Solubilities and Thermodynamic Properties of NH3 in Glycerin and its

Article Cite This: J. Chem. Eng. Data 2019, 64, 1131−1139

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Solubilities and Thermodynamic Properties of NH3 in Glycerin and its Derivatives Xiuzhi Duan, Yanhong Cui, Chao Zhang, Bao Gao, and Dongshun Deng*

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Biodiesel Laboratory of China Petroleum and Chemical Industry Federation, Zhejiang Province Key Laboratory of Biofuel, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China ABSTRACT: The solubilities of ammonia (NH3) in glycerin (G) as well as its derivatives were determined at 303.15, 313.15, 323.15, and 333.15 K and pressure scope of 0−570.0 kPa by isochoric saturation method. Three glycerin derivatives include DL-1,2-isopropyli-deneglycerol (GAK), glycerol formal (GF), and 3-methoxy-1,2-propanediol (MP). Henry’s law constants together with thermodynamic property changes of dissolution Gibbs free energy, enthalpy, and entropy during NH3 dissolving were derived by fitting the experimental data. The results showed that the gravimetric solubilities of NH3 in these solvents changes along with the sequence of G > GF > MP > GAK. The increasing pressure or the decreasing temperature led to improvement of the solubility of NH3 in each solvent. The dissolution of NH3 presented as a spontaneous process due to the dissolving enthalpy less than zero at each condition. By comprehensive comparison of dissolving ability, properties, price, and environmental impact between present solvents and other absorbents in the literatures, glycerin was believed as a potential NH3 captures in the industry.

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reported as NH3 absorbent.17−19 By relating the high NH3 dissolving ability with the structure of reported ILs and DESs, how to construct a hydrogen bond between absorbing agents and NH3 is the crucial strategy to improve their absorption capacity for NH3. The simple and direct method is to introduce a hydroxyl group into the structure of the absorbents. With the rapid development and massive production of biodiesel in recent years, glycerin as a main byproduct from biodiesel becomes far more of an overabundance than market and is available at a lower price.20 Furthermore, the chemical conversion of glycerin has also attracted extensive attention with many new chemicals constantly appearing. Among them, the excellent representatives of DL-1,2-isopropyli-deneglycerol (GAK), glycerol formal (GF), and 3-methoxy-1,2-propanediol (MP) have been ranged as typical biobased solvents.21,22 Considering their abundant hydroxyl group and appealing physiochemical properties, such as low volatility, biodegradation, chemical stability, low toxicity, and noncorrosivity, herein glycerin and the three derivatives are selected as physical absorbents for NH3. Their properties make them have advantage in recycling absorbent, safety production, and equipment selection. In present research, new solubilities of NH3 in four glycerin compounds were determined at 303.15, 313.15, 323.15, and 323.15 K and pressure close to 570 kPa. Henry’s law constants and standard Gibbs free energy, dissolution enthalpy, and dissolution entropy were calculated.

INTRODUCTION The large emission of ammonia (NH3) will bring serious environmental pollution. NH3 can easily react with SO2 and nitrogen oxides in the air to form ammonium salt aerosols, which is an indispensable component of PM2.5 (particulate matter with a mean aerodynamic diameter of 2.5 μm).1,2 Simultaneously, NH3 plays as a basic raw material in chemical fertilizers, pharmaceuticals, and synthetic fibers. Ammonia is also used as high purity gas in semiconductor industry for light emission diodes (LED).3 Thus, how to efficiently remove or recover NH3 from exhausted gas is an important issue in the NH3-based chemical industry chain. As classical absorbents, water and acidic solution are widely used in NH3 sorption process.4 However, acidic aqueous solutions suffer from the huge energy consumption during the separation of NH3 due to large volatility and specific heat capacity of water and high affinity between the absorbent and NH3.5 Large amount of wastewater discharge and equipment corrosion were further limitations. Therefore, developing novel and environmental friendly absorbents for NH3 is believed to be a feasible strategy for solving this problem. In the recent 20 years, ionic liquids (ILs) have been reported as encouraging gas-absorbing agents in terms of absorption performance, special properties, and tuning structure.6−11 Compared with classical NH3 absorbents, ILs have the superiority in the recovery of pure NH3 with less energy consumption and almost no wastewater discharge. Several research groups studied ILs as NH3 absorbents from experimental measurement, theoretical correlation, and structure performance relationship analysis.12−16 Recently, deep eutectic solvent (DES), a new IL analogue, was also © 2019 American Chemical Society

Received: November 6, 2018 Accepted: February 20, 2019 Published: March 5, 2019 1131

DOI: 10.1021/acs.jced.8b01042 J. Chem. Eng. Data 2019, 64, 1131−1139

Journal of Chemical & Engineering Data

Article

Table 1. Description of Chemicals Used in Present Work chemicals

abbreviation

CAS No.

source

purification method

mass fraction purity

analysis method

ammonia glycerin glycerol formal DL-1,2-isopropyli-deneglycerol 3-methoxy-1,2-propanediol choline chloride urea

NH3 G GF GAK MP ChCl U

7664-41-7 56-81-5 5464-28-8 4740-78-7 100-79-8 623-39-2 67-48-1 57-13-6

Jingong Special Gas Co., Ltd. Aladdin Industrial Co., Ltd. Aladdin Industrial Co., Ltd. Aladdin Industrial Co., Ltd. Aladdin Industrial Co., Ltd. Aladdin Industrial Co., Ltd. Aladdin Industrial Co., Ltd.

none none none none none none none

0.999 0.995 0.980 0.980 0.985 0.990 0.990

none GCa GCa GCa GCa none none

a

Gas−liquid chromatography.

Table 2. Thermophysical Properties of Glycerin and Its Derivatives23

Furthermore, present glycerin derivatives and some ILs as well as DESs were systematically compared from the viewpoint of absorption ability.

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EXPERIMENTAL SECTION Materials. NH3 was supplied by Jingong Special Gas Co., Ltd. Glycerin (G), DL-1,2-isopropyli-deneglycerol (GAK), glycerol formal (GF), and 3-methoxy-1,2-propanediol (MP) were bought from Aladdin Industrial Corporation. All chemicals were used directly. Glycerol formal includes 66% 5-hydroxy-1,3-dioxane and 34% 4-hydroxymethyl-1,3-dioxolane (molar percentage according to 1H NMR result). Table 1 is the description of the chemicals used in detail. Table 2 presented some thermophysical properties of the glycerin as well as its derivatives from literatures. The weighting operation was completed using an electronic balance (Mettler-Toledo AL204) with the standard uncertainty of 0.0002 g. Viscosities of the solvents were measured using Pinkevitch method with the relative standard uncertainty of 2.0%. Apparatus and Procedure. The NH3 solubility in present solvents was determined by isochoric saturation method, which was extensively applied to measure the solubilities of CO2 and SO2 in the literatures.24−26 A stainless apparatus was graphically shown in Figure 1. It mainly composed NH3 cylinder (1), constant temperature water bathe (2, 5), NH3 equilibrium cell (6, EC) with magnetic stirrer to accelerate equilibrium, NH3 reservoir (3, GR), pressure transmitter (9, 13) with digital indicator, and temperature controller (8, 11). The volumes of the EC and GR were 48.45 and 118.43 cm3 as

Figure 1. Schematic diagram of the NH3 solubility determination apparatus. 1, NH3 gas cylinder; 3, NH3 gas reservoir; 6, NH3 gas equilibrium cell; 2, 5, temperature-constant baths; 7, 10, 12, 14, valves; 8, 10, temperature controllers; 9, 13, pressure transmitter and digital indicator; 4, vacuum pump.

previously determined, respectively. The temperature was measured by a thermometer with a precision of ±0.05 K and the pressure by a pressure transmitter (Rosemount 3051T, 0− 605.0 kPa, with an accuracy of 0.15% full scale). To verify the reliability of experimental apparatus, the solubilities of NH3 in DES ChCl-U (1:2) at 313.15 and 323.15 K under pressures close to 400 kPa were measured with the results listed in Table 3. The comparison between experimental data and the values taken from literature27 are illustrated as Figure 2. It can be seen that the data from two independent groups were highly consistent. When the Henry’s 1132



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Table 3. Experimental NH3 molality (m1) in DES ChCl-U (1:2) at Temperature (T) under Equilibrium Pressure (p)a T/K

p/kPa

313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15

18.6 40.8 79.4 103.6 141.0 195.1 293.0 408.6

m1/mol·kg−1

T/K

p/kPa

± ± ± ± ± ± ± ±

323.15 323.15 323.15 323.15 323.15 323.15 323.15

26.2 68.4 95.9 127.8 199.2 281.9 400.6

0.2566 0.6113 1.1582 1.5052 2.0307 2.7906 4.1954 5.7868

0.0126 0.0126 0.0126 0.0126 0.0126 0.0131 0.0131 0.0133

m1/mol·kg−1 0.2963 0.7579 1.0006 1.3106 2.0139 2.8055 3.8903

± ± ± ± ± ± ±

0.0205 0.0205 0.0205 0.0205 0.0214 0.0214 0.0216

Standard uncertainties u are u(T) = 0.05 K, u(p) = 0.9 kPa; standard uncertainties of solubility are reported following ± sign.

a

closed and 7 opened, NH3 in the gas cylinder was charged into GR to be pressure p1. After that, with valve 14 opened slowly a certain amount of NH3 in GR was introduced into EC and the absorption was started. After the pressure of equilibration cell (p2) changed less than 0.005 kPa in 15 min at temperature (T), the equilibrium was assumed to be reached. Then the pressure of GR was recorded as p3. The quantity of NH3 absorbed could be determined by deducting the NH3 charged into the GR from remaining NH3 in GR and gaseous NH3 in EC. The next equilibrium data was obtained by introducing a further amount NH3 into the EC from GR according to the similar procedure. At the end of the experiment, the ammonia gas remaining in the tank was introduced into the aqueous solution for tail gas absorption treatment.

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Figure 2. Comparison of NH3 solubilities (molarity) in choline chloride-urea (1:2). ◊, 313.15 K and ☆, 323.15 K from literature; ○, 313.15 K and □, 323.15 K from experimental data.

RESULTS AND DISCUSSION Solubilites of NH3 in the Absorbents. The mole amount of dissolved NH3 (nNH3) was determinedby the following equation

law constants were obtained by fitting the solubilities and pressure, the relative deviations were within 1.15%. Then the reliability of present apparatus is guaranteed. In a typical operation, the temperature of GR was kept at 303.15 K. After a given amount of DES was loaded into the EC, keeping valves 7, 14 closed and 10, 12 open, the gases in the system was evacuated for 1−2 h. With valves 10, 12, 14

nNH3 = ρg (p1 , T )VGR − ρg (p3 , T )VGR − ρg (p2 , T ) (VEC − Vliquid)

(1) −3

where ρg(pi,T) is the density of NH3 in mol·cm under temperature T and pressure pi (i = 1, 2, 3) and can be found

Table 4. Experimental NH3 Mole Fraction (x1) and Molality (m1) in G at Temperature (T) under Equilibrium Pressure (p)a T/K

p/kPa

303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15

16.1 50.0 81.8 135.3 180.9 238.1 284.0 372.0 445.4 496.0 13.2 87.6 139.1 216.6 303.8 386.8 463.5 526.5 20.1

m1/mol·kg−1 1.8458 4.6038 6.5895 9.4293 11.5057 13.9059 15.8403 19.4337 22.5691 24.9235 1.2302 5.6514 7.8270 10.6545 13.5185 16.1277 18.4325 20.4452 1.2032

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0501 0.0501 0.0501 0.0501 0.0501 0.0508 0.0508 0.0508 0.0508 0.0508 0.0515 0.0515 0.0515 0.0515 0.0515 0.0526 0.0526 0.0526 0.0537

x1 0.1453 0.2977 0.3777 0.4648 0.5145 0.5615 0.5933 0.6415 0.6752 0.6965 0.1017 0.3423 0.4189 0.4952 0.5545 0.5976 0.6293 0.6531 0.0997

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0071 0.0071 0.0071 0.0071 0.0071 0.0073 0.0073 0.0073 0.0073 0.0073 0.0085 0.0085 0.0085 0.0085 0.0085 0.0085 0.0086 0.0086 0.0085

T/K

p/kPa

323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15

54.3 90.6 131.1 191.4 257.2 328.3 400.8 467.8 565.8 41.5 79.1 122.5 160.8 209.6 301.4 345.7 378.8 430.4 462.5

m1/mol·kg−1 2.7438 4.1055 5.4645 7.2056 8.9404 10.7275 12.4352 13.9701 15.6631 1.5988 2.9112 4.0734 4.9992 6.1002 7.9893 8.7955 9.4082 10.3438 10.9247

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0537 0.0537 0.0537 0.0537 0.0537 0.0537 0.0550 0.0550 0.0550 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 0.0562 0.0570 0.0570 0.0570

x1 0.2017 0.2744 0.3348 0.3989 0.4515 0.4970 0.5338 0.5627 0.5996 0.1283 0.2114 0.2728 0.3152 0.3597 0.4239 0.4475 0.4642 0.4879 0.5015

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0085 0.0085 0.0085 0.0085 0.0085 0.0085 0.0092 0.0092 0.0092 0.0101 0.0101 0.0101 0.0101 0.0101 0.0101 0.0101 0.0109 0.0109 0.0109


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Table 5. Experimental NH3 Mole Fraction (x1) and Molality (m1) in GAK at Temperature (T) under Equilibrium Pressure (p)a T/K

p/kPa

303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15

12.9 62.0 102.1 180.9 246.4 293.2 336.8 397.5 432.8 467.0 503.6 75.6 169.1 257.2 337.8 426.8 479.7 511.7

m1/mol·kg−1 0.7619 2.4027 3.3741 5.0207 6.2879 7.1759 8.0387 9.3323 9.8826 10.7096 11.5858 2.2330 3.8041 5.0527 6.3054 7.7864 8.6410 8.9454

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0311 0.0311 0.0311 0.0311 0.0311 0.0311 0.0312 0.0312 0.0312 0.0312 0.0312 0.0326 0.0326 0.0326 0.0326 0.0326 0.0329 0.0329

x1 0.0915 0.2410 0.3084 0.3989 0.4539 0.4868 0.5151 0.5522 0.5664 0.5860 0.6049 0.2280 0.3147 0.3888 0.4421 0.4940 0.5222 0.5378

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0037 0.0037 0.0039 0.0039 0.0039 0.0039 0.0039 0.0039 0.0039

T/K

p/kPa

323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15

41.1 77.0 133.0 204.9 271.8 325.8 366.0 417.3 453.5 494.1 33.7 89.2 138.5 241.3 300.7 383.1 436.0 499.1

m1/mol·kg−1 0.9097 1.6485 2.5083 3.4248 4.2777 4.9275 5.4249 6.0669 6.4994 7.0206 0.4991 1.2905 1.8938 2.9861 3.5911 4.3791 4.8537 5.4452

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0334 0.0334 0.0334 0.0334 0.0334 0.0334 0.0334 0.0334 0.0336 0.0336 0.0347 0.0347 0.0347 0.0347 0.0347 0.0347 0.0350 0.0350

x1 0.1073 0.1789 0.2490 0.3116 0.3612 0.3944 0.4176 0.4450 0.4621 0.4813 0.0619 0.1457 0.2002 0.2830 0.3218 0.3666 0.3908 0.4185

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0041 0.0041 0.0041 0.0041 0.0041 0.0041 0.0041 0.0041 0.0043 0.0043 0.0043 0.0043 0.0043 0.0043 0.0043 0.0043 0.0044 0.0044


a

Table 6. Experimental NH3 Mole Fraction (x1) and Molality (m1) in GF at Temperature (T) under Equilibrium Pressure (p)a T/K

p/kPa

303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15

26.1 74.1 139.8 202.5 260.9 320.4 381.9 443.4 48.2 87.1 157.1 240.9 295.3 332.7 391.6 460.7 502.7 68.5

m1/mol·kg−1 2.2405 4.4775 6.8133 8.6091 10.3394 11.9974 13.9171 15.8705 2.8001 3.9072 5.9654 7.9637 9.1643 10.0401 11.3355 12.8988 13.8980 2.5803

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0355 0.0355 0.0355 0.0355 0.0355 0.0357 0.0357 0.0357 0.0361 0.0361 0.0361 0.0361 0.0361 0.0361 0.0363 0.0363 0.0363 0.0368

x1 0.1891 0.3179 0.4150 0.4727 0.5184 0.5554 0.5917 0.6230 0.2257 0.2892 0.3831 0.4533 0.4883 0.5111 0.5413 0.5732 0.5913 0.2118

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0042 0.0042 0.0042 0.0042 0.0042 0.0043 0.0043 0.0043 0.0046 0.0046 0.0046 0.0046 0.0046 0.0046 0.0047 0.0047 0.0047 0.0049

T/K

p/kPa

323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15

141.0 164.6 210.2 264.3 319.4 395.8 451.2 518.3 38.2 58.8 101.4 162.4 203.9 260.3 323.9 393.5 423.0 482.9

m1/mol·kg−1 4.2865 4.8774 5.6836 6.5912 7.4419 8.9073 9.7768 10.8459 1.2372 1.7142 2.5715 3.5827 4.2173 4.9915 5.8352 6.7259 7.1074 7.8269

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0368 0.0368 0.0368 0.0368 0.0368 0.0368 0.0369 0.0369 0.0354 0.0354 0.0354 0.0354 0.0354 0.0354 0.0354 0.0356 0.0356 0.0356

x1 0.3086 0.3368 0.3717 0.4070 0.4365 0.4812 0.5044 0.5303 0.1141 0.1514 0.2112 0.2717 0.3051 0.3420 0.3779 0.4118 0.4253 0.4490

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0049 0.0049 0.0049 0.0049 0.0049 0.0049 0.0050 0.0050 0.0041 0.0041 0.0041 0.0041 0.0041 0.0041 0.0041 0.0042 0.0042 0.0042


a

out in NIST database.28 VGR and VEC are the volume values of GR and EC, respectively. Vliquid is the volume occupied by the liquid absorbent, which can be directly calculated by the mass and density at equilibrium temperature for each absorbent. The concentrations of NH3 in liquid phase, expressed as molality (mNH3) and mole fraction (xNH3), were deduced according to two formulas as below n NH3 m NH3 = (2) w x NH3 =

experiments for each absorbent. The measuring uncertainties consist of system errors from temperature, pressure, mass, and volume.27 The total uncertainties of gas solubility data can be estimated according to error propagation theory. With u(T) = 0.05 K, u(p) = 0.9 kPa, u(V) = 0.05 mL, u(msol) = 2 × 10−4 g, the uncertainties are obtained and presented in Tables 4−8. The solubility of NH3 in the glycerin and its derivatives was determined at temperatures of 303.15, 313.15, 323.15, and 333.15 K and pressure scope of 0−570.0 kPa. The measured data were presented in Tables 4−7, including liquid phase molality (m1) and molar fraction (x1) of NH3 and equilibrium pressure (p) in gas phase. Figures 3 and 4 demonstrated the profiles of solubility (m1 and x1) in glycerin along with the changing of temperature and pressure, respectively. It can be seen that the solubility of NH3 in all the selected solvents

n NH3 (n NH3 + nsol)

(3)

where nsol presents mole amounts of the used solvent and is calculated as the quotient of the mass (w) divided by molecular mass. The solubility data was the average results of duplicate 1134



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Table 7. Experimental NH3 Mole Fraction (x1) and Molality (m1) in MP at Temperature (T) under Equilibrium Pressure (p)a T/K

p/kPa

303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15

32.3 65.8 109.8 216.9 255.5 291.2 376.1 404.4 466.2 494.9 63.0 113.6 194.0 276.7 360.2 415.8 465.8 530.4 31.7

m1/mol·kg−1 2.1372 3.4969 4.9711 8.0674 9.1063 10.0538 12.4716 13.3435 15.3556 16.0807 2.6114 4.1114 6.2465 8.2221 10.1426 11.4142 12.6263 14.3178 1.0911

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

x1

0.0345 0.0345 0.0345 0.0345 0.0345 0.0345 0.0345 0.0345 0.0346 0.0346 0.0350 0.0350 0.0350 0.0350 0.0350 0.0351 0.0351 0.0351 0.0357

0.1849 0.2707 0.3454 0.4612 0.4914 0.5162 0.5696 0.5861 0.6197 0.6348 0.2170 0.3038 0.3986 0.4660 0.5184 0.5478 0.5726 0.6031 0.1036

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0031 0.0031 0.0031 0.0031 0.0031 0.0031 0.0031 0.0031 0.0032 0.0032 0.0034 0.0034 0.0034 0.0034 0.0034 0.0035 0.0035 0.0035 0.0036

T/K

p/kPa

323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15

78.5 118.5 185.5 288.3 332.4 348.9 395.1 440.2 486.7 29.1 73.6 163.8 193.2 250.3 321.8 368.1 408.6 449.2 516.7

m1/mol·kg−1 2.3969 3.3495 4.8081 6.7366 7.5400 7.9064 8.7427 9.5421 10.3351 0.7310 1.5857 3.1047 3.5459 4.3399 5.2868 5.8754 6.3942 6.9198 7.7483

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

x1

0.0357 0.0357 0.0357 0.0357 0.0357 0.0357 0.0359 0.0359 0.0359 0.0343 0.0343 0.0343 0.0343 0.0343 0.0343 0.0343 0.0343 0.0344 0.0344

0.2024 0.2618 0.3374 0.4163 0.4439 0.4557 0.4807 0.5026 0.5225 0.0720 0.1440 0.2478 0.2734 0.3153 0.3593 0.3840 0.4042 0.4233 0.4511

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0037 0.0037 0.0037 0.0030 0.0030 0.0030 0.0030 0.0030 0.0030 0.0030 0.0030 0.0031 0.0031


a

Table 8. Henry’s constants (Hm, Based on Molality and Hx, based on molar fraction) of NH3 in Selected Solvents at Different Temperaturesa Hm/kPa·kg·mol−1 solvents G GF GAK MP

303.15 K 7.94 9.03 15.32 13.05

± ± ± ±

0.13 0.16 0.28 0.21

313.15 K 10.51 14.31 25.17 20.63

± ± ± ±

0.20 0.22 0.33 0.30

Hx/kPa

323.15 K 16.58 20.70 39.52 27.25

± ± ± ±

0.29 0.34 0.36 0.35

333.15 K 23.10 27.05 63.74 38.26

± ± ± ±

0.38 0.42 0.44 0.47

303.15 K 114.01 133.12 178.31 167.98

± ± ± ±

1.05 1.25 1.88 1.83

313.15 K 139.98 181.15 279.01 231.77

± ± ± ±

1.12 1.95 2.97 2.64

323.15 K 205.01 252.76 340.16 284.42

± ± ± ±

1.68 2.81 3.25 2.89

333.15 K 272.11 308.02 497.37 401.61

± ± ± ±

2.06 3.14 3.69 3.37

Standard uncertainty u is u(T) = 0.05 K; standard uncertainties of Henry’s constants are reported following ± sign.

a

Figure 3. Solubilities of NH3 (molarity) in glycerin. □, 293.15 K; ○, 303.15 K; ◊, 313.15 K; ☆, 323.15 K; , correlation results.

Figure 4. Solubilities of NH3 (moalr fractiony) in glycerin. □, 293.15 K; ○, 303.15 K; ◊, 313.15 K; ☆, 323.15 K; , correlation results.

increases slowly with the increasing pressure and decreasing temperature. Absorption Rate and Recycling of Absorbent. With glycerin as representative absorbent, NH3 absorption curve with time was determined at 313.15 K using the similar method reported by Zhong et al.27 By charging some amount of NH3 into the EC (with an initial pressure of about 300 kPa), the pressure decay in the EC was recorded online until to a stable value. Equation 1 was used to calculate the absorbed amount of NH3 along with the time and results were presented in Figure 5. It can be found that NH3 absorption rate in G was

fast and the NH3 pressure in the EC rapidly decreased to constant within about 200 s. Because of the highest viscosity of glycerin, as shown in Table 2, the other three glycerin derivatives with lower viscosity were believed to possess similar or better absorption rate. For further investigation of the reversible absorption of NH3 in glycerin, the NH3-saturated glycerin was regenerated at 333.15 K and vacuum of 0.5 kPa. Then the renewed absorbent was again used for the absorption experiment by the same procedure mentioned above. Figure 6 showed that the equilibrium absorption capacity of NH3 in glycerin almost 1135



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Figure 7. Most stable geometry for G···NH3 with G, GF, GAK, and MP complexes. Bond length in Å: (a) G···NH3,N (NH3) . . .H (−OH in G) = 1.842, H (NH3)···O (−OH in G) = 2.060; (b) GF···NH3, (NH3) ···H (−OH in GF) = 1.865; (c) MP···NH3, (NH3) ···H (−OH in MP) = 2.081 and 2.071; (d) GAK···NH3, (NH3) ···H (−OH in GAK) = 1.872. Color legend: N blue, C gray, O red, and H white. Figure 5. NH3 absorption equilibrium time in G at 313.15 K.

Figure 8. 1H NMR spectra of glycerin before and after absorption of NH3. Figure 6. NH3 absorption in G for 5 cycles.

kept unchanged after five cycles. Such result reveals that glycerin compounds demonstrate greatly reversible absorption/desorption performance for NH3 and the absorbed NH3 could be easily released by heating and vacuuming operation. Henry’s Law Constant. The Henry’s law constant is a conventional parameter for quantitative description of gas solubility in a solvent. If a gaseous phase and a liquid phase are in equilibrium, then for NH3 the fugacities in both phases must be the same f 2liq (p , T , m2) = f 2vap (p , T , y2 ) = y2 pϕ2(p , T , y2 )

(4) Figure 9. Linear fit of ln Hm with 1/T: ○, GAK; ◊, MP; □, GF; ☆, G; lines, fitting results.

where y2 is the gaseous phase mole fraction of NH3. φ2 is the fugacity coefficient of NH3, calculated using two-term virial

Table 9. Comparison of NH3 Solubility in Present Solvents and Other Absorbents absorbents

temperature (K)

pressure (MPa)

NH3 solubility (g NH3.g−1 solvent)

G GF MP GAK [Bmim][BF4] [Emim][SCN] [Bmim][PF6] [EtOHmim][BF4] [EtOHmim][DCA] [Emim]2[Co(NCS)4] [Mim][NTf2] NH4SCN-G (2:3) choline chloride/resorcinol/glycerol (1:3:5) [bmim][MeSO3]/Urea = 1:1

303.15 303.15 303.15 303.15 313.15 298.1 298 313 313 303.15 313 303.15 313.15 303

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.103 0.1 0.1 0.1

0.130 0.093 0.076 0.056 0.029 0.045 0.021 0.070 0.059 0.198 0.126 0.223 0.13 0.015

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Table 10. Standard Gibbs Free Energy (ΔdisG), Enthalpy (ΔdisH), and Entropy (ΔdisS) of Dissolution of NH3 in Present Solvents at 0.1 MPa and 303.15 K solutions

ΔdisG0/(kJ·mol−1)

ΔdisH0/(kJ·mol−1)

ΔdisS0/(J·mol−1 K−1)

G + NH3 GF + NH3 GAK + NH3 MP + NH3

−6.38 −6.06 −4.73 −5.13

−30.68 −30.82 −39.69 −29.53

−80.15 −81.67 −115.32 −80.48

oborate ([Bmim][BF4]), 1-ethyl-3-methylimidazolium thiocyanate ([Emim][SCN]), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), and 1-butyl-3-methylimidazolium methanesulfonate−urea DES ([bmim][MeSO3]/urea = 1:1). When hydroxyl group is introduced into the cations, the obtained functionized ILs (1-2(-hydroxyethyl)-3-methylimadazolium tetrafluoroborate, [EtOHmim][BF4] and 1-2(hydroxyethyl)-3-methylimadazolium dicyamide, [EtOHmim][DCA]) demonstrates similar NH3 solubility as glycerin derivatives. Glycerin also possesses considerable solubility for NH3 with hybrid DES of choline chloride/resorcinol/glycerol eutectic mixture (ChCl/Res/G = 1:3:5) and protic ILs (1methylimidazolium bis(trifluoromethylsulfonyl)imide, [Mim][NTf2]) reported in the most recent work, while far lower than top-performing protic DES of NH4SCN-G (2:3) and metalcontaining IL (1-ethyl-3-methylimidazolium tetraisothiocyanatocobaltate(II), [Emim]2[Co(NCS)4]). By comprehensive consideration of commercial availability, environmental impact, and absorption performance, present glycerin compounds are still satisfactory absorbents for NH3. For exploring the interaction model theoretically, the binding behaviors between NH3 and glycerin compounds were calculated using sing DMol3 code of Material Studios.32,33 The geometry parameters are optimized with generalized gradient corrections/Perdew and Wang, 1991 (GGA/PW91) function and double-numerical + d-DNP basis except that no p functions are used on hydrogen (DND) basis set of the density functional theory (DFT). The self-consistent field (SCF) tolerance in the optimization is set as 1.0 × 10−5 Ha, the max force as 0.02 Ha/nm, and max displacement as 0.0005 nm. The optimized structure and stable geometries of NH3 with G, GF, MP, and GAK are illustrated in Figure 7. The NH3 interacts with G by forming mutual hydrogen-bond between N, H atoms in NH3 and H, O atoms in the hydroxyl group of G. In the other three glycerin derivatives, the hydrogen-bond mainly constructs between N atom in NH3 and hydroxyl group in GF, MP, and GAK. It is clear that the gaseous binding energies of NH3 with G, GF, MP, and GAK as low as 15.17, 13.01, 11.73, and 10.59 kJ/mol, respectively, means that the interaction between these glycerin compounds and NH3 is merely a relatively weak interaction. Such result and the dissolution profile of NH3 in G is consistent. Morever, NMR spectroscopy was used to give some insight on the interaction between glycerin and NH3. 1H NMR spectra were taken in drive pipe with CDCl3 charged into the inner tube. 1H NMR spectral of glycerin with and without NH3 are depicted in Figure 8. The chemical shift of H atom (hydroxyl group in glycerol) shifted upfield from 5.12 to 4.07 ppm. It implies that NH3 binds with hydroxyl group and all the active H atoms exchange each other in the solution. If the peak area of H atoms linked to C atoms in skeleton of glycerin is chosen as the calculation references, the amount of dissolved NH3 could be determined on the basis of incremental quantity of peak area from original area of −OH. It was found that the H numbers from calculation and

equation at the low experimental pressure. In this work, the vapor pressures of glycerin and its derivatives were small at the experimental temperatures, then the gas phase could be regarded as pure NH3 and y2 was approximately equal to unity. Because of the relatively low pressure of pe, the values of φ2 e) were approximately close to unity and f liq 2 (T, p was simplified to be the same as the equilibrium pressure pe. Then at a very diluent region of NH3 in the absorbents, the Henry’s law constant based on molality is defined and simplified as follows ÄÅ ÉÑ ÅÅ liq Ñ e e ÅÅ f (p , T , m2) ÑÑÑ Å ÑÑ ≅ pϕ2(p , T ) ≅ p 2 Hm(p , T ) ≡ lim ÅÅÅ Ñ ÑÑ m2 m2 m2 p → 0Å ÅÅÅ ÑÑÑ 0 0 m0 m m ÅÇ ÑÖ

( )

( )

( )

(5)

Similarly, Henry’s law constant Hm based on mole fraction is also defined as follows ÄÅ liq É e ÅÅ f (p , T , x ) ÑÑÑ e ÅÅ 2 2 Ñ ÑÑ ≅ pϕ2(p , T ) ≅ p Hx(p , T ) ≡ lim ÅÅÅ ÑÑ p → 0Å ÑÑ x2 x2 x2 ÅÅÇ ÑÖ (6) 0

−1

where m = 1 mol·kg , and m2 represents liquid phase molality of NH3. In this work, Hx and Hm were obtained by extrapolation of the pe/x2 or pe/m2 versus pressure curves to zero pressure by simple linear regression method. Henry’s law constants in present four solvents at T = 303.15−333.15 K were determined and presented in Table 8. As expected, Henry’s law constants varied evidently along with the changing temperatures. Therefore, the temperature swing supported a good choice to trip out the absorbed NH3 in the saturated absorbents. Within each experimental temperature region, the solubility and pressure basically present linear relation. This is a physical solubility behavior as similar to literature observations, which includes hydrogen bonding. Here Hx offers a simple way to verify the above-mentioned solubility rules merely from the absorbent structure without regard for molecular weight. The absorption capacity can be ranked as the sequence of G > GF > MP > GAK. On the other hand, the capture capacity considering molar mass of absorbent can provide further evaluation from economic and practical application. Interestingly, the gravimetric solubility sequence (as shown with Hm) based on absolute mass was the same as the above-mentioned result. Such order is generally consistent with the quantity of the hydroxyl group in the molecular structure. While GF demonstrates special dissolution ability for NH3, the reasons may come from the slightly acidic ethylene group which connected with the two oxygen atoms. For systematically evaluating the ability of present glycerin derivatives as NH3 absorbent, Table 9 listed the comparative results of NH3 absorption capacities between these solvents and some ILs and DESs from literatures at approximately 303.15 K and 0.1 MPa. It is known that glycerin derivatives possesses evidently higher absorption ability than common ILs and DES, including 1-butyl-3-methylimidazolium tetrafluor1137



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practical absorption capacity of NH3 were consistent. Such result means that the amount of water in the materials and the effect of strong H-bond involving water on the solubility of NH3 in glycerin are relatively small. Thermodynamic Properties. The dissolving process of NH3 in the absorbents always related to the changes of thermodynamic parameters. A calculation of thermodynamics properties is essential, not only for investigating the NH3 capture process but also for process design of gas separation technology. Thus, the changes of Gibbs free energy and entropy of NH3 in four absorbents at various temperatures could be derived by fitting the Henry law constant as obtained above using the following famous thermodynamic relations34 ij H (T , p) yz zz ΔdisG = RT lnjjj m 0 zz j p k {

jij ∂ln Hm(T0 , p) jj p ΔdisH = R jjjj 1 jj ∂ T jj k

(

()

ΔdisS =

ΔdisH − ΔdisG T

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Dongshun Deng: 0000-0001-7125-1833 Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS This research was supported by Zhejiang Provincial Natural Science Foundation of China under Grant LY17B060010. REFERENCES

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(7)

) zyzzzzzz

zz zz z {p

Article

(8)

(9)

where ΔdisG, ΔdisH, and ΔdisS are Gibbs free energy, enthalpy, and entropy during NH3 solvation, respectively. The typical relationship between the natural logarithm of Hm and the reciprocal of temperature was graphically presented as Figure 9. The thermodynamic properties of NH3 in the researched absorbents were calculated at normal condition (p0 = 0.1 MPa) and listed in Table 10. The values of ΔdisH are negative at each temperature for all the glycerin compounds, which illustrates the absorption of NH3 is an exothermic process and the solvation of NH3 in present solvents is thermodynamically favorable in terms of enthalpy. As shown from the aspect of molecular interaction, the ΔdisS can partly provide information on the solvent organization around the soluble NH3. The more negative value of ΔdisS obtained, the ordering degree of solution structure becomes higher when NH3 dissolves into the absorbents. As a comprehensive result of ΔdisH and ΔdisS, the negative ΔdisG values mean that the process of dissolution is spontaneous.

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CONCLUSION In the present work, the solubilities of NH3 in biobased glycerin and its derivatives were systematically measured under various temperatures and pressures. NH3 mainly dissolved into glycerin compounds via forming weak hydrogen-bonding between N, H atoms in NH3 and H, O atoms in the hydroxyl group of G, respectively.. The quantity of hydroxyl group and absorption capacity of NH3 demonstrated positive correlation for present solvents. Henry’s law constants were derived by correlating solubilities data and further used to calculate thermodynamic properties (ΔdisH, ΔdisG, ΔdisS). The values of dissolution enthalpy were slightly negative at each condition. By comprehensive considering absorption performance, thermodynamic property, and environmental effect, present glycerin compounds demonstrated somewhat superiority as physical absorbents for NH3. 1138



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Solubilities and Thermodynamic Properties of NH3 in Glycerin and its

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