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Solubility in the KVO3-KCl-H2O System from 293 to 323 K Mieczysław Trypuc´ ,* Katarzyna Białowicz, and Krzysztof Mazurek Faculty of Chemistry, Nicolaus Copernicus University, 7 Gagarin Street, 87-100 Torun´ , Poland
Solubility of potassium metavanadate and potassium chloride in aqueous solutions within temperature range of 293 K to 323 K was measured employing the isothermal solution saturation method. The vanadium ion concentration was determined using a spectrophotometric method with hydrogen peroxide. The chloride ion concentration was measured by means of the potentiometric titration method with prior reduction of vanadium ions with sodium sulfite(IV). These results were used to the construction of a polytherm section in the KVO3-KCl-H2O system. Additionally, the density interdependence of equilibrium solutions versus both salt concentrations, expressed in mole fractions, is presented. Introduction No experimental data has been found in a thorough literature review on the KHCO3 production process based on carbonation of water + ammonia solutions of respective salts, especially KCl. The fragmentary experimental data reported by Schuˆtze et al.1 and by Trypuc´ and Koneczny2 and Trypuc´3 concerning the reciprocal salt system of KCl-NH4HCO3-H2O clearly indicate that the proposed alternative route of carbonation of KCl ammonia solutions cannot be applied practically in conventional large scale production process because of the very low yield obtained. The expected yield is calculated to be of about 16.08% at T ) 30 °C, with 90% carbonation degree in the isothermal invariant point (triple point) of the described system. The value is increased up to 22.50% in the presence of 8.26 mol‚dm-3 urea for the same processing parameters. The authors’ investigations revealed the potential possibility of K2CO3 production based on the carbonation of KVO3-ammonia solutions.4,5 KVO3 is generated from KCl and V2O5 in the presence of steam or oxygen according to the reactions given below:
2KCl + V2O5 + H2O(steam) f 2KVO3 + 2HCl (1) 4KCl + 2V2O5 + O2 f 4KVO3 + 2Cl2
(2)
K2CO3 production process can be described by a general equation:
KVO3 + NH3 + CO2 + H2O T NH4VO3 + KHCO3 (3) In the course of carbonation of a KVO3 ammonia solution, a sparingly soluble precipitate of NH4VO3 is formed, whereas a mixture of KHCO3 and K2CO3 salts remain in solution. The detected proportion of these salts is correlated to the degree of carbonation of the system. Solids of NH4VO3, after the filtration stage, are calcinated as follows:
2NH4VO3 f 2NH3 + V2O5 + H2O
and the evolved NH3 and V2O5, after condensation of the steam, are recycled to the appropriate stages, i.e., KVO3 brine ammonization (reaction 3) and potassium metavanadate synthesis (reactions 1 and 2). The preliminary studies on the KVO3 synthesis based on KCl and V2O5 in the presence of steam or oxygen suggest that the conversion degree of vanadium oxide(V) into a final product of potassium metavanadate is linked to certain operating parameters such as temperature, time of processing, amount of KCl, steam, or oxygen excess in the reaction mixture. When a neutral carrier is introduced into the reaction mixture, the conversion degree of V2O5 is increased.6,7 A KVO3 synthesis was carried out in a flow reactor in the presence of air oxygen according to reaction 2 under the following conditions: temperature of 873 K, 4 h time of processing, 50% excess of KCl, and an air flux rate of 182 cm3‚min-1. The measured value of V2O5 conversion was 0.80. In the case of using steam for the KVO3 synthesis, the highest obtainable conversion of V2O5 was 0.73. The other processing parameters were as follows: temperature of 823 K, 4 h time of processing, 30% excess of KCl, and a steam flux rate of 1.22 g‚h-1.6 The conversion degree was increased up to 0.94 when the neutral carrier, i.e., SiO2 was introduced. The SiO2 a grain diameter was characterized by about 3 mm and used at a 160% excess relative to the overall reaction mixture mass. A thorough knowledge of the mutual salts solubility of KCl, V2O5 and KVO3 in water is essential for the determination of optimum operating conditions for the potassium metavanadate regeneration step out of the postreaction mixture. Equilibrium investigations in the following systems were carried out, i.e., (i) KCl-V2O5H2O; (ii) KVO3-V2O5-H2O; (iii) KCl-KVO3-H2O. The present paper deals with the results obtained on the mutual solubility in the KCl-KVO3-H2O system studied within 293 K to 323 K. No experimental data has been found in a thorough literature search concerning the solubility of the title system. Experimental Section
(4)
* Corresponding author. E-mail:
[email protected]. Phone: (0048) 566114569. Fax: (0048)566542477.
Chemicals. All substances used in experiments were of analytical purity grade: KVO3 (purity better than 98%, Aldrich Chemical Co., Inc.) and KCl (pure for analysis, POCh Gliwice, Poland).
10.1021/ie011004v CCC: $22.00 © 2002 American Chemical Society Published on Web 07/19/2002
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Experimental Procedure. The mutual salt solubility in the KVO3-KCl-H2O system was determined by the isothermal solution saturation method over the temperature range from 293 to 323 K. The main objective of the present paper was the designation of respective experimental points located along the solubility isotherms of the studied system employing the chemical analysis of equilibrium solutions. A typical experimental run can be described as follows. Erlenmeyer flasks, each of 100 cm3 volume, were equipped with a magnetic stirrer, and a weighed amount of KVO3, KCl, and distilled water was entered. Then, flasks were capped with rubber stoppers and transferred into a thermostated bath. Each sample solution was stirred continuously to achieve an equilibrium state between solution and the solid phase. The time to reach equilibrium was determined to be one week. Constant temperature was maintained applying the BIBLOCK-SCENTYFIC thermorelay with an accuracy of (0.02 K. After the desired time interval, stirring was discontinued and the solid phase was allowed to settle. Next, the clear equilibrium solution was decanted and sampled into a calibrated Ostwald pycnometer over temperature range 293 to 323 K. The overall content of the pycnometer was used for the density determinations of equilibrium solutions. The density measurements were performed with accuracy of (0.002 g‚cm-3. Next, samples were transferred quantitatively to graduated flasks, diluted with an appropriate amount of distilled water, and the chemical analysis was carried out to determine of the respective salt concentrations in the equilibrium solutions. A detailed description of the sampling procedure employed for the density determination and quantitative transfer of the pycnometer’s content has been described in earlier papers reported by the authors.8,9 Analytical Methods. The potassium chloride concentration in equilibrium solution was determined from the chloride ion concentration, which was evaluated by means of the argentometric method (0.1 M AgNO3) and the potentiometric titration method with a combined silver electrode (716 DMS Titrino titrator, Switzerland).10,11 The average relative error of the measurement was less than 1%. Because of the presence of undesirable vanadium(V) in solution, the analysis was performed after prior reduction of vanadium(V) to vanadium(IV) using sodium sulfite(IV) in a diluted (1: 7), heated solution of sulfuric acid.10 The overall potassium metavanadate concentration was evaluated on the basis of VO3- ion concentration in equilibrium. The VO3- ion concentration was measured by a UV-vis spectrophotometric method. This method is based on the reaction of the VO3- ion with H2O2 under acidic conditions to form V(O2)X3 or [V(O2)X5]2- type (where X is defined as an univalent anion).10,12 Schaeppi and Treadwell12 reported that, in the presence of sulfuric(VI) acid, substrates react under the equimolar conditions as expressed in the reaction given below:
(VO)2(SO4)3 + 2H2O2 u [V(O2)]2(SO4)3 + 2H2O (5) to form a red-brown stable complex. Its chemical stability was confirmed by the value of the reaction equilibrium constant K (equal to 1.2 × 105). The molar absorbency coefficient with wavelength of 450 nm is evaluated to be 300. Even such a small value enables the extensive analysis of the salt concentrations.
Figure 1. Course of branch I (corresponding to the saturated solutions of KVO3) of the solubility polytherm in the KVO3-KClH2O system. (b) T ) 293 K; (3) T ) 303 K; (9) T ) 313 K; ()) T ) 323 K.
Absorbency measurements were performed using a UV-vis U-2000 double beam spectrophotometer (HITACHI). A detailed description of the techniques used can be found in earlier papers reported by the authors.13 The error of the vanadium determination is approximately of 2%. Identification of Solid Phases. The identification of the solid phase in equilibrium with the mother solution was carried out by an X-ray method for randomly chosen points lying on the respective isotherm curves for the temperature range studied. Quantitative analysis of the selected precipitates was performed on the X-ray diffractometer HZG-4/A-2 (Germany). The X-ray determination of the solid phase was based on the distribution curves of the dispersed radiation intensity expressed as I ) f(θ). For each separate diffractogram, the interplanar distance d and the relative intensities I were given and then the comparison with numeric data listed in the “Powder diffraction file” was interpreted.14 Results and Discussion The qualitative analysis data of the equilibrium solutions are tabulated in Table 1. In respective columns are presented solution density, expressed in g‚cm-3, ion species amount, expressed both in mol‚dm-3 and mole fractions, and temperature, expressed in K. These results allowed the construction of solubility isotherms in the KVO3-KCl-H2O system, which are presented in Figure 1 and Figure 2. Each of the solubility isotherms is constructed of two branches. The branch marked I of the solubility isotherm refers to the concentration changes of potassium metavanadate with increasing concentrations of potassium chloride in equilibrium solution (Figure 1). The branch is limited by two specific points: the starting point defined by a saturated solution of KVO3 at each respective temperature and the finishing pointsthe eutonic point E (isothermal invariant point). Figure 1 indicates that the eutonic points are located almost along the OY axis. Therefore, branch II, which is defined by saturated solutions of KCl, of the respective isotherms is invisible in such a scale. Branch II describes
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Table 1. Solubility in the KVO3 + KCl + H2O System c/mol‚dm-3 F/g‚cm-3
KVO3
KCl
xa KVO3
KCl
solid phase
0 0.8787 0.9741 0.9905 0.9954 0.9975 0.9976 0.9978 0.9982 0.9983 0.9987 0.9992 1
KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 + KCl KCl KCl KCl KCl KCl
1.064 1.052 1.079 1.109 1.137 1.177 1.177 1.179 1.177 1.177 1.175 1.174 1.173
0.604 0.128 0.0463 0.0233 0.0146 0.00993 0.00962 0.00898 0.00722 0.00679 0.00512 0.00313 0
T ) 293 K 0 1 0.927 0.1213 1.742 0.0259 2.439 0.0095 3.190 0.0046 3.993 0.0025 4.010 0.0024 4.087 0.0022 4.081 0.0018 4.076 0.0017 4.07 0.0013 4.051 0.0008 4.015 0
1.085 1.065 1.060 1.063 1.105 1.130 1.186 1.185 1.185 1.183 1.182 1.181 1.181 1.180
0.842 0.490 0.236 0.0703 0.0319 0.0157 0.0108 0.0107 0.0104 0.00743 0.00676 0.00526 0.00351 0
T ) 303 K 0 1 0.354 0.5806 0.778 0.2327 1.264 0.0527 2.363 0.0133 2.853 0.0055 4.374 0.0025 4.369 0.0024 4.366 0.0024 4.363 0.0017 4.352 0.0016 4.334 0.0012 4.328 0.0008 4.280 0
0 0.4194 0.7673 0.9473 0.9867 0.9945 0.9975 0.9976 0.9976 0.9983 0.9984 0.9988 0.9992 1
KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 + KCl KCl KCl KCl KCl KCl KCl KCl
1.121 1.090 1.074 1.079 1.105 1.130 1.157 1.191 1.190 1.188 1.187 1.187
1.176 0.801 0.434 0.136 0.0691 0.0312 0.0205 0.0158 0.0106 0.00785 0.00525 0
T ) 313 K 0 1 0.339 0.7026 0.815 0.3475 1.548 0.0808 2.308 0.02901 3.04 0.0102 3.536 0.0058 4.605 0.0034 4.598 0.0023 4.574 0.0017 4.570 0.0011 4.533 0
0 0.2974 0.6525 0.9192 0.9709 0.9898 0.9942 0.9966 0.9977 0.9983 0.9989 1
KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 + KCl KCl KCl KCl KCl
1.171 1.130 1.109 1.094 1.094 1.088 1.085 1.088 1.089 1.133 1.192 1.198 1.196 1.195 1.193 1.192
1.768 1.286 0.900 0.687 0.648 0.476 0.402 0.241 0.222 0.0490 0.0203 0.0180 0.0168 0.0101 0.00819 0
T ) 323 K 0 1 0.328 0.7968 0.554 0.6190 0.852 0.4464 0.875 0.4255 1.039 0.3142 1.143 0.2602 1.612 0.1301 1.680 0.1167 3.149 0.0153 4.569 0.0044 4.822 0.0037 4.821 0.0035 4.820 0.0021 4.819 0.0017 4.818 0
0 0.2032 0.3810 0.5536 0.5745 0.6858 0.7398 0.8699 0.8833 0.9847 0.9956 0.9963 0.9965 0.9979 0.9983 1
KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 KVO3 + KCl KCl KCl KCl KCl
the concentration changes of KCl with increasing concentration of KVO3. It seemed reasonable to present branch II on a separate diagram (Figure 2). When additional mass portions of KCl are introduced into a saturated solution of KVO3, at each studied temperature, points that compose branches I of the isotherms are located along the curves shown in Figure 1. The specific course of respective curves indicates clearly that even a small increase in the KCl concentration causes a significant decrease in the KVO3 concentration values in equilibrium solution toward the eutonic points E.
Figure 2. Course of branch II (corresponding to the saturated solutions of KCl) of the solubility polytherm in the KVO3-KClH2O system. (b) T ) 293 K; (3) T ) 303 K; (9) T ) 313 K; ()) T ) 323 K.
A detected effect of the common ion effect existence was also observed in the NaCl-NaVO3-H2O system within temperature range 293 K to 323 K.13 When potassium metavanadate is introduced into a saturated solution of potassium chloride, it influences the solubility of KCl only insignificantly, and all the experimental points are located along a straight line, as shown in Figure 2. When the KVO3 concentration values are increased in the KCl saturated solution within studied temperature range, the concentration of potassium chloride is increased only insignificantly toward the eutonic points E. The smallest increment is detected at T ) 323 K. The specific course of the respective curves plotted in Figures 1 and 2 implies that the solubility of KVO3 and KCl is increased with temperature rise. It is also apparent that temperature influences the solubility of potassium chloride more than that of potassium metavanadate. Data analysis of the results collected in Table 1 points out that for each studied temperature densities of KVO3 saturated solutions are at first decreased with increasing concentration of KCl. Then, with the increasing concentrations of potassium chloride, the density values in equilibrium solution are increased, reaching the maximum at the eutonic point E. When these specific points are crossed over, the density values are slightly diminished and reach the level of those of saturated solutions of KCl. The existence of only one eutonic point on each of the plotted isotherm confirms that no binary salts are generated in the studied system. Concentration values of respective compounds in the studied system, expressed in mole fractions, are presented in Table 1. These data gave grounds for construction of the equilibrium diagram of propertycomposition type. The interdependence between the density of KVO3 saturated solution and the salt concentration expressed in mole fractions is presented in Figure 3. The similar relationship for the saturated solutions of KCl is presented in Figure 4. The plotted diagrams are employed for the identifications of binary
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Conclusions We draw the following conclusions from this work. (1) The presence of potassium chloride in saturated solutions of KVO3 is linked with a strong common ion effect on potassium metavanadate, within the temperature range of 293 K to 323 K. (2) Potassium metavanadate influences on the solubility of potassium chloride only insignificantly. (3) The solubility of KVO3 and KCl increases with increasing temperature. (4) The density of equilibrium solutions is dependent upon the concentration of potassium chloride. (5) In the system studied no new chemical compounds are created. Acknowledgment This manuscript was supported by a grant (No. 3 T09B 04218) from Komitet Badan´ Naukowych (State Committee for Scientific Research). Literature Cited Figure 3. Density relationship of KVO3 saturated equilibrium solutions versus the salts amount expressed in mole fractions. (b) T ) 293 K; (3) T ) 303 K; (9) T ) 313 K; ()) T ) 323 K.
Figure 4. Density relationship of KCl saturated equilibrium solutions versus the salt amounts expressed in mole fractions. (b) T ) 293 K; (3) T ) 303 K; (9) T ) 313 K; ()) T ) 323 K.
salt or other addition compounds detected in the system.15 The monotonic mode of the curves plotted in Figures 3 and 4 indicates clearly that there are no changes related to the creation of a new solid phase. The same confirmation was obtained from an X-ray analysis of the solid phase. Over the temperature range studied, the solid phase is composed of KVO3 for points that compose branch I, KCl for points that compose the branch II of the solubility isotherm, or the mixture of both salts detected in the eutonic points E.
(1) Schu¨tze, H.; Piechowicz, T.; Pustelnik, W. Helv. Chim. Acta. 1943, 26, 238 (cited in Pelsh, A. D. Spravotschnik po Rastvorimosti Solyevykh System; Nauka, Goskchimisdat: Leningrad, Russia, 1961). (2) Trypuc´, M.; Koneczny, H. Badanie ro´wnowagi układu KClNH3-CO2-H2O w temperaturze 30 °C. Chem. Stos. 1973, 2, 147. (3) Trypuc´, M. Badanie ro´wnowagi układu KCl-NH3-CO2H2O w obecnos’ci mocznika w temperaturze 30 °C. Chem. Stos. 1973, 2, 135. (4) Trypuc´, M.; Stefanowicz, D. I. Solubility in the KVO3 + NH4VO3 + H2O System. J. Chem. Eng. Data 1997, 42, 1140. (5) Praca zbiorowa. Technologia chemiczna na przel-omie wieko´ w; Wydawnictwo Stałego Komitetu Kongreso´w Technologii Chemicznej: Gliwice, Poland, 2000. (6) Trypuc´, M.; Torski, Z.; Kiełkowska, U. Experimental Determination of the Optimum Conditions of KVO3 Synthesis Based on KCl and V2O5 in the Presence of Steam. Ind. Eng. Chem. Res. 2001, 40, 1022. (7) Trypuc´, M.; Torski, Z.; Białowicz, K. Investigations on the influence of silicon dioxide introduced as a neutral carrier into the reaction mixture on V2O5 conversion into KVO3. Pol. J. Chem. Technol. 2001, 1, 28. (8) Trypuc´, M.; Białowicz, K. Solubility of NH4VO3 in Water + Ammonia. J. Chem. Eng. Data 1997, 42, 318. (9) Trypuc´, M.; Białowicz, K. Solubility in the System NaVO3 + NH4VO3 + NH3 + H2O from 293 to 323 K. J. Chem. Eng. Data 2000, 45, 492. (10) Williams, W. J. Oznaczanie aniono´ w; PWN: Warsaw, Poland, 1985. (11) Minczewski, J.; Marczenko, Z. Chemia analityczna; PWN: Warsaw, Poland, 1987. (12) Sandell, G. Calorimetric metal analysis; Interscience Publishers: New York, 1959. (13) Trypuc´, M.; -Lyjak, G. Solubility in the NaVO3-NaCl-H2O system. Pol. J. Appl. Chem. 1997, XLI, 187. (14) Powder Diffraction File; Joint Committee on Powder Diffraction Standards: USA, 1976. (15) Sułajmankułov, K. Sojedinienia karbamida s nieorganitscheskimi soliami; ILIM: Frunze, Russia, 1971.
Received for review December 12, 2001 Revised manuscript received May 15, 2002 Accepted June 9, 2002 IE011004V
