Method for preparing high-concentration hydroquinone by electrolyzing phenol

Abstract

The invention belongs to the technical field of electrolytic preparation, and discloses a method for preparing high-concentration hydroquinone by electrolyzing phenol. The method comprises the following steps: adding a sulfuric acid aqueous solution into an anode chamber and a cathode chamber of an H-shaped electrolytic cell, adding phenol into the anode chamber, and electrifying for electrolysis to obtain a sulfuric acid solution containing p-benzoquinone; extracting the sulfuric acid solution containing p-benzoquinone to obtain a p-benzoquinone organic solution and an anode chamber circulating sulfuric acid solution; adding a sulfuric acid aqueous solution into an anode chamber and a cathode chamber of another H-shaped electrolytic cell, adding a p-benzoquinone organic solution into the cathode chamber, and electrifying for electrolysis to obtain a sulfuric acid solution containing hydroquinone and a liquid separation extraction agent; and the obtained sulfuric acid solution containing hydroquinone is repeatedly added into the cathode chamber, so that hydroquinone obtained through reduction of p-benzoquinone is enriched in the cathode chamber, and the concentration of the hydroquinone product is improved. The concentration of hydroquinone in the electrolyte can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytic preparation, and more specifically, relates to a method for preparing high-concentration hydroquinone by electrolyzing phenol. Background Art

[0002] Hydroquinone is a relatively expensive chemical raw material with a wide range of uses. Its main uses include the following: (1) used in the manufacture of black-and-white developers, dyes, electroplating materials, stabilizers and antioxidants for photographic films; (2) as a petroleum anticoagulant, ammonia synthesis catalyst, etc.; (3) as an inhibitor for polymer monomers, such as styrene, butadiene, isoprene, ethyl acetate, acrylonitrile, etc.; (4) as an intermediate for the synthesis of carbofuran, propoxur, berberine, epinephrine, vanillin, piperonal, etc.; (5) used in the manufacture of urease inhibitors. When added before ordinary urea granulation, a new type of urea with high utilization rate and long fertilizer effect period can be obtained.

[0003] There are many methods for synthesizing hydroquinone, including the peroxidation of diisopropylbenzene, the bisphenol A method, the aniline oxidation method, the direct oxidation of phenol with hydrogen peroxide, the electrochemical method, etc. Among them, the electrochemical method has the advantages of simple process flow, operation at room temperature and pressure, simple operation, easy control, low raw material price, good product quality, and less pollution of three wastes, which has attracted the research interest of more and more chemists. The existing technology for synthesizing hydroquinone by electrochemical method is to oxidize phenol or benzene to p-benzoquinone at the anode, and then reduce the synthesized p-benzoquinone at the cathode to obtain hydroquinone. For example, Zheng Keli et al. used tetrabutylammonium bromide as a phase transfer catalyst, in an H-type electrolytic cell with sulfuric acid as the supporting electrolyte and lead-based lead dioxide as the anode to oxidize benzene to p-benzoquinone. Yu Chengkai et al. studied the oxidation of phenol to p-benzoquinone using phenol as the raw material, sulfuric acid as the supporting electrolyte and lead electrode as the anode in an H-type electrolytic cell, and the yield of p-benzoquinone was 68%. However, the above-mentioned prior art obtains a benzoquinone solution through the anode reaction, and directly sends it to the cathode chamber for reduction to obtain hydroquinone, which will have the following problems: in the process of electrosynthesizing p-benzoquinone from phenol, the concentration of p-benzoquinone obtained is low, and increasing the concentration of the raw material phenol will reduce the yield of p-benzoquinone. In addition, since the concentration of p-benzoquinone obtained by the anode reaction is low, the concentration of hydroquinone obtained by reduction by this method is low. After separating hydroquinone by extraction, organic matter such as methyl isobutyl ketone will be introduced and accumulated in the electrolyte, and the electrolyte needs to be further treated by methods such as stripping before recycling, which greatly increases the cost.

[0004] Therefore, it is urgent to propose a method for preparing high-concentration hydroquinone by electrolyzing phenol. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing high-concentration hydroquinone by electrolyzing phenol in view of the shortcomings of the prior art. The method of the present invention can effectively increase the concentration of hydroquinone in the electrolyte through a simple electrochemical reaction, and also realizes the direct reuse of the electrolyte and the extractant.

[0006] In order to achieve the above object, the present invention provides a method for preparing high-concentration hydroquinone by electrolyzing phenol, the method comprising the following steps:

[0007] S1: Phenol electrooxidation reaction

[0008] A sulfuric acid solution is added as an electrolyte to the anode chamber and cathode chamber of an H-type electrolytic cell respectively, phenol is added to the anode chamber, and electrolysis is performed by powering on to obtain a sulfuric acid solution containing p-benzoquinone;

[0009] S2: Extraction reaction

[0010] The sulfuric acid solution containing p-benzoquinone is subjected to extraction treatment to obtain a p-benzoquinone organic solution and an anode chamber circulating sulfuric acid solution after liquid separation;

[0011] S3: p-Benzoquinone reduction reaction

[0012] Add sulfuric acid aqueous solution as electrolyte to the anode chamber and cathode chamber of another H-type electrolytic cell respectively, add the p-benzoquinone organic solution to the cathode chamber, apply power for electrolysis, and stand for stratification to obtain a sulfuric acid solution containing hydroquinone and a liquid separation extractant;

[0013] S4: repeat steps S1-S3, and repeatedly add the sulfuric acid solution containing hydroquinone obtained in step S3 as part of the electrolyte to the cathode chamber of step S3, so that the hydroquinone obtained by the reduction of benzoquinone is enriched in the cathode chamber of step S3, thereby increasing the concentration of the hydroquinone product.

[0014] In the present invention, the sulfuric acid solution containing hydroquinone is repeatedly added to the cathode chamber of step S3 as a part of the electrolyte, and the hydroquinone will not be further reduced in the cathode chamber. Therefore, the hydroquinone obtained by the reduction of benzoquinone can be enriched in the cathode chamber of step S3, thereby increasing the concentration of the hydroquinone product.

[0015] According to the present invention, preferably, in step S1:

[0016] The anode plate and cathode plate of the H-type electrolytic cell are independently made of lead plate and / or lead dioxide plate;

[0017] The concentration of the sulfuric acid aqueous solution is 0.2 mol / L to 2 mol / L;

[0018] The temperature of electrolysis is 10℃~50℃;

[0019] The concentration of the phenol in the anode chamber is 0.05 mol / L to 0.2 mol / L.

[0020] According to the present invention, preferably, in step S2:

[0021] The extractant for the extraction treatment is at least one organic solvent selected from the group consisting of benzene, toluene, chlorobenzene, dichloromethane, chloroform, carbon tetrachloride, methyl isobutyl ketone and ethyl acetate;

[0022] The conditions for the extraction treatment include: a temperature of 5°C to 40°C, a volume ratio of the organic phase to the aqueous phase of (0.3 to 0.8): (0.8 to 1.2), and the number of extractions of 1 to 8 times.

[0023] According to the present invention, preferably, the temperature for performing the extraction treatment is 10°C to 30°C.

[0024] According to the present invention, preferably, the method further comprises adding the anode chamber circulating sulfuric acid solution to the anode chamber in step S1 for repeated use as an electrolyte.

[0025] According to the present invention, preferably, in step S3:

[0026] The anode plate and cathode plate of the H-type electrolytic cell are independently made of lead plate and / or lead dioxide plate;

[0027] The concentration of the sulfuric acid aqueous solution is 0.2 mol / L to 5 mol / L;

[0028] In the cathode chamber, the volume ratio of the p-benzoquinone organic solution to the sulfuric acid aqueous solution is 1:(1-10);

[0029] The current density of electrolysis is 10 mA / cm 2 ~50mA / cm 2 ; The temperature of electrolysis is 10℃~80℃; The amount of electrolysis is 2F / mol~8F / mol.

[0030] According to the present invention, preferably, in step S3:

[0031] The concentration of the sulfuric acid aqueous solution is 0.2 mol / L to 2 mol / L;

[0032] In the cathode chamber, the volume ratio of the p-benzoquinone organic solution to the sulfuric acid aqueous solution is 1:(1-5);

[0033] The current density of electrolysis is 10 mA / cm 2 ~30mA / cm 2 ; The electrolysis temperature is 20℃~40℃.

[0034] In the present invention, hydroquinone obtained by electrolytic reduction of p-benzoquinone is mainly dissolved in a sulfuric acid aqueous solution. Therefore, in step S3, standing and stratifying are performed to obtain a sulfuric acid solution containing hydroquinone and a liquid separation extractant.

[0035] According to the present invention, preferably, the method further comprises repeatedly using the liquid separation extractant as the extractant for the extraction treatment in step S2.

[0036] According to the present invention, preferably, the method repeats steps S1-S3 4 to 10 times.

[0037] According to the present invention, preferably, the method further comprises separating the hydroquinone product and the aqueous sulfuric acid solution by cooling crystallization; the concentration of the hydroquinone product obtained by the method is 5 g / L to 60 g / L.

[0038] The beneficial effects of the technical solution of the present invention are as follows:

[0039] 1. The method of the present invention circulates the sulfuric acid solution containing hydroquinone, and the hydroquinone obtained by reducing p-benzoquinone will be enriched in the sulfuric acid solution, thereby obtaining a high-concentration hydroquinone product.

[0040] 2. The concentration of the hydroquinone product obtained by the method of the present invention is much higher than that of the traditional method, and the sulfuric acid electrolyte and hydroquinone can be separated by simple cooling crystallization. After cooling crystallization separation, the sulfuric acid electrolyte can be recycled. The method of the present invention solves the problem in the traditional method that the extractant accumulates excessively in the electrolyte due to the separation of hydroquinone and the electrolyte by extraction, so that the electrolyte cannot be directly reused, and has good application value.

[0041] 3. The method of the present invention can effectively increase the concentration of hydroquinone in the electrolyte through a simple electrochemical reaction. In addition, it also realizes the direct reuse of the electrolyte and the extractant. The method of the present invention is safe and efficient, simple to operate, green and environmentally friendly, and has a great cost advantage.

[0042] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

[0044] Figure 1 The present invention shows a process flow chart of a method for preparing high-concentration hydroquinone by electrolyzing phenol. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0046] Example 1

[0047] This embodiment provides a method for preparing high-concentration hydroquinone by electrolyzing phenol, the method comprising the following steps:

[0048] S1: Phenol electrooxidation reaction

[0049] Weigh 0.37 g of phenol (concentration 0.056 mol / L) and add it to the anode chamber of an H-type electrolytic cell equipped with a stirring device; add 70 mL of 1 mol / L sulfuric acid aqueous solution to the anode chamber and cathode chamber respectively;

[0050] Lead plates are used as anode and cathode, the distance between the cathode and anode plates is 10 cm, and the electrode plate area is 15 cm 2 ;

[0051] Turn on the power of the stirring device and the constant temperature water bath device, set the reaction temperature to 30°C, and set the electrolysis current density to 20mA / cm 2 When the solution temperature in the H-type electrolytic cell reaches the set reaction temperature, electrolysis begins. When the amount of electricity introduced reaches 0.7A·h, the electrolysis reaction ends, and a sulfuric acid solution containing p-benzoquinone is obtained. Samples are taken to measure the p-benzoquinone content.

[0052] S2: Extraction reaction

[0053] Using chlorobenzene as an extractant to extract and separate the sulfuric acid solution containing p-benzoquinone, the volume ratio of the chlorobenzene as the extractant to the sulfuric acid solution containing p-benzoquinone is 0.5, using single-stage extraction, the extraction temperature is 30° C., and separating the liquids to obtain a p-benzoquinone organic solution and an anode chamber circulating sulfuric acid solution;

[0054] The content of p-benzoquinone in the circulating sulfuric acid solution in the anode chamber is detected, and the circulating sulfuric acid solution in the anode chamber is not reused.

[0055] S3: p-Benzoquinone reduction reaction

[0056] The p-benzoquinone organic solution obtained in step S2 is transferred to the cathode chamber of another H-type electrolytic cell, 40 ml of 1 mol / L sulfuric acid aqueous solution is added to the cathode chamber, and 70 ml of 1 mol / L sulfuric acid aqueous solution is added to the anode chamber;

[0057] Lead plates are used as anode and cathode, the distance between the cathode and anode plates is 10 cm, and the electrode plate area is 15 cm 2;

[0058] Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature at 30°C and the current density at 20mA / cm 2 After the solution temperature in the H-type electrolytic cell reaches the set temperature, the power is turned on to perform electrolysis. The electrolysis reaction is terminated when the current is 0.45A·h, and the solution is allowed to stand for stratification to obtain a sulfuric acid solution containing hydroquinone and an extractant chlorobenzene, wherein the extractant chlorobenzene is returned to step S2 for repeated use.

[0059] S4: Repeat steps S1-S3 5 times, and repeatedly add the sulfuric acid solution containing hydroquinone obtained in step S3 as part of the electrolyte to the cathode chamber of step S3, so that the hydroquinone obtained by the reduction of benzoquinone is enriched in the cathode chamber of step S3, thereby increasing the concentration of the hydroquinone product.

[0060] The hydroquinone product and the sulfuric acid aqueous solution are separated by cooling crystallization.

[0061] In this embodiment, the extractant chlorobenzene is reused 5 times, and the extraction efficiency of benzoquinone is 79.81%, 78.24%, 78.1%, 77.87% and 79.97% respectively, and the extraction efficiency remains basically unchanged, indicating that the extractant can be reused; the sulfuric acid solution containing hydroquinone obtained in step S3 is recycled 5 times, and the concentration of hydroquinone in the cathode chamber is increased from 4.68 g / L to 21.24 g / L, indicating that the recycling of the sulfuric acid solution containing hydroquinone obtained in step S3 can enrich hydroquinone in the sulfuric acid aqueous solution in the cathode chamber, thereby obtaining a high-concentration hydroquinone product.

[0062] Examples 2-1 to 2-7 explore the optimal operating parameters for electroreduction of p-benzoquinone organic solution to hydroquinone

[0063] Example 2-1

[0064] 30 ml of chlorobenzene and 0.6 g of p-benzoquinone were added to the cathode chamber of the H-type electrolytic cell. After sufficient stirring, 40 ml of aqueous sulfuric acid solution was added. 70 mL of aqueous sulfuric acid solution was added to the anode chamber. The sulfuric acid concentration was 1 mol / L.

[0065] Lead plates are used for both the anode and cathode, the distance between the anode and cathode plates is 10 cm, and the electrode plate area is 15 cm 2 .

[0066] Turn on the stirring device and the constant temperature water bath device, keep the reaction temperature at 30°C and the current density at 20mA / cm 2After the solution temperature in the H-type electrolytic cell reaches the set temperature, the power supply is turned on to perform electrolysis. When the current is 0.45A·h, the electrolysis reaction is terminated, the solution is allowed to stand for stratification, and the aqueous phase is taken to detect the concentration of hydroquinone. The yield of hydroquinone obtained is 85.54%.

[0067] Example 2-2

[0068] The difference between this embodiment and embodiment 2-1 is that the current density is adjusted to 10 mA / cm 2 , other parameters were the same as those in Example 2-1, and the yield of hydroquinone was 94.6%.

[0069] Example 2-3

[0070] The difference between this embodiment and embodiment 2-1 is that the current is adjusted to 0.55A·h, and the other parameters are the same as those of embodiment 2-1. The yield of hydroquinone obtained is 93.36%.

[0071] Embodiment 2-4

[0072] The difference between this embodiment and embodiment 2-1 is that the amount of current is adjusted to 0.65A·h, and the other parameters are the same as those of embodiment 2-1. The yield of hydroquinone obtained is 93.36%.

[0073] Embodiment 2-5

[0074] The only difference between this embodiment and embodiment 2-1 is that the reaction temperature is adjusted to 40° C., and the other parameters are the same as those of embodiment 2-1. The yield of hydroquinone obtained is 87.69%.

[0075] Embodiment 2-6

[0076] The only difference between this embodiment and embodiment 2-1 is that the reaction temperature is adjusted to 20° C., and the other parameters are the same as those in embodiment 2-1. The yield of hydroquinone obtained is 62.43%.

[0077] Embodiment 2-7

[0078] The only difference between this embodiment and embodiment 2-1 is that the concentration of sulfuric acid in the reaction is adjusted to 1.6 mol / L, and the other parameters are the same as those in embodiment 2-1. The yield of hydroquinone obtained is 91.03%.

[0079] Examples 3-1 to 3-5 explore whether the sulfuric acid solution circulating in the anode chamber of step S2 can be reused

[0080] Example 3-1

[0081] In this example, 1 mL of the sulfuric acid solution containing p-benzoquinone of Example 1 was analyzed, and the results showed that the current efficiency of generating p-benzoquinone was 38.27%, and the yield was 72.64%;

[0082] In this embodiment, step S2 of embodiment 1 is carried out to obtain a circulating sulfuric acid solution in the anode chamber, which is recorded as circulating solution 1.

[0083] Example 3-2

[0084] Weigh 0.37 g of phenol (concentration of 0.056 mol / L) and add it to the anode chamber of an H-type electrolytic cell with a stirring device, add the circulating liquid 1 obtained in Example 3-1 to the anode chamber; and add 70 mL of 1 mol / L sulfuric acid aqueous solution to the cathode chamber.

[0085] Other parameters are the same as those in Example 3-1.

[0086] The results showed that the current efficiency of generating p-benzoquinone was 40.15% and the yield was 76.20%;

[0087] In this embodiment, step S2 of embodiment 1 is carried out to obtain a circulating sulfuric acid solution in the anode chamber, which is recorded as circulating liquid 2.

[0088] Example 3-3

[0089] Weigh 0.37 g of phenol (concentration of 0.056 mol / L) and add it to the anode chamber of an H-type electrolytic cell with a stirring device, add the circulating liquid 2 obtained in Example 3-2 to the anode chamber; and add 70 mL of 1 mol / L sulfuric acid aqueous solution to the cathode chamber.

[0090] Other parameters are the same as those in Example 3-1.

[0091] The results showed that the current efficiency of generating p-benzoquinone was 39.25% and the yield was 74.49%;

[0092] In this embodiment, step S2 of embodiment 1 is carried out to obtain a circulating sulfuric acid solution in the anode chamber, which is recorded as circulating liquid 3.

[0093] Embodiment 3-4

[0094] Weigh 0.37 g of phenol (concentration of 0.056 mol / L) and add it to the anode chamber of an H-type electrolytic cell with a stirring device, add the circulating liquid 3 obtained in Example 3-3 to the anode chamber; and add 70 mL of 1 mol / L sulfuric acid aqueous solution to the cathode chamber.

[0095] Other parameters are the same as those in Example 3-1.

[0096] The results showed that the current efficiency of generating p-benzoquinone was 40.26% and the yield was 76.41%;

[0097] In this embodiment, step S2 of embodiment 1 is carried out to obtain a circulating sulfuric acid solution in the anode chamber, which is recorded as circulating liquid 4.

[0098] Embodiment 3-5

[0099] Weigh 0.37 g of phenol (concentration of 0.056 mol / L) and add it to the anode chamber of an H-type electrolytic cell with a stirring device, add the circulating liquid 4 obtained in Example 3-4 to the anode chamber; and add 70 mL of 1 mol / L sulfuric acid aqueous solution to the cathode chamber.

[0100] Other parameters are the same as those in Example 3-1.

[0101] The results showed that the current efficiency of generating p-benzoquinone was 39.29% and the yield was 74.56%;

[0102] In this embodiment, step S2 of embodiment 1 is carried out to obtain a circulating sulfuric acid solution in the anode chamber, which is recorded as circulating liquid 5.

[0103] It can be concluded from the above Examples 3-1 to 3-5 that after using chlorobenzene as an extractant to extract and separate aqueous sulfuric acid solution and p-benzoquinone, the obtained anode chamber circulating sulfuric acid solution can be repeatedly used as an anode chamber electrolyte, and the yield and current efficiency of preparing p-benzoquinone from phenol remain basically unchanged.

[0104] In order to verify the effectiveness of the extraction scheme of the extractant and the sulfuric acid solution containing p-benzoquinone, the following studies were conducted. Among them, Examples 4-1 to 4-6 simulate the process of separating the sulfuric acid solution containing p-benzoquinone from the extractant. The amount of the extractant and the extraction method will affect the extraction efficiency of p-benzoquinone in the aqueous sulfuric acid solution.

[0105] Example 4-1

[0106] Prepare 20ml of sulfuric acid solution containing p-benzoquinone, wherein the concentration of sulfuric acid is 1mol / L and the concentration of p-benzoquinone is 0.04mol / L; add 10ml of chlorobenzene to the sulfuric acid solution containing p-benzoquinone, stir for 15min at 30℃, and stand for 10min to obtain an extract and a raffinate, wherein the upper aqueous phase is the raffinate (anode chamber circulating sulfuric acid solution), and the lower organic phase is the extract (p-benzoquinone organic solution), wherein the total amount of p-benzoquinone is the sum of the organic phase and the aqueous phase, and p-benzoquinone is mainly distributed in the organic phase. Use the iodine titration method to measure the concentration of p-benzoquinone in the upper aqueous phase.

[0107] Example 4-2

[0108] The only difference between this embodiment and embodiment 4-1 is that the volume of chlorobenzene is adjusted to 20 ml, and the other parameters are the same as those of embodiment 4-1.

[0109] Example 4-3

[0110] The only difference between this embodiment and embodiment 4-1 is that the extraction temperature is adjusted to 10° C., and other parameters are the same as embodiment 4-1.

[0111] Example 4-4

[0112] The only difference between this embodiment and embodiment 4-1 is that the extraction temperature is adjusted to 5° C., and other parameters are the same as embodiment 4-1.

[0113] Embodiment 4-5

[0114] The only difference between this embodiment and embodiment 4-1 is that: 60 ml of sulfuric acid solution containing p-benzoquinone is prepared, wherein the sulfuric acid concentration is 1 mol / L and the p-benzoquinone concentration is 0.04 mol / L, multi-stage extraction is adopted at 30°C, 10 ml of chlorobenzene is added to the sulfuric acid solution containing p-benzoquinone each time, extraction is performed 6 times, the solution is allowed to stand for stratification, and the concentration of p-benzoquinone in the upper aqueous phase is measured by iodine titration.

[0115] Embodiment 4-6

[0116] The difference between this embodiment and embodiment 4-5 is that the number of extractions is adjusted to 3 times, and other parameters are the same as those of embodiment 4-5.

[0117] Table 1

[0118]

[0119] It can be seen from Table 1 that increasing the volume ratio of the extractant to the sulfuric acid solution containing p-benzoquinone (increasing the ratio) can improve the extraction efficiency of p-benzoquinone (extraction efficiency = (concentration of benzoquinone relative to water before extraction - concentration of benzoquinone relative to water after extraction) / concentration of benzoquinone relative to water before extraction). At the same time, lowering the temperature is also beneficial to the separation of p-benzoquinone. When the ratio is 0.5, the extraction efficiency of p-benzoquinone in single-stage extraction is 82.91%, and when the number of extraction stages is 3, the extraction efficiency of p-benzoquinone is increased to 92.54%.

[0120] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing high-concentration hydroquinone by electrolyzing phenol, characterized in that: The method comprises the following steps: S1: Phenol electrooxidation reaction A sulfuric acid solution is added as an electrolyte to the anode chamber and cathode chamber of an H-type electrolytic cell respectively, phenol is added to the anode chamber, and electrolysis is performed by powering on to obtain a sulfuric acid solution containing p-benzoquinone; S2: Extraction reaction The sulfuric acid solution containing p-benzoquinone is subjected to extraction treatment to obtain a p-benzoquinone organic solution and an anode chamber circulating sulfuric acid solution after liquid separation; S3: p-Benzoquinone reduction reaction Add sulfuric acid aqueous solution as electrolyte to the anode chamber and cathode chamber of another H-type electrolytic cell respectively, add the p-benzoquinone organic solution to the cathode chamber, apply power for electrolysis, and stand for stratification to obtain a sulfuric acid solution containing hydroquinone and a liquid separation extractant; S4: repeat steps S1-S3, and repeatedly add the sulfuric acid solution containing hydroquinone obtained in step S3 as part of the electrolyte to the cathode chamber of step S3, so that the hydroquinone obtained by the reduction of benzoquinone is enriched in the cathode chamber of step S3, thereby increasing the concentration of the hydroquinone product.

2. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1, wherein: In step S1: The anode plate and cathode plate of the H-type electrolytic cell are independently made of lead plate and / or lead dioxide plate; The concentration of the sulfuric acid aqueous solution is 0.2 mol / L to 2 mol / L; The temperature of electrolysis is 10℃~50℃; The concentration of the phenol in the anode chamber is 0.05 mol / L to 0.2 mol / L.

3. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1, wherein: In step S2: The extractant for the extraction treatment is at least one of benzene, toluene, chlorobenzene, dichloromethane, chloroform, carbon tetrachloride, methyl isobutyl ketone and ethyl acetate; The conditions for the extraction treatment include: a temperature of 5°C to 40°C, a volume ratio of the organic phase to the aqueous phase of (0.3 to 0.8): (0.8 to 1.2), and the number of extractions of 1 to 8 times.

4. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 3, wherein: The temperature for the extraction treatment is 10°C to 30°C.

5. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1, wherein: The method further comprises adding the anode chamber circulating sulfuric acid solution to the anode chamber in step S1 for repeated use as an electrolyte.

6. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1, wherein: In step S3: The anode plate and cathode plate of the H-type electrolytic cell are independently made of lead plate and / or lead dioxide plate; The concentration of the sulfuric acid aqueous solution is 0.2 mol / L to 5 mol / L; In the cathode chamber, the volume ratio of the p-benzoquinone organic solution to the sulfuric acid aqueous solution is 1:(1-10); The current density of electrolysis is 10 mA / cm 2 ~50mA / cm 2 ; The temperature of electrolysis is 10℃~80℃; The amount of electrolysis is 2F / mol~8F / mol.

7. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 6, wherein: In step S3: The concentration of the sulfuric acid aqueous solution is 0.2 mol / L to 2 mol / L; In the cathode chamber, the volume ratio of the p-benzoquinone organic solution to the sulfuric acid aqueous solution is 1:(1-5); The current density of electrolysis is 10 mA / cm 2 ~30mA / cm 2 ; The electrolysis temperature is 20℃~40℃.

8. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1, wherein: The method further comprises repeatedly using the liquid separation extractant as the extractant for the extraction treatment in step S2.

9. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1, wherein: The method repeats steps S1-S3 4 to 10 times.

10. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1 or 9, wherein: The method further comprises separating the hydroquinone product and the sulfuric acid aqueous solution by cooling crystallization; the concentration of the hydroquinone product obtained by the method is 5g / L to 60g / L.

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