A method for preparing high-concentration hydroquinone by electrolyzing phenol

Abstract

The present invention belongs to the technical field of electrolytic preparation and discloses a method for preparing high-concentration hydroquinone by electrolyzing phenol. The method comprises: adding a sulfuric acid aqueous solution to the anode chamber and cathode chamber of an H-type electrolytic cell, adding phenol to the anode chamber, and applying electricity 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 a sulfuric acid solution circulating in the anode chamber; adding a sulfuric acid aqueous solution to the anode chamber and cathode chamber of another H-type electrolytic cell, adding the p-benzoquinone organic solution to the cathode chamber, and applying electricity for electrolysis to obtain a sulfuric acid solution containing hydroquinone and a liquid separation extractant; repeatedly adding the obtained sulfuric acid solution containing hydroquinone to the cathode chamber, so that the hydroquinone obtained by reducing p-benzoquinone is enriched in the cathode chamber, thereby increasing the concentration of the hydroquinone product. The present invention can effectively increase the concentration of hydroquinone in the electrolyte.

Description

Technical Field

[0001] The present 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 a polymerization inhibitor for polymer monomers such as styrene, butadiene, isoprene, ethyl acetate, acrylonitrile, etc.; (4) as an intermediate for the synthesis of chlorpyrifos, propoxur, berberine, epinephrine, vanillin, piperonal, etc.; (5) used in the manufacture of urease inhibitors. When added before the granulation of ordinary urea, a new type of urea with high utilization rate and long fertilizer effect can be obtained.

[0003] There are numerous methods for synthesizing hydroquinone, including the p-diisopropylbenzene peroxidation method, the bisphenol A method, the aniline oxidation method, the direct oxidation of phenol with hydrogen peroxide, and electrochemical methods. Among these, the electrochemical method has attracted increasing research interest from chemists due to its simple process flow, operation at room temperature and pressure, ease of operation and control, low raw material costs, high product quality, and minimal waste pollution. Existing electrochemical methods for synthesizing hydroquinone involve oxidizing phenol or benzene at the anode to p-benzoquinone, followed by reduction of the synthesized p-benzoquinone at the cathode to yield hydroquinone. For example, Zheng Keli et al. oxidized benzene to p-benzoquinone in an H-type electrolytic cell using tetrabutylammonium bromide as a phase transfer catalyst, sulfuric acid as the supporting electrolyte, and lead-based lead dioxide as the anode. Yu Chengkai et al. oxidized phenol to p-benzoquinone in an H-type electrolytic cell using sulfuric acid as the supporting electrolyte and a lead electrode as the anode, achieving a p-benzoquinone yield of 68%. However, the aforementioned prior art, which involves directly feeding a p-benzoquinone solution obtained through the anodic reaction into the cathode chamber for reduction to produce hydroquinone, presents the following problems: The resulting p-benzoquinone concentration in the electrosynthesis of p-benzoquinone from phenol is relatively low, and increasing the concentration of the raw phenol decreases the yield of p-benzoquinone. Furthermore, due to the low p-benzoquinone concentration obtained through the anodic reaction, the resulting hydroquinone concentration obtained through this reduction method is relatively low. After separating the hydroquinone through extraction, organic matter such as methyl isobutyl ketone (MIBK) can be introduced and accumulated in the electrolyte, necessitating further treatment of the electrolyte through methods such as steam stripping before recycling, significantly increasing costs.

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

[0005] The present invention addresses the shortcomings of existing technologies and proposes a method for preparing high-concentration hydroquinone by electrolyzing phenol. The method effectively increases the concentration of hydroquinone in the electrolyte through a simple electrochemical reaction and also allows for the direct reuse of the electrolyte and 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] Aqueous sulfuric acid solution is added as 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 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] A sulfuric acid aqueous solution is added as an electrolyte to the anode chamber and cathode chamber of another H-type electrolytic cell respectively, and the p-benzoquinone organic solution is added to the cathode chamber, and electrolysis is carried out, and the solution is allowed to stand for separation 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. 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 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, the hydroquinone obtained by electrolytic reduction of p-benzoquinone is mainly dissolved in the aqueous sulfuric acid solution. Therefore, in step S3, the sulfuric acid solution containing hydroquinone and the liquid separation extractant are obtained by standing and separating the layers.

[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 sulfuric acid aqueous 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 recycles 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 hydroquinone product concentration obtained by the present method is much higher than that of traditional methods. The sulfuric acid electrolyte and hydroquinone can be separated by simple cooling crystallization. Furthermore, after separation by cooling crystallization, the sulfuric acid electrolyte can be recycled. This method solves the problem of excessive accumulation of extractant in the electrolyte during the traditional extraction separation of hydroquinone and electrolyte, which prevents direct reuse of the electrolyte, and thus has great 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, 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 provides 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. Instead, 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 20 mA / cm 2 When the solution temperature in the H-type electrolytic cell reaches the set reaction temperature, electrolysis begins. When the amount of electricity flowing reaches 0.7 A·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] The sulfuric acid solution containing p-benzoquinone is extracted and separated using chlorobenzene as an extractant, wherein the volume ratio of the chlorobenzene as the extractant to the sulfuric acid solution containing p-benzoquinone is 0.5, a single-stage extraction is used, the extraction temperature is 30° C., and the p-benzoquinone organic solution and the anode chamber circulating sulfuric acid solution are separated;

[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] Transfer the p-benzoquinone organic solution obtained in step S2 to the cathode chamber of another H-type electrolytic cell, add 40 ml of 1 mol / L sulfuric acid aqueous solution to the cathode chamber, and add 70 ml of 1 mol / L sulfuric acid aqueous solution 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 constant temperature water bath device, keep the reaction temperature at 30℃ and the current density at 20mA / cm 2 After the solution temperature in the H-type electrolytic cell reaches the set temperature, the power supply is turned on to allow electrolysis to proceed. The electrolysis reaction ends when the current reaches 0.45 A·h. The solution is allowed to stand for separation to obtain a sulfuric acid solution containing hydroquinone and chlorobenzene as the extractant. The chlorobenzene as the extractant is returned to step S2 for reuse.

[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 was reused five times, and the extraction efficiency of benzoquinone was 79.81%, 78.24%, 78.1%, 77.87%, and 79.97%, respectively. The extraction efficiency remained basically unchanged, indicating that the extractant can be reused. The sulfuric acid solution containing hydroquinone obtained in step S3 was recycled five times, and the concentration of hydroquinone in the cathode chamber increased from 4.68 g / L to 21.24 g / L, indicating that the recycled 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 electrochemical reduction 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 an H-type electrolytic cell. After thorough 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] Both the anode and cathode are lead plates, 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 constant temperature water bath device, keep the reaction temperature at 30℃ and the current density at 20mA / cm 2After the solution temperature in the H-type electrolytic cell reached the set temperature, the power was turned on to allow electrolysis to proceed. The electrolysis reaction was terminated when the current reached 0.45 A·h. The solution was allowed to stand for separation, and the aqueous phase was sampled to measure the hydroquinone concentration. The yield of hydroquinone was 85.54%.

[0067] Example 2-2

[0068] The only 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 only difference between this embodiment and embodiment 2-1 is that the current was adjusted to 0.55 A·h. Other parameters were the same as those in embodiment 2-1. The yield of hydroquinone obtained was 93.36%.

[0071] Examples 2-4

[0072] The only difference between this embodiment and embodiment 2-1 is that the current was adjusted to 0.65 A·h. Other parameters were the same as those in embodiment 2-1. The yield of hydroquinone obtained was 93.36%.

[0073] Examples 2-5

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

[0075] Examples 2-6

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

[0077] Examples 2-7

[0078] The only difference between this example and Example 2-1 is that the concentration of sulfuric acid in the reaction was adjusted to 1.6 mol / L. Other parameters were the same as Example 2-1. The yield of hydroquinone obtained was 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 from Example 1 was analyzed. 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 liquid 1.

[0083] Example 3-2

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

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

[0086] The results showed that the current efficiency of p-benzoquinone production 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] 0.37 g of phenol (concentration of 0.056 mol / L) was weighed and added to the anode chamber of an H-type electrolytic cell equipped with a stirring device. The circulating liquid 2 obtained in Example 3-2 was added to the anode chamber; 70 mL of a 1 mol / L sulfuric acid aqueous solution was added to the cathode chamber.

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

[0091] The results showed that the current efficiency of p-benzoquinone production 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] Examples 3-4

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

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

[0096] The results showed that the current efficiency of p-benzoquinone production 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] Examples 3-5

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

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

[0101] The results showed that the current efficiency of p-benzoquinone production 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 the extractant to extract and separate the aqueous sulfuric acid solution and p-benzoquinone, the obtained anode chamber circulating sulfuric acid solution can be reused as the anode chamber electrolyte multiple times, and the yield and current efficiency of preparing p-benzoquinone from phenol remain basically unchanged.

[0104] Examples 4-1 through 4-6 were conducted to verify the effectiveness of the extraction scheme using an extractant and a sulfuric acid solution containing p-benzoquinone. Examples 4-1 through 4-6 simulated the separation process between a sulfuric acid solution containing p-benzoquinone and the extractant. The amount of extractant used and the extraction method both affected the extraction efficiency of p-benzoquinone from the aqueous sulfuric acid solution.

[0105] Example 4-1

[0106] Prepare 20ml of a sulfuric acid solution containing p-benzoquinone (1 mol / L sulfuric acid and 0.04 mol / L p-benzoquinone). Add 10ml of chlorobenzene to the solution, stir at 30°C for 15 minutes, and let it stand for 10 minutes to obtain an extract and a raffinate. The upper aqueous phase is the raffinate (sulfuric acid solution recycled from the anode chamber), and the lower organic phase is the extract (organic p-benzoquinone solution). The total amount of p-benzoquinone is the sum of the organic and aqueous phases, with p-benzoquinone primarily distributed in the organic phase. Measure the p-benzoquinone concentration in the upper aqueous phase using iodine titration.

[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 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 those of 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 those of embodiment 4-1.

[0113] Examples 4-5

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

[0115] Examples 4-6

[0116] The only 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] Table 1 shows that increasing the volume ratio of the extractant to the sulfuric acid solution containing p-benzoquinone (increasing the ratio) improves the extraction efficiency of p-benzoquinone (extraction efficiency = (benzoquinone concentration in aqueous solution before extraction - benzoquinone concentration in aqueous solution after extraction) / benzoquinone concentration in aqueous solution before extraction). Lowering the temperature also facilitates the separation of p-benzoquinone. When the ratio is 0.5, the p-benzoquinone extraction efficiency in a single-stage extraction is 82.91%, and with three extraction stages, the p-benzoquinone extraction efficiency increases to 92.54%.

[0120] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations 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 Aqueous sulfuric acid solution is added as 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 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; The volume ratio of the organic phase to the aqueous phase is (0.3-0.8): (0.8-1.2); S3: p-Benzoquinone reduction reaction A sulfuric acid aqueous solution is added as an electrolyte to the anode chamber and cathode chamber of another H-type electrolytic cell respectively, and the p-benzoquinone organic solution is added to the cathode chamber, and electrolysis is carried out, and the solution is allowed to stand for separation to obtain a sulfuric acid solution containing hydroquinone and a liquid separation extractant; 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 ~50 mA / cm 2 The electrolysis temperature is 30°C to 80°C; the electrolysis current is 2 F / mol to 8 F / mol; 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 and a 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 includes 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 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 ~30 mA / cm 2 ; The electrolysis temperature is 30 ℃ ~ 40 ℃.

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

8. 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.

9. The method for preparing high-concentration hydroquinone by electrolyzing phenol according to claim 1 or 8, 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 5 g / L to 60 g / L.

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