Article pubs.acs.org/EF
Thermal Degradation of Aminosilicone Carbamates Robert J. Perry,*,† Matthew P. Rainka,† Mark D. Doherty,† Benjamin R. Wood,† Omkar Namjoshi,‡ Daniel Hatchell,‡ Hanbi Liu,‡ and Gary T. Rochelle‡ †
GE Global Research, 1 Research Circle, Niskayuna, New York 12309, United States McKetta Department of Chemical Engineering, The University of Texas at Austin, 200 East Dean Keeton Street, Austin, Texas 78712, United States
‡
S Supporting Information *
ABSTRACT: The major thermal degradation pathway seen with 1,5-bis(3-aminopropyl)-1,1,3,3,5,5-hexamethyltrisiloxane/ triethylene glycol (GAP-1/TEG) is the formation of a urea-containing compound. Degradation is increased at higher temperatures, longer reaction times, higher CO2 concentrations (in the form of carbamate loading), and low water levels. A judicious choice of operating conditions can significantly decrease urea byproduct formation. Reducing the desorption temperature from 140 to 100 °C and adding 5 wt % water to the 60:40 mixture of GAP-1/TEG resulted in a 500-fold reduction in amine loss after 4 days in a CO2-rich environment. After 56 days of continuous heating under the same conditions, ∼87% original GAP-1 was retained at 100 °C compared to only ∼20% at 140 °C. The urea byproduct appears to be the only major degradation pathway under these conditions, with 100% of the mass balance accounted for by the urea and amine components.
■
INTRODUCTION The benchmark technology for the post-combustion capture of CO2 from coal-fired power plants, to which other processes are compared, is an aqueous solution of monoethanolamine (MEA).1 Aminosilicones have been examined as alternatives to aqueous amines for CO2 capture. These have included primary amines, such as 1,3-bis(3-aminopropyl)-1,1,3,3tetramethyldisiloxane (GAP-0) and 1,5-bis(3-aminopropyl)1,1,3,3,5,5-hexamethyltrisiloxane (GAP-1), which are currently under investigation as solvents for a phase-changing process2 and a non-aqueous solution process,3 respectively. Other primary and secondary aminosilicones have also been considered.4−6
A common feature of the amine-based systems is the exothermic reaction of the primary or secondary amine with CO2 to form a carbamate salt in an absorber unit. The amine solvent is then thermally regenerated to reconstitute the original starting amine, which is recycled back to an absorber unit for further CO2 capture. This is illustrated in eq 1 for the GAP-1/triethylene glycol (TEG) process. GAP-1, shown below in eq 1, is a mixture of homologues with the structure having, on average, one dimethylsiloxy repeat unit, as shown. TEG is employed as a co-solvent with GAP-1 because it is capable of solubilizing both GAP-1 and the GAP-1 carbamate as well as being non-aqueous and non-volatile, which has substantial energy benefits during regeneration.3
The thermal degradation of aqueous amines used in CO2 capture processes has been well-documented and studied for a number of years. MEA has been shown to afford a variety of byproducts, including 2-oxazolidinone, N-(2-hydroxyethyl)imidazolidinone, N-(2-hydroxyethyl)ethylenediamine, N,N′-di(hydroxyethyl)urea, N-(2-aminoethyl)-N′-(2-hydroxyethyl)imidazolinone, and oligomeric alkylamines, among others.7−10 Secondary amines provide an additional set of degradation byproducts that include piperazine derivatives.11−13 Like MEA, the GAP-1/TEG solvent system employed for CO2 capture also contains a primary amine reactive site. However, it is a substantially anhydrous system that might be expected to show significant differences in reaction products during thermal treatment. Additionally, while this aminosilicone system starts water-free, the low-pressure post-combustion flue © 2016 American Chemical Society
gas is saturated with water vapor, and therefore, during operation, the GAP-1/TEG solution will contain a steady-state amount of water. This paper reports on the thermal degradation of the GAP-1/TEG system in the presence of CO2 and with varying levels of water.
■
RESULTS AND DISCUSSION Early work on the thermal stability of the aminosilicones indicated that the inherent stability of the GAP-1 material was excellent, with less than 5% loss of activity after 90 days of Received: September 9, 2016 Revised: November 9, 2016 Published: November 14, 2016 10671
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels continuous heating at 150 °C with periodic exposure to air. The same level of chemical integrity was also observed in a 60/40 wt % mixture of GAP-1/TEG.14 However, the tests were conducted in the absence of CO2. To observe the behavior of the solvent system in a CO2-rich environment, which would more closely mimic the conditions seen in operation, small stainless-steel tubular reactors were constructed (Figure 1) and charged with GAP-1 carbamate/TEG
Table 1. Degradation of GAP-1 Aminosilicone Solvent (60 wt % GAP-1/40 wt % TEG) at 150 °C and 83 Days loading (% carbamate)
added water (%)
initial GAP concentration (gravimetric) (mmol/kg)
12 12 12 72 72
0 10 20 0 10
1970 1794 1540 1920 1749
final GAP concentration (cation) (mmol/kg) 1778 2027 2103 500 936
± ± ± ± ±
128 57 86 38 168
Table 1 shows that a small amount of amine functionality was lost under lean loading conditions (∼10%), and it appeared that, in the presence of additional water, the amine concentration increased. It is believed that this is an artifact of the chromatography method, wherein some of the thermal decomposition products overlapped with the starting amine, producing an apparent increase in the amine concentration. This may also explain why the 210 h point at 175 °C and 5% added water in Figure 3 is so high. However, a substantial loss of amine functionality (46−74%) occurred under rich loading conditions during this time period. While cation chromatography provided a quantitative measure of the loss of free amine content in the sample, it did not allow for identification of the byproducts formed. 1 H and 13C Nuclear Magnetic Resonance (NMR) analyses of the reactor contents identified the major product formed during the thermal treatment as a urea derivative. Several routes that have been proposed to generate these ureas are shown in Scheme 1.15,16 Dependent upon the environment and chemical nature of the amine, various workers have proposed carbamic acids, carbamates, diaminodiols, or isocyanates as intermediate reactive species.17−22 On the basis of the reaction scheme below, higher levels of urea derivatives would be expected to form at high carbamate concentrations, high temperatures, and low water concentrations. To more fully explore the effects of the temperature, carbamate loading, and water content on the thermal degradation of the GAP-1/TEG mixture to generate ureas, an experimental design was constructed with the elements shown in Table 2. Temperatures were chosen to bracket the expected range that would be seen in the desorption unit of the process. The 100 and 25% carbamate loadings replicated the rich and lean loadings expected entering and leaving the desorber, while the 62% loading was a midpoint. The 0% added water level was chosen on the basis of a nearly completely anhydrous system,23 and the 5% level was what could be expected for water content from the flue gas after passing through a direct contact cooler (DCC). One set of experiments was conducted at the 10% level of water to determine if additional water had a significant impact on urea formation. Tubular reactors were charged with ∼6 g of solvent mixture, sealed, and placed in forced air convection ovens for the allotted time. To confirm that no material was lost, the reactors were weighed before and after heating as well as after opening. The latter measurement was taken to ensure that no significant amounts of volatile byproducts were generated and lost after unsealing. After cooling, the contents of the reactors were removed by inverting the tubes over pre-tared vials and collecting the solvent mixture. Gentle heating was required in some cases to assist in content removal. The contents of the vials were heated
Figure 1. Tubular reactor.
mixtures and heated for a prescribed period of time and the contents were analyzed by cation chromatography. Initial tests were run at low carbamate loadings (10% carbamate loading), high temperatures (165 and 175 °C), and with and without added water. Percent carbamate loading is defined as the amount of CO2 reacted with the solvent divided by the theoretical maximum and multiplied by 100. Figures 2 and 3
Figure 2. Degradation of GAP-1/TEG at 165 °C at 10% carbamate loading.
Figure 3. Degradation of GAP-1/TEG at 175 °C at 10% carbamate loading.
show that, at both temperatures, most of the loss of amine functionality occurred within the first 100 h. From these data, it did not appear that the presence of water had a significant effect on the degradation rate but slightly more degradation occurred at 175 °C than at 165 °C. The effects of rich (72%) and lean (12%) carbamate loading, presence of additional water at long times (83 days), and slightly lower temperature (150 °C) are shown in Table 1. 10672
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels Scheme 1. Aminosilicone Urea Formation
sample was indicative of CO2 that reacted with the available amine groups still present. A representative plot of the CO2 uptake capacity versus degradation time for 100% carbamate-loaded samples is shown in Figure 4. As expected, there was much more rapid loss of CO2 uptake capacity at higher temperatures. However, all three temperatures ultimately approached a common end point for a given loading of carbamate and water. With no additional water present, approximately 20% CO2 uptake remained after 8 weeks. With 5% water present, that end point appeared to level off at ∼40%, and with 10% water added, around 50% uptake capacity remained after the same period of time. Similar uptake experiments were also performed on the 62 and 25% carbamate-loaded materials. The theoretical CO2 uptake values start at approximately 115% rather than 100% because the small amount of water present in TEG permitted some CO2 to react via a bicarbonate pathway24 and, thus, contributed to the overall CO2 uptake values. The approach to an asymptotic limit in these experiments was expected because these are static systems in which reagents are depleted. With no opportunity for replenishment, the reaction
Table 2. Variables in Thermal Degradation Experiments temperature (°C)
carbamate loading (%)
added water level (wt %)
100 110 120 130 140
100 62 25
0 5 10
to 100 °C for 1 h with magnetic stirring to affect complete decarboxylation. Control experiments confirmed that this was sufficient time to completely decompose any carbamate remaining but did not result in any significant loss of GAP-1 or TEG or decomposition of the urea byproduct. Decarboxylation was necessary for both analysis methods employed to determine the loss of activity. The first method was determination of the CO2 uptake capacity of the aged solvent. This was accomplished by mechanically stirring ∼4 g of the solvent with 100% CO2 at 40 °C for 45 min. Again, control experiments showed that this protocol was sufficient for complete reaction with CO2. The weight increase of the
Figure 4. CO2 uptake capacity versus degradation time for 100% carbamate loading with no additional water added. 10673
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels
Figure 6 shows a representative 1H NMR spectrum of a GAP-1/TEG mixture that had generated some urea. Red letters indicate the methylene groups from the urea component, and the blue letters indicate the unchanged aminopropyl groups. The ratio of the urea methylenes (a at 3.1 ppm) to the total of the methylenes adjacent to the Si−Me2 groups (c + f at 0.5 ppm) indicates the degree of urea formation. Similarly, the ratio of the amino methylenes (d at 2.6 ppm) to the total of the methylenes adjacent to the Si−Me2 groups (c + f) indicates the degree of amine group retention. If no other side reactions are occurring, then the sum of the integrations of the urea methylene protons (a) and the primary amine methylene protons (d) should add to 4, the same value as the methylene groups adjacent to the Si−Me2 groups. In Figure 6, that sum is 3.94, which indicates that little, if any, other side reaction is occurring, at least at the detectable level using this technique. The resonance at 1.0 ppm is due to the presence of ∼14% β isomer,26 as are the smaller peaks seen at ∼2.5 and 2.9 ppm.
becomes reagent-starved and slows accordingly. For the 100% carbamate-loaded experiments, the theoretical limit of amine degradation is 100%, or 0% retention of amine functionality. Similarly, the limits for 62 and 25% carbamate-loaded samples were 62 and 25% loss, respectively. The data showed that the 62% experiments approached ∼60% loss and the 25% experiments approached ∼10% loss.25 The second, complementary method for calculating amine retention was based on 1H NMR. NMR spectra were taken of all thermally treated samples, and the amount of remaining amine was compared to the CO2 uptake measurements. Figure 5 shows excellent agreement of CO2 uptake with NMR-determined amine content. The small amount of water present in the GAP-1/TEG solvent mixture resulted in some CO2 uptake via bicarbonate formation,4 which accounted for greater than 100% CO2 uptake. Because the CO2 uptake measurements could vary slightly based on the water content and took approximately 1 h to complete, NMR spectroscopy was used as the tool for further analyses.
Figure 5. Comparison of CO2 uptake values with NMR-determined amine content.
Figure 6. Typical 1H NMR spectrum of a mixture of amine and urea components recorded in methanol-d4. 10674
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels
100 and 110 °C reactions. Figures 9 and 10 show the same plots as above but with the area zoomed in to 4 days and lines drawn to illustrate the relative rates. While the data are not sufficient for a rigorous kinetic interpretation, they do provide insight into the effects that the
On the basis of the NMR results, plots of amine loss versus time as a function of carbamate loading and water content were constructed. These were similar in appearance to the CO2 uptake plots generated earlier (Figure 4) but had less spread in the early time point data. Two representative plots are shown in Figures 7 and 8.27
Figure 7. Loss of amine functionality by NMR versus time for 100% carbamate with 0% added water.
Figure 10. Rate of amine loss versus time for 100% carbamate with 5% added water.
Table 3. Relative Rates of Amine Loss loading (% carbamate)
added water (%)
temperature (°C)
amine loss (%)a
relative rate of amine loss
100
0
100 110 120 130 140 100 110 120 130 140 120 130 140 100 110 120 130 140 100 110 120 130 140 100 110 120 130 140 100 110 120 130 140
0.25 1.75 13.2 24 51.2 0.1 0.25 5.7 16.25 37.5 6.2 10.75 33.2 0.1 0.75 7.25 11.75 28.75 0.1 0.1 10.75 12.25 15.2 0.25 0.25 4.25 8 14.75 0.1 0.1 9.7 7 9.7
2.5 17.5 132 240 512 1 2.5 57 163 375 62 108 332 1 8 73 118 288 1 1 108 123 152 2.5 2.5 42.5 80 148 1 1 97 70 97
5
Figure 8. Loss of amine functionality by NMR versus time for 100% carbamate with 5% added water. 10
It is quite clear from these two plots that higher temperatures result in a greater loss of amine than at lower temperatures and that the presence of water appears to decrease the initial rate of urea formation. To more clearly demonstrate these points, the relative rates of amine loss have been determined on the basis of the initial slope of the NMR versus time curves. Linear fits were used to obtain the initial slopes, with the time cutoff being 4 days for 120−140 °C experiments and 14 days for the
62
0
5
25
0
5
Amine loss is after 4 days of reaction for 120, 130, and 140 °C samples and after 14 days of reaction for 100 and 110 °C samples. Negative loss is assumed to be 0.1. The error of these measurements is estimated to be ±2%.
a
Figure 9. Rate of amine loss versus time for 100% carbamate with 0% added water. 10675
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels
of ±2%. To provide a meaningful estimate of the relative rates of degradation, any negative amine loss after 4 days was defined as 0.1%. Thermal degradation of several organic primary amines in 20−40 wt % aqueous solutions with 80% carbamate loading has been reported at temperatures of 135, 150, and 165 °C.28 These experiments showed 13−45% loss of amine in 4 days at a higher temperature of 165 °C, while at 135 °C, a temperature closer to our study, only a 5% loss of amine was commonly observed. The difference in these values compared to those seen in our system is likely due to the lower concentration of organic amines studied coupled with the large quantities of water present as solvent, which is shown to significantly suppress urea formation in this work. The same analysis was applied to urea formation, as shown in Figures 11 and 12 for 100% loaded carbamate with 0 and 5% added water. These are data from the same experiments in Figures 9 and 10. Table 3 consolidates all of these data. It is clear that the temperature has a huge impact on the formation of urea and concomitant loss of amine functionality as does the carbamate loading. Water plays an important but lesser role in this degradation process. The only degradation products identified in the aged reaction mixtures were the urea materials. Confirmation that no other significant byproducts were formed is shown in Figure 13. This plot shows the mole percent amine and urea present at an observed CO2 uptake capacity. The slopes are nearly equal and opposite, indicating that urea is being formed at the same rate as amine is being lost. The sum of the urea and amine components is ∼100%, indicating that no other material was being produced.
Figure 11. Rate of urea formation versus time for 100% carbamate with 0% added water.
Figure 12. Rate of urea formation versus time for 100% carbamate with 5% added water.
■
temperature, carbamate loading, and water content have on the degradation of GAP-1. Table 3 tabulates the relative rates of amine loss based on the total amine loss observed after 4 days. At very low levels of degradation, the NMR data indicated an increase in the amount of amine present. For example, the 62% carbamate loading, 0% added water, and 100 °C sample showed −0.5% amine loss after 4 days. This is an artifact of the error in the NMR integration, which was estimated to be in the range
CONCLUSION The major thermal degradation pathway seen with GAP-1/TEG is the formation of a urea-containing compound. Degradation is increased at higher temperatures, longer reaction times, higher CO2 concentrations (in the form of carbamate loading), and low water levels. A judicious choice of operating conditions can
Figure 13. Comparison of amine loss and urea formation with CO2 uptake. 10676
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels significantly decrease urea byproduct formation. For instance, reducing the desorption temperature from 140 to 100 °C and adding 5 wt % water to the 60:40 mixture of GAP-1/TEG resulted in a 500-fold reduction in amine loss after 4 days in a CO2-rich environment. After 56 days of continuous heating under the same conditions, ∼87% of the original GAP-1 was retained at 100 °C compared to only ∼20% at 140 °C. The urea byproduct appears to be the only major degradation pathway under these conditions, with 100% of the mass balance accounted for by the urea and amine components. These findings have suggested several engineering approaches to mitigating the thermal degradation of the GAP-1/TEG solvent, which include lowering the desorption temperature and deliberately introducing small quantities of water. With these mitigation strategies adopted, GAP-1/TEG remains a viable nonaqueous post-combustion carbon capture solvent. However, new classes of aminosilicones are also under investigation that will suppress urea formation. These will be reported in due course.
■
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Robert J. Perry: 0000-0003-2027-4829
EXPERIMENTAL SECTION
Notes
Degradation Experiments. Tubular reactors were constructed from 1/4 in. 316 stainless steel with Swagelok end caps and charged with 6 g of GAP-1 carbamate/TEG mixtures as indicated and placed horizontally in forced air convection ovens for a predetermined length of time. Sample tubes were removed, cooled in an upright position, and opened, and the contents were removed by inversion of the tubes with gentle heating. Weights were recorded at each step of the process to determine mass loss. Analyses. Recovered test samples were placed in 20 dram scintillation vials containing a magnetic stir bar and heated at 100 °C for 1 h. After this time, weights were again recorded and a known amount of decarboxylated sample was placed in a 25 mL, three-neck roundbottom flask equipped with a mechanical stirrer, a gas inlet tube, and a gas bubbler that was immersed in a 40 °C oil bath. Pure CO2 was introduced into the system, and the mixture was heated and stirred for 45 min after which time the pre-tared flask was weighed and the amount of CO2 absorption was calculated. 1H NMR spectra were recorded on a Bruker 400 MHz instrument. Suppressed cation chromatography was used to resolve and quantify the parent amine species in degraded and undegraded samples. Samples were diluted by a factor of 10 000 prior to analysis to keep the total amine concentration below 100 wppm. A Dionex ICS-2100 chromatograph with a CSRS-300 suppressor was used. The mobile phase consisted of a gradient of methylsulfonic acid (MSA) in 18.2 μΩ deionized water. The separation was carried out using a Dionex CG17 4 × 50 mm guard column and a Dionex CS17 4 × 250 mm analytical column with an eluent flow of 0.5 mL/min and a suppressor current of 50 mA. Ion chromatography was conducted, and the MSA gradient ramp schedule used in the program is shown in Table 4.
Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. The authors declare no competing financial interest.
■ ■
ACKNOWLEDGMENTS This work was supported by the United States Department of Energy under Award DE-FE0013755.
time (min)
acid concentration (mM)
0−16.4 16.4−16.5 16.5−26.4 26.4−36.4 36.4−47.4 47.4−47.5 47.5−50
constant at 5.5 linear ramp from 5.5 to 11 constant at 11 linear ramp from 11 to 38.5 constant at 38.5 linear ramp from 38.5 to 5.5 constant at 5.5
REFERENCES
(1) National Energy Technology Laboratory (NETL), United States Department of Energy (DOE). Cost and Performance Baseline for Fossil Energy Plants Volume 1a: Bituminous Coal (PC) and Natural Gas to Electricity, Revision 3; NETL, DOE: Washington, D.C., July 6, 2015; DOE/NETL-2015/1723, http://www.netl.doe.gov/File%20Library/ Research/Energy%20Analysis/Publications/Rev3Vol1aPC_NGCC_ final.pdf (accessed Oct 30, 2015). (2) Perry, R. J.; Wood, B. R.; Genovese, S.; O’Brien, M. J.; Westendorf, T.; Meketa, M. L.; Farnum, R.; McDermott, J.; Sultanova, I.; Perry, T. M.; Vipperla, R.-K.; Wichmann, L. A.; Enick, R. M.; Hong, L.; Tapriyal, D. Energy Fuels 2012, 26, 2528. (3) Perry, R. J.; Grocela-Rocha, T. A.; O’Brien, M. J.; Genovese, S.; Wood, B. R.; Lewis, L. N.; Lam, H.; Soloveichik, G.; Rubinsztajn, M.; Kniajanski, S.; Draper, S.; Enick, R. M.; Johnson, J. K.; Xie, H.-b.; Tapriyal, D. ChemSusChem 2010, 3, 919. (4) Perry, R. J.; O’Brien, M. J. Energy Fuels 2011, 25, 1906. (5) Perry, R. J.; Davis, J. L. Energy Fuels 2012, 26, 2512. (6) O’Brien, M. J.; Farnum, R. L.; Perry, R. J.; Genovese, S. E. Energy Fuels 2014, 28, 3326. (7) Strazisar, B. R.; Anderson, R. R.; White, C. M. Energy Fuels 2003, 17, 1034.
Table 4. MSA Gradient Ramp Schedule
■
Percent amine remaining from NMR data (Appendix 1), percent urea formed from NMR data (Appendix 2), CO2 uptake plot with 100% carbamate loading and 0, 5, and 10% added water (Appendix 3), CO2 uptake plot with 62% carbamate loading and 0 and 5% added water (Appendix 4), CO2 uptake plot with 25% carbamate loading and 0 and 5% added water (Appendix 5), percent amine remaining by NMR with 100% carbamate loading and 0, 5, and 10% added water (Appendix 6), percent amine remaining by NMR with 62% carbamate loading and 0 and 5% added water (Appendix 7), and percent amine remaining by NMR with 25% carbamate loading and 0 and 5% added water (Appendix 8) (PDF)
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.6b02284. 10677
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
Article
Energy & Fuels (8) Lepaumier, H.; Picq, D.; Carrette, P.-L. Ind. Eng. Chem. Res. 2009, 48, 9061. (9) Polderman, L. D.; Dillon, C. P.; Steele, A. B. Oil Gas J. 1955, 54, 180. (10) Yazvikova, N. V.; Zelenskaya, L. G.; Balyasnikova, L. V. Zh. Prikl. Khim. 1975, 48, 674. (11) Lepaumier, H.; DaSilva, E. F.; Einbu, A.; Grimstvedt, A.; Knudsen, J. N.; Zahlsen, K.; Svendsen, H. F. Energy Procedia 2011, 4, 1652. (12) Lepaumier, H.; Martin, S.; Picq, D.; Delfort, B.; Carrette, P.-L. Ind. Eng. Chem. Res. 2010, 49, 4553. (13) Lepaumier, H.; Picq, D.; Carrette, P.-L. Energy Procedia 2009, 1, 893. (14) Wood, B. Bench-scale silicone process for low-cost CO2 capture. Proceedings of the NETL CO2 Capture Technology Meeting; Pittsburgh, PA, July 2013; http://www.netl.doe.gov/File%20Library/Events/ 2013/Co2%20Capture/B-Wood-GE-Bench-Scale-Silicone-Process.pdf (accessed Oct 30, 2015). (15) Wu, C.; Cheng, H.; Liu, R.; Wang, Q.; Hao, Y.; Yu, Y.; Zhao, F. Green Chem. 2010, 12, 1811. (16) Peterson, S. L.; Stucka, S. M.; Dinsmore, C. J. Org. Lett. 2010, 12, 1340. (17) Xie, H.-b.; Johnson, J. K.; Perry, R. J.; Genovese, S.; Wood, B. R. J. Phys. Chem. A 2011, 115, 342. (18) Dijkstra, Z. J.; Doornbos, A. R.; Weyten, H.; Ernsting, J. M.; Elsevier, C. J.; Keurentjes, J. T. F. J. Supercrit. Fluids 2007, 41, 109. (19) Ramachandran, B. R.; Halpern, A. M.; Glendening, E. D. J. Phys. Chem. A 1998, 102, 3934. (20) Aresta, M.; Ballivet-Tkatchenko, D.; Dell’Amico, D. B.; Bonnet, M. C.; Boschi, D.; Calderazzo, F.; Faure, R.; Labella, L.; Marchetti, F. Chem. Commun. 2000, 1099. (21) Johnson, S. L.; Morrison, D. L. J. Am. Chem. Soc. 1972, 94, 1323. (22) Arstad, B.; Blom, R.; Swang, O. J. Phys. Chem. A 2007, 111, 1222. (23) The typical water content of the GAP-1/TEG mixture was ∼1 wt %, as determined by Karl Fischer titration. This level of water is what was commonly found in TEG used as the co-solvent. (24) Park, J.-Y.; Yoon, S. J.; Lee, H. Environ. Sci. Technol. 2003, 37, 1670. (25) See Appendices 3−5 of the Supporting Information for plots of amine loss by CO2 uptake measurements. (26) The manufacturing process used by the current supplier results in the formation of some β isomer in addition to the predominant γ isomer, as shown below.
(27) See Appendices 1 and 2 for tables of amine and urea contents by NMR analyses and Appendices 6−8 for plots of amine loss by NMR analysis. (28) Hatchell, D.; Namjoshi, O.; Fischer, K.; Rochelle, G. T. Energy Procedia 2014, 63, 1558.
10678
DOI: 10.1021/acs.energyfuels.6b02284 Energy Fuels 2016, 30, 10671−10678
