Method for recovering elemental iodine from perfluoroalkyl iodide

Abstract

The invention discloses a method for recovering elemental iodine from perfluoroalkyl iodide, which comprises the following steps: (1) mixing perfluoroalkyl iodide and an alkaline solution to form a reaction solution, and heating and stirring to form a deiodinated solution; (2) adjusting the pH value of the deiodinated solution to 6-7 by using an acidic solution, and distilling to obtain an inorganic iodized salt solid; and (3) adding water to dissolve the inorganic iodized salt solid to obtain an inorganic iodized salt solution, adding an acidic solution to maintain the pH value to be strongly acidic, adding an oxidizing agent to carry out an oxidation-reduction reaction, filtering and separating to obtain wet iodine, and drying and dehydrating to obtain the iodine simple substance. The method is used for treating perfluoroiodo alkane which is high in iodine content and difficult to treat, an alkaline solution is adopted for reacting with perfluoroiodo alkane for deiodination, the deiodination solution is subjected to acidification and oxidation reaction to prepare high-purity iodine simple substance, and the iodine simple substance can be directly used as a product to be applied to production of iodine-containing compounds.

Description

Technical Field

[0001] This invention relates to the field of organic iodide treatment technology, specifically to a method for recovering elemental iodine from perfluoroiodoalkanes. Background Technology

[0002] 1,4-Diiodooctafluorobutane and 1,6-diiodoperfluorohexane belong to the α,ω-diiodoperfluoroalkane family. These compounds are important specialty monomers for fluoropolymers and can be derived into various fluorinated specialty monomers through terminal iodine. Their application in the synthesis of fluoropolymers imparts characteristics such as high and low temperature resistance (≥200 ℃, ≤-200 ℃), resistance to ultraviolet radiation and chemical corrosion, and good electrical and mechanical properties. The synthesis of these compounds generates high-boiling-point fluorinated organic iodine compounds with high iodine content, complex composition, and difficult disposal. Furthermore, due to the high price of elemental iodine, directly treating these high-boiling-point fluorinated organic iodine compounds as waste would waste iodine resources. Therefore, recovering iodine from these high-boiling-point organic iodine compounds is of great significance.

[0003] Chinese patent document CN103508421A discloses a method for recovering iodine from waste liquid produced by X-CT contrast agents. The method involves first converting iodine in iodinated organic matter in the waste liquid into inorganic iodine, then concentrating the solution. The concentrate is then oxidized with a composite oxidant, causing iodine anions to oxidize into elemental iodine, which is then separated by filtration. The remaining elemental iodine in the filtrate is then extracted with an organic solvent, resulting in the complete recovery of the low-concentration elemental iodine. This method is suitable for industrial waste liquids with high iodine content (≥1 wt%), achieving a recovery rate of 87%–90%, and possesses both resource recycling and environmental protection value. However, this method also has significant drawbacks: the organic matter treated is benzene-based, with low iodine content; the reduction and deiodization using sodium hydroxide and zinc powder is incomplete, resulting in crude iodine with low iodine content, requiring further purification to obtain refined iodine; the process is complex, involving multiple steps; it requires high-quality equipment and energy; it uses large amounts of chemical reagents; and it may introduce secondary pollution. Organic extractants pose safety and environmental risks and have limited adaptability to wastewater with low concentrations or complex compositions. The economic and environmental benefits of their practical industrial applications still need to be optimized.

[0004] Chinese patent document CN110662713A discloses a method for recovering and recycling iodine from an aqueous solution containing iodine-containing aromatic compounds. The iodine contained in these aromatic compounds can be directly converted from organic iodine to molecular iodine under strongly acidic (pH≤1) and high-temperature (80~300 ℃) conditions without a catalyst, achieving efficient recovery through sublimation, oxidation, and adsorption. This method is particularly suitable for treating highly acidic, high-iodide industrial wastewater generated during contrast agent production, offering advantages such as high recovery rate (≥95%) and no need for a catalyst. However, this method also has significant drawbacks: the strong acid and high-temperature environment places extremely high demands on the corrosion resistance and pressure resistance of the reaction equipment, increasing equipment costs; high-temperature operation consumes a large amount of energy, and lowering the temperature significantly prolongs the reaction time; the process effectiveness is highly dependent on the iodide content in the wastewater (the iodide / organic iodine weight ratio must be ≥0.5), otherwise the conversion rate decreases, requiring additional treatment; and if the reaction conditions are not well controlled, multiple remedial steps are required, making the operation cumbersome, and the overall applicability is still limited to specific types of industrial wastewater.

[0005] Traditional methods for iodine recovery, such as ion exchange, air purging, flotation, activated carbon adsorption, and liquid membrane technology, are often designed for inorganic forms of iodine (I). - IO3 - While elemental iodine can be recovered through reduction or oxidation, effective separation, recovery, and recycling of organic iodine, especially high-boiling-point fluorinated organic iodine compounds, is difficult. Therefore, there is an urgent need to find methods to recover elemental iodine from high-boiling-point perfluoroiodoalkane compounds to address the recycling of high-boiling-point fluorinated organic iodine compounds. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for recovering elemental iodine from perfluoroiodoalkanes. This method is used to process perfluoroiodoalkanes with high iodine content (10-40 wt%) that are difficult to process, thereby obtaining high-purity elemental iodine, which can be directly used as a product in the production of iodine-containing compounds.

[0007] A method for recovering elemental iodine from perfluoroiodoalkanes includes the following steps: (1) Mix perfluoroiodoalkane and alkaline solution to form a reaction solution, and heat and stir to form a deiodination solution; (2) The pH of the deiodizing solution was adjusted to 6-7 using an acidic solution, and inorganic iodized salt solid was obtained after distillation; (3) After dissolving the inorganic iodine salt solid in water, an inorganic iodine salt solution is obtained. An acidic solution is added to maintain a strong acidic pH, and an oxidant is added to carry out an oxidation-reduction reaction. After filtration and separation, wet iodine is obtained. After drying and dehydration, elemental iodine is obtained.

[0008] This invention addresses the problem of high-iodine-content (10-40 wt%) and difficult-to-process perfluoroiodoalkanes. It employs an alkaline solution to react with these iodine-containing compounds, resulting in mild and thorough deiodination. The pH of the deiodinated solution is adjusted by acidification to ensure the removal of potentially high-valence iodine-containing inorganic compounds (such as IO3) after alkaline hydrolysis. - The iodine is converted into iodide anions, which are then oxidized by adding an oxidant under acidic conditions. By controlling the redox potential at the endpoint during the reaction, high-purity iodine can be obtained and can be directly used as a product in the production of iodine-containing compounds.

[0009] Preferably, in step (1), the perfluoroiodoalkane is a fluorinated iodinated compound with an iodine content of 10-40 wt%.

[0010] Preferably, in step (1), the solute of the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, and aluminum hydroxide; and the solvent is one or more of methanol, ethanol, and dichloromethane.

[0011] Preferably, in step (1), the concentration of the alkaline solution is 15~30 wt%, which affects the deiodination effect. Higher alkalinity results in a higher deiodination rate.

[0012] Preferably, in step (1), the mass ratio of the perfluoroiodoalkane to the alkaline solution is 1~2:1.

[0013] Preferably, in step (1), the heating and stirring temperature is 60~90 ℃, the stirring speed is 200~400 rpm, and the time is 1~4 h. A longer reaction time results in better deiodination of organic iodine.

[0014] Preferably, in steps (2) and (3), the acidic solution is hydrochloric acid or sulfuric acid.

[0015] Preferably, in step (3), an acidic solution is added to the inorganic iodine salt solution to maintain the pH at ≤5.

[0016] Preferably, in step (3), the oxidant is one or more of hypochlorite, chlorate, hydrogen peroxide, and ferric salt.

[0017] Preferably, in step (3), the molar ratio of the oxidant to the iodine content in the inorganic iodine salt solution is 1:1 to 1.2.

[0018] Preferably, in step (3), the oxidation endpoint of the redox reaction is determined by the potential of the reaction solution, and the potential is 400~600 mV.

[0019] Preferably, in step (3), the purity of the iodine is ≥99% and the recovery rate is ≥89%.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: Based on the high iodine content (10-40 wt%) and difficult-to-treat perfluoroiodoalkanes, an alkaline solution is used for deiodination. The reaction conditions are mild, and deiodination is thorough. The pH of the deiodinated solution is adjusted by acidification to ensure the removal of potentially high-valence iodine-containing inorganic compounds (such as IO3) after alkaline hydrolysis. - The iodine is converted into iodide anions, which are then oxidized by adding an oxidant under acidic conditions. By controlling the redox potential at the endpoint during the reaction, high-purity iodine can be obtained and can be directly used as a product in the production of iodine-containing compounds. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the following embodiments.

[0022] The perfluoroiodoalkanes processed in this invention are high-boiling byproducts generated during the synthesis of 1,4-diiodooctafluorobutane and 1,6-diiodoperfluorohexane, as referenced in patent CN115677452A. Tests showed that the iodine content of different batches of byproducts varied, but all ranged from 10 to 40 wt%. All other raw materials used were commercially available.

[0023] Example 1 (1) Place 120 g of perfluoroiodoalkane (iodine content 38 wt%) in a three-necked flask, add 26% potassium hydroxide methanol solution to the three-necked flask, the mass ratio of perfluoroiodoalkane to potassium hydroxide methanol solution is 1:1.8; while heating in an oil bath, stir with a stirring paddle at a speed of 400 rpm, control the oil bath temperature at 90 ℃, and after reacting for 2 hours, obtain the deiodinated solution; (2) After adjusting the pH of the deiodizing solution to 6 with hydrochloric acid, the solvent was removed by distillation to obtain 118 g of inorganic iodized salt solid (mainly potassium iodide and potassium chloride). (3) Dissolve the inorganic iodine salt solid in 240 mL of water to obtain an inorganic iodine salt solution. Adjust the pH to ≤1 with hydrochloric acid. Control the iodine content of hydrogen peroxide and inorganic iodine solution to a molar ratio of 1:1.08. Add 1 / 3 of the hydrogen peroxide to the inorganic iodine solution by peristaltic pump within 30 minutes. Add the remaining oxidant within the next 60 minutes. During the process, control the pH of the solution to ≤1 with hydrochloric acid. Stop the reaction when the redox potential of the solution reaches 500 mV and filter to obtain wet iodine. Dehydrate the wet iodine by purging with nitrogen to obtain 43.6 g of elemental iodine with a purity of 99.5% and a recovery rate of 95.14%.

[0024] Example 2 (1) Place 120 g of perfluoroiodoalkane (iodine content 38 wt%) in a three-necked flask, add 20% potassium hydroxide methanol solution to the three-necked flask, the mass ratio of perfluoroiodoalkane to potassium hydroxide methanol solution is 1:1.6; while heating in an oil bath, stir with a stirring paddle at a speed of 300 rpm, control the oil bath temperature at 90 ℃, and after reacting for 4 hours, obtain the deiodinated solution; (2) After adjusting the pH of the deiodizing solution to 6 with hydrochloric acid, the solvent was removed by distillation to obtain 93 g of inorganic iodized salt solid (mainly potassium iodide and potassium chloride). (3) Dissolve the inorganic iodine salt solid in 190 mL of water to obtain an inorganic iodine salt solution. Adjust the pH to ≤1 with hydrochloric acid. Control the iodine content of hydrogen peroxide and inorganic iodine solution in a molar ratio of 1:1.12. Add 1 / 3 of the hydrogen peroxide to the inorganic iodine solution by peristaltic pump within 30 minutes. Add the remaining oxidant within the next 60 minutes. During the process, control the pH of the solution to ≤1 with hydrochloric acid. Stop the reaction when the redox potential of the solution reaches 500 mV and filter to obtain wet iodine. Purge the wet iodine with nitrogen to obtain 42.6 g of elemental iodine with a purity of 99.3% and a recovery rate of 92.77%.

[0025] Example 3 (1) Place 120 g of perfluoroiodoalkane (iodine content 38 wt%) in a three-necked flask, add 15% potassium hydroxide methanol solution to the three-necked flask, the mass ratio of perfluoroiodoalkane to potassium hydroxide methanol solution is 1:1.8; while heating in an oil bath, stir with a stirring paddle at a speed of 300 rpm, control the oil bath temperature at 90 ℃, and after reacting for 3 hours, obtain the deiodinated solution; (2) After adjusting the pH of the deiodizing solution to 6 with hydrochloric acid, the solvent was removed by distillation to obtain 85 g of inorganic iodized salt solid (mainly potassium iodide and potassium chloride). (3) Dissolve the inorganic iodine salt solid in 170 mL of water to obtain an inorganic iodine salt solution. Adjust the pH to ≤1 with hydrochloric acid. Control the iodine content of hydrogen peroxide and inorganic iodine solution in a molar ratio of 1:1.12. Add 1 / 3 of the hydrogen peroxide to the inorganic iodine solution by peristaltic pump within 30 minutes. Add the remaining oxidant within the next 60 minutes. During the process, control the pH of the solution to ≤1 with hydrochloric acid. Stop the reaction when the redox potential of the solution reaches 500 mV and filter to obtain wet iodine. Dehydrate the wet iodine by purging with nitrogen to obtain 41.3 g of elemental iodine with a purity of 99.1% and a recovery rate of 89.76%.

[0026] Example 4 (1) Place 120 g of perfluoroiodoalkane (iodine content 20 wt%) in a three-necked flask, add 30% potassium hydroxide methanol solution to the three-necked flask, the mass ratio of perfluoroiodoalkane to potassium hydroxide methanol solution is 1:1.6; while heating in an oil bath, stir with a stirring paddle at a speed of 300 rpm, control the oil bath temperature at 70 ℃, and after reacting for 2 hours, obtain the deiodinated solution; (2) After adjusting the pH of the deiodizing solution to 6 with hydrochloric acid, the solvent was removed by distillation to obtain 104 g of inorganic iodized salt solid (mainly potassium iodide and potassium chloride). (3) Add 210 mL of water to dissolve the inorganic iodine salt solid to obtain an inorganic iodine salt solution, and adjust the pH to ≤1 with hydrochloric acid. Control the iodine content of hydrogen peroxide and inorganic iodine solution at a molar ratio of 1:1.08. Add 1 / 3 of the hydrogen peroxide to the inorganic iodine solution by peristaltic pump within 30 minutes, and add the remaining oxidant within the next 60 minutes. During the process, use hydrochloric acid to control the pH of the solution to ≤1. Stop the reaction when the redox potential of the solution reaches 500 mV, and filter to obtain wet iodine. The wet iodine is purged and dehydrated with nitrogen to obtain 22.74 g of elemental iodine with a purity of 99.4% and a recovery rate of 94.18%.

[0027] Example 5 (1) Place 120 g of perfluoroiodoalkane (iodine content 30 wt%) in a three-necked flask, add 20% potassium hydroxide ethanol solution to the three-necked flask, the mass ratio of perfluoroiodoalkane to potassium hydroxide methanol solution is 1:1.8; while heating in an oil bath, stir with a stirring paddle at a speed of 200 rpm, control the oil bath temperature at 80 ℃, and after reacting for 4 hours, obtain the deiodinated solution; (2) After adjusting the pH of the deiodizing solution to 6 with hydrochloric acid, the solvent was removed by distillation to obtain 93 g of inorganic iodized salt solid (mainly potassium iodide and potassium chloride). (3) Dissolve the inorganic iodine salt solid in 190 mL of water to obtain an inorganic iodine salt solution. Adjust the pH to ≤1 with hydrochloric acid. Control the iodine content of hydrogen peroxide and inorganic iodine solution in a molar ratio of 1:1.08. Add 1 / 3 of the hydrogen peroxide to the inorganic iodine solution by peristaltic pump within 30 minutes. Add the remaining oxidant within the next 60 minutes. During the process, control the pH of the solution to ≤1 with hydrochloric acid. Stop the reaction when the redox potential of the solution reaches 500 mV and filter to obtain wet iodine. Dehydrate the wet iodine by purging with nitrogen to obtain 33.8 g of elemental iodine with a purity of 99.4% and a recovery rate of 93.30%.

[0028] Example 6 (1) Place 120 g of perfluoroiodoalkane (iodine content 15 wt%) in a three-necked flask, add 23% potassium hydroxide methanol solution to the three-necked flask, the mass ratio of perfluoroiodoalkane to potassium hydroxide ethanol solution is 1:1.8; while heating in an oil bath, stir with a stirring paddle at a speed of 400 rpm, control the oil bath temperature at 80 ℃, and after reacting for 4 hours, obtain the deiodinated solution; (2) After adjusting the pH of the deiodizing solution to 6 with hydrochloric acid, the solvent was removed by distillation to obtain 89g of inorganic iodized salt solid (mainly potassium iodide and potassium chloride). (3) Dissolve the inorganic iodine salt solid in 180 mL of water to obtain an inorganic iodine salt solution. Adjust the pH to ≤1 with hydrochloric acid. Control the iodine content of hydrogen peroxide and inorganic iodine solution to a molar ratio of 1:1.08. Add 1 / 3 of the hydrogen peroxide to the inorganic iodine solution by peristaltic pump within 30 minutes. Add the remaining oxidant within the next 60 minutes. During the process, control the pH of the solution to ≤1 with hydrochloric acid. Stop the reaction when the redox potential of the solution reaches 500 mV and filter to obtain wet iodine. Dehydrate the wet iodine by purging with nitrogen to obtain 17.01 g of elemental iodine with a purity of 99.5% and a recovery rate of 94.02%.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering elemental iodine from perfluoroiodoalkanes, characterized in that, Includes the following steps: (1) Mix perfluoroiodoalkane and alkaline solution to form a reaction solution, and heat and stir to form a deiodination solution; (2) The pH of the deiodizing solution was adjusted to 6-7 using an acidic solution, and inorganic iodized salt solid was obtained after distillation; (3) After dissolving the inorganic iodine salt solid in water, an inorganic iodine salt solution is obtained. An acidic solution is added to maintain the pH at a strong acidity. An oxidant is added to the solution to carry out an oxidation-reduction reaction. After filtration and separation, wet iodine is obtained. After drying and dehydration, elemental iodine is obtained.

2. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (1), the perfluoroiodoalkane is a fluorinated iodinated compound with an iodine content of 10-40 wt%.

3. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (1), the solute of the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, and aluminum hydroxide; the solvent is one or more of methanol, ethanol, and dichloromethane; and the concentration of the alkaline solution is 15-30 wt%.

4. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (1), the mass ratio of the perfluoroiodoalkane to the alkaline solution is 1~2:

1.

5. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (1), the heating and stirring temperature is 60~90 ℃, the stirring speed is 200~400 rpm, and the time is 1~4 h.

6. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In steps (2) and (3), the acidic solution is hydrochloric acid or sulfuric acid.

7. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (3), an acidic solution is added to the inorganic iodine salt solution to maintain the pH at ≤5.

8. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (3), the oxidant is one or more of hypochlorite, chlorate, hydrogen peroxide, and ferric salt.

9. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (3), the molar ratio of the oxidant and the iodine content in the inorganic iodine salt solution is 1:1 to 1.

2.

10. The method for recovering elemental iodine from perfluoroiodoalkanes according to claim 1, characterized in that, In step (3), the oxidation endpoint of the redox reaction is determined by the potential of the reaction solution, which is 400~600 mV.