Treatment method of alkali wastewater generated in production of methyl benzoylformate
By combining flocculant/acid system purification with distillation and waste salt crystallization, the problems of high COD and low methanol recovery rate in alkaline wastewater from methyl benzoate production were solved. This approach achieved efficient removal of organic matter and resource utilization of inorganic salts, reduced treatment costs, and complied with green chemistry principles.
Patent Information
- Application Number
- CN202511295641.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-11
- Publication Date
- 2026-01-02
AI Technical Summary
Existing technologies for treating alkaline wastewater generated during the production of methyl benzoate suffer from problems such as high COD values, low methanol recovery rates, high levels of organic residues, and difficulty in treating solid waste. Furthermore, traditional methods are costly, prone to secondary pollution, and difficult to achieve resource utilization.
A method of purification using a flocculant/acid system, temperature-controlled distillation, and waste salt crystallization is adopted. Organic matter is separated through flocculation and precipitation, and combined with distillation and waste salt crystallization, methanol is recovered and inorganic salts are utilized as resources, thereby reducing processing costs.
It achieves efficient removal of organic matter from alkaline wastewater, recovery and utilization of methanol, and conversion of inorganic salts into high-purity crystalline sodium sulfate, reducing treatment costs, meeting green chemistry requirements, and improving production efficiency and resource utilization.
Smart Images
Figure CN121248036A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of alkaline wastewater treatment for photoinitiators, and more specifically, to a method for treating alkaline wastewater from the production of methyl benzoate photoinitiators. Background Technology
[0002] In the production of methyl benzoate, alkaline wastewater is mainly generated from the esterification reaction, washing, and distillation stages. This wastewater typically contains inorganic substances such as suspended solids, large particulate matter, sodium bicarbonate, and sulfates, as well as organic pollutants such as methanol, methyl benzoate salts, benzoylformates, styrene, and acrylonitrile. Its COD value is usually high, and its pH is alkaline, requiring specific treatment processes.
[0003] Traditional treatment methods mainly include acid-base neutralization, coagulation and sedimentation, and biological treatment. Traditional methods often rely on purchased reagents (such as sodium hydroxide and sulfuric acid) for neutralization, increasing operating costs. For example, while acid-base neutralization can quickly adjust the pH value, it requires large amounts of reagents (such as sulfuric acid or hydrochloric acid) and is prone to secondary pollution; coagulation and sedimentation can remove suspended solids, but its effectiveness in removing dissolved organic matter (such as benzoyl carboxylates) is limited; and biological treatment methods have low degradation efficiency for highly toxic organic matter (such as acrylonitrile) and require long retention times.
[0004] In addition, the recovery and utilization of methanol in the production of methyl benzoate (such as methanol recovery through distillation) is often difficult to achieve in traditional processes due to high energy consumption or complex equipment; if inorganic salts such as sodium carbonate and sulfate contained in wastewater are directly discharged, it may cause soil salinization and groundwater pollution.
[0005] Therefore, there is an urgent need to provide a simple, low-cost method for treating alkaline wastewater from methyl benzoate production that conforms to green chemistry principles. Summary of the Invention
[0006] To address the problems existing in the prior art, the present invention aims to provide a method for treating alkaline wastewater from the production of methyl benzoate. This method solves the problems of low methanol recovery rate, high organic residue, and difficult solid waste treatment in alkaline wastewater through a closed-loop technology of flocculant / acid system purification, temperature-controlled distillation, and waste salt crystallization. It combines high efficiency, economy, and environmental protection, and provides an innovative solution for the resource utilization of chemical wastewater.
[0007] To solve the above problems, the present invention adopts the following technical solution.
[0008] A method for treating alkaline wastewater from methyl benzoate production includes the following steps: S1: After the alkaline wastewater from the production of methyl benzoate is allowed to stand and filtered, flocculant and acid are added simultaneously to adjust the pH value to 6-7. After stirring and settling, the purified mother liquor is obtained by filtration. S2: The refined mother liquor is heated for distillation, and the fraction collected at low temperature and the residue are collected; the fraction collected at low temperature is condensed and then heated to purify methanol, which is reused in the production of methyl benzoate; the residue is heated and distilled multiple times, and the fraction and bottom liquid are collected. The fraction is condensed to obtain distilled water; the bottom liquid is cooled and kept warm until it no longer clumps and there is suspension in the bottom liquid; the distilled water is reused in the production of methyl benzoate. S3: The distillation bottom liquid obtained in step S2 is filtered to obtain the still liquid and inorganic salt crystals. The collected inorganic salt crystals are sodium sulfate solid.
[0009] Furthermore, in step S1, the flocculant is one or a mixture of two or more of polyacrylamide, ferrous sulfate, and aluminum trichloride.
[0010] Furthermore, in step S1, the flocculant is aluminum trichloride.
[0011] Furthermore, in step S1, the molar ratio of flocculant to acid is in the range of 1:0.3-5; preferably 1:0.3-2.
[0012] Furthermore, in step S1, the acid is sulfuric acid or hydrochloric acid, and the mass percentage concentration of the acid is 15-30%.
[0013] Furthermore, in step S1, the acid is sulfuric acid, and the mass percentage concentration of sulfuric acid is preferably 15-25%.
[0014] Furthermore, in step S2, the temperature for distilling the refined mother liquor is 70-90℃; the condensation temperature for obtaining methanol from the distillate is 50-60℃, and the temperature is then raised to 70-80℃ after condensation.
[0015] Furthermore, in step S2, the temperature of the residual liquid is heated to 100-150℃; the distillation is carried out 3-4 times, preferably 4 times; the distillation time for each distillation is 0.5-1h, preferably 0.75-1h.
[0016] Furthermore, in step S2, the temperature of the distillation bottom liquid is reduced to 50-70°C, preferably 50-60°C.
[0017] Furthermore, the alkaline wastewater produced by methyl benzoate production has a COD value of 120,000-132,554 mg / L and a pH of 8-14, with a preferred pH of 8-10.
[0018] Compared with the prior art, the advantages of this invention are: I. This solution solves the problem of excessively high COD value in alkaline wastewater through simple distillation, while also recovering and reusing a small amount of methanol in the water (methanol is required for esterification reaction).
[0019] Second, in the treatment of alkaline wastewater in this scheme, useless solid waste salts can be disposed of through micro-acidification. At the same time, the acid used for micro-acidification is the acid solution of the reaction, and this method can also make reasonable use of the acid solution.
[0020] Third, this scheme utilizes a simple acid-base neutralization method to enable the rational transformation of organic matter in the inorganic and organic phases, thereby greatly reducing the cost of treating waste.
[0021] IV. This solution converts solid waste salt into inorganic crystals (sodium sulfate), achieving not only the resource recovery and reuse of the waste salt, allowing it to return to the production process, but also expanding the enterprise's economic development path as a high-value-added byproduct. Furthermore, this process eliminates the need for difficult-to-remove ions when treating alkaline wastewater, making the entire treatment process simple, environmentally friendly, and energy-efficient. This method fully aligns with the development concepts and requirements of green chemistry.
[0022] Fifth, this solution solves the problem of alkaline wastewater treatment, enabling the obtained distilled water to be reused in the production process of methyl benzoate, and the resulting methyl benzoate has high purity and yield.
[0023] VI. This scheme utilizes a flocculant / acid system and precise temperature control for esterification, and employs multi-stage distillation to efficiently recover methanol and distilled water. Residual solids in the wastewater are converted into high-purity inorganic crystalline sodium sulfate, achieving resource utilization. Furthermore, this method significantly reduces production costs and environmental pollution through residual liquid recycling and waste salt conversion. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the alkaline wastewater treatment process in Example 1. Detailed Implementation
[0025] Example 1:
[0026] The alkaline wastewater generated by a chemical company during the production of methyl benzoate contains suspended solids and large particulate matter, as well as inorganic substances such as sodium bicarbonate and sulfates, and organic substances such as methanol, methyl benzoate salt, benzoylformate, styrene, and acrylonitrile. The wastewater's COD was measured to be 127,354 mg / L; pH = 12.
[0027] Processing steps (specific processing flow as follows) Figure 1 (as shown) Step 1, Methanol Separation: The alkaline wastewater (2L) was allowed to stand for 15 minutes, filtered to obtain filter residue and mother liquor. Then, 10g of aluminum trichloride was added to the mother liquor, along with 0.01L of 15% sulfuric acid, stirred continuously. The pH was adjusted to 6-7 (the pH measurement method is a conventional sampling method, therefore not described in detail). Flocculation and sedimentation were performed, and after 20 minutes, filtration was conducted to obtain 2.01L of refined mother liquor (containing inorganic phase and a small amount of product and raw material miscibility, the same below). Aluminum ions existed in the filtered solid as colloidal Al(OH)3. The refined mother liquor was then heated to 70-90℃ for distillation, yielding crude methanol (containing some water) and residual methanol-removed mother liquor (mostly water and organic matter). The crude methanol was condensed at 50℃, then heated to 70℃ for purification to obtain refined methanol with a purity of 99.98% and a recovery rate of 89.56%.
[0028] Step 2: Heat the methanol-removed mother liquor obtained in Step 1 to 145°C and perform 4 distillations, each lasting 1 hour. The collected fraction is the distilled water, and the residue at the bottom of the column is the distilled bottom liquid. Step 3: The distillation bottom liquid obtained in Step 2 is heated to 147℃ and distilled again for 1 hour to obtain a small amount of distilled water. Then, the remaining distillation bottom liquid is cooled to 70℃ and kept at this temperature until the bottom liquid no longer clumps and some of it is suspended. The bottom liquid is then filtered to obtain the bottom liquid and residual solids. Liquid phase analysis of the bottom liquid shows that it contains methyl benzoate and benzoate esters. The residual solids are then separated by filtration to obtain crystalline sodium sulfate with a purity of 95.24% and a yield of 98.41%.
[0029] Step four: The distilled water obtained in steps two and three can be combined and reused in the production of methyl benzoate.
[0030] The distilled water obtained in step four was subjected to rational analysis, and the COD of the wastewater was determined to be 215 mg / L; pH=7.
[0031] Example 2:
[0032] The alkaline wastewater generated during the production of methyl benzoate by a chemical company contains suspended solids and large particulate matter, as well as inorganic substances such as sodium bicarbonate and sulfates, and organic substances such as methanol, methyl benzoate salt, benzoylformate, styrene, and acrylonitrile. The wastewater's COD was measured to be 132,554 mg / L; pH = 12.
[0033] Processing steps: Step 1, Methanol Separation: Alkaline wastewater (2L) was allowed to stand for 15 minutes, filtered to obtain filter residue and mother liquor. Then, 10g of ferrous sulfate was added to the mother liquor, along with 0.01L of 30% hydrochloric acid, stirred continuously. The pH was adjusted to 6-7 (pH measurement was performed using a conventional sampling method, therefore not described in detail). Flocculation and precipitation were carried out, and after 20 minutes, 2.01L of purified mother liquor was obtained by vacuum filtration. Ferrous ions existed as hydroxides in the filtered solid. The purified mother liquor was then heated to 70-90℃ for distillation, yielding crude methanol (containing some water) and a residual methanol-removing mother liquor (mostly water and organic matter). The crude methanol was condensed at 66℃, then heated to 70℃ for purification to obtain purified methanol with a purity of 99.97% and a recovery rate of 87.57%.
[0034] Step 2: Heat the methanol-removed mother liquor obtained in Step 1 to 150°C and perform 4 distillations, each lasting 1 hour. The collected fraction is the distilled water, and the residue at the bottom of the column is the distilled bottom liquid. Step 3: The distillation bottom liquid obtained in Step 2 is heated to 150℃ and distilled again for 2 hours to obtain a small amount of distilled water. Then, the remaining distillation bottom liquid is cooled to 70℃ and kept at this temperature until the bottom liquid no longer clumps and some of it is suspended. The bottom liquid is then filtered to obtain the bottom liquid and residual solids. Liquid phase analysis of the bottom liquid reveals that it contains methyl benzoate and benzoate esters. The residual solids are then separated by filtration to obtain crystalline sodium sulfate with a purity of 96.20% and a yield of 97.55%.
[0035] Step four: Combine the distilled water obtained in steps two and three and reuse it in the production of methyl benzoate.
[0036] The distilled water obtained in step four was subjected to rational analysis, and the COD of the wastewater was determined to be 305 mg / L; pH=7.
[0037] Example 3:
[0038] The alkaline wastewater generated during the production of methyl benzoate by a chemical company contains suspended solids and large particulate matter, as well as inorganic substances such as sodium bicarbonate and sulfates, and organic substances such as methanol, methyl benzoate salt, benzoylformate, styrene, and acrylonitrile. The wastewater's COD was measured to be 120086 mg / L; pH = 12.
[0039] Processing steps: Step 1, Methanol Separation: Alkaline wastewater (2L) was allowed to stand for 15 minutes, filtered to obtain filter residue and mother liquor. Then, 10g of polyacrylamide was added to the mother liquor, along with 0.015L of 20% sulfuric acid, stirred continuously. The pH was adjusted to 6-7 (pH measurement was performed using conventional sampling methods, therefore not described in detail). Flocculation and sedimentation were carried out, and after 20 minutes, the mixture was filtered to obtain 2L of purified mother liquor. The purified mother liquor was then heated to 70-90℃ for distillation, yielding crude methanol (containing some water) and a residual methanol-removing mother liquor (mostly water and organic matter). The crude methanol was condensed at 55℃, then heated to 70℃ for purification to obtain purified methanol with a purity of 99.94% and a recovery rate of 87.56%.
[0040] Step 2: Heat the methanol mother liquor obtained in Step 1 to 147°C and perform 4 distillations, each lasting 1 hour. The collected fraction is the distilled water, and the residue at the bottom of the column is the distilled bottom liquid. Step 3: Heat the distillation bottom liquid obtained in Step 2 to 150℃ and distill again for 1 hour to obtain a small amount of distilled water. Then, cool the remaining distillation bottom liquid to 70℃ and keep it at this temperature until the bottom liquid no longer clumps and some of it is suspended. Filter the bottom liquid to obtain the bottom liquid and residual solids. Perform liquid phase analysis on the bottom liquid, and the results show that it contains methyl benzoate and benzoate. Separate the residual solids to obtain crystalline sodium sulfate with a purity of 95.87% and a yield of 88.24%.
[0041] Step four: Combine the distilled water obtained in steps two and three and reuse it in the production of methyl benzoate.
[0042] The distilled water obtained in step four was subjected to rational analysis, and the COD of the wastewater was determined to be 257 mg / L; pH=7.
[0043] Application Example 1: The recovered methanol and benzoylformic acid from Example 1 were added to a reaction vessel, and sulfuric acid was slowly added with stirring. After heating under reflux for 12 hours, excess methanol was recovered. The esterified product was then neutralized multiple times with a dilute sodium carbonate solution (which can be prepared using recycled distilled water). The oil layer was separated, dried with anhydrous sodium sulfate prepared in Example 1, and then distilled. First, low-boiling fractions were distilled off under reduced pressure, and then the fraction at 137-146℃ (2.4 kPa) was collected as methyl benzoylformate. The yield of methyl benzoylformate was 80.26%, and the purity was 99.87%.
[0044] Application Example 2: This application example differs from Application Example 1 in that it uses methanol recovered from Example 2, distilled water, and crystalline sodium sulfate to prepare methyl benzoate. The yield of the obtained methyl benzoate was 78.59%, and the purity was 99.89%.
[0045] Application Example 3: This application example differs from Application Example 1 in that it uses the methanol recovered in Example 3, distilled water, and crystalline sodium sulfate to prepare methyl benzoate. The yield of the obtained methyl benzoate was 79.54%, and the purity was 99.94%.
[0046] By comparing the experimental results of Application Example 1, Application Example 2, and Application Example 3, it can be seen that the yield and purity of the product obtained by using recycled methanol, distilled water, and crystalline sodium sulfate are both ideal, and the differences between the application examples are small, indicating that the recycled material has good reusability and is suitable for the needs of industrial continuous production.
Claims
1. A method for treating alkaline wastewater from the production of methyl benzoate, characterized in that: Includes the following steps: S1: After the alkaline wastewater from the production of methyl benzoate is allowed to stand and filtered, flocculant and acid are added simultaneously to adjust the pH value to 6-7. After stirring and settling, the purified mother liquor is obtained by filtration. S2: The refined mother liquor is heated for distillation, and the fraction collected at low temperature and the residue are collected; the fraction collected at low temperature is condensed and then heated to purify methanol, which is reused in the production of methyl benzoate; the residue is heated and distilled multiple times, and the fraction and bottom liquid are collected. The fraction is condensed to obtain distilled water; the bottom liquid is cooled and kept warm until it no longer clumps and there is suspension in the bottom liquid; the distilled water is reused in the production of methyl benzoate. S3: The distillation bottom liquid obtained in step S2 is filtered to obtain the still liquid and inorganic salt crystals. The collected inorganic salt crystals are sodium sulfate solid.
2. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S1, the flocculant is one or a mixture of two or more of polyacrylamide, ferrous sulfate, and aluminum trichloride.
3. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S1, the flocculant is aluminum trichloride.
4. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S1, the molar ratio of flocculant to acid is in the range of 1:0.3-5.
5. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S1, the acid is sulfuric acid or hydrochloric acid, and the mass percentage concentration of the acid is 15-30%.
6. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S2, the temperature for distilling the refined mother liquor is 70-90℃; the temperature for condensing the methanol obtained from the distillate is 50-65℃, and the temperature is then raised to 70-80℃ after condensation.
7. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S2, the residual liquid is heated to 100-150℃; distillation is performed 3-4 times; each distillation lasts 0.5-1 hour.
8. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: In step S2, the temperature of the distillation bottom liquid is reduced to 50-70°C.
9. The method for treating alkaline wastewater from methyl benzoate production according to claim 1, characterized in that: The alkaline wastewater from the production of methyl benzoate has a COD value of 120,000-132,554 mg / L and a pH of 8-14.