Physicochemical Properties of Aqueous Potassium Salts of Basic

Article pubs.acs.org/jced

Physicochemical Properties of Aqueous Potassium Salts of Basic Amino Acids as Absorbents for CO2 Capture Yangyang Bian,† Shufeng Shen,*,† Yue Zhao,† and Ya-nan Yang† †

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

ABSTRACT: Aqueous amino acid salt (AAS) solutions could be attractive absorbents for CO2 removal from flue gases. Density, viscosity, and solubility of N2O in aqueous potassium salts of lysine, histidine, and arginine were measured over the temperature range from (293 to 353) K and molality concentration range from (0.26 to 3.6) mol·kg−1. Experimental results were correlated well with empirical correlations. The ion specific parameters (hAA−), based on the Weisenberger and Schumpe model, were fitted using the solubility data of N2O in the aforementioned AAS systems, valid up to 328 K. The models using temperature dependence of hAA− predict well within 2.5% AAD. The physical solubility of CO2 in the aqueous AAS solutions was also estimated.

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INTRODUCTION Carbon dioxide (CO2) is one of the major greenhouse gases, which could result in global climate change. Postcombustion CO2 capture technology can effectively reduce CO2 emissions from the main sources such as coal-fired power plants.1,2 Among the available methods, chemical absorption is one of the most feasible options for a large-scale implementation. In recent years, amino acid salts (AAS) have been recognized as potential solvents for CO2 absorption over benchmark aminebased solvents.2−4 Since they have identical functional group as alkanolamines, AAS are expected to have fast kinetics with CO2. They also have a number of advantages such as low volatility, resistance to oxidative degradation, and high surface tension.5,6 Knowledge of the physicochemical properties of AAS solutions is essential to deduce chemical reaction kinetics from CO2 absorption experiments and design the absorber in their CO2 absorption processes, since they are related to the mass transfer coefficients. Physical properties along with the kinetics of CO2 absorption for several amino acid salts such as glycinate,7 taurate,8 alaninate,9,10 prolinate,4,5,11,12 threonate,13 sarcosinate,14,15 and serinate,16 have been reported recently. Physical solubility of CO2 in reactive absorbents cannot be measured directly because the absorbents can react with CO2. N2O is often widely accepted and used as a nonreacting gas with similarities in configuration, molecular volume, and electronic structure with CO2.17 Therefore, solubility property can be estimated indirectly by the ion and gas specific parameters derived from the solubility data of N2O using the model of Schumpe for electrolyte solutions.5,18,19 van Holst et al. investigated ion-specific parameters for several amino acids such as alanine, sarcosine, proline, 6-aminohexanoic acid, arginine using the Schumpe model at 298 K and a concentration of 0.5 mol·L−1.5 According to the original model of Weisenberger and Schumpe,19 the ion specific parameters © 2016 American Chemical Society

should be a constant value with respect of temperature. The temperature-independence ion specific parameter of taurate has been reported by Kumar et al. (2001).6 However, the temperature dependence of anion specific parameters for glycinate, threonate, and prolinate were observed by Portugal et al. and Paul and Thomsen.11−13 Further investigation regarding this issue is demanding. Three amino acids (lysine, histidine, and arginine, shown in Figure 120) with basic side chains have been considered as promising absorbents or promoters for carbonate solutions in our previous work.21,22 However, their detailed physical properties and reaction kinetics has not been reported in the literature and needs to be revealed. In the present work, the physicochemical properties of aqueous potassium salts of lysine (LysK), histidine (HisK), and arginine (ArgK) have been investigated. The density and viscosity of their solutions were measured in a temperature range of 293−353 K and concentration range of 0.26−3.6 mol·kg−1, and the solubility of N2O under a concentration of 0.25−2.6 mol·kg−1 and a temperature of 293−328 K. Owing to the limited solubility of ArgK in water, the properties of aqueous ArgK were determined at the concentrations up to 1.15 mol·kg−1 in this work. Experimental data were correlated with empirical correlations. The anion specific parameters (hAA−) of AAS in the Weisenberger and Schumpe model were also obtained.

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EXPERIMENTAL SECTION Materials. The amino acids, L-lysine (Lys, ≥ 98% purity), L-histidine (His, ≥ 99% purity) and L-arginine (Arg, ≥ 98% purity) Received: January 6, 2016 Accepted: May 25, 2016 Published: June 7, 2016 2391

DOI: 10.1021/acs.jced.6b00013 J. Chem. Eng. Data 2016, 61, 2391−2398

Journal of Chemical & Engineering Data

Article

Figure 1. Chemical structures of amino acids with basic side chain: (a) lysine (pKa: 2.15, 9.16, 10.67); (b) histidine (pKa: 1.70, 9.09, 6.04); and (c) arginine (pKa: 2.03, 9.00, 12.10). The pKa is for the −COOH, α-NH2 group and groups in side chain, respectively.20

a known volume of solution (Vs, 0.70−0.80 L) was fed into the reactor and degassed by vacuum at 293 K until the pressure of about 2.3 kPa was obtained in the reactor. The system was allowed to come to the vapor−liquid equilibrium at various temperatures. This pressure was recorded as the solvent vapor pressure Ps. The N2O gas vessel was filled in the vessel and the initial pressure P1 was recorded. Then, the gas was allowed to enter into the reactor and the pressure decreased to P2. The total amount of N2O entering the reactor can be calculated. After this, the reactor system can reach vapor−liquid equilibrium at which point the pressure was called Peq. The pressures in vessel and reactor were recorded by two pressure transducers (GS4200, ESI) with a range of 0−3.5 bar absolute and accuracy of 0.05% of full range. The temperatures were also recorded by PT-100 thermocouples as TV and TR, respectively. The physical solubility of N2O can be then calculated:

and potassium hydroxide solution (KOH, Semiconductor grade, 48.8 w/w %) were purchased from Aladdin reagent, China. N2O, with a given purity of 99.9%, was purchased from Dalian Date Gas Co. Ltd., China. Certified viscosity standard S3 (lot no. 15101) was purchased from Cannon Instrument Company, USA. Water was produced from Merck-Millipore Aquelix 5. All the chemicals were used without further purification. The aqueous potassium solutions of amino acids were prepared by neutralizing the amino acid dissolved in deionized water with an equimolar amount of KOH in a volumetric flask at 293 K. Density Measurement. The densities of aqueous potassium salts of three amino acids were measured by a density meter (DMA 4100M, Anton Paar) having a stated precision of ±1.0 × 10−4 g·cm−3. The temperatures were controlled at (293 to 353) K, and the concentrations were prepared between 0.26−3.6 mol·kg−1. The density meter was calibrated using dry air and deionized water before daily measurement. Viscosity Measurement. The viscosities were measured at temperatures of 293−353 K and concentrations up to 3.6 mol·kg−1. A digital rolling ball microviscometer (Lovis 2000ME, Anton Paar) with the precision up to 1.0% was used to measure the data. The viscometer was validated with deionized water and S3 viscosity standard. The viscosity of our samples is within the viscosity range in the investigated temperature range. N2O Solubility. Solubility of N2O into the aqueous potassium salts of amino acids was measured in a stainless steel vessel which was placed in a temperature-controlled water bath, as shown in Figure 2. The method was reported in the

PN2O = HN2OC N2O

(1)

PN2O = Peq − Ps

(2)

C N2O =

nadded − ng VS

nadded =

VV ⎡ P1 P ⎤ − 2⎥ ⎢ RTV ⎣ Z1 Z2 ⎦

ng =

(3)

(4)

PN2O(VR − VS) ZeqRTR

(5)

where nadded and ng are the added amount of N2O and the amount of N2O in the gas phase in the reactor, respectively. PN2O is the partial pressure of N2O present in the gas phase at the controlled temperature, Pa, and CN2O is the concentration of N2O in the solution, mol m−3. 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 the critical temperature of 309.57 K, critical pressure of 7245 kPa, and acentric factor of 0.143.24 Weisenberger and Schumpe Model. For amino acid salt solutions, the presence of salts can decrease the solubility of N2O in the solutions. An empirical model was proposed by Schumpe and extended by Weissenberger and Schumpe to estimate the ion-specific parameters and the Sechenov constant.18,19 ⎛ HN O,AAS ⎞ ⎟⎟ = log⎜⎜ 2 ⎝ HN2O,H2O ⎠

Figure 2. Experimental setup for N2O solubility experiments. 5,6,23

The apparatus consists of a stainless steel vessel literature. (Vv, 1.325 L) for storing the N2O gas and a stainless steel reactor (VR, 1.010 L) with a magnetic-drive stirrer with impellers inside for the gas and liquid phases. In each experiment,

∑ (hi + hg)Ci

= (hK+ + hAA− + 2h N2O,g)CS = K N2OCs 2392

(6) DOI: 10.1021/acs.jced.6b00013 J. Chem. Eng. Data 2016, 61, 2391−2398


Article

Table 1. Density of Aqueous Solutions of LysK, HisK, and ArgK at Pressure 101.3 ± 0.5 kPaa mb

T/K

mol·kg−1

293.15

298.15

303.15

308.15

313.15

318.15

323.15

328.15

333.15

338.15

343.15

348.15

353.15

1.0034 1.0165 1.0302 1.0463 1.0724 1.1006 1.1256

1.0008 1.0139 1.0275 1.0436 1.0696 1.0977 1.1225

0.9981 1.0112 1.0248 1.0407 1.0666 1.0947 1.1194

0.9953 1.0084 1.0219 1.0378 1.0636 1.0916 1.1162

0.9924 1.0054 1.0189 1.0347 1.0605 1.0885 1.1130

0.9893 1.0023 1.0158

1.0073 1.0273 1.0472 1.0679 1.1027 1.1349

1.0047 1.0247 1.0445 1.0652 1.1000 1.1320

1.0020 1.0218 1.0417 1.0624 1.0971 1.1291

0.9992 1.0187 1.0388 1.0594 1.0941 1.1261

0.9962 1.0157 1.0358 1.0564 1.0910 1.1229

0.9931 1.0126 1.0326 1.0532 1.0879 1.1198

1.0094 1.0302 1.0505 1.0700

1.0068 1.0275 1.0476 1.0672

1.0040 1.0246 1.0448 1.0641

1.0012 1.0217 1.0417 1.0610

0.9982 1.0186 1.0385 1.0577

0.9951 1.0154 1.0352 1.0543

−1

a

0.267 0.517 0.846 1.124 1.867 2.570 3.642

1.0168 1.0303 1.0450 1.0621 1.0897 1.1192 1.1459

1.0155 1.0289 1.0434 1.0602 1.0875 1.1168 1.1419

1.0139 1.0272 1.0415 1.0582 1.0853 1.1143 1.1391

1.0121 1.0253 1.0395 1.0561 1.0829 1.1117 1.1375

1.0102 1.0235 1.0374 1.0538 1.0804 1.1091 1.1346

0.265 0.551 0.817 1.154 1.849 2.554

1.0209 1.0415 1.0625 1.0840 1.1200 1.1531

1.0194 1.0401 1.0606 1.0820 1.1178 1.1507

1.0178 1.0384 1.0587 1.0799 1.1156 1.1483

1.0161 1.0365 1.0567 1.0778 1.1132 1.1457

1.0141 1.0344 1.0545 1.0755 1.1107 1.1432

0.264 0.542 0.848 1.155

1.0233 1.0450 1.0660 1.0864

1.0218 1.0436 1.0649 1.0851

1.0202 1.0417 1.0628 1.0829

1.0183 1.0397 1.0606 1.0805

1.0163 1.0375 1.0583 1.0781

ρ/kg·L Potassium of Lysine 1.0081 1.0058 1.0213 1.0190 1.0351 1.0327 1.0514 1.0489 1.0778 1.0752 1.1063 1.1035 1.1316 1.1287 Potassium of Histidine 1.0120 1.0097 1.0322 1.0298 1.0522 1.0497 1.0731 1.0706 1.1082 1.1054 1.1405 1.1377 Potassium of Arginine 1.0142 1.0117 1.0352 1.0327 1.0558 1.0532 1.0755 1.0728

1.0573 1.0853 1.1097

The standard uncertainties u are u(T) = 0.02 K, u(ρ) = 0.002 g·cm−3, u(m) = 0.005 mol·kg−1. bThe m is the molality of AAS in the water solvent.

Table 2. Viscosity of Aqueous Solutions of LysK, HisK and ArgK at Pressure 101.3 ± 0.5 kPaa mb mol·kg

a

T/K −1

293.15

298.15

303.15

308.15

313.15

0.267 0.517 0.846 1.124 1.867 2.570 3.642

1.1834 1.3933 1.5991 1.9195 2.7830 4.1743 6.6454

1.0506 1.2265 1.4078 1.6833 2.4082 3.5570 5.5444

0.9411 1.0923 1.2510 1.4899 2.1081 3.0707 4.7103

0.8470 0.9834 1.1195 1.3278 1.8606 2.6761 4.0486

0.7675 0.8868 1.0099 1.1945 1.6552 2.3511 3.5175

0.265 0.551 0.817 1.154 1.849 2.554

1.0903 1.2424 1.4211 1.6617 2.2802 3.0478

0.9617 1.0932 1.2516 1.4567 2.0019 2.6319

0.8629 0.9797 1.1191 1.2985 1.7684 2.3147

0.7803 0.8847 1.0070 1.1669 1.5782 2.0492

0.7087 0.8025 0.9131 1.0530 1.4168 1.8276

0.264 0.542 0.848 1.155

1.1009 1.3107 1.5798 1.9232

0.9793 1.1624 1.4407 1.7084

0.8793 1.0401 1.2523 1.5167

0.7934 0.9362 1.1232 1.3564

0.7202 0.8483 1.0145 1.2195

318.15

323.15

η/mPa·s Potassium of Lysine 0.7007 0.6435 0.8069 0.7376 0.9160 0.8358 1.0769 0.9784 1.4829 1.3373 2.0939 1.8719 3.0814 2.7220 Potassium of Histidine 0.6480 0.5955 0.7344 0.6734 0.8323 0.7621 0.9568 0.8736 1.2794 1.1640 1.6410 1.4837 Potassium of Arginine 0.6587 0.6057 0.7734 0.7088 0.9217 0.8424 1.1037 1.0047

328.15

333.15

338.15

343.15

348.15

353.15

0.5935 0.6796 0.7669 0.8953 1.2134 1.6843 2.4235

0.5507 0.6294 0.7064 0.8217 1.1066 1.5256 2.1774

0.5133 0.5856 0.6548 0.7578 1.0140 1.3892 1.9620

0.4809 0.5441 0.6157 0.7025 0.9338 1.2714 1.7803

0.4516 0.5154 0.5673 0.6537 0.8639 1.1685 1.6240

0.4262 0.4858 0.5320

0.5515 0.6209 0.7022 0.8032 1.0629 1.3484

0.5137 0.5755 0.6494 0.7412 0.9765 1.2322

0.4805 0.5364 0.6048 0.6878 0.9002 1.1310

0.4494 0.5010 0.5644 0.6418 0.8351 1.0427

0.4239 0.4714 0.5280 0.5985 0.7753 0.9650

0.4016 0.4451 0.4970 0.5619 0.7232 0.8969

0.5588 0.6532 0.7748 0.9193

0.5191 0.6052 0.7130 0.8449

0.4846 0.5624 0.6616 0.7796

0.4546 0.5252 0.6144 0.7222

0.4283 0.4925 0.5738 0.6709

0.4050 0.4635 0.5374 0.6259

0.8024 1.0803 1.4862

The standard uncertainties u are u(T) = 0.02 K, u(m) = 0.005 mol·kg−1, ur(η) = 5%. bm is the molality of AAS in the water solvent.

where K is sechenov constant; hi is the ion-specific parameter; hg is the gas-specific parameter; Ci and Cs are the molar concentration of ion i and the AAS at 293 K, respectively; cation and gas specific parameters are listed in Supporting Information (SI) Table S1. From the experimental data of N2O in the solutions of LysK, HisK and ArgK studied in this work, the anion specific parameters (hAA−) were fitted in the Schumpe model and the physical solubility of CO2 in the aqueous AAS solutions can be

estimated since the solubility of CO2 in water is well correlated:3,5 HCO2,AAS = HCO2,H2O10(hK+ + hAA = HCO2,H2O10 KCO2CS

− + 2hCO ,g )CS 2

(7)

Density and viscosity measurements were performed at normal pressure, 101.3 ± 0.5 kPa. The deviations between the models 2393



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and the experimental data were given by the average absolute deviation (AAD): AAD(%) =

1 n

n

∑

yi exp − yi mod

i=1

yi exp

100 (8)

where n is the number of experimental points and yiexp and yimod represent the experimental data and the values from the models or literature.

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RESULTS AND DISCUSSION Density and Viscosity. Validation of the experimental methods was performed in order to ensure the validity of the experimental data. The density and viscosity of a certified calibration standard S3 and deionized water were measured and the results are given in the Supporting Information, Table S2. It can be observed that the experimental results in the present work agree well with the reference data.25 The AADs are within 0.05% for density and within 0.7% for viscosity. The densities and viscosities of aqueous potassium solutions of lysine (0.26−3.64 mol·kg−1), histidine (0.26−2.55 mol·kg−1), and arginine (0.26−1.16 mol·kg−1) at temperatures of (293− 353) K were determined and presented in Tables 1 and 2 and Figures 3−5. It can be seen from the figures that similar trends were observed for all AAS studied. Both densities and viscosities of the solutions generally increase with the increasing concentration of AAS and decrease with the temperature. The experimental results were also compared with the available data for LysK and ArgK in the literature.5,22,26 The graphs are presented in Supporting Information, Figures S1 and S2. It can be seen that the results from the present work match well with those from van Holst et al. (2008) and our previous work within a deviation of 0.4% for density and 5% for viscosity, respectively. However, significant deviations were observed from the scattered results by Mazinani et al. (2015).26 The possible reasons are due to the measuring methods with different measuring principles, which results in different errors. In this work, the density and viscosity were measured with high accuracy by oscillating U-tube principle and capillary rollingball measuring principle, respectively. The pycnometer and Ubbelohde viscometers with various capillary sizes were used in the literature. To represent the obtained results as a function of temperature and molar concentration, the correlation models from the experimental data fitted by the nonlinear regression can be obtained as follows: ρ = k1T + k 2C + k 3

⎡ k exp(k 3C) ⎤ η = k1 exp⎢ 2 ⎥ exp(k4C) ⎦ ⎣ RT

Figure 3. Density (a) and viscosity (b) of aqueous LysK solutions at different temperatures and concentrations. Lines: calculated from the models (eqs 9 and 10).

Table 3. Fitting Parameters of Empirical Equationa for Density of Aqueous Potassium Solution of Amino Acids k1·104 potassium salt of amino acid

k3

kg·L−1·K−1 kg·mol−1 −5.088 −5.299 −5.090

arginine lysine histidine

(9)

k2·102

8.114 5.583 7.746

kg·L−1

R2

AAD, %b

1.155 1.162 1.155

0.9982 0.9978 0.9984

0.08 0.18 0.13

Empirical equation for density: ρ = k1T + k2C + k3. bAverage absolute deviation: a

(10)

AAD% =

where k1, k2, k3, k4 are the fitted parameters of equation; ρ is the density in kg·L−1; η is the viscosity in mPa·s; T is the absolute temperature in K; C is the molar concentration of AAS in mol·L−1 at 293 K; R is the gas constant, 8.3145 m3·Pa·K−1·mol−1. The optimized parameters from the experimental densities and viscosities fitted by the least-squares method are summarized in Table 3 and Table 4, respectively. The calculated values from the correlation models are presented as curved lines in Figures 3−5. The well-fitted curved lines suggest that the values from the correlation models are in very good agreement with the experimental. The average absolute deviation (AAD) values are 0.08− 0.18% for density and 1.52−2.47% for viscosity, respectively.

1 n

n

∑ i=1

ρiexp − ρi mod ρiexp

100

Physical Solubility of N2O and CO2. To validate the solubility method, the solubility of N2O in water was measured in the experimental apparatus and compared with the data from literature.23,27,28 The results are given in Figure 6 and Supporting Information Table S3. It can be observed that the experimental data in this study give a reasonable agreement within 3% relative error in the temperature range investigated. The solubility data of N2O in aqueous solutions of LysK, HisK, and ArgK with temperatures from 293 to 323 K are given 2394



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Table 4. Fitting Parameters of Empirical Equationa for Viscosity of Aqueous Potassium Solution of Amino Acids concn range Potassium salt of amino acid arginine lysine histidine a

mol·L

−1

0.25 to 1.0 0.25 to 2.5 0.25 to 2.0

k1·103

k2·10−3

k3

k4

mPa·s

J·mol−1

L·mol−1

L·mol−1

R2

AAD, %b

2.720 2.110 2.510

14.154 15.050 14.406

0.1546 0.1371 0.1078

−0.2314 −0.2756 −0.1186

0.9984 0.9985 0.9985

1.52 2.47 1.80

Empirical equation for viscosity:

⎡ k exp(k 3C) ⎤ η = k1 exp⎢ 2 ⎥ exp(k4C) ⎣ ⎦ RT b

Average absolute deviation:

AAD% =

1 n

n

∑ i=1

ηiexp − ηi mod ηiexp

100

Figure 4. Density (a) and viscosity (b) of aqueous HisK solutions at different temperatures and concentrations. Lines: calculated from the models (eqs 9 and 10).

Figure 5. Density (a) and viscosity (b) of aqueous ArgK solutions at different temperatures and concentrations. Lines: calculated from the models (eqs 9 and 10).

in Supporting Information Tables S4−S6 and Table 5. The Henry’s constants of N2O in solutions increase with the increasing AAS concentrations and temperatures, which suggests the solubility of N2O decreases probably due to the typical salting-out effect. According to the Weisenberger and Schumpe model, the anion specific parameters (hAA−) were obtained. The values of anion specific parameter for Lys− (hLys−), His− (hHis−) and Arg− (hArg−) from the model were fitted for different

concentrations at constant temperatures, presented in Table 6. The related Sechenov constants were also estimated and listed in Table 6. A value of 0.1549 for hArg− at 298 K was obtained from the solubility data of N2O in ArgK concentrations from 0.26 to 1.16 mol·kg−1, which is about 6% higher than the reported (hArg− = 0.1452 at 298 K).3,5 It should be noted that the temperature range for N2O gas specific parameter (hg) in this study is outside the original reported range (from 273 to 313 K), 2395



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and the literature value was determined only at 0.5 M ArgK and 298 K. The anion specific parameters are quite different for different amino acids. The values of hLys− and hHis− are 0.8398 and 0.05493 at 298 K, respectively. At a constant temperature, the hAA− in the aqueous AAS solutions varies as follows: hArg− > hLys−> hHis−. It should be noted that the values of hAA− in this work decrease with the increasing temperature. This phenomenon was also observed for other amino acids such as threonate and prolinate in the literature.12,13 The detailed information can be found in the Supporting Information, Table S7. The obtained data for hLys−, hHis−, and hArg− as a function of temperature are presented in Figure 7 alongside with hAA− for threonate, prolinate, and taurate. The ion specific parameter of taurate is the only temperature-independence reported by Kumar et al. (2001).6 However, for hGly− , it generally increases up to 0.0417 from 293 to 303 K and then decreases to 0.0409

Figure 6. Solubility of N2O into water at temperatures of 293−333 K.

Table 5. Henry Constants of N2O in Aqueous Potassium Solutions of Amino Acids: Lysine, Histidine, and Arginine mb mol·kg

T/K −1

293.35

298.45

303.35

308.35

313.35

318.35

323.35

328.35

6990 7590 8271 8755 9627 10750

7580 8225 8923 9440 10199 11317

8170 8831 9545 10065 10812 11898

6974 7851 9956

7537 8480 9475 10648

7079 7982 8550 9689

7670 8583 9115 10285

HN2O,AAS,a kPa·m3·kmol−1 0.249 0.540 0.841 1.155 1.908 2.638

a

0.527 1.135 1.859 2.645

4068

0.263 0.541 0.842 1.154

4112 4838 5310 6155

4488 5061 5574 6056 6990 8040

5128 5672 6209 6687 7650 8792

4622 5449 6387 7386

5184 6064 7010 8031

4686 5441 5949 6781

5285 6097 6641 7520

Potassium of Lysine 5745 6362 6329 6973 6897 7573 7371 8088 8319 8964 9446 10065 Potassium of Histidine 5783 6379 6669 7262 7663 8295 8679 9345 Potassium of Arginine 5891 6486 6742 7358 7254 7904 8267 8993

9071 11242

The standard uncertainties u are u(T) = 0.1 K, u(m) = 0.005 mol·kg−1, ur(H) = 3%. bm is the molality of AAS in the water solvent.

Table 6. Sechenov Constants and Ion Specific Parameters of Schumpe Model for the Solubility of N2O and CO2 in AAS solutions T potassium salt of amino acid lysine

histidine

arginine

a

hN2Oa

hK+a

hAA−

KCO2

0.0840 0.0765 0.0615 0.0465 0.0549 0.0490 0.0372 0.0254 0.1671 0.1549 0.1426 0.1181 0.0936

0.1419 0.1310 0.1092 0.0875 0.1128 0.1035 0.0850 0.0664 0.2284 0.2128 0.1971 0.1659 0.1346

m3 kmol−1

K 298 303 313 323 298 303 313 323 293 298 303 313 323

hCO2a

−0.0084 −0.0108 −0.0156 −0.0204 −0.0084 −0.0108 −0.0156 −0.0204 −0.0060 −0.0084 −0.0108 −0.0156 −0.0204

0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922 0.0922

−0.0171 −0.0188 −0.0222 −0.0256 −0.0171 −0.0188 −0.0222 −0.0256 −0.0155 −0.0171 −0.0188 −0.0222 −0.0256

Values taken from Weisenberger and Schumpe (1996). 2396



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at 313 K (see Table S7).7 The clear temperature-dependent anion specific parameters in this study were fitted to be a linear function of the temperature, which is similar to gas specific parameter expression, as hLys− = 8.375 × 10−2 − 1.50 × 10−3 × (T − 298.15)

hHis− = 5.475 × 10−2 − 1.18 × 10−3 × (T − 298.15) (12)

hArg − = 0.1545 − 2.45 × 10−3 × (T − 298.15)

(11)

(13)

As can be seen in Figure 8a−d, the correlated anion specific parameters used in the Weisenberger and Schumpe model are proven to be well suited to represent the values over the investigated AAS concentrations and temperature range. The prediction of physical solubility of N2O from the Schumpe model is generally within 2.5% AAD in a parity plot (Figure 8d). The Sechenov constants of CO2 in the aqueous AAS solutions was also estimated and presented in Table 6. Estimated physical solubility of CO2 in the solutions of LysK, Hisk, and ArgK are presented in Table S8. On the basis of eq 7, the Henry’s constants of CO2 in ArgK solutions are greater than those in HisK solutions at the same concentration and temperature. Therefore, the physical solubilities of CO2 in the aqueous AAS solutions vary as follows: ArgK < LysK < HisK.

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CONCLUSION The physicochemical properties of aqueous LysK, HisK, and ArgK solutions were measured at temperatures up to 353 K and concentrations up to 3.6 mol·kg−1. The values from the empirical models are in good agreement with the experimental data with 0.08−0.18% AAD for density and 1.52−2.47% AAD

Figure 7. Anion specific parameters for different amino acids as a function of temperature.

Figure 8. Physical solubility of N2O in the solutions of LysK (a), Hisk (b), ArgK(c). (d) Parity plot between the experimental and the predicted. Dot lines (a, b, c): Estimated data from the Schumpe model with correlated anion specific parameters hAA-. 2397



Article

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for viscosity, respectively. The physical solubilities of N2O in aqueous AAS solutions were measured at temperatures from (293 to 328) K. Temperature-dependent ion parameters hLys−, hHis−, and hArg− were proposed and reliable to estimate the Henry’s constants of CO2 by the Weisenberger and Schumpe model. The physical solubilities of CO2 in their solutions vary as follows: ArgK < LysK < HisK. These correlations proposed in this work could be useful for kinetic study and process evaluation utilizing the AAS systems investigated.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00013. Cation, anion, and gas specific parameters; solubility of N2O in water and aqueous solutions of the studied salts (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86 311 88632183. Fax: +86 311 88632183. Funding

The authors acknowledge National Natural Science Foundation of China (No.21206029), Hebei Provincial Natural Science Foundation for Distinguished Young Scholars of China (B2015208067), and Hebei Provincial Science and Technology Research Project of College and University (QN2015070) for financial support. Notes

The authors declare no competing financial interest.

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Physicochemical Properties of Aqueous Potassium Salts of Basic

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