Ind. Eng. Chem. Res. 2008, 47, 3767-3770
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APPLIED CHEMISTRY Solubility in the NH4NO3 + NaNO3 + H2O System Mieczysław Trypuc´ * and Sebastian Druz3 yn´ ski Faculty of Chemistry, Nicolaus Copernicus UniVersity, 7 Gagarin Street, 87-100 Torun´ , Poland
The mutual solubility of salts in the ternary system NH4NO3 + NaNO3 + H2O was investigated in the temperature range 293-323 K by the method of isothermal saturation of solutions. The data obtained were used for plotting the section of the solubility polytherm for the system investigated. Knowledge of the course of the solubility polytherm is necessary for developing a new method of utilization of the post-filtration lye from the soda-chlorine-saltpeter method (SCS) of soda production. 1. Introduction The soda-chlorine-saltpeter (SCS) method is a modification of the classic Solvay method of sodium carbonate production. In this method, the ammoniated brine of sodium nitrate is carbonized, instead of using sodium chloride, according to eq 1.1,2
NaNO3 + NH3 + CO2 + H2O T NaHCO3 + NH4NO3 (1) The final product is obtained by precipitation of sodium bicarbonate, which is subsequently washed with water and calcinated, according to eq 2.
2NaHCO3 f Na2CO3 + CO2 + H2O
(2)
The yield of carbonization process (described by eq 1) related to the sodium ions WNa+, for the triple point P1 at 303 K and the NaNO3 concentration of 22.5 mol‚1000 g-1 H2O, for NH3 concentration 15.9 mol‚1000 g-1 H2O, it reaches a maximum of 81.2%. After separation of bicarbonate, the post-filtration lye has the following composition:3 NaNO3, 10.4 mass %; NH4NO3, 56.1 mass %; NH4HCO3, 3.6 mass %; NaCl, 1.4 mass %. There have been suggestions that the lye, after thermal decarbonization, can be used as a material in production of a nitrogenous fertilizer, in the form of as a mixed ammoniumsodium saltpeter.1-3 The presence of chloride ions in the postfiltration liquor in the process of NaNO3 production from NaCl with the use of HNO3 significantly complicates both the concentration, crystallization steps, and storage of the mixed ammonium-sodium saltpeter. Research on the influence of different substances on the uncontrolled decomposition of ammonium nitrate has shown that chloride ions catalyzes a process, which creates a real threat of explosion during heating of the solution and subsequent storage of the saltpeter.4, 5 A possible solution of this problem is conversion of the ammonium nitrate into sodium nitrate, which exhibits greater * Corresponding author: Tel.: (+48) 566114537, Fax: (+48) 566542477, E-mail address:
[email protected].
thermal stability. This process is based on the double exchange between ammonium nitrate and sodium vanadate(V) as described by eq 3.6-8
NH4NO3 + NaVO3 T NH4VO3 + NaNO3
(3)
After filtration of the sparingly soluble precipitate of ammonium vanadate(V), the lye contains almost exclusively sodium nitrate. The solution is subsequently concentrated and the salt obtained by crystallization can be used as a nitrogenous fertilizer. The detailed description of the soda production from sodium nitrate and utilization of the lye produced in that process can be found in our previous paper.8 Optimization of conditions for the preciptiation of ammonium vanadate(V) from the post-filtration lye with sodium vanadate(V) requires the precise knowledge of the equilibrium plots in the planar projection with the Janecke procedure for the pairs of reprocical salts NH4NO3 + NaVO3 + NH4VO3 + NaNO3 + H2O as well as four ternary systems: NaVO3 + NaNO3 + H2O, NH4VO3 + NaVO3 + H2O, NaNO3 + NH4NO3 + H2O, NH4NO3 + NH4VO3 + H2O. These systems are components of the quaternary system mentioned above, and are positioned on the respective edges of the square of the Janecke equilibrium plot. There are published reports on the mutual solubility of salts in the systems NaVO3 + NaNO3 + H2O,8 NH4VO3 + NaVO3 + H2O,9 but neither the quaternary system nor the ternary NH4NO3 + NH4VO3 + H2O system have been investigated so far. Because of the specificity of our research, the literature data10-14 for the NaNO3 + NH4NO3 + H2O system are not sufficient. Previous authors10-14 conducted the experiments in a broad range of temperatures, but they reported the equilibrium concentrations only for single salts and in the eutonic points. Therefore, we decided to complete the data for the mutual solubility of salts in the NaNO3 + NH4NO3 + H2O system. 2. Experimental Section 2.1. Reagents. In the research, the analytical grade reagents were used, NaNO3 and NH4NO3 (pure for analysis POCh Gliwice). 2.2. Method. Mutual solubility of salts in the NaNO3-NH4NO3-H2O system was determined at 293, 303, 313, and 323 K by the method of isothermal saturation of solutions.6-10 The
10.1021/ie0709741 CCC: $40.75 © 2008 American Chemical Society Published on Web 03/19/2008
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Table 1. Solubility in NH4NO3-NaNO3-H2O System c (mol‚dm-3) no.
F
(g‚cm-3)
NH4NO3
x NaNO3
NH4NO3
NaNO3
solid-phase composition
1.000 0.923 0.851 0.827 0.803 0.780 0.729 0.682 0.624 0.586 0.535 0.395 0.312 0.172 0.000
0.000 0.077 0.149 0.173 0.197 0.220 0.271 0.318 0.376 0.414 0.465 0.605 0.688 0.828 1.000
NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 + NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3
1 2 3 4 5 6 7 8 (E) 9 10 11 12 13 14 15
1.306 1.328 1.339 1.363 1.376 1.383 1.406 1.439 1.423 1.419 1.412 1.403 1.396 1.389 1.382
10.525 10.248 9.927 9.775 9.585 9.467 9.302 8.853 7.566 6.798 5.968 3.958 2.906 1.474 0.000
T ) 293 K 0.000 0.856 1.742 2.045 2.359 2.678 3.458 4.131 4.556 4.805 5.187 6.062 6.413 7.113 7.622
1 2 3 4 5 6 7 8 (E) 9 10 11 12 13 14
1.330 1.349 1.368 1.382 1.392 1.396 1.410 1.451 1.423 1.418 1.412 1.403 1.389 1.400
11.464 11.272 10.785 10.564 10.540 10.346 10.207 9.733 8.089 6.958 5.882 3.950 1.374 0.000
T ) 303 K 0.000 0.649 1.743 2.015 2.220 2.500 2.782 3.750 4.641 5.107 5.572 6.414 7.471 8.253
1.000 0.946 0.861 0.840 0.826 0.805 0.786 0.722 0.635 0.577 0.514 0.381 0.155 0.000
0.000 0.054 0.139 0.160 0.177 0.195 0.214 0.278 0.365 0.423 0.486 0.619 0.845 1.000
NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 + NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3
1 2 3 4 5 6 (E) 7 8 9 10 11 12
1.343 1.370 1.403 1.416 1.436 1.468 1.449 1.441 1.434 1.423 1.419 1.418
12.078 11.669 11.187 11.059 10.756 10.553 8.106 5.394 3.762 3.183 2.003 0.000
T ) 313 K 0.000 1.088 2.260 2.855 3.232 3.496 4.742 6.098 6.851 7.020 7.577 8.555
1.000 0.915 0.832 0.795 0.769 0.751 0.631 0.469 0.354 0.312 0.157 0.000
0.000 0.085 0.168 0.205 0.231 0.249 0.369 0.531 0.646 0.688 0.843 1.000
NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 + NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3
1 2 3 4 5 6 7 (E) 8 9 10 11 12 13
1.418 1.379 1.396 1.410 1.418 1.421 1.484 1.472 1.458 1.442 1.437 1.434 1.359
12.828 12.503 12.243 12.043 11.861 11.745 11.170 10.132 8.186 6.689 5.407 4.137 0.000
T ) 323 K 0.000 0.875 1.334 1.829 2.292 2.505 3.397 3.974 4.753 5.531 6.437 7.063 8.941
1.000 0.935 0.902 0.868 0.838 0.824 0.767 0.718 0.633 0.547 0.456 0.369 0.000
0.000 0.065 0.098 0.132 0.162 0.176 0.233 0.282 0.367 0.453 0.544 0.631 1.000
NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 NH4NO3 + NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3 NaNO3
required amounts of components, one of them used in an amount larger than its water solubility, were put into the Erlenmeyer flasks with the required amount of redistilled water. The solutions were thermostated and stirred until an equilibrium between phases was reached. The equilibration time was determined experimentally as 24 h. After that time the stirring was stopped, the mixture was left for 20 min to allow for sedimentation, and the samples of clear equilibrated solutions were transferred into the Ostwald pycnometer, precalibrated and preheated to the appropriate temperature, for the determination of density. The samples were collected at an increased pressure generated by the micrometering pump. This prevented the crystallization of the solid components during this procedure,
especially at the higher temperatures. The pycnometer’s contents were subsequently transferred quantitatively into the 500 cm3 measuring flask and diluted with redistilled water. The composition of the equilibrated solutions was determined by chemical analyses. Three independent analyses of ions mentioned above have been performed for each collected sample. The precision of the analyses, estimated as the relative standard deviation (RSD) error, did not exceed 2%. 2.3. Analytical Methods. The concentration of ammonium ions was determined by the formalin method. It is based on the reaction of methanal with NH4+ ions, in which hexamethylenetetraamine is formed together with an equivalent amount of
Ind. Eng. Chem. Res., Vol. 47, No. 10, 2008 3769
Figure 3. Diffraction pattern for the solid phase of branch I of the solubility isotherm at T ) 303 K. Figure 1. Section of the polytherm for the NH4NO3-NaNO3-H2O system at the temperature range 293-323 K.
Figure 4. Diffraction pattern for the solid phase of branch II of the solubility isotherm at T ) 303 K.
Figure 2. Density of the equilibrated solutions as a function of the ammonium nitrate molar ratio.
acid (eq 4), which is determined by titration with sodium hydroxide.15
4NH4NO3 + 6HCHO f (CH2)6N4 + 4HNO3 + 6H2O
(4)
The sum of ammonium and nitrate ions (NH3 total) was determined by the distillation method. The nitrate ions were reduced with Deward’s alloy in a concentrated solution of sodium hydroxide. The distilled ammonia was absorbed in an excess of a standard solution of sulfuric acid, the excess of acid was then titrated with sodium hydroxide.15,16 The concentration of sodium ions in the equilibrated solutions was determined by the gravimetric method of Kolthoff and Barber as sodium-zinc-uranyl acetate.15 The equilibrium concentrations of ammonium nitrate and sodium nitrate were calculated from the following relations:
[NH4NO3] ) [NH4+]; [NaNO3] ) [NH3 total] - 2[NH4+] For chosen points, the analyses of the solid phase were performed using a Philips X-Pert PRO X-ray powder diffractometer. To determine the solid-phase composition, the diffraction patterns were compared with the standards.17 3. Results and Discussion The data obtained on the mutual solubility of NaNO3 and NH4NO3 in water at 293, 303, 313, and 323 K are presented in Table 1. The equilibrium concentrations of salts (mol‚dm-3),
Figure 5. Diffraction pattern for the solid phase at the eutonic point at T ) 303 K.
density of equilibrated solutions (g‚cm-3) and the calculated molar fractions for salts, without taking into account the solvent and composition of the solid phase, are tabulated. The data from Table 1 have been used to prepare a plot of the section of the solubility polytherm for the system investigated (Figure 1). The solubility isotherms displayed at 293, 303, 313, and 323 K consist of branches denoted as I and II, that correspond to the solutions saturated with NaNO3 and NH4NO3, respectively. The eutonic points marked (E) correspond to the solutions saturated with both salts. The course of branches I of the solubility isotherms for the investigated temperatures is linear. The NaNO3 concentration decreases with an increase of the NH4NO3 concentration until the eutonic point E is reached. A decrease in the solubility of sodium nitrate was observed at the E points, when compared to its solubility in water by 4.131 M at 293 K; 3.750 M at 303 K; 3.496 M at 313 K and 3.397 M at 323 K. Branches II correspond to solutions saturated with ammonium nitrate. They also reveal a linear decrease of the NH4NO3 solubility with an increasing concentration of sodium nitrate.
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It is found that at the eutonic points, the sodium nitrate concentration decreases, while the NH4NO3 concentration increases with increasing temperature, and these changes are linear. The possibility of formation of the double salts or other addition compounds in the system was investigated with the use of the property-composition equilibrium plot. If a new phase would be formed, such a plot would reveal characteristic inflections or breaks corresponding to the new phase being formed.18 Data tabulated in Table 1 have been used for constructing the plot of density of the equilibrated solutions as a function of the concentration of the ammonium nitrate molar ratio (Figure 2). Analysis of this plot reveals that at the temperature range investigated, the solid phase for branches I consists of sodium nitrate, while for branches II it is ammonium nitrate. The molar fractions, without taking into account the solvent, were calculated from the following formulas:
XNH4NO3 )
[NH4NO3]
,
[NH4NO3] + [NaNO3]
XNaNO3 )
[NaNO3] [NH4NO3] + [NaNO3]
Also, for select experimental points, the X-ray diffraction analysis of the solid-phase samples was performed. Figures 3, 4, and 5 present the representative diffraction patterns for samples of the solid phase for branches I and II, as well as for the eutonic points. Figures 3 and 4 reveal only the patterns characteristic for sodium nitrate and ammonium nitrate, respectively. In contrast, Figure 5 contains diffraction peaks from both NaNO3 and NH4NO3. None of the diffractograms reveals a diffraction peak corresponding to any other component, suggesting that at the investigated temperature range no double salts or hydrates are formed in the solid phase.
Literature Cited (1) Collaborative paper. Research on the New method of soda production; Nicolaus Copernicus University: Torun˜, Poland, 1969. (2) Niederlin´ski, A.; Bukowski, A.; Koneczny, H. Soda and accompanying products; Scientific and Technical Publishers: Warsaw, 1978. (3) Koneczny, H. Course of process of soda production from NaNO3; Nicolaus Copernicus University: Torun˜, Poland, 1967. (4) Kołczkowski, A. Spontaneous decomposition of ammonium nitrate; Scientific papers Institute of Inorganic Technology and Mineral Fertilizers, Wroclaw Technical University: Wroclaw, Poland, 1980. (5) Bobrownicki, W.; Biskupski, A.; Kołaczkowski, A. On the thermal decomposition of ammonium-sodium nitrate. Appl. Chem. 1977, 21, 3-18. (6) Trypuc´, M.; Łyjak, G. Application of NaVO3 for the utilization of the after-filtration liquor from Solvay’s process. Ind. Eng. Chem. Res. 2000, 40, 2188-2192. (7) Trypuc´, M.; Łyjak, G. Solubility investigations in the NH4Cl+NaVO3+NH4VO3+NaCl +H2O system at 303K. J. Chem. Eng. Data 2000, 45, 872-875. (8) Trypuc´, M.; Druz˘ yn´ski, S. Investigation of the solubility in the NaVO3-NaNO3-H2O system. Ing. Eng. Chem. Res. 2007, 46, 2688-2692. (9) Trypuc´, M.; Kiełkowska, U. Solubility in the NaVO3 + NH4VO3 + H2O system. J. Chem. Eng. Data 1997, 42, 523 - 525. (10) Koneczny, H.; Lango, M. Research on the ternary system NaNO3NH4NO3-H2O; Nicolaus Copernicus University: Torun˜, Poland, 1967. (11) Bergman, A. G.; Shulyak, L. F. Zh. Neorg. Khim. 1972, 11411145. (12) Karnaukhov, A. S. Dokl. Akad. Nauk 1951, 81, 593-595. (13) Nikitina, E. A. Zh. Obshch. Kim. 1933, 3, 513-518. (14) Shenkin, Y. S.; Ruchnova, S. A.; Rodionova, N. A. Zh. Neorg. Khim.. 1975, 20, 2852-2854. (15) Struszyłn˜ski, M. QuantitatiVe and technical analysis; Polish Scientific Publishers: Warsaw, 1954; Vol. II. (16) Williams, W. J. Handbook of anion determination; Butterworth and Co Ltd.: London, 1979 (Polish translation Anion analysis; Polish Scientific Publishers: Warsaw, 1985). (17) Joint Committee on Powder Diffraction Standards, Powder Diffraction File, U.S.A. 1976. (18) Sułajmankułow, K. ILIM: Frunze, Russia, 1971.
ReceiVed for reView July 18, 2007 ReVised manuscript receiVed February 11, 2008 Accepted February 17, 2008 IE0709741
