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Section 14. Chemistry
Kaipbergenov Atabek Tulepbergenovich, Doctor of Technical Science Nukus State Pedagogical Institute
Karajanova Shahnoza Daryabaevna, students, Nukus State Pedagogical Institute, E-mail: [email protected]
GRAPHANALYTICAL METHOD FOR DETERMINING TECHNOLOGICAL PARAMETERS USING FOUR-COMPONENT SYSTEM Na2CO3-NaHCO3-NaCl-H2O
Abstract. The graphic-analytical technique of determination of parameters of receiving sodium sesquicarbonate with application of a horizontal and orthogonal projection of an isotherm of Na2CO3-NaHCO3-NaCl-H2O system at 30 and 100 °C.
Keywords: sodium sesquicarbonate, sodium carbonate, crystallization, system
Known methods for producing sesquicarbonate sodium, based on the mixing of powdered sodium carbonate and aqueous suspension of sodium bicarbonate [1]. The disadvantage of these methods is the presence in the synthesis products, in addition to sodium sesquicarbonate, Na2CO3 • H2O and NaHCO3 and, therefore, low content of the basic substance. At the same time, it was noted that polythermal crystallization from a saturated solution makes it possible to obtain a product with a content of 96-98 wt.% Na2CO3 • NaHCO3 • 2H2O, and in [3] it was shown that it can be obtained in the system Na2CO3-NaHCO3-NaCl-H2O.
However, the authors did not take into account the effect of the composite components on the solubilities of each other [2]. In [3], the temperature and concentration limits of the existence of trona are shown in detail, but their application of the technology is not indicated.
The aim of the work is to develop a graph-analytical method for determining the technological parameters of obtaining trona using the solubility diagram of the Na2CO3-NaHCO3-NaCl-H2O system.
When creating a graph analytical method for determining the optimal parameters for the process of obtaining thrones at 30 and 100 °C, the isotherms of the Na2CO3-NaHCO3-NaCl-H2O system diagram given in [3; 4] were used. The technique is based on the rule of the connecting straight line and the lever [5].
To simplify graph analytical calculations, the concentration of the salt part in the diagram is expressed as a percentage, and water in grams per 100 g of the amount of salts. The
composition of the salt residue is shown on the orthogonal projection, and the amount ofwater is shown on the horizontal projection (Fig). This diagram allows you to theoretically determine the optimal range of variation of the technological parameters of the process of obtaining trona from carbonate and sodium bicarbonate in the presence of sodium chloride. It can be seen from the diagram that the ratios of sodium carbonate and bicarbonate lie in the intervals of points located on the faces (sides) of sodium carbonates and bicarbonates 3, 4 (at 100 °C) and 5, 6 (at 30 °C), respectively. To determine the effect of adding sodium chloride on the process, we conduct a straight line from the HX angle to the side of carbonate and sodium bicarbonate with NaHCO3 : Na2CO3 ratios from 0.235 to 0.15, which are located at points A and B. When adding sodium chloride, the salt composition of the system moves along straight lines ANX and VNH to the top of the NC. The amount of added sodium chloride was varied in quantities of 0.5; 1.0; 5.0; 15.0 and 30.0%. The composition of the salt part of the system in the figures is reflected in the figurative points A1, A2, A3, A4, A5 and B1, B2, B3, B4, B5 with the ratios of NaHCO3: Na2CO3 equal to 0.235 (A) and 0.15 (B).
To determine the amount ofwater on the horizontal projection of the system, we carry out an auxiliary curve corresponding to the water projections of lines A1A7 and B1B7. To construct the curve of the line on the water horizontal proj ec-tion of the thrones on the curve of the 4'3 'line, put the points A'1 and B'1, and on the curve of the 1'7' and 4'1' points A'7 and B'7 respectively. On the found point we draw the curves A'XA'7 and B'XB'7 with the simbate curves 3'7 '.
GRAPHANALYTICAL METHOD FOR DETERMINING TECHNOLOGICAL PARAMETERS USING FOUR-COMPONENT SYSTEM Na2CO3-NaHCO3-NaCl-H2O
Figure. Graphical analysis of the production of trona on the horizontal and orthogonal projection of the isotherm of the four-component system Na2CO3-NaHCO3-NaCl-H2O at 30 and 100 °C
Table 1. - The chemical composition of the initial samples and the liquid phase after separation of the solid phase
№ experiences Designations of figurative points in Fig. The initial composition of the system, wt.% The composition of the liquid phase at 30 °C, wt.% Coefficients Product yield,%
a, NaCl b, NaHCO3 c, Na2CO3 d, H2O a1, NaCl NaHCO3 c1, №2CO3 H2O x y z
1. Ai 0 6.09 25.96 67.95 0 1.740 27.33 70.930 0.13 0.728 0.38 79.3
2. Bi 0 4.28 28.62 67.11 0 1.740 27.33 70.930 0.07 0.923 -14.29 60.8
3. ^ 0.16 6.08 25.91 67.85 0.220 1.610 27.505 70.675 0.13 0.716 1.32 79.5
4. B2 0.16 4.25 28.48 67.11 0.292 1.674 27.189 70.845 0.07 0.921 -14.07 61.2
5. ^ 0.32 6.07 25.87 67.74 0.368 1.510 27.534 70.588 0.14 0.711 1.62 85.7
6. B3 0.33 4.25 28.43 67.00 0.440 1.589 27.297 70.674 0.08 0.912 -13.39 70.0
7. A4 1.61 5.82 24.82 67.74 2.315 1.285 27.265 69.134 0.13 0.682 4.66 83.0
8. B4 1.66 4.09 27.37 66.89 2.744 1.387 26.765 69.104 0.08 0.888 -10.4 72.7
9. A5 4.85 5.23 22.28 67.64 7.310 0.881 24.280 67.529 0.13 0.676 6.06 92.4
10. A6 9.71 4.30 18.35 67.64 13.76 0.610 19.850 66.445 0.11 0.677 6.73 95.1
The intersection point of the found curves with perpendicular lines drawn from the figurative point shows the amount of water in the solid phase in grams per 100 g of the sum of salts with the formation of a saturated solution at 100°C. The resulting solution is purified from the insoluble part and cooled to 30 °C, as a result of which the throne
precipitates and a saturated solution is formed. If the initial and final composition of the system component is known, the material balance of the process can be calculated. When the composition of the system and the solid phase is known, the composition of the liquid phase can be determined from the connecting line. Therefore, from the point Tr. and a given
composition of the system at 100 °C, for example, from point A5, we draw a crystallization line to the intersection with the saturation line of the thrones and Na2CO3 • 7H2O (curves 7-8 at 30 °C). The intersections of the lines show the salt composition of the saturated solution at point e. The intersection of el perpendicular with the horizontal projections of 7'-8' at point 1 indicates the amount ofwater in saturated solutions in grams per 100 g of the total salt. As a result of using the above methodology, the composition of saturated solutions at 100 and 30 °C is determined, which allows you to perform a material calculation of the process using the formula: (a, NaCl + b, NaHCO3 + c, Na2CO3 + d, H2O) = x (37.1 NaHCO3+46.50 Na2CO3+15.93 H2O)+y(a1, NaCl+b1, NaHCO3+c1, Na2CO3+d1, H2O) + z H2O where a, b, c, d and a1, bl, cl, dl are the contents of NaCl, NaHCO3, Na2CO3, H2O, respectively, in saturated solutions at 100 and 30 °C. The effect of the content of NaHCO3 : Na2CO3 and sodium chloride in the system on the product yield was also determined. From the results of the calculation (Table)
it can be seen that with an increase in the ratio of NaHCO3: : Na2CO3, the yield of the product increases by 10-15%. With an increase in the content of sodium chloride from 0 to 9.71%, the product yield increases from 79.3 to 95.1 and from 60.8 to 72.7%, respectively, with NaHCO3: Na2CO3 = 0.234 and 0.15. It also follows from table that whenNaH^: Na2CO3 = 0.234, the values of z are positive, and at 0.15 they are negative. A positive sign means that for given compositions of salt systems, the water content is greater, and a negative sign is the amount of missing water.
Thus, in order to achieve more than 90% yield of the product, the process must be conducted with sodium chloride content of more than 2%, and the ratio of NaHCO3: Na2CO3 must be maintained in the intervals of 0.200-0.280. The obtained information allows you to pre-select the intervals of variation of technological parameters. The real optimal values of the parameters are determined by specific experimental data, taking into account the techno-analytical and physic-chemical parameters of intermediate and final products.
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