Method for recycling 1, 4-dioxane rectification wastewater

Abstract

The invention discloses a 1, 4-dioxane rectification wastewater recovery treatment method, and relates to the technical field of wastewater recovery treatment. The 1, 4-dioxane rectification wastewater recovery treatment method comprises the following steps: (1) adding an acid catalyst into 1, 4-dioxane rectification wastewater, and fully stirring; (2) heating the mixed solution in the step (1) for complete hydrolysis, performing reduced pressure distillation to obtain pure diethylene glycol, and collecting distillate; (3) adding an acid catalyst into the distillate obtained in the step (2), and fully stirring; and (4) pressurizing, heating and completely hydrolyzing the mixed solution in the step (3), carrying out reduced pressure distillation to obtain pure ethylene glycol, and treating distillate in a rectifying tower to recover acetaldehyde in the distillate. According to the method disclosed by the invention, the treatment of the wastewater with a high COD value can be realized without adding water for dilution, and organic components in the wastewater are converted into diethylene glycol and ethylene glycol with high economic values, so that the method has great economic values and environmental protection benefits.

Description

Technical Field

[0001] This invention relates to the field of wastewater recycling and treatment technology, specifically to a method for recycling and treating 1,4-dioxane distillation wastewater. Background Technology

[0002] 1,4-Dioxane is an important high-grade organic solvent with significant applications in chemical industries such as pharmaceutical synthesis, pesticide preparation, and rubber products. Currently, it is primarily produced via batch reactors through the dehydration of diethylene glycol under acidic catalyst catalysis. However, this reaction generates numerous side reactions, producing byproducts such as 2-methyl-dioxane, ethanol, and acetaldehyde, with 2-methyl-dioxane being the predominant byproduct. Due to the existence of various azeotropic systems between 1,4-dioxane and these byproducts, conventional distillation is insufficient for effective separation.

[0003] Existing technologies generally suffer from the following problems: 1. In the separation and purification process of 1,4-dioxane, the light components, mainly 2-methyl-dioxane, in the reaction solution are first removed by distillation. However, there are complex binary and ternary azeotropic relationships between 2-methyl-dioxane, water, ethanol, and 1,4-dioxane. When removing components such as 2-methyl-dioxane, acetaldehyde, and ethanol by distillation, a large amount of 1,4-dioxane and water will be carried out, and the COD value of the wastewater is very high, making treatment difficult and limiting the application of distillation method in the separation and purification of 1,4-dioxane.

[0004] 2. High-COD 1,4-dioxane distillation wastewater generally requires dilution with water to reduce its COD before entering the biological treatment process, resulting in water waste. Furthermore, the wastewater contains high concentrations of 2-methyldioxane and 1,4-dioxane, which have high recycling value. However, existing technologies for the recovery and treatment of 1,4-dioxane distillation wastewater are limited. How to achieve low-COD treatment of 1,4-dioxane distillation wastewater and the recovery and utilization of its organic components is a pressing technical problem that needs to be solved in this field.

[0005] Therefore, a new wastewater recycling and treatment technology is needed to achieve a significant reduction in wastewater COD, complete conversion of organic components (1,4-dioxane, 2-methyl-dioxane), and effective recovery of high-value products (diethylene glycol, ethylene glycol, acetaldehyde). Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for the recovery and treatment of 1,4-dioxane distillation wastewater.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for recovering and treating 1,4-dioxane distillation wastewater includes the following steps: (1) Add acid catalyst to 1,4-dioxane distillation wastewater and stir thoroughly; (2) The mixture in step (1) is heated and hydrolyzed completely, and then distilled under reduced pressure to obtain pure diethylene glycol. The distillate is collected. (3) Add the acid catalyst to the distillate obtained in step (2) and stir thoroughly; (4) The mixture in step (3) is subjected to pressure and heating to hydrolyze completely, and pure ethylene glycol is obtained by vacuum distillation. The distillate is then processed in a distillation column to recover the acetaldehyde.

[0008] In steps (1) and (3), the acid catalyst is phosphotungstic acid / aluminum chloride composite supported silica, prepared by the following method: Deionized water and silica were ultrasonically dispersed evenly, filtered, dried, and calcined to obtain a pretreated silica support; anhydrous ethanol and phosphotungstic acid were mixed, added to the pretreated silica support, stirred, rotary evaporated, dried, and calcined to obtain phosphotungstic acid-loaded silica; anhydrous ethanol and AlCl3·6H2O were mixed, added to the phosphotungstic acid-loaded silica, stirred, aged, rotary evaporated, and calcined to obtain phosphotungstic acid / aluminum chloride composite-loaded silica.

[0009] The mass ratio of silicon dioxide, phosphotungstic acid, and aluminum chloride is 10:2:3.

[0010] In step (1), the amount of acid catalyst used is 1 to 10% of the total mass of dioxane distillation wastewater.

[0011] In step (2), the hydrolysis temperature is 50~90℃ and the hydrolysis time is 6~10h.

[0012] In step (2), the vacuum degree of the vacuum distillation is -0.02 to -0.098 MPa, and the temperature of the vacuum distillation is 50 to 100℃.

[0013] In step (3), the amount of acid catalyst used is 1 to 10% of the total mass of dioxane distillation wastewater.

[0014] In step (4), the hydrolysis temperature is 80~150℃, the hydrolysis time is 6~10h, and the hydrolysis pressure range is 0.1~0.5MPa.

[0015] In step (4), the vacuum degree of the vacuum distillation is -0.02 to -0.098 MPa, and the temperature of the vacuum distillation is 50 to 100 °C.

[0016] In step (4), the reflux ratio of the distillation column is 3~5, the bottom temperature is 80~100℃, and the top temperature is 15~25℃.

[0017] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include: 1. During hydrolysis, because 2-methyl-dioxapentane is more stable than 1,4-dioxane, the two substances can be hydrolyzed separately under different hydrolysis conditions to obtain different hydrolysis products. Furthermore, due to the high boiling point of the hydrolysis products, they can be separated and purified by vacuum distillation. This method has low requirements for production and separation / purification equipment, resulting in low equipment investment.

[0018] 2. The hydrolysis catalyst used in this invention is a bifunctional solid acid. Through the synergistic effect of the two acid sites, it can significantly promote the selective hydrolysis efficiency of 1,4-dioxane. Moreover, this catalyst has a solid supported structure, exhibiting high stability, no acid loss, no equipment corrosion, reusability, low energy consumption, and significantly reduced side reactions, thereby obtaining high-purity diethylene glycol, ethylene glycol, and acetaldehyde products. Compared with the traditional liquid acid method, it has lower energy consumption, no secondary pollution, and can significantly reduce wastewater COD, achieving resource utilization of organic wastewater and possessing excellent industrial application value.

[0019] 3. The method used in this invention can treat high COD wastewater without dilution with water. At the same time, the organic components in the waste liquid are converted into diethylene glycol and ethylene glycol with high economic value through simple operations such as hydrolysis and vacuum distillation, which has great economic value and environmental benefits. Detailed Implementation

[0020] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments.

[0021] Example 1: Preparation of phosphotungstic acid / aluminum chloride composite supported silica Mix 100ml of deionized water with 10g of silica (specific surface area 300m²). 2 Mix 2g of anhydrous ethanol with 2g of phosphotungstic acid, add the pretreated silica support, stir at 300rpm for 2h, dry at 120℃ for 4h, and then calcine in a muffle furnace at 500℃ for 3h to obtain a pretreated silica support; mix 40ml of anhydrous ethanol with 2g of phosphotungstic acid, add the pretreated silica support, stir at 300rpm for 2h, evaporate in a water bath at 40℃ for 2h to remove the solvent, dry at 90℃ for 12h, and then calcine at 200℃ under a nitrogen atmosphere for 2h to obtain phosphotungstic acid-supported silica; mix 50ml of anhydrous ethanol with 3g of AlCl3·6H2O, add the phosphotungstic acid-supported silica, stir at 300rpm for 1h, age at room temperature for 12h, evaporate at 60℃ for 1h to remove the solvent, and calcine at 150℃ under a nitrogen atmosphere for 1.5h to obtain phosphotungstic acid / aluminum chloride composite supported silica.

[0022] Example 2: Method for Recovering and Treating 1,4-Dioxane Distillation Wastewater (1) Add 60g of phosphotungstic acid / aluminum chloride composite supported silica catalyst to 6000g of 1,4-dioxane distillation wastewater (wastewater with COD index of 871403mg / L) and stir thoroughly; (2) The mixture in step (1) was heated to 50°C and reacted for 10 h. The degree of hydrolysis of 1,4-dioxane in the reaction solution was 99.4%, and no hydrolysis of 2-methyl-dioxane was detected. The reaction solution was distilled under reduced pressure at 50°C with a vacuum degree of -0.02 MPa. Ethanol, acetaldehyde, water and 2-methyl-dioxane were distilled off until no more distillate was distilled off. 3314 g of distillate was collected to obtain 2686 g of diethylene glycol with a purity of 99.5% and a water content of 0.14 wt%. (3) Add 1000g of the distillate obtained in step (2) to the high-pressure hydrolysis reactor, and then add 10g of phosphotungstic acid / aluminum chloride composite supported silica catalyst to the reactor and stir thoroughly. (4) The mixture from step (3) was sealed and heated to 80°C. The pressure in the reactor was 0.1 MPa. After reacting for 10 h, 2-methyl-dioxane was completely hydrolyzed. The pressure was released to atmospheric pressure. The reaction solution was distilled under reduced pressure at 50°C with a vacuum degree of -0.02 MPa. Ethanol, acetaldehyde and water were distilled off until no distillate was obtained. 624 g of distillate was collected to obtain 376 g of ethylene glycol with a purity of 99.4% and a water content of 0.2 wt%. 500 g of the obtained distillate was added to the distillation column. The column was distilled intermittently at atmospheric pressure. The column height was 700 mm and the inner diameter was 25 mm. The packing material was Dixon packing. The reflux ratio was controlled at 5. The temperature of the bottom of the column was 100°C and the temperature of the top of the column was 15°C. 196 g of acetaldehyde with a purity of 99.5% and a water content of 0.1 wt% was obtained, along with 89 g of transition fraction and 215 g of bottom wastewater (COD value of 23498 mg / L).

[0023] Example 3: Method for Recycling and Treating 1,4-Dioxane Distillation Wastewater (1) Add 300g of phosphotungstic acid / aluminum chloride composite supported silica catalyst to 6000g of 1,4-dioxane distillation wastewater (wastewater with COD index of 811426mg / L) and stir thoroughly; (2) The mixture in step (1) was heated to 70°C and reacted for 8 hours. The degree of hydrolysis of 1,4-dioxane in the reaction solution was 99%, and no hydrolysis of 2-methyl-dioxane was detected. The reaction solution was distilled under reduced pressure at 60°C with a vacuum degree of -0.09 MPa. Ethanol, acetaldehyde, water and 2-methyl-dioxane were distilled off until no more distillate was distilled off. 3322 g of distillate was collected to obtain 2678 g of diethylene glycol with a purity of 99.5% and a water content of 0.2 wt%. (3) Add 1000g of the distillate obtained in step (2) to the high-pressure hydrolysis reactor, and then add 50g of phosphotungstic acid / aluminum chloride composite supported silica catalyst to the reactor and stir thoroughly. (4) The mixture from step (3) was sealed and heated to 130°C. The pressure in the reactor was 0.3 MPa. After 8 hours of reaction, 2-methyl-dioxane was completely hydrolyzed. The pressure was released to atmospheric pressure. The reaction solution was distilled under reduced pressure at 60°C with a vacuum of -0.09 MPa. Ethanol, acetaldehyde and water were distilled off until no more distillate was obtained. 631 g of distillate was collected to obtain 369 g of ethylene glycol with a purity of 99.1% and a water content of 0.16 wt%. 500 g of the obtained distillate was added to the distillation column. The column was distilled intermittently at atmospheric pressure. The column height was 700 mm and the inner diameter was 25 mm. The packing material was Dixon packing. The reflux ratio was controlled at 4. The temperature of the bottom of the column was 90°C and the temperature of the top of the column was 20°C. 193 g of acetaldehyde with a purity of 99.2% and a water content of 0.14 wt% was obtained, along with 94 g of transition fraction and 213 g of bottom wastewater (COD value of 26721 mg / L).

[0024] Example 4: Method for Recycling and Treating 1,4-Dioxane Distillation Wastewater (1) Add 600g of phosphotungstic acid / aluminum chloride composite supported silica catalyst to 6000g of 1,4-dioxane distillation wastewater (wastewater with COD index of 831403mg / L) and stir thoroughly; (2) The mixture in step (1) was heated to 90°C and reacted for 6 hours. The degree of hydrolysis of 1,4-dioxane in the reaction solution was 99.5%, and no hydrolysis of 2-methyl-dioxane was detected. The reaction solution was distilled under reduced pressure at 100°C with a vacuum degree of -0.098 MPa. Ethanol, acetaldehyde, water and 2-methyl-dioxane were distilled off until no more distillate was distilled off. 3306 g of distillate was collected to obtain 2694 g of diethylene glycol with a purity of 99.5% and a water content of 0.17 wt%. (3) Add 1000g of the distillate obtained in step (2) to the high-pressure hydrolysis reactor, and then add 100g of phosphotungstic acid / aluminum chloride composite supported silica catalyst to the reactor and stir thoroughly. (4) The mixture from step (3) was sealed and heated to 150°C. The pressure in the reactor was 0.5 MPa. After reacting for 6 hours, 2-methyl-dioxane was completely hydrolyzed. The pressure was released to atmospheric pressure, and the reaction solution was distilled under reduced pressure at 100°C with a vacuum degree of -0.098 MPa. Ethanol, acetaldehyde and water were distilled off until no distillate was obtained. 629 g of distillate was collected, and 371 g of ethylene glycol with a purity of 99.1% and a water content of 0.14 wt% was obtained. 500 g of the obtained distillate was added to the distillation column. The column was distilled intermittently at atmospheric pressure. The column height was 700 mm and the inner diameter was 25 mm. The packing material was Dixon packing. The reflux ratio was controlled at 3. The temperature of the bottom of the column was 80°C and the temperature of the top of the column was 25°C. 208 g of acetaldehyde with a purity of 99.2% and a water content of 0.14 wt% was obtained, along with 74 g of transition fraction and 218 g of bottom wastewater (COD value of 23659 mg / L).

[0025] The distillation column used in this embodiment is model ZY-5, manufactured by Hebei Zhongyu Instrument Equipment Co., Ltd.

[0026] Comparative Examples 1-11 are methods for the recovery and treatment of 1,4-dioxane distillation wastewater. The methods are basically the same as those in Example 3. The difference is that the acid catalyst used in step (1) is different. The recovery amounts of diethylene glycol, ethylene glycol, and acetaldehyde, as well as the COD values ​​after treatment, are shown in Table 1.

[0027] Table 1

[0028] By comparing the data from Examples 2-4 with those from Comparative Examples 1-11, it can be seen that the phosphotungstic acid / aluminum chloride composite supported silica bifunctional solid acid catalyst used in Examples 2-4 of this application can significantly reduce the COD of 1,4-dioxane distillation wastewater and effectively recover high-value products (diethylene glycol, ethylene glycol, acetaldehyde).

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A 1,4-dioxane rectification wastewater recovery treatment method characterized by, The method comprises the following steps: (1) adding an acid catalyst to 1,4-dioxane rectification wastewater and stirring thoroughly; (2) heating the mixture in step (1) to hydrolyze completely, and performing vacuum distillation to obtain pure diethylene glycol, and collecting the distillate; (3) adding an acid catalyst to the distillate obtained in step (2) and stirring thoroughly; (4) pressurizing and heating the mixture in step (3) to hydrolyze completely, and performing vacuum distillation to obtain pure ethylene glycol, and feeding the distillate into a rectification tower to recover acetaldehyde therein.

2. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In steps (1) and (3), the acid catalyst is phosphotungstic acid / aluminum chloride composite supported on silica, which is prepared by the following method: Deionized water is uniformly ultrasonically dispersed on silica, filtered, dried, and calcined to obtain a pretreated silica carrier; anhydrous ethanol is uniformly mixed with phosphotungstic acid, and the pretreated silica carrier is added, stirred, rotary evaporated, dried, and calcined to obtain phosphotungstic acid supported on silica; anhydrous ethanol is uniformly mixed with AlCl3·6H2O, and the phosphotungstic acid supported on silica is added, stirred, aged, rotary evaporated, and calcined to obtain phosphotungstic acid / aluminum chloride composite supported on silica.

3. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 2, characterized by, The mass ratio of the silica, phosphotungstic acid, and aluminum chloride is 10:2:

3.

4. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (1), the amount of the acid catalyst is 1-10% of the total mass of the 1,4-dioxane rectification wastewater.

5. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (2), the hydrolysis temperature is 50-90°C, and the hydrolysis time is 6-10 h.

6. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (2), the vacuum degree of the vacuum distillation is -0.02 to -0.098 MPa, and the vacuum distillation temperature is 50-100°C.

7. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (3), the amount of the acid catalyst is 1-10% of the total mass of the 1,4-dioxane rectification wastewater.

8. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (4), the hydrolysis temperature is 80-150°C, the hydrolysis time is 6-10 h, and the hydrolysis pressure ranges from 0.1 to 0.5 MPa.

9. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (4), the vacuum degree of the vacuum distillation is -0.02 to -0.098 MPa, and the vacuum distillation temperature is 50-100°C.

10. The 1,4-dioxane rectification wastewater recovery treatment method according to claim 1, characterized by, In step (4), the rectification reflux ratio is 3-5, the column bottom temperature is 80-100°C, and the column top temperature is 15-25°C.

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