Polycarbonate production wastewater resource treatment process

Abstract

The application provides a polycarbonate production wastewater resource treatment process, which comprises the following steps: separating dichloromethane and triethylamine in the wastewater by steam stripping, and recycling after rectification and purification; evaporating the steam stripping water to evaporate water for recycling in a circulating cooling water system; outsourcing disposal of the mother liquor after drying; crystallizing salt through water salting, plate and frame filtration of flocculation in water, removal of carbonate and bicarbonate by acidification, rejection of impure salt by nanofiltration, advanced oxidation process by O3 / H2O2, and deep treatment, and oxidizing the effluent water as brine for an ion membrane caustic soda system; after the new salt is compounded to form saturated brine, electrolysis is carried out, and the produced liquid caustic soda and chlorine gas are recycled in production or sold as commodities. The application can effectively realize resource utilization of water, dichloromethane, triethylamine and salt in polycarbonate production wastewater, and avoid pollution to the environment.

Description

Technical Field

[0001] This invention relates to the field of chemical production wastewater treatment technology, and particularly to a resource-based treatment process for polycarbonate production wastewater. Background Technology

[0002] Polycarbonate is a high-performance thermoplastic engineering plastic with outstanding impact resistance, creep resistance, good dimensional stability, heat resistance, low water absorption, non-toxicity, and excellent dielectric properties. It is widely used in electronics, power tools, transportation, automobiles, machinery, instrumentation, construction, information storage, optical materials, medical devices, sporting goods, consumer products, and security industries. It is the only one of the five major engineering plastics with good transparency and has been the fastest-growing general-purpose engineering plastic in recent years. The average annual growth rate of my country's polycarbonate market is projected to reach 10.2%, with demand approaching 4 million tons by 2010. Annual polycarbonate production growth is expected to reach 9%, and annual sales growth is projected to reach 10%.

[0003] Currently, most manufacturers worldwide use interfacial polycondensation or melt transesterification, with 80% using interfacial polycondensation. The production process generates a large amount of wastewater. This wastewater has a complex composition, mainly consisting of macromolecular intermediate polymers, dichloromethane, triethylamine, bisphenol A, etc., and also has a high salt content, making it difficult to completely remove using a single treatment method.

[0004] Currently, the main methods for treating this wastewater include physicochemical methods (reverse osmosis, osmosis, distillation, incineration, and electrochemical methods), biochemical methods, and combinations of biological methods with other methods (liquid / liquid extraction-membrane bioreactor combination process, activated sludge process, and granular activated carbon combination process). These methods are costly and often fail to meet discharge standards. Finding an effective way to treat this type of wastewater and recycle its useful materials has become a pressing issue for the development of the domestic polycarbonate industry. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an improved process for the resource-based treatment of polycarbonate production wastewater. Addressing the shortcomings of existing technologies, the process design for polycarbonate production wastewater incorporates stripping, distillation, evaporation, salting, filtration, acidification, nanofiltration, advanced oxidation, electrolysis, and drying processes, significantly improving wastewater treatment efficiency. After treatment, the overall wastewater removal efficiency is effectively enhanced, enabling the resource utilization of polycarbonate production wastewater and waste salts, achieving a green circular economy.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] (1) The production wastewater enters the stripping tower and is stripped by steam. The organic steam passes through the condenser and is condensed to obtain crude dichloromethane and triethylamine.

[0008] (2) The stripping condensate enters the distillation column to separate dichloromethane and triethylamine, which are then reused in production.

[0009] (3) The steam-extracted water enters the evaporator. The MVR evaporator is used. The evaporated condensate is recycled to the circulating cooling water system. The mother liquor and crystallized salt are separated by centrifugation. The centrifuged mother liquor enters the drying treatment system, and the centrifuged crystallized salt enters the salting section.

[0010] (3) Dissolve the centrifuged crystallized salt in pure water to prepare a 10%-15% salt solution, and stir until it is completely dissolved;

[0011] (4) The brine enters the plate and frame filter press to remove suspended solids from the wastewater, and the sludge enters the drying treatment system;

[0012] (5) The brine filtrate is acidified by adjusting the pH to 4.0-5.0 with hydrochloric acid to remove carbonate and bicarbonate ions. After acidification, the pH is adjusted to 7.0-7.5 with liquid alkali.

[0013] (6) Acidified effluent enters the nanofiltration system, with the temperature controlled at 15-30℃ and the operating pressure at 0.2-0.4MPa. Nanofiltration removes large molecular organic matter from the wastewater. Nanofiltration concentrate contains impurities and salts. Nanofiltration concentrate enters the drying treatment system, and nanofiltration desalinated water enters the advanced oxidation system.

[0014] (7) Nanofiltration freshwater enters the advanced oxidation system and is deeply treated by the O3 / H2O2 advanced oxidation process. The oxidized water is used as brine in the ion-exchange membrane caustic soda system.

[0015] (8) The oxidized water is compounded with new salt to make saturated brine, which is then electrolyzed. The resulting liquid alkali and chlorine are reused in production or sold as commodities.

[0016] (9) The sludge and mother liquor generated in each process section are dried and then outsourced for treatment. The dried condensate enters the sewage treatment system and is treated together with domestic sewage.

[0017] The advantages of this invention compared to existing technologies are: it achieves over 90% resource recovery of water, dichloromethane, triethylamine, and salt, while the salt purification process saves 60%-80% in operating costs compared to high-energy mineralization technologies such as carbonization and melting. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a process for the resource utilization treatment of polycarbonate production wastewater disclosed in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of an apparatus used in a polycarbonate production wastewater resource utilization process according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide a more detailed description of the invention. It should be noted that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0021] like Figure 1 As shown, this invention provides a process for the resource-based treatment of polycarbonate production wastewater. The process design for polycarbonate production wastewater includes the following steps: (1) The production wastewater is discharged into a stripping tower to remove dichloromethane and triethylamine from the wastewater, and then purified for use in the production process; (2) The stripped water enters the evaporation system, the evaporation condensate is recycled to the circulating cooling water system, the mother liquor and crystalline salt are centrifuged, the evaporation mother liquor is dried and then outsourced for treatment, and the dried condensate enters the wastewater treatment system; (3) The evaporation centrifuged crystalline salt is desalted with pure water, dissolved and then filtered through a plate and frame filter to remove suspended solids from the wastewater, and the sludge is dried. (3) The effluent is treated by outsourcing after oxidation, and the dried condensate enters the wastewater treatment system; (4) The effluent is acidified to adjust the pH value to 4.0-5.0 to remove carbonate and bicarbonate ions, and then the pH value is adjusted to 7.0; (5) The acidified effluent is treated by nanofiltration to remove large molecular organic matter in the wastewater. The concentrate contains mixed salts. The concentrate is dried and then treated by outsourcing. The dried condensate enters the wastewater treatment system; (6) The nanofiltration desalinated water is treated by O3 / H2O2 advanced oxidation process. The oxidized effluent is used as brine for the ion-exchange membrane caustic soda system. After being compounded with new salt to make saturated brine, it is electrolyzed. The liquid alkali and chlorine produced are recycled for production or sold as commodities. This invention can effectively realize the resource utilization of polycarbonate production wastewater and waste salt, and avoid pollution of environmental water bodies.

[0022] like Figure 2 As shown, the processing equipment used in this invention includes a stripping tower, a distillation tower, an evaporator, a salt treatment system, a filter press, an acidification system, a nanofiltration membrane system, an advanced oxidation system, an ion-exchange membrane caustic soda system, a clear water tank, a drying treatment system, regulating valves, water pumps, and process pipelines.

[0023] The following specific data examples illustrate the invention.

[0024] Example 1

[0025] The following describes the present invention in further detail using the production wastewater of a certain enterprise as the research object, through specific implementation methods, and verifies the feasibility and accuracy of the method of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The company's main business is the production of polycarbonate, which is produced using an interfacial polycondensation reaction. Wastewater from polycarbonate production is fed into a stripping tower, where steam is heated to remove dichloromethane and triethylamine. After condensation, a crude product is obtained, which is then separated into pure dichloromethane and triethylamine by distillation and reused in the production process. The stripped water enters an MVR evaporator, and the condensate is used as makeup water for the circulating cooling water system. The mother liquor and crystalline salt are separated by centrifugation. The centrifuged mother liquor is dried and then outsourced for further treatment. The dried condensate is sent to a wastewater treatment plant. The centrifuged crystalline salt is desalinated using pure water to prepare a 10% brine solution, which is then stirred... The solution is completely dissolved, and the brine enters a plate and frame filter press to remove suspended solids from the wastewater. The sludge is dried and then outsourced for treatment. The dried condensate enters the wastewater treatment plant. The brine filtrate is acidified by adding dilute hydrochloric acid to a pH of 4.0, and carbonate and bicarbonate ions are removed by stirring or aeration. Then, the pH is adjusted to 7.0 using liquid alkali. The acidified effluent enters a nanofiltration system to remove large molecular organic matter from the wastewater. The nanofiltration concentrate is tested for impurities and salts. The concentrate is dried and then outsourced for treatment. The dried condensate enters the wastewater treatment plant, and the nanofiltration desalination enters the advanced oxidation system.

[0027] The O3 / H2O2 advanced oxidation system controls the pH value to 8.5-9.0, and the O3 dosage is approximately equal to the COD in the water. Cr The mass of 27.5% hydrogen peroxide added is approximately 1.1-1.8 times that of O3 added, with a residence time of 0-30 minutes. The oxidized effluent is mixed with fresh salt to form saturated brine, which then enters the ion-exchange membrane caustic soda system. After electrolysis, the liquid alkali and chlorine produced are recycled for production, achieving a green cycle. The specific results are shown in Table 1 below.

[0028] Table 1

[0029]

[0030] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A polycarbonate production wastewater resourceful treatment process, characterized in that, The treatment process comprises a stripping section, a rectification section, an evaporation section, a salt dissolving section, a filtration section, an acidification section, a nanofiltration section, an advanced oxidation section, an electrolysis section, and a drying treatment section. (1) The stripping section and the rectification section: the production wastewater is discharged into a stripping tower to remove dichloromethane and triethylamine from the wastewater, and then the wastewater is purified and used for production; (2) The evaporation section: the stripped wastewater is fed into an evaporation system, the evaporation condensate is recycled to a circulating cooling water system, the mother liquor and the crystallized salt are centrifuged, the evaporation mother liquor is dried and then outsourced for treatment, and the dried condensate is fed into a sewage treatment system; (3) The salt dissolving section and the filtration section: the centrifuged crystallized salt is dissolved in pure water to prepare a 10%-15% brine, the brine is stirred to completely dissolve the salt, the brine is fed into a plate-and-frame filter to remove suspended solids in the wastewater, the sludge is dried and then outsourced for treatment, and the dried condensate is fed into the sewage treatment system; (4) The acidification section: the salt-dissolved filtrate is acidified by adjusting the pH value to 4.0-5.0 to remove carbonate and bicarbonate ions, and then the pH value is adjusted to 7.0; (5) The acidified effluent is subjected to nanofiltration to remove macromolecular organic substances in the wastewater, the concentrated water contains impurity salt, the concentrated water is dried and then outsourced for treatment, and the dried condensate is fed into the sewage treatment system; (6) The advanced oxidation section, the electrolysis section, and the drying treatment section: the nanofiltration water is subjected to O3 / H2O2 advanced oxidation process for deep treatment, the oxidized effluent is used as brine for an ion-exchange membrane caustic soda system, the brine is compounded to prepare saturated brine, the saturated brine is subjected to electrolysis to produce liquid caustic soda and chlorine gas, and the liquid caustic soda and the chlorine gas are recycled to production or sold as products.

2. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, The treatment process adopts devices including a stripping tower, a rectification tower, an evaporator, a salt dissolving system, a filter press, an acidification system, a nanofiltration membrane system, an advanced oxidation system, an ion-exchange membrane caustic soda system, a clean water tank, a drying treatment system, regulating valves, water pumps, and process pipelines.

3. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, In step (1), the production wastewater is fed into the stripping tower, steam stripping is adopted, organic steam is condensed by a condenser to obtain crude dichloromethane and triethylamine, the stripping condensate is fed into the rectification tower, dichloromethane and triethylamine are separated, and the dichloromethane and the triethylamine are recycled to the production process.

4. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, In step (2), the stripped wastewater is fed into an MVR evaporator, the evaporation condensate is recycled to a circulating cooling water system, the evaporation mother liquor and the crystallized salt are centrifuged, the centrifuged mother liquor is fed into a drying treatment system, and the centrifuged crystallized salt is fed into a salt dissolving system.

5. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, In step (3), the centrifuged crystallized salt is dissolved in pure water to prepare a 10%-15% brine, the brine is stirred to completely dissolve the salt, the brine is fed into a plate-and-frame filter to remove suspended solids in the wastewater, the sludge is fed into a drying treatment system, and the filtrate is fed into an acidification section.

6. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, In step (4), the brine filtrate is acidified by adjusting the pH value to 4.0-5.0 using hydrochloric acid to remove carbonate and bicarbonate ions, and then the pH value is adjusted to 7.0-7.5 using liquid caustic soda.

7. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, In step (5), the acidified effluent is fed into a nanofiltration system, the temperature is controlled at 15-30℃, the operating pressure is 0.2-0.4 MPa, nanofiltration is used to remove macromolecular organic substances in the wastewater, the nanofiltration concentrated water contains impurity salt, the nanofiltration concentrated water is fed into a drying treatment system, and the nanofiltration water is fed into an advanced oxidation system.

8. The polycarbonate production wastewater resourceful treatment process according to claim 1, characterized in that, In the step (6), the nanofiltration fresh water enters the advanced oxidation system, and is treated by the O3 / H2O2 advanced oxidation process, and the oxidized water is used for the brine of the ion-exchange membrane caustic soda system; the ion-exchange membrane caustic soda system is used, the oxidized water is compounded with new salt, saturated brine is prepared, and then electrolysis is carried out, and the produced liquid caustic soda and chlorine gas are used in production or sold as commodities.

9. The polycarbonate production wastewater resourceful treatment process according to any one of claims 1-8, characterized in that, The sludge and mother liquor generated in each process section are outsourced after drying, and the dried condensate enters the sewage treatment system for combined treatment with domestic sewage.

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