A EDB wastewater recovery process

Abstract

This invention relates to the field of EDB (Electrode Dewatering) processes, specifically to an EDB wastewater recovery process. This invention uses lime and ethylene glycolamine, through a polysaccharide reaction, to effectively reduce the formaldehyde content in the wastewater. The resulting polysaccharide is concentrated by membrane distillation to obtain industrial-grade polysaccharide. This polysaccharide can be used to cultivate bacteria for wastewater treatment in the company. Methanol is recovered by distillation for use in product manufacturing. The treated wastewater is then treated by biochemical bacteria before being discharged in a green manner, significantly reducing the costs of EDB production and wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of EDB processes, and more specifically to an EDB wastewater recovery process. Background Technology

[0002] Ethyl p-dimethylaminobenzoate, abbreviated as "EDB", is a highly efficient amine accelerator. It is generally used in conjunction with free radical photoinitiators and is mainly used for UV curing of varnish coating systems on paper, wood, metal and plastic surfaces. It can also be used for UV radiation polymerization reactions of single or multiple monomers. Summary of the Invention

[0003] This invention aims to provide an EDB wastewater recovery process, the specific solution of which is as follows:

[0004] An EDB wastewater recycling process includes the following steps:

[0005] (1) EDB wastewater pretreatment: Use a pump to transfer EDB wastewater from the waste liquid tank to the pretreatment vessel, turn on the chilled water of the pretreatment vessel to cool the vessel down to 6-8℃, the residual EDB in the residual liquid crystallizes out, and the EDB in the waste liquid is recovered by centrifuge, and the waste liquid is transferred to the polysaccharide reaction vessel by a pump.

[0006] (2) Add quicklime into the polysaccharide reactor through the feed port;

[0007] (3) Turn on the polysaccharide reactor and stir thoroughly;

[0008] (4) Add an appropriate amount of ethylene glycolamine catalyst into the polysaccharide reactor through the feed port;

[0009] (5) Use steam to heat the polysaccharide reactor and control the temperature inside the polysaccharide reactor to 50-60℃. Open the material inlet valve of the reflux condenser and the cooling water valve of the condenser so that the formaldehyde and methanol vapor entering the condenser are cooled and refluxed back into the reactor to prevent methanol from being lost. The formaldehyde will then fully participate in the polysaccharide reaction.

[0010] (6) Keep the temperature of the polysaccharide reactor at 50-60℃ and control the saccharification time at 1h-3h until the solution turns yellow and no longer deepens. Use the formaldehyde test method to determine the formaldehyde content in the wastewater after the reaction.

[0011] (7) Open the cooling water valve to cool the polysaccharide reactor to 20-30℃, remove solid waste from the polysaccharide solution after formaldehyde removal through plate and frame filtration, and press the solution into the temporary storage vessel;

[0012] (8) Open the distillation valve of the temporary storage vessel, use steam to heat the temporary storage vessel to 70-90℃, open the cooling water valve of the horizontal condenser, and recover methanol to the methanol receiving tank through the horizontal condenser. After the temperature is constant, the methanol recovery is completed. After purification by the distillation column, 95% methanol can be obtained. The polysaccharide solution enters the feed side of the direct contact membrane module through the diaphragm pump. The feed side of the direct contact membrane module is a circulating chilled water, and the temperature is maintained at 5-25℃. After repeated concentration until crystallization occurs, the membrane distillation concentration is completed to obtain polysaccharide.

[0013] (9) After EDB waste liquid is converted into polysaccharide and methanol, it is transported to the sewage treatment plant. The sewage treatment plant uses Fenton oxidation and electrode treatment, and then dilutes the waste liquid with water before sending it to the biochemical treatment system. After reaching the Class III water body discharge standard, it is discharged into the pipeline for green discharge. Testing revealed that the COD concentration of the EDB wastewater was approximately 120,000 mg / L. After EDB, formaldehyde, and methanol recovery, the COD concentration was reduced to approximately 30,000 mg / L. Further treatment with Fenton oxidation and electrodes to break down recalcitrant macromolecules resulted in a COD concentration of 4,000-5,000 mg / L and a formaldehyde concentration of less than 50 mg / L. This water then entered the biological treatment system, which boasts a treatment efficiency of over 95%. The COD concentration of the discharged water was 200-300 mg / L, meeting the Class III water body discharge standard of the Integrated Wastewater Discharge Standard (GB8978-1996), which requires a COD concentration of less than 500 mg / L. This aligns with the discharge compliance requirements.

[0014] In step (2), the molar ratio of quicklime to HCHO is (0.1-0.3):(0.9-1.2).

[0015] In step (2), the quicklime content is greater than 90%.

[0016] The pH of the solution in step (3) is ≥11.

[0017] If the pH in step (3) is less than 11, continue adding lime until the pH is greater than 11.

[0018] In step (6), the formaldehyde content in the wastewater after the reaction is determined using the formaldehyde test method. When the formaldehyde content in the polysaccharide reaction vessel is less than 0.2%, the reaction ends.

[0019] The amount of catalyst added in step (4) is as follows: 1-1.25 kg of ethylene glycolamine is added per 1000 liters of wastewater.

[0020] The raw materials required for EDB production include ethyl p-nitrobenzene, hydrogen, paraformaldehyde, and methanol as solvent. After hydrogenation, the resulting product is paraformaldehyde, which is present in excess during the design of this reaction. Calculations show that approximately 5% EDB, 10% formaldehyde, and 10% methanol are present in the wastewater. This wastewater is directly sent to a wastewater treatment plant, resulting in resource waste. Furthermore, during wastewater biochemical treatment, if the formaldehyde content exceeds 200 mg / L, microbial activity is almost completely inhibited, potentially paralyzing the wastewater treatment system. Using lime and ethylene glycolamine, a polysaccharide reaction can effectively reduce the formaldehyde content in the wastewater. The resulting polysaccharide is concentrated by membrane distillation to obtain industrial-grade polysaccharide, which can be used to cultivate bacteria for the company's wastewater treatment. Methanol is recovered by distillation and used in product production. The treated wastewater is then treated by biochemical bacteria before being discharged in a green manner, significantly reducing the costs of EDB production and wastewater treatment.

[0021] Furthermore, this invention first recovers EDB, which prevents EDB from deteriorating during the polysaccharide reaction and being stored in the plate and frame filter, thus becoming waste. During the polysaccharide reaction, the increased temperature may cause methanol and formaldehyde to volatilize. Therefore, gaseous methanol and formaldehyde need to be condensed and refluxed into the polysaccharide reactor. Formaldehyde can fully participate in the polysaccharide reaction. After the formaldehyde is recovered from the polysaccharide reaction, the methanol in the waste liquid is finally recovered by distillation. After distillation in a distillation column, methanol with a purity of over 95% can be obtained and can be used for EDB production. Attached Figure Description

[0022] Figure 1 A schematic diagram of an EDB wastewater recycling process according to the present invention. Detailed Implementation

[0023] Example 1

[0024] (1) EDB wastewater pretreatment: EDB wastewater (4000L wastewater in this case) is transferred from the waste liquid tank to the pretreatment vessel using a pump. The chilled water in the pretreatment reactor is turned on to cool the reactor down to 6-8℃. The residual EDB crystals in the residual liquid precipitate out. The EDB in the waste liquid is recovered by centrifuge. The waste liquid is transferred to the polysaccharide reactor by a pump. The EDB recovery rate is 7%.

[0025] (2) Add quicklime into the polysaccharide reactor through the feeding port; the molar ratio of quicklime to HCHO in step (2) is 0.2:1; the content of quicklime in step (2) is greater than 90%.

[0026] (3) Open the polysaccharide reactor and stir thoroughly; the pH of the solution in step (3) is ≥11; if the pH of step (3) is less than 11, continue to add lime until the pH is greater than 11 (the pH in this example is 11).

[0027] (4) Add 5 kg of ethylene glycolamine catalyst into the polysaccharide reactor through the feed port;

[0028] (5) Use steam to heat the polysaccharide reactor and control the temperature inside the polysaccharide reactor to 60°C. Open the material inlet valve of the reflux condenser and the cooling water valve of the condenser so that the formaldehyde and methanol vapor entering the condenser are cooled and refluxed back into the reactor to prevent methanol from being lost. The formaldehyde then fully participates in the polysaccharide reaction.

[0029] (6) Keep the temperature of the polysaccharide reactor at 60°C and control the saccharification time at 2h until the solution turns yellow and no longer deepens. Use the formaldehyde test method to determine the formaldehyde content in the wastewater after the reaction. In step (6), use the formaldehyde test method to determine the formaldehyde content in the wastewater after the reaction. The formaldehyde content in the solution in the polysaccharide reactor is 0.18%, and the reaction ends.

[0030] (7) Open the cooling water valve to cool the polysaccharide reactor to 25°C, remove solid waste from the polysaccharide solution after formaldehyde removal through plate and frame filtration, and press the solution into the temporary storage vessel;

[0031] (8) Open the distillation valve of the temporary storage vessel, use steam to heat the temporary storage vessel to 70°C, keep the steam pressure constant at 0.05 MPa, open the cooling water valve of the horizontal condenser, and recover methanol to the methanol receiving tank through the horizontal condenser. After the temperature is kept constant at 90°C, the methanol recovery is completed. After purification by the distillation column, 95% methanol can be obtained. The polysaccharide solution enters the feed side of the direct contact membrane module through the diaphragm pump. The feed side of the direct contact membrane module is filled with circulating chilled water and the temperature is kept at 15°C. After repeated concentration until crystallization occurs, the membrane distillation concentration is completed to obtain polysaccharide.

[0032] (9) After EDB waste liquid is converted into polysaccharide and methanol, it is transported to the sewage treatment plant. The sewage treatment plant uses Fenton oxidation and electrode treatment, and then dilutes the waste liquid with water before sending it to the biochemical treatment system. After reaching the Class III water body discharge standard, it is discharged into the pipeline for green discharge.

[0033] Examples 2-3 (used to study the effect of temperature in step (1) on EDB recovery)

[0034] Examples 2-3 are identical to Example 1 except for the temperature in step (1). Studies have shown that below 6°C, the effect (recovery rate) does not improve further, and instead results in energy waste.

[0035] Step (1) Temperature Results (e.g., EDB recovery rate) Example 2 5℃ 7% Example 3 10℃ 5%

[0036] Examples 4-5 (used to study the effect of pH in step (3) on the polysaccharide reaction)

[0037] Step (3) pH Effect (formaldehyde content) Example 4 10 0.5% Example 5 12 0.19%

[0038] Examples 6-11 (used to study the effect of ethylene glycolamine on polysaccharide reactions)

[0039] Amount of ethylene glycolamine added Effect (formaldehyde content) Example 6 3kg 0.5% Example 7 4kg 0.2% Example 8 6kg 0.21%

[0040] The above embodiments are only used to explain the inventive concept of the present invention, and are not intended to limit the protection of the present invention. Any non-substantial modifications made to the present invention using this concept should fall within the protection scope of the present invention.

Claims

1. An EDB wastewater recycling process, characterized in that, Includes the following steps: (1) EDB wastewater pretreatment: EDB wastewater is transferred from the waste liquid tank to the pretreatment vessel by pump. Chilled water is introduced into the pretreatment vessel to cool it down to 6-8℃. The residual EDB crystals in the residual liquid precipitate out. The EDB in the waste liquid is recovered by centrifuge. The waste liquid is transferred to the polysaccharide reaction vessel by pump. (2) Add quicklime into the polysaccharide reactor through the feed port; (3) Turn on the polysaccharide reactor and stir thoroughly; (4) Add an appropriate amount of ethylene glycolamine catalyst into the polysaccharide reactor through the feed port; (5) Use steam to heat the polysaccharide reactor and control the temperature inside the polysaccharide reactor to 50-60℃. Open the material inlet valve of the reflux condenser and open the cooling water valve of the condenser so that the formaldehyde and methanol vapor entering the condenser are cooled and refluxed back into the polysaccharide reactor to prevent methanol loss. The formaldehyde will then fully participate in the polysaccharide reaction. (6) Keep the temperature of the polysaccharide reactor at 50-60℃ and control the saccharification time at 1h-3h until the solution turns yellow and no longer deepens. Use the formaldehyde test method to determine the formaldehyde content in the wastewater after the reaction. (7) Open the cooling water valve to cool the polysaccharide reactor to 20-30℃, remove solid waste from the polysaccharide solution after formaldehyde removal through plate and frame filtration, and press the solution into the temporary storage vessel; (8) Open the distillation valve of the temporary storage vessel, use steam to heat the temporary storage vessel to 70-90℃, open the cooling water valve of the horizontal condenser, and recover methanol to the methanol receiving tank through the horizontal condenser. After the temperature is constant, the methanol recovery is completed. After purification by the distillation column, 95% methanol can be obtained. The polysaccharide solution enters the feed side of the direct contact membrane module through the diaphragm pump. The non-feed side of the direct contact membrane module is circulated chilled water, and the temperature is maintained at 5-25℃. After repeated concentration until crystallization occurs, the membrane distillation concentration is completed to obtain polysaccharide. (9) After EDB wastewater pretreatment, formaldehyde conversion to polysaccharide and methanol recovery, the wastewater is transported to the sewage treatment plant. The sewage treatment plant uses Fenton oxidation and electrode treatment, and after dilution water adjustment, it goes to the biochemical treatment system. After reaching the Class III water body discharge standard, it is discharged into the pipeline for green discharge.

2. The EDB wastewater recovery process as described in claim 1, characterized in that: In step (2), the molar ratio of quicklime to HCHO is (0.1-0.3):(0.9-1.2).

3. The EDB wastewater recovery process as described in claim 1, characterized in that: In step (2), the quicklime content is greater than 90%.

4. The EDB wastewater recycling process as described in claim 1, characterized in that: The pH of the solution in step (3) is ≥11.

5. The EDB wastewater recovery process as described in claim 4, characterized in that: If the pH in step (3) is less than 11, continue adding lime until the pH is greater than 11.

6. The EDB wastewater recovery process as described in claim 1, characterized in that: In step (6), the formaldehyde content in the wastewater after the reaction is determined using the formaldehyde test method. When the formaldehyde content in the polysaccharide reaction vessel is less than 0.2%, the reaction ends.

7. The EDB wastewater recovery process as described in claim 1, characterized in that, The amount of catalyst added in step (4) is as follows: 1-1.25 kg of ethylene glycolamine is added per 1000 liters of wastewater.

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