The main contributor for adverse effect on climate is excessive CO2 emissions due to fossil fuel combustion, and other relative activities to meet the increasing energy demand
In such operations, alkanolamine-based absorbents and their combinations with other compounds are being used extensively
Physicochemical property such as density of absorbents are necessary for detailed characterization of the solvent for CO2 capture and they are required in the process modelling, simulation and construction of gas–liquid contactor for CO2 absorption and regeneration
Many physicochemical studies of amino acids salt solutions have been presented density data previously but all at higher concentrations and using different method. To the best of our knowledge for aqueous sodium salt solutions of cysteine, leucine, proline, and valine such data have not yet been reported in the open literature at such lower concentrations range (0.01 to 0.15) mol L-1. Thus, in the present work, we presented new experimental data on density and apparent molar volumes (Vϕ), the partial molar volumes (Vϕ0), expansion coefficient (Eꝏ) and Hepler’s constant
The amino acids L-cysteine (CAS No. 52-90-4, 99.0% purity) and L-leucine (CAS No. 61-90-5, 99.0% purity) were purchased from LOBA CHEMIE PVT. LTD., while L-proline (CAS No. 147-85-3, 99.0% purity) and L-valine (CAS No. 72-18-4, 99.0% purity) were supplied by S D Fine-Chem Ltd, India. Sodium hydroxide (CAS No. 1310-73-2, GR, 98 % purity) was purchased from Merck. The aqueous amino acid salt solutions were prepared on weight by weight method by neutralizing amino acid dissolved in triply distilled water with an equimolar amount of NaOH
The neutralised sodium salts of amino acids react with CO2 in a similar manner to that of "regular" a primary or secondary amines, i.e., by forming carbamate and bicarbonate.
The reaction between a particular amino acid salt and CO2 is influenced by a number of variables, such as the amino acid's structure and on the chemical environment of amine group in a single molecule.
The densities were measured using a 15-cm3 double-arm bi-capillary Pycnometer
The measured density values for aqueous solutions of Na-AAS at concentrations ranging between 0.01 to 0.15 m and at temperatures 298.15, 303.15, 308.15, and 313.15 K are presented in
By using experimental density data, the apparent molar volumes
where
Following observations can be seen from
i. For all studied Na-AAS solutions, the apparent molar volume increase with molality of the solutions.
ii. Apparent molar volume increase with increasing temperature for all studied Na-AAS aqueous solutions.
where Vϕ0, Vs and m are the partial molar volume, solute-solute interaction parameter and molality, respectively. For calculating Vϕ0 and Vs values the least square method was employed.
Both Vϕ0 and Vs values increases as temperature increases. This indicates that with increase in the temperature, the electrostriction effect of water reduces and water molecules in secondary solvation layer release into the bulk of the water. All the values of (Vϕ0) are positive which indicates strong (Na-AAS)-water interactions. Vϕ0 is an important parameter that shows the solute-solvent interactions.
The partial molar volumes at same temperature of studied sodium salt of amino acids is observed to increase in the order:
Vϕ0 (Na-leucinate) > Vϕ0 (Na-valinate) > Vϕ0 (Na-prolinate) > Vϕ0 (Na-cysteinate)
Variation of Vϕ0 with the temperature can be explained by
where a0, a1 and a2 are constants and their values were calculated using Scilab application.
The partial molar expansion (Eꝏ) is obtained from expression 3 on differentiation with respect to temperature.
Eꝏ values are positive and increases with increase in temperature. The positive values of Eꝏ indicate strong solute (amino acid salt)-solvent(water) interactions in all investigated amino acids salt solutions.
The Hepler’s constant
The Hepler’s constant
(Na-cysteinate)
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0 |
997.044 |
995.646 |
994.032 |
992.211 |
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0 |
997.044 |
995.646 |
994.032 |
992.211 |
0.00975 |
997.721 |
996.322 |
994.706 |
992.882 |
|
0.01002 |
997.497 |
996.097 |
994.48 |
992.656 |
0.03061 |
999.163 |
997.762 |
996.141 |
994.311 |
|
0.03050 |
998.417 |
997.013 |
995.39 |
993.559 |
0.05147 |
1000.598 |
999.195 |
997.569 |
995.733 |
|
0.05098 |
999.330 |
997.922 |
996.293 |
994.456 |
0.07099 |
1001.935 |
1000.530 |
998.900 |
997.058 |
|
0.06973 |
1000.161 |
998.749 |
997.114 |
995.271 |
0.09091 |
1003.294 |
1001.887 |
1000.250 |
998.404 |
|
0.08976 |
1001.043 |
999.627 |
997.986 |
996.137 |
0.11083 |
1004.648 |
1003.239 |
1001.600 |
999.745 |
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0.10979 |
1001.920 |
1000.500 |
998.853 |
996.998 |
0.13075 |
1005.997 |
1004.586 |
1002.940 |
1001.081 |
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0.13074 |
1002.832 |
1001.408 |
999.755 |
997.893 |
0.15066 |
1007.341 |
1005.927 |
1004.280 |
1002.410 |
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0.15169 |
1003.739 |
1002.311 |
1000.65 |
998.783 |
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0.01179 |
997.683 |
996.284 |
994.668 |
992.844 |
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0.00990 |
997.515 |
996.115 |
994.499 |
992.675 |
0.03411 |
998.886 |
997.485 |
995.865 |
994.035 |
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0.02581 |
998.268 |
996.865 |
995.245 |
993.417 |
0.05323 |
999.911 |
998.508 |
996.884 |
995.050 |
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0.04506 |
999.174 |
997.767 |
996.143 |
994.309 |
0.06950 |
1000.779 |
999.375 |
997.748 |
995.909 |
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0.07777 |
1000.702 |
999.288 |
997.658 |
995.814 |
0.09007 |
1001.872 |
1000.466 |
998.835 |
996.991 |
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0.09722 |
1001.604 |
1000.187 |
998.552 |
996.702 |
0.11114 |
1002.986 |
1001.578 |
999.944 |
998.094 |
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0.11135 |
1002.257 |
1000.837 |
999.199 |
997.345 |
0.12918 |
1003.936 |
1002.527 |
1000.890 |
999.034 |
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0.13112 |
1003.167 |
1001.743 |
1000.100 |
998.240 |
0.15700 |
1005.394 |
1003.981 |
1002.340 |
1000.477 |
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0.15192 |
1004.119 |
1002.690 |
1001.040 |
999.177 |
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0.00975 |
73.6670 |
73.7756 |
73.9893 |
74.3090 |
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0.01002 |
108.0824 |
108.3717 |
108.7769 |
109.1976 |
0.03061 |
73.7716 |
73.8761 |
74.1141 |
74.4206 |
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0.03050 |
108.1769 |
108.4638 |
108.8655 |
109.3159 |
0.05147 |
73.8420 |
73.9460 |
74.1890 |
74.4933 |
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0.05098 |
108.2540 |
108.5409 |
108.9424 |
109.3793 |
0.07099 |
73.8965 |
74.0023 |
74.2378 |
74.5469 |
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0.06973 |
108.3046 |
108.5965 |
109.0057 |
109.4450 |
0.09091 |
73.9441 |
74.0506 |
74.2920 |
74.6028 |
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0.08976 |
108.3583 |
108.6505 |
109.0599 |
109.4963 |
0.11083 |
73.9840 |
74.0909 |
74.3363 |
74.6482 |
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0.10979 |
108.4036 |
108.6961 |
109.1059 |
109.5407 |
0.13075 |
74.0197 |
74.1271 |
74.3753 |
74.6882 |
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0.13074 |
108.4461 |
108.7375 |
109.1455 |
109.5849 |
0.15066 |
74.0487 |
74.1631 |
74.4135 |
74.7338 |
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0.15169 |
108.4830 |
108.7737 |
109.1807 |
109.6236 |
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0.01179 |
82.9459 |
83.0712 |
83.2890 |
83.6000 |
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0.00990 |
91.6396 |
91.9049 |
92.1809 |
92.5702 |
0.03411 |
83.0435 |
83.1724 |
83.3971 |
83.7184 |
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0.02581 |
91.7235 |
91.9808 |
92.2881 |
92.6457 |
0.05323 |
83.0999 |
83.2352 |
83.4724 |
83.7742 |
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0.04506 |
91.7941 |
92.0579 |
92.3550 |
92.7308 |
0.06950 |
83.1477 |
83.2756 |
83.5123 |
83.8294 |
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0.07777 |
91.8886 |
92.1592 |
92.4406 |
92.8247 |
0.09007 |
83.1954 |
83.3260 |
83.5648 |
83.8788 |
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0.09722 |
91.9383 |
92.1987 |
92.4910 |
92.8782 |
0.11114 |
83.2417 |
83.3737 |
83.6040 |
83.9240 |
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0.11135 |
91.9660 |
92.2289 |
92.5210 |
92.9066 |
0.12918 |
83.2745 |
83.4024 |
83.6388 |
83.9615 |
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0.13112 |
92.0012 |
92.2652 |
92.5634 |
92.9506 |
0.15700 |
83.3210 |
83.4592 |
83.6951 |
84.0098 |
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0.15192 |
92.0410 |
92.3111 |
92.6058 |
92.9922 |
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298.15 K |
303.15 K |
308.15 K |
313.15 K |
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298.15 K |
303.15 K |
308.15 K |
313.15 K |
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106 Vϕ0 |
73.5390 |
73.6428 |
73.8542 |
74.1634 |
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107.9376 |
108.2239 |
108.6249 |
109.0535 |
106 Vs |
1.3299 |
1.3443 |
1.4473 |
1.4556 |
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1.4014 |
1.4161 |
1.4364 |
1.4699 |
106 Eꝏ |
0.01080 |
0.0314 |
0.0521 |
0.07270 |
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0.05362 |
0.06785 |
0.08209 |
0.09632 |
106 |
0.00413 |
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0.00285 |
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106 Vϕ0 |
82.8010 |
82.9249 |
83.1415 |
83.4502 |
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91.5012 |
91.7614 |
92.0480 |
92.4177 |
106 Vs |
1.3150 |
1.3399 |
1.3971 |
1.4215 |
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1.3883 |
1.4035 |
1.4251 |
1.4695 |
106 Eꝏ |
0.01562 |
0.03406 |
0.05251 |
0.07096 |
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0.0466 |
0.0617 |
0.0768 |
0.0919 |
106 |
0.00369 |
|
0.00302 |
The apparent molar volume increases both with the temperature and molality of the solutions for all studied Na-salt of amino acids + water systems. This could be due to increase in size of alkyl group in side chain of amino acids. This suggests that at higher temperature the electrostriction effect of water reduces and water molecules in secondary solvation layer release into the bulk of the water. All the values of partial molar volume (Vϕ0) are positive which indicates strong (Na-AAS) + water interactions. The positive values of Vϕ0 and Eꝏ indicate strong sodium amino acids -water interactions. Higher value of Vϕ0 and Eꝏ for Na-leucinate suggest greater solute-solvent interaction and for Na-cysteinate the lower Vϕ0 and Eꝏ values suggest weaker solute-solvent interaction among all four studied AAS. Hepler's constants also have positive values, which indicates that sodium amino acids in aqueous solution have a structure making tendency.
MBD thanks Director, Government Vidarbha Institute of Science and Humanities, Amravati, India and Principal, HPT Arts and RYK Science College, Nashik, India.