A method for removing acetic acid from a nitric acid solution containing acetic acid

Abstract

The application provides a method for removing acetic acid from a nitric acid solution containing acetic acid, which comprises the following steps: adjusting the concentration of nitric acid in the nitric acid solution containing acetic acid, mixing electrolytic reagents, and performing boron-doped diamond electrolysis on the obtained electrolysis solution to remove acetate and obtain an electrolysis solution. The method for removing acetic acid from the nitric acid solution containing acetic acid can efficiently remove trace acetic acid in the nitric acid solution, improve the purity of the nitric acid, and has a wide application prospect.

Description

Technical Field

[0001] This application relates to the field of separation technology, and in particular to a method for removing acetic acid from a nitric acid solution containing acetic acid. Background Technology

[0002] Nitric acid is an important basic chemical raw material, widely used in fertilizers, explosives, dyes, pharmaceuticals, liquid crystal manufacturing, and fine chemicals. In industrial applications, nitric acid is often used as a nitrating agent in organic synthesis reactions or as an etching solution in the processing of electronic components. The resulting nitric acid waste liquid often contains acetic acid impurities. For example, in processes such as the acetaldehyde-nitric acid oxidation method to prepare glyoxal, cellulose nitration, and liquid crystal and semiconductor manufacturing, the dilute nitric acid produced often contains acetic acid with a mass concentration of 0.1% to 5%.

[0003] Purifying nitric acid from acetic acid not only enables the recycling of nitric acid resources and reduces production costs, but also reduces environmental pollution caused by waste acid emissions, thus having significant industrial application value and environmental significance.

[0004] Currently, the main technical routes for separating acetic acid from nitric acid containing acetic acid can be divided into physical separation methods, chemical conversion methods, and membrane separation / adsorption methods, but each of the existing methods has its own limitations.

[0005] (a) Distillation and Rectification Method Distillation is a common method for separating nitric acid and acetic acid by utilizing the difference in their boiling points. Nitric acid has a boiling point of approximately 83°C, while acetic acid has a boiling point of approximately 118°C, a difference that theoretically allows for separation through distillation. However, nitric acid and water form an azeotrope at a concentration of approximately 68% (with an azeotropic point of approximately 120.5°C), while acetic acid and water do not form an azeotrope, but the relative volatility of the water-acetic acid binary system is close to 1. Therefore, ordinary distillation alone is insufficient to completely separate them. If direct distillation is used to process dilute nitric acid containing acetic acid, the product will have a high residual concentration of acetic acid, and the nitric acid will decompose significantly at high temperatures. Furthermore, direct distillation requires high operating temperatures, leading to increased thermal decomposition losses of nitric acid, and the appearance of yellow fumes in the distillation column, resulting in unsatisfactory separation. While vacuum distillation can lower the operating temperature and reduce nitric acid decomposition, single-stage vacuum distillation has limited effectiveness in purifying dilute nitric acid with an acetic acid content of 0.1%–5%, often failing to achieve the required high purity. Therefore, it is difficult to achieve efficient purification of dilute nitric acid containing acetic acid by using distillation or rectification alone.

[0006] (ii) Alkali neutralization method The alkaline neutralization method involves adjusting the pH of the mixed acid with alkaline substances such as calcium oxide or sodium hydroxide, converting acetic acid to acetate and nitric acid to nitrate. The acetic acid solution is then recovered by vacuum distillation, and the remaining nitrate solution is cooled and crystallized to obtain the nitrate product. For example, the pH of the mixed acid is adjusted with calcium oxide, and then the acetic acid solution is obtained by vacuum distillation. The remaining calcium nitrate solution is cooled and crystallized to obtain the calcium nitrate product. Another method involves reacting quicklime with a mixed acid containing hydrofluoric acid, nitric acid, and acetic acid, followed by a series of steps including vacuum evaporation, neutralization, and solid-liquid separation to separate and recover the acid components. The main drawbacks of the alkaline neutralization method are: it converts nitric acid to nitrate instead of recovering it as free nitric acid, failing to meet the demand for high-purity free nitric acid products; furthermore, this method consumes a large amount of alkaline reagent, resulting in high processing costs, and the post-processing steps are cumbersome.

[0007] (III) Extraction method Extraction methods utilize extractants such as tributyl phosphate and trialkylamine to selectively extract acetic acid or nitric acid, thereby achieving their separation. Studies have shown that tributyl phosphate has a certain complexing extraction ability for both acetic acid and nitric acid, enabling its extraction from the aqueous phase to the organic phase. However, extraction methods face several challenges in practical applications: the extractants are costly, extractant loss occurs during extraction, requiring regular replenishment, the extracted organic phase requires back-extraction regeneration, and the operation process is complex, some extractants lack stability in highly oxidizing nitric acid systems, leading to long-term performance degradation, and the extraction method generates secondary organic wastewater, increasing the burden of subsequent treatment. Therefore, extraction methods are significantly limited in large-scale industrial applications.

[0008] (iv) Adsorption distillation method In recent years, adsorption distillation has attracted attention as an emerging separation method. Some studies have used adsorption distillation to separate acetic acid from electronic waste acid liquid after filtering to remove mechanical impurities. Molecular sieves were used as the adsorbent, and the acetic acid content in the distillate was controlled below 5000 ppm. This method shows significant removal efficiency for acetic acid, but the regeneration and replacement of the adsorbent introduces additional operating costs and process complexity. Furthermore, adsorption distillation has limited adaptability to specific concentration ranges of raw materials, and the recovered acetic acid often contains residual nitric acid, indicating room for improvement in separation purity.

[0009] In summary, the current methods for separating acetic acid from nitric acid solutions containing acetic acid all present challenges such as high residual acetic acid content, low separation purity, high separation energy consumption, and heavy burden on subsequent processing. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for removing acetic acid from a nitric acid solution containing acetic acid. This method can remove acetic acid to obtain nitric acid product, and the process is simple, reduces equipment and reagent costs, is environmentally friendly, and is conducive to industrial application.

[0011] To achieve this objective, the following technical solution is adopted in this application: This application provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method includes: adjusting the concentration of nitric acid in the nitric acid solution containing acetic acid, mixing an electrolytic agent, and performing boron-doped diamond electrolysis on the obtained electrolyte to remove acetate ions, thereby obtaining an electrolyte solution.

[0012] In some technical solutions of this application, the concentration of nitric acid in the acetic acid-containing nitric acid solution is 45~65wt%.

[0013] In some technical solutions of this application, the concentration of acetic acid in the nitric acid solution containing acetic acid is 0.1~1wt%.

[0014] In some technical solutions of this application, the concentration of nitric acid in the acetic acid-containing nitric acid solution after adjustment is 19~25wt%.

[0015] In some technical solutions of this application, the electrolytic agent includes any one or a combination of at least two of sodium nitrate, potassium nitrate, sodium hydroxide, or potassium hydroxide.

[0016] In some technical solutions of this application, the concentration of the electrolyte in the electrolyte solution is 10~30g / L.

[0017] In some technical solutions of this application, the sodium nitrate and potassium nitrate are added independently in solid form.

[0018] In some technical solutions of this application, the sodium hydroxide and potassium hydroxide are added independently in solution form.

[0019] In some technical solutions of this application, the concentration of sodium hydroxide in the sodium hydroxide solution is 10~32wt%.

[0020] In some technical solutions of this application, the concentration of potassium hydroxide in the potassium hydroxide solution is 10~32wt%.

[0021] In some technical solutions of this application, the current density of the boron-doped diamond electrolysis is 475~500 A / m. 2 .

[0022] In some technical solutions of this application, the electrolytic anode of the boron-doped diamond electrolysis includes a silicon-based anode.

[0023] In some technical solutions of this application, the electrolytic cathode of the boron-doped diamond electrolysis includes titanium material.

[0024] In some technical solutions of this application, the silicon-based anode includes a silicon substrate and a boron-doped diamond layer disposed on the surface of the silicon substrate.

[0025] In some technical solutions of this application, the thickness of the boron-doped diamond layer in the silicon-based anode is 2~3mm.

[0026] In some technical solutions of this application, the thickness of the electrolytic cathode of the boron-doped diamond electrolysis is 0.5~1.5mm.

[0027] In some technical solutions of this application, the electrolyte after electrolysis is distilled to obtain nitric acid product and distillation bottom liquid, respectively.

[0028] In some technical solutions of this application, the distillation base liquid is recycled to a nitric acid solution containing acetic acid.

[0029] In some technical solutions of this application, the distillation is negative pressure distillation.

[0030] In some technical solutions of this application, the distillation pressure is 0.05~0.065MPa.

[0031] In some technical solutions of this application, the distillation temperature is 90~95℃.

[0032] Compared with the prior art, this application has at least the following beneficial effects: The method for removing acetic acid from nitric acid solution containing acetic acid provided in this application can remove acetate ions while retaining the free nitrate ions in the nitric acid solution containing acetic acid. The resulting nitric acid product has high purity, with the concentration of acetic acid in the nitric acid product reaching less than 0.001 wt% and the concentration of nitric acid in the nitric acid product reaching more than 41 wt%. The recovery rate of nitric acid can reach more than 85%. Moreover, the process of this application is short, does not require the addition of additional difficult-to-handle reagents, has virtually no subsequent burden, is easy to apply in industrial applications, and has broad application prospects. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the method for removing acetic acid from a nitric acid solution containing acetic acid, as provided in a specific embodiment of this application. Detailed Implementation

[0034] To facilitate understanding of this application, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of this application.

[0035] Currently, all methods for removing acetic acid from nitric acid solutions containing acetic acid have their own limitations: distillation has limited separation efficiency and significant losses due to thermal decomposition of nitric acid; alkali neutralization converts nitric acid into nitrates, making it impossible to recover free nitric acid; extraction is costly, has a complex process, and causes secondary pollution; and adsorption distillation has problems with adsorbent regeneration and is also a complex process.

[0036] Therefore, this application develops a simple, reagent-free, and efficient method for purifying dilute nitric acid while retaining the free acid form of nitric acid, which has significant industrial application value.

[0037] This application provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method includes: adjusting the concentration of nitric acid in the nitric acid solution containing acetic acid, mixing an electrolytic agent, and performing boron-doped diamond electrolysis on the obtained electrolyte to remove acetate ions, thereby obtaining an electrolyte solution.

[0038] The method for removing acetic acid from nitric acid solutions containing acetic acid provided in this application employs boron-doped diamond electrolysis. The boron-doped diamond electrode maintains good stability and activity in the nitric acid solution environment and is not easily contaminated, exhibiting a self-cleaning effect. During electrolysis, highly reactive oxides such as hydroxyl radicals are generated on the surface of the boron-doped diamond electrode, which can oxidize acetic acid without significantly negatively impacting the nitric acid, thus achieving the removal of acetic acid from the nitric acid solution. Furthermore, the nitrate ions after acetic acid removal still exist in free form in the solution, resulting in high-purity nitric acid with a high recovery rate and broad application prospects.

[0039] In this application, an electrolytic agent needs to be added, which can reduce resistance and improve current efficiency during the electrolysis process.

[0040] In some specific embodiments, the concentration of nitric acid in the acetic acid-containing nitric acid solution is 45~65wt%, for example, it can be 45wt%, 48wt%, 50wt%, 52wt%, 54wt%, 57wt%, 59wt%, 61wt%, 63wt%, or 65wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0041] In some specific embodiments, the concentration of acetic acid in the nitric acid solution containing acetic acid is 0.1~1wt%, for example, it can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] In some specific implementations, the concentration of nitric acid in the acetic acid-containing nitric acid solution after adjustment is 19~25wt%, for example, it can be 19wt%, 19.7wt%, 20.4wt%, 21wt%, 21.7wt%, 22.4wt%, 23wt%, 23.7wt%, 24.4wt%, or 25wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] This application dilutes the concentration of nitric acid in the acetic acid-containing nitric acid solution to the above-mentioned range before electrolysis. When the concentration of nitric acid in the acetic acid-containing nitric acid solution entering the electrolysis is too high, the corrosiveness to the electrolysis equipment is enhanced, leading to a decrease in the lifespan of the electrolysis equipment. When the concentration of nitric acid in the acetic acid-containing nitric acid solution entering the electrolysis is too low, the energy consumption of subsequent distillation will increase.

[0044] Moreover, controlling the concentration of nitric acid within a reasonable range can better improve the conductivity of the electrolyte and increase the electrolysis efficiency. Specifically, a certain concentration of nitric acid can provide the electrolyte with higher conductivity. On the other hand, the presence of nitric acid will provide hydrogen ions in the solution system. When the hydrogen ion content is too high, it will inhibit the ionization of acetic acid, so that acetic acid will exist in the solution system in the form of acetic acid molecules, which will affect the rate of acetic acid being electrolyzed at the electrode.

[0045] In some specific embodiments, the electrolyte comprises any one or a combination of at least two of sodium nitrate, potassium nitrate, sodium hydroxide, or potassium hydroxide, wherein typical but non-limiting combinations are combinations of sodium nitrate and potassium nitrate, combinations of sodium hydroxide and potassium nitrate, combinations of sodium nitrate and sodium hydroxide, and combinations of potassium hydroxide and potassium nitrate.

[0046] This application selects the above-mentioned substances as electrolytic agents, wherein sodium nitrate and / or potassium nitrate can increase conductivity and reduce resistance during electrolysis; sodium hydroxide and / or potassium hydroxide can increase conductivity and reduce resistance during electrolysis, and the addition of sodium hydroxide and / or potassium hydroxide can promote the ionization equilibrium of acetic acid, thereby improving the reaction efficiency of acetic acid on the electrode.

[0047] In some specific embodiments, the concentration of the electrolyte in the electrolyte solution is 10~30g / L, for example, it can be 10g / L, 13g / L, 15g / L, 17g / L, 19g / L, 22g / L, 24g / L, 26g / L, 28g / L or 30g / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] This application controls the concentration of the electrolyte in the electrolyte to be electrolyzed within the above-mentioned concentration range. When the concentration of the electrolyte is too high, too many cations are introduced, which leads to the problem that the mother liquor cannot be effectively reused after enrichment. When the concentration of the electrolyte is too low, the electrolyte resistance is high and the electrolysis efficiency is low.

[0049] In some specific embodiments, the sodium nitrate and potassium nitrate are added independently in solid form.

[0050] In some specific embodiments, the sodium hydroxide and potassium hydroxide are added independently in solution form.

[0051] In some specific embodiments, the concentration of sodium hydroxide in the sodium hydroxide solution is 10~32wt%, for example, it can be 10wt%, 13wt%, 15wt%, 18wt%, 20wt%, 23wt%, 25wt%, 28wt%, 30wt%, or 32wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In some specific embodiments, the concentration of potassium hydroxide in the potassium hydroxide solution is 10~32wt%, for example, it can be 10wt%, 13wt%, 15wt%, 18wt%, 20wt%, 23wt%, 25wt%, 28wt%, 30wt% or 32wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] In some specific embodiments, the current density of the boron-doped diamond electrolysis is 475~500 A / m. 2 For example, it could be 475A / m 2 478A / m 2 481A / m 2 484A / m 2 487A / m 2 489A / m 2 492A / m 2 495A / m 2 498A / m 2 Or 500A / m 2 This includes, but is not limited to, the listed values; other unlisted values ​​within this range also apply.

[0054] In some specific embodiments, the electrolytic anode of the boron-doped diamond electrolysis includes a silicon-based anode.

[0055] In some specific embodiments, the electrolytic cathode of the boron-doped diamond electrolysis comprises titanium.

[0056] In some specific embodiments, the silicon-based anode includes a silicon substrate and a boron-doped diamond layer disposed on the surface of the silicon substrate.

[0057] In some specific embodiments, the thickness of the boron-doped diamond layer in the silicon-based anode is 2 to 3 mm, for example, it can be 2 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm or 3 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] In some specific embodiments, the thickness of the electrolytic cathode of the boron-doped diamond electrolysis is 0.5~1.5mm, for example, it can be 0.5mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm or 1.5mm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0059] In some specific implementations, the electrolyte after electrolysis is distilled to obtain nitric acid product and distillation bottom liquid, respectively.

[0060] After electrolysis, this application employs a distillation step to process the post-electrolysis liquid, thereby obtaining nitric acid product and distillation bottom liquid. The distillation bottom liquid can be recycled to a nitric acid solution containing acetic acid, diluted again, mixed with the electrolytic reagent, and subjected to boron-doped diamond electrolysis.

[0061] In some specific implementations, the distillate is recycled to a nitric acid solution containing acetic acid.

[0062] In some specific implementations, the distillation is negative pressure distillation.

[0063] In some specific embodiments, the distillation pressure is 0.05~0.065MPa, for example, it can be 0.05MPa, 0.052MPa, 0.054MPa, 0.055MPa, 0.057MPa, 0.059MPa, 0.06MPa, 0.062MPa, 0.064MPa or 0.065MPa, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0064] In some specific embodiments, the distillation temperature is 90~95℃, for example, it can be 90℃, 90.6℃, 91.2℃, 91.7℃, 92.3℃, 92.8℃, 93.4℃, 93.9℃, 94.5℃ or 95℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0065] In some specific implementation plans, such as Figure 1As shown, the method includes the following steps: S1. Dilute the concentration of nitric acid in a nitric acid solution containing acetic acid with a concentration of 0.1~1wt% to 19~25wt%, and mix it with an electrolytic agent, wherein the electrolytic agent includes any one or a combination of at least two of sodium nitrate, potassium nitrate, sodium hydroxide or potassium hydroxide, to obtain an electrolyte solution with a concentration of 10~30g / L.

[0066] S2. Using a silicon-based anode (comprising a silicon substrate and a 2-3 mm boron-doped diamond layer disposed on the surface of the silicon substrate) as the anode and a 0.5-1.5 mm thick titanium material as the cathode, boron-doped diamond electrolysis is performed on the electrolyte at a current density of 475-500 A / m. 2 To remove acetate ions, an electrolyte solution was obtained.

[0067] S3. The electrolyte obtained in step S2 is subjected to negative pressure distillation at 0.05~0.065MPa and 90~95℃ to obtain nitric acid product and distillation bottom liquid respectively; the distillation bottom liquid is recycled to step S1.

[0068] The method for removing acetic acid from nitric acid solution containing acetic acid provided in this application can retain the free form of nitrate ions in the nitric acid solution containing acetic acid while removing acetate ions, resulting in a high purity nitric acid product. Moreover, the process of this application is short, does not require the addition of difficult-to-process reagents, has virtually no subsequent burden, is easy to apply in industrial applications, and has broad application prospects.

[0069] The following detailed description uses specific embodiments.

[0070] Example 1 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid, the method comprising the following steps: S1. Dilute the concentration of nitric acid in the acetic acid-containing nitric acid solution with an acetic acid concentration of 0.7wt% and a nitric acid concentration of 50wt% to 27wt%, and add an electrolytic agent (sodium nitrate) to obtain an electrolyte solution with an electrolytic agent concentration of 20g / L.

[0071] S2. Using a silicon-based anode (comprising a silicon substrate and a 2.5mm boron-doped diamond layer with a boron content of 50ppm) as the anode and a 1.0mm thick titanium cathode, boron-doped diamond electrolysis is performed on the electrolyte at a current density of 475A / m. 2 Electrolysis was performed for 15 hours to remove acetate ions, yielding the electrolyte solution.

[0072] S3. The electrolyte obtained in step S2 is subjected to negative pressure distillation at 0.06 MPa and 92 °C to obtain nitric acid product and distillation bottom liquid respectively; the distillation bottom liquid is recycled to step S1.

[0073] Example 2 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid, the method comprising the following steps: S1. Dilute the concentration of nitric acid in the acetic acid-containing nitric acid solution with an acetic acid concentration of 1.0 wt% and a nitric acid concentration of 45 wt% to 19 wt%, and add an electrolytic agent (potassium nitrate) to obtain an electrolyte solution with an electrolytic agent concentration of 30 g / L.

[0074] S2. Using a silicon-based anode (comprising a silicon substrate and a 3mm boron-doped diamond layer with a boron content of 50ppm disposed on the surface of the silicon substrate), and a 1.5mm thick titanium cathode, boron-doped diamond electrolysis is performed on the electrolyte at a current density of 500A / m. 2 Electrolysis was performed for 12 hours to remove acetate ions, yielding the electrolyte solution.

[0075] S3. The electrolyte obtained in step S2 is subjected to negative pressure distillation at 0.065 MPa and 90 °C to obtain nitric acid product and distillation bottom liquid respectively; the distillation bottom liquid is recycled to step S1.

[0076] Example 3 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid, the method comprising the following steps: S1. Dilute the nitric acid concentration in the acetic acid-containing nitric acid solution with an acetic acid concentration of 0.1wt% and a nitric acid concentration of 65wt% to 20wt%, and add an electrolytic agent (a sodium hydroxide solution with a concentration of 32wt%) to obtain an electrolyte solution with an electrolytic agent concentration of 10g / L.

[0077] S2. Using a silicon-based anode (comprising a silicon substrate and a 2mm boron-doped diamond layer with a boron content of 50ppm) as the anode and a 0.5mm titanium cathode, boron-doped diamond electrolysis is performed on the electrolyte at a current density of 490A / m. 2 Electrolysis was performed for 13 hours to remove acetate ions, yielding the electrolyte solution.

[0078] S3. The electrolyte obtained in step S2 is subjected to negative pressure distillation at 0.05 MPa and 95 °C to obtain nitric acid product and distillation bottom liquid respectively; the distillation bottom liquid is recycled to step S1.

[0079] Example 4 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid. Except for the concentration of the electrolytic agent (sodium nitrate) being 40 g / L, the method is the same as in Example 1 and will not be repeated here.

[0080] Example 5 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid. Except for the concentration of the electrolytic agent (sodium nitrate) being 5 g / L, the method is the same as in Example 1 and will not be repeated here.

[0081] Example 6 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method is the same as in Example 1 except that sodium nitrate is replaced with sodium sulfate in the electrolytic agent, and will not be described again here.

[0082] Example 7 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method is the same as that in Embodiment 1 except that step S3 is omitted, and will not be described again here.

[0083] Example 8 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid, wherein the method involves a current density of 450 A / m during boron-doped diamond electrolysis. 2 Except for the above, everything else is the same as in Example 1, and will not be repeated here.

[0084] Example 9 This embodiment provides a method for removing acetic acid from a nitric acid solution containing acetic acid, wherein the method involves a current density of 520 A / m during boron-doped diamond electrolysis. 2 Except for the above, everything else is the same as in Example 1, and will not be repeated here.

[0085] Comparative Example 1 This comparative example provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method is the same as in Example 1 except that the dilution in step S1 is omitted, i.e., a nitric acid solution containing acetic acid with a concentration of 0.7 wt% and a nitric acid concentration of 50 wt% is directly used, and 20 g / L of electrolytic agent (sodium nitrate) is added to directly perform boron-doped diamond electrolysis. The rest of the method is the same as in Example 1 and will not be described again here.

[0086] Comparative Example 2 This comparative example provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method is the same as in Example 1 except that boron-doped diamond electrolysis is not performed, i.e., the anode is directly a silicon substrate anode and does not have a boron-doped diamond layer. Therefore, it will not be described again here.

[0087] Comparative Example 3 This comparative example provides a method for removing acetic acid from a nitric acid solution containing acetic acid. The method is the same as in Example 1 except that no electrolytic agent (sodium nitrate) is added, and will not be described again here.

[0088] Test Method: Nitric Acid Content Test: Pour 15 ml of water into a stoppered, light-bodied iodine flask and weigh it, recording the weight as m1. Add 0.8 ml of sample, immediately stopper the flask, gently shake to mix, cool, and weigh again, recording the weight as m2. The second weighing must be accurate to 0.0001 g. Add 10 drops of bromocresol green-methyl red indicator (weigh 0.2 g of methyl red, dissolve in 95% ethanol, dilute to 100 ml; mix in a 3:1 ratio to obtain the bromocresol green-methyl red indicator). Titrate with 0.05 mol / L NaOH standard solution until the solution turns green. Calculate the content using the following formula: X= Determination of acetic acid content: Weigh 1g of sample, accurate to 0.0002g, and place it in a 250ml stoppered conical flask. The flask should be pre-filled with 80ml of freshly boiled and cooled water. Add 2 drops of phenolphthalein indicator (10g / L), and titrate with standard sodium hydroxide solution (1.0mol / L) until the solution turns a pale pink color that does not fade for 30 seconds. The endpoint is indicated by the following calculation formula: W1 = V × c × M × 100 / m The acetic acid content is expressed as a mass fraction w1, with the value expressed as a percentage (%). W1 = V × c × M × 100 / m Where: c—the actual concentration of the sodium hydroxide standard titration solution, mol / L; V—Volume of standard sodium hydroxide titration solution, mL; m—mass of the sample (g); M—Molar mass of acetic acid, M (CH3COOH=0.06005).

[0089] The test results of the above embodiments and comparative examples are shown in Table 1.

[0090] Table 1 The following points can be observed from Table 1: (1) As can be seen from the comprehensive examples 1 to 3, the method for removing acetic acid from nitric acid solution containing acetic acid provided in this application has the effect of short process and removal of trace amount of acetic acid, wherein the concentration of acetic acid in nitric acid product is less than 0.001 wt%, the concentration of nitric acid in nitric acid product is more than 41 wt%, and the recovery rate of nitric acid is more than 85%.

[0091] (2) As can be seen from Examples 1 and 4-5, the concentration of the electrolytic agent in Example 1 was 20 g / L, compared to 40 g / L and 5 g / L in Examples 4-5 respectively. In Example 1, the concentration of acetic acid in the nitric acid product was 0.001 wt%, and the concentration of nitric acid in the nitric acid product was 46 wt%, with a nitric acid recovery rate as high as 92%. In Example 4, although a higher sodium nitrate concentration was used, it not only failed to improve the quality of the final product but also resulted in reagent waste. Furthermore, due to the high concentration of sodium nitrate in Example 4, the distillate after subsequent separation could not be effectively recycled. In Example 5, the concentration of the electrolytic agent was too low, leading to a decrease in electrolysis efficiency. Within the same electrolysis time, the electrolysis effect was not as good as in Example 1, and the nitric acid recovery rate decreased. This indicates that by controlling the concentration of the electrolytic agent within a reasonable range, this application can better improve the removal effect of trace amounts of acetic acid in nitric acid.

[0092] (3) As can be seen from the combined examples of Examples 1 and 6, sodium sulfate was used as an additive in Example 6, which introduced sulfate ions, resulting in the enrichment of sodium sulfate in the subsequent distillation bottom liquid. Consequently, the nitric acid product obtained contained sulfate ions, leading to the product failing to meet the standards. As can be seen from the combined examples of Examples 1 and 7, nitric acid product could not be obtained without distillation in Example 7, as the electrolyte could not be effectively removed, resulting in the product failing to meet the standards.

[0093] (4) As can be seen from the combined examples 1 and 8-9, this application can improve the removal effect of acetic acid and increase the recovery rate of nitric acid by controlling the current density of boron-doped diamond electrolysis within a reasonable range.

[0094] (5) In Comparative Example 1, no concentration control was performed, which led to corrosion of the electrolysis equipment and a significant decrease in electrolysis efficiency. In Comparative Example 2, there was no boron-doped diamond layer, which resulted in a lack of acetic acid removal effect. In Comparative Example 3, no electrolytic reagent was added, and even if the voltage was increased, it was difficult to reach the set current value, and the effect of electrolytic removal of acetic acid was significantly reduced.

[0095] In summary, the method for removing acetic acid from nitric acid solutions containing acetic acid provided in this application has a short process and can remove trace amounts of acetic acid. In some technical solutions of this application, the concentration of acetic acid in the nitric acid product is less than 0.001 wt%, the concentration of nitric acid in the nitric acid product is above 41 wt%, and the recovery rate of nitric acid is above 85%. This application illustrates its detailed features through the above embodiments, but this application is not limited to the above detailed features, that is, it does not mean that this application must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the selected technical features, additions of auxiliary technical features, and selection of specific methods all fall within the protection scope and disclosure scope of this application.

Claims

1. A method for removing acetic acid from a nitric acid solution containing acetic acid, characterized in that, The method includes: The concentration of nitric acid in a nitric acid solution containing acetic acid is adjusted, and an electrolytic agent is mixed. The resulting electrolyte is then subjected to boron-doped diamond electrolysis to remove acetate ions, yielding the electrolyte solution.

2. The method according to claim 1, characterized in that, The concentration of nitric acid in the acetic acid-containing nitric acid solution is 45-65 wt%. And / or, the concentration of acetic acid in the nitric acid solution containing acetic acid is 0.1~1wt%.

3. The method according to claim 1 or 2, characterized in that, The concentration of nitric acid in the acetic acid-containing nitric acid solution after adjustment is 19~25wt%.

4. The method according to any one of claims 1 to 3, characterized in that, The electrolyte includes any one or a combination of at least two of sodium nitrate, potassium nitrate, sodium hydroxide, or potassium hydroxide. And / or, the concentration of the electrolyte in the electrolyte solution is 10~30g / L.

5. The method according to claim 4, characterized in that, Sodium nitrate and potassium nitrate are added independently in solid form; And / or, the sodium hydroxide and potassium hydroxide are each added independently in solution form; And / or, the concentration of sodium hydroxide in the sodium hydroxide solution is 10~32 wt%; And / or, the concentration of potassium hydroxide in the potassium hydroxide solution is 10~32wt%.

6. The method according to any one of claims 1 to 5, characterized in that, The current density of the boron-doped diamond electrolysis is 475~500 A / m. 2 .

7. The method according to any one of claims 1 to 6, characterized in that, The electrolytic anode of the boron-doped diamond electrolysis includes a silicon-based anode; And / or, the electrolytic cathode of the boron-doped diamond electrolysis comprises titanium.

8. The method according to claim 7, characterized in that, The silicon-based anode includes a silicon substrate and a boron-doped diamond layer disposed on the surface of the silicon substrate; And / or, the thickness of the boron-doped diamond layer in the silicon-based anode is 2~3 mm; And / or, the thickness of the electrolytic cathode of the boron-doped diamond electrolysis is 0.5~1.5 mm.

9. The method according to any one of claims 1 to 8, characterized in that, The method further includes: distilling the electrolyte to obtain nitric acid product and distillation bottom liquid, respectively.

10. The method according to claim 9, characterized in that, The distillate is recycled to a nitric acid solution containing acetic acid; And / or, the distillation is a negative pressure distillation; And / or, the distillation pressure is 0.05~0.065 MPa; And / or, the distillation temperature is 90~95℃.

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