Physical Properties of a Complex Solution of (Potassium Citrate +

Article pubs.acs.org/jced

Physical Properties of a Complex Solution of (Potassium Citrate + Piperazine) as a CO2 Capture Agent Jian-Gang Lu,* Ai-Chun Hua, Zheng-Wen Xu, Ling Cheng, Feng-Ying Lin, and Fan Fan Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China ABSTRACT: Piperazine (PZ) as an additive was added into a solution of potassium citrate (PC) to form a novel complex solution of the aqueous (PC + PZ) system. Research for the physical properties, density, viscosity, and surface tension, of the aqueous (PC + PZ) system was carried out. Densities and viscosities of the aqueous (PC + PZ) system have been determined at (293.15, 303.15, 313.15, and 323.15) K, and surface tensions of the aqueous (PC + PZ) system have been measured at 293.15 K. Correlations for the physical properties were fitted using the method of mathematics. Predictions of the physical properties of the aqueous (PC + PZ) system were conducted. Performances were compared and discussed between the (PC + PZ) system and other complex systems such as the (PG (glycinate) + PZ) system. Results show that the densities and viscosities of the aqueous (PC + PZ) system decrease with the increase of temperature and PZ mole fraction in the system. The surface tensions of the studied system decrease as the PZ mole fraction in the system increases at 293.15 K. The physical properties of the aqueous (PC + PZ) system are basically similar to that of the aqueous (PG + PZ) system. As opposed to the (PG + PZ) system, the viscosity of the aqueous (PC + PZ) system decreases, while the viscosity of the aqueous (PG + PZ) system increases as the PZ mole fraction in the system increases. The surface tension of the aqueous (PG + PZ) system decreases linearly, while the surface tension of the aqueous (PC + PZ) system is nonlinear with the increase of PZ mole fraction in the system. The prediction values from correlations for the physical properties are in good agreement with the experimental values. The correlations for the physical properties of the aqueous (PC + PZ) system can offer additional data.

■

INTRODUCTION The Climate Change Report of the United Nations Framework Convention on Climate Change (UNFCCC) pointed out that the global average temperature may rise by about (1.4 to 5.8) °C by the year 2100 from various estimations of climate models.1 One of the major causes for the climate change is the greenhouse effect. CO2 as a primary greenhouse gas, currently responsible for over 60 % of the enhanced greenhouse effect, is regarded as one of the contributions to the climate change such as global warming.2,3 The emission of bulk CO2 from the combustion of fossil fuels has resulted in an increase in atmospheric concentration of CO2.3,4 It has turned to be a worldwide issue to reduce CO2 emission and decrease CO2 concentration in the atmosphere. Absorption is one of the most efficient processes for the removal of bulk CO2 from industrial gas streams. Aqueous amines are generally the most favorable absorbents, for instance, monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), triethanolamine (TEA), N-methyldiethanolamine (MDEA), and 2-amino-2methyl-1-propanol (AMP).5−7 Although the amine solutions have been widely used in industries, the existing problems are amine solvent degradation and loss due to the sides of irreversible reactions and evaporative volatilization.8 Some aqueous organic acid salts as the CO2 absorbents, for example, amino acid salts, amino sulfonic acid salts, and citrate, caused researchers' concern over the recent years. These organic acid salts possess nontoxic, odor-free, nonflammable, thermally stable, environmentally friendly, able to be regenerated, and © 2012 American Chemical Society

commercially available properties and especially have low vapor pressure.8−10 The aqueous citrates, for example, potassium and sodium citrate, have stable physical properties and comparatively a good solubility in water. Citric acid, a polyhydric acid, is a biochemical reagent, and its salt can offer a higher absorption capacity for CO2 capture.11 Citrate as a promising CO2 absorbent should be used in industry. Piperazine (PZ) as an efficient amine activator has been an important component in amine-based aqueous solutions for CO2 absorption.12 It has a particular structure and unique characters, a symmetrical diamino and cyclic structure. The reaction of PZ with CO2 presents high activity.13 PZ is more effective than conventional accelerators.14 Consequently, the novel absorbents of the (citrates + PZ) system are promising for CO2 absorption. They could become efficient CO2 absorbents and simultaneously almost have no vapor pressure, and thus solvent loss should be decreased. The combination of (PC + PZ) could maintain a high absorption rate and decrease generation energy consumption. Physical properties such as density, viscosity, and surface tension of the absorbent can influence the mass transfer in the absorption and regeneration process.15 Therefore, data of the physical property of citrates and their complex system are very important for the design, simulation, and operation of gas absorption. Received: March 15, 2012 Accepted: June 5, 2012 Published: June 15, 2012 2044

dx.doi.org/10.1021/je3003354 | J. Chem. Eng. Data 2012, 57, 2044−2052

Journal of Chemical & Engineering Data

Article

Table 1. Concentration Settings of the Aqueous (PC + PZ) System Cov

a

mol·kg−1

mol·L−1 a

0.45 0.83 1.16 1.48

0.5 1.0 1.5 2.0

xPC/xPZ/mol·mol−1 0.5:0.0 1.0:0.0 1.5:0.0 2.0:0.0

0.4:0.1 0.9:0.1 1.4:0.1 1.8:0.2

0.3:0.2 0.8:0.2 1.3:0.2 1.6:0.4

0.7:0.3 1.2:0.3 1.4:0.6

0.6:0.4 1.1:0.4 1.2:0.8

0.5:0.5 1.0:0.5 1.0:1.0

0.9:0.6

0.8:0.7

At 293.15 K for molarity.

viscosities was measured with an accurate ± 0.01 s stop-watch. The experimental uncertainties for density, viscosity, and surface tension were estimated to be ± 0.05 %, ± 0.5 %, and 1.7 %, respectively. The experimental details including the apparatus and procedures can be found in our previous work.25 Validation. Validations for experimental procedures and data of the measurements were carried out using MDEA aqueous solutions. Errors of results were evaluated by the average absolute deviation (AAD) between experimental and calculated values. Validation details can be also found in our previous work.25 The AADs of the measurements are 0.07 % for densities, 0.48 % for viscosities, and 0.51 % for surface tensions. The measured data in this work are in good agreement with the data of literature.

Physical properties of aqueous amines have been investigated widely.16−19 Experimental data of the density, viscosity, and surface tension of aqueous PZ,20 aqueous (AMP + PZ),21,22 and (MDEA + PZ)22 can be obtained from open literature. The physical properties of aqueous amino acid salts and their blends are also available in published literature.23−25 However, the physical properties of (citrates + PZ) system are scarce in existing literature. Physical properties, density, viscosity and surface tension, of (potassium citrate (PC) + PZ) system are characterized by experimental research in this work. The density and viscosity of the studied system were determined in the range of (293.15 to 323.15) K, and the surface tension was measured at 293.15 K. The performance of (PC + PZ) system was compared with other complex systems such as the (PG + PZ) system. The density and viscosity as a function of temperature or concentration and surface tension as a function of concentration were correlated. A prediction for the physical properties was carried out and compared with experimental values.

■

■

RESULTS AND DISCUSSION Density. The densities for the aqueous (PC + PZ) system were measured at (293.15, 303.15, 313.15, and 323.15) K. Due to limits of solubility of potassium citrate in water, the concentration of the complex solution cannot be too high. Settings of concentration for series of the aqueous (PC + PZ) system are given in Table 1. Cov is the overall concentration of the complex solution of (PC + PZ) and presented in mol·kg−1 and mol·L−1, respectively. xPG and xPZ are the mole fractions of PG and PZ in the complex solution, respectively. Results of the measured densities are given in Table 2. The results indicate that the densities of aqueous (PC + PZ) system increase with an increase of overall concentration of the complex solution. The densities of aqueous (PC + PZ) system decrease as the temperature and mole fraction of PZ in the complex solution increase. Because the molecular weight of PZ is smaller than that of PC, the densities of aqueous (PC + PZ) system decrease with an increase of mole fraction of PZ in the complex solution. The density results follow general law and are consistent with other authors.22,23 Compared with the aqueous (PG + PZ) system, the densities of aqueous (PC + PZ) system are larger than that of the (PG + PZ) system under the same conditions of temperature, total concentration, and mole fraction.25 For example, at 303.15 K, Cov = 0.83 mol·kg−1 (i.e., 1.0 mol·L−1), and xPC/xPZ = 0.8:0.2, the densities of the aqueous (PC + PZ) and (PG + PZ) systems are 1.1656 and 1.0520 (g·cm−3), respectively.25 A major cause for this is that the molecular weight of PC is larger than that of PG. It is important to note that, otherwise, as the total concentration of the complex solution reached 1.48 mol·kg−1 (i.e., 2.0 mol·L−1) at xPC/xPZ = 1.0/1.0 and a temperature less than 313 K, citrate crystals appeared in the solution. At this time the solution was the saturated solution of potassium citrate. It shows that PZ in the complex solution could affect the solubility of citrate. Therefore, the total concentration of the complex solution needs to take into account both the solubility of citrate and the effect of PZ in the complex solution.

EXPERIMENTAL SECTION

Materials. All reagents were reagent grade and commercially available. Their purities were the following: citric acid monohydrate, ≥ 99.5 % (Nanjing Chemical Reagent Co., Ltd., China); piperazine, ≥ 99.5 % (Shanghai Ling Feng Chemical Reagent Co., Ltd., China); potassium hydroxide (KOH), 82 % (Shanghai Ling Feng Chemical Reagent Co., Ltd., China); Nmethyldiethanolamine (MDEA), ≥ 99.0 % (Feixiang Chemical Industry Co., Ltd., Suzhou, China). Potassium citrate aqueous solution was prepared with doubly distilled and deionized water that was degassed by boiling. The 1 M citric acid was neutralized with 3 M quantities of KOH to form the potassium citrate. Metered citric acid monohydrate was dissolved into the water to form a citrate acid solution, and then KOH tripled molar quantities of metered citric acid were added into the solution gradually until the end of reaction to form the potassium citrate solution. The potassium citrate solution was transferred into a 50 mL standard flask, and then deionized water was added into the flask to the mark. PZ as a component was added into the potassium citrate solution to form the complex solution of the (PC + PZ) system. Reagent weights were quantified with an analytical balance (FA2004, Shanghai Shang Tian Precision Instrument Co., Ltd., China) with a precision and accuracy of ± 0.0001 g. Density, Viscosity, and Surface Tension Measurements. The density (ρ, g·cm−3), viscosity (η, mPa·s), and surface tension (γ, mN·m−1) of the (PC + PZ) system were measured with a Gay−Lussac pycnometer (5 mL), a suspended level Ubbelohde viscometer, and a surface tension meter, respectively. The measurements were performed in a constant temperature water bath, in which the temperature could be controlled within ± 0.001 K precision. The flow time for 2045



Article

Table 2. Densities (g·cm−3) of the (PC + PZ + H2O) System from (293.15 to 323.15) K ρ/g·cm−3

xPC/xPZ mol·mol

−1

0.5:0.0 0.4:0.1 0.3:0.2 1.0:0.0 0.9:0.1 0.8:0.2 0.7:0.3 0.6:0.4 0.5:0.5 1.5:0.0 1.4:0.1 1.3:0.2 1.2:0.3 1.1:0.4 1.0:0.5 0.9:0.6 0.8:0.7 2.0:0.0 1.8:0.2 1.6:0.4 1.4:0.6 1.2:0.8 1.0:1.0

decrease with the increase of temperature and PZ mole fraction in the aqueous (PC + PZ) system and rapidly increase as total concentrations of the aqueous (PC + PZ) system increase. The viscosity, as expected, usually decreases with an increase of temperature. The results of viscosity with regard to temperature in this work conform to general law. However, the results of viscosity regarding PZ mole fraction in the system in this work are different from the aqueous (PG + PZ) system.25 In contrast to the results in this work, the viscosity of the aqueous (PG + PZ) system increased with an increase of PZ mole fraction in the complex solution. It demonstrates that, although potassium citrate is a salt of organic acid, the inorganic property of the citrate is stronger than that of glycinate. As the total concentration of the complex solution was 1.48 mol·kg−1 (i.e., 2.0 mol·L−1) at xPC/xPZ = 1.0:1.0 and the temperature less than 313 K, no viscosity data were measured due to citrate crystallized out in the solution. Surface Tension. The measurement of surface tensions for the aqueous (PC + PZ) system was performed at 293.15 K. Results of the surface tensions are shown in Table 4. It can be

293.15 K

303.15 K

313.15 K

323.15 K

1.1177 1.1015 1.0821 1.2011 1.1874 1.1691 1.1552 1.1368 1.1223 1.2946 1.2757 1.2666 1.2483 1.2273 1.2091 1.1809 1.1580 1.3557 1.3347 1.2945 1.2677 1.2251

1.1129 1.0979 1.0769 1.1992 1.1836 1.1656 1.1503 1.1300 1.1116 1.2850 1.2676 1.2579 1.2408 1.2205 1.1972 1.1741 1.1513 1.3432 1.3218 1.2837 1.2556 1.2193

1.1101 1.0931 1.0694 1.1974 1.1780 1.1624 1.1473 1.1265 1.1059 1.2756 1.2612 1.2496 1.2318 1.2135 1.1852 1.1683 1.1421 1.3319 1.3121 1.2761 1.2503 1.2065 1.1863

1.1080 1.0903 1.0645 1.1940 1.1739 1.1592 1.1421 1.1229 1.0983 1.2707 1.2542 1.2419 1.2213 1.2061 1.1767 1.1626 1.1350 1.3278 1.2972 1.2683 1.2353 1.1995 1.1762

Table 4. Surface Tensions (mN·m−1) of the (PC + PZ + H2O) System at 293.15 K xPC/xPZ −1

mol·mol

0.5:0.0 0.4:0.1 0.3:0.2 1.0:0.0 0.9:0.1 0.8:0.2 0.7:0.3 0.6:0.4 0.5:0.5 1.5:0.0 1.4:0.1 1.3:0.2 1.2:0.3 1.1:0.4 1.0:0.5 0.9:0.6 0.8:0.7 2.0:0.0 1.8:0.2 1.6:0.4 1.4:0.6 1.2:0.8 1.0:1.0

Viscosity. Viscosity measurements of the aqueous (PC + PZ) system were carried out at (293.15, 303.15, 313.15, and 323.15) K. The results of viscosity are shown in Table 3. It can be found that the viscosities of the aqueous (PC + PZ) system Table 3. Viscosities (mPa·s) of the (PC + PZ + H2O) System from (293.15 to 323.15) K η/mPa·s

xPC/xPZ mol·mol

−1

0.5:0.0 0.4:0.1 0.3:0.2 1.0:0.0 0.9:0.1 0.8:0.2 0.7:0.3 0.6:0.4 0.5:0.5 1.5:0.0 1.4:0.1 1.3:0.2 1.2:0.3 1.1:0.4 1.0:0.5 0.9:0.6 0.8:0.7 2.0:0.0 1.8:0.2 1.6:0.4 1.4:0.6 1.2:0.8 1.0:1.0

293.15 K

303.15 K

313.15 K

323.15 K

1.342 1.294 1.259 1.891 1.796 1.719 1.663 1.615 1.568 2.933 2.750 2.601 2.415 2.295 2.192 2.129 2.088 4.989 3.975 3.317 2.976 2.683

1.050 1.013 0.977 1.448 1.372 1.317 1.284 1.229 1.188 2.205 2.034 1.940 1.815 1.752 1.610 1.590 1.520 3.560 2.889 2.435 2.124 1.928

0.845 0.809 0.780 1.127 1.077 1.039 0.996 0.967 0.934 1.644 1.546 1.480 1.389 1.304 1.231 1.215 1.196 2.597 2.243 1.852 1.575 1.384 1.239

0.695 0.661 0.629 0.925 0.882 0.853 0.814 0.796 0.759 1.291 1.221 1.174 1.104 1.045 0.992 0.985 0.956 1.816 1.642 1.447 1.207 1.113 1.024

γ mN·m−1 71.49 70.51 69.39 75.75 74.80 73.72 72.76 70.72 69.19 79.08 78.34 77.70 76.64 75.41 73.82 71.88 70.32 81.10 79.21 77.72 75.53 72.40

observed that the surface tensions of the aqueous (PC + PZ) system increase with an increase of total concentration of the complex solution and decrease with an increase of PZ mole fraction in the solutions. As a rule, surface tensions of aqueous solutions have a law, ion inorganic > inorganic > ion organic > organic. Surface tensions of organic compounds are the smallest. Citrate is an ion organic compound, and PZ is an organic compound. Therefore, as the PZ mole fraction in the complex solution gets bigger, namely, the PC mole fraction in the complex solution gets smaller, the surface tension of the complex solution decreases at a constant total concentration. The results in this work are identical with that of the (PG + PZ) system and other ones.25,26 It demonstrates that, as an 2046



Article

organic salt and an organic compound are blended into a complex solution such as (PC + PZ) and (PG + PZ), the surface tension of the complex solution depends on the proportion of the organic salt to organic compound. If the fraction of the organic salt in proportion is larger, the surface tension of the complex solution gets larger. Conversely, it gets smaller. Correlation for Prediction of Density. Density data of aqueous (PC + PZ) system in this work are transformed into graphs, expressed in density versus temperature (ρ vs T). Data fittings are also carried out for correlations. Based on a concentration series, these are presented in Figure 1 for

Figure 3. Density of the aqueous (PC + PZ) system (ρ versus T) at Cov = 1.5 mol·L−1: ■, xPC/xPZ = 1.5:0.0; ●, xPC/xPZ = 1.4:0.1; ▲, xPC/ xPZ = 1.3:0.2; ▼, xPC/xPZ = 1.2:0.3; ◀, xPC/xPZ = 1.1:0.4; ▶, xPC/xPZ = 1.0:0.5; ⧫, xPC/xPZ = 0.9:0.6; solid pentagon, xPC/xPZ = 0.8:0.7, solid lines correlated from eq 1.

Figure 1. Density of the aqueous (PC + PZ) system (ρ versus T) at Cov = 0.5 mol·L−1: ■, xPC/xPZ = 0.5:0.0; ●, xPC/xPZ = 0.4:0.1; ▲, xPC/ xPZ = 0.3:0.2, solid lines correlated from eq 1.

Figure 4. Density of the aqueous (PC + PZ) system (ρ versus T) at Cov = 2.0 mol·L−1: ■, xPC/xPZ = 2.0:0.0; ●, xPC/xPZ = 1.8:0.2; ▲, xPC/ xPZ = 1.6:0.4; ▼, xPC/xPZ = 1.4:0.6; ◀, xPC/xPZ = 1.2:0.8, solid lines correlated from eq 1.

system.25 The variation regularity of density of the aqueous (PC + PZ) system is similar to that of the aqueous (PG + PZ) system. A correlation was developed to allow the prediction of density for the aqueous (PC + PZ) system as a function of temperature by means of linear-fitting utilizing the data of Figures 1 to 4. The fitted correlation is the following equation, ρ = a + b·T

(1) −3

where ρ is the density in g·cm , T is the temperature in K, and a and b are fitting parameters. The values of a and b and average absolute deviations (AAD) are expressed in Table 5. The maximal value of AAD is 0.16 % between the prediction and the experimental values, and the average AAD is 0.06 %. The prediction from the correlation eq 1 is in good agreement with the experimental values. To achieve the prediction value of density depended on multifactors, the density data of aqueous (PC + PZ) system are expressed in the form density versus PZ concentration (ρ vs CPZ) and transformed into graphs. Fittings by the method of mathematics are also performed for correlations regarding PZ

Figure 2. Density of the aqueous (PC + PZ) system (ρ versus T) at Cov = 1.0 mol·L−1: ■, xPC/xPZ = 1.0:0.0; ●, xPC/xPZ = 0.9:0.1; ▲, xPC/ xPZ = 0.8:0.2; ▼, xPC/xPZ = 0.7:0.3; ◀, xPC/xPZ = 0.6:0.4; ▶, xPC/xPZ = 0.5:0.5, solid lines correlated from eq 1.

Cov(mol·L−1) = 0.5, Figure 2 for Cov(mol·L−1) = 1.0, Figure 3 for Cov(mol·L−1) = 1.5, and Figure 4 for Cov(mol·L−1) = 2.0, respectively. The results illustrate that the density is in a linear relationship with temperature and decreases as the temperature increases. The observed linear relationship of ρ versus T has already been reported with regard to the aqueous (PG + PZ) 2047



Article

Table 5. Values of a and b Parameters for Equation 1 and Average Absolute Deviation xPC/xPZ mol·mol−1

a

104 b

R2

AAD %

0.5:0.0 0.4:0.1 0.3:0.2 1.0:0.0 0.9:0.1 0.8:0.2 0.7:0.3 0.6:0.4 0.5:0.5 1.5:0.0 1.4:0.1 1.3:0.2 1.2:0.3 1.1:0.4 1.0:0.5 0.9:0.6 0.8:0.7 2.0:0.0 1.8:0.2 1.6:0.4 1.4:0.6 1.2:0.8

1.2105 1.2140 1.2590 1.2691 1.3228 1.2655 1.2824 1.2683 1.3490 1.5314 1.4832 1.5079 1.5129 1.4344 1.52855 1.3585 1.3876 1.6324 1.6930 1.5463 1.5681 1.4887

−3.1900 −3.8400 −6.0300 −2.3100 −4.6100 −3.2900 −4.3300 −4.5200 −7.7700 −8.1100 −7.0900 −8.2400 −9.0000 −7.0600 −10.9000 −6.0700 −7.8200 −9.5000 −12.200 −8.6200 −10.300 −8.9600

0.9458 0.9864 0.9900 0.9613 0.9924 0.9992 0.9923 0.9553 0.9766 0.9712 0.9966 0.9989 0.9917 0.9994 0.9912 0.9917 0.9946 0.9380 0.9910 0.9887 0.9564 0.9687

0.06 0.03 0.04 0.05 0.03 0.01 0.03 0.07 0.08 0.04 0.03 0.02 0.06 0.01 0.07 0.02 0.04 0.16 0.09 0.06 0.13 0.10

Figure 6. Density of the aqueous (PC + PZ) system (ρ versus CPZ) at Cov = 1.0 mol·L−1: ■, 293.15 K; ●, 303.15 K; ▲, 313.15 K; ▼, 323.15 K, solid lines correlated from eq 2.

concentration. Results are shown in Figures 5 to 8 from (293.15 to 323.15) K for Cov(mol·L−1) = 0.5, 1.0, 1.5 and 2.0,



respectively. To express the fittings clearly, the figures are separately described with regards to the four PZ concentrations. The results show that, under a constant total concentration of the complex solution, the density of the complex solution decreases as the amine PZ is added into the citrate solution. Similar to the relation between density and temperature, the density of the complex solution is almost linear with respect to PZ concentration. Similarly, a correlation was developed to obtain the prediction of the density of the aqueous (PC + PZ) system. The correlation uses the following expression, ρ = c + d ·C PZ


where ρ is the density in g·cm−3, CPZ is the PZ concentration in complex solutions in mol·L−1, and c and d are fitting

(2) 2048



Article

parameters. The values of c and d and AAD are given in Table 6. The average AAD is 0.64 % between the prediction and the Table 6. Values of c and d Parameters for Equation 2 and Average Absolute Deviation T/K

c

d

R2

AAD %

0.9946 0.9816 0.9821 0.9772

1.62 1.64 1.86 2.00

0.9982 0.9965 0.9956 0.9925

0.08 0.10 0.13 0.20

0.9832 0.9843 0.9831 0.9877

0.43 0.39 0.38 0.35

0.9854 0.9914 0.9882 0.9974

0.35 0.24 0.35 0.14

−1

293.15 303.15 313.15 323.15

1.1182 1.1139 1.1112 1.1094

293.15 303.15 313.15 323.15

1.2020 1.2007 1.1986 1.1947

293.15 303.15 313.15 323.15

1.3002 1.2912 1.2830 1.2760

293.15 303.15 313.15 323.15

1.3612 1.3475 1.3370 1.3282

Cov = 0.45 mol·kg −0.1780 −0.1800 −0.2035 −0.2175 Cov = 0.83 mol·kg−1 −0.1599 −0.1752 −0.1817 −0.1853 Cov = 1.16 mol·kg−1 −0.1933 −0.1912 −0.1917 −0.1927 Cov = 1.48 mol·kg−1 −0.1641 −0.1570 −0.15294 −0.15487

Figure 10. Viscosity of aqueous (PC + PZ) system (η versus T) at Cov = 1.0 mol·L−1: ■, xPC/xPZ = 1.0:0.0; ●, xPC/xPZ = 0.9:0.1; ▲, xPC/xPZ = 0.8:0.2; ▼, xPC/xPZ = 0.7:0.3; ◀, xPC/xPZ = 0.6:0.4; ▶, xPC/xPZ = 0.5:0.5, solid lines correlated from eq 3.

experimental values. R2 values of linear fitting are close to 1, and good linear relations are obtained. The prediction of the density for eq 2 is consistent with the experimental data. Correlation for Prediction of Viscosity. The process for viscosity data was the same as that of density data for correlation and prediction. The experimental data are expressed in the forms of viscosity versus temperature (η vs T) and viscosity versus PZ concentrations (η vs CPZ), respectively. The experimental data are transformed into graphs, and fittings are also conducted by the mathematical method. All results are separately given in Figures 9 to 12 at Cov (mol·L−1) = 0.5, 10, 1.5, and 2.0 and Figures 13 to 16 at temperatures ranging from (293.15 to 323.15) K, respectively. The results show that the change of viscosity for the aqueous (PC + PZ) system is smaller at high temperatures than that at low temperatures. The change

Figure 11. Viscosity of aqueous (PC + PZ) system (η versus T) at Cov = 1.5 mol·L−1: ■, xPC/xPZ = 1.5:0.0; ●, xPC/xPZ = 1.4:0.1; ▲, xPC/xPZ = 1.3:0.2; ▼, xPC/xPZ = 1.2:0.3; ◀, xPC/xPZ = 1.1:0.4; ▶, xPC/xPZ = 1.0:0.5; ⧫, xPC/xPZ = 0.9:0.6, regular pentagon, xPC/xPZ = 0.8:0.7, solid lines correlated from eq 3.

Figure 12. Viscosity of aqueous (PC + PZ) system (η versus T) at Cov = 2.0 mol·L−1: ■, xPC/xPZ = 2.0:0.0; ●, xPC/xPZ = 1.8:0.2; ▲, xPC/xPZ = 1.6:0.4; ▼, xPC/xPZ = 1.4:0.6; ◀, xPC/xPZ = 1.2:0.8, solid lines correlated from eq 3.

Figure 9. Viscosity of the aqueous (PC + PZ) system (η versus T) at Cov = 0.5 mol·L−1: ■, xPC/xPZ = 0.5:0.0; ●, xPC/xPZ = 0.4:0.1; ▲, xPC/ xPZ = 0.3:0.2, solid lines correlated from eq 3. 2049



Article

Figure 16. Viscosity of aqueous (PC + PZ) system (η versus CPZ) at Cov = 2.0 mol·L−1: ■, 293.15 K; ●, 303.15 K; ▲, 313.15 K; ▼, 323.15 K, solid lines correlated from eq 4.


PZ concentration are basically similar to that with regard to temperature. The aqueous (PC + PZ) system is similar to the aqueous (PG + PZ) system concerning viscosity;25 both follow identical laws of viscosity. Correlations were developed to allow the prediction of the viscosity for the aqueous (PC + PZ) system by means of polynomial fitting as functions of temperature and PZ concentration, respectively. The regression equations of the viscosity data use the following expressions, η = k + m·T + n·T 2

(3)

η = l + p ·C PZ + q·C PZ 2

(4)

where η is the viscosity in mPa·s, and k, m, n, l, p and q are parameters. The values of the parameters and AAD are listed in Tables 7 and 8, respectively. The AADs for the viscosities are Table 7. Values of the k, m, and n Parameters in Equation 3 and Average Absolute Deviation


xPC/xPZ


of viscosity of the aqueous (PC + PZ) system is larger at low PZ concentrations than that at high PZ concentrations. The changes of the viscosity of the complex solutions with regard to 2050

mol·mol−1

k

m

104n

R2

AAD %

0.5:0.0 0.4:0.1 0.3:0.2 1.0:0.0 0.9:0.1 0.8:0.2 0.7:0.3 0.6:0.4 0.5:0.5 1.5:0.0 1.4:0.1 1.3:0.2 1.2:0.3 1.1:0.4 1.0:0.5 0.9:0.6 0.8:0.7 2.0:0.0 1.8:0.2 1.6:0.4 1.4:0.6 1.2:0.8

41.2610 38.9561 38.3996 68.4030 64.9312 61.3034 56.6298 60.5022 57.9749 107.8309 110.2241 100.5710 89.7928 81.9590 95.0855 81.7934 78.9776 189.1677 117.8537 109.7757 134.7618 132.7132

−0.2402 −0.2260 −0.2227 −0.4035 −0.3832 −0.3616 −0.3319 −0.3584 −0.3427 −0.6326 −0.6532 −0.5944 −0.5289 −0.4802 −0.5683 −0.4936 −0.4660 −1.1032 −0.6706 −0.6398 −0.8043 −0.7983

3.5500 3.3250 3.2750 6.0250 5.7250 5.4000 4.9250 5.3750 5.1250 9.3750 9.7750 8.8750 7.8750 7.1100 8.5750 7.2250 6.9500 16.2000 9.6300 9.4250 12.1000 12.1000

0.9994 0.9997 0.9990 1 0.9997 0.9996 0.9999 0.9996 0.9991 0.9998 0.9995 0.9997 0.9998 0.9986 0.9993 0.9997 1 0.9978 0.9996 1 0.9987 0.9996

0.33 0.23 0.44 0.03 0.25 0.29 0.14 0.31 0.47 0.22 0.38 0.27 0.20 0.64 0.44 0.31 0.07 0.98 0.38 0.11 0.69 0.39



Article

of the surface tension of the aqueous (PC + PZ) system as a function of PZ concentration. The correlation is the following regression equation

Table 8. Values of the l, p, and q Parameters in Equation 4 and Average Absolute Deviation T/K

l

293.15 303.15 313.15 323.15

1.3420 1.0500 0.8450 0.6950

293.15 303.15 313.15 323.15

1.8880 1.4426 1.1261 0.9231

293.15 303.15 313.15 323.15

2.9447 2.2005 1.6534 1.2969

293.15 303.15 313.15 323.15

4.9615 3.5749 2.6119 1.8296

p Cov = 0.45 −0.5450 −0.3750 −0.395 −0.3500 Cov = 0.83 −0.9504 −0.6597 −0.4903 −0.3881 Cov = 1.16 −2.1079 −1.5678 −1.1040 −0.7800 Cov = 1.48 −5.3184 −3.4831 −2.1756 −1.0848

q

R2

AAD %

γ = u + v ·C PZ + w·C PC 2

−1

mol·kg 0.6500 0.0500 0.3500 0.1000 mol·kg−1 0.6357 0.3125 0.2161 0.1321 mol·kg−1 1.2482 0.9440 0.6208 0.4119 mol·kg−1 3.1411 1.7732 0.7857 0.2054

0.9979 0.9903 0.9984 0.9908

0.22 0.42 0.19 0.45

0.9974 0.9873 0.9889 0.9899

0.39 0.89 0.84 0.74

0.9939 0.9969 0.9960 0.9799

1.23 0.65 0.91 1.77

(5) −1

0 0 0 0

where γ is the surface tension in mN·m , and u, v, and w are parameters. The values of the u, v, and w parameters and AAD are given in Table 9. Prediction values from eq 5 for the surface Table 9. Values of u, v, and w Parameters for Equation 5 and Average Absolute Deviation Cov mol·kg−1

u

v

w

R2

AAD %

0.45 0.83 1.16 1.48

71.4900 75.7079 79.0529 80.9537

−6.3000 −7.1250 −4.8482 −5.9971

−21.0000 −12.0357 −11.1845 −5.6786

0.9926 0.9979 0.9916

0 0.17 0.12 0.23

tension of the aqueous (PC + PZ) system are with a maximal AAD of 0.23 %, which is completely acceptable. The correlation of eq 5 can be used to predict surface tension of the aqueous (PC + PZ) system over the whole concentration range at 293.15 K.

0.35 % for eq 3 and 0.725 % for eq 4, respectively. The deviation values for viscosities are small and acceptable. With a few individual exceptions, R2 values of fitting are more than 0.999. Good fitting relations are obtained. The predictions from eqs 3 and 4 are in good agreement with the experimental values. Correlation eqs 3 and 4 can be completely used to predict the viscosity of the aqueous (PC + PZ) system. Correlation for Prediction of Surface Tension. The measured data of surface tension are similarly expressed in the form surface tension versus PZ concentration (γ vs CPZ). Fittings are also carried out for correlation. Results are shown in Figure 17. It can be found that, at the given temperature, the surface tensions of the aqueous (PC + PZ) system nonlinearly decrease with the increase of the PZ concentration. It is different from the aqueous (PG + PZ) system for which surface tensions linearly decreased as the PZ concentration increased.25 Similarly, a correlation is also developed to allow the prediction

■

CONCLUSIONS Physical properties, density, viscosity, and surface tension, of the aqueous (PC + PZ) system have been measured. Correlations by the method of mathematical fitting were developed for the prediction of the physical properties of the aqueous (PC + PZ) system. The densities of the system increased with an increase of overall concentration of the solution and decreased with an increase of temperature or mole fraction of PZ in the solutions. The viscosities of the solutions decreased as the temperature or PZ mole fraction in the solutions increased. The surface tensions of the solutions increased with an increase of total concentration of the solutions and decreased with an increase of PZ mole fraction in the solutions at 293.15 K. Five correlations have been obtained in this work. The prediction values from the correlations for density, viscosity, and surface tension were in good agreement with the experimental values. The average deviations were small and acceptable. Correlations can be used as theory calculation and engineering designs.

■

AUTHOR INFORMATION

Corresponding Author

*Telephone: 86-25-58731090. Fax: 86-25-58731089. E-mail: [email protected]. Funding

This work was supported by the National Natural Science Foundation of China (Grant No. 21107050) and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. Notes

The authors declare no competing financial interest.

■

Figure 17. Surface tension γ of the (PC + PZ + H2O) system as a function of PZ concentration: ■, Cov = 0.5 mol·L−1; ●, Cov = 1.0 mol·L−1; ▲, Cov = 1.5 mol·L−1; ▼, Cov = 2.0 mol·L−1, solid lines correlated from eq 5.

ACKNOWLEDGMENTS We acknowledge Haiou Zhang and Jun Gao for their assistance to this work for the determination of surface tension. 2051



■

Article

aqueous amino acid salt solutions. J. Chem. Eng. Data 2001, 46, 1357− 1361. (24) Matubayasi, N.; Namihira, J.; Yoshida, M. Surface properties of aqueous amino acid solutions I. Surface tension of hydrochloric acid glycine and glycine sodium hydroxide systems. Colloid Interface Sci. 2003, 267, 144−150. (25) Lu, J.-G.; Fan, F.; Liu, C.; Zhang, H.; Ji, Y.; Chen, M.-d. Density, Viscosity, and Surface Tension of Aqueous Solutions of Potassium Glycinate + Piperazine in the Range of (288.15 to 323.15) K. J. Chem. Eng. Data 2011, 56 (5), 2706−2709. (26) Alvarez, E.; Cancela, A.; Maceieras, R. Surface tension of aqueous binary mixtures of 1-amino-2-propanol and 3-amino-1propanol, and aqueous ternary mixtures of these amines with diethanolamine, triethanolamine, and 2-amino-2-methyl-1-propanol from (298.15 to 323.15) K. J. Chem. Eng. Data 2003, 48, 32−35.

REFERENCES

(1) Williams, M. Climate change: information kit; United Nations Environment Programme (UNEP) and the United Nations Framework Convention on Climate Change (UNFCCC): Geneva, 2002. (2) Herzog, H.; Eliasson, B.; Kaarstad, O. Capturing greenhouse gases. Sci. Am. 2000, 182 (2), 72−79. (3) Wuebbles, D. J.; Jain, A. K. Concerns about climate change and the role of fossil fuel use. Fuel Process. Technol. 2001, 71, 99−119. (4) Intergovernmental Panel on Climate Change (IPCC) 2007, United Nations. http://www.ipcc-data.org/ddc_co2.html. (5) Rochelle, G. T. Amine Scrubbing of CO2 Capture. Science 2009, 325, 1652−1654. (6) Mandal, B. P.; Guha, M.; Biswas, A. K.; Bandyopadhyay, S. S. Removal of carbon dioxide by absorption in mixed amines: modeling of absorption in aqueous MDEA/MEA and AMP/MEA solutions. Chem. Eng. Sci. 2001, 56, 6217−6224. (7) Hoff, K. A.; Juliussen, O.; Falk-Pedersen, O.; Svendsen, H. F. Modeling and Experimental Study of Carbon Dioxide Absorption in Aqueous Alkanolamine Solutions Using a Membrane Contactor. Ind. Eng. Chem. Res. 2004, 43, 4908−4921. (8) Jamal, A.; Meisen, A. Kinetics of CO2 induced degradation of aqueous diethanolamine. Chem. Eng. Sci. 2001, 56, 6743−6760. (9) Kumar, P. S.; Hogendoorn, J. A.; Feron, P. H. M.; Versteeg, G. F. New absorption liquids for the removal of CO2 from dilute gas streams using membrane contactors. Chem. Eng. Sci. 2002, 57, 1639−1651. (10) Chakravarty, T.; Phukan, U. K.; Weiland, R. H. Reaction of acid gases with mixtures of amines. Chem. Eng. Prog. 1985, 81, 32−36. (11) Xue, J.-Q.; Wang, K.-F.; Yang, J.-J.; Ju, K.-J.; Wang, X.; Wang, Y.L. Mechanism of flue gas desulfurization with citrate solution. J. Chem. Ind. Eng. 2008, 59 (4), 1022−1027. (12) Lu, J.-G.; Wang, L.-J.; Sun, X.-Y.; Li, J.-S.; Liu, X.-D. Absorption of CO2 into aqueous solutions of methyldiethanolamine and activated methyldiethanolamine from a gas mixture in a hollow fiber contactor. Ind. Eng. Chem. Res. 2005, 44, 9230−9238. (13) Tan, C.-S.; Chen, J.-E. Absorption of carbon dioxide with piperazine and its mixture in a rotating packed bed. Sep. Purif. Technol. 2006, 49, 174−180. (14) Lu, J.-G.; Ji, Y.; Zhang, H.; Chen, M.-D. CO2 capture using activated amino acid salt solutions in a membrane contactor. Sep. Sci. Technol. 2010, 45, 1240−1251. (15) Fathi, J.; Baheri, H. R. Amine Plant Simulation by Mass Transfer and Kinetic Approach. Chem. Eng. Technol. 1995, 18, 397−402. (16) Xu, S.; Wang, Y.; Otto, F. D.; Mather, A. E. Physicochemical properties of 2-piperidineethanol and its aqueous solutions. J. Chem. Eng. Data 1992, 37, 407−411. (17) Xu, S.; Otto, F. D.; Mather, A. E. Physical Properties of Aqueous AMP Solutions. J. Chem. Eng. Data 1991, 36, 71−75. (18) Maham, Y.; Lebrette, L.; Mather, A. Viscosities and Excess Properties of Aqueous Solutions of Mono and Diethanolamines at Temperatures between 298.15 and 353.15 K. J. Chem. Eng. Data 2002, 47, 550−553. (19) Rebolledo-Libreros, M. E.; Trejo, A. Density and Viscosity of Aqueous Blends of Three Alkanolamines: N-Methyldiethanolamine, Diethanolamine, and 2-Amino-2-methyl-1-propanol in the Range of (303 to 343) K. J. Chem. Eng. Data 2006, 51, 702−707. (20) Derks, P. W.; Hogendoorn, Kees, J.; Versteeg, G. F. Solubility of N2O in and density, viscosity, and surface tension of aqueous piperazine solutions. J. Chem. Eng. Data 2005, 50 (6), 1947−1950. (21) Samanta, A.; Bandyopadhyay, S. S. Density and viscosity of aqueous solutions of piperazine and (2-amino-2-methyl-1-propanol + piperazine) from 298 to 333 K. J. Chem. Eng. Data 2006, 51 (2), 467− 470. (22) Paul, S.; Mandal, B. Density and viscosity of aqueous solutions of (N-methyldiethanolamine + piperazine) and (2-amino-2-methyl-1propanol + piperazine) from (288 to 333) K. J. Chem. Eng. Data 2006, 51 (5), 1808−1810. (23) Kumar, P. S.; Hogendoorn, J. A.; Feron, P. H. M.; Versteeg, G. F. Density, viscosity, solubility and diffusion coefficient of N2O in 2052


Physical Properties of a Complex Solution of (Potassium Citrate +

Recommend Documents