Density, Viscosity, and N2O Solubility of Aqueous Solutions of MEA

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Density, Viscosity, and N2O Solubility of Aqueous Solutions of MEA, BmimBF4, and Their Mixtures from 293.15 to 333.15 K Lingjun Xu and Shujuan Wang* Department of Energy and Power Engineering, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Beijing Engineering Research Center for Ecological Restoration and Carbon Fixation of Saline-alkaline and Desert Land, Tsinghua University, Beijing 100084, China

J. Chem. Eng. Data Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 06/19/18. For personal use only.

S Supporting Information *

ABSTRACT: Densities and viscosities of aqueous solutions of ethanolamine (MEA), 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4), and their mixtures were measured. The experiments covered the following mole fraction ranges: 1.00−9.38 mol % of BmimBF4 in its aqueous solutions, 3.94− 21.97 mol % of MEA in its aqueous solutions, and 1.32−17.01 mol % of MEA + 5.10−34.02 mol % of BmimBF4 in the mixtures. The results are compared with available data in the literature and correlated using a semiempirical formula as functions of the temperature and concentration of MEA and BmimBF4. At the concentration suitable for the CO2 capture, the viscosity of the hybrid absorbent did not significantly increase by the addition of BmimBF4. Moreover, the addition of BmimBF4 reduced the Henry’s law constant, which is significant for reaction kinetics.

1. INTRODUCTION Chemical absorption is the most viable near-term approach to postcombustion CO2 capture, and it has been commercially used for decades in industrial processes.1,2 Development of new solvents and better processes is the current emphasis because of the disadvantages of this technology, including large stripping energy consumption, unfavorable degradation, and corrosion problems.3−5 Because only part of the absorbent needs to pass through the desorption tower, liquid−liquid biphasic solvents have the potential to reduce the energy consumption of regeneration. Many biphasic solvents have been developed, such as DMX, 5 M DEEA + 2 M MAPA, 2 M BDA + 4 M DEEA, DEEA + MAPA, and DETA/DEEA.6−11 In our previous study, the CO2 absorption rate, cyclic capacity, and CO2 loading of the aqueous mixture of MEA and BmimBF4 have been studied. Results showed that, under some conditions, MEA−H2O−BmimBF4 solvent became a liquid− liquid biphasic system when a certain amount of CO2 was loaded. The distribution of substances in each phase was obtained using NMR spectroscopy, and carbamate was found mainly concentrated in one phase. The liquid−liquid stratification means this new absorbent, the aqueous mixture of MEA and BmimBF4, has the potential to reduce energy consumption, too. Therefore, it is necessary to study the basic properties of the absorbent. Physical properties are basic data for absorbent screening.12,13 Densitometers and viscometers are effective tools for obtaining density and viscosity data. As for physical solubility, © XXXX American Chemical Society

which can be used to derive the kinetics parameters in the experiments of the mass transfer process, due to the chemical reactions between CO2 and amine, it is impossible to measure the physical solubility directly. “N2O analogy”14−17 is a method to determine the physical solubility of CO2 in conventional alkanolamine systems. Since N2O resembles CO2 in terms of configuration, molecular volume, and electronic structure and it does not react with amine, the physical solubility of CO2 can be measured by an indirect way which is shown in eq 1 ij HN O − solvent yz zzH HCO2 − solvent = jjjj 2 z j HN O − H O zz CO2 − H2O 2 2 k {

(1)

where HCO2−solvent and HN2O−solvent are the physical solubility of CO2 and N2O in solvents with uniform units of Pa·m3·mol−1. The available data for HCO2−H2O and HN2O−H2O, the physical solubility of CO2 and N2O in water, were proposed by Versteeg and Van Swaaij.18 At present, there are some experiments in which the physical properties such as density, viscosity, and physical solubility of MEA or BmimBF419−31 were measured (as shown in Table 1), but the data are not much and most of them are about binary systems like BmimBF4−H2O and MEA−H2O. As for the BmimBF4−MEA−H2O ternary system, Yin et al.32 measured the viscosity and the density in a wide range of concentrations, Received: January 21, 2018 Accepted: June 5, 2018

A

DOI: 10.1021/acs.jced.8b00070 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. A Brief Review of Studies in Physical Properties Related to MEA and BmimBF4 absorbent

physical property

pressure (MPa)

BmimBF4 BmimBF4 + H2O

temperature (K)

concentration

source

density and viscosity density, viscosity, and surface tension BmimBF4 + H2O densities, viscosities, excess molar volume, and viscosity derivation MEA and MEA loaded with density and viscosity CO2 density MEA + H2O MEA + H2O density and viscosity MEA + H2O density and viscosity

0.101 0.101

278.15−373.15 298.15

pure cBmimBF4 = 0−0.005130 kg/m3

ref 19 ref 20

0.101

303.15−353.15

mole fraction of BmimBF4 is 0−1

ref 21

0.101

298.15

CO2 loading = 0−0.5 mol/mol

ref 22

0.101 0.101 0.101

303.15−353.15 303.15−353.15 303.15−343.15

ref 23 ref 24 ref 25

BmimBF4 + H2O BmimBF4 + MEA + H2O

viscosity density and viscosity

0.101 0.101

293.15 303.15−343.15

BmimBF4 BmimBF4

solubility and diffusivity of CO2 solubility of CO2

mass fraction of MEA is 0.3 mass fraction of MEA is 0.2 mass fractions of MEA are 0.3 and 0.153 mole fraction of BmimBF4 is 0−1 mass fractions of MEA are 0 and 0.3; mass fractions of BmimBF4 are 0, 0.3, and 1 pure pure

MEA + H2O

solubility and diffusivity of N2O

BmimBF4

solubility of CO2

BmimBF4 + MEA + H2O

density and viscosity

0.01017−1.99990 10−10−1.3 0.101 10−10−1.3

282.75−348.05 283.15, 293.15, 323.15 292−313 283.15, 298.15, 323.15 293.15−333.15

0.101

but there were not many concentrations which were suitable as CO2 absorbents. Therefore, more data are needed to summarize more accurate rules and to fit semiempirical formulas. In this work, densities and viscosities of aqueous solutions of MEA, BmimBF4, and their mixtures were measured at 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, 323.15, 328.15, and 333.15.K and solubilities of N2O in the solutions were measured at 293.15, 303.15, 313.15, 323.15, and 333.15 K. The experimental temperatures can cover the temperature range commonly used in the absorption tower. The experiments covered the following mole fraction ranges: 1.00−9.38% of BmimBF4 in its aqueous solutions, 3.94−21.97% of MEA in its aqueous solutions, and 1.32−17.01% of MEA + 5.10− 34.02% of BmimBF4 in the mixtures. The results are compared with available data in the literature and correlated using a semiempirical formula as a function of the temperature and concentration of MEA and BmimBF4.

ref 26 ref 27 ref 28 ref 29

cBmimBF4 = 2.0−3.0 kmol/m3

ref 30

pure

ref 31

mole fraction of BmimBF4 is 0.0990−0.8982

ref 32

Figure 1. Structures of BmimBF4 (a) and MEA (b).

2.2. Density and Viscosity. The densities of solutions were measured by a KEM DA640 density meter, with a measurement range of 0−3 g/cm3, and the total accuracy of viscosity given by the manufacturer is ±0.0001 g/cm3. The result of every point was the average value of three repeated trials. Calibration was done by measuring the densities of H2O, and as shown in Figure 2, the data fit well with the literature33 (the experimental data are collected in Table S1). The viscosities of solutions were measured by an A&D SV10 viscometer, with a measurement range of 0.3−1000 mPa·s.

2. EXPERIMENTAL SECTION 2.1. Material. In this work, the chemicals used are listed in Table 2 and the structures of MEA and BmimBF4 are shown in Figure 1. Table 2. Chemical Sample Table chemical name

CAS registry number

BmimBF4a

174501-65-6

MEAb

141-43-5

CO2

124-38-9

N2O

10024-97-2

source Lanzhou Yulu Fine Chemical Co., Ltd. Sinopharm Chemical Reagent Co., Ltd. Air Liquide (Tianjin) Co., Ltd. Beijing Huayuan Gas Company

fraction purity ≥99 wt % ≥99 wt % ≥99.99 mol % ≥99 mol %

Figure 2. Density ρ of H2O in this work and the literature as a function of temperature T at a pressure of p = 1.013 × 105 Pa. Red ◆, this work; △, ref 33.

a

BmimBF4 = 1-butyl-3-methylimidazolium tetrafluoroborate. bMEA = ethanolamine. B



Article

where R and ω represent the universal gas constant and the acentric factor, respectively, and Tc and Pc are the critical temperature and the critical pressure, respectively. The total volume of the reactor and the auxiliary was calculated from the pressures inside the reactor before and after adding N2O. The results showed that the volume of the tank, Vtank, was 2.214 × 10−3 m3, and the volume of the reactor and the auxiliary, Vreactor, was 5.439 × 10−4 m3. About 120 g absorbents were weighed by electronic analytical balance and added to the reactor. Then, the reactor was sealed from the atmosphere environment and vacuumed by a vacuum pump. After that, the stirrer and water bath were turned on, and when the vapor liquid equilibrium at the set temperature in the reactor was reached, N2O was injected into the reactor from the gas tank. The number of moles of N2O added to the reactor, nNadded , 2O was calculated from the initial and final equilibrium pressures in the gas tank with the Peng−Robinson equation. The amount of N2O in the gas phase of the reactor, nNg 2O, was calculated from the equilibrium partial pressure of N2O in the reactor with the Peng−Robinson equation. The N2O amount in the liquid phase, nNl 2O, was calculated by eq 6

The total accuracy of the viscosity given by the manufacturer is ±1%. Calibration of the viscometer was done by measuring the viscosity of Standard Liquid BW2085-1 and BW2085-5 produced by National Institute of Metrology of China and approved by AQSIQ. The calibration method is the two-point method provided by the instrument itself. The data for the calibration are given in Table 3. Table 3. Viscosity μ of Standard Solutions for Calibration at 293.15 K, 1.01 × 105 Pa viscosity μ (mm2/s) standard

measurement

ref

deviation

BW2085-1 BW2085-5

2.04 50.2

2.036 50.17

0.20% 0.06%

2.3. Solubility of N2O. The N2O solubility apparatus was reformed from that of Xu et al.,16 and it consists of a jacketed stirred quartz glass reactor and a stainless steel gas tank, as shown in Figure 3. Before experiment, the tank was filled with water and the volume was calculated. Then, a known amount of N2O was added into the reactor and the auxiliary pipe from the gas tank. The amount of the added N2O was calculated from the pressures inside the gas tank before and after adding N2O into the reactor with the Peng−Robinson equation (eqs 2−5)34 P=

RT a − 2 v−b v + abv − b2 2

a = 0.457235 ×

b = 0.07780

(2)

C Nl 2O

R Tc [1 + (0.37464 + 1.54226ω pc

T Tc

=

n Nl 2O Vsolvent

(7)

Then, the N2O solubility was expressed by Henry’s law constant, HN2O, which can be calculated by eq 8

(3)

PN2O = HN2O·C Nl 2O

(4)

RTc Pc

(6)

and the N2O concentration in the liquid phase, CNl 2O, was calculated by eq 7, where Vsolvent was the volume of the solvent in the reactor.

2

− 0.26992ω 2)(1 − Tr 0.5)]2 Tr =

n Nl 2O = n Nadded − n Ng 2O 2O

(8)

Calibrations were done by measuring the solubility of N2O in water, and the data for the calibration and the comparisons with literature references are given in Figure 4 and Table S2.

(5)

Figure 3. Experimental setup of N2O solubility. C



Article

3. RESULT AND DISCUSSION

The deviation from ref 18 is less than 7.2%, which is less than the deviation of Xu’s calibration data.16

3.1. Density. The measured densities for the aqueous solutions of MEA, BmimBF4, and MEA/BmimBF4 blends are presented in Table 4. For BmimBF4 solutions, the deviations are less than 1.2% when compared with refs 20 and 21, as shown in Figure 5. For MEA solutions, the deviations are less than 0.4% compared with literature references, as shown in Figure 6. The densities of the binary and ternary mixtures increase with increasing mole fractions of BmimBF4 or MEA in the mixture and decrease with increasing temperature. Figure 7 shows the density calculated values in this work and experimental values in the literature for ternary systems.32 The concentration selected for comparison is the concentration suitable as a CO2 absorbent in ref 32, and the deviation is less than 0.14%. The experimental density data for the binary and ternary mixtures were fitted as a function of temperature and concentration using the equation proposed by Liu et al.,35 as shown in eq 9

Figure 4. Henry’s law constant H of N2O in water at Temperatures of T = 288.15−338.15 K. Orange ◆, this work; blue △, ref 16; black line, ref 18.

Table 4. Densities of Aqueous BmimBF4 (Mole Fraction x1), MEA (Mole Fraction x2), and BmimBF4/MEA Blended Solutions at Temperatures of T = 293.15−333.15 K and a Pressure of p = 1.01 × 105 Paa Density, ρ·103 (kg/m3) x1 T (K)

0.0100

0.0227

0.0392

0.0616

0.0938

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

1.0189 1.0171 1.0152 1.0132 1.0109 1.0086 1.0061 1.0018 0.9992

1.0381 1.0360 1.0335 1.0313 1.0286 1.0259 1.0234 1.0198 1.0176

1.0604 1.0580 1.0553 1.0526 1.0498 1.0469 1.0440 1.0414 1.0406 x2

1.0795 1.0767 1.0736 1.0707 1.0675 1.0643 1.0612 1.0583 1.0574

1.1037 1.1006 1.0972 1.0939 1.0905 1.0874 1.0841 1.0809 1.0799

T (K)

0.0394

0.0870

0.1456

0.2197

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

1.0053 1.0038 1.0021 1.0003 0.9982 0.9960 0.9938 0.9889 0.9872

1.0118 1.0099 1.0077 1.0056 1.0032 1.0007 0.9982 0.9958 0.9951

1.0189 1.0163 1.0137 1.0112 1.0085 1.0057 1.0028 1.0001 0.9993

1.0257 1.0227 1.0197 1.0168 1.0136 1.0105 1.0073 1.0044 1.0032

x1/x2 T (K)

0.0132/0.1322

0.0255/0.0510

0.0337/0.2024

0.0792/0.1188

0.0977/0.2442

0.1701/0.3402

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

1.0355 1.0329 1.0302 1.0274 1.0244 1.0215 1.0185 1.0156 1.0147

1.0461 1.0437 1.0410 1.0383 1.0355 1.0326 1.0296 1.0268 1.0258

1.0612 1.0578 1.0544 1.0511 1.0476 1.0442 1.0407 1.0375 1.0361

1.0944 1.0909 1.0872 1.0838 1.0801 1.0765 1.0729 1.0695 1.0681

1.0979 1.0941 1.0903 1.0866 1.0828 1.0790 1.0748 1.0717 1.0703

1.1179 1.1139 1.1099 1.1060 1.1021 1.0982 1.0943 1.0907 1.0892

Standard uncertainties are u(x1) = 0.0002, u(x2) = 0.0002, u(T) = 0.1K, u(p) = 1 kPa, and u(ρ) = 0.001 g·cm−3.

a

D



Article

Figure 7. Densities ρ of aqueous BmimBF4 (mole fraction x1 = 0.0996) and MEA (mole fraction x2 = 0.0896) solutions calculated by this work and compared with literature data at a pressure of p = 1.01 × 105 Pa. Red line, this work, calculated; blue ●, ref 32, experimental.

Figure 5. Densities ρ of aqueous BmimBF4 (mole fraction x1) solutions measured and calculated by this work and compared with literature data at a pressure of p = 1.01 × 105 Pa. Blue ◇, 298.15 K, ref 20; blue ◆, 298.15 K, this work, experimental; blue line, 298.15 K, this work, calculated; red ○, 318.15 K, ref 21; red ●, 318.15 K, this work, experimental; red line, 318.15 K, this work, calculated; orange △, 333.15 K, ref 21; orange ▲, 333.15 K, this work, experimental; yellow line, 333.15 K, this work, calculated.

ρBmimBF − MEA − H O (10−3 (kg·m−3)) 4 2 ÄÅ É k4 ÑÑÑÑ k2 ÅÅÅ = ÅÅk1 + (x BmimBF4 + k 3xMEA ) + 2 ÑÑ ÅÅÇ T T ÑÑÖ ÄÅ ÉÑ ÅÅ k ÑÑ expÅÅÅ 5 + k6(x BmimBF4 + k 3xMEA )ÑÑÑ ÑÑÖ ÅÅÇ T

using Origin 9, and the fit was considered converged when the chi-square tolerance value was less than 10−9. The calculated parameters, the average absolute deviations (AADs), and the adjusted squared correlation coefficients (adj. R2) are listed in Table 5. As shown in Table 4, the calculated densities from the correlation eq 9 are in good agreement with the experimental data of this work. The adj. R2 of the correlation for BmimBF4, MEA, and BmimBF4/MEA blended solutions are 0.9964, 0.9871, and 0.9929, respectively. 3.2. Viscosity. The measurements of viscosities in this work also comprise the aqueous solutions of MEA, BmimBF4, and MEA/BmimBF4 blends. The experimental data are presented in Table 6. For the BmimBF4 and MEA solutions, the experimental data of this work are compared with literature data in Figures 8 and

(9)

where ρ is the density of the mixture, T is the temperature, and x is the mole fraction of BmimBF4 or MEA. k1−k6 are the correlation parameters. The correlation parameters were fitted

Figure 6. Densities ρ of aqueous MEA (mole fraction x2) solutions measured and calculated by this work and compared with literature data at a pressure of p = 1.01 × 105 Pa. Orange △, 298.15 K, ref 22; orange ▲, 298.15 K, this work, experimental; yellow line, 298.15 K, this work, calculated; red □, 313.15 K, refs 23 and 24; red ■, 313.15 K, this work, experimental; red line, 313.15 K, this work, calculated; blue ○, 333.15 K, refs 23 and 24; blue ●, 333.15 K, this work, experimental; blue line, 333.15 K, this work, calculated. E



Article

Table 5. Correlation Parameters, AADs, and adj. R2 for Densities of Aqueous BmimBF4, MEA, and BmimBF4/MEA Blended Solutions BmimBF4 + H2O MEA + H2O BmimBF4 + MEA + H2O a

AAD =

k1

k2

k3

k4

k5

k6

AADa

adj. R2

1.16306 0.76526 1.15097

−2320.45 4.6743 2023.76

−6774420 10.9625 0.01321

136678 −8845.90 82689.5

−294.953 121.2808 −213.637

4.33267 −0.01332 −2.05976

0.00130 0.0007 0.00178

0.9964 0.9871 0.9929

ρexp, i 1 N ·∑i = 1 |ρ − ρ | N cal, i exp, i

Table 6. Viscosities of Aqueous BmimBF4 (Mole Fraction x1), MEA (Mole Fraction x2), and BmimBF4/MEA Blended Solutions at Temperatures of T = 293.15−333.15 K and a Pressure of p = 1.01 × 105 Paa Viscosity, μ (mPa·s) x1 T (K)

0.0100

0.0227

0.0392

0.0616

0.0938

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

1.07 0.95 0.84 0.76 0.69 0.64 0.59 0.55 0.53

1.35 1.19 1.05 0.95 0.86 0.79 0.74 0.69 0.62

1.84 1.60 1.40 1.25 1.13 1.02 0.94 0.88 0.82

2.28 1.98 1.75 1.56 1.40 1.27 1.16 1.07 0.99

3.04 2.69 2.34 2.06 1.84 1.66 1.48 1.31 1.26

1.0027

68.90 44.73 30.81 22.28

x2 T (K)

0.0394

0.0870

0.1456

0.2197

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

1.19 1.06 0.94 0.85 0.76 0.69 0.63 0.58 0.54

2.10 1.71 1.47 1.30 1.15 1.03 0.93 0.85 0.79

3.06 2.69 2.29 1.91 1.69 1.50 1.33 1.17 1.05

5.58 4.67 3.91 3.28 2.77 2.39 2.11 1.85 1.65

x1/x2 T (K)

0.0132/0.1322

0.0255/0.0510

0.0337/0.2024

0.0792/0.1188

0.0977/0.2442

0.1701/0.3402

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

2.96 2.63 2.40 2.11 1.79 1.59 1.44 1.30 1.18

2.35 1.99 1.73 1.53 1.38 1.24 1.13 1.02 0.94

7.02 5.46 4.54 3.82 3.28 2.85 2.48 2.20 1.97

6.12 4.73 3.96 3.38 2.94 2.57 2.29 2.06 1.85

11.38 9.00 7.32 6.05 5.13 4.34 3.72 3.30 2.90

18.40 14.32 11.17 9.03 7.55 6.47 5.49 4.72 4.14

a Standard uncertainties are u(x1) = 0.0002, u(x2) = 0.0002, u(T) = 0.1K, and u(p) = 1 kPa, and the relative standard uncertainty in viscosity is ur(μ) = 0.15.

μBmimBF − MEA − H O (mPa ·s) 4 2 ÄÅ k1 ÅÅÅ = ÅÅ1 + (x BmimBF4 + k 2xMEA ) ÅÅÇ T ÉÑ ÑÑ k3 + 2 (x BmimBF4 + k 2xMEA )2 ÑÑÑ T ÑÑÖ ÄÅ ÉÑ Ñ k5 ÅÅÅ k4 2Ñ expÅÅ + 2 + k6(x BmimBF4 + k 2xMEA ) ÑÑÑ ÅÅÇ T ÑÑÖ T

9.20,21,24,25 The viscosities of the binary and ternary mixtures increase with increasing mole fraction of BmimBF4 or MEA and decreasing temperature. The effect of BmimBF 4 concentration on viscosity is greater than that of MEA concentration or H2O concentration, because the viscosity of pure BmimBF4 is bigger than that of pure MEA or H2O. As can be seen from the overall trend of the data, the viscosity of mixtures can be maintained at a lower level (compared with the viscosity of pure BmimBF427), when the mass fraction of BmimBF4 is less than 50%. The experimental viscosity data for the mixtures were also fitted by Liu’s equation35 as a function of the temperature and concentrations of BmimBF4 and MEA (eq 10)

(10)

where μ is the mixture viscosity, T is the temperature, x is the mole fraction of BmimBF4 or MEA, and k1−k6 are the F



Article

The calculated parameters, the average absolute deviations (AADs), and the adjusted squared correlation coefficients (adj. R2) are listed in Table 7. As shown in Figure 8 and Figure 9, the calculated viscosities from correlation eq 10 agree well with the experimental data in this paper and in the literature. The adj. R2 of the correlation for BmimBF4, MEA, and BmimBF4/ MEA blended solutions are 0.9975, 0.9959, and 0.9943, respectively. Due to the high viscosity of pure ionic liquids, viscosity is a physical property that needs to be focused on for the hybrid absorbents. In the BmimBF4−MEA−H2O system, the suitable concentration of MEA is about 30 wt %, which can guarantee the absorption capacity and absorption rate of the absorbent. When the mass fraction of MEA is fixed at 30%, the suitable BmimBF4 concentration for CO2 absorbents is about 10−40 wt %, because, under this concentration, ionic liquids can promote the absorption reaction. Figure 10 shows the

Figure 8. Viscosities μ of aqueous BmimBF4 (mole fraction x1) solutions measured and calculated by this work and compared with literature data at a pressure of p = 1.01 × 105 Pa. Orange △, 298.15 K, ref 20; orange ▲, 298.15 K, this work, experimental; yellow line, 298.15 K, this work, calculated; blue ○, 318.15 K, ref 21; blue ●, 318.15 K, this work, experimental; blue line, 318.15 K, this work, calculated; red □, 333.15 K, ref 21; red ■, 333.15 K, this work, experimental; red line, 333.15 K, this work, calculated.

Figure 10. Viscosities μ of CO2 absorbents against temperature T at a pressure of p = 1.01 × 105 Pa. Black ■, 30.0 wt % MEA + 70 wt % H2O, ref 36; orange ●, 30.1 wt % MDEA + 69.9 wt % H2O, ref 37; blue ▲, 31.8 wt % DEA + 68.2 wt % H2O, ref 37; red ◆, 11.3 wt % BmimBF4 + 30.5 wt % MEA + 58.2 wt % H2O, this work.

comparison of viscosity between 11.3 wt % BmimBF4 + 30.5 wt % MEA + 58.2 wt % H2O and the MEA, MDEA, and DEA aqueous solutions in typical concentratio ns.36,37 It is found that, compared with 30.0 wt % MEA, the addition of BmimBF4 did not increase the viscosity of the hybrid absorbent too much. Compared with 31.8 wt % DEA absorbents, the viscosity is even smaller. 3.3. Solubility of N2O. The Henry’s law constants of N2O in BmimBF4, MEA, and BmimBF4/MEA solutions are listed in Table 8. The data of the pressure of N2O and the solubility of N2O are collected in Table S3. Figure 11 shows the comparison of the N2O solubility data of aqueous MEA in this work with the data under the same conditions as the literature.30,38−41 From Table 8, it can be

Figure 9. Viscosities μ of aqueous MEA (mole fraction x2) solutions measured and calculated by this work and compared with literature data at a pressure of p = 1.01 × 105 Pa. Blue ○, 303.15 K, ref 24; blue △, 303.15 K, ref 25; blue ■, 303.15 K, this work, experimental; blue line, 303.15 K, this work, calculated; red ○, 313.15 K, ref 24; red △, 313.15 K, ref 25; red ■, this work, experimental; red line, this work, calculated; orange ○, 333.15 K, ref 24; orange △, 333.15 K, ref 25; orange ■, 333.15 K, this work, experimental; yellow line, 333.15 K, this work, calculated.

correlation parameters. The correlation method was the same as that for the density data.

Table 7. Correlation Parameters, AADs, and adj. R2 for Viscosities of Aqueous BmimBF4, MEA, and BmimBF4/MEA Blended Solutions BmimBF4 + H2O MEA + H2O BmimBF4 + MEA + H2O a

AAD =

k1

k2

k3

k4

k5

k6

AADa

adj. R2

7366.29 1322.35 931.629

−799051 1.82431 0.70088

6568640 1132350 8434840

−2212.05 −2862.29 −3104.75

635969 836185 951633

−16.1525 0.89563 −3.20497

0.01957 0.04461 0.07315

0.9975 0.9959 0.9943

μexp, i 1 N ·∑i = 1 |μ − μ | N cal, i exp, i

G



Article

Table 8. Henry’s Law Constant H of N2O in Aqueous BmimBF4 (Mole Fraction x1), MEA (Mole Fraction x2), and BmimBF4/ MEA Blended Solutions at Temperatures of T = 293.15−323.15 Ka H (Pa·m3·mol−1) x1 T (K)

0.0100

0.0227

0.0392

0.0616

0.0938

293.15 303.15 313.15 323.15

3462 4532 5785 7182

3430 4476 5702 7155

3410 4428 5630 7038 x2

3368 4339 5567 6903

3250 4211 5299 6720

T (K)

0.0394

0.0870

0.1456

0.2197

293.15 303.15 313.15 323.15

3720 4651 5713 6910

3932 4798 5760 6774

4311 5104 5461 6259

4325 4965 5359 6202

x1/x2 T (K)

0.0132/0.1322

0.0255/0.0510

0.0337/0.2024

0.0792/0.1188

0.0977/0.2442

0.1701/0.3402

293.15 303.15 313.15 323.15

3396 4532 5759 7278

3455 4488 5652 7203

3442 4455 5660 7132

3365 4267 5499 6867

3299 4253 5340 6752

3010 4011 5038 6359

Standard uncertainties are u(x1) = 0.0002, u(x2) = 0.0002, u(T) = 0.1 K, and u(p) = 0.1 kPa. The expanded uncertainty is U(H) = 51 Pa·m3·mol−1 (0.95 level of confidence). a

the gap of ions (or ion pairs). It is found that the larger the molecule of ionic liquid, the greater the solubility of CO2 in the ionic liquid.42 After BmimBF4 is added, the physical solubility of the solution tends to become larger. This phenomenon can be explained by the fact that the molecular size of ionic liquids is obviously larger than that of MEA and H2O. The Arrhenius relationship43 (eq 11) is a common method for determining how Henry’s law constants change with temperature, where H0 is a constant for the Arrhenius equation and Δhabs is the enthalpy of absorption i Δh y H = H0 expjjjj− abs zzzz k RT {

Figure 11. N2O physical solubility of aqueous MEA in this work and compared with the literature. Gray ▲, 323.15 K, this work; red ▲, 313.15 K, this work; blue ▲, 303.15 K, this work; green ▲, 293.15 K, this work; orange ■, 333.15 K, refs 39 and 41; gray ■, 323.15 K, refs 40 and 41; red ■, 313.15 K, refs 30, 38, and 41; blue ■, 303.15 K, refs 30 and 38−41; green ■, 293.15 K, refs 30 and 41.

(11)

The enthalpy of physical absorption can be written as Δhabs = R( −B + CT + DT 2 + 2ET 3)

(12)

where B, C, D, and E are correlation parameters.17 Therefore, the experimental Henry’s law constant data for the binary and ternary mixtures were fitted by eq 13 as a function of the temperature and concentrations of BmimBF4 and MEA

found that the Henry’s law constant of N2O in mixtures decreases with the increasing BmimBF4 concentration in the mixtures. The interaction between BmimBF4 and CO2/N2O is a physical process. This physical absorption is closely related to

Table 9. Correlation Parameters, AADs, and adj. R2 for Henry’s Law Constants of N2O in Aqueous BmimBF4, MEA, and BmimBF4/MEA Blended Solutions k1 BmimBF4 + H2O MEA + H2O BmimBF4 + MEA + H2O a

AAD =

2.78627 −916970 −0.00923

k2 −16009500 −2.08465 × 10−6 −0.07501

k3 −631.348 19.1955 432.901

k4 −3.3075 810365 −0.52943

k5 0.05126 0.03942 0.01774

k6 −5

−5.4819 × 10 −3.8426 × 10−5 1.7370 × 10−5

AADa

Adj. R2

0.00368 0.05401 0.01453

0.9996 0.9086 0.9956

Hexp, i 1 N ·∑i = 1 |H − H | N cal, i exp, i

H



Article

of MEA + 5.10−34.02 mol % of BmimBF4 in the mixtures. The results are compared with available data in the literature. The experimental data were correlated using semiempirical correlations as functions of the temperature and concentration of MEA and BmimBF4. The experimental results were compared with classical amine absorbents, too. The densities and viscosities of mixtures increase with increasing mole fractions of BmimBF4 or MEA in the mixture and decrease with increasing temperature. Because of the bigger viscosity of pure BmimBF4, the effect of BmimBF4 concentration on viscosity is greater than that of MEA concentration or H2O concentration. However, the viscosity of mixtures can be maintained at a lower level (compared with the viscosity of pure BmimBF4), when the mass fraction of BmimBF4 is less than 50%. At the concentration suitable for the CO2 capture, the viscosity of the hybrid absorbent did not significantly increase by the addition of BmimBF4. Moreover, the addition of BmimBF4 reduced the Henry’s law constant, which is significant for reaction kinetics.

HBmimBF4 − MEA − H2O (Pa·m 3·mol−1) = [1 + k1(x BmimBF4 + k 2xMEA )] ÅÄÅ k ÑÉÑ Å Ñ expÅÅÅ 3 + k4(x BmimBF4 + k 2xMEA ) + k5T + k6T 2 ÑÑÑ ÅÅÇ T ÑÑÖ (13)

where H is the Henry’s law constant, T is the temperature, x is the mole fraction of BmimBF4 or MEA, and k1−k6 are the correlation parameters. The correlation method was the same as that for the density and viscosity data. The calculated parameters, the average absolute deviations (AADs), and the adjusted squared correlation coefficients (adj. R2) are listed in Table 9. The adj. R2 of the correlation for BmimBF4, MEA, and BmimBF4/MEA blended solutions are 0.9996, 0.9086, and 0.9956, respectively. In the classical reaction kinetics theory, such as the two-film theory, the Henry’s law constant is the key data to decide the mass transfer of the gas−liquid interface. For CO2 chemical absorbent, the smaller Henry’s law constant is expected. Figure 12 gives a comparison of the physical solubility between 11.3 wt % BmimBF4 + 30.5 wt % MEA + 58.2 wt %

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00070.

■

Experimental data (Tables S1−S3) (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lingjun Xu: 0000-0003-3687-5303 Funding

Financial support from the National Natural Science Foundation of China (No. 51576108) is greatly appreciated. Notes

The authors declare no competing financial interest.

■

Figure 12. Henry’s law constants H of N2O in CO2 absorbents against temperature T. Green ▲, 30.0 wt % MEA, ref 38; orange ●, 30.0 wt % MDEA, ref 40; black ■, 30.0 wt % AMP, ref 40; red ◆, 11.3 wt % BmimBF4 + 30.5 wt % MEA + 58.2 wt % H2O, this work.

ACKNOWLEDGMENTS We thank Dr. Qi Yang from CSIRO Manufacturing for enlightening discussions.

■

H2O and the MEA, MDEA, and AMP aqueous solutions in typical concentrations.38,40 It is found that, compared with 30.0 wt % MEA, the addition of ionic liquids reduces the Henry’s law constant slightly. By the overall analysis of the Henry’s law constant data, it can be judged that, if the mass fraction of the BmimBF4 is increased, the Henry’s law constant of the absorbent will become smaller. Compared with 30.0 wt % AMP, the Henry’s law constant of 11.3 wt % BmimBF4 + 30.5 wt % MEA + 58.2 wt % H2O is significantly smaller.

REFERENCES

(1) Zhang, X.; Zhang, X.; Dong, H.; Zhao, Z.; Zhang, S.; Huang, Y. Carbon Capture with Ionic Liquids: Overview and Progress. Energy Environ. Sci. 2012, 5, 6668−6681. (2) Kanniche, M.; Gros-Bonnivard, R.; Jaud, P.; Valle-Marcos, J.; Amann, J. M.; Bouallou, C. Pre-combustion, Post-combustion and Oxy-combustion in Thermal Power Plant for CO2 Capture. Appl. Therm. Eng. 2010, 30, 53−62. (3) Rochelle, G. T. Amine Scrubbing for CO2 Capture. Science 2009, 325, 1652−1654. (4) Strazisar, B. R.; Anderson, R. R.; White, C. M. Degradation Pathways for Monoethanolamine in a CO2 Capture Facility. Energy Fuels 2003, 17, 1034−1039. (5) Yeh, J. T.; Resnik, K. P.; Rygle, K.; Pennline, H. W. Semi-batch Absorption and Regeneration Studies for CO2 Capture by Aqueous Ammonia. Fuel Process. Technol. 2005, 86, 1533−1546. (6) Raynal, L.; Alix, P.; Bouillon, P. A.; Gomez, A.; de Nailly, M. F.; Jacquin, M.; Kittel, J.; di Lella, A.; Mougin, P.; Trapy, J. The DMX Process: an Original Solution for Lowering the Cost of Postcombustion Carbon Capture. Energy Procedia 2011, 4, 779−786.

4. CONCLUSION Densities and viscosities of aqueous solutions of MEA, BmimBF4, and their mixtures were measured at 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, 323.15, 328.15, and 333.15 K, and solubilities of N2O in the solutions were measured at 293.15, 303.15, 313.15, and 323.15 K. The experiments cover the following mole fraction ranges: 1.00− 9.38 mol % of BmimBF4 in its aqueous solutions, 3.94−21.97 mol % of MEA in its aqueous solutions, and 1.32−17.01 mol % I



Article

(7) Ciftja, A. F.; Hartono, A.; Svendsen, H. F. Experimental Study on Phase Change Solvents in CO2 Capture by NMR Spectroscopy. Chem. Eng. Sci. 2013, 102, 378−386. (8) Zhicheng, X.; Shujuan, W.; Bo, Z.; Changhe, C. Study on Potential Biphasic Solvents: Absorption Capacity, CO2 Loading and Reaction Rate. Energy Procedia 2013, 37, 494−498. (9) Xu, Z.; Wang, S.; Chen, C. CO2 Absorption by Biphasic Solvents: Mixtures of 1, 4-Butanediamine and 2-(Diethylamino)Ethanol. Int. J. Greenhouse Gas Control 2013, 16, 107−115. (10) Liebenthal, U.; Pinto, D. D. D.; Monteiro, J. G. S.; Svendsen, H. F.; Kather, A. Overall Process Analysis and Optimisation for CO2 Capture from Coal Fired Power Plants Based on Phase Change Solvents Forming Two Liquid Phases. Energy Procedia 2013, 37, 1844−1854. (11) Wang, L.; An, S.; Yu, S.; Zhang, S.; Zhang, Y.; Li, M.; Li, Q. Mass Transfer Characteristics of CO2 Absorption into a Phase-change Solvent in a Wetted-wall Column. Int. J. Greenhouse Gas Control 2017, 64, 276−283. (12) Gao, H.; Gao, G.; Liu, H.; Luo, X.; Liang, Z.; Idem, R. O. Density, Viscosity, and Refractive Index of Aqueous CO2-Loaded andUnloaded Ethylaminoethanol (EAE) Solutions from 293.15 to 323.15 K for Post Combustion CO2 Capture. J. Chem. Eng. Data 2017, 62, 4205−4214. (13) Luo, X.; Su, L.; Gao, H.; Wu, X.; Idem, R. O.; Tontiwachwuthikul, P.; Liang, Z. Density, Viscosity, and N2O Solubility of Aqueous 2-(Methylamino) ethanol Solution. J. Chem. Eng. Data 2017, 62, 129−140. (14) Laddha, S. S.; Diaz, J. M.; Danckwerts, P. V. The N2O Analogy: the Solubilities of CO2 and N2O in Aqueous Solutions of Organic Compounds. Chem. Eng. Sci. 1981, 36, 228−229. (15) Sada, E.; Kumazawa, H.; Butt, M. A. Solubility and Diffusivity of Gases in Aqueous Solutions of Amines. J. Chem. Eng. Data 1978, 23, 161−163. (16) Xu, Z.; Wang, S.; Chen, C. Solubility of N2O in and Density and Viscosity of Aqueous Solutions of 1, 4-Butanediamine, 2(Diethylamino)-ethanol, and Their Mixtures from (298.15 to 333.15) K. J. Chem. Eng. Data 2013, 58, 1633−1640. (17) Gao, J.; Cao, L.; Dong, H.; Zhang, X.; Zhang, S. Ionic liquids Tailored Amine Aqueous Solution for Pre-combustion CO2 Capture: Role of Imidazolium-based Ionic Liquids. Appl. Energy 2015, 154, 771−780. (18) Versteeg, G. F.; Van Swaaij, W. P. Solubility and Diffusivity of Acid Gases (Carbon Dioxide, Nitrous Oxide) in Aqueous Alkanolamine Solutions. J. Chem. Eng. Data 1988, 33, 29−34. (19) Salgado, J.; Regueira, T.; Lugo, L.; Vijande, J.; Fernández, J.; García, J. Density and Viscosity of Three (2, 2, 2-Trifluoroethanol+ 1Butyl-3-Methylimidazolium) Ionic Liquid Binary Systems. J. Chem. Thermodyn. 2014, 70, 101−110. (20) Liu, W.; Zhao, T.; Zhang, Y.; Wang, H.; Yu, M. The Physical Properties of Aqueous Solutions of The Ionic Liquid [BMIM][BF4]. J. Solution Chem. 2006, 35, 1337−1346. (21) Zhou, Q.; Wang, L. S.; Chen, H. P. Densities and Viscosities of 1-Butyl-3-Methylimidazolium Tetrafluoroborate+ H2O Binary Mixtures from (303.15 to 353.15) K. J. Chem. Eng. Data 2006, 51, 905− 908. (22) Weiland, R. H.; Dingman, J. C.; Cronin, D. B.; Browning, G. J. Density and Viscosity of Some Partially Carbonated Aqueous Alkanolamine Solutions and Their Blends. J. Chem. Eng. Data 1998, 43, 378−382. (23) Li, M. H.; Shen, K. P. Densities and Solubilities of Solutions of Carbon Dioxide in Water+ Monoethanolamine+ N-Methyldiethanolamine. J. Chem. Eng. Data 1992, 37, 288−290. (24) Li, M. H.; Lie, Y. C. Densities and Viscosities of Solutions of Monoethanolamine+ N-Methyldiethanolamine+ Water and Monoethanolamine+ 2-Amino-2-Methyl-1-Propanol+ Water. J. Chem. Eng. Data 1994, 39, 444−447. (25) Song, J. H.; Park, S. B.; Yoon, J. H.; Lee, H.; Lee, K. H. Densities and Viscosities of Monoethanolamine+ Ethylene Glycol+ Water. J. Chem. Eng. Data 1996, 41, 1152−1154.

(26) Seddon, K. R.; Stark, A.; Torres, M. J. Influence of Chloride, Water, and Organic Solvents on the Physical Properties of Ionic Liquids. Pure Appl. Chem. 2000, 72, 2275−2287. (27) Zhao, Y.; Zhang, X.; Zeng, S.; Zhou, Q.; Dong, H.; Tian, X.; Zhang, S. Density, Viscosity, and Performances of Carbon Dioxide Capture in 16 Absorbents of Amine+ Ionic Liquid+ H2O, Ionic Liquid+ H2O, and Amine+ H2O Systems. J. Chem. Eng. Data 2010, 55, 3513−3519. (28) Shiflett, M. B.; Yokozeki, A. Solubilities and Diffusivities of Carbon Dioxide in Ionic Liquids: [bmim][PF6] and [bmim][BF4]. Ind. Eng. Chem. Res. 2005, 44, 4453−4464. (29) Cadena, C.; Anthony, J. L.; Shah, J. K.; Morrow, T. I.; Brennecke, J. F.; Maginn, E. J. Why Is CO2 So Soluble in Imidazolium-based Ionic Liquids? J. Am. Chem. Soc. 2004, 126, 5300−5308. (30) Mandal, B. P.; Kundu, M.; Bandyopadhyay, S. S. Physical Solubility and Diffusivity of N2O and CO2 into Aqueous Solutions of (2-Amino-2-Methyl-1-Propanol+ Monoethanolamine) and (N-Methyldiethanolamine+ Monoethanolamine). J. Chem. Eng. Data 2005, 50, 352−358. (31) Anthony, J. L.; Anderson, J. L.; Maginn, E. J.; Brennecke, J. F. Anion Effects on Gas Solubility in Ionic Liquids. J. Phys. Chem. B 2005, 109, 6366−6374. (32) Yin, Y.; Zhu, C.; Ma, Y. Volumetric and Viscometric Properties of Binary and Ternary Mixtures of 1-Butyl-3-Methylimidazolium Tetrafluoroborate, Monoethanolamine and Water. J. Chem. Thermodyn. 2016, 102, 413−428. (33) Perry, R. H.; Green, D. W.; Maloney, J. O. Perry’s Chemical Engineers’ Handbook, 6th ed.; McGraw-Hill: New York, 1984. (34) Peng, D. Y.; Robinson, D. B. A New Two-constant Equation of State. Ind. Eng. Chem. Fundam. 1976, 15, 59−64. (35) Liu, J.; Wang, S.; Hartono, A.; Svendsen, H. F.; Chen, C. Solubility of N2O in and Density and Viscosity of Aqueous Solutions of Piperazine, Ammonia, and Their Mixtures from (283.15 to 323.15) K. J. Chem. Eng. Data 2012, 57, 2387−2393. (36) Amundsen, T. G.; Øi, L. E.; Eimer, D. A. Density and Viscosity of Monoethanolamine+ Water+ Carbon Dioxide from (25 to 80) °C. J. Chem. Eng. Data 2009, 54, 3096−3100. (37) Teng, T. T.; Maham, Y.; Hepler, L. G.; Mather, A. E. Viscosity of Aqueous Solutions of N-Methyldiethanolamine and of Diethanolamine. J. Chem. Eng. Data 1994, 39, 290−293. (38) Tsai, T. C.; Ko, J. J.; Wang, H. M.; Lin, C. Y.; Li, M. H. Solubility of Nitrous Oxide in Alkanolamine Aqueous Solutions. J. Chem. Eng. Data 2000, 45, 341−347. (39) Littel, R. J.; Versteeg, G. F.; Van Swaaij, W. P. Solubility and Diffusivity Data for the Absorption of Carbonyl Sulfide, Carbon Dioxide, and Nitrous Oxide in Amine Solutions. J. Chem. Eng. Data 1992, 37, 49−55. (40) Li, M. H.; Lai, M. D. Solubility and Diffusivity of N2O and CO2 in (Monoethanolamine+ N-Methyldiethanolamine+ Water) and in (Monoethanolamine+ 2-Amino-2-methyl-1-propanol+ Water). J. Chem. Eng. Data 1995, 40, 486−492. (41) Jamal, A. Absorption and Desorption of CO2 and CO in Alkanolamine Systems. Ph.D. Thesis, University of British Columbia, Canada, 2002. (42) Mortazavi-Manesh, S.; Satyro, M.; Marriott, R. A. A Semiempirical Henry’s Law Expression for Carbon Dioxide Dissolution in Ionic Liquids. Fluid Phase Equilib. 2011, 307, 208−215. (43) Camper, D.; Becker, C.; Koval, C.; Noble, R. Diffusion and Solubility Measurements in Room Temperature Ionic Liquids. Ind. Eng. Chem. Res. 2006, 45, 445−450.

J


Density, Viscosity, and N2O Solubility of Aqueous Solutions of MEA

Recommend Documents