Method for co-production of benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid

Abstract

The invention discloses a method for co-producing benzoic acid and chromic hydroxide from methylbenzene and chromium-containing waste liquid. The method comprises the following steps: sequentially adding methylbenzene, a catalyst aqueous solution and an organic solvent into a reaction kettle; adding chromium-containing waste liquid to adjust the pH value of a reaction system in the reaction kettle; setting reaction temperature and reaction pressure, keeping the temperature for a certain time, and reacting; adding alkali liquor into the reaction liquid, adjusting the pH to be alkaline, filtering to obtain chromium hydroxide precipitate, and calcining chromium hydroxide to produce chromium oxide green; and adding an extracting agent into the filtrate, extracting and separating to obtain an organic phase, removing the organic solvent by using a rotary evaporator, and carrying out silica gel column chromatography to obtain benzoic acid. The characteristic that the chromium-containing waste liquid is acidic is utilized, the chromium-containing waste liquid is recycled, and the preparation method can improve the yield of chromium oxide green, reduce the usage amount of sulfuric acid and reduce the discharge of the chromium-containing waste liquid, and has important economic and environment-friendly significance.

Description

Technical Field

[0001] The invention belongs to the technical field of fine organic synthesis, and more specifically, the invention relates to a method for co-producing benzoic acid and chromium hydroxide by using toluene and chromium-containing waste liquid. Background Art

[0002] Benzoic acid is the simplest aromatic acid, also known as benzoic acid. Due to the weak acidity and special chemical structure of benzoic acid, benzoic acid derivatives are widely used as preservatives, antibacterial agents, feed acidifiers and mildew inhibitors, resin plasticizers and flavoring agents. Benzoic acid is an important chemical raw material that can be used to prepare benzoic acid salicylic acid paste, which can be used to analyze elements, determine alkali and iodine quantitative standards and calorific value standards. In addition, benzoic acid and sodium benzoate are often used as preservatives in food. Benzoic acid generates corresponding esters with diethylene glycol and triethylene glycol, respectively, and is widely used in the fields of resins and coatings.

[0003] Benzoic acid is widely used in various industries. With the increase in people's demand for chemical products, the market demand for benzoic acid will inevitably increase. At present, the annual output of benzoic acid in the world is more than two million tons. Benzoic acid is widely used in various industries. With the increase in people's demand for chemical products, the market demand for benzoic acid will inevitably increase. At present, the annual output of benzoic acid in the world is more than two million tons. However, since my country is relatively backward in the production and manufacturing of benzoic acid, it is also of great significance to study advanced production technology for the production of benzoic acid and promote the development of my country's chemical industry.

[0004] Most of the β-methyl menaphoquinone synthesis processes in China use the chromic acid oxidation method, which has the disadvantage of producing a large amount of chromium-containing waste liquid, and the concentration and pH of the waste liquid are both low, and direct discharge has a great impact on the environment. Therefore, the co-production of chromium oxide green and benzoic acid using β-methyl menaphoquinone chromium-containing waste liquid and toluene has important economic and environmental significance. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages according to the present invention, a method for co-producing benzoic acid and chromium hydroxide with toluene and chromium-containing waste liquid is provided, comprising the following steps:

[0007] Step 1, adding toluene, catalyst aqueous solution and organic solvent into the reaction kettle in sequence;

[0008] Step 2: adding chromium-containing waste liquid to adjust the pH of the reaction system in the reactor;

[0009] Step 3, setting the reaction temperature and reaction pressure, keeping the temperature for a certain time, and reacting;

[0010] Step 4: add alkali solution to the reaction solution, adjust the pH to weak acidity, filter to obtain chromium hydroxide precipitate, and calcine the chromium hydroxide to produce chromium oxide green; then add an extractant to the filtrate, let it stand for stratification, take the upper organic phase, remove the organic solvent with a rotary evaporator, and obtain benzoic acid through silica gel column chromatography.

[0011] Preferably, in the step 1, the organic solvent is acetonitrile.

[0012] Preferably, in the step 1, the volume ratio of the organic solvent to toluene is 0.5 to 1:1.

[0013] Preferably, in the step 1, the molar ratio of the toluene to the catalyst in the catalyst aqueous solution is 1:1 to 1.3:1.

[0014] Preferably, in the step 1, the catalyst aqueous solution is a sodium chromite aqueous solution, a potassium chromite aqueous solution or a chromic anhydride solution.

[0015] Preferably, in step 1, the main content of sodium chromite, potassium chromite or chromic anhydride in the catalyst aqueous solution is 20-40%.

[0016] Preferably, in the step 2, chromium-containing waste liquid is added to adjust the pH of the reaction system in the reactor to between 2.0 and 4.0.

[0017] Preferably, in the step three, the reaction temperature is set at 190-280° C., the reaction pressure is set at 1.00-4.20 MPa, and the insulation time is set at 2-8 h.

[0018] Preferably, in step 4, the alkali solution added is sodium hydroxide or potassium hydroxide, and the pH is adjusted to 6-7.

[0019] Preferably, in step 4, the added extractant is a saturated sodium thiosulfate solution, and the volume of the saturated sodium thiosulfate solution is 0.5 to 1.5 times the volume of the filtrate.

[0020] The specific method of calcining chromium hydroxide to produce chromium oxide green in step 4 and refining the chromium oxide green to obtain ultrafine chromium oxide includes:

[0021] S1. Dry-milling the obtained chromium hydroxide using stainless steel grinding balls, the mass of which is 2 to 3 times the mass of the chromium hydroxide, the ball milling speed is 30 to 50 rpm, the ball milling time is 3 to 10 hours, and the ball milling is followed by sieving with a sieving mesh size of 40 to 80 to obtain chromium hydroxide powder;

[0022] S2, calcining the chromium hydroxide powder obtained by screening, the calcination temperature is 500-900° C., the calcination time is 4-12 hours, and the temperature is lowered along with the furnace to separate and obtain chromium oxide powder;

[0023] S3, wet-milling the chromium oxide powder, using anhydrous ethanol as the ball milling medium, stainless steel grinding balls for ball milling, using modified polyacrylamide as the dispersant, the ball milling time is 3 to 6 hours, and the ball milling speed is 30 to 50 rpm; after ball milling, the chromium oxide powder is filtered out and the modified polyacrylamide is washed with water to remove the modified polyacrylamide, and then dried to obtain the chromium oxide powder; wherein the amount ratio of chromium oxide powder, anhydrous ethanol, stainless steel grinding balls, and modified polyacrylamide is 100 to 110 kg: 150 to 200 L: 180 to 300 kg: 1 to 5 kg;

[0024] S4. Slurry-disperse the wet-milled and dried chromium oxide powder, disperse the chromium oxide powder in deionized water, add polyacrylic acid as a dispersant, and ultrasonically disperse for 1 to 3 hours at an ultrasonic frequency of 50 to 80 kHz; add a surfactant, cetyltrimethylammonium bromide, stir evenly and heat to 50 to 90°C, keep warm for 1 to 6 hours, cool to room temperature, filter, wash, and dry to obtain ultrafine chromium oxide powder; wherein the amount ratio of chromium oxide powder, deionized water, polyacrylic acid, and cetyltrimethylammonium bromide is 1 to 5 g: 100 to 300 mL: 0.1 to 0.5 g: 0.2 to 0.4 g.

[0025] Among them, the modification method of the modified polyacrylamide used in S3 is:

[0026] Polyacrylamide and urea are dissolved in deionized water to obtain a mixed solution, the mixed solution is heated to 40-80°C, and then polyethylene glycol-1000 is added and stirred to obtain a blended solution, the blended solution is dried at 50-70°C for 12 hours to obtain a blend, and the blend is vacuum dried at a vacuum degree of 2.5×10 -3 Pa or less, and the drying time is 24 to 72 hours to obtain modified polyacrylamide; wherein the dosage ratio of polyacrylamide, urea, deionized water and polyethylene glycol-1000 is 2 to 5 g: 1 g: 150 to 200 mL: 0.5 to 1 g.

[0027] The present invention includes at least the following beneficial effects: the present invention utilizes the acidic characteristic of chromium-containing waste liquid to recycle and utilize the chromium-containing waste liquid. The preparation method can increase the yield of chromium oxide green, reduce the usage of sulfuric acid, and reduce the discharge of chromium-containing waste liquid, which has important economic and environmental significance.

[0028] At the same time, the present invention prepares chromium oxide green (chromium oxide) by calcining the separated chromium hydroxide through dry ball milling, and then uses modified polyacrylamide as a dispersant to perform wet ball milling, followed by slurry dispersion, to prepare ultrafine chromium oxide powder with smaller particle size and more concentrated particle size distribution range.

[0029] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0030] The present invention is described in further detail below so that those skilled in the art can implement it according to the description.

[0031] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0032] Example 1

[0033] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0034] Weigh 50.66g toluene and 673g sodium chromium sulfate aqueous solution (20% sodium chromium sulfate), add 53mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust the pH to 3. After reacting for 5h at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, extract and separate to obtain an organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 28.19g benzoic acid by silica gel column chromatography, with a mass yield of 41.98%.

[0035] Example 2

[0036] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0037] Weigh 50.66g toluene and 673g sodium chromium sulfate aqueous solution (20% sodium chromium sulfate), add 53mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust pH to 3. After reacting for 5h at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and calcine to produce chromium oxide green, add a saturated sodium thiosulfate solution with the same volume as the filtrate, stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 50.81g benzoic acid by silica gel column chromatography, with a mass yield of 75.66%.

[0038] Example 3

[0039] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0040] Weigh 50.66g toluene and 455g sodium chromium sulfate aqueous solution (30% sodium chromium sulfate), add 53mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust the pH to 3. After reacting for 5h at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, extract and separate to obtain an organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 51.97g benzoic acid by silica gel column chromatography, with a mass yield of 77.39%.

[0041] Example 4

[0042] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0043] Weigh 50.66g toluene and 345.5g sodium chromium sulfate aqueous solution (40% sodium chromium sulfate), add 53mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust the pH to 3. After reacting for 5h at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 47.89g benzoic acid by silica gel column chromatography, with a mass yield of 71.32%.

[0044] Example 5

[0045] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0046] Weigh 50.66g toluene and 490.17g potassium chromium sulfate aqueous solution (30% potassium chromium sulfate), add 53mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust the pH to 3. After reacting for 5h at a reaction temperature of 270°C and a reaction pressure of 3MPa, add potassium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 40.02g benzoic acid by silica gel column chromatography, with a mass yield of 59.59%.

[0047] Example 6

[0048] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0049] Weigh 50.66g toluene and 283.3g chromic anhydride aqueous solution (30% chromic anhydride), add 53mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust the pH to 3. After reacting for 5h at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 46.04g benzoic acid through silica gel column chromatography, with a mass yield of 68.55%.

[0050] Example 7

[0051] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0052] Weigh 50.66g toluene and 490.17g sodium chromium sulfate aqueous solution, add 53mL acetonitrile and place in a reactor, and use chromium sulfate waste liquid to adjust the pH to 2. After reacting for 5 hours at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 56.16g benzoic acid by silica gel column chromatography, with a mass yield of 83.63%.

[0053] Example 8

[0054] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0055] Weigh 50.66g toluene and 490.17 sodium chromium sulfate aqueous solution, add 50mL acetonitrile and place in a reactor, use chromium sulfate waste liquid to adjust the pH to 2.5. After reacting for 5 hours at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, let stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 55.58g of benzoic acid by silica gel column chromatography, with a mass yield of 82.77%.

[0056] Example 9

[0057] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0058] Weigh 55.26g toluene and 490.17g sodium chromium sulfate aqueous solution, add 53mL acetonitrile and place in a reactor, and use chromium sulfate waste liquid to adjust the pH to 2. After reacting for 5 hours at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, stand and separate, take the upper organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 56.85g benzoic acid by silica gel column chromatography, with a mass yield of 77.60%.

[0059] Example 10

[0060] This embodiment provides a method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, comprising:

[0061] Weigh 59.87g toluene and 490.17g sodium chromium sulfate aqueous solution, add 53mL acetonitrile and place in a reactor, and use chromium sulfate waste liquid to adjust the pH to 2. After reacting for 5 hours at a reaction temperature of 270°C and a reaction pressure of 3MPa, add sodium hydroxide to the reaction solution to adjust the pH to 6.5, filter to obtain chromium hydroxide solid, wash and dry several times, and then calcine to produce chromium oxide green; add a saturated sodium thiosulfate solution with the same volume as the filtrate, extract and separate to obtain an organic phase, remove the organic solvent acetonitrile with a rotary evaporator, and obtain 56.37g benzoic acid by silica gel column chromatography, with a mass yield of 71.02%.

[0062] Embodiment 11

[0063] For the chromium hydroxide solid obtained in Example 1, this example calcines the chromium hydroxide solid to generate chromium oxide green, and refines the chromium oxide green, specifically including:

[0064] S1. Dry-milling the obtained chromium hydroxide using stainless steel grinding balls, the mass of which is twice that of the chromium hydroxide, the ball milling speed is 30 rpm, the ball milling time is 6 h, and the sieving is performed after ball milling, the sieving mesh number is 40 mesh, and chromium hydroxide powder with a particle size distribution of less than 40 mesh is obtained;

[0065] S2, calcining the chromium hydroxide powder obtained by screening, the calcination temperature is 800° C., the calcination time is 6 hours, and the temperature is lowered along with the furnace to separate and obtain chromium oxide powder;

[0066] S3, 100 kg of chromium oxide powder was wet-milled, using 150 L of anhydrous ethanol as the ball milling medium, 200 kg of stainless steel grinding balls for ball milling, 2 kg of modified polyacrylamide was selected as the dispersant, the ball milling time was 4 h, and the ball milling speed was 50 rpm; after ball milling, the chromium oxide powder was filtered out and the modified polyacrylamide was washed with water, and the chromium oxide powder was dried to obtain the chromium oxide powder; the modification method of the modified polyacrylamide is:

[0067] 5 g of polyacrylamide and 1 g of urea were dissolved in 150 mL of deionized water to obtain a mixed solution. The mixed solution was heated to 40 °C, and then 1 g of polyethylene glycol-1000 was added and stirred to obtain a blended solution. The blended solution was dried at 70 °C for 12 h to obtain a blend. The blend was vacuum dried with a vacuum degree of 2.5 × 10 -3 Pa or less, the drying time is 36h, and the modified polyacrylamide is obtained;

[0068] S4. Disperse 50 g of chromium oxide powder in 1500 mL of deionized water, add 1 g of polyacrylic acid as a dispersant, and ultrasonically disperse for 3 hours at an ultrasonic frequency of 50 kHz; add 2 g of hexadecyltrimethylammonium bromide, stir evenly and heat to 70°C, keep warm for 3 hours, cool to room temperature, filter, wash, and dry to obtain ultrafine chromium oxide powder.

[0069] Example 12

[0070] For the chromium hydroxide solid obtained in Example 1, this example calcines the chromium hydroxide solid to generate chromium oxide green, and refines the chromium oxide green, specifically including:

[0071] S1, dry ball milling the obtained chromium hydroxide, using stainless steel grinding balls, the mass of the stainless steel grinding balls is 3 times the mass of the chromium hydroxide, the ball milling speed is 50 rpm, the ball milling time is 5 hours, and the ball milling is followed by sieving, the sieving mesh number is 40 mesh, and chromium hydroxide powder with a particle size distribution of less than 40 mesh is obtained;

[0072] S2, calcining the chromium hydroxide powder obtained by screening, the calcination temperature is 800° C., the calcination time is 5 hours, and the temperature is lowered along with the furnace to separate and obtain chromium oxide powder;

[0073] S3, 100 kg of chromium oxide powder was wet-milled, using 200 L of anhydrous ethanol as the ball milling medium, 250 kg of stainless steel grinding balls for ball milling, 2.5 kg of modified polyacrylamide was selected as the dispersant, the ball milling time was 6 h, and the ball milling speed was 50 rpm; after ball milling, the chromium oxide powder was filtered out and the modified polyacrylamide was washed with water, and the chromium oxide powder was dried to obtain the chromium oxide powder; the modification method of the modified polyacrylamide was as follows:

[0074] 5 g of polyacrylamide and 1 g of urea were dissolved in 150 mL of deionized water to obtain a mixed solution. The mixed solution was heated to 40 °C, and then 1 g of polyethylene glycol-1000 was added and stirred to obtain a blended solution. The blended solution was dried at 70 °C for 12 h to obtain a blend. The blend was vacuum dried with a vacuum degree of 2.5 × 10 -3 Pa or less, the drying time is 36h, and the modified polyacrylamide is obtained;

[0075] S4. Disperse 50 g of chromium oxide powder in 2000 mL of deionized water, add 3 g of polyacrylic acid as a dispersant, and perform ultrasonic dispersion for 3 h at an ultrasonic frequency of 50 kHz; add 0.4 g of surfactant hexadecyltrimethylammonium bromide, stir evenly and heat to 80°C, keep warm for 2 h, cool to room temperature, filter, wash, and dry to obtain ultrafine chromium oxide powder.

[0076] Comparative Example 1

[0077] In this comparative example, the chromium hydroxide solid obtained in Example 1 is calcined to prepare chromium oxide green, and the chromium oxide green is refined. The difference from Example 11 is that in S3, an equal mass of polyacrylamide is used to replace the modified polyacrylamide, and the process parameters of the remaining steps of this comparative example are the same as those of Example 11.

[0078] Comparative Example 2

[0079] In this comparative example, the chromium hydroxide solid obtained in Example 1 is calcined to prepare chromium oxide green, and the chromium oxide green is refined. The difference from Example 11 is that the dispersant polyacrylic acid and the surfactant hexadecyltrimethylammonium bromide are not used in S4 of this comparative example, and the process parameters of the remaining steps of this comparative example are the same as those of Example 11.

[0080] The particle size distribution of the ultrafine chromium oxide powders of Example 11, Example 12, Comparative Example 1, and Comparative Example 2, as well as the particle size distribution of the chromium oxide of Example 11 before and after wet ball milling, were measured respectively, and the following table was obtained:

[0081] D10(μm) D90(μm) Before wet ball milling 105.2 247.4 After wet ball milling 52.0 89.5 Embodiment 11 12.3 37.2 Example 12 18.7 45.4 Comparative Example 1 38.6 156.0 Comparative Example 2 29.4 108.2

[0082] It can be seen from the above table that the particle size distribution of the chromium oxide powder after the refinement treatment of Example 11 and Example 12 is more concentrated, and the particle size is significantly reduced, while the particle size of Comparative Example 1 and Comparative Example 2 has a certain reduction, but the reduction degree is less than that of Example 11, and the particle size distribution concentration is also not as good as the ultrafine chromium oxide powder of Example 11. It shows that the ultrafine chromium oxide powder obtained by wet ball milling with modified polyacrylamide after calcination and then slurry dispersion with a dispersant and a surfactant has a smaller particle size and particle size distribution range.

[0083] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0084] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. A method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid, characterized in that: The following steps are involved: Step 1, adding toluene, catalyst aqueous solution and organic solvent into the reaction kettle in sequence; Step 2: adding chromium-containing waste liquid to adjust the pH of the reaction system in the reactor; Step 3, setting the reaction temperature and reaction pressure, keeping the temperature for a certain time, and reacting; Step 4: add alkali solution to the reaction solution, adjust the pH to weak acidity, filter to obtain chromium hydroxide precipitate, and calcine the chromium hydroxide to produce chromium oxide green; then add an extractant to the filtrate, let it stand for stratification, take the upper organic phase, remove the organic solvent with a rotary evaporator, and obtain benzoic acid through silica gel column chromatography.

2. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 1, the organic solvent is acetonitrile.

3. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 1, the volume ratio of the organic solvent to toluene is 0.5 to 1:

1.

4. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 1, the molar ratio of the toluene to the catalyst in the catalyst aqueous solution is 1:1 to 1.3:

1.

5. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 1, the catalyst aqueous solution is a sodium chromite aqueous solution, a potassium chromite aqueous solution or a chromic anhydride solution.

6. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 5, characterized in that: In the step 1, the main content of sodium chromite, potassium chromite or chromic anhydride in the catalyst aqueous solution is 20-40%.

7. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 2, chromium-containing waste liquid is added to adjust the pH of the reaction system in the reactor to between 2.0 and 4.

0.

8. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step three, the reaction temperature is set at 190-280° C., the reaction pressure is set at 1.00-4.20 MPa, and the insulation time is set at 2-8 h.

9. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 4, the alkali solution added is sodium hydroxide or potassium hydroxide, and the pH is adjusted to 6-7.

10. The method for co-producing benzoic acid and chromium hydroxide from toluene and chromium-containing waste liquid as claimed in claim 1, characterized in that: In the step 4, the added extractant is a saturated sodium thiosulfate solution, and the volume of the saturated sodium thiosulfate solution is 0.5 to 1.5 times the volume of the filtrate.