Method for purifying Stefan acid from dinitrobenzene nitration byproduct mixture

Abstract

The invention relates to the technical field of Stefan acid purification, in particular to a method for purifying Stefan acid from a dinitrobenzene nitration byproduct mixture, which comprises the following steps: S1, dissolving the dinitrobenzene nitration byproduct mixture in water, adjusting the pH value to be alkaline, and filtering to obtain filtrate and filter residue dinitrobenzene solid; s2, adding the filtrate into an organic solvent, extracting, separating liquid, and retaining a water phase; and S3, adjusting the pH value of the water phase to be acidic, heating for acid precipitation, and then cooling for crystallization to obtain a mixed crystal of Stefan acid and picric acid. And S4, heating and mixing the mixed crystal and toluene, and filtering to obtain the high-purity Stefan acid. According to the method, efficient separation is realized through a two-step core process of'alkali dissolution-acidification 'and'selective dissolution'. In the final product, the content of dinitrobenzene can be reduced to 0%, the content of picric acid can be reduced to 1% or below, and the purity of Stefan acid can reach 99% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stefen acid purification, and particularly relates to a method for purifying stefen acid from a by-product mixture of dinitrobenzene nitration. BACKGROUND

[0002] In the industrial production process of preparing dinitrobenzene (DNB) by two-stage nitration of benzene, in addition to the target product dinitrobenzene, a large amount of by-products will be generated, mainly including stefen acid (2,4,6-trinitro-1,3-benzene diol, also known as TNR) and picric acid (2,4,6-trinitrophenol, also known as TNP). The mixture of these by-products and dinitrobenzene has complex components, close melting points and similar properties, and is extremely difficult to separate and purify.

[0003] At present, the treatment of such a mixture usually adopts multiple recrystallization or complex column chromatography separation method. These methods have problems such as long process flow, large solvent consumption, low product yield, high cost, etc., and are difficult to be applied to industrial production. For this reason, the existing improved technical solutions are: taking m-dihydroxybenzene as raw material, carrying out sulfonation in concentrated sulfuric acid, directly adding nitric acid for nitration after sulfonation, carrying out heat preservation under the condition of 95 DEG C water bath, and then diluting and washing the nitration liquid with water to obtain the product. However, this method has the following problems: the technology sulfonates m-dihydroxybenzene first and then nitrates, which has three shortcomings: first, the process involves high-risk nitration operation, which has high risk; second, water needs to be used to cool the reactor in time during the sulfonation process, and the process condition control is difficult; third, the use of sulfuric acid and nitric acid makes the procurement cost too high, and the treatment cost of a large amount of waste water and waste acid is also extremely high.

[0004] Stefen acid is a yellow crystal, and its properties are very similar to those of picric acid. Because three nitro groups are introduced on the aromatic ring, the acidity of the phenolic group is enhanced, so stefen acid has strong acidity and can form stefen acid metal salt with explosive performance, and can also be used as a component of explosive primer, analytical reagent, etc. It is a very important chemical raw material. Therefore, if high-purity stefen acid can be safely, low-cost and efficiently separated from the by-product mixture of dinitrobenzene nitration, it will have high economic value.

[0005] In summary, there is an urgent need to develop a stefen acid preparation method which is simple to operate, high in separation efficiency, good in product purity and suitable for large-scale production. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and provide a method for separating and purifying styphnic acid from a by-product mixture of dinitrobenzene nitration, so as to achieve high-efficiency separation of styphnic acid, dinitrobenzene and picric acid, obtain a high-purity styphnic acid product, and have the effects of simple process, high separation efficiency and high product purity.

[0007] The purpose of the present application is achieved by the following technical solutions. A method for purifying styphnic acid from a by-product mixture of dinitrobenzene nitration, the by-product mixture of dinitrobenzene nitration comprising styphnic acid and picric acid, comprising the following steps: S1: mixing the by-product mixture of dinitrobenzene nitration with water, adjusting the pH to alkaline, filtering to obtain a filtrate and dinitrobenzene solid as a filter residue; S2: adding the filtrate into an organic solvent for extraction, separating the liquid, and retaining the aqueous phase; S3: adjusting the pH of the aqueous phase to acid, heating for acid precipitation, and then cooling for crystallization to obtain a mixed crystal of styphnic acid and picric acid.

[0008] S4: heating and mixing the mixed crystal with toluene, filtering to obtain high-purity styphnic acid.

[0009] In some embodiments, in step S1, the mass ratio of the by-product mixture of dinitrobenzene nitration to the water is 25:350-450.

[0010] In some embodiments, in step S1, the pH is adjusted to 12.0-13.0; preferably, the pH is 12.5.

[0011] In some embodiments, in step S2, the organic solvent comprises at least one of benzene and toluene.

[0012] In some embodiments, in step S3, the pH is adjusted to 1.5-2.5; preferably, the pH is 1.8.

[0013] In some embodiments, in step S3, the temperature of the acid precipitation is 60-70℃.

[0014] In some embodiments, in step S3, the cooling crystallization is slow cooling to room temperature with an oil bath.

[0015] In some embodiments, in step S4, the mass ratio of the mixed crystal to the toluene is 1:5.

[0016] In some embodiments, in step S4, the temperature of the heating and mixing is 110℃.

[0017] Notably, the present application first soaks the above mixture in a certain amount of water, and then adjusts the pH to about 12.5 with a NaOH solution. The mixture begins to dissolve in large quantities, and the styphnic acid and picric acid in the mixture react with alkali metal ions to form salts and dissolve into water, while the DNB and other impurities do not. Next, filtration is performed to remove the insoluble substances, and the remaining solution is first extracted with benzene to remove all the DNB, and then acid-precipitated to cause the above generated salts to react with acid again to form insoluble substances and separate from the solution. Finally, toluene reflux is used to separate the picric acid and styphnic acid. Hot toluene selectively dissolves the picric acid without dissolving the styphnic acid, so that the obtained styphnic acid has high purity.

[0018] The beneficial effects of the present application are: 1. The present application takes advantage of the solubility differences of TNR, TNP and DNB under different pH conditions, and the large solubility difference of TNR and TNP in toluene. The present application realizes efficient separation through the two core processes of "alkali dissolution-acid precipitation" and "selective dissolution". The content of DNB in the final product can be reduced to 0%, the content of picric acid can be reduced to below 1%, and the purity of styphnic acid can be above 99%.

[0019] 2. The process of the present application is simple and easy to operate: the entire process only involves conventional chemical unit operations such as dissolution, pH adjustment, extraction, filtration, and reflux, and requires low equipment and is easy to realize industrial production and automatic control.

[0020] 3. The method of the present application has low cost and good environmental protection: the main solvents used are water and toluene, which are low in price and can be recycled. The use of expensive special solvents is avoided, reducing production cost and environmental burden. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The process flow chart of the method of the present application is shown in Figure 1. Figure 2 The photo of the DNB nitration by-product mixture used in the experiment in the example is shown in Figure 2. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be described in further detail below with reference to the accompanying drawings, but the scope of protection of the present application is not limited to the following description.

[0023] The source of the DNB nitration by-product mixture used in the following examples is as follows: In the process of preparing DNB by two-stage nitration of benzene, the by-products produced on site are taken, such as Figure 2As shown, the components include: dinitrobenzene (DNB), stearic acid (2,4,6-trinitroresorcinol), picric acid (2,4,6-trinitrophenol), and a small amount of unknown substances. HPLC analysis revealed the following specific proportions:

[0024] Example 1 This embodiment provides a method for purifying styrene from a mixture of dinitrobenzene nitration byproducts. The specific method is as follows: Take 25g of the byproduct mixture from the second-stage nitration of benzene and add it to 400ml of pure water. Stir mechanically for 30 minutes to ensure thorough dispersion. While stirring, slowly add a 50% sodium hydroxide solution dropwise to precisely adjust the pH of the system to 12.5, and continue stirring for another 30 minutes. At this point, both styracitric acid and picric acid form soluble sodium salts that enter the aqueous phase, while dinitrobenzene remains insoluble. Filter using a Buchner funnel; the filter cake is a brownish-yellow solid of dinitrobenzene. Collect the filtrate. Analyze the content of the compounds in the filtrate as follows:

[0025] Add 100 ml of benzene to the filtrate, stir and extract for 30 minutes, allow to stand and separate, discard the benzene layer (containing trace amounts of dinitrobenzene), and retain the aqueous phase. Transfer the aqueous phase to a 1000 ml round-bottom flask, place it in a 65°C oil bath, and add 98% concentrated sulfuric acid dropwise using a constant-pressure dropping funnel while stirring vigorously. Control the dropping rate to ensure the pH of the system eventually stabilizes at 1.8. Continue stirring at this pH for 30 minutes. After completion, turn off the oil bath heating and allow the reaction system to cool slowly overnight (approximately 12 hours) in the oil bath environment. The next day, a large amount of yellow crystals precipitate. Filter, collect the crystals, and wash with a small amount of ice water to obtain a crude mixture of stearic acid and picric acid crystals. The composition of the crude crystals is: DNB 0.19%, stearic acid 96.95%, picric acid 2.53%, and an unknown substance 0.33%, with a wet weight of approximately 15 g. The entire mixture of crystals was added to a round-bottom flask containing 75 ml of toluene. The system was placed in an oil bath at 110°C with a reflux condenser installed, and stirred under reflux for 30 minutes. After the reaction was complete, the mixture was immediately filtered while hot (using a preheated Buchner funnel and vacuum filtration apparatus). The filter cake was washed with a small amount of hot toluene. The filter cake was then dried in a vacuum drying oven at 50°C for 4 hours to obtain purified Stefanic acid, which was a bright yellow crystal. The specific component contents were analyzed as follows.

[0026]

[0027] Example 2 This embodiment provides a method for purifying styrene from a mixture of dinitrobenzene nitration byproducts. The specific method is as follows: Take 25g of the byproduct mixture from the second-stage nitration of benzene and add it to 350ml of pure water. Stir mechanically for 30 minutes to ensure thorough dispersion. While stirring, slowly add a 50% sodium hydroxide solution dropwise to precisely adjust the pH to 13.0, and continue stirring for another 30 minutes. At this point, both styracitric acid and picric acid form soluble sodium salts that enter the aqueous phase, while dinitrobenzene remains insoluble. Filter using a Buchner funnel; the filter cake is a brownish-yellow dinitrobenzene solid, which should be discarded; collect the filtrate. Add 100ml of benzene to the filtrate, stir and extract for 30 minutes, allow to stand and separate, discarding the benzene layer (containing trace amounts of dinitrobenzene), and retain the aqueous phase. Transfer the aqueous phase to a 1000ml round-bottom flask and place it in a 65℃ oil bath. Under vigorous stirring, add 98% concentrated sulfuric acid dropwise using a constant-pressure dropping funnel. Control the dropping rate to ensure the pH of the system eventually stabilizes at 2.5. Continue stirring at this pH for another 30 minutes. After completion, the oil bath heating was turned off, and the reaction system was allowed to cool slowly and naturally overnight (approximately 12 hours) in the oil bath environment. The next day, a large amount of yellow crystals were observed to precipitate. The crystals were collected by suction filtration and washed with a small amount of ice water to obtain a crude mixture of stearic acid and picric acid crystals, with a wet weight of approximately 15g. All of the above mixed crystals were added to a round-bottom flask containing 75ml of toluene, and the system was placed in a 110℃ oil bath with a reflux condenser installed and stirred under reflux for 30 minutes. After the reaction was completed, the mixture was immediately filtered while hot (using a preheated Buchner funnel and suction filtration apparatus). The filter cake was washed with a small amount of hot toluene. The filter cake was dried in a 50℃ vacuum drying oven for 4 hours to obtain purified stearic acid product, which was a bright yellow crystal. High-performance liquid chromatography analysis showed that the product purity was 99%, with no detectable dinitrobenzene and a picric acid content of 1%.

[0028] Example 3 This embodiment provides a method for purifying styrene from a mixture of dinitrobenzene nitration byproducts. The specific method is as follows: Take 25g of the byproduct mixture from the second-stage nitration of benzene and add it to 450ml of pure water. Stir mechanically for 30 minutes to ensure thorough dispersion. While stirring, slowly add a 50% sodium hydroxide solution dropwise to precisely adjust the pH to 12.0, and continue stirring for another 30 minutes. At this point, both styracitric acid and picric acid form soluble sodium salts that enter the aqueous phase, while dinitrobenzene remains insoluble. Filter using a Buchner funnel; the filter cake is a brownish-yellow solid of dinitrobenzene, which should be discarded; collect the filtrate. Add 100ml of benzene to the filtrate, stir and extract for 30 minutes, allow to stand and separate the layers, discarding the benzene layer (containing trace amounts of dinitrobenzene), and retain the aqueous phase. Transfer the aqueous phase to a 1000ml round-bottom flask and place it in a 65℃ oil bath. Under vigorous stirring, add 98% concentrated sulfuric acid dropwise using a constant-pressure dropping funnel. Control the dropping rate to ensure the pH of the system eventually stabilizes at 1.5. Continue stirring at this pH for another 30 minutes. After completion, the oil bath heating was turned off, and the reaction system was allowed to cool slowly and naturally overnight (approximately 12 hours) in the oil bath environment. The next day, a large amount of yellow crystals were observed to precipitate. The crystals were collected by suction filtration and washed with a small amount of ice water to obtain a crude mixture of stearic acid and picric acid crystals, with a wet weight of approximately 15g. All of the above mixed crystals were added to a round-bottom flask containing 75ml of toluene, and the system was placed in a 110℃ oil bath with a reflux condenser installed and stirred under reflux for 30 minutes. After the reaction was completed, the mixture was immediately filtered while hot (using a preheated Buchner funnel and suction filtration apparatus). The filter cake was washed with a small amount of hot toluene. The filter cake was dried in a 50℃ vacuum drying oven for 4 hours to obtain purified stearic acid product, which was a bright yellow crystal. High-performance liquid chromatography analysis showed that the product purity was 99%, with no detectable dinitrobenzene and a picric acid content of 1%.

[0029] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for purifying styracibic acid from a mixture of dinitrobenzene nitration byproducts, wherein the mixture comprises styracibic acid and picric acid, characterized in that, Includes the following steps: S1: Mix the dinitrobenzene nitration by-product mixture with water, adjust the pH to alkaline, filter, and obtain filtrate and filter residue dinitrobenzene solid; S2: Add the filtrate to an organic solvent for extraction, separate the liquids, and retain the aqueous phase; S3: Adjust the pH of the aqueous phase to acidic, heat it for acid precipitation, and then cool it to crystallize, to obtain a mixed crystal of styracitric acid and picric acid; S4: The mixed crystals and toluene are heated and mixed, then filtered to obtain high-purity styracitric acid.

2. The method according to claim 1, characterized in that: In step S1, the mass ratio of the dinitrobenzene nitration by-product mixture to the water is 25:350~450.

3. The method according to claim 1, characterized in that: In step S1, the pH is adjusted to 12.0~13.

0.

4. The method according to claim 1, characterized in that: In step S2, the organic solvent includes at least one of benzene and toluene.

5. The method according to claim 1, characterized in that: In step S3, the pH is adjusted to 1.5~2.

5.

6. The method according to claim 1, characterized in that: In step S3, the acid precipitation temperature is 60~70℃.

7. The method according to claim 1, characterized in that: In step S4, the mass ratio of the mixed crystal to the toluene is 1:

5.

8. The method according to claim 1, characterized in that: In step S4, the temperature of the heating mixture is 110°C.

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