Ind. Eng. Chem. Res. 1998, 37, 1095-1098
1095
GENERAL RESEARCH Investigations on the Optimum Conditions of NaCl Conversion into NaVO3 Mieczysław Trypuc´ * and Zbigniew Torski Faculty of Chemistry, Nicolaus Copernicus University, 7 Gagarin Street, 87-100 Torun´ , Poland
Investigations on setting down the optimum conditions for running the synthesis of NaVO3 and HCl based on NaCl and V2O5 in the presence of steam at temperature point T ) 823 K have been carried out. On the basis of these results, the optimum NaCl excess as compared to V2O5 in the reaction mixture and time of processing have been determined. It has been concluded that the conversion degree of V2O5 into NaVO3 is strictly connected with the granulometric composition of the reaction mixture. Introduction Nowadays, calcined soda in most countries is manufactured almost exclusively according to the traditional Solvay’s method (Niederlin´ski et al., 1978). This method consists of the absorption of ammonia and carbon dioxide by the NaCl aqueous solution. Precipitated crystals of sodium bicarbonate after their separation from the solution when heated undergo a transformation into sodium carbonate. These processes can be described with the following reactions:
NaCl + NH3 + CO2 + H2O ) NaHCO3 + NH4Cl (1) 2NaHCO3 ) Na2CO3 + H2O + CO2
(2)
The final liquor, containing ammonium chloride in equivalent quantities as compared to the precipitated NaHCO3, is treated with limestone milk (distillation process) according to the following reaction:
2NH4Cl + Ca(OH)2 ) 2NH3 + CaCl2 + 2H2O (3) Gaseous NH3, evolved in this reaction, both with the one generated from the decomposition of (NH4)2CO3 and NH4HCO3 salts, employing indirect heating, is recycled to the ammonization of the saturated brine. Calcium chloride generated in reaction 3 together with the unreacted NaCl (reaction 1) are passed through settling tanks to the opened water basins. This method marks out with both very low energy and raw material efficiency and is considered to be environmentally unfriendly. As it follows, 100% of the chloride ion, introduced into the process as brine (the concentration ) 310 g/dm3), is entirely not utilized. Essential for the industrial purposes Cl2 is obtained mainly from employing the electrolysis of the saturated NaCl aqueous solution together with NaOH lye, which is only partly utilized in our country. * Author to whom correspondence should be addressed. E-mail:
[email protected].
Ongoing investigations are being carried on to modify the process of producing calcined soda, either by the change of the raw materials, to avoid introducing into the process the useless chloride ion (Na2SO4, NaNO3) (Biełopolski, 1970; Koneczny and Trypuc´, 1967), or by eliminating the ammonia recycling step, to prevent producing the distillation wastes (Koneczny and Trypuc´, 1969). In the case of introducing for example NaNO3 to the sodium production process, after the carbonization of an ammonia brine solution and separation of the precipitated NaHCO3, a final liquor is obtained, being a mixture of the unreacted NaNO3 and NH4NO3. When that liquor is vaporized, important for agriculture purposes, mixed fertilizer is produced (i.e., NaNO3 + NH4NO3). Required for that process, NaNO3 is generated due to the respective reaction:
6NaCl + 6HNO3 + 1.5O2 ) 6NaNO3 + 3Cl2 + 3H2O (4) The above-described method has not been yet industrially exploited in our country. Since eliminating the laborious step of regenerating NH3 in the sodium production process is required, as in the case of the original Japanese method “Dual” (Masayocki, 1965), NH4Cl is used as a fertilizer or processed to generate both phosphatic fertilizers and Cl2. The basic raw material is solid NaCl and not the saturated brine solution as compared to Solvay’s process. In our domestic conditions, a basic raw material used for the soda production is still NaCl; however, the investigations are focused on finding a new method, where the Cl- ion would be totally utilized, not being harmful to the natural environment (Koneczny and Trypuc´, 1967, 1969; Aarts, 1967). This method is based on heating the mixture of NaCl and V2O5 in the presence of steam or oxygen, to generate the following reaction products: NaVO3 and HCl or NaVO3 and Cl2, according to the below given reactions:
2NaCl + V2O5 + H2O(steam) ) 2NaVO3 + 2HCl (5)
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1096 Ind. Eng. Chem. Res., Vol. 37, No. 3, 1998
Generated NaVO3 is then put through the similar unit
4NaCl + 2V2O5 + O2 ) 4NaVO3 + 2Cl2
(6)
operations as in Solvay’s process, that is, ammonization and carbonization, which results in forming scarcely soluble NH4VO3 precipitate, and in the solution NaHCO3 and Na2CO3 salts are found, as follows:
NaVO3 + NH3 + CO2 + H2O ) NH4VO3 + NaHCO3 (7) 2NaVO3 + 2NH3 + CO2 + H2O ) 2NH4VO3 + Na2CO3 (8) The obtained NaVO3 crystals undergo a decomposition process according to the following equation:
2NH4VO3 ) 2NH3 + V2O5 + H2O
(9)
and the following products are recycled back to the appropriate steps of the process. The main components of the aqueous solution are NaHCO3 and Na2CO3, respectively. This solution is used for the soda production method or for the generation of NaOH employing Ca(OH)2 causticization. This method ensures a total utilization of the Cl- ion, and the utilization degree would be strictly limited to the demands of the industry for both chlorine and hydrogen chloride. There is no available literature data describing the conditions of running reaction 5sexcept for its general equation. On the basis of the preliminary lab tests carried out (Trypuc´ and Torski, 1996, 1997), it was concluded that NaVO3 synthesis from NaCl and V2O5 in the presence of steam is limited to the specific temperature point T ) 823 K. It was observed that crossing this point over causes a partial melting of the reaction mixture, whereas at T ) 973 K the mixture transforms to the liquid state and after being cooled it down is totally not soluble in water. For the beginning of NaVO3 creation, with maintained stoichiometric ratio NaCl:V2O5 ) 2:1 (see reaction 5) and the conversion degree (n) equal to 0.0034, the temperature point T ) 523 K was assumed. The conversion degree is strictly limited to a number of reaction operating parameters, that is, temperature, time of processing, excess of the introduced substances (NaCl and H2O) as compared to the V2O5 quantity, and the grinding degree of all the reactants. Formerly, the optimum processing temperature and 10 times the steam excess have been reported (Trypuc´ and Torski, 1996, 1997). It was also found that an excessive reagents granulation, especially for V2O5 below 0.045 mm, enables one to run the process effectively. It is well-recognized in the reaction initial stage that the outer layer of the reaction mixture and then more distant ones become agglomerated. Obviously, the surface is less extended (lower voidage) and steam flow is impeded. This effect causes a significant decrease in the conversion degree and the obtained postreactive mixture is hard-soluble in water. The present paper reports a number of operating parameters for running the NaVO3 synthesis to find the highest attainable V2O5 conversion degree in the reaction mixture. Furthermore, our research work will be focused on choosing such parameters to guarantee the conversion degree equal to 1 with the only product NaVO3. This way it would be possible to convert NaVO3
into sodium carbonate, omitting the NaNO3 purification process of the residual unreacted V2O5. Experimental Part On the basis of the investigations (Trypuc´ and Torski, 1996, 1997) carried out, the optimum conditions of running the process were determined, which are T ) 823 K and 10 times the excess of steam. It was also found out that the increase of NaCl excess above 50%sin comparison to the stoichiometric quantity in reaction 5sin the reaction mixture has no influence on the growth of the conversion degree for the studied process. These investigations have been carried out for the following purposes: (a) To determine the dependence of the V2O5 conversion degree into NaVO3 on the composition of the stoichiometric reaction mixture resulting from reaction 5 and also 10, 20, 30, and 50% excess of NaCl on the time of processing, which was 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 h, respectively. A granulometric composition of the given reaction mixture varied for NaCl from 0.16 to 0.32 mm and for V2O5 from 0.045 to 0.063 mm. (b) To determine the influence of the granulometric composition of the reaction mixture on the V2O5 conversion degree for the optimum excess of NaCl found out in the former step of lab tests with alternating times of processing. The granulometric composition of NaCl from the former step was kept up, and the V2O5 granulometric composition was changed and varied from 0.32 to 0.71 mm. (c) To maintain the granulometric composition of the reaction mixture from the second step, the measurements of NaCl excess influence on the conversion degree V2O5 for a fixed time limit of processing (4.0 h) were done. According to the estimated plan of experimental lab tests, 12 series of measurements were carried out and consisted of 126 separate experiments. The granulometric composition of each reacting substance was determined on the basis of the sieve analysis using a set by FRITSCH (Germany). The following analytical purity grade chemicals were applied: V2O5 (99%, Fluka), NaCl (p.a., POCh Poland), without further purification. The investigations were carried out introducing to an apparatus made of quartz glass (schematic described in detail) (Trypuc´ and Torski, 1996) weighed portions (approximately of 5 g) of the reaction mixture with a fixed granulometric and quantitative composition. The reactor was electrically heated up to a desirable temperature, and the steam was passed over. The temperature control was done to an accuracy of (1 K. Hydrogen chloride, evolved in that process, was absorbed in two gas-washing bottles filled up with a NaOH aqueous solution. The set was connected to the suction pump to achieve a slightly negative pressure in order to overcome the resistance of gases passing over the layer of the reaction mixture and solution in the gas-washing bottles. The measurements were done three times, keeping up the specified conditions. After the reactor was cooled off, the reaction mixture was dissolved in distilled water. Then the whole content was filtered, and the filtrate was sampled into a 1 dm3 capacity measuring flask. Solutions from the gas-washing bottles with absorbed hydrogen chloride were sampled into a 0.5 dm3 capacity
Ind. Eng. Chem. Res., Vol. 37, No. 3, 1998 1097 Table 1. Influence of the Reaction Time and the Reaction Mixture Composition on the Conversion Degree of V2O5 reaction time [h]
% excess NaCl
conversion degree [n]
standard deviation
1.5 2.0 2.5 3.0 3.5 4.0
0 0 0 0 0 0
0.61 0.64 0.66 0.70 0.75 0.80
0.033 0.029 0.017 0.023 0.020 0.018
1.5 2.0 2.5 3.0 3.5 4.0
10 10 10 10 10 10
0.62 0.66 0.72 0.77 0.80 0.87
0.032 0.033 0.018 0.007 0.033 0.028
1.5 2.0 2.5 3.0 3.5 4.0
20 20 20 20 20 20
0.65 0.68 0.73 0.78 0.83 0.89
0.018 0.029 0.018 0.012 0.033 0.035
1.5 2.0 2.5 3.0 3.5 4.0
30 30 30 30 30 30
0.67 0.71 0.75 0.81 0.85 0.91
0.031 0.032 0.031 0.023 0.033 0.018
1.5 2.0 2.5 3.0 3.5 4.0
50 50 50 50 50 50
0.68 0.73 0.79 0.83 0.88 0.92
0.013 0.007 0.032 0.029 0.012 0.029
measuring flask. The given solutions were then potentiometrically titrated for the quantitative determination of chloride ions, employing 716 DMS Titrino titrator with a silver combined electrode (Switzerland). This apparatus enables a very fast and accurate titration and also observation of the titration curve on the screen. The accuracy of the measurements was less than (1%. The concentration of sodium ions in the solution (being taken from the reactor) was determined by weight using the method by Kolthof and Barbera in the form of sodium-zinc-uranyl-acetate (Furman, 1962). The average relative error of the determination being less than (1%. Results and Discussion The results concerning the influence of the stoichiometric composition and the time of processing on the NaCl conversion degree into NaVO3 are summarized in Table 1. The average degree of conversion has been calculated as an arithmetic average on the basis of three readings. These results are included in Figure 1, which shows the dependence of the conversion degree on the time of processing. Data presented in Table 1 and Figure 1 point out that by having a given excess of NaCl in the reaction mixture, the degree of conversion is limited to the reaction time and this dependence in most cases is approximately of a linear mode. The comparison of the increases in the conversion degree in the case of applied NaCl excesses in the reaction mixture, as compared to the value of the conversion degree (n) for the stoichiometric mixture (0% of NaCl excess in the reaction mixture), shows that 20% excess of NaCl is economically acceptable for the given granulometric composition of
Figure 1. Influence of the reaction time and the reaction mixture composition on the conversion degree of V2O5.
NaCl and V2O5. Increases in the conversion degree values with 10% excess of NaCl, as compared to the stoichiometric composition for the fixed time of processing (4 h), are determined to be 0.07, 0.02, and 0.02, respectively, whereas with 20% of NaCl excess amount the increase is only to 0.01. The similar compliance was observed for 3.5 h time of processing. The studies carried out earlier (Trypuc´ and Torski, 1996, 1997) indicate that the granulometric composition of the reaction mixture with other parameters set up (NaCl excess, temperature, and intensity of the steam flow) influences the conversion degree values. Too high disintegration of the reaction mixture results in a decrease in the conversion degree, since the steam flow is impeded. This effect occurs especially for the lower range of temperatures, whereas at higher temperatures a gradual agglomeration of each sample was observed. Figure 2 presents data referring to the conversion degree dependence on the time of processing with 20% excess of NaCl. The granulometric composition of NaCl stayed the same as in the first step of the investigations (from 0.6 to 0.32 mm), whereas the granulometric composition of V2O5 was changed and varied from 0.32 to 0.71 mm. In the first step the V2O5 granulometric composition was 0.045-0.063 mm; it is evident that the diameters of V2O5 grains were increased approximately by 10 times. It is important to note that the increase in particle size distribution of the reaction mixture influences the growth of the conversion degree values. For example, for the 4-h time of processing with 20% excess of NaCl and the granulometric composition taken from the first step, the conversion degree was 0.89; whereas with the same parameters except that of the changed granulometric composition, the conversion degree was 0.95. Data enclosed in a paper by Trypuc´ and Torski (1996), indicate clearly that drawing out the time of processing over 4.0 h has no further influence on the value of the conversion degree. Irrespective of 20% NaCl excess in the reaction mixture for the assumed parameters of the process, it
1098 Ind. Eng. Chem. Res., Vol. 37, No. 3, 1998
stoichiometric values following reaction 5 to 20% excess of NaCl in the reaction mixture, achieving the value of 0.95. The growth of NaCl excess up to 50% has no further influence on its values. Data enclosed in a paper by Trypuc´ and Torski (1997) show that the discussed process runs according to reaction 5. No oxygen compounds of chlorine among gaseous products were detected, and an X-ray analysis revealed only the presence of NaVO3, NaCl, and the residual V2O5 traces in the solid phase. The conversion degree n ) 0.95 is relatively high, as compared to that given in the literature [U.S. Patent, 1967], which is n ) 0.90. Since the cited authors do not discuss precisely the conditions of carrying out the process, it makes it difficult to compare the results. Further on our researches will be focused on shortening the time of processing by introducing to the reaction mixture a neutral carrier of an appropriate granulation. It can be assumed that the conversion degree of V2O5 into NaVO3 would be still higher for the given granulometric composition than without a carrier (it means easier steam access, an extended surface, etc.). Figure 2. Influence of the reaction time on the conversion degree of V2O5 for 20% excess of NaCl in the reaction mixture. NaCl varies from 0.16 to 0.32 mm and V2O5 from 0.32 to 0.71 mm.
Conclusions (1) The optimum NaCl excess in the reaction mixture as compared to V2O5 was determined to be 20%. (2) The changes introduced in the V2O5 granulometric composition increase the conversion degree. The V2O5 particle size composition in the second step of lab tests was increased approximately 10 times. (3) The optimum time of processing was estimated to be 4 h and the obtained conversion degree with maintained 20% NaCl excess was equal to 0.95. Literature Cited
Figure 3. Influence of NaCl excess in the reaction mixture on the conversion degree of V2O5 (for the constant time). Granulometric composition of NaCl varies from 0.16 to 0.32 mm and of V2O5 from 0.32 to 0.71 mm.
ensures the highest attainable degree of NaCl conversion into NaVO3. Figure 3 indicates clearly the dependence of the conversion degree for the given time with maintained granulometric composition from the second step on NaCl excess in the reaction mixture. The conversion degree increases systematically from the
Aarts, W. H. Process for the production of sodium carbonate and hydrochloric acid and/or chlorine. U.S. Patent 3,313,593, 1967. Biełopolski, A. P. Proizwodstwo sody i sulfata ammonia iz mirabilita, Trudy NIUIF-u, SSSR, 1970. Furman, N. H. Standard Method of Chemical Analysis; D. Van Nostrand Co.: Princeton, New Jersey, 1962; Vol. 1. Koneczny, H.; Trypuc´, M. Badania nad nowa¸ metoda¸ otrzymywania sody; UMK: Torun´, Poland, 1967. Koneczny, H.; Trypuc´, M. Badania nad nowa¸ metoda¸ otrzymywania sody; UMK: Torun´, Poland, 1969. Masayocki, I. Emergence of ammonium chloride plant in Japan. Ind. Eng. Chem. 1965, 57, 2. Niederlin´ski, A.; Bukowski, A.; Koneczny, H. Soda i produkty towarzysza¸ ce; WNT: Warsaw, Poland, 1978. Trypuc´, M.; Torski, Z. Conversion rate of NaCl into NaVO3 in the presence of V2O5 and steam. Pol. J. Appl. Chem. 1996, 3, 301306. Trypuc´, M.; Torski, Z. Investigation on obtaining NaVO3 and HCl based on NaCl and V2O5 in the presence of steam. Przem. Chem. 1997, 7, 319-320 (in Polish).
Received for review February 25, 1997 Revised manuscript received November 11, 1997 Accepted November 25, 1997 IE9701783
