Performance evaluation of newly developed absorbents for solvent

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Environmental and Carbon Dioxide Issues

Performance evaluation of newly developed absorbents for solvent-based carbon dioxide capture Chenxu Li, Xiaoqin Shi, and Shufeng Shen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b02158 • Publication Date (Web): 26 Aug 2019 Downloaded from pubs.acs.org on August 29, 2019

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Energy & Fuels

Performance

evaluation

of

newly

developed

absorbents

for

solvent-based carbon dioxide capture Chenxu Li, Xiaoqin Shi, Shufeng Shen* School of Chemical and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, P.R. China

ABSTRACT Solvent-based absorption using aqueous monoethanolamine (MEA) is the most mature and commercially available carbon dioxide capture technique. However, high capital cost and large energy consumption required for solvent regeneration still remain major disadvantages which results in delaying the worldwide large-scale deployment of this technology. Several newly developed absorbents have been recently proposed to solve the main issue as for energy-efficient capture process. In this work, several advanced solvents, i.e. aqueous and water-lean amino acid salts (potassium lysinate, potassium prolinate or potassium sarcosinate) and blends of amines with glycol ethers, were selected as the representatives for aqueous, non-aqueous and phase-change systems. The CO2 absorption-desorption performance of these absorbents was characterized. The relative heat duty of those CO2-loaded absorbents was also evaluated and compared with the conventional aqueous 30 mass% MEA. Primarily results indicate that non-aqueous and phase-change absorbents investigated in this work have huge potential in reducing energy consumption of regeneration, about 40-60% reduction. Key Words ： CO2 capture; Absorbent; Energy reduction; Solvent development; Solvent regeneration

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1. INTRODUCTION Global climate change, primarily caused by carbon dioxide (CO2) emissions, has become a significant environmental issue. Carbon capture, utilization and storage (CCUS) has been considered as one of the promising solutions for effective CO2 reduction. Chemical absorption with aqueous amine-based solvents is the most widely studied among the current capture technologies and aqueous 30 wt% monoethanolamine (MEA) is the benchmark absorbent for this technology.1 However, the huge regeneration energy, mainly due to high specific heat and enthalpy of vaporization of water solvent, remains the major drawback of this technique. In particular, the energy requirement for solvent regeneration accounts for around 70% of the total CCUS cost, which is the main hindrance of its worldwide large-scale deployment.2 To address this issue, extensive researches have focused on the design and development of advanced absorbents that have superior performance to MEA in several aspects such as high capacity, low regeneration energy, high capture rate and high stability from various sources such as flue gas treatment, biogas upgrading and nature gas processing.3,4 In addition, some promising solid adsorbents with excellent CO2 uptake and stability for CO2 capture, such as nitrogen-doped carbons5-9 and metal-organic frameworks10, have also been proposed in recent years as the alternative technology to amine scrubbing. However, in order to make these technologies more practical in the near future, it is essential to reduce the regeneration energy greatly. Substantial effort on development of new energy-efficient absorbents has been devoted to reducing the energy consumption. Recently, phase change absorbents have shown a promising perspective.11 Since a homogenous solution can undergo a phase transition into a biphasic system during CO2 absorption and the absorbed CO2 can be concentrated into one phase, it should have potential to significantly reduce energy consumption by regenerating only the CO2-rich phase. Liquid biphasic systems, such as diethylenetriamine/sulfolane/water,12 2-(ethylamino)ethanol with diethylene glycol diethyl ether,13 MEA/alcohol/H2O blends,14 methyldiethanolamine/C4-C6 alcohol/H2O blends15 and amine/ether/H2O blends,16 have also been proposed for energy efficient CO2 capture. Additionally, some blend systems such as triethylenetetramine/ethanol blend,17 diethylenetriamine in ethanol, diethylene glycol dimethyl ether, N-methyl-pyrrolidone, or 2


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Energy & Fuels

dimethyl carbonate,18 potassium prolinate/ethanol/water solution,19 amine/ethylene glycol derivative systems20 and piperazine/N, N-dimethylformamide solution21 were developed to produce CO2-rich solid precipitates after CO2 absorption and were considered as liquid-to-solid phase-changing absorbents. Single-liquid phase absorption by water-free absorbents consisting of amines and organics has been recently attracted special attention. Using organic solvents can provide significant advantages as for saving regeneration energy and reducing corrosiveness and degradation due to their lower specific heat than water and low desorption temperature.4,22 In recent years, plenty significant research has been done in this field and most of them focus on the absorption and desorption performance, reaction mechanism and reaction kinetics for CO2 capture. Organics are commonly used as nonaquoues diluents as components. Specifically, these nonaquoues systems include the use of alcohols,23-26 glycols,27,28 ketone,29 dimethyl sulphoxide,30 dimethyl formamide,31 ionic liquids32 and ethers.33 Guo et al.22,

34

have recently proposed amine-based

absorbents in glycol ethers as nonaqueous absorbents for CO2 removal from biogas upgrading and natural gas processing. Although a large amount of research regarding of advanced absorbents has been reported, the experimental data of regeneration energy for these solvents are still insufficient. Therefore, we focused our efforts on the comparison of absorption and desorption performance, especially for evaluation of relative heat duty of those CO2-loaded absorbents using 30 mass% MEA as a baseline. In this work, aqueous amino acid salts, non-aqueous absorbents and phase-change absorbents were investigated and evaluated. The absorbents are aqueous potassium lysinate, blends

of

MEA

with

2-methoxyethanol

(EGME)

and

2-ethoxyethanol

(EGEE),

2-(methylamino)ethanol (MAE) with diethylene glycol dimethyl ether (DEGDME), potassium prolinate/EGME/water and potassium sarcosinate/EGME/water. 2. MATERIALS AND METHODS 2.1. Chemicals MEA (99.12% GC purity), MAE (99.25% GC purity), Lysine (98.25% HPLC purity), Proline (99.90% HPLC purity), Sarcosine (98.26% HPLC purity), 2-methoxyethanol (EGME, 99.10% GC 3


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purity), 2-ethoxyethanol (EGEE, 99.18% GC purity), DEGDME (99.83% GC purity) and KOH (≥ 95% GR purity) were all purchased from Aladdin reagent, China. N2 (99.99%, v/v), CO2 (99.995%, v/v) and mixed standard gases (20.01 % CO2 balanced with N2) were obtained from Shijiazhuang Xisanjiao oxygen generation station. Water was produced from Merck-Millipore Aquelix 5. Amino acid salt solutions were prepared by dissolving amino acid in solvents (glycol ethers or water) with an equimolar amount of KOH in a volumetric flask at 298 K. Reagents were weighed on electronic analytical balances (OHAUS, CP214, Scout SE 1501F). The concentrations of amines or amino acid salts can be measured in an automatic titrator (ZDJ-5, INESA Scientific Instrument Co., Ltd). 2.2. CO2 absorption and desorption experiments The CO2 capture performance was measured on a screening apparatus. A schematic diagram of the experimental set-up is presented in Figure 1. The batch experiments of CO2 absorption (313K)-desorption (353K) for each absorbent were performed at near atmospheric pressure. In this apparatus, temperatures were measured by PT-100 thermocouples and recorded by an online MIK200D from MEACON China. A thermostatic water bath with magnetic stirrer was used to maintain constant conditions. The CO2 analyzer (GXH-3011N, 0-20%, Institute of Beijing HUAYUN Analytical Instrument) was calibrated with a standard gas before experiments, and then the mixture of N2 and CO2 was introduced into the apparatus. About 13 vol% CO2 gas mixture was obtained at a total flow rate of 0.5 L min–1. The fresh solution with known mass, preheated to 313K, was poured into the flask when the temperature of water bath reached 313K. The outlet CO2 concentration, temperature and pressure were recorded in the whole process. The absorption was stopped when the outlet CO2 concentration was higher than 12.5%. The solution was then desorbed at 353K by bubbling pure N2 with a flow rate of 0.2 L min–1. Desorption wasn’t stopped until the outlet CO2 concentration was less than 2%. Samples were taken after absorption and desorption and then the CO2 loadings were determined. For the phase change systems, only the CO2-rich phase was desorbed and the samples were taken and measured after mixing with the CO2-lean phase. 2.3. Evaluation of relative heat duty

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Energy & Fuels

The experimental apparatus for evaluating the overall energy consumption of solvent regeneration is shown in Figure 2. A gas condenser was connected to the flask for cooling the CO2 and solvent vapor before entering the mass flow meter or gas analyzer. A heating mantle (ZNCL-TS2000mL, Zhengzhou Kechuang Instrument Co., Ltd, China) with magnetic stirrer was provided to maintain the working temperature. For each run, fresh solution was first absorbed at 313K using a gas mixture with CO2 partial pressure at about 15kPa. The absorption was stopped when the CO2 concentration in the gas outlet is higher than 13.5%. Desorption was then carried out at 373K without N2 gas flushing. An electric energy meter (eSensor, Altenergy Power System Inc., China, stated accuracy of 0.001 kWh) was used to determine the energy consumption and a CO2 mass flow meter (CS200A, 0 – 3.7 L min–1, Beijing Sevenstar Flow Co., Ltd, China) with a cumulative volume function was used to measure the desorbed CO2. Temperature, pressure, and CO2 flowrate were recorded on the computer. Desorption lasted for 2 h. The amount of desorbed CO2 was obtained by cumulative gas volume at standard conditions. The overall energy consumption of regeneration (kJ/mol CO2) is defined as the cumulative electricity energy divided by the corresponding amounts of CO2 released in the first 60 min or 30 min and the calculation results are listed in Table 3. It should be pointed out that, the heat dissipation was not considered and thus the relative heat duty was used for comparison under the same operating conditions. The heat duty for aqueous 30 mass% (5.0M) MEA was taken as the baseline case. 2.4. Analytical methods Density and viscosity of solutions were measured by a combined microvisco/density meter (Lovis 2000M/DMA-4100 M, Anton Paar). For analyzing CO2 loading (α) in the moles of CO2 per kg CO2-free solution, the volume amount of captured CO2 in the sample of known mass was measured by acid titration in a modified Chittick CO2 apparatus.19 Cyclic loading is defined as the CO2 loading difference between the CO2-rich and the CO2-lean solutions. 3. RESULTS AND DISCUSSION 3.1. Physicochemical properties of different absorbent systems

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The newly developed absorbents were formulated based on the replacement of water by organics, with the purpose of maintaining the good performances of conventional aqueous amines yet removing, at least in part, their disadvantages. These proposed solvents are EGME, EGEE and DEGDME. The polarity (e.g. dielectric constant ε) of solvents used is much weaker than that of water, which may affect the solubility and the stability of reaction products. A comparison of physicochemical properties of solvents used in this work is presented in Table 1.35 It can be seen that, compared with water, the proposed solvents have several advantages such as high boiling point, low specific heat capacity and low vaporization enthalpy. These properties can be favorable for reducing energy consumption for solvent regeneration by lowering sensible heat and latent heat of the absorbent systems. It is noted that the viscosity of EGME and EGEE is much higher than that of water. MEA and MAE, as representative primary and secondary amines, were used for reactive components and still remain competitive in the future due to its low cost and rapid reaction rate with CO2. Amino acid salts are also of great interest as alternative solvents for CO2 capture because of high kinetics, low volatility, and good resistance to degradation. Among them, aqueous potassium salt of lysine, proline and sarcosine were considered to be the most promising solvents in terms of reaction kinetics.36-38 The physical properties of different combinations of absorbents with solvents were also measured before and after CO2 absorption at 313 K. The results are presented in Table 2. It can be seen that the addition of reactive absorbents into solvents greatly increased their viscosity. It is worth noting that, the viscosity of all CO2-loaded solutions increase about 2-6 times after CO2 absorption. For nonaqueous blends, e.g. 5.0M MEA/EGEE, its viscosity increased from 3.1 to 22.4 mPa.s, which will be unfavorable for mass transfer during CO2 absorption. Especially for the liquid biphasic system of MAE/DEGDME, the viscosity of the bottom CO2-loaded phase is extremely high, e.g. 68.1 mPa.s at 353K. For solid-liquid phase-change systems, the viscosities of the CO2-loaded systems were not measured in this work. 3.2. Comparison of CO2 absorption-desorption performance Phase behaviors during CO2 absorption, absorption and cyclic capacity for six proposed absorbent systems were investigated in the apparatus (Fig.1). Aqueous 5.0M MEA was used for

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Energy & Fuels

comparison. Results are shown in Table 2 and the graphic comparison is presented in Fig. 3. Different phase behaviors were observed during the CO2 absorption. For the nonaqueous blends of amine and glycol ethers, the mixture of MAE and DEGDME can form two liquid phases after CO2 absorption. However, the mixtures of MEA and EGME or EGEE showed similar single-phase behavior to the conventional aqueous 5.0M MEA. In the nonaqueous solution,22,33 CO2 can react with MEA to yield the ionic products, i.e. amine carbamate and protonated amine. Polar solvents can make the ionic products stable and soluble. While the weak polarity of DEGDME (ε=7.2) is used, the ionic couples have limited solubility and can form new phase at a certain loading. Similar to the system of ProK/ethanol/water,19 the two newly water-lean AAS systems can form liquid-solid phase change. In these phase-change systems, the CO2 was found to be enriched in the new phases and the CO2 loadings were measured in the range of 2.5-4.9 mol CO2/kg solution, as shown in Table 2. The solvent cyclic absorption capacity (Δα) can be estimated from the difference of CO2 loadings under the absorption and desorption conditions (absorption at 313 K and desorption with N2 strip method at 353 K), which can affect the required circulation rate of absorbent and then the regeneration energy. The graphic results are also presented in Fig.3. It is noted that desorption for MAE/DEGDME system was operated at 393 K without N2 gas stripping, due to its high viscosity. Aqueous 5.0M MEA solution was found to have a cyclic capacity of 0.841 mol CO2/kg solution. For the newly single-phase systems, the desorption performance improved greatly and their cyclic capacities increased by 45-65%. By replacing the water with glycol ether solvents, the cyclic capacity was greatly enhanced. For liquid-solid phase change systems, 2.0M SarK/EGME/water solution showed lower cyclic capacity than 3.0M ProK/EGME/water solution. For the liquid biphasic system, above 90% of CO2 absorbed was captured in the lower phase with small portion of the total volume. Regenerating the CO2-rich phase to reuse the absorbents should have great potential to reduce energy consumption although necessary modification on the conventional capture process is required. 3.3 Evaluation of relative heat duty The desorption profiles in terms of electricity energy, amounts of CO2 desorbed along with 7


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desorption time for seven absorbent systems are presented in Fig.4 (a-g). Before desorption tests, all the solutions were absorbed at 313K in the same experimental rig (Fig.2). The summary results about the relative heat duty are shown in Table 3 and Fig.4 (h). Data in the first 60min (30min for liquid-solid systems) was used for calculation and comparison. It can be found that the released amounts of CO2 and energy consumption increased gradually for the aqueous 5.0M MEA, while CO2 desoption almost finished in the first 30 min for the other systems. Small change was observed for all three systems after 60 min. It should be pointed out that the heat dissipation was not considered in this work. It is surprisingly noting that the overall electricity consumption in kWh for the nonaqueous or phase change systems is more than 40% lower than that for aqueous 5.0M MEA. However, the released amounts of CO2 also varied greatly for different systems. Therefore, the relative energy consumption was also used for comparison under the same operating conditions using aqueous 5.0M MEA as the baseline case. The overall heat duty for aqueous 5.0M MEA was estimated to be 415 kJ/mol CO2 and 455 kJ/mol CO2 for aqueous 2.5M LysK. The proposed nonaqueous blends or water-lean solvents have lower overall energy consumption, in the range of 165-255 kJ/mol CO2. It should be pointed out that all the experiments were performed in a simplified setup with heating mantle at the same/similar operating conditions without sufficient insulation. The heat dissipation was not estimated separately and lumped into the total electric energy consumption. Moreover, energy conversion factor is not considered for calculation of converting electrical energy to thermal energy in this work. Therefore, the heat duty for aqueous 5.0M MEA was observed to be higher than those (about 4.0 GJ/t CO2) reported under the practical industrial conditions.3,39 Nevertheless, this method was accepted for initial evaluation of desorption performance in recent literature.22,40 For single-phase nonaqueous absorbents, they showed similar CO2 desorption efficiency but about 50% decrease in overall energy consumption. As for liquid biphasic systems, about 40% of overall electricity energy was required compared with the baseline case, probably due to the highly concentrated lower phase and less solvent evaporation resulting in the high energy efficiency. Liquid-solid phase change absorbents also showed lower energy requirement for CO2 desorption. Considering the effect of EGME solvent in the slurry mixture on the sensible heat, most of CO2-lean phase was removed after phase separation for regeneration in comparison with the slurry 8


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Energy & Fuels

mixture without phase separation. Significant reduction in heat duty was observed due to solid-liquid phase separation. Removal of CO2-lean phase is beneficial for decreasing the energy which necessarily preheats the CO2-loaded solution to regeneration temperature. The system of 3.0M ProK/EGME/water shows less energy consumption than the system of 2.0M SarK/EGME/water. Preliminary evaluation shows that nonaqueous absorbents have advantages in terms of regeneration energy consumption over the traditional aqueous absorbents for energy-efficient CO2 capture, as presented in Fig.4(h). These nonaqueous systems can be applied for CO2 removal from biogas upgrading and natural gas processing. Moreover, water-lean solvents also show huge potential to lower the regeneration energy, but have relative low CO2 cyclic capacity. Therefore, we note continued work needed to assess on long-term capture performance at the pilot scale from various CO2 sources before any real implementation can occur. 4. CONCLUSION Physical properties, phase behavior and CO2 absorption-desorption performance for several newly advanced absorbents including nonaqueous and water-lean systems were characterized and compared under the same operating conditions. Compared with the aqueous MEA, the desorption efficiency for the single-phase nonaqueous blends of MEA and glycol ethers was observed to increase greatly and their cyclic capacities increased by 45-65%. Phase change systems can enrich the CO2 absorbed in the new formed phase. Primarily evaluation on the relative heat duty indicate that nonaqueous can potentially reduce about 50% overall energy consumption meanwhile maintain good absorption and desorption performance. Liquid biphasic absorbents have also potential application if the transfer of CO2-loaded phase with super high viscosity can be solved. Water-lean solvents have relative low CO2 cyclic capacity but show advantages in regeneration energy consumption over the aqueous MEA system. AUTHOR INFORMATION *Corresponding Author E-mail: [email protected], [email protected]; 9


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Tel.: +86 311 88632183. Fax: +86 311 88632183. ORCID Shufeng Shen: 0000-0003-0625-133X Funding The authors would like to acknowledge Key Program of Hebei Provincial Natural Science Foundation (B2018208154), Training Program for Talent Engineers of Hebei Province (A2017002022) and Program for Hundred Outstanding Innovation Talents in Hebei Universities (SLRC2019051) for financial support. Notes The authors declare no competing financial interest.

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Energy & Fuels

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[32] Xiao, M.; Liu, H.; Gao, H.; Olson, W.; Liang, Z. CO2 capture with hybrid absorbents of low viscosity imidazolium-based ionic liquids and amine. Appl. Energy 2019,235, 311–319.

[33] Barzagli, F.; Giorgi, C.; Mani, F.; Peruzzini, M. Reversible carbon dioxide capture by aqueous and non-aqueous amine-based absorbents: A comparative analysis carried out by 13C NMR spectroscopy. Appl. Energy 2018, 220, 208–219.

[34] Guo, H.; Li, H.; Shen, S. Monoethanolamine+2-methoxyethanol mixtures for CO2 capture: Density, viscosity and CO2 solubility. J. Chem. Thermody. 2019, 132, 155–163.

[35] Lide, D. R.; Ed. CRC Handbook of Chemistry and Physics, 90th ed., (CD-ROM, version 2010); CRC Press: Boca Raton, FL, 2010.

[36] Shen, S.; Yang, Y.; Bian, Y.; Zhao, Y. Kinetics of CO2 absorption into aqueous basic amino acid salt: potassium salt of lysine solution. Environ. Sci. Technol. 2016, 50, 2054 –2063.

[37] Majchrowicz, M. E.; Kersten, S.; Brilman, W. Reactive absorption of carbon dioxide in L-prolinate salt solutions. Ind. Eng. Chem. Res. 2014, 53, 11460–11467.

[38] Shen, S.; Yang, Y. Carbon Dioxide Absorption into Aqueous Potassium Salt Solutions of Arginine for Post-Combustion Capture, Energy Fuels 2016, 30, 6585 – 6596.

[39] Rochelle, G. T. Amine scrubbing for CO2 capture. Science 2009, 325, 1652–1654. [40] Zhang, X.; Zhang, X.; Liu, H.; Li, W.; Xiao, M.; Gao, H., Liang, Z. Reduction of energy requirement of CO2 desorption from a rich CO2-loaded MEA solution by using solid acid catalysts. Appl. Energy 2017, 202, 673–684.

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Page 14 of 21

Captions

Table 1 Physicochemical property data of solvents. Table 2 CO2 absorption-desorption performance of several absorbents. Table 3 Evaluation of overall energy consumption for different absorbents by thermal regeneration at 373K.a

Fig.1. Schematic diagram of experimental apparatus for CO2 absorption and desorption. Fig.2. Schematic diagram of evaluating heat duty for solvent regeneration. Fig.3. Comparison of CO2 absorption and cyclic capacity of different absorbent systems: absorption at 313K and desorption with N2 strip at 353K. Note: thermal desorption for MAE/DEGDME system at 393K. Fig.4. Energy consumption and the amounts of desorbed CO2 during CO2 desorption for different absorbent systems. Data were taken for evaluation of relative heat duty (h) in the first 60 min for a-e systems and the first 30 min for (f and g) systems.

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Energy & Fuels

Table 1 Physicochemical property data of solvents35

Viscosity at 298K, Solvent

CAS NO.

Boiling point at 101.3

Molar mass (g·mol-1) mPa s

Specific heat (Cp), kJ ΔvapH (bp), kJ kg-1

kPa, K

Dielectric constant ε

kg-1 K-1

Water

7732-18-5

18.02

0.890

373.2

2256.4

4.18

80.1

EGME

109-86-4

76.10

1.527

397.3

493.3

2.25

17.2

EGEE

110-80-5

90.12

1.845

408.2

435.2

2.34

13.4

DEGDME

111-96-6

134.17

0.992

435.2

269.6

2.04

7.2

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Energy & Fuels 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

Page 16 of 21

Table 2 CO2 absorption-desorption performance of several absorbents. Density (g.cm-3, 313K)

Viscosity (mPa·s, 313K)

Absorbents

CO2 loading α （mol CO2/kg solution）a

Cyclic loading ∆α (mol CO2/kg solution)

CO2-free

CO2-loaded

CO2-free

CO2-loaded

absorption

desorption

T: 313-353K

5.0M MEA/H2O

1.0036

1.0984

1.5781

2.4175

2.198

1.357

0.841

2.5M LysK/H2O

1.1346

1.2127

3.5175

6.1033

2.425

1.188

1.237

5.0M MEA/EGME

0.9681

1.0579

2.6194

13.717

2.041

0.568

1.473

5.0M MEA/EGEE

0.9438

1.0345

3.1120

22.450

2.062

0.681

1.381

Single-phase system

Phase change system b 2.266 (Rich: 4.912; 0.870 d Lean: 0.085) c 1.770 (Solid: 2.574; 3.0M ProK/EGME/H2O 1.1179 N/A (slurry) 16.7940 N/A(slurry) 0.952 Liquid: 0.748) c 0.943 (Solid: 3.046; 2.0M SarK/EGME/H2O 1.0497 N/A(slurry) 5.7530 N/A(slurry) 0.336 Liquid: 0.551) c a CO absorption at 313 K and desorption with N strip method at 353 K. α is defined as the moles of CO per kg CO -free solution after CO absorption or 2 2 2 2 2 5.0M MAE/DEGDME

0.9231

N/A

1.4094

Rich: 68.1 (353K)

1.396 0.818 0.607 desorption. Cyclic

loading is defined as the CO2 loading difference between the CO2-rich and the CO2-lean solutions. bDensity cThe d In

and viscosity data were not determined due to liquid-liquid or liquid-solid phase change after CO2 absorption.

CO2 loading α (the moles of CO2 per kg sample) in the CO2-rich and the CO2-lean phases was also measured respectively.

this run, desorption experiment was performed at 393K for 60 min.

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Energy & Fuels

Table 3 Evaluation of overall energy consumption for different absorbents by thermal regeneration at 373K.a Absorbent system

Amount of CO2-loaded solution

5.0M MEA/H2O

1.8 L

2.5M LysK/H2O

1.8 L

5.0M MEA/EGME

1.8 L

5.0M MEA/EGEE

1.8 L

5.0M MAE/DEGDMEb

0.5 kg (CO2-rich phase) b 0.9 L (slurry) c

3.0M ProK/EGME/H2O

1.9 L (slurry)c 1.4 L (CO2-rich slurry) d

a

Run No.

CO2 loading α (mol/kg)

Amount of CO2 desorbed (g)

Overall energy consumption (kWh)

1

2.403

78.04

0.204

414.0

2

2.390

75.61

0.199

416.9

1

2.375

56.30

0.163

458.6

2

2.379

58.04

0.166

453.0

1

2.188

77.79

0.110

224.0

2

2.206

82.11

0.111

214.1

1

2.184

70.50

0.102

229.2

2

2.152

83.06

0.107

204.1

1

4.503

64.80

0.065

158.9

2

4.419

66.64

0.071

168.8

1

1.656

27.57

0.031

178.2

2

1.656

27.57

166.6

1

1.683

49.13

0.029 0.069

2

1.674

47.37

0.064

214.0

1

1.920

39.01

0.045

182.7

2

2.015

35.44

0.045

201.1

Heat duty (kJ/mol CO2)

222.4

415.5±1.5 455.8±2.8 219.1±5.0 216.7±12.6 163.9±5.0 172.4 ± 5.8 218.2±4.2 191.9±9.2

2.0M SarK/EGME/H2O 0.9 L (slurry) c 1 0.960 17.41 0.013 254.8 254.8 α is referred to the CO2 loading after CO2 absorption at the same conditions (313K). Heat duty is defined as the energy consumption per mol CO2 desorbed in the first 60min.

b

In this run, desorption experiment using the CO2-rich phase only was performed at 393K for 60 min.

c

In these runs, solid phase was not separated from the mixture and slurry solution was used for solvent regeneration. Data were taken for heat duty calculation in the first 30 min.

d

In these runs, CO2-lean phase (about 0.5 L) was removed from the mixture and CO2-rich slurry solution was used for solvent regeneration. Data were taken for heat duty

calculation in the first 30 min.

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Page 18 of 21

Figure 1

Fig.1. Schematic diagram of experimental apparatus for CO2 absorption and desorption.

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Energy & Fuels

Figure 2

Fig.2. Schematic diagram of evaluating heat duty for solvent regeneration.

19


Energy & Fuels

Figure 3 3.0 After absorption After desorption Cyclic loading

2.5

2.0 CO2 loading (mol/kg)

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

Page 20 of 21

1.5

1.0

0.5

0.0

MEA/H2O

LysK/H2O

MEA/EGME

MEA/EGEE MAE/DEGDME ProK/EGME/H2O SarK/EGME/H2O

Fig.3. Comparison of CO2 absorption and cyclic capacity of different absorbent systems: absorption at 313K and desorption with N2 strip at 353K. Note: thermal desorption for MAE/DEGDME system at 393K.

20


Page 21 of 21

Figure 4

800

800

80

400 40

5.0M MEA-H2O

200

0

10

20

30

40

50

60

400 40

0

0

60

10

20

30

60

0

80

5.0M MEA-EGME

0

10

20

30

40

20

50

60

Amounts of CO2 released (g)

200

Electricity consumption (kJ)

40


400

60

400 40

5.0M MEA-EGEE

200

0

0

0

10

20

Time (min)

30

40

20

50

60

0

Time (min)

800

800

(e)

(f)

80

400 40

5.0M MAE-DEGDME

200

20

0

10

20

30

40

50

60


60

3.0M ProK-EGME

80

slurry without sepration (0.9 L) slurry without sepration (1.9 L) CO2-rich slurry with phase sepration (1.4L)

600


600


50

600 60

0

40

(d)

80

600


0

800

(c)

0

20

Time (min)

Time (min)

800

2.5M LysK-H2O

200

60

400 40

200

0

0

20

0

5

10

Time (min)

15

20

25

30


0

20

80

600


60

(b)



600


(a)

0

Time (min)

800

(g)

80

(h) 100

400

40

2.0M SarK-EGME

200

20

Experimental heat duty (kJ/mol CO2)

400

Relativve heat duty (%)

60


600


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

Energy & Fuels

80

300 60

200 40

100

20

0

0

5

10

15

20

25

30

0

0

MEA/H2O

LysK/H2O

MEA/2ME

MEA/2EE

MAE/DEGDME

ProK/2ME/H2O SarK/2ME/H2O

0

Time (min)

Fig.4. Energy consumption and the amounts of desorbed CO2 during CO2 desorption for different absorbent systems. Data were taken for evaluation of relative heat duty (h) in the first 60 min for a-e systems and the first 30 min for (f and g) systems.

21


Performance evaluation of newly developed absorbents for solvent

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