Method for extracting maleic acid monosalt crystal by using maleate production wastewater

Abstract

The invention provides a method for extracting maleic acid monosalt crystals by using maleate production wastewater, and relates to the technical field of wastewater treatment.The maleate production wastewater is hydrolyzed in alkali metal hydroxide, maleate in the wastewater is converted into maleate disalt, the maleate disalt reacts with maleic anhydride to generate maleic acid monosalt, and the maleate monosalt is separated out. Sodium carbonate is continuously added into the filtrate in which the maleic acid monosalt is collected, and the filtrate can be continuously used for an alkali washing process in maleic ester production. Therefore, the method provided by the invention realizes the extraction of effective substances in the maleate production wastewater and the cyclic utilization of the waste liquid, has no wastewater discharge, is high in operability, and has important practical application value.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater and relates to a method for extracting maleic acid monosalt crystals by utilizing maleate production wastewater. Background Art

[0002] Diethyl maleate needs alkali washing process in the production process, and alkaline waste water will be produced. The solid content in alkaline waste water is generally 12-25wt%, and in addition to containing sodium carbonate, it also contains organic substances such as monoethyl maleate, diethyl maleate, maleic acid, fumarate, and wherein the content of organic substances is generally 2-12wt%. Therefore, even if the above-mentioned alkaline waste water is neutralized, it cannot be directly discharged, otherwise the organic substances inside will cause pollution. If conventional wastewater treatment methods are adopted, multi-stage waste liquid treatment devices are needed, including steps such as chemical precipitation, adsorption filtration, biological fermentation, Fenton oxidation, membrane separation, etc., not only the input of wastewater treatment equipment and treatment materials and daily operation and maintenance are needed, but also the treated bottom mud still needs to be processed separately as polluting waste residue, further increasing the processing cost. The applicant has applied for Chinese patent CN117800527A and proposed the process method of converting diethyl maleate process waste water into polyepoxy sodium succinate solution.

[0003] The applicant believes that further research is necessary on the treatment of maleate process wastewater. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for extracting maleic acid monosalt crystals using maleate production wastewater.

[0005] The technical solution of the present invention is as follows:

[0006] A method for extracting maleic acid monosalt crystals using maleate production wastewater comprises the following steps:

[0007] Adding an excess of alkali metal hydroxide to the maleate production wastewater, stirring until hydrolysis is complete, and dealcoholization is performed to obtain pretreated wastewater;

[0008] The pretreated wastewater is added to a reaction vessel containing molten maleic anhydride, the pH is adjusted to 4-5, stirred at 70-85° C. until the reaction system is clear and transparent, cooled to room temperature, allowed to stand and solids precipitated, and the solids are collected to obtain the maleic acid monosalt crystals.

[0009] Preferably, the weight of the alkali metal hydroxide is 0.5-5 times the weight of the maleate in the maleate production wastewater.

[0010] Preferably, the reaction temperature during stirring until the hydrolysis is complete is 55-80°C.

[0011] Preferably, the end point of the dealcoholization is that the difference between the refractive index of the dealcoholization distillate and the refractive index of pure water does not exceed 0.001.

[0012] Preferably, the weight content of alkali in the pretreated wastewater is 20-25%.

[0013] Preferably, the weight ratio of the maleic anhydride to the pretreated wastewater is 1:3-10.

[0014] Preferably, the time for standing and precipitating solid is 6-48 hours.

[0015] Preferably, sodium carbonate is added to the filtrate remaining after the solid is collected to prepare an alkaline solution, which is used in an alkaline washing process in the production process of maleic esters.

[0016] More preferably, the weight of the sodium carbonate is 5-15% of the weight of the filtrate.

[0017] Preferably, the maleate is diethyl maleate

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention proposes a method for converting maleic acid ester production wastewater into maleic acid monosalt through a relatively simple treatment method. The maleic acid ester production wastewater is converted into maleic acid disalt after alkaline hydrolysis, and then maleic anhydride is added to react and converted into maleic acid monosalt. The purity of the obtained maleic acid monosalt can reach 99% or above.

[0020] (2) After collecting and obtaining maleic acid monosalt in the treatment method of the present invention, the remaining filtrate can be further used in the alkali washing process in the production process of maleic acid esters after sodium carbonate is added, thereby realizing the recycling of maleic acid ester production wastewater with basically no waste liquid output. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the FT-IR spectrum of the monosodium maleate obtained in Example 1. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further illustrated and described below through specific implementation methods.

[0023] In order to effectively recycle the active ingredients in maleate production wastewater and realize the recycling of wastewater, the present invention proposes a method for extracting maleic acid monosalt crystals using maleate production wastewater, comprising the following steps:

[0024] Adding excess alkali metal hydroxide to the maleic acid ester production wastewater, stirring until hydrolysis is complete, dealcoholization, and obtaining pretreated wastewater;

[0025] Add pretreated wastewater to a reaction vessel containing molten maleic anhydride, adjust the pH to 4-5, stir at 70-85°C until the reaction system becomes clear and transparent, cool to room temperature, stand and precipitate solids, collect the solids, and obtain maleic acid monosalt crystals.

[0026] The chemical formula of the above alkali metal hydroxide is MOH, where M is Na + , K + , Cs + Etc. From the cost point of view, M is Na + More preferably, the alkali metal hydroxide is NaOH.

[0027] Maleate production wastewater contains a certain amount of organic substances such as maleic acid monoester, maleic acid, maleic acid diester, etc., which cannot be directly discharged after a simple neutralization reaction. In the treatment method of the present invention, alkali metal hydroxide is first used to treat maleate production wastewater, and organic substances such as maleic acid monoester, maleic acid, maleic acid diester, etc. are converted into maleic acid disalt through hydrolysis or neutralization, and maleate production wastewater is converted into pre-treated wastewater containing maleic acid disalt. Maleic anhydride is added to the pre-treated wastewater, and reacts with maleic acid disalt and alkali metal hydroxide to generate maleic acid monosalt. The solubility of maleic acid monosalt in water at room temperature is low, so the reaction solution is converted into a supersaturated solution after cooling, and maleic acid monosalt will slowly precipitate in the form of crystals. Crystals are collected by filtering and the like to obtain high-purity maleic acid monosalt crystals. After testing, the purity of the maleic acid monosalt crystals obtained by the present invention can reach 99.7% or higher.

[0028] In the present invention, there is no particular limitation on the criteria for stirring until hydrolysis is complete. One method may be: the reaction solution has no stratification and is in a uniform and transparent state.

[0029] In a preferred embodiment of the present invention, the weight of the alkali metal hydroxide is 0.5-5 times the weight of the maleate in the maleate production wastewater. In the present invention, the alkali metal hydroxide can be added in the form of a solid or a solution. If it is a solution, the weight of the alkali metal hydroxide is the weight of the alkali metal hydroxide in the solution. The content of maleate in the maleate production wastewater can be tested by high performance liquid chromatography or gas chromatography. In the present invention, in order to completely hydrolyze the maleate in the wastewater, the weight of the alkali metal hydroxide added needs to be excessive. Taking the maleic acid ester in the maleic acid ester production wastewater as diethyl maleate as an example, the weight of 1 mol of diethyl maleate is 172.2g, and the added weight of NaOH is 0.5 times that of diethyl maleate, which is 172.2g×0.5=86.1g, which is converted to 2.15mol. The theoretical amount of NaOH required for the complete hydrolysis of 1 mol of diethyl maleate is 2mol, so the actual weight of NaOH input is calculated as 0.5 times the weight of diethyl maleate. However, as needed, the excess amount of alkali metal hydroxide can be further increased, which can be more than 0.5 times. Further, the weight of the alkali metal hydroxide can be any value of 0.5 times, 0.8 times, 1 times, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, etc. of the weight of maleic acid ester in the maleic acid ester production wastewater, without special restrictions. Further preferably, the weight of the alkali metal hydroxide is 0.5-1 times the weight of the maleate in the maleate production wastewater.

[0030] In a preferred embodiment of the present invention, the reaction temperature during stirring until the hydrolysis is complete is 55-80° C. At this temperature, the maleate has a faster hydrolysis rate and is hydrolyzed more completely. For example, the reaction temperature during stirring until the hydrolysis is complete can be any value of 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., etc., without particular limitation.

[0031] In a preferred embodiment of the present invention, the end point of dealcoholization is that the difference between the refractive index of the dealcoholized distillate and the refractive index of pure water does not exceed 0.001. Maleic acid esters will produce organic alcohols after hydrolysis, such as dimethyl maleate and monomethyl maleate to produce methanol, diethyl maleate and monoethyl maleate to produce ethanol. In the present invention, dealcoholization has three purposes: (1) further promote the hydrolysis reaction to the right and the hydrolysis of maleic acid esters, and achieve complete hydrolysis of maleic acid esters; (2) reduce the solubility of the product maleic acid monosalt crystals in the reaction solution, which is conducive to the formation and precipitation of maleic acid monosalt crystals; (3) after the production wastewater removes maleic acid monosalt crystals and then adds sodium carbonate, it can be reused in the alkali washing process in the production of maleic acid esters. As the dealcoholization proceeds, the organic alcohol content in the dealcoholized distillate gradually decreases, and the water content increases. By detecting the difference between the refractive index of the dealcoholized distillate and the refractive index of pure water, the water content in the dealcoholized distillate can be determined. When the difference between the refractive index of the dealcoholization distillate and the refractive index of pure water does not exceed 0.001, the component of the dealcoholization distillate is basically water, and it can be judged that the dealcoholization step can be completed.

[0032] In a preferred embodiment of the present invention, the weight content of alkali in the pre-treated wastewater is 20-25%. The alkali in the pre-treated wastewater includes sodium carbonate and excess unreacted alkali metal hydroxide, and the weight content of alkali in the pre-treated wastewater can be detected by titration. Controlling the weight content of alkali in the pre-treated wastewater within a certain range is conducive to the reaction with maleic anhydride and the generation and precipitation of maleic acid monosalt crystals. For example, the weight content of alkali in the pre-treated wastewater can be any value of 20%, 21%, 22%, 23%, 24%, 25%, etc., without special restrictions.

[0033] In order to obtain a higher yield of maleic acid monosalt, the weight ratio of maleic anhydride to pretreated wastewater can be within a certain range, and can be adjusted according to the content of maleic acid disalt, alkali metal hydroxide, etc. in the pretreated wastewater, so that the yield of maleic acid monosalt crystals is as high as possible. In a preferred embodiment of the present invention, the weight ratio of maleic anhydride to pretreated wastewater is 1:3-10, for example, the weight ratio can be any value of 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc., without special restrictions, and further, the weight ratio can be 1:5-8.

[0034] In a preferred embodiment of the present invention, the time for standing and precipitating solids is 6-48 hours, which is conducive to the slow precipitation of maleic acid monosalt. For example, the time can be 6 hours, 8 hours, 12 hours, 16 hours, 24 hours, 30 hours, 36 hours, 48 ​​hours, etc. From the perspective of obtaining the highest possible yield of maleic acid monosalt crystals and production efficiency, the time for standing and precipitating solids can be 8-16 hours.

[0035] In a preferred embodiment of the present invention, sodium carbonate is added to the filtrate remaining after the solid is collected to prepare an alkali solution, which is used in the alkali washing process in the production process of maleic esters. In the present invention, the main component of the filtrate remaining after the solid is collected is sodium carbonate, but the concentration of sodium carbonate is low and does not meet the requirements of the alkali washing process in the production process of maleic esters. Therefore, a portion of sodium carbonate can be added to meet the requirements of the alkali washing process in the production process of maleic esters for alkali solution, thereby realizing the recycling of maleic ester production wastewater without wastewater discharge.

[0036] In a more preferred embodiment of the present invention, the weight of sodium carbonate is 5-15% of the weight of the filtrate. The concentration of sodium carbonate in the alkali solution and the content of sodium carbonate in the filtrate can be determined according to the requirements of the alkali washing process. For example, the weight of sodium carbonate can be any value of 5%, 6%, 8%, 10%, 12%, 15% of the weight of the filtrate, etc., without special restrictions.

[0037] In a preferred embodiment of the present invention, the maleate is diethyl maleate. Diethyl maleate is the most commonly used maleate, which is mainly used to synthesize aspartic acid ester resin and further used to prepare aspartic acid polyurea products, such as aspartic acid polyurea coating, aspartic acid polyurea seam beautifying agent, etc.

[0038] The technical solution of the present invention is further described and illustrated according to various embodiments below.

[0039] Example 1

[0040] Gas chromatography detection showed that the content of maleate (including diethyl maleate, maleic acid, and monoethyl maleate) in the diethyl maleate production wastewater was 10 wt %.

[0041] 800g of diethyl maleate production wastewater and 40g of sodium hydroxide solid were added to a 1L three-necked flask, and the mixture was stirred and hydrolyzed at 70-75°C until there was no stratification on the surface of the reaction solution and the solution was in a uniform and transparent state. Under the condition of 70-75°C, the hydrolyzed solution was vacuumed and dealcoholized, and the refractive index of the distillate was tracked and tested until the difference between the refractive index of the distillate and the refractive index of pure water did not exceed 0.001, and the dealcoholization was stopped to obtain the pre-treated wastewater after dealcoholization. The alkali content in the pre-treated wastewater was measured to be 22wt% by acid-base titration.

[0042] Add 80g of maleic anhydride to a 1L three-necked flask, heat to 50℃ to dissolve, slowly add 480g of the above pretreated wastewater under stirring, and test the solution pH value to be 4-4.5 after the addition. Stir the solution at 75-80℃ until the solution is clear and transparent, stop stirring and heating, cool naturally to room temperature 20℃, stand for 12h, filter and collect the solid to obtain monosodium maleate crystals.

[0043] The purity of the monosodium maleate crystals was measured by high performance liquid chromatography to be 99.7%. The FT-IR spectrum of the monosodium maleate crystals obtained is shown in the attached figure. Figure 1 shown.

[0044] After the solids are collected, 10.5% of the weight of the filtrate is added to the remaining filtrate to prepare an alkaline solution for use in the diethyl maleate alkaline washing process.

[0045] Example 2

[0046] The difference between Example 2 and Example 1 is that in Example 1, the sodium hydroxide solid is adjusted from 40 g to 80 g, and the maleic anhydride is adjusted from 80 g to 140 g. The other steps remain unchanged.

[0047] The purity of the monosodium maleate crystals obtained in this example was measured by high performance liquid chromatography to be 99.0%.

[0048] Example 3

[0049] The difference between Example 3 and Example 1 is that in Example 1, the sodium hydroxide solid is adjusted from 40 g to 60 g, and the maleic anhydride is adjusted from 80 g to 110 g. The other steps remain unchanged.

[0050] The purity of the monosodium maleate crystals obtained in this example was measured by high performance liquid chromatography to be 99.2%.

[0051] Example 4

[0052] Gas chromatography detection showed that the content of maleate (including diethyl maleate, maleic acid, and monoethyl maleate) in the wastewater produced by diethyl maleate was 5wt%.

[0053] 800g of diethyl maleate production wastewater and 30g of sodium hydroxide solid were added to a 1L three-necked flask, and the mixture was stirred and hydrolyzed at 70-75°C until there was no stratification on the surface of the reaction solution and the solution was in a uniform and transparent state. Under the condition of 70-75°C, the hydrolyzed solution was vacuumed and dealcoholized, and the refractive index of the distillate was tracked and tested until the difference between the refractive index of the distillate and the refractive index of pure water did not exceed 0.001, and the dealcoholization was stopped to obtain the pre-treated wastewater after dealcoholization. The alkali content in the pre-treated wastewater was measured to be 20wt% by acid-base titration.

[0054] Add 60g of maleic anhydride to a 1L three-necked flask, heat to 50℃ to dissolve, slowly add 480g of the above pretreated wastewater under stirring, and test the solution pH value to be 4-4.5 after the addition. Stir the solution at 75-80℃ until the solution is clear and transparent, stop stirring and heating, cool naturally to room temperature 25℃, stand for 16h, filter and collect the solid to obtain monosodium maleate crystals.

[0055] The purity of the monosodium maleate crystals measured by high performance liquid chromatography was 99.8%.

[0056] After the solids are collected, 12% sodium carbonate solid by weight of the filtrate is added to the remaining filtrate to prepare an alkaline solution for use in the diethyl maleate alkaline washing process.

[0057] Example 5

[0058] The difference between Example 5 and Example 4 is that in Example 1, the sodium hydroxide solid is adjusted from 30 g to 80 g, and the maleic anhydride is adjusted from 60 g to 100 g. The other steps remain unchanged.

[0059] The purity of the monosodium maleate crystals obtained in this example was measured by high performance liquid chromatography to be 99.6%.

[0060] As described above, the basic principles, main features and advantages of the present invention are shown and described. Those skilled in the art should understand that the present invention is not limited by the above embodiments, which are only preferred embodiments of the present invention and cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the scope of the present invention and the content of the specification should still be within the scope of the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for extracting maleic acid monosalt crystals using maleate production wastewater, characterized in that: The following steps are involved: Adding an excess of alkali metal hydroxide to the maleate production wastewater, stirring until hydrolysis is complete, and dealcoholization is performed to obtain pretreated wastewater; The pretreated wastewater is added to a reaction vessel containing molten maleic anhydride, the pH is adjusted to 4-5, stirred at 70-85° C. until the reaction system is clear and transparent, cooled to room temperature, allowed to stand and solids precipitated, and the solids are collected to obtain the maleic acid monosalt crystals.

2. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: The weight of the alkali metal hydroxide is 0.5-5 times the weight of the maleate in the maleate production wastewater.

3. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: The reaction temperature during stirring until the hydrolysis is complete is 55-80°C.

4. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: The end point of the dealcoholization is that the difference between the refractive index of the dealcoholization distillate and the refractive index of pure water does not exceed 0.

001.

5. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: The weight content of alkali in the pre-treated wastewater is 20-25%.

6. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: The weight ratio of the maleic anhydride to the pretreated wastewater is 1:3-10.

7. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: The time for standing and precipitating solid is 6-48h.

8. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 1, characterized in that: Sodium carbonate is added to the filtrate remaining after the solid is collected to prepare an alkaline solution, which is used in the alkaline washing process in the production process of maleic esters.

9. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to claim 8, characterized in that: The weight of the sodium carbonate is 5-15% of the weight of the filtrate.

10. The method for extracting maleic acid monosalt crystals using maleate production wastewater according to any one of claims 1 to 9, characterized in that: The maleate is diethyl maleate.

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