Phenol Recovery by Hollow Fiber Membrane Contactor



Supporting Information

Nonaqueous Amine-based Absorbents for Energy Efficient CO2 Capture

Hui Guo, Chenxu Li, Xiaoqin Shi, Hui Li and Shufeng Shen*

School of Chemical and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, P.R. China

*Corresponding author’s e-mail: sfshen@hebust.; shufengshen@

Tel.: +86 311 88632183. Fax: +86 311 88632183.

Number of pages: 17

Number of tables: 4

Number of figures: 8

■ Experimental Section

CO2 Absorption and Desorption

The absorption (313K)-desorption (353K) experiments were investigated on a screening apparatus at near atmospheric pressure, as shown in Figure S1. This method can provide the detailed information of the absorbents on the absorption capacity, the relative absorption and desorption rate, and cyclic capacity [1,2]. Aqueous 5.0M (30 mass%) MEA were used as a reference system for comparison. For CO2 absorption experiment, N2 and CO2 gases controlled by mass flow controllers (D07-7C, Beijing Sevenstar, China, with ± 1.5% F.S. accuracy), are mixed in the mixing tank with a total flow rate of 0.54 L/min. Then the gas mixture (13 vol% CO2) was sent to a 250 mL reactor controlled by thermostat bath (DF-101S, Yuhua, China, with ± 1.0% F.S. accuracy). The outlet gas stream was cooled by a Graham condenser (C544300, Synthware, Beijing). The CO2 concentration was determined by the GXH-3011N CO2 analyzer. Aqueous or water-free absorbent (150 mL) with known mass was preheated to 313K and quickly introduced into the reactor to start the absorption process, which was monitored by measuring the CO2 concentration of the outlet gas along with time. Absorption was finished at 3.5 hrs. No phase separation was observed. Meanwhile, liquid samples were taken for CO2 loading analysis. Then, the reactor was removed overhead and back to the water bath when the temperature 353 K was reached. CO2 desorption was started by bubbling pure N2 in the loaded solution with a flow rate of 0.2 L /min. The CO2 concentration was monitored by the CO2 gas analyzer (SKS-BA-CO2, 0 – 100%, uncertainty 1.0% FS, Guangdong Skesen Gas Detection Equipment Co., Ltd.). Desorption was stopped until the CO2 concentration was below 2%, and then liquid samples were also taken. For the continuous cycles of absorption-desorption, CO2 lean solutions from desorption process were used instead of fresh absorbent solution. Desorption performance was also investigated by the thermo-desorption technique. The CO2-loaded solution were heated in a heating mantle with magnetic stirrer to 373 ± 1.0 K to release the captured CO2 resulting in a CO2 lean solution.

Based on the logged data, the absorption and desorption rate at a given time, rCO2, with units of mole /(kg solution• s), is calculated as:

[pic] (S1)

where ms is the mass of CO2-free absorbent solution in the flask, kg. QCO2In and QN2 are the volumetric flow rates in standard liter per second (SLS) of CO2 and N2 fed into the reaction flask from mass flow controller, respectively and yCO2Out is the CO2 molar fraction in the outlet gas stream as a function of time from the CO2 analyzer. CO2 loading (α) of samples is generally expressed in two ways. One is the moles of CO2 per mole of absorbent, mol CO2 / mole absorbent, the other is the moles of CO2 per kilogram of CO2-free absorbent solution for the samples, mol CO2 / kg. Thus, the CO2 loadings (αrich and αlean) in mol CO2 / kg absorbent solution can be calculated by integration over period of time, expressed as:

[pic] (S2)

[pic] (S3)

[pic] (S4)

The CO2 cyclic capacity, αcyc, can be defined by the difference of CO2 rich loading after absorption and CO2 lean loading after desorption, with units in mole CO2 per mole absorbent or mole CO2 per kg CO2-free absorbent solution.

The CO2 loadings can also be measured by acid titration using a modified Chittick CO2 apparatus (Figure S2) [3]. The amount of captured CO2 in the sample of known volume and mass was measured in a flask which is connected to a graduated gas measuring tube and an adjustable leveling bulb reservoir. The colored non-reactive liquid was kept at the same level to maintain the normal atmosphere pressure in the flask controlled by a digital pressure manometer (GM520, Shenzhen Jumaoyuan Science and Technology Co., Ltd.). In order to obtain the α in mol CO2 / mole absorbent, the concentrations of amines were titrated using an automatic potentiometric titrator (ZDJ-5, INESA Scientific Instrument Co., Ltd).

[pic] (S5)

[pic] (S6)

where P is the atmospheric pressure; VCO2 is the CO2 gas volume produced from the solution; T is the gas temperature; R is the gas constant; ms is the mass of CO2-free sample; C is the molar concentration of the standard H2SO4 solution for titration; V1 is the acid volume. Each liquid sample was determined three times to obtain an average CO2 loading. The error of loadings is about 0.005.

Equilibrium Solubility of CO2 in non-aqueous amine systems

The experiments on solubility of CO2 in aqueous 30 mass % (5 M) MEA solutions at 313 K and 373 K were performed to validate the experimental method used in the present work. The results are compared with the data reported in literature [4,5], as shown in Figure S5. A good agreement with each other was observed over the range investigated, which suggests that the method in this work is reliable.

Vapor–liquid equilibrium (VLE) in CO2-MEA-Glycol ether systems was performed in a thermostatted stirred cell reactor. A schematic diagram of the experimental set-up was presented in Figure S3 [2,6]. The set-up consists of a vessel (Vv, 2.15 L) for storing the CO2 gas and an equilibrium reactor (VR, 0.61 L) with pressure transducers (MIK-P300, 0 – 6 bar, MEACON China; GS4200-USB,0 – 3.5 bar, ESI). The temperatures (TV and TR) were recorded by PT-100 thermocouples (WZP-293) and a recorder (MIK200D) from MEACON China. In each run, a known mass and volume (Vs) of the absorbent solution was fed into the reactor. The system was degassed by vacuum pump (2XZ-1, Shanghai Shuang’e, China) and then was allowed to come to the vapor-liquid equilibrium at a desired temperature. In this case, the gas phase consists of solvent vapor and residual nitrogen in the equilibrium reactor. This gas pressure over the solution was defined as the initial pressure P0. Then, the pure CO2 was fed into the reactor and the total amount of added CO2 can be calculated from pressure changes (i.e. P1 down to P2) in the CO2 stored vessel by a modified Peng-Robinson equation of state. After the system can again reach VLE at which point the total pressure was called Pt. The CO2 partial pressure can be obtained (Equation S7). By adding more CO2 into the reactor, new VLE in the reactor can be obtained. A set of VLE data, i.e. partial pressure of CO2 present in the gas phase vs the CO2 loading (α) in the liquid phase (Equation S8), can be then obtained.

[pic] (S7)

[pic] (S8)

[pic] (S9)

where PCO2 is the partial pressure of CO2 present in the gas phase at vapor-liquid equilibrium. z1 , z2 and zeq are the compressibility factors of gas at different conditions, respectively, which were calculated using the Peng-Robinson equation of state using critical temperature of 304.21 K, critical pressure of 7383 kPa and acentric factor of 0.2236 [7].

REFERENCE

1. Guo, H.; Li, H.; Shen, S. CO2 capture by water-lean amino acid salts: absorption performance and mechanism. Energy Fuels 2018, 32, 6943–6954.

2. Zhao, Y.; Bian, Y.; Li, H.; Guo, H.; Shen, S.; Han, J.; Guo, D. A comparative study of aqueous potassium lysinate and aqueous monoethanolamine for postcombustion CO2 capture. Energy Fuel 2017, 31, 14033–14044.

3. Bian, Y.; Zhao, Y.; Shen, S. Characteristics of potassium prolinate + water + ethanol solution as a phase changing absorbent for CO2 Capture. J. Chem. Eng. Data 2017, 62, 3169–3177.

4. Lee, J. I.; Otto, F. D.; Mather. A. E. Equilibrium between carbon dioxide and aqueous monoethanolamine solutions. J. Appl. Chem. Biotechnol. 1976, 26, 541–549.

5. Shen, P. K.; Li, M. H. Solubility of carbon dioxide in aqueous mixtures of monoethanolamine with methyldiethanolamine. J. Chem. Eng. Data 1992, 37, 96–100.

6. Shen, S.; Zhao, Y.; Bian, Y.; Wang, Y.; Guo, H.; Li, H. CO2 absorption using aqueous potassium lysinate solutions: Vapor - liquid equilibrium data and modelling. J. Chem. Thermody. 2017, 115, 209–220.

7. Poling, B.E.; Thomson, G.H.; Friend, D.G.; Rowley, R.L.; Wilding, W.V. Perry´s Chemical Engineers Handbook, 8th Ed., The McGraw-Hill-Companies Inc., Columbus, USA. 2011. p:2-141.

8. Joung, S. N.; Yoo, C. W.; Shin, H. Y.; Kima, S. Y.; Yoo, K. P.; Lee, C. S.; Huh, W. S. Measurements and correlation of high-pressure VLE of binary CO2-alcohol systems (methanol, ethanol, 2-methoxyethanol and 2-ethoxyethanol). Fluid Phase Equilibria 2001, 185, 219–230.

9. Gui, X.; Tang, Z. G.; Fei, W, Y. Solubility of CO2 in alcohols, glycols, ethers, and ketones at high pressures from (288.15 to 318.15) K. J. Chem. Eng. Data 2011, 56, 2420–2429.

10. Bian, Y.; Shen S. CO2 absorption into a phase change absorbent: water-lean potassium prolinate/ethanol solution. Chin. J. Chem. Eng. 2018, 26, 2318–2326.

11. Luo, X.; Su, L.; Gao, H.; Wu, X.; Idem, R.O.; Tontiwachwuthikul, P.; Liang, Z. Density, viscosity and N2O solubility of aqueous 2-(methylmaino)ethanol solution. J. Chem. Eng. Data 2017, 62, 129–140.

12. Jackson, P.; Robinson, K.; Puxty G.; Attalla. M. In situ fourier transform-infrared (FT-IR) analysis of carbon dioxide absorption and desorption in amine solutions. Energy Procedia 2009, 1, 985–994.

13. Sun, C.; Dutta, P.K. Infrared spectroscopic study of reaction of carbon dioxide with aqueous monoethanolamine solutions. Ind. Eng. Chem. Res. 2016, 55, 6276−6283.

Table S1

Comparison of measurements in terms of mass balance and mass flow meter methods using different absorbent systems at 373 K based on the first 2 h desorption.

|5.0M absorbent |Run No. |Mass of CO2 released (g) |ARD,% a |

| | |Mass flow meter |Mass balance | |

|MEA-H2O |1 |90.0 |91.4 |1.6 |

| |2 |66.6 |71.9 |6.4 |

| |3 |68.5 |73.2 |7.4 |

|MEA-EGME |1 |77.4 |80.0 |3.3 |

| |2 |71.9 |76.3 |5.8 |

| |3 |81.7 |78.6 |4.0 |

|MEA-EGEE |1 |83.5 |87.7 |4.8 |

|AARD,% b |4.7 |

a [pic]

b [pic]

Table S2

Physical solubility of CO2 into EGME and water.

| |T/K |HCO2 / Pa.m3·mol-1 |Reference |

|EGME |322.90 |1332 |Joung et al.(2001) [8] |

| |329.80 |1479 | |

| |336.65 |1616 | |

| |343.70 |1714 | |

| |288.15 |502 |Gui et al.(2011) [9] |

| |298.15 |758 | |

| |308.15 |992 | |

| |318.15 |1237 | |

|Water |293.2 |2595 |Bian and Shen (2018) [10] |

| |303.2 |3347 | |

| |313.2 |4156 | |

| |323.2 |5016 | |

| |298.86 |3085.9 |Luo et al. (2017) [11] |

| |314.22 |4148.9 | |

| |326.65 |5231.9 | |

Table S3

Infrared Peak Assignments for CO2-Loaded MEA/2ME Solution.

|Wavenumber (cm-1） |Assignment [12,13] |

|2131 |Protonated MEA, -NH3+ bend |

|1574 |Carbamate, COO- asymmetric stretch |

|1486 |Carbamate, COO- asymmetric stretch |

|1385 |Carbonate, -C-O stretch |

|1366 | Free MEA/bicarbonate, -NH2 twist/-C-O stretch |

|1322 |Carbamate, N-COO- stretch |

|1156 |Carbamate, -NH-COO- stretch |

|1069 |Protonated MEA, C-N stretch/twist |

Table S4

CO2 desorption performance of aqueous and non-aqueous 5.0 M MEA solutions in the first 1h a.

|Solvent |Run No. |Rich |Amount of CO2 |Overall energy |Heat duty of regeneration |

| | |loading(αrich，mol|desorbed (L) |consumption (kWh) | |

| | |CO2/kg ) | | | |

| | | | | |MJ/kgCO2 |Average |

|MEA/H2O |1 |2.363 |41.07 |0.226 |10.09 |10.89 ± 0.45 |

| |2 |2.378 |35.34 |0.217 |11.26 | |

| |3 |2.291 |35.67 |0.207 |10.64 | |

| |4 |2.455 |34.95 |0.216 |11.33 | |

| |5 |2.344 |45.92 |0.279 |11.14 | |

|MEA/2ME |1 |2.188 |39.60 |0.110 |5.09 |5.06 ± 0.20 |

| |2 |2.206 |41.80 |0.111 |4.87 | |

| |3 |2.237 |40.81 |0.110 |4.94 | |

| |4 |2.218 |36.89 |0.107 |5.32 | |

|MEA/2EE |1 |2.184 |35.89 |0.102 |5.21 |4.98 ± 0.25 |

| |2 |2.152 |42.29 |0.107 |4.64 | |

| |3 |2.198 |37.78 |0.105 |5.10 | |

a CO2 absorption at 313 K and desorption at 373 K. α is defined as the moles of CO2 per kg CO2-free solution. Heat duty is defined as the energy consumption per kg desorbed CO2 amounts.

Figure S1

[pic]

Fig.S1 Schematic diagram of the absorption-desorption apparatus

Figure S2

[pic]

Figure S2 A modified Chittick CO2 apparatus

Figure S3

[pic]

Figure S3. Schematic diagram of vapor–liquid equilibrium apparatus for CO2 solubility.

Figure S4

[pic]

Figure S4. Comparison of CO2 capture performance between aqueous and non-aqueous MEA solution under the same conditions: absorption at 313K and thermal desorption at 373K.

Figure S5

[pic]

Figure S5. CO2 solubility in aqueous 30 mass % MEA solutions compared with literature data [4,5].

Figure S6

[pic]

Figure S6. 13C NMR spectra of MEA/2ME solutions with different CO2 loadings in DMSO-d6. (a) CO2-free MEA/2ME absorbent; (b) α = 1.25 mol CO2 / kg; (c) α = 2.21 mol CO2 / kg.

Figure S7

[pic]

Figure S7. 13C NMR spectra of aqueous MEA solutions with different CO2 loadings in D2O. (a) Aqueous CO2-free MEA absorbent; (b) α = 0.95 mol CO2 / kg; (c) α = 2.51 mol CO2 / kg.

Figure S8

[pic]

Fig.S8. FTIR spectra of CO2-free and CO2-loaded MEA/2ME solutions.

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