Article pubs.acs.org/jced
Measurement and Correlation of the Physicochemical Properties of Novel Aqueous Bis(3-aminopropyl)amine and Its Blend with N‑Methyldiethanolamine for CO2 Capture Bisweswar Das, Binay Deogam, Yatindra Agrawal, and Bishnupada Mandal* Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India S Supporting Information *
ABSTRACT: Physicochemical properties such as density and viscosity of aqueous novel bis(3-aminopropyl)amine (APA) and an aqueous novel blend of N-methyldiethanolamine (MDEA) and APA solutions as well as solubility and diffusivity of N2O into these binary and ternary solutions were measured from temperature T = 298 to 323 K at atmospheric pressure. In this study, experiments cover the molality range for APA = 0−1.291 mol·kg−1 and MDEA = 2.915−4.416 mol·kg−1. The diffusivity and solubility experiments were conducted with a wetted wall column absorber and Corning glass equilibrium cell, respectively. The experimental binary and ternary density data as well as binary viscosity data were correlated by Redlich−Kister equation whereas ternary viscosity data were correlated by the Grunberg and Nissan model. On the other hand, solubility and diffusivity were correlated with different models. All of the correlations based on the different model performed are capable of adequately predicting experimental physicochemical data.
1. INTRODUCTION Global warming and climate change issues, which are caused by greenhouse gas emission and its inherent effects, have gotten extensive attention in recent years.1,2 According to the various climate estimation models, the effect of global warming will enhance the earth’s temperature nearly 1.4−5.8 °C until the end of 21st century.3 Among the greenhouse gases, CO2 has a great role due to its abundance. To mitigate this problem and to provide sustainable development of society, research and development must be focused on reducing or controlling the level of CO2 in the atmosphere.4 There are many ways to reduce the CO2 emission such as absorption, adsorption, membrane separation, and cryogenic distillation, but most of them are not feasible for bulk CO2 removable and some of these technologies are highly expensive, so it draws attention toward absorption using a chemical solvent.5 Currently, this is considered a well-established and proven technology, and the capability of handling a large amount of industrial gas, but still it is very energy demanding.6 Therefore, it has become a global demand to develop affordable and environmentally acceptable solutions for the reduction of CO2 from flue gas, natural gas, refinery off-gases, synthesis gas, and other industrial gases by the regenerative chemical absorption process. However, the selection of a highly effective solvent, the candidate which can fulfill the desired requirements, i.e., fast reaction kinetics, high absorption capacity, great savings of energy for regeneration, negligible vapor pressure, high thermal and chemical stability, and low corrosiveness, is one of the most pivotal points of this technology.4,7,8 Initially a wide variety of alkanolamines, such as monoethanolamine (MEA), diisopropanolamine (DIPA), diethanol© XXXX American Chemical Society
amine (DEA), methyldiethanolamine (MDEA), triethanolamine (TEA), and N-2-amino-2-methyl-1-propanol (AMP), has been suggested for industrial gas treatment.9 Although a single amine such as MEA has a higher reaction rate with CO2, it has lower CO2 loading capacity, whereas tertiary amine, i.e., MDEA has higher loading capacity and lower heat of regeneration, it is limited by slow kinetics. So, it draws attention toward blended alkanolamine.10 Numerous studies on several blends such as blends of MEA with MDEA, DEA with MDEA, and MEA and AMP have been reported in the literature.7,11 More recently, the technique of adding small amounts of rate activators such as piperazine (PZ) to aqueous alkanolamine, i.e., MDEA for CO2 absorption, has been used to take advantage of the substantially high rate of reaction between CO2 and PZ with the benefits of high loading capacity of MDEA with the lower cost of regeneration of the activated solvent.12−15 The negative logarithm of the acid dissociation constant (pKa) of conjugate acid is the measurement of the basicity of a solvent; i.e., the higher the value of pKa, greater the absorption rate is.4,16 The pKa value of bis(3-aminopropyl)amine (APA) is 10.85 which is much higher than the pKa value of PZ (9.73), and it is found naturally in bacteria, algae, and plants.17 In addition, MDEA offers higher degradation resistance advantages over MEA and DEA. So, one can expect novel APA and (APA + MDEA) solutions to be more promising absorbents than others. Received: October 30, 2015 Accepted: June 16, 2016
A
DOI: 10.1021/acs.jced.5b00922 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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by cooling to ambient temperature under vacuum, and then the resulting water was used for preparing amine solutions. To clarify the strength of amine solutions, titration against standard HCl using an autotitrator (DL 50, Mettler Toledo) was conducted. Thus, the concentration measurement of amine solutions was determined with uncertainty within 0.01%. 2.2. Density and Viscosity. A 34.73 × 10−6 m3 Pyrex pycnometer (Sigma-Aldrich) was used for the density measurement of the aqueous amine solutions in the temperature range T = 298−323 K. The pycnometer along with the amine solution was immersed in a constant temperature bath where a circulating temperature controller (RW 2025G, Jeio Tech) was used to control the desired temperature. The approximate uncertainty of bath temperature was 0.25 K. After reaching the desired temperature of a constant temperature bath, the pycnometer along with the amine solution was weighed with an analytical balance (BSA 224S-CW). A minimum of three experiments were done before reporting every density data. The combined expanded uncertainties in the experimental measured density were estimated to be 4.17 and 4.41 kg·m−3 for APA and (APA + MDEA) solutions, respectively. For the viscosity measurement of the amine solutions, an Ostwald viscometer (Stanhope-seta) was used. The viscometer along with the amine solution was immersed in a thermostatic bath where a circulating temperature controller, similar to density measurement, was used to control the desired temperature. Each reported value was the average of three measurements. For the viscosity measurement, the combined expanded uncertainties were estimated to be 0.0153 and 0.068 mPa·s for APA and (APA + MDEA) solutions, respectively. 2.3. Physical Solubility of N2O. The physical solubility experiment was performed in a Corning glass equilibrium cell which was similar to one used by Paul et al.18 with the volume of 6.5 × 10−4 m3. The amount of N2O absorbed at equilibrium inside a closed vessel of known volume of liquid with gas at constant temperature and atmospheric pressure was used to determine the solubility (Henry’s law constants) of N2O. For quickly attaining equilibrium, a magnetic stirrer was used for enhancing the liquid phase mass transfer, and two four-bladed impellers mounted on a shaft were used for enhancing the gas phase mass transfer driven by a DC motor. The temperature and pressure of the equilibrium cell were controlled with a circulating temperature controller operated on external control mode (RW 2025G, Jeio Tech) and precise U-tube manometric device with an adjustable limb, respectively. The schematic of the experimental setup is shown in Figure 1. Here the uncertainty of the temperature measurement was 0.25 K. For every solubility measurement, the attainment of thermal equilibrium inside the equilibrium cell was allowed to reach the desired temperature. Then purging was done with the desired gas. To ensure uniform gas phase concentration throughout the cell, a gas phase stirrer was run at 70 rpm during purging. The temperature of the gas stream was maintained by passing the gas through a water vapor saturator. Then the cell was sealed after filling 10 mL of a freshly prepared aqueous amine solution of known concentration, and the stirrer was turned on to commence absorption. The attainment of equilibrium was considered once there was no change in volume of absorption for at least 1 h. Equilibrium was established within 5−6 h. To maintain atmospheric pressure in the equilibrium cell throughout the experiment, a precise manomatric device was employed. The difference between the initial and final levels of the cell side limb (precise U-tube manometric device) was the
The accurate values of physical properties are necessary for more reliable and appropriate equipment design as well as these data are basic requirements to finding the mass transfer coefficient by using mass transfer rate modeling.18 Furthermore, 10% discrepancy in the measurement of CO2 solubility may lead to 20% inconsistency in the reaction kinetics constant because the kinetic rate constant varies with the square of Henry’s law constant. Besides mass transfer rate modeling, solubility data of CO2 are also used in thermodynamic modeling to calculate the real activity coefficient.19 In this present study, density and viscosity of aqueous solutions of 0.102−1.291 mol·kg−1 APA and an aqueous blend of 0−1.688 mol·kg−1 APA and 2.915−4.416 mol·kg−1 MDEA solutions as well as solubility and diffusivity of N2O into these binary and ternary solutions were measured from temperature T = 298 to 323 K at atmospheric pressure. At the same time different models were exploited to correlate the experimental data in the entire range of temperature and concentration. Physical solubility and diffusivity of CO2 are not possible to be measured directly due to the chemical reactions between CO2 and amine solution.18 To overcome the aforementioned problem “N2O analogy”, proposed by Clarke,20 was used to estimate the solubility and diffusivity of CO2 using N2O because of similar properties such as electronic structure, configuration, molecular weight, and molar volume, and it is a nonreactive gas in amine solvents.19 Thus, solubility and diffusivity of N2 O in amine solutions were measured experimentally, and the solubility and diffusivity of CO2 were determined in aqueous amine solutions by using N2O analogy, shown as follows. ⎛ HCO − H O ⎞ 2 2 ⎟⎟HN O − Am HCO2 − Am = ⎜⎜ 2 ⎝ HN2O − H2O ⎠
(1)
⎛ DCO − H O ⎞ 2 2 ⎟⎟DN O − Am DCO2 − Am = ⎜⎜ 2 ⎝ DN2O − H2O ⎠
(2)
2. EXPERIMENTAL SECTION 2.1. Materials. The purities of amines with their structures and sources are given in Table 1. In the present study, water purification has been done by a Millipore water purification system whose conductivity and surface tension were 1 × 10−7 Ω−1·cm−1 and 72 mN·m−1 (at 298 K), respectively. Water degassing was carried out through prolonged boiling followed Table 1. Details of the Materials Used in This Work
B
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Figure 1. Schematic of experimental setup for solubility measurement.
Table 2. Comparison of the Densities (ρ) and Viscosities (η) of Pure MDEA and Aqueous MDEA Solutions (Mass % w) Measured in This Work with Literature Values at Temperature T at a Pressure of 0.1 MPaa pure MDEA T/K
Al-Ghawas et al.22
10% MDEA this work
Al-Ghawas et al.22
298 308 323
1037.4 1030.2 1019.4
1036.7 1029.4 1018.5
1005.4 1002.5 996.0
298 308 323
76.900 44.140 21.980
77.600 44.330 22.300
1.290 1.011 0.748
20% MDEA this work ρ/(kg·m−3) 1005.7 1001.9 995.9 η/(mPa·s) 1.295 1.007 0.748
30% MDEA
Al-Ghawas et al.22
this work
Al-Ghawas et al.22
this work
1015.2 1011.3 1004.7
1015.0 1010.9 1003.4
1025.0 1020.5 1013.0
1024.6 1020.2 1012.0
1.941 1.474 1.051
1.925 1.468 1.033
3.092 2.250 1.505
3.031 2.251 1.491
a Standard uncertainties (u) are u(T) = 0.25 K, u(w) = 0.01%, and u(p) = 0.2 kPa. The combined expanded uncertainty for density measurement Uc(ρ) = 4.71 kg·m−3 and viscosity measurement Uc(η) = 0.102 mPa·s (95% level of confidence, k = 2).
reached thermal equilibrium at the desired temperature by using a circulator temperature controller (RW 2025G, Jeio Tech) with uncertainty of 0.25 K. The pressure inside the absorption chamber was nearly 100 kPa. The combined expanded uncertainties in the experimental diffusivity measurement were estimated to be 35.1 × 10−12 and 18.2 × 10−12 m2· s−1 for APA and (APA + MDEA) solutions, respectively. Among the various diffusivity experiments at the same condition, the repeatability was within ±1.0%.
absorbed amount of N2O. The value of the vapor pressure of the solution was taken to correct the partial pressure of N2O in the cell. The calculation for Henry’s law constant was done as described by our group elsewhere.17,21 The combined expanded uncertainties in determining Henry’s law constant for N2O were estimated to be 66.2 × 103 and 66.0 × 103 kPa·kg·kmol−1 for APA and (APA + MDEA) solutions, respectively. The reproducibility between the different experiments at the same condition was within ±1.0%. 2.4. Diffusivity of N2O. The diffusivity of N2O in aqueous amine solutions was performed using a stainless steel wetted wall column absorber whose outer diameter was 2.81 × 10−2 m. The apparatus and procedure were the same for measuring the diffusivity as described by Paul et al.18 The height of the absorption column during the experiment was kept at 7 × 10−2 m. The volume uptake method was adopted to measure the rate of absorption of gas with the help of a soap film meter. A calibrated rotameter was used to measure the flow rate of liquid. During every experiment the absorption chamber
3. RESULTS AND DISCUSSION 3.1. Density and Viscosity. Experimentally measured values of density as well as viscosity of pure MDEA and its aqueous solutions at various temperatures were exploited for validation of pycnometer, the viscometer, and the experimental procedure of the measurements. These values were compared with data reported by Al-Ghawas et al.22 as shown in Table 2. There was excellent agreement with the average absolute deviations (AAD) for density and viscosity were 0.06% and C
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Table 3. Density (ρ) and Viscosity (η) for APA (1) + H2O (2) at Different Molalities (m) and Temperatures (T) at a Pressure of 0.1 MPaa m1/(mol·kg−1)
298 K
303 K
308 K
313 K
318 K
323 K
992.55 992.43 992.27 992.10 991.92 991.73
990.18 989.94 989.71 989.48 989.3 989.09
987.58 987.36 987.13 986.93 986.74 986.55
0.69 0.77 0.88 0.99 1.11 1.23
0.61 0.69 0.80 0.90 1.00 1.11
0.55 0.63 0.73 0.81 0.90 0.98
−3
0.102 0.313 0.537 0.773 1.024 1.291
997.56 997.47 997.32 997.12 996.90 996.71
996.21 996.12 995.98 995.83 995.67 995.53
0.102 0.313 0.537 0.773 1.024 1.291
0.95 1.07 1.23 1.41 1.57 1.74
0.84 0.95 1.09 1.24 1.39 1.55
ρ/(kg·m ) 994.48 994.37 994.17 994.00 993.82 993.64 η/(mPa·s) 0.76 0.85 0.98 1.10 1.24 1.38
Standard uncertainties (u) are u(T) = 0.25 K, u(m) = 0.001 mol·kg−1, and u(p) = 0.2 kPa. The combined expanded uncertainty for density measurement Uc(ρ) = 4.17 kg·m−3 and for viscosity measurement Uc(η) = 0.0153 mPa·s (95% level of confidence, k = 2). Solvent = water. a
Table 4. Density (ρ) and Viscosity (η) for APA (1) + MDEA (2) + H2O (3) at Different Molalities (m) and Temperatures (T) at a Pressure of 0.1 MPaa m1/(mol·kg−1)/m2/(mol·kg−1)
298 K
303 K
308 K
313 K
318 K
323 K
1030.94 1028.71 1025.64 1023.62 1021.60 1019.58 1017.56
1027.61 1025.06 1022.81 1020.71 1018.61 1016.51 1014.26
1024.05 1021.52 1019.54 1017.34 1015.14 1012.94 1010.74
1020.68 1018.53 1016.34 1013.80 1011.26 1008.72 1006.18
2.700 2.903 3.140 3.350 3.561 3.771 3.982
2.215 2.368 2.610 2.770 2.949 3.128 3.307
1.890 2.040 2.200 2.390 2.570 2.731 2.892
1.620 1.773 1.940 2.060 2.200 2.354 2.508
−3
ρ/(kg·m ) 0/4.416 0.148/4.294 0.447/4.025 0.751/3.753 1.058/3.478 1.371/3.199 1.688/2.915
1036.91 1034.21 1031.94 1029.81 1027.40 1024.98 1022.67
1034.27 1031.54 1029.05 1026.64 1024.71 1022.78 1020.45
0/4.416 0.148/4.294 0.447/4.025 0.751/3.753 1.058/3.478 1.371/3.199 1.688/2.915
3.851 4.210 4.540 4.860 5.180 5.500 5.820
3.220 3.468 3.763 3.980 4.207 4.434 4.661
η/(mPa·s)
a Standard uncertainties (u) are u(T) = 0.25 K, u(m) = 0.001 mol·kg−1, and u(p) = 0.2 kPa. The combined expanded uncertainty for density measurement Uc(ρ) = 4.41 kg·m−3 and for viscosity measurement Uc(η) = 0.068 mPa·s (95% level of confidence, k = 2). Solvent = water.
n
0.79%, respectively. The average absolute deviation was calculated by the following equation.23 %AAD =
1 n
n
∑ i=1
Xexptl, i − Xcalcd, i Xexptl, i
V jkE /(m 3·kmol‐1) = xjxk ∑ Ai (xj‐xk)i i=0
Ai = a + b(T /K) + c(T /K)2
× 100
(4) (5)
where Ai are pair parameters and these are a function of temperature as shown in eq 5. The excess volume (VE) of the binary system is VE12, and for the ternary system, it is the sum of VE12, VE23, and VE13, and these were calculated by eq 6. The molar volumes (Vm) of the solutions were calculated by eq 7.
(3)
The density and viscosity of pure APA were experimentally measured and correlated, and these have been presented in Supporting Information Tables S1 and S2. The obtained densities and viscosities of APA and (APA + MDEA) solutions are given in Tables 3 and 4, respectively. For binary and ternary solutions, both densities and viscosities decreased with increasing temperature, whereas with increasing molar concentration of APA in both solutions densities decreased and viscosities increased. The experimental data of densities were correlated using the Redlich−Kister equation24,25 for binary and ternary solutions as shown in
V E = Vm −
Vm =
∑ xiVi0
∑ xiMi ρm
(6)
(7)
V0i
where and Mi are the molar volume and molar mass of pure components at the system temperature. ρm is the measured liquid density and xi is the mole fraction of the pure fluid i. In this density measurement, the computed values using Redlich− D
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Kister equation deviate (AAD) from experimental values of binary and ternary solutions by 0.08% and 0.16%, respectively. The parameters of eq 4 are shown in Tables 5 and 6. The
ln(η /(mPa· s)) =
parameters for density a b 103c parameters for kinematic viscosity a b c
A1
A2
517.68 −3.4618 5.7639
1080.1 −7.2228 12.026
563.72 −3.7697 6.2764
−42.575 214.25 245.36
−55.098 −1670.6 −211.49
(11)
where Gij in eq 11 are a function of temperature as shown in Gij = a + b(T /K) + c(T /K)2
Table 5. Binary Redlich−Kister Parameters A0, A1, and A2 for the Excess Volume of Density (ρ) and Kinematic Viscosity (υ) for APA (1) + H2O (2) (Equations 4, 5, 9, and 10)a A0
∑ xi ln ηi + ∑ ∑ xixjGij
(12)
The correlated values deviated from experimental data with AAD of 2.28%, and the parameters are presented in Table 7. Table 7. Parameters of Grunberg and Nissan Model G12, G23, and G13 for Ternary Viscosity of APA (1) + MDEA (2) + H2O (3) (Equations 11 and 12)a
a
parameter
G12
G23
G13
a b 103·c
3149.3 −18.5 29.3
620.61 −3.7123 5.6581
936.62 −5.8117 9.1678
AAD for ternary viscosity, 2.28%.
a
AAD for binary density and viscosity are 0.08% and 1.42%, respectively.
3.2. Solubility of N2O. The experimental values of solubility of N2O (in terms of Henry’s constant) in APA and (APA + MDEA) solutions at T = 298−323 K and various concentrations of APA are tabulated in Tables 8 and 9. The measured values of solubility of pure APA and correlation parameters are presented in Tables S1 and S2. To validate the experimental method and data for solubility measurement, we considered the solubility measurements of CO2 and N2O in water at T = 298−323 K and compared the values with the literature data reported by different authors22,26−28 as shown in Figures S1 and S2. It demonstrates that the experimental data were in good agreement with the literature data. It was elucidated from the experimental results that Henry’s constants (HN2O) of both APA and (APA + MDEA) solutions increased with increasing temperature as well as increasing APA concentration in amine solutions. To correlate experimental solubility data at various temperatures and compositions, several models were applied in the literature such as the semiempirical model,2,29 Arrhenius type equation,18 and polynomial model.2 In this study, the experimental data of the solubility of N2O in amine solutions were also correlated by different models as follows. 3.2.1. Semiempirical Model. A semiempirical model was used to correlate excess Henry’s constant (R) shown in eq 13, which is a function of the volume fraction and the temperature as shown in eqs 14 and 15.
experimental data of viscosities were also correlated using the Redlich−Kister equation24 for the binary solutions taking kinematic viscosity as a variable. The modified viscosity deviation expression24 is given in eqs 8 and 9. n
δν /(10−3 m 2·s−1) = ln νm −
∑ xi ln νi
(8)
i=1 n
δν12/(10−3 m 2·s−1) = x1x 2 ∑ Ai (x1 − x 2)i
(9)
i=0
where υ (η/ρ) is the kinematic viscosity, η is the viscosity, ρ is the density, and Ai are pair parameters and it is a function of temperature as shown Ai = a +
b (T /K) + c
(10)
In this binary viscosity measurement, the correlated values using eq 9 are in excellent agreement with the experimental data whereas the AAD value was 1.42%. The regressed parameters from eq 9 are given in Table 5. The Grunberg and Nissan model24 was used to correlate the viscosity data of ternary solutions, shown as follows.
Table 6. Ternary Redlich−Kister Parameters A0, A1, and A2 for the Excess Volume of Density for APA (1) + MDEA (2) + H2O (3) (Equations 4 and 5)a binary pair parameter A0
A1
A2
a
a b c a b c a b c
APA (1) + AMP (2)
AMP (2) + H2O (3)
APA (1) + H2O (3)
2.4338 −0.1069 0.0562 −3.402 −0.8171 −0.0856 −1.5899 1.5981 −0.3623
1.4403 0.518 0.3536 −0.1320 1.2175 0.8287 −2.1 0.7151 0.4856
−1.6031 −1.1156 0.2168 −6.1226 −2.4746 0.4410 −4.7438 −1.368 0.2178
AAD for ternary density 0.16%. E
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Table 8. Measured Henry’s Constant of N2O ( HN2O) and Estimated Henry’s Constant of CO2 (HCO2) in APA (1) + H2O (2) at Temperature T Using the N2O Analogy as a Function of Molality (m) at a Pressure of 0.1 MPaa 10−3HN2O/(kPa·kg·kmol−1) −1
10−3HCO2/(kPa·kg·kmol−1)
m1/(mol·kg )
298 K
303 K
308 K
313 K
318 K
323 K
298 K
303 K
308 K
313 K
318 K
323 K
0.102 0.313 0.537 0.773 1.024 1.291
4055 4224 4383 4522 4656 4749
4488 4645 4784 4905 5013 5135
4803 4991 5150 5263 5395 5540
5269 5438 5611 5732 5860 6048
5753 5925 6072 6218 6366 6523
6256 6413 6579 6736 6853 7029
3073 3202 3322 3427 3529 3600
3396 3515 3619 3710 3794 3886
3643 3785 3905 3991 4091 4201
3799 3921 4045 4133 4226 4361
4130 4254 4360 4465 4571 4683
4442 4553 4671 4783 4866 4991
Standard uncertainties (u) are u(T) = 0.25 K, u(m) = 0.001 mol·kg−1, and u(p) = 0.2 kPa. The combined expanded uncertainty for solubility measurement Uc(HN2O) = 66.2 × 103 kPa·kg·kmol−1 (95% level of confidence, k = 2). Solvent = water. a
Table 9. Measured Henry’s Constant of N2O (HN2O) and Estimated Henry’s Constant of CO2 (HCO2) in APA (1) + MDEA (2) + H2O (3) at Temperatures T Using the N2O Analogy as a Function of Molality (m) at a Pressure of 0.1 MPaa 10−3HN2O/(kPa·kg·kmol−1)
10−3HCO2/(kPa·kg·kmol−1)
m1/(mol·kg−1)/m2 /(mol·kg−1)
298 K
303 K
308 K
313 K
318 K
323 K
298 K
303 K
308 K
313 K
318 K
323 K
0/4.416 0.148/4.294 0.447/4.025 0.751/3.753 1.058/3.478 1.371/3.199 1.688/2.915
5221 5229 5264 5298 5313 5323 5337
5507 5533 5555 5580 5593 5609 5621
5840 5879 5926 5945 5961 5978 5993
6294 6325 6347 6374 6386 6399 6405
6754 6784 6829 6852 6875 6886 6894
7283 7317 7323 7348 7358 7360 7361
3957 3963 3989 4016 4026 4034 4046
4167 4187 4203 4222 4232 4244 4253
4429 4458 4494 4508 4521 4533 4543
4538 4559 4576 4595 4604 4614 4618
4849 4871 4903 4919 4936 4944 4950
5171 5196 5200 5217 5224 5225 5226
Standard uncertainties (u) are u(T) = 0.25 K, u(m) = 0.001 mol·kg−1, and u(p) = 0.2 kPa. The combined expanded uncertainty for solubility measurement Uc(HN2O) = 66.0 × 103 kPa·kg·kmol−1 (95% level of confidence, k = 2). Solvent = water. a
Table 10. Parameters k1, k2, k3, k4, and α123 for the Excess Henry’s Constant for Binary and Ternary Solvent Systems and AAD for N2O Solubility of APA (1) + MDEA (2) + H2O (3) (Equations 14 and 15) system
k1
k2
104k3
k4
APA (1) + H2O (2) MDEA (1) + H2O (2) APA (1) + MDEA (2) APA (1) + MDEA (2 )+ H2O (3)
2.44287 64.497 −422.04
−1.247 −0.352 1.812
17.8 5.117 −23.447
−31.313 −4.048 70.213
α123
AAD/% 7.03 0.82
78.858
0.65
Table 11. Parameters for Solubility and Diffusivity of N2O in the Binary Solution of APA (1) + H2O (2) and Ternary Solution of APA (1) + MDEA (2) + H2O (3) with AAD using Arrhenius Type Equations (Equations 16, 20, and 21) solubility parameter
diffusivity
binary
ternary
binary
ternary
a b c d e f h
7.7447 × 105 120660 −20595
1.4409 × 10−5 6.8608 × 10−6 3.0581 × 10−5 −2690.3
1565.3
−4.172 × 108 1.8882 × 108 −2.1345 × 107 1.6912 × 108 −1.7124 × 107 −3.8234 × 107 1295.2
−546.9
9.5522 × 10−5 −9.7622 × 10−5 1.5849 × 10−5 −2.8175 × 10−5 1.8571 × 10−6 1.9431 × 10−5 2723.4
AAD/%
0.56
0.73
4.61
2.98
where φi are the volume fractions of amines and water, α123 is a constant of three body interaction parameter, and k1, k2, k3, and k4 are constants for the two body interaction parameter. An attempt was made to validate the constants of eq 15 for MDEA and water solutions by the solubility data obtained from Mandal et al.,30 and the determined value of AAD was 0.82% whereas the author reported value was 0.81%. The value of AAD for the aqueous APA solutions was 7.03% and that for the aqueous (APA + MDEA) solutions was 0.65%, so predicted
n
R = ln(HN2O − solution) −
∑ φi ln(Hi) i=1
R=
1 2
n
(13)
n
∑∑
αijφφ + φ1φ2φ3α123 i j
i=1 i≠j=1
αij = k1 + k 2T + k 3T 2 + k4φj
(14) (15) F
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results from this model do not correlate well with the experimental results for the binary system but gave good estimation for ternary solutions. The values of parameters are given in Table 10 for binary and ternary solutions. 3.2.2. Arrhenius Type Equation. The Arrhenius type equation is suggested to correlate solubility data at various molalities (mol·kg−1) of APA (m1) and MDEA (m2) and temperatures (T) as follows: HN2O/(kPa·kg·kmol−1) = (a + bm1 + cm12 + dm2 + em2 2 + fm1m2) exp(−h/(T /K))
(16)
In the preceding equation when the molality of MDEA is zero, then this equation is applicable to the binary system of APA and water. The values of constant used are given in Table 11 for binary and ternary solutions, respectively. The values of AAD for APA and (APA + MDEA) solutions were 0.56% and 0.73%, respectively. 3.2.3. Polynomial Model. Polynomial models are proposed to predict the solubility of binary solutions as a function of mole fraction of APA (x1) and ternary solution as a function of the mole fraction of APA (x1) and MDEA (x2), and the temperature (T) is defined in eqs 17 and 18, respectively.
Figure 2. Comparison between experimental and predicted results of Henry’s constant of N2O, HN2O, in aqueous APA solutions by parity plot.
HN2O/(kPa·kg·kmol−1) = A1 + A 2x1 + A3x12 + A4 (T /K) + A5x1(T /K) + A 6x12(T /K)
(17) HN2O/(kPa·kg·kmol−1) = A1 + A 2x1 + A3x 2 2 + A4 (T /K) + A5x1(T /K) + A 6x 2 2(T /K)
(18)
where Ai are the parameters for binary and ternary solutions. The values of the constant are tabulated in Table 12 for binary Table 12. Parameters A1, A2, A3, A4, A5, and A6 for Solubility and Diffusivity of N2O in the Binary Solutions of APA (1) + H2O (2) and Ternary Solutions of APA (1) + MDEA (2) + H2O (3) with AAD Using Polynomial Models (Equations 17, 18, 22, and 23) solubility parameter
Figure 3. Comparison between experimental and predicted results of Henry’s constant of N2O, HN2O, in aqueous blend of APA and MDEA solutions by parity plot.
diffusivity
binary
ternary
binary
ternary
A1 A2 102A3 103A4 103A5 103A6
6.4046 52.743 −494.49 6.2854 −98. 388 1226.3
4.7674 0.3842 −4347.1 13.221 9.1894 48.438
−27.88 −5385.46 2.573 33812 −53.2 0.7168
−25.745 −183.489 −48969.4 18.318 511.99 1256.51
AAD/%
0.35
0.55
1.75
2.17
3.3. Diffusivity of N2O. The experimental values of diffusivity of N2O in APA and (APA + MDEA) solutions at T = 298−323 K and various concentrations of APA and MDEA are presented in Tables 13 and 14 in terms of binary diffusion coefficient. The diffusivity measurement of CO2 and N2O in water were considered, similar to solubility measurement, at T = 298−323 K and the values compared with the literature data reported by different authors22,26−28,31 as shown in Figures S3 and S4. As depicted from these figures, the experimental data were in good agreement with the literature data. From the investigation of the present experimental data, we observed that DN2O in both APA and (APA + MDEA) solutions increased with increasing temperature as well as decreased with increasing APA molality in amine solutions. To correlate experimental diffusivity data at various temperature and composition, several models were reported in the literature such as the modified Stokes−Einstein model,2 Arrhenius type equation,2 and polynomial model. The experimental data of the
and ternary solutions. It was observed that the computed values using this model gave good agreement with the experimental results and had AAD of 0.35% and 0.55%, respectively. Comparisons of the experimental values with three predicting models (the semiempirical model, Arrhenius type equation, and polynomial model) for N2O solubility in aqueous APA and (APA + MDEA) solutions are shown in the parity charts (Figures 2 and 3). It was prominent that the polynomial model led to the best fit among the three models for binary and ternary solutions. G
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Table 13. Measured Diffusivity of N2O (DN2O) and Estimated Diffusivity of CO2 (DCO2) in APA (1) + H2O (2) at Temperature T Using the N2O Analogy as a Function of Molality (m) at a Pressure of 0.1 MPaa 109DN2O/(m2·s−1) −1
109DCO2/(m2·s−1)
m1/(mol·kg )
298 K
303 K
308 K
313 K
318 K
323 K
298 K
303 K
308 K
313 K
318 K
323 K
0.102 0.313 0.537 0.773 1.024 1.291
1.48 1.31 1.14 0.99 0.84 0.68
1.74 1.57 1.41 1.26 1.12 0.96
2.20 1.91 1.72 1.54 1.40 1.25
2.44 2.26 2.05 1.86 1.70 1.54
2.76 2.51 2.32 2.14 2.00 1.84
2.95 2.72 2.48 2.35 2.20 2.05
1.60 1.41 1.23 1.07 0.91 0.73
1.91 1.72 1.55 1.38 1.23 1.05
2.37 2.06 1.86 1.66 1.51 1.35
2.71 2.51 2.28 2.06 1.89 1.71
3.03 2.81 2.60 2.39 2.24 2.06
3.33 3.07 2.87 2.65 2.48 2.31
Standard uncertainties (u) are u(T) = 0.25 K, u(m) = 0.001 mol·kg−1, and u(p) = 0.2 kPa. The combined expanded uncertainty for diffusivity measurement Uc(DN2O) = 35.1 × 10−12 m2·s−1 (95% level of confidence, k = 2). Solvent = water. a
Table 14. Measured Diffusivity of N2O (DN2O) and Estimated Diffusivity of CO2 (DCO2) in APA (1) + MDEA (2) + H2O (3) at Temperature T Using the N2O Analogy as a Function of Molality (m) at a Pressure of 0.1 MPaa 109DN2O/(m2·s−1)
109DCO2/(m2·s−1)
m1/(mol·kg−1)/m2/ (mol·kg−1)
298 K
303 K
308 K
313 K
318 K
323 K
298 K
303 K
308 K
313 K
318 K
323 K
0/4.416 0.148/4.294 0.447/4.025 0.751/3.753 1.058/3.478 1.371/3.199 1.688/2.915
0.82 0.77 0.71 0.65 0.59 0.53 0.47
0.95 0.90 0.85 0.78 0.72 0.66 0.60
1.09 1.05 0.99 0.93 0.87 0.81 0.74
1.24 1.19 1.13 1.07 1.01 0.94 0.88
1.37 1.33 1.28 1.22 1.15 1.08 1.01
1.54 1.48 1.43 1.37 1.30 1.23 1.16
0.88 0.83 0.77 0.70 0.64 0.57 0.51
1.04 0.99 0.93 0.86 0.79 0.72 0.66
1.18 1.13 1.07 1.00 0.94 0.87 0.80
1.38 1.32 1.25 1.19 1.12 1.04 0.98
1.53 1.49 1.43 1.37 1.29 1.21 1.13
1.74 1.67 1.61 1.55 1.47 1.39 1.31
Standard uncertainties (u) are u(T) = 0.25 K, u(m) = 0.001 mol·kg−1, and u(p) = 0.2 kPa. The combined expanded uncertainty for diffusivity measurement Uc(DN2O) = 18.2 × 10−12 m2·s−1 (95% level of confidence, k = 2). Solvent = water. a
diffusivity of N2O in amine solutions were correlated by different models as follows. 3.3.1. Modified Stokes−Einstein Model. The experimental values of diffusivity of N2O in APA and (APA + MDEA) solutions are proposed to correlate by the modified Stokes− Einstein model. This model relates the viscosity of solution (η), which is a function of temperature and concentration, to diffusivity of solution (DN2O) as follows. (DN2O/(m 2·s−1))(η /(mPa·s)) p (T /K)
=C
The values of the parameters in eqs 20 and 21 are also given in Table 11. The values of AAD for APA and (APA + MDEA) solutions were 4.61% and 2.98%, respectively. 3.3.3. Polynomial Model. Polynomial models are considered to correlate diffusivity data, for binary solutions as a function of the mole fraction of APA (x1) and temperature (T), and for ternary solutions as a function of mole fraction of APA (x1), MDEA (x2), and temperature (T) are given as follows. ln(DN2O/(m 2· s−1)) = A1 + A 2x1 + A3(T /K) + A4 x1(T /K) + A5x1(T /K)2
(19)
+ A 6x12(T /K)2
where p and C are constant parameters. For the binary system, the values of p and C were 1.1255 and 5.3552 × 10−12, and for the ternary system, the values of p and C were 0.8087 and 7.6392 × 10−12. The AAD values for binary and ternary solutions were 8.48% and 3.73%, respectively. 3.3.2. Arrhenius Type Equation. The Arrhenius type equation for N2O diffusivity of aqueous APA solutions were used to correlate experimental data at various molalities of APA (m1) and temperature (T) as given in eq 20. Diffusivity of (APA + MDEA) solutions were also correlated as the function of molalities of APA (m1) and MDEA (m2) and temperature as shown in eq 21.
(22)
ln(DN2O/(m 2· s−1)) = A1 + A 2x1 + A3x 2 2 + A4 (T /K) + A5x1(T /K) + A 6x 2 2(T /K)
(23)
Parameters of eqs 22 and 23 are also included in Table 12 for both binary and ternary solutions. The values of AAD for APA and (APA + MDEA) solutions were 1.75% and 2.17%, respectively. We obtained values of all of the model parameters for solubility and diffusivity using regression performed by Matlab software (2013b). Comparisons of the experimental values with three predicting models (the modified Stokes−Einstein model, Arrhenius type equation, and polynomial model) for N2O diffusivity in aqueous APA and (APA + MDEA) solutions are shown in the parity charts (Figures 4 and 5). It was observed from the parity plots that the polynomial model gave the best fit among the three models for binary and ternary solutions.
DN2O/(m 2 · s−1) = (a + bm1 + cm12) exp((d + hm1)/(T /K)) (20) D N2O/(m 2·s−1) = (a + bm1 + cm12 + dm2 + em2 2 + fm1m2) exp(−h/(T /K))
(21) H
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for CO2 removal as well as developed correlation would be employed satisfactorily in engineering estimation.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b00922. Variation of density, viscosity, and Henry’s constant of N2O in pure APA at various temperatures (Table S1), parameter values after correlating the density, viscosity, and Henry’s constant of N2O in pure APA (Table S2), variation of solubility of N2O in aqueous APA and aqueous (APA + MDEA) solutions (Tables S3 and S4), variations of Henry’s law constants of CO2 and N2O in water at various temperatures (Figures S1 and S2), variations of diffusivity of CO2 and N2O in water at various temperatures (Figures S3 and S4), and variation of density and viscosity of MDEA at various temperature and weight percent and compared with literature (Figures S5 and S6) (PDF)
Figure 4. Comparison between experimental and predicted results of N2O diffusivity in aqueous APA solutions by parity plot.
■
AUTHOR INFORMATION
Corresponding Author
*Tel.: 91-361-2582256. Fax: 91-361-2582291. E-mail:
[email protected]. Funding
The financial support by the Department of Science and Technology (DST; Grant No. DST/IS-STAC/CO2-SR-137/ 12G), New Delhi, Government of India is gratefully acknowledged. Notes
The authors declare no competing financial interest.
■ Figure 5. Comparison between experimental and predicted results of N2O diffusivity in aqueous blend of APA and MDEA solutions by parity plot.
4. CONCLUSIONS In this work density and viscosity of aqueous novel 0.102− 1.291 mol·kg−1 APA and an aqueous novel blend of 0−1.688 mol·kg−1 APA and 2.915−4.416 mol·kg−1 MDEA solutions as well as solubility and diffusivity of N2O into these binary and ternary solutions were measured at 298, 303, 308, 313, 318, and 323 K in order to evaluate the potential of binary and ternary solutions for CO2 removal from gas mixtures. The physical solubility and diffusivity of CO2 into these solutions were estimated through N2O analogy. Experimentally determined density and viscosity data were correlated by the well-known model in order to compute the predicted data. The obtained predicted data were in good agreement with measured values. In the case of both the solubility and diffusivity measurements, three different models were applied to correlate experimental data. However, the polynomial model led to the best result for both solubility and diffusivity data. The predicted data determined by the entire model in this study showed significantly in an acceptable range of less than 10% (AAD). Hence, reported experimental data on novel amine solutions I
NOTATIONS AAD = average absolute deviations AMP = N-2-amino-2-methyl-1-propanol APA = bis(3-aminopropyl)amine DCO2 = diffusivity of CO2, m2·s−1 DN2O = diffusivity of N2O, m2·s−1 DEA = diethanolamine DIPA = diisopropanolamine HCO2 = Henry’s constant of CO2, kPa·kg·kmol−1 Hi = Henry constant of pure component, kPa·kg·kmol−1 HN2O = Henry’s constant for solubility, kPa·kg·kmol−1 m1 = molality of APA, mol·kg−1 m2 = molality of MDEA, mol·kg−1 Mi = molar mass of pure components, kg·kmol−1 MN2O = mole of gas absorbed per kilogram of liquid, mol· kg−1 MDEA = N-methyldiethanolamine MEA = monoethanolamine ρ = liquid density, kg·m−3 pKa = negative logarithm of the acid dissociation constant PZ = piperazine R = excess Henry’s constant T = temperature, K TEA = triethanolamine VE = excess volume, m3·kmol−1 V0i = molar volume of pure components, m3·kmol−1 Vm = molar volumes of solution, m3·kmol−1 xi = mole fraction of the pure fluid i x1 = mole fraction of APA DOI: 10.1021/acs.jced.5b00922 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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x2 = mole fraction of MDEA Greek Letters
αij α123 η υ (η/ρ) φi
■
two body interaction parameter three body interaction parameter viscosity, mPa·s kinematic viscosity, m2·s−1 volume fraction of amines and water
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