Article pubs.acs.org/jced
Phase Equilibrium for the Ternary Systems (KCl + K2SO4 + H2O) and (KH2PO4 + K2SO4 + H2O) at 288.15 K and Atmospheric Pressure Wei Liu,†,‡ Jun Zhou,*,§ Zi-wei Zhang,† Shuang Chen,† and Shang-yu Liu† †
College of Energy Resources, Chengdu University of Technology, Chengdu, Sichuan 610059, P. R. China Post-Doctoral Research Cente, Tarim Oilfield Company, PetroChina, Korla, XinJiang 841000, P. R. China § Research Institute of Petroleum Engineering, Sinopec, Beijing 100101, P. R. China ‡
ABSTRACT: The phase equilibrium of (KCl + K2SO4 + H2O) and (KH2PO4 + K2SO4 + H2O) at 288.15 K is studied by isothermal solution saturation method and wet residues. The equilibrium solid phases are analyzed by the Schreinemaker’s method of wet residues and verified by X-ray diffraction (XRD). On the basis of the experimental data, the diagram of density versus composition and the phase diagram are plotted. The crystallization regions are determined. In the two systems, KCl and KH2PO4 have a strong salting-out effect on K2SO4, and the salting-out effect of KCl on K2SO4 is stronger than that of KH2PO4 on K2SO4. There are in all two crystalline regions, two univariant curves, and one invariant point. The crystalline region of K2SO4 is the largest, whereas that of KCl is the smallest. All results can offer fundamental data support for optimizing processes and further theoretical studies.
■
INTRODUCTION KH2PO4, as an important compound fertilizer and chemical material, is widely applied in pharmaceutical, agricultural, and food industries.1,2 Many processes, such as solvent extraction technology, neutralization, ion exchange, and metathesis, are applied to produce KH2PO4.2,3 In the solvent extraction technology, the product often contains many impurities.4−8 The Cl− and SO42− accumulate in the crystalline mother liquid and cannot be removed after a series of removing impurity processes, which brings about a low quality of potassium dihydrogen phosphate. Therefore, to optimize the process and prepare a high quality of potassium dihydrogen phosphate, it is essential to study the phase equilibrium. Wang et al.9 reported the phase equilibrium data of KH2PO4 + K2SO4 + H2O at 298.15 and 333.15 K. In the literature,10 the phase equilibrium of K2SO4 + KCl + H2O at 303.15 K has been reported. However, these data are insufficient to resolve the separation above, and therefore, an extensive study at other temperatures needs to be done. The phase equilibrium of the systems (KH2PO4 + K2SO4 + H2O) and (K2SO4 + KCl + H2O) at 288.15 K have not been reported yet. This paper is conducive to fill the blank of data and new experimental data given in this study are useful for optimizing the crystallization and separation processes. Additionally, the research can offer fundamental data support for further theoretical studies.
Table 1. Purities and Suppliers of Chemicals mass fraction purity
KH2PO4
≥0.995
K2SO4
≥0.995
KCl
≥0.995
source Tianjin Bodi Chemical Holding Co. Ltd., China Tianjin Bodi Chemical Holding Co. Ltd., China Chengdu Kelong Chemical Reagent Co. Ltd., China
work is purchased from Kelong Chemical Reagent Co. Ltd., Chengdu, China. The sources and purity of the chemicals are listed in Table 1. Doubly deionized water (electrical conductivity ≤1 × 10−4 S·m−1) is used in the work. Apparatus. ASHZ-88 type constant temperature water bath oscillator with a precision of 0.3 K is employed to measure phase equilibrium and made in Jintan Medical Instrument Corporation, Jiangsu, China. The Philips X Pert Pro MPD X-ray diffraction (XRD) analyzer is employed for XRD characterizations. Experimental Methods. The method of isothermal solution saturation11−13 is employed to determine the solubility of the ternary system. The famous Schreinemaker’s method of moist residues13−15 is applied to determine the equilibrium solid phase in the experiments indirectly, and the solid phase is also tested by XRD to verify the crystalloid composition. On the basis of a fixed ratio and ensuring that one of the components is excessive, the experimental components are added into a
■
METHODOLOGY Materials. Potassium dihydrogen phosphate (KH2PO4, ≥0.995 mass fraction) and potassium sulfate (K2SO4, ≥0.995 mass fraction) are purchased from Bodi Chemical Holding Co. Ltd., Tianjin, China. Potassium chloride (KCl, ≥0.995 mass fraction) used in the © XXXX American Chemical Society
chemical
Received: December 31, 2015 Accepted: May 17, 2016
A
DOI: 10.1021/acs.jced.5b01111 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
series of conical flasks (250 mL) gradually, and the sealed flask is placed into the oscillator. The oscillator vibrates continuously at 288.15 K (the standard uncertainty of 0.3 K). In a pre-experiment, the liquid phase of the samples is analyzed at every 2 h. It demonstrates that the equilibrium is reached when the analytical results keep constant. It is shown that the phase equilibrium is reached in 10 h. After equilibrium, the oscillation is stopped and the system is allowed to stand for 2 h to make sure that all the suspended crystals settle. The wet residues and liquid phase are transferred to a 250 mL volumetric flask, respectively. Simultaneously, some other liquid phases are used to determine density individually. Finally, these samples are quantitatively analyzed by chemical methods. More details of the experimental method and the procedure of the transfer, collection and preparation of samples are presented in the previous papers.9,10,12 Analysis. The concentration of H2PO4− is analyzed by the quinoline phosphomolybdate gravimetric method,16 and the relative standard uncertainty is 0.01. The sulfate concentration is determined by the gravimetric method of barium chloride,17,18 and the relative standard uncertainty is 0.01 by this method. The chloride is measured by Volhard method,19,20 and the relative standard uncertainty is 0.02. The density is measured by a specific weighing bottle method, and the relative standard uncertainty is 0.001. Each experimental result is achieved from the average value of three parallel measurements. The equilibrium solid phase is analyzed by XRD characterizations.
Table 2. Mass Fraction Solubility of the Ternary KCl + K2SO4 + H2O System at Temperature = 288.15 K and Pressure = 0.1 MPaa composition of liquid phase, 100w
composition of wet residue phase, 100w
no.d
100w1b
100w2
100w1
100w2
1, N 2 3 4 5 6 7 8 9 10 11, F 12, F 13 14, E
0.00 2.29 4.45 6.58 8.98 10.64 12.93 16.30 19.43 22.84 24.21 24.21 24.45 24.72
9.12 7.44 5.98 4.63 3.83 3.19 2.70 1.98 1.51 1.16 1.01 1.01 0.51 0.00
c
c
1.25 2.19 3.39 4.45 5.52 6.14 7.65 9.09 10.53 27.33 43.89 57.61 ND
51.39 54.00 50.63 52.49 50.46 54.00 53.92 54.09 54.59 45.24 14.32 0.29 ND
densities of liquid phase ρ/(g·cm−3)
equilibrium solid phase
1.0756 1.0765 1.0783 1.0814 1.0897 1.0969 1.1080 1.1258 1.1437 1.1651 1.1746 1.1742 1.1711 1.1682
K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 + KCl K2SO4 + KCl KCl KCl
a
Standard uncertainties u(T) = 0.3 K, ur(p) = 0.05, ur(w1) = 0.02, ur(w2) = 0.01, ur(ρ) = 0.001. bw1, mass fraction of KCl; w2, mass fraction of K2SO4. cNot determined. dE, F, and N have the same meaning as described in Figure 2.
■
concentration with the KCl concentration increasing in the equilibrium solution. The K2SO4 concentration decreases sharply with increasing the KCl concentration, which illustrates that KCl has a strong salting-out effect on K2SO4. As indicated in Figure 2, along the curve EF, we connect the composition points of wet residue phase with liquid phase and then extend, the intersection of these straight lines is approximately the equilibrium solid phase for KCl. The same method is utilized to analyze the equilibrium solid phase of NF, and the intersection is K2SO4. As indicated in Figure 3, the equilibrium solid phase of F is analyzed by XRD and verified to be coexistence of K2SO4 and KCl. Consequently, the ternary system is a simple eutectic type at 288.15 K. Figure 2 shows that WEFN denotes unsaturated region at 288.15 K. AFN denotes crystallization region of K2SO4, while BFE denotes crystallization region of KCl. Zone AFB represents the mixed crystalline region of K2SO4 + KCl. It is obvious that crystallization region of KCl is much smaller than that of K2SO4. Figure 4 indicates the relationship between the mass fraction of KCl and the density in the solution. With increasing the KCl concentration, the density has the tendency to increase and then the density declines slightly afterward. At the cosaturated point F, the density reaches a maximum value. Solid−Liquid Phase Equilibrium for (KH2PO4 + K2SO4 + H2O). The phase equilibrium experimental data is shown in Table 3, and the ternary phase diagram is drawn in Figure 5. As indicated in Figure 5, A, C, and W denote solid K2SO4, solid KH2PO4, and H2O, respectively; Point D, an invariant point, reflects the cosaturated solution of K2SO4 and KH2PO4 at 288.15 K; N and M represent the solubility of K2SO4 and KH2PO4 in water at 288.15 K, respectively. The saturated liquid line MDN consists of two branches. Branch MD corresponds to the saturated KH2PO4 solution and visualizes changes of the KH2PO4 concentration with increasing the K2SO4 concentration. Branch ND corresponds to the saturated K2SO4 solution and indicates changes of the K2SO4 concentration with
RESULTS AND DISCUSSION In Figure 1, the experimental data is compared with literature data21,22 and it is found that the experimental values coincide
Figure 1. Solubility for KH2PO4, KCl, or K2SO4 in pure water at 288.15 K.
with the values from the references, which demonstrates that the experimental devices and methods are feasible. Solid−Liquid Phase Equilibrium for (KCl + K2SO4 + H2O). The experimental data is listed in Table 2, and the phase diagram is plotted in Figure 2. As indicated in Figure 2, A, B, and W denote solid K2SO4, solid KCl, and H2O, respectively; Point F, an invariant point, reflects the cosaturated solution of K2SO4 and KCl at 288.15 K; N and E represent the solubility of K2SO4 and KCl in water at 288.15 K, respectively. The saturated liquid line EFN consists of two branches. Branch EF corresponds to the saturated KCl solution and visualizes changes of the KCl concentration with increasing the K2SO4 concentration. Branch NF corresponds to the saturated K2SO4solution and indicates changes of the K2SO4 B
DOI: 10.1021/acs.jced.5b01111 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Figure 2. Equilibrium phase diagram of the ternary system KCl + K2SO4 + H2O at 288.15 K: ■, equilibrium liquid phase composition; ●, moist solid phase composition; A, pure solid of K2SO4; B, pure solid of KCl; W, water; E, solubility of KCl in water; N, solubility of K2SO4 in water; F, cosaturated point of KCl and K2SO4.
Figure 3. X-ray diffraction pattern of the invariant point F.
As indicated in Figure 5, along the curve MD, we connect the composition points of wet residue phase with liquid phase and then extend, the intersection of these straight lines is approximately the equilibrium solid phase for KH2PO4. The same way is utilized to analyze the equilibrium solid phase of DN, and the intersection is K2SO4. As indicated in Figure 6, the equilibrium solid phase of D is analyzed by XRD and verified to be coexistence of K2SO4 and KH2PO4. Consequently, the ternary system is a simple eutectic type at the investigated temperature. Figure 5 shows that WMDN denotes unsaturated region at 288.15 K. ADN denotes crystallization region of K2SO4, while MDC denotes crystallization region of KH2PO4. Zone ADC denotes the mixed crystalline region of K2SO4 + KH2PO4. It is obvious that crystallization region of KH2PO4 is much smaller than that of K2SO4. In the two systems, the crystalline region of KCl is the smallest, while that of K2SO4 is the largest. Figure 7 indicates the relationship between the mass fraction of KH2PO4 and the density in the solution. With an increase of the concentration of KH2PO4, the density has the tendency to increase and then the density declines slightly afterward. At the cosaturated point D, the density reaches a maximum value.
Figure 4. Density vs 100w (KCl) in the ternary system (KCl + K2SO4 + H2O). N, F, and E have the same meaning as described in Figure 2.
increasing the KH2PO4 concentration. The solubility of K2SO4 decreases sharply with increasing the concentration KH2PO4, which illustrates that KH2PO4 has a strong salting-out effect on K2SO4. In the two ternary systems, the salting-out effect of KCl on K2SO4 is stronger than that of KH2PO4 on K2SO4. C
DOI: 10.1021/acs.jced.5b01111 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Table 3. Mass Fraction Solubility of the Ternary KH2PO4 + K2SO4 + H2O System at Temperature = 288.15 K and Pressure = 0.1 MPaa composition of liquid phase, 100w no.d 1, N 2 3 4 5 6 7 8, D 9, D 10 11 12, M
100w1b 9.12 8.33 7.62 6.73 6.08 5.64 5.30 5.00 5.00 3.53 1.94 0.00
100w2 0.00 2.07 4.39 6.48 8.51 10.36 12.14 14.33 14.33 14.82 15.55 16.53
composition of wet residue phase, 100w 100w1
100w2
c
c
50.41 45.83 48.90 51.03 47.84 45.33 35.74 16.11 2.00 1.13
1.26 2.70 3.62 4.55 5.81 7.08 17.61 51.14 52.99 55.18
c
c
densities of liquid phase ρ/(g·cm−3)
equilibrium solid phase
1.0756 1.0843 1.0952 1.1049 1.1151 1.1255 1.1365 1.1502 1.1504 1.1425 1.1332 1.1229
K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 KH2PO4 + K2SO4 KH2PO4 + K2SO4 KH2PO4 KH2PO4 KH2PO4
a
Standard uncertainties u(T) = 0.3 K, ur(p) = 0.05, ur(w1) = 0.01, ur(w2) = 0.01, ur(ρ) = 0.001. bw1, mass fraction of K2SO4; w2, mass fraction of KH2PO4. cNot determined. dN, D, and M have the same meaning as described in Figure 4.
Figure 5. Equilibrium phase diagram of the ternary system KH2PO4 + K2SO4 + H2O at 288.15 K: ■, equilibrium liquid phase composition; ●, moist solid phase composition; A, pure solid of K2SO4; C, pure solid of KH2PO4; W, water; M, solubility of KH2PO4 in water; N, solubility of K2SO4 in water; D, cosaturated point of KH2PO4 and K2SO4.
Figure 6. X-ray diffraction pattern of the invariant point D. D
DOI: 10.1021/acs.jced.5b01111 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
(9) Wang, P.; Li, J.; Luo, J. H.; Jin, Y.; Yang, Z. P. Solid−Liquid Phase Equilibrium for the Ternary System K2SO4+ KH2PO4+ H2O at (298.15 and 333.15) K. J. Chem. Eng. Data 2012, 57 (3), 836−839. (10) Liu, W.; Xiao, Y.; Liu, Y. S.; Zhang, F. X.; Qu, J. F. Phase Equilibrium for the Ternary System K2SO4 + KCl + H2O in Aqueous Solution at 303.15 K. J. Chem. Eng. Data 2015, 60 (4), 1202−1205. (11) Shu, Y. G.; Lu, B. L.; Wang, X. R. Phase Diagram Analyses of Inorganic Chemical Production: Basic Theory; Chemical Industry Press: Beijing, 1985 (in Chinese). (12) Zhang, X. R.; Ren, Y. S.; Li, P.; Ma, H. J.; Ma, W. J.; Liu, C.; Wang, Y.; Kong, L.; Shen, W. Solid−Liquid Equilibrium for the Ternary Systems (Na2SO4 + NaH2PO4 + H2O) and (Na2SO4 + NaCl + H2O) at 313.15 K and Atmospheric Pressure. J. Chem. Eng. Data 2014, 59 (12), 3969−3974. (13) Niu, Z. D.; Cheng, F. Q. The Phase Diagram of Salt−Water System and its Application; Tianjin University Press: Tianjin, China, 2002. (14) Schott, H. A Mathematical Extrapolation for the Method of Wet Residues. J. Chem. Eng. Data 1961, 6, 324−324. (15) Schreinemakers, F. A. H. Graphical deductions from the solution isotherms of a double salt and its components. Z. Physiol. Chem. 1893, 11, 109−765. (16) ESO/TC 47. ISO 3706-1976. Phosphoric Acid for Industrial Use (Including Foodstuffs)-Determination of Total Phosphorus (V) Oxide Content-Quinoline Phosphomolybdate Gravimetric Method; ISO Information Handling Services: Switzerland, 1976. (17) Deng, T.; Yin, H.; Guo, Y. Metastable Phase Equilibrium in the Aqueous Ternary System Li2SO4 + MgSO4 + H2O at 323.15 K. J. Chem. Eng. Data 2011, 56 (9), 3585−3588. (18) Zhao, C. W.; Ma, P. S.; Guo, W. L.; Liu, G. X. Measurement and Research on the Solubility of K2SO4-(NH4)2SO4-H2O System at 35 °C. J. Tianjin Univ. 2002, 35 (16), 772−774. (19) Sheen, H. T.; Kahler, H. L. Effect of ions on Mohr method for chloride determination. Ind. Eng. Chem., Anal. Ed. 1938, 10 (11), 628− 629. (20) Zhu, T.; Li, C. M. Determination of the content of chloride ion in fertilizer material by Volhard method. Chem. Fert. Ind. 2002, 1, 23−26. (21) Long, J.; Tang, J. H.; You, Y. K.; Guo, L. M.; Chen, K. Phase equilibrium in the aqueous ternary system KH2PO4 + KCl + H2O at (288.15 and 303.15) K. J. Chem. Eng. Data 2015, 60, 1906−1909. (22) Deng, T. L.; Zhou, H.; Chen, X. The Phase Diagram of Salt−Water System and its Application; Chemical Industry Press: Beijing, 2013.
Figure 7. Density vs 100w (KH2PO4) in the ternary system (KH2PO4 + K2SO4 + H2O). N, D, and M have the same meaning as described in Figure 4.
■
CONCLUSIONS The phase equilibrium of (KH2PO4 + K2SO4 + H2O) and (KCl + K2SO4 + H2O) at 288.15 K is investigated. The solubility and density of the ternary systems are obtained. The ternary phase diagrams are plotted, the equilibrium solid phase is analyzed, and the crystallization regions are determined. There are in all two crystallization regions, one invariant point, and two univariant curves in the ternary phase diagrams. In the two ternary systems, KH2PO4 and KCl have a strong salting-out effect on K2SO4, and the salting-out effect of KCl on K2SO4 is stronger than that of KH2PO4 on K2SO4. The crystallization regions of K2SO4 in the two systems are much larger than crystallization regions of KH2PO4 and KCl. The crystallization region of K2SO4 is the largest, whereas that of KCl is the smallest. All results can offer fundamental data support for optimizing the processes and further theoretical studies.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Fan, L.; Zhao, J. G. The current status and prospect of potassium dihydrogen phosphate in China. Phosphate Compd. Fert. 2006, 21 (3), 34−37. (2) Xie, Y.; Liu, J.; Yuan, J.; Zhu, H. The Methods of Producing Potassium Dihydrogen Phosphate. J. Salt Chem. Ind. 2005, 34, 9−11. (3) Yang, L.; Zhang, Z. Y.; Chen, Z. Y. Summary of processes for production of potassium dihydrogen phosphate. Phosphate Compd. Fert. 2004, 19 (1), 54−56. (4) Yang, W. H.; Li, X. Z.; Hu, Z. P. Summary for preparation of potassium dihydrogen phosphate from wet-process phosphoric acid. Inorg. Chem. Ind. 2014, 46 (4), 7−9. (5) Elierer, R. Production of KH2PO4 from KCl and H3PO4 in an Organic Liquid Medium. Ind. Eng. Chem. Process Des. Dev. 1978, 17 (4), 460−468. (6) Dang, Y. G.; Fei, D. J.; Hu, X. Y. Effects of Impurities on Crystallization Process of Potassium Dihydrogen Phosphate. J. Chem. Eng. Chin. Univ. 2008, 22 (6), 911−914. (7) Wang, P.; Li, J.; Luo, J. H. Technology for Production of Potassium Dihydrogen Phosphate with Dicalcium Phosphate. Inorg. Chem. Ind. 2001, 43 (2), 50−52. (8) Zhou, K.; Li, J.; Li, Y. F.; Tang, X. H. Study on K2O recovery in production of potassium dihydrogen phosphate with monocalcium phosphate. Ind. Miner. Process. 2007, 4, 4−7. E
DOI: 10.1021/acs.jced.5b01111 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
