A Novel Phase-Changing Nonaqueous Solution for CO2 Capture with

Subscriber access provided by UNIV OF DURHAM

General Research

A Novel Phase-changing Nonaqueous Solution for CO2 Capture with High Capacity, Thermostability, and Regeneration Efficiency Mengna Tao, Jinzhe Gao, Wei Zhang, Yu Li, Yi He, and Yao Shi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b01775 • Publication Date (Web): 25 Jun 2018 Downloaded from http://pubs.acs.org on June 26, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

A Novel Phase-changing Nonaqueous Solution for CO2 Capture with High Capacity, Thermostability, and Regeneration Efficiency

Mengna Tao1,2, Jinzhe Gao2, Wei Zhang 1,2, Yu Li2, Yi He2,3*, and Yao Shi1,2* 1. Key Laboratory of Biomass Chemical Engineering of Ministry of Education, China 2. College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China 3. Department of Chemical Engineering, University of Washington, Seattle, WA 98195, USA

*Yi He, E-mail: [email protected]; Yao Shi, E-mail: [email protected]

1

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract A novel nonaqueous solution, triethylenetetramine (TETA) blended with polyethylene glycol (PEG200), was developed for CO2 absorption, with which phase-changing phenomena was observed after the absorption. A reaction mechanism for TETA-PEG200 solution and CO2 was proposed based on 13C NMR analysis. It was found that PEG200 not only acts as a solvent that contributes to biphasic separation but also gets involved in the reactions, leading to an increased CO2 absorption capacity. Results show that 1 M TETA-PEG200 solution exhibits a high CO2 capacity of 1.63 mol /mol TETA, which is comparable to TETA-water solution. The capacity is only slightly affected when the temperature rises up to 60 °C. Moreover, the solution demonstrates good thermostability similar to typical functionalized ionic liquids (ILs) while presenting much lower viscosity than the ILs. For regeneration processes, microwave heating was identified to be a more effective method than classic heating. The solution shows a regeneration efficiency as high as 96% after four absorption-desorption cycles.

2


Page 2 of 32

Page 3 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction Anthropogenic greenhouse gas (GHGs) emissions are the main cause of global warming. As a primary contributor, CO2 accounts for over 80% GHGs.1 The CO2 concentration in the atmosphere has already surpassed 400 ppm2, 3 and is expected to keep rising if fossil fuels continue to serve as the major energy source for human being.4 Therefore, various approaches have been examined for the cost-effective capture of CO2. Aqueous amine solvents, such as monoethanolamine(MEA), are often considered to be the industrial benchmark for CO2 capture from flue gas.5 However, aqueous amine based processes often suffer from severe amine degradation and volatilization, and equipment corrosion.6 Meanwhile, high energy penalty for the regeneration of absorbent, which accounts for 25~40% of the output loss from power plants,7 also impede the application of aqueous amines for CO2 capture. Recently, increasing attention has been focused on the use of nonaqueous solutions for CO2 capture,8-10 which may provide significant advantages such as reduced solvent loss and low-cost regeneration. Several types of organic solvents can be used in the solutions, which include ethylene glycol, diethylene glycol, and triethylene glycol. Thereinto, poly (ethylene glycol) (PEG) is an environmentally benign solvent with some appealing properties similar to ionic liquids (ILs), such as low toxicities, good chemical and thermal stability, and negligible vapor pressure.11-13 Moreover, PEGs are inexpensive and have lower viscosity than ILs.14 Some studies indicate that CO2 also exhibits high solubility in PEGs due to the quadrupole interaction of CO2 with polar ether oxygens.15-17 Hence, some researchers use PEGs as a co-solvent for ILs to decrease the viscosity of ILs after CO2 absorption. Hui and Yang18 reported that ILs of diethylenetriamine hydrobromide ([DETAH]Br) dissolved in PEG200 has 3



Page 4 of 32

a CO2 absorption capacity of 1.184 mol/mol [DETAH]Br and a regeneration efficiency of 86.67% after five consecutive cycles. Similarly, Yu et al. 14 investigated the CO2 absorption by ILs of tetraethylenepentamine acetic acid ([TEPA]Ac) and PEG200 mixtures, and results show that the absorption capacity can reach 1.24 mol/mol [TEPA]Ac at 353.15 K. Some researchers have also tried using PEGs only as the solvent for primary or secondary amines. Li and coworkers7 studied the PEG200 solution of diglycolamine (DGA) or MEA for CO2 absorption, respectively. Both were found to have relatively higher CO2 cyclic capacity and regeneration efficiency compared with the aqueous solution of MEA or DGA. For instance, the DGA-PEG 200 solution exhibits a regeneration efficiency of 94.6%. Zhao et al. 19

demonstrated that a mixture of ethanediamine (EDA) and PEG300 was found to be able to

form solid precipitates after the absorption, similar to earlier reported triethylenetetramine (TETA)-ethanol solution.20,

21

However, the regeneration of the EDA-PEG300 was not

discussed in the work. As EDA is very volatile, it is likely a significant loss of EDA may happen during the regeneration of EDA-PEG300 solvent. While the previously reported solvents are attractive in one way or another, it is desirable to develop a solvent with small loss of solvents, high absorption capacity, and having phase-changing

feature

regeneration.22-25).

(This may

significantly

reduce

the

energy

loss during

To this end, several combinations of TETA and organic solvents

including PEG200 were examined for CO2 capture in this study. TETA not only exhibits relatively low vapor pressure, but also has a higher capacity for CO2 capture than other amines, such as MEA, DGA, and EDA. After the solution for CO2 capture is chosen, its performance was evaluated, which included the capacity and kinetics of CO2 absorption, as 4


Page 5 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


well as cyclic absorption/desorption efficiency. The products from CO2 absorption was also analyzed for the discussion of reaction mechanism for CO2 and the solution. 2. Experimental section 2.1 Chemicals Triethylenetetramine (TETA, ≥99.5%), dimethylacetamide (DMAC, >99.0%), diethylene glycol (DEG, ≥99.7%), triethylene glycol (TEG, ≥99.7%), polyethylene glyol 200 (PEG200, ≥99.5%), polyethylene glyol 300 (PEG300, ≥99.5%), and polyethylene glyol 400 (PEG400, ≥99.5%) were purchased from Sinopharm Chemical Reagent Co., Ltd. The chemical pure grade diethylene glycol monomethyl ether (DGME, >99.0%), diethylene glycol dimethyl ether (DGDE, >99.0%), and N-Methyl pyrrolidone (NMP, >99.0%) were purchased from Aladdin Chemistry Co., Ltd. Compressed CO2 (≥99.99% vol.), and Compressed N2 (≥99.99% vol.) were purchased from Jingong Specialty Gases Co., Ltd. All the materials were used as received. 2.2 Apparatus and procedures CO2 absorption experiments were carried out in a three-necked flask with a mechanical agitator. The flask was immersed in a water bath to maintain at specific temperature (20 °C~60 °C). A mass flow meter was used to adjust gas flow rate. In a typical absorption experiment, 100ml solution was freshly prepared in the flask, and the flow rate of pure CO2 or simulated flue gas (15%vol CO2: 85%vol N2) was controlled at 100 mL/min under the atmospheric pressure. The outlet gas flow rate was measured by a calibrated soap-membrane flowmeter, and the outlet gas concentration was measured by a gas chromatograph (TCD, GC9750, Fuli Analytical Instrument Company, China) at an interval of 2 min. The mechanical 5



Page 6 of 32

agitator was set at 300 r/min to ensure intensive mixing of the gas and liquid. The absorption process is considered to reach its equilibrium when the rate of outlet gas flow is equal to the rate of inlet one. CO2 desorption experiments were carried out in the same three-necked flask. The flask was placed in a lab-microwave oven (Model: NAI-SY-WBL, Shanghai Na AI Precision Instrument Co., Ltd.) operated at a microwave frequency of 2.45 GHz. The maximum power of the oven was 800 W. No purge gas was used. A thermocouple was inserted into the flask to measure the temperature during the regeneration. In addition, the flask was equipped with a mechanical stirrer and a reflux condenser. The whole absorption and desorption cycles were conducted as follows: In the process of absorption, the absorbent was bubbled with CO2 until the absorption reached equilibrium at 40 °C. During a desorption cycle, the weight of flask was first measured, and then the CO2 loaded solution was heated in the lab-microwave oven with an input power of 480 W. Once the temperature of the solution reached 120 °C, the power of the oven was turned off. After the solution cooled down to 60 °C, the weight of flask was measured again and compared with the previous measurement. These steps were repeated until there is no significant weight loss of flask before and after heating, which indicates that CO2 was completely desorbed from the solution. The CO2 desorption capacity in the solution was calculated based on the total weight difference of flask during the desorption process. Each experiment in this work was repeated at least once under identical conditions. 2.3 Calculation and analysis methods Based on the ideal gas law, the absorption rate of pure CO2 was calculated as follows: rୟୠୱ =

୔∙∆୚ిోమ

（1）

ୖ∙୘

6


Page 7 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


where rୟୠୱ is the absorption rate of CO2 (mL min-1), P is pressure (Pa), ∆Vେ୓మ is the volumetric flow difference value of inlet and exit CO2 (mL min-1), R is the ideal gas constant, and T is absorption temperature (K). Assuming the inert gas N2 was not absorbed by solvents, the absorption rate of CO2 from flue gas was determined by the following equation: ୭୳୲ xେ୓ = మ

୚ృ౗౩ ୶౟౤ ిోమ ି୰౗ౘ౩

（2）

୚ృ౗౩ ି୰౗ౘ౩

୭୳୲ ୧୬ where Vୋୟୱ is the flow rate and was set to 100mL/min in this work, xେ୓ , and xେ୓ are the మ మ

CO2 molar fraction of the inlet and outlet gas, respectively. Accordingly, the absorption rate of CO2 was simplified as rୟୠୱ =

౥౫౪ ୚ృ౗౩ (୶౟౤ ిోమ ି୶ిోమ )

（3）

ଵି୶౥౫౪ ిో

మ

The absorption capacity of CO2 was obtained by integrating rୟୠୱ with time. The characteristics of solid products generated after CO2 absorption were examined by 13

C NMR (taken in D2O), operated at room temperature with a Bruker Avance III DMX500

spectrometer. The decomposition behaviors of the pure absorbents and the solid products were carried out using TG-DSC analyzer (TA instrument SDT-Q600). During the TGA analysis, the sample was heated up to 400 °C at a heating rate of 10 °C per minute under N2 atmosphere. Before the analysis, the solid phase was filtered and washed thoroughly with ethanol, dried at 20 °C for 12 h in the vacuum, and then stored at the room temperature. 3. Results and discussion 3.1 Absorption of CO2 in nonaqueous TETA solutions As shown in Table 1, nine organic solvents were examined in this study. Each solution made with TETA and one of the solvents can form solid precipitate after CO2 absorption. The 7



boiling points of the solvents in Table 1 are all higher than 150 °C. In addition, the solvents exhibit low volatility with a vapor pressure less than 0.5 kPa at 25 °C. Table 1 also shows that the solvents themselves can capture CO2 through physical absorption, the capacity of which is strongly correlated to the viscosity of the solvent. Solvent with a larger viscosity exhibits a lower capacity for the absorption. However, after mixing TETA with the solvents, a significantly different ranking between the total absorption capacity of the solutions and the absorption capacity of the solvents can be observed. Although the absorption capacity of PEG200 is only about half of the capacity of some solvents, such as DMAC, and DGDE, TETA in PEG200 solution shows a capacity of 1.87 mol/mol TETA, which is the highest one among all the nine solutions investigated in this work. This may be due to the solvent effect, meaning that the interaction between PEG200 and TETA can greatly promote the absorption of CO2 by TETA. Among the three solvents which belong to PEG family, a PEG solvent with higher molecular weight shows a higher CO2 absorption capacity, which is consistent with the work of Li et al.

26

Nevertheless, the CO2 capacity of TETA-PEG solution shows a decrease as the

molecular weight of PEG increases from 200 to 400. This decrease in capacity is likely due to the increase in the viscosity of PEG (from 25 to 44 mPa·s at 40 °C).26 The high viscosity leads to greater mass transfer resistance,27 which impedes the absorption process, resulting in a reduction in observed CO2 absorption capacity within limited time. In addition, using PEG200 as the solvent also enhances the thermal stability of the amine based solution. The thermal stability was measured by TG-DSC. Figure 1 shows the decomposition temperature of TETA, PEG200, and the TETA-PEG200 solution. The apparent 8


Page 8 of 32

Page 9 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


volatile loss of TETA began at ~80 °C, however, when it is dissolved in PEG200 with a concentration of 0.6 M, the decomposition temperature of the TETA-PEG200 solution was increased significantly to ~203 °C, almost as high as the decomposition temperature for PEG200, which is comparable to typical functionalized ILs reported previously in the literature.28,

29

The enhancement in decomposition temperature of TETA is due to the

hydrogen bonding between –NH2 of TETA and –OH of PEG200.18 Meanwhile, the TETA-PEG200 solution shows a significant advantage in viscosity over the functionalized ILs for CO2 capture. For instance, the functionalized ILs listed in Table 2 have viscosities larger than 81 mPa·s,28, 29. Although this is much lower than the viscosity of many other ILs for CO2 capture,30-32 it is still three times of the viscosity of the TETA-PEG200 solution. In addition, TETA-PEG200 solution exhibits another appealing feature. Unlike typical ILs, its viscosity will not keep rising with the continued absorption of CO2. Results in Figure 2 shows that the viscosity of TETA-PEG200 solution reaches its maximum of ~75 mPa·s at the critical point of biphasic formation after CO2 absorption. Then a dramatic drop in the viscosity of the solution was observed after the precipitation of the products. The viscosity is finally stabilized around a value slightly higher than the initial one. Therefore, the solution can maintain a relatively low viscosity with the continuous absorption of CO2 if the precipitation and separation process are performed frequently enough. Moreover, the absorption capacity of functionalized ILs, such as [N2222][Ala], [N2222][β-Ala], and [P2228][2-CN-Pyr] solutions, is less than half of TETA-PEG200 solution. The TETA-PEG200 solution also has 20% more absorption capacity than [TETA][NO3] aqueous solution.33 Thus, the TETA-PEG200 solution is further examined for CO2 capture. 9



Page 10 of 32

3.2 Formation of solid products and 13C NMR analysis. Figure 3(a) show the visual change of the TETA-PEG200 solution with the absorption of CO2. The solution was homogeneous and clear in its initial state, with the continuous absorption of CO2, flocculant precipitation is first formed and gradually turns into amorphous pasty substance. Biphasic separation can be easily achieved by centrifugal separation, as shown in Figure 3(b). To characterize the constituents of the solid products, the

13

C NMR analysis was

performed, as shown in the Figure 4. Similar to the reaction in amine aqueous solutions, the signals in the range of 163.74-164.77 ppm revealed the formation of carbamate carboxyl carbon.34, 35 The carbamate signal was not a peak but a cluster of peaks revealing that the products were consisted of several kinds of carbamates, including monocarbamates formed by different amino groups of TETA. Furthermore, the value of CO2 absorption capacity was larger than 1 mol/mol TETA, indicating the existence of multi-carbamates. The signal of carbonyl carbon, observed at 160.31 ppm, indicates a formation of carbonate. However, this carbonate is unlikely produced from the reaction between CO2 and water in a nonaqueous solution. Barzagli and co-workers reported that alcohols can attack the carbon atom in the carbonyl group of unstable carbamate as a nucleophile, and form carbonate and amine.36 Similar to their study, the peak at 160.31 ppm can be interpreted as alkylcarbonate formed by a nucleophilic attack of PEG200 on TETA-carbamate, which suggests in the involvement of PEG200 when capturing CO2 with TETA. Based on these

13

C NMR analysis, a reaction

mechanism for CO2 with TETA-PEG200 solution was proposed, as shown in Scheme 1. 3.3 Absorb CO2 with TETA-PEG200 solution under various conditions. 10


Page 11 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In order to assess the applicability of TETA-PEG200 solution for CO2 capture from coal fired power plants, the CO2 absorption performance of TETA-PEG200 solution was investigated at different operating conditions using simulated flue gas, which has a CO2 partial pressure of ~0.15 bar. Both amine concentration and temperature were varied for further investigation. Figure 5 shows CO2 absorption rates of TETA-PEG200 solution at different amine concentrations. It shows that the initial absorption rate is not sensitive to the change of the amine concentration in the range of 0.2 M to 1 M, which is similar to the performance of TETA-ethanol solution reported in the previous study.20 At a relatively low concentration, for instance, 0.2 M or 0.4 M, the absorption rate of TETA-PEG200 solution drops dramatically soon after the absorption process. Nevertheless, at a higher concentration of 1 M, the TETA-PEG200 solution maintains at its maximal absorption rate for about 125 min before a significant decrease. The temperature dependence of CO2 absorption rate with TETA-PEG200 solution and TETA-water solution is shown in Figure 6 (a) and (b). Control experiments with TETA-water solution were carried out for comparison. Figure 6 demonstrates that TETA-PEG200 solution has an absorption rate comparable to TETA-water solution. The CO2 absorption rate only slightly decreased with an increase in the temperature range of 20 °C~60 °C. It is interesting to note that the curves in Figure 6 (a) began to fluctuate periodically after passing a certain time when experiments were performed at a temperature of 45 °C or higher. TETA-water solution also exhibits similar behavior at a temperature of 60 °C. The CO2 absorption capacity, corresponding to the fluctuations, is calculated to be ~7% of the total CO2 absorption capacity. 11



The fluctuations may be due to the absorption and desorption equilibrium of certain unstable products. Further studies still need to be done to elucidate of these fluctuations. The temperature dependence of CO2 absorption capacity with TETA-PEG200 solutions at different concentration were shown in Table 3, which demonstrates that the lower concentration of TETA is, the more significant impact the temperature has on the capacity. The 0.2 M TETA-PEG200 solution shows a 44.7% loss in absorption capacity for the same temperature variation as 1 M TETA-PEG200 solution. As a comparison, 1 M TETA-PEG200 solution exhibits only 8.4% loss in absorption capacity for CO2 when the temperature increases from 40 °C to 60 °C. This phenomenon can be explained as follows. The reaction between TETA and CO2 is an exothermic one, therefore, as temperature increases, the reaction equilibrium shifts towards the desorption of CO2, leading to a lower absorption capacity. However, an increase in TETA concentration shifts the equilibrium to the opposite direction, leading to more absorption of CO2, which effectively offsets the decrease of absorption capacity due to rising temperature in the temperature range investigated. Additionally, the 1M MEA-PEG200 solution has a CO2 absorption capacity of only 0.468 mol/mol MEA.7 By replacing MEA with TETA, the 1 M TETA-PEG200 solution has the absorption capacity comparable to 1.23 M TETA-water solution at 40 °C, which is 1.71 mol/mol TETA, reported by Schäffer and coworkers.37 The TETA-PEG200 solution also shows negligible volatility at the operating conditions examined in this work. Figure 7 displays the weight loss of water, PEG200 and their TETA-solutions at 60 °C when blew with N2. It demonstrates that the weight loss of both water and TETA-water solution varies linearly with time, nearly 0.45% /h and 0.31% /h, 12


Page 12 of 32

Page 13 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively. As a comparison, both TETA-PEG200 and PEG200 solutions, shows no observable weight loss during the whole period investigated. 3.4 Absorption and Desorption Cycles of TETA/PEG200 Solution. The cyclic absorption and desorption performance of the solution is important as it is directly related to the energy consumption and economic costs. Before conducting the absorption-desorption experiment, the decomposition of solid products was studied using TG-DSC analyzer. Results in Figure 8 indicate that the decomposition of products commences at ~110 °C. The decomposition accelerated quickly. Due to the release of large amounts of CO2, a large endothermic peak was observed when the temperature increased to ~150 °C. The fast weight loss when the temperature is beyond 150 °C was attributed to the evaporation/decomposition of PEG and TETA, which reaches a maximum at ~208 °C. When it comes to the regeneration of solid products, conventional conductive heating is ineffective as significant aggregation of partitial products can be observed. We found out that microwave heating can avoid the aggregation and complete the regeneration of solid product effectively because microwave can offer instantaneous and volumetric heating without heat transfer restrictions.38 A typical regeneration process in this work is composed with six rounds of heating from 60 °C to 120 °C. During the break of each rounds, CO2-containing solution was cooled down to prevent possible solvent loss due to its overheating. The total time of heating takes about 14 min. It’s worth noting that after only two rounds of heating, the regenerated capacity has already reached ~90%. The cyclability of the TETA-PEG200 solution was also studied. Figure 9 shows that the regeneration efficiency of the TETA-PEG200 solution remains as high as 96% after four 13



absorption-desorption cycles. The TETA-PEG200 solution exhibits an advantage in cyclic absorption capacity than the TETA-water solution, as well. Results in Figure 10 show that when compared with the TETA-water solution which was also regenerated by microwave heating, the absorption capacity of the TETA-PEG200 solution is ~22% higher than that of TETA-water solution for the second run, despites that there is only 3% difference in absorption capacity in their first runs. 4. Conclusions In this work, an environmentally friendly and cost-effective solution, TETA-PEG200, was identified by screening several amine/solvent combinations. The TETA-PEG200 solution exhibits a phase-changing feature after absorbing CO2. It was found that PEG200 not only serves as a solvent, but also gets involved in the reaction between TETA and CO2, which further enhances CO2 absorption. Notably, 1 M TETA-PEG200 solution shows a high CO2 capacity of 1.63 mol/mol TETA, comparable to TETA-water solution. The CO2 absorption capacity of the solution is only slightly decreased when the temperature increases to 60 °C. Besides, the solution exhibits very low vapor pressure. It has a decomposition temperature of ~203 °C and shows a similar thermostability as typical functional ILs while demonstrating much lower viscosity than ILs. Moreover, the solution has sound cyclability after multiple absorption/desorption runs with the introduction of microwave-heating process. It shows an efficiency of regeneration as high as 96% after four absorption-desorption cycles. Author information Corresponding Author *Yi He, E-mail: [email protected]; Yao Shi, E-mail: [email protected] 14


Page 14 of 32

Page 15 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Conflicts of interest There are no conflicts of interest to declare. Acknowledgements The authors would like to thank the National Natural Science Foundation of China (grant number 21676245 and 21476191) for financial support. References (1) D'alessandro, D. M.; Smit, B.; Long, J. R. Carbon dioxide capture: Prospects for new materials. Angew. Chem. Int. Edit. 2010, 49, 6058. (2) Glikson, A. Cenozoic mean greenhouse gases and temperature changes with reference to the anthropocene. Global. Change. Biol. 2016, 22, 3843. (3) Zhai, Y. X.; Chuang, S. S. C. The nature of adsorbed carbon dioxide on immobilized amines during carbon dioxide capture from air and simulated flue gas. Energy. Technol-Ger. 2017, 5, 510. (4) Dutcher, B.; Fan, M. H.; Russell, A. G. Amine-based CO2 capture technology development from the beginning of 2013-a review. Acs. Appl. Mater. Inter. 2015, 7, 2137. (5) Macdowell, N.; Florin, N.; Buchard, A.; Hallett, J.; Galindo, A.; Jackson, G.; Adjiman, C. S.; Williams, C. K.; Shah, N.; Fennell, P. An overview of CO2 capture technologies. Energ. Environ. Sci. 2010, 3, 1645. (6) Kenarsari, S. D.; Yang, D. L.; Jiang, G. D.; Zhang, S. J.; Wang, J. J.; Russell, A. G.; Wei, Q.; Fan, M. H. Review of recent advances in carbon dioxide separation and capture. Rsc. Adv. 2013, 3, 22739. (7) Li, J.; You, C. J.; Chen, L. F.; Ye, Y. M.; Qi, Z. W.; Sundmacher, K. Dynamics of CO2 absorption and desorption processes in alkanolamine with cosolvent polyethylene glycol. Ind. Eng. Chem. Res. 2012, 51, 12081. (8) Kassim, M. A.; Sairi, N. A.; Yusoff, R.; Alias, Y.; Aroua, M. K. Evaluation of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide-alkanolamine sulfolane based system as solvent for absorption of carbon dioxide. Ind. Eng. Chem. Res. 2016, 55, 7992. (9) Malhotra, D.; Page, J. P.; Bowden, M. E.; Karkamkar, A.; Heldebrant, D. J.; Glezakou, V. A.; Rousseau, R.; Koech, P. K. Phase-change aminopyridines as carbon dioxide capture solvents. Ind. Eng. Chem. Res. 2017, 56, 7534. (10) Wang, X.; Akhmedov, N. G.; Hopkinson, D.; Hoffman, J.; Duan, Y.; Egbebi, A.; Resnik, K.; Li, B. Phase change amino acid salt separates into CO2-rich and CO2-lean phases upon interacting with CO2. Appl. Energ. 2016, 161, 41. (11) Jessop, P. G.; Jessop, D. A.; Fu, D. B.; Phan, L. Solvatochromic parameters for solvents of interest in green chemistry. Green. Chem. 2012, 14, 1245. (12) Blackbeard, T.; Demidyuk, V.; Hill, S. L.; Whitehead, J. C. The effect of temperature on the plasma-catalytic destruction of propane and propene: A comparison with thermal catalysis. 15



Plasma. Chem. Plasma. P. 2009, 29, 411. (13) Anderson, K.; Atkins, M. P.; Estager, J.; Kuah, Y. C.; Ng, S.; Oliferenko, A. A.; Plechkova, N. V.; Puga, A. V.; Seddon, K. R.; Wassell, D. F. Carbon dioxide uptake from natural gas by binary ionic liquid-water mixtures (vol 17, pg 4340, 2015). Green. Chem. 2015, 17, 4500. (14) Zhang, B.; Bogush, A.; Wei, J. X.; Zhang, T. S.; Hu, J.; Li, F. X.; Yu, Q. J. Reversible carbon dioxide capture at high temperatures by tetraethylenepentamine acetic acid and polyethylene glycol mixtures with high capacity and low viscosity. Energ. Fuel. 2017, 31, 4237. (15) Shi, W.; Siefert, N. S.; Baled, H. O.; Steckel, J. A.; Hopkinson, D. P. Molecular simulations of the thermophysical properties of polyethylene glycol siloxane (PEGs) solvent for precombustion CO2 capture. J. Phys. Chem. C. 2016, 120, 20158. (16) Hamrahi, Z.; Kargari, A. Modification of polycarbonate membrane by polyethylene glycol for CO2/CH4 separation. Sep. Sci. Technol. 2017, 52, 544. (17) Gacal, B. N.; Filiz, V.; Abetz, V. The synthesis of poly(ethylene glycol) (PEG) containing polymers via step-growth click coupling reaction for CO2 separation. Macromol. Chem. Phys. 2016, 217, 672. (18) Chen, Y.; Hu, H. Carbon dioxide capture by diethylenetriamine hydrobromide in nonaqueous systems and phase-change formation. Energ. Fuel. 2017, 31, 5363. (19) Zhao, T. X.; Guo, B.; Li, Q.; Sha, F.; Zhang, F.; Zhang, J. B. Highly efficient CO2 capture to a new-style CO2-storage material. Energ. Fuel. 2016, 30, 6555. (20) Tao, M. N.; Gao, J. Z.; Zhang, P.; Zhang, W.; Liu, Q.; He, Y.; Shi, Y. Biogas upgrading by capturing CO2 in non-aqueous phase-changing diamine solutions. Energ. Fuel. 2017, 31, 6298. (21) Zheng, S. D.; Tao, M. N.; Liu, Q.; Ning, L. Q.; He, Y.; Shi, Y. Capturing CO2 into the precipitate of a phase-changing solvent after absorption. Environ. Sci. Technol. 2014, 48, 8905. (22) Raynal, L.; Bouillon, P. A.; Gomez, A.; Broutin, P. From mea to demixing solvents and future steps, a roadmap for lowering the cost of post-combustion carbon capture. Chem. Eng. J. 2011, 171, 742. (23) Zhuang, Q.; Clements, B.; Dai, J. Y.; Carrigan, L. Ten years of research on phase separation absorbents for carbon capture: Achievements and next steps. Int. J. Greenh. Gas. Con. 2016, 52, 449. (24) Zhang, W. D.; Jin, X. H.; Tu, W. W.; Ma, Q.; Mao, M. L.; Cui, C. H. Development of mea-based CO2 phase change absorbent. Appl. Energ. 2017, 195, 316. (25) Quan Zhuang, B. C., Bingyun Li. Emerging new types of absorbents for postcombustion carbon capture. In: Recent advances in carbon capture and storage. Intech, 2017. (26) Li, J.; Ye, Y. M.; Chen, L. F.; Qi, Z. W. Solubilities of CO2 in poly(ethylene glycols) from (303.15 to 333.15) K. J. Chem. Eng. Data. 2012, 57, 610. (27) Whyatt, G. K.; Zwoster, A.; Zheng, F.; Perry, R. J.; Wood, B. R.; Spiry, I.; Freeman, C. J.; Heldebrant, D. J. Measuring CO2 and N2O mass transfer into gap-1 CO2-capture solvents at varied water loadings. Ind. Eng. Chem. Res. 2017, 56, 4830. (28) Jiang, Y. Y.; Wang, G. N.; Zhou, Z.; Wu, Y. T.; Geng, J.; Zhang, Z. B. Tetraalkylammonium amino acids as functionalized ionic liquids of low viscosity. Chem. 16


Page 16 of 32

Page 17 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Commun. 2008, 505. (29) Seo, S.; Desilva, M. A.; Xia, H.; Brennecke, J. F. Effect of cation on physical properties and CO2 solubility for phosphonium-based ionic liquids with 2-cyanopyrrolide anions. J. Phys. Chem. B. 2015, 119, 11807. (30) Wang, C. M.; Luo, X. Y.; Luo, H. M.; Jiang, D. E.; Li, H. R.; Dai, S. Tuning the basicity of ionic liquids for equimolar CO2 capture. Angew. Chem. Int. Edit. 2011, 50, 4918. (31) Zhang, Y.; Zhang, S.; Lu, X.; Zhou, Q.; Fan, W.; Zhang, X. Dual amino-functionalised phosphonium ionic liquids for CO2 capture. Chem-Eur. J. 2009, 15, 3003. (32) Zhang, J.; Zhang, S.; Dong, K.; Zhang, Y.; Shen, Y.; Lv, X. Supported absorption of CO2 by tetrabutylphosphonium amino acid ionic liquids. Chem-Eur. J. 2006, 12, 4021. (33) Hu, P. C.; Zhang, R.; Liu, Z. C.; Liu, H. Y.; Xu, C. M.; Meng, X. H.; Liang, M.; Liang, S. S. Absorption performance and mechanism of CO2 in aqueous solutions of amine-based ionic liquids. Energ. Fuel. 2015, 29, 6019. (34) Zhou, X. B.; Jing, G. H.; Liu, F.; Lv, B. H.; Zhou, Z. M. Mechanism and kinetics of CO2 absorption into an aqueous solution of a triamino-functionalized ionic liquid. Energ. Fuel. 2017, 31, 1793. (35) Bhattacharyya, S.; Shah, F. U. Ether functionalized choline tethered amino acid ionic liquids for enhanced CO2 capture. Acs. Sustain. Chem. Eng. 2016, 4, 5441. (36) Barzagli, F.; Mani, F.; Peruzzini, M. Efficient CO2 absorption and low temperature desorption with non-aqueous solvents based on 2-amino-2-methyl-1-propanol (AMP). Int. J. Greenh. Gas. Con. 2013, 16, 217. (37) Schaffer, A.; Brechtel, K.; Scheffknecht, G. Comparative study on differently concentrated aqueous solutions of mea and teta for CO2 capture from flue gases. Fuel. 2012, 101, 148. (38) Cherbanski, R.; Molga, E. Intensification of desorption processes by use of microwaves-an overview of possible applications and industrial perspectives. Chem. Eng. Process. 2009, 48, 48. (39) Cheng, N. L. Solvents handbook; Chemical industry press: Beijing, 2015. (40) Aschenbrenner, O.; Supasitmongkol, S.; Taylor, M.; Styring, P. Measurement of vapour pressures of ionic liquids and other low vapour pressure solvents. Green. Chem. 2009, 11, 1217.

17



Page 18 of 32

Table 1. CO2 absorption capacity of different organic solvents and their TETA solutions. Absorption experiments were carried out at 40°C with an inlet CO2 concentration of 100%.

Solvent

Polyethylene glycol(200) diethylene glycol triethylene glycol diethylene glycol monomethyl ether N-Methyl pyrrolidone Polyethylene glycol(300) Polyethylene glycol(400) dimethylacetamide diethylene glycol dimethyl ether

Abbreviation

Molecular Weight (g/mol)

Boiling Point39 (°C)

Viscosity39 (mPa·s, 20°C)

Vapor Pressure (Pa, 25°C)

Absorption Capacity of Organic Solvents (g/kg)

Absorption Capacity of 0.6M TETA Solutions (mol /mol TETA)

wt%

PEG200 DEG TEG

~200 106.1 150.2

>250 245 285

64 36 49

9.9a 0.625 0.18

5.15 4.66 4.98

1.87 1.76 1.74

4.36 4.21 4.13

DGME

120.2

193

3.0

0.024

7.34

1.73

4.43

NMP PEG300 PEG400 DMAC

99.1 ~300 ~400 87.1

166 >250 >250 166

1.7 81 116 0.9

66 1.5a

A Novel Phase-Changing Nonaqueous Solution for CO2 Capture with

Recommend Documents