Ind. Eng. Chem. Res. 2009, 48, 6937–6942
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Phase Diagram for the NH4NO3 + NaVO3 + NH4VO3 + NaNO3 + H2O System at 293 and 303 K Mieczysław Trypuc´* and Sebastian Druz˙yn´ski Faculty of Chemistry, Department of Chemical Technology, Nicolaus Copernicus UniVersity, Gagarina 7, 87-100 Torun´, Poland
The solubility isotherms were determined for the NH4NO3 + NaVO3 + NH4VO3 + NaNO3 + H2O system at 293 and 303 K. Based on these isotherms, the maximum yields have been determined for the conversion of ammonium nitrate to ammonium meta-vanadate. The location of the triple points P1 and P2 has been determined on the equilibrium plots prepared as the planar projection, according to the Ja¨necke method. The results are necessary for determining the optimal conditions for utilization of post-filtration lye obtained from the soda-chloride-saltpeter (SCS) method of soda ash production. 1. Introduction Sodium carbonate is used in many branches of industry, such as the production of glass, drugs, and cosmetics or in the food industry.1,2 Currently, the most frequently used methods of soda ash production are the Solvay method (Europe) and DUAL (Japan, China). A convenient alternative for these processes is the soda-chloride-saltpeter method (SCS), which is based on the carbonization of the ammoniated brine of sodium nitrate (eq 1) and subsequent calcination of the obtained sodium bicarbonate (eq 2).2,3
meta-vanadate does not cause the risk of explosion. The flow diagram of the proposed modification is presented in Figure 2. Determination of the optimal conditions for the conversion of ammonium nitrate into sodium nitrate (and determination of the yield of that reaction) requires detailed knowledge of the course of the isotherms that separate the specific areas of salt co-crystallization on the phase diagrams for the pairs of exchanging salts in the NH4NO3 + NaVO3 + H2O system.8,9 Currently, there are no literature data available on mutual solubility for the previously mentioned pairs of exchanging salts.
NaNO3 + NH3 + CO2 + H2O T NaHCO3 + NH4NO3 (1) 2NaHCO3 f Na2CO3 + CO2 + H2O
(2)
In the SCS process of soda ash production, valuable byproducts are obtained, such as chlorine and ammonium-sodium nitrate, which defines the waste-less character of this technology. The flow diagram of the sodium carbonate production from sodium nitrate is presented in Figure 1. The significant disadvantage of the SCS method are the steps of concentration of the solutions that remain after the filtration of sodium bicarbonate and after the crystallization of ammonium-sodium nitrate. These processes are dangerous because of the explosive properties of ammonium nitrate.4-6 One must consider that the solution remaining after the filtration of sodium bicarbonate contains a small amount of sodium chloride from the production of sodium nitrate. During the process of concentration of that solution at the elevated temperature, Clions catalyze the uncontrolled decomposition of ammonium nitrate.4-6 That problem can be solved by modification of the SCS process with the double exchange reaction between ammonium nitrate and sodium meta-vanadate, according to eq 3.6-9 NH4NO3 + NaVO3 T NH4VO3 + NaNO3
(3)
According to eq 3, the sparingly soluble ammonium metavanadate precipitates from the reaction mixture in the amount equivalent to that of ammonium nitrate, while sodium nitrate remains in the solution. Isolation of the solid sodium nitrate from the solution generated after the filtration of ammonium * To whom correspondence should be addressed. Tel.: (+48) 566114569. Fax: (+48) 566542477. E-mail:
[email protected].
Figure 1. Flow diagram of the soda-chloride-saltpeter method (SCS) method.2
10.1021/ie9004139 CCC: $40.75 2009 American Chemical Society Published on Web 07/02/2009
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Ind. Eng. Chem. Res., Vol. 48, No. 15, 2009 Table 1. Preparation of Solutions Corresponding to Different Sections of the Isotherm
Figure 2. Flow diagram of the process of utilization of the post-filtration lye from the SCS method.9
Data on the mutual solubility in the ternary subsystems of the quaternary system of interest are available for the NaVO3 + NH4VO3 + H2O system,10 whereas, for the NH4NO3 + NaNO3 + H2O system, only partial data are published.11-16 Therefore, in the first step of the reported research, the mutual solubility was determined for three ternary systems (NaVO3 + NaNO3 + H2O, NH4NO3 + NaNO3 + H2O, and NH4NO3 + NH4VO3 + H2O) at a temperature range of 293-323 K. The obtained results have been published in previously published papers.6-8 The next stage of research focused on the determination of the solution composition and the location of triple points (P1 and P2) on the equilibrium plots for the pairs of the exchanging salts, as well as on determination of the time necessary for the system equilibration. The obtained results have also been published previously.9 In connection with the aforementioned statements, in the next stage of our research, we decided to determine the curves of the isotherms that separate the specific areas of salt co-crystallization on the equilibrium plot in the planar projection for the pairs of exchanging salts in the NH4NO3 + NaVO3 + H2O system. 2. Experimental Section 2.1. Instruments and Reagents. The research was conducted with the use of a water thermostat (Polystat CC1) with a precision of (0.02 K; the required temperature was controlled with a mercury thermometer that had a precision of (0.1 K. The powder X-ray diffraction (XRD) experiments for the solid phase were performed with an X-ray diffractometer (Model
section of isotherm
initial point
solid phases
additive
E1-P2 E4-P2 E3-P1 E2-P1 P1-P2
E1
NH4NO3, NH4VO3
NaNO3
E3 E2 P1
NaNO3, NaVO3 NaVO3, NH4VO3 NH4VO3, NaNO3
NH4VO3 NaNO3 NH4NO3
X-Pert PRO, Philips). The spectrophotometric analyses were performed with the Hitachi Model U-2000 double-beam apparatus. In the research, analytical-grade reagents were used: NH4VO3 (g99% purity, Aldrich), NaVO3 (g98% purity, Fluka), NH4NO3 (g99% purity, POCH), and NaNO3 (g99.5% purity, POCH). 2.2. Methods. The equilibrium investigation for the NH4NO3 + NaVO3 + H2O system was performed with the method of isothermal saturation of solutions at 293 K and 303 K. For the preparation of solutions with compositions that determine the course of the isotherm branches, the required eutonic solution saturated with two salts was used and the increasing amounts of the third salt were added until the solution was saturated with three salts (P1 or P2). The section of the isotherm between P1 and P2 was determined using a similar procedure. There was only one difference: increasing amounts of ammonium nitrate were added to the starting solution of the composition corresponding to P1. The scheme of preparation of the required mixtures is presented in Table 1. Preparation of solutions corresponding to the E4-P2 section of the isotherm was not possible, because of the low solubility of ammonium metavanadate in the saturated solutions of sodium and ammonium nitrates. The required amounts of salts were placed into a Erlenmeyer flask with a volume capacity of 100 cm3; a magnetic stirring bar was placed into the flask and an appropriate amount of redistilled water was added. The solutions were thermostatted at the required temperature and stirred for 240 h. The stirring then was stopped, and after the necessary amount of time for sedimentation, the equilibrated solution was sampled into the Ostwald pycnometer, to determine the density (with a precision of (0.002 g/cm3). The solution from the pycnometer was subsequently transferred quantitatively into a measuring flask with a volume capacity of 500 cm3. The obtained solutions were analyzed to determine the concentration of sodium, ammonium, and vanadate ions, while the concentration of nitrate ions was calculated from the ion balance. The obtained data for the sodium and vanadate ions indicated that their molar fractions were determined to be in the range of 0-1. 2.3. Analytical Methods. Vanadate ions at concentrations larger than 2 × 10-2 M were determined spectrophotometrically as a complex with hydrogen peroxide. In the presence of concentrated sulfuric acid and a 3% solution of hydrogen peroxide, vanadate(V) ions form the compounds V(O2)X3 and/ or V(O2)X52-, where X is a monoanion (eq 4): (VO)2(SO4)3 + 2H2O2 T [V(O2)]2(SO4)3 + 2H2O
(4)
This compound has a maximum absorbance at a wavelength of 450 nm, and the molar absorption coefficient is 300 dm3 mol-1 cm-1.17 For samples of solutions with a vanadium concentration of 303 K. At the specified temperature, the thermodynamical equilibrium state between β-NaVO3 and NaVO3 · 2H2O was attained the experiment had been conducted for 240 h. Under these conditions, the position of the determined isotherms is stable with time and is dependent only on temperature changes. For other samples of the solid phase, the formation of hydrates or double salts was not detected. Typical diffractograms of the solid phase at triple points P1 and P2 at 293 and 303 K are presented in Figure 5. 4. Conclusions Based on the experimental data, the phase diagrams for the NaVO3 + NH4NO3 + NaNO3 + NH4VO3 + H2O system at 293 and 303 K were plotted. The position of the triple points on the equilibrium indicates that points P1 are inconvergently saturated while points P2 are convergently saturated. The obtained results allowed us to conclude that the chemically stable pair of salts in the investigated system is sodium nitrate and ammonium meta-vanadate, whereas an unstable pair is formed by sodium meta-vanadate and ammonium nitrate.
Ammonium meta-vanadate is the salt that reveals the smallest solubility in the investigated system; the area of its crystallization is larger than the areas corresponding to other components of the investigated system. Low solubility of ammonium metavanadate at point P1 determines the high yield of precipitation of that salt from the post-filtration lye generated in the SCS method. The determined maximum yields of conversion at 293 and 303 K are 93.6% and 92.8%, respectively. Literature Cited (1) Niederliski, A.; Bukowski, A.; Koneczny, H. Soda and Accompanying Products; Scientific and Technical Publishers: Warsaw, Poland, 1978. (2) Research on the New Method of Soda Production (collaborative paper); Nicolaus Copernicus University: Torun´, Poland, 1969. (3) Koneczny, H. Course of Process of Soda Production from NaNO3; Nicolaus Copernicus University: Torun´, Poland, 1967. (4) Kołaczkowski, A. Spontaneous Decomposition of Ammonium Nitrate Scientific papers Institute of Inorganic Technology and Mineral Fertilizers: Wrocław Technical University, Wrocław, Poland, 1980. (5) Bobrownicki, W.; Biskupski, A.; Kołaczkowski, A. On the thermal decomposition of ammonium-sodium nitrate. Pol. J. Appl. Chem. 1977, 21, 3–18. (6) Trypuc´, M.; Druz˙yn´ski, S. Investigation of the solubility in the NaVO3-NaNO3-H2O System. Ind. Eng. Chem. Res. 2007, 46, 2688–2692. (7) Trypuc´, M.; Druz˙yn´ski, S.; Kiełkowska, U.; Mazurek, K. Utilization of the post-filtration lye from the SCS method of soda production. Pol. J. Chem. Technol. 2007, 9 (4), 59–62. (8) Trypuc´, M.; Druz˙yn´ski, S. Solubility in the NaNO3 + NH4NO3 + H2O System. Ind. Eng. Chem. Res. 2008, 47, 3767–3770. (9) Trypuc´, M.; Druz˙yn´ski, S.; Mazurek, K. Plotting of the solubility isotherm for the NH4NO3 + NaVO3 + H2O system. Pol. J. Chem. Technol. 2008, 10 (4), 11–14. (10) Trypuc´, M.; Kiełkowska, U. Solubility in the NaVO3 + NH4VO3 + H2O system. J. Chem. Eng. Data 1997, 42, 523–525. (11) El Guendouzi, M.; Marouani, M. Thermodynamic properties of aqueous mixed electrolyte {yNH4NO3 + (1- y)NaNO3}(aq) at T ) 298.15 K. J. Chem. Eng. Data 2005, 50, 334–339. (12) Koneczny, H. Research on the ternary system NaNO3-NH4NO3H2O; Nicolaus Copernicus University: Torun´, Poland, 1967. (13) Bergman, A. G.; Shulyak, L. F. Ammonium nitrate-sodium nitrate-water system. Zh. Neorg. Khim. 1972, 1141–1145. (14) Karnaukov, S. The solubility isotherm of the ternary system sodium nitrate-ammonium nitrate-water at 25 °C. Dokl. Akad. Nauk 1951, 81, 593–595. (15) Nikitina, E. A. Equilibrium in the system NH4NO3-NaNO3-H2O. Zh. Obshch. Kim. 1933, 3, 513–518. (16) Shenkin, Y. S.; Ruchnova, S. A.; Rodionova, N. A. Sodium nitrateammonium nitrate-water system. Zh. Neorg. Khim. 1975, 20, 2852–2854. (17) Williams, W. J. Handbook of Anion Determination; Butterworth and Co., Ltd.; London, 1979. (18) Struszyn´ski, M. QuantitatiVe and Technical Analysis; Polish Scientific Publishers: Warsaw, Poland, 1954; Vol. II. (19) Powder Diffraction File; Joint Committee on Powder Diffraction Standards: Newtowne Square, PA, 1976.
ReceiVed for reView March 13, 2009 ReVised manuscript receiVed May 27, 2009 Accepted June 14, 2009 IE9004139
