA solution was heated to 1258C for 10–15 minutes
to purge the set up with CO2. Next, the bubbler was replaced with
a gas line with a needle in the end. The target organic reaction
(1 mmol scale) was set up separately in a Schlenk flask under inert
conditions. The line from the captured CO2 solution and the vent line
with a bubbler were introduced into the target reaction flask while
CO2 evolution continued. The reaction flask was purged with CO2 gas
from the MEA solution for 5 minutes. Next, the vent line was
exchanged with a balloon. CO2 was captured in the balloon for 10–
25 minutes until no more CO2 evolved from the captured material.
Next, the line from the CO2 source was closed, and the reaction flask
was isolated. The reaction continued under closed conditions with the
equipped CO2 balloon (see Figures 1S and 2S).
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Received: September 24, 2013
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Keywords: carbon dioxide capture · carbon dioxide fixation ·
ethanolamine · renewable resources · sustainable chemistry
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