A method for recovering sodium fluoride from waste solids generated in the production of hexafluoroacetone

Abstract

The invention belongs to the field of chemical technology, and specifically relates to a method for recovering sodium fluoride from waste solids generated by the production of hexafluoroacetone. The method for recovering sodium fluoride from waste solids generated by the production of hexafluoroacetone can efficiently recover and utilize the fluorine element in the waste solids, and the obtained sodium fluoride product meets the industry standard YS / T517-2009. The method does not require an organic solvent, does not generate waste liquid, is simple to operate, has low cost, is easy to realize large-scale industrial production, and has great environmental and economic significance.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a method for recovering sodium fluoride from waste solid generated in the production of hexafluoroacetone. Background Art

[0002] Sodium fluoride is an important fluoride salt and a raw material for making other fluorides. Sodium fluoride has a wide range of uses and can be used in chemical industry, metallurgy, wood preservative, agricultural pesticide, papermaking and other industries. The production methods of sodium fluoride reported in the existing literature include melt leaching method, hydrofluoric acid neutralization method and fluosilicic acid method. Different enterprises adopt different production processes according to their own resource allocation and local conditions.

[0003] The main method for producing sodium fluoride in China is to use the fluosilicate method, first converting the fluorine in the acidic fluorine-containing waste liquid into fluosilicate acid, then precipitating fluosilicate, and then reacting the obtained fluosilicate with sodium carbonate / sodium hydroxide to obtain sodium fluoride. In this method, due to the low solubility of NaF, the NaF and SiO2 precipitates produced in the reaction process are easy to form peritectic, that is, the precipitated NaF and SiO2 are difficult to be effectively separated, and the SiO2 content in the NaF product is as high as 0.4%-0.5%, which seriously affects the quality of the sodium fluoride product and its production efficiency. Another method is to change the process of producing sodium fluoride from fluosilicate into an ammonium salt conversion method, first reacting fluosilicate with ammonia to obtain an ammonium fluoride solution, and then reacting the ammonium fluoride solution with sodium carbonate / sodium hydroxide to crystallize and precipitate sodium fluoride. Although this method realizes the effective separation of NaF and SiO2, it requires two-step reaction and the reaction temperature is relatively high.

[0004] At present, the production process of hexafluoroacetone is generally that hexafluoropropylene undergoes oxidation reaction to obtain hexafluoropropylene oxide, and hexafluoropropylene oxide is isomerized and separated to obtain hexafluoroacetone. A large amount of fluorine-containing waste solids are generated during the isomerization absorption process, which not only pollutes the environment, but also causes raw material loss and product waste. However, there is no relevant literature report on the treatment method of the waste solids generated in the production process of hexafluoroacetone.

[0005] Based on this, there is an urgent need for a method for recovering sodium fluoride from waste solids generated by the production of hexafluoroacetone, so as to effectively utilize the fluorine resources in the waste, which has great environmental and economic significance. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention provides a method for recovering sodium fluoride from waste solids generated in the production of hexafluoroacetone. The method does not require an organic solvent, does not generate waste liquid, can reduce environmental pollution, and create benefits.

[0007] The present invention is specifically implemented through the following solutions:

[0008] A method for recovering sodium fluoride from waste solids generated in the production of hexafluoroacetone comprises the following steps: adding water to the mixed waste solids and stirring, then slowly adding a sodium hydroxide solution, controlling the temperature and stirring the reaction, while monitoring the pH value of the solution, filtering, washing and drying after the reaction is completed.

[0009] Preferably, the mixed waste solid contains 70-76% sodium bifluoride and 20-25% sodium fluoride.

[0010] Preferably, the reaction temperature is not higher than 40°C, with 30-35°C being particularly preferred.

[0011] Preferably, the reaction ends when the solution pH reaches 7-11.

[0012] More preferably, the reaction ends when the solution pH reaches 9-10.

[0013] Preferably, the concentration of the sodium hydroxide solution is 20-40wt%.

[0014] Preferably, the mass volume ratio of the mixed waste solid and water is 1:1-10, g / ml.

[0015] Preferably, a method for recovering sodium fluoride from waste solids generated by the production of hexafluoroacetone specifically comprises the following steps: adding water to the mixed waste solids and stirring, then slowly adding sodium hydroxide solution, controlling the temperature to 30-35°C and stirring the reaction, while monitoring the pH of the solution, stopping the addition of sodium hydroxide solution when the pH of the solution is 7-11, terminating the reaction, filtering, washing with the filtrate and water in turn, and drying to obtain sodium fluoride.

[0016] In a preferred embodiment, a method for recovering sodium fluoride from waste solids generated by the production of hexafluoroacetone specifically comprises the following steps: adding water to the mixed waste solids and stirring, the mass volume ratio of the mixed waste solids to water is 1:1-3, g / ml, and then slowly adding 20-40wt% sodium hydroxide solution, controlling the temperature to react at 30-35°C, and monitoring the pH of the solution at the same time. When the pH of the solution is 10, stop adding the sodium hydroxide solution, end the reaction, filter, wash with the filtrate and water in turn, and dry to obtain.

[0017] Compared with the prior art, the present invention has the following advantages: the present invention provides a method for recovering sodium fluoride from waste solids generated by the production of hexafluoroacetone, which can efficiently recover and utilize the fluorine element in the waste solids, and the obtained sodium fluoride product meets the industry standard YS / T517-2009. The method does not require an organic solvent, does not generate waste liquid, is simple to operate, has low cost, is easy to realize large-scale industrial production, and has great environmental and economic significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : Quality test report of the sodium fluoride product obtained in Example 1;

[0019] Figure 2 : The quality test report of the sodium fluoride product obtained in Example 2. DETAILED DESCRIPTION

[0020] The present invention is further described below by way of examples. It should be correctly understood that the examples of the present invention are provided only for illustrating the present invention, rather than limiting the present invention, and therefore, simple modifications of the present invention under the premise of the method of the present invention are within the scope of protection claimed by the present invention.

[0021] The components of the hexafluoroacetone production waste solid used in the Examples and Comparative Examples are as follows: sodium fluoride content is 23.4%, and sodium bifluoride content is 75.4%.

[0022] Example 1

[0023] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 70 L of water was added. Stirring was started, and 30 wt% sodium hydroxide solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction. When the pH of the solution reached 10, the addition of sodium hydroxide solution was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and then washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 95.7% and a content of 99.19%.

[0024] Example 2

[0025] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 50 L of water was added. Stirring was started, and 20 wt% sodium hydroxide solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction. When the pH of the solution reached 9, the addition of sodium hydroxide solution was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and then washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 92.5% and a content of 98.54%.

[0026] Example 3

[0027] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 70 L of water was added. Stirring was started, and 30 wt % sodium hydroxide solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction. When the pH of the solution was 7, the addition of sodium hydroxide solution was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 89.6%, a content of 95.52%, and unqualified acidity.

[0028] Example 4

[0029] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 150 L of water was added. Stirring was started, and 40 wt% sodium hydroxide solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction. When the pH of the solution was 10, the addition of sodium hydroxide solution was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and then washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 94.7% and a content of 99.02%.

[0030] Example 5

[0031] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 70 L of water was added. Stirring was started, and 30 wt % sodium hydroxide solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction. When the pH of the solution was 8, the addition of sodium hydroxide solution was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 90.9%, a content of 97.61%, and an unqualified acidity.

[0032] Example 6

[0033] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 70 L of water was added. Stirring was started, and 30 wt% sodium hydroxide solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction. When the pH of the solution reached 11, the addition of sodium hydroxide solution was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and then washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 95.0% and a content of 99.05%.

[0034] Comparative Example 1

[0035] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 50 L of water was added. Stirring was started, and a saturated sodium carbonate solution was slowly added. The temperature was controlled at 30-35° C. and stirred for reaction to generate a large number of bubbles. When the pH of the solution was 9, the addition of sodium carbonate was stopped and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and then washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 87.3% and a content of 96.05%.

[0036] Comparative Example 2

[0037] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 70 L of water was added. Stirring was started, and sodium bicarbonate was slowly added. The temperature was controlled at 30-35° C. and the reaction was stirred. When the pH of the solution was 8, the addition of sodium bicarbonate was stopped, and the reaction was terminated. The solid was centrifuged and filtered. The solid was washed twice with the filtrate and washed with purified water. The solid was collected and dried in a vacuum at 50-70° C. to obtain sodium fluoride with a yield of 86.5% and a content of 95.26%.

[0038] Comparative Example 3

[0039] 50 kg of solid waste from hexafluoroacetone production was added to a stainless steel reactor, and then 50 L of water was added. Stirring was started, and ammonia (obtained by gasification of liquid ammonia) was slowly introduced. The ammonia introduction rate was adjusted by temperature control to control the material temperature at 25-30° C. When the pH value of the material was 8, the introduction of ammonia was stopped. After the reaction was completed, the solid was filtered while hot, and the solid obtained by filtration was a crude sodium fluoride. Boiling water was added for pulping and washing, centrifugal drying was performed for separation, and vacuum drying was performed at 50-70° C. to obtain sodium fluoride with a yield of 89.2% and a content of 97.57%.

[0040] Verification Example

[0041] The products of the embodiments and comparative examples were subjected to quality analysis, and the results are shown in Table 1.

[0042] Table 1 Sodium fluoride mass analysis results

[0043]

[0044] As can be seen from Table 1, the sodium fluoride product obtained by the recovery method of the present invention has high purity and low impurity content, which meets the industry standard YS / T517-2009.

Claims

1. A method for recovering sodium fluoride from waste solids generated in the production of hexafluoroacetone, characterized in that: The method comprises the following steps: adding water to the mixed waste solid and stirring, then slowly adding sodium hydroxide solution, controlling the temperature and stirring for reaction, and monitoring the pH value of the solution at the same time, filtering, washing and drying after the reaction is finished, so as to obtain the product; the reaction temperature is not higher than 40 DEG C; the reaction is finished when the pH value of the solution is 7-11; the mass volume ratio of the mixed waste solid and water is 1:1-10, g / ml; the mixed waste solid contains 70-76% of sodium bifluoride and 20-25% of sodium fluoride.

2. The method for recovering sodium fluoride as claimed in claim 1, characterized in that: The reaction temperature is 30-35°C.

3. The method for recovering sodium fluoride as claimed in claim 1, characterized in that: When the pH is 9-10, the reaction is finished.

4. The method for recovering sodium fluoride as claimed in claim 1, characterized in that: The concentration of the sodium hydroxide solution is 20-40 wt %.

5. The method for recovering sodium fluoride as claimed in claim 1, characterized in that: The method specifically comprises the following steps: adding water to the mixed waste solid and stirring, then slowly adding sodium hydroxide solution, controlling the temperature at 30-35°C and stirring for reaction, while monitoring the pH value of the solution, stopping adding the sodium hydroxide solution when the pH value of the solution is 7-11, terminating the reaction, filtering, washing with the filtrate and water in turn, and drying to obtain the product.

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