A treatment method and device for waste liquid in polyvinyl alcohol production process and application thereof

Abstract

The application discloses a treatment method of waste liquid in a polyvinyl alcohol production process, which comprises the following steps: carrying out sedimentation treatment on the waste liquid, and mixing and filtering the waste liquid after the sedimentation treatment with liquid containing methanol and methyl acetate discharged in the polyvinyl alcohol production process; and further comprising the steps that the waste liquid after the mixing and filtering treatment is subjected to sedimentation overflow treatment, the waste liquid is subjected to the sedimentation overflow treatment for more than 6.5 hours, and the flow rate of the waste liquid is less than 1.0 m / s. The scheme reduces the treatment cost of the waste liquid in the polyvinyl alcohol production process, and further avoids the problem of heat exchanger blockage caused by waste liquid recovery.

Description

Technical Field

[0001] This invention relates to a method, apparatus, and application for treating waste liquid generated during the production of polyvinyl alcohol. Background Technology

[0002] Polyvinyl alcohol (PVA) is a water-soluble polymer with excellent film-forming, emulsifying, adhesive, and spinning properties. PVA possesses both hydrophilic and hydrophobic functional groups, thus exhibiting surface activity and making it suitable as a protective colloid in polymer emulsification and suspension polymerization reactions.

[0003] The production process of PVA mainly consists of polymerization, alcoholysis, and recycling. Using vinyl acetate as raw material and methanol as solvent, polyvinyl acetate-methanol is produced by solution polymerization. It is then mixed with sodium hydroxide-methanol solution and transported on a belt while solidifying due to PVA precipitation. At the end of the belt, PVA and mother liquor become one to form an elastic, thick plate-like substance. Subsequent equipment is needed to crush, press, and dry the plate-like substance to finally obtain the PVA product.

[0004] The alcoholysis process involves feeding plate-shaped PVA from a conveyor belt into a first pulverizer to initially pulverize it into strips, then into a second pulverizer for final pulverization into granules. The wet PVA discharged from the second pulverizer's screen enters a press (the pressing speed is adjusted to control the degree of pressing). The pressed PVA is then sent to a dryer for drying. During the dryer's operation, condensate containing methanol and methyl acetate evaporates. During the press's operation, a large amount of liquid is separated from the PVA. The condensate discharged from the dryer and the liquid discharged from the press together constitute the waste liquid generated during polyvinyl alcohol production. This waste liquid is then recycled after sedimentation treatment in a settling tank. In actual use, it was found that with prolonged use of the waste liquid, the heat exchanger used for waste liquid recycling is prone to clogging, leading to a significant reduction in heat exchange efficiency and severely impacting production efficiency. Furthermore, subsequent processing of the recycled waste liquid for discharge as process water proved quite difficult.

[0005] Chinese patent document CN118267969A discloses a composite adsorbent, its preparation method, and a wastewater treatment process. The wastewater treatment process includes the following steps: S1, subjecting wastewater to a Fenton reaction after initial sedimentation; S2, subjecting the Fenton reaction-treated wastewater to adsorption precipitation treatment, wherein at least a portion of the adsorbent in the adsorption precipitation treatment is the aforementioned composite adsorbent and / or the composite adsorbent prepared by the aforementioned method; S3, purifying the wastewater after the adsorption precipitation treatment. The raw material components of the adsorbent include: Fenton iron sludge, raw coal, waste adsorbent, and binder. The advantages of this existing technical solution are as follows: The composite adsorbent uses Fenton iron sludge and waste adsorbent as the main raw materials, combined with raw coal and binder. The iron oxides in the iron sludge enable the composite adsorbent to have a rich pore structure and good adsorption performance. In the treatment of high CODcr wastewater or high-salt + high-CODcr wastewater, it can achieve a high CODcr removal rate and improve the treatment efficiency of wastewater. Among them, Fenton iron sludge and waste adsorbent are solid waste generated by the wastewater treatment system. The preparation and application of the composite adsorbent can not only realize the comprehensive recycling of solid waste generated in the wastewater treatment process and avoid resource waste, but also reduce manufacturing costs, thereby reducing the operating costs of high CODcr wastewater or high-salt + high-CODcr wastewater treatment.

[0006] Chinese patent document CN219031959U discloses a treatment system for high CODcr and / or high salinity wastewater. The treatment process is as follows: wastewater is filtered through a screen and then enters a pre-conditioning tank for water quality equalization. It then enters a primary sedimentation tank for flocculation and sedimentation before being fed into a Fenton reaction unit for Fenton reaction treatment. The Fenton reaction treatment includes: adjusting the pH of the wastewater to acidic in a pH adjustment tank; then, the wastewater flows from the inlet of a ferrous salt mixing tank through a channel formed by a first and second mixing guide plate to its outlet, ensuring that the wastewater mixes with ferrous salt for at least 10 minutes; and then... The wastewater enters the oxidation reaction tank through the inlet of the first oxidation tank. After being stirred and mixed by the oxidation agitator in the first oxidation tank, it flows through the channel formed by the first and second oxidation guide plates to the outlet of the first oxidation tank and then enters the inlet of the second oxidation tank. After being stirred and mixed by the oxidation agitator in the second oxidation tank, it flows through the channel formed by the first and second oxidation guide plates to the outlet of the second oxidation tank, so that the wastewater undergoes an oxidation reaction with the oxidant for no less than 40 minutes. Finally, the wastewater enters the neutralization tank and the degassing tank from the outlet of the second oxidation tank for neutralization and degassing in sequence. The advantages of this existing technical solution are as follows: Wastewater is treated using a pretreatment unit, a Fenton reaction unit, and an adsorption sedimentation unit, making the wastewater suitable for biochemical treatment or evaporation purification in the purification unit; the iron precipitate generated by the Fenton reaction unit undergoes self-flocculation in the primary sedimentation tank to form iron sludge, and the iron sludge is recycled to the primary and secondary sedimentation tanks as a sedimentation tank additive via the iron sludge conveying unit. This achieves comprehensive recycling of the Fenton iron sludge generated by the treatment system itself, and reduces the dosage of flocculants / coagulants in the primary and secondary sedimentation tanks, thereby reducing the operating cost of the treatment system for wastewater treatment.

[0007] Chinese patent document CN207845534U discloses a device for recovering alcoholysis waste liquid powder. The specific operation of this device is as follows: An alcoholysis waste liquid is generated by a centrifugal dehydrator and enters an alcoholysis waste liquid pipeline. An alkaline methanol solution is pumped into the second input end of the alcoholysis waste liquid pipeline. The addition of the alkaline methanol solution causes the degree of alcoholysis of the incompletely alcoholyzed powder in the alcoholysis waste liquid to shift towards complete alcoholysis. This increases the number of -OH groups on the polyvinyl alcohol chains and enhances the effect of hydrogen bonding. The association of hydrogen bonds causes the polyvinyl alcohol powder particles to gradually increase in size, thus settling in a sedimentation tank. After passing through the second output end at the bottom of the sedimentation tank, the powder is pumped into a filter and then transported to a tank collection area for recovery. The supernatant from the settled waste liquid is sent to a waste liquid collection tank and finally transported to the tank collection area for recovery as well. The effect of this existing technical solution is as follows: by adding a certain concentration of alkaline methanol solution to the alcoholysis waste liquid, the addition of alkaline methanol will cause the degree of alcoholysis of the incompletely alcoholyzed powder in the waste liquid to change towards complete alcoholysis. In this way, the number of -OH on the polyvinyl alcohol chain will increase and the effect of hydrogen bonding will be enhanced. The association of hydrogen bonds will cause the polyvinyl alcohol powder particles to gradually become larger and thus settle down in the sedimentation tank, thereby effectively solving the problem of powder clogging the pipe.

[0008] In the aforementioned existing technologies, either the waste liquid is treated by adding composite adsorbents, flocculants, or coagulants, but this method significantly increases the cost and creates new solid waste treatment problems; or the wastewater is treated by adding alkaline methanol solution, but this method also significantly increases the cost, has unsatisfactory treatment results, and still easily causes heat exchanger blockage during waste liquid recycling, leading to a decrease in heat exchange efficiency and seriously affecting production efficiency. Summary of the Invention

[0009] The purpose of this invention is to provide a method and apparatus for treating waste liquid in the production process of polyvinyl alcohol, so as to solve the problems of high treatment cost and easy clogging of heat exchangers during waste liquid recovery in the prior art.

[0010] To achieve the above objectives, the basic solution of the present invention provides a method for treating waste liquid in the production process of polyvinyl alcohol, including precipitating the waste liquid, mixing and filtering the precipitated waste liquid with a liquid containing methanol and methyl acetate discharged during the production process of polyvinyl alcohol; further including settling and overflowing the mixed and filtered waste liquid, wherein the settling and overflowing time of the waste liquid is greater than 6.5 hours and the flow rate of the waste liquid is less than 1.0 m / s.

[0011] The beneficial effects of this basic scheme are as follows: after the waste liquid in the polyvinyl alcohol production process is treated using this scheme, the waste liquid is less likely to cause heat exchanger blockage in the subsequent recycling process, which significantly improves production efficiency; at the same time, when the waste liquid is processed after recycling, the COD (chemical oxygen demand) is reduced, which is conducive to the implementation of the process.

[0012] Preferably, in order to further improve the effect of the waste liquid not causing heat exchanger blockage in subsequent recycling processes, the sedimentation and overflow treatment of the waste liquid is carried out in the original liquid storage tank.

[0013] Preferably, in order to further improve the effect of the waste liquid not causing heat exchanger blockage in subsequent recycling processes, the sedimentation and overflow treatment of the waste liquid is carried out in at least two consecutive raw liquid storage tanks.

[0014] Preferably, in order to further improve the effect of preventing the waste liquid from clogging the heat exchanger in the subsequent recycling process, an overflow pipe is used between adjacent raw liquid storage tanks for overflow.

[0015] Preferably, in order to further improve the effect of the waste liquid not causing heat exchanger blockage in subsequent recycling processes, the waste liquid is treated by gradually reducing the volume of the raw liquid storage tank along the sedimentation overflow path.

[0016] Preferably, in order to further improve the effect of the waste liquid not causing heat exchanger blockage in subsequent recycling processes, the liquid containing methanol and methyl acetate is the condensate evaporated from the dryer during the production of polyvinyl alcohol.

[0017] Secondly, the present invention provides a treatment apparatus for treating waste liquid in the polyvinyl alcohol production process according to the present invention, comprising a raw liquid storage tank for settling and overflow treatment of the waste liquid, wherein the inlet end of the raw liquid storage tank is connected to the waste liquid discharge end of the polyvinyl alcohol production process. Using this treatment apparatus facilitates waste liquid treatment and improves the waste liquid treatment effect.

[0018] Preferably, in order to further improve the treatment effect of waste liquid, at least two raw liquid storage tanks are provided, and adjacent raw liquid storage tanks are connected by an overflow pipe.

[0019] Preferably, in order to further improve the treatment effect of waste liquid, the volume of all the raw liquid storage tanks is set to gradually decrease along the sedimentation overflow path.

[0020] Thirdly, the present invention provides the application of the processing device described herein in the treatment of waste liquid during the production of polyvinyl alcohol.

[0021] The present invention has the following beneficial effects: 1. Compared with existing technologies, when using this solution to treat waste liquid in the production process of polyvinyl alcohol, no additional materials are needed to prevent the treated waste liquid from clogging the heat exchanger, thereby reducing treatment costs. It also ensures heat exchange efficiency and improves production efficiency by preventing the treated waste liquid from clogging the heat exchanger.

[0022] 2. The waste liquid treated using this method has a lower COD, which helps to reduce the difficulty of subsequent process treatment. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a waste liquid treatment device in the production process of polyvinyl alcohol according to the present invention. Detailed Implementation

[0024] The following detailed description illustrates the specific implementation method: The reference numerals in the accompanying drawings include: sedimentation tank 1, filter 2, first raw liquid storage tank 3, overflow pipe 4, and second raw liquid storage tank 5.

[0025] Example 1: A method for treating waste liquid in the production process of polyvinyl alcohol (PVA), comprising precipitation treatment of the waste liquid. In this example, the waste liquid in the PVA production process is mainly the waste liquid discharged from the press during the PVA production process. The waste liquid is subjected to precipitation treatment, specifically, the waste liquid is discharged into a waste liquid sedimentation tank for sedimentation.

[0026] The treatment method also includes mixing and filtering the waste liquid after precipitation treatment with the liquid containing methanol and methyl acetate discharged during the polyvinyl alcohol production process. In this embodiment, the waste liquid after precipitation treatment overflows from the waste liquid sedimentation tank. The liquid containing methanol and methyl acetate is the condensate evaporated from the dryer during the polyvinyl alcohol production process. The waste liquid overflowing from the waste liquid sedimentation tank and the condensate evaporated from the dryer are mixed together and then filtered in a filter.

[0027] The treatment method also includes settling and overflowing the waste liquid after mixing and filtration. The settling and overflowing time of the waste liquid is greater than 6.5 hours, and the flow rate of the waste liquid is less than 1.0 m / s. Specifically, a raw liquid storage tank is used to settling and overflow the waste liquid after mixing and filtration. In this embodiment, it is preferable to use at least two continuously arranged raw liquid storage tanks for settling and overflowing the waste liquid. An overflow pipe is used between adjacent raw liquid storage tanks for overflow, and the height of the overflow pipe is sufficient to allow the raw liquid storage tank to hold 80% of the material. In this embodiment, it is more preferable to use a method in which the volume of the raw liquid storage tank gradually decreases along the settling and overflowing path to settling and overflow the waste liquid. In this embodiment, the two raw liquid storage tanks are raw liquid storage tank A and raw liquid storage tank B. The volume of raw liquid storage tank A is 235 m³, and the volume of raw liquid storage tank B is 153 m³. The overflow method is from raw liquid storage tank A to raw liquid storage tank B. The residence time of waste liquid in raw liquid storage tank A is 5.88 hours, the residence time of waste liquid in raw liquid storage tank B is 3.82 hours, the total settling and overflow time of waste liquid is 9.70 hours, and the flow velocity of waste liquid is 0.885 m / s.

[0028] After running for 8000 hours, observe the bottom accumulation of the raw liquid storage tank: there is a large amount of material accumulation at the bottom of the raw liquid storage tank, with less material accumulation only at the feed port and discharge port, and the material accumulation height in other parts is basically the same.

[0029] Example 2: A method for treating waste liquid in the production process of polyvinyl alcohol (PVA), comprising precipitation treatment of the waste liquid. In this example, the waste liquid in the PVA production process is mainly the waste liquid discharged from the press during the PVA production process. The waste liquid is subjected to precipitation treatment, specifically, the waste liquid is discharged into a waste liquid sedimentation tank for sedimentation.

[0030] The treatment method also includes mixing and filtering the waste liquid after precipitation treatment with the liquid containing methanol and methyl acetate discharged during the polyvinyl alcohol production process. In this embodiment, the waste liquid after precipitation treatment overflows from the waste liquid sedimentation tank. The liquid containing methanol and methyl acetate is the condensate evaporated from the dryer during the polyvinyl alcohol production process. The waste liquid overflowing from the waste liquid sedimentation tank and the condensate evaporated from the dryer are mixed together and then filtered in a filter.

[0031] The treatment method also includes settling and overflowing the waste liquid after mixing and filtration. The settling and overflowing time of the waste liquid is greater than 6.5 hours, and the flow rate of the waste liquid is less than 1.0 m / s. Specifically, a raw liquid storage tank is used to settling and overflow the waste liquid after mixing and filtration. In this embodiment, it is preferable to use at least two continuously arranged raw liquid storage tanks for settling and overflowing the waste liquid. An overflow pipe is used between adjacent raw liquid storage tanks for overflow, and the height of the overflow pipe is sufficient to allow the raw liquid storage tank to hold 80% of the material. In this embodiment, it is more preferable to use a method in which the volume of the raw liquid storage tank gradually decreases along the settling and overflowing path to settling and overflow the waste liquid. In this embodiment, the two raw liquid storage tanks are raw liquid storage tank C and raw liquid storage tank D. The volume of raw liquid storage tank C is 155 m³, and the volume of raw liquid storage tank D is 118 m³. The overflow method is from raw liquid storage tank C to raw liquid storage tank D. The residence time of waste liquid in raw liquid storage tank C is 3.88 hours, the residence time of waste liquid in raw liquid storage tank D is 2.94 hours, the total settling and overflow time of waste liquid is 6.82 hours, and the flow velocity of waste liquid is 0.829 m / s.

[0032] After running for 8000 hours, observe the bottom accumulation of the raw liquid storage tank: there is a large amount of material accumulation at the bottom of the raw liquid storage tank, with less material accumulation only at the feed port and discharge port, and the material accumulation height in other parts is basically the same.

[0033] Comparative Example 1: A method for treating waste liquid in the production process of polyvinyl alcohol (PVA), comprising precipitation treatment of the waste liquid. In this embodiment, the waste liquid in the PVA production process is mainly the waste liquid discharged from the press during the PVA production process. The waste liquid is subjected to precipitation treatment, specifically, the waste liquid is discharged into a waste liquid sedimentation tank for sedimentation.

[0034] The treatment method also includes mixing and filtering the waste liquid after precipitation treatment with the liquid containing methanol and methyl acetate discharged during the polyvinyl alcohol production process. In this embodiment, the waste liquid after precipitation treatment overflows from the waste liquid sedimentation tank. The liquid containing methanol and methyl acetate is the condensate evaporated from the dryer during the polyvinyl alcohol production process. The waste liquid overflowing from the waste liquid sedimentation tank and the condensate evaporated from the dryer are mixed together and then filtered in a filter.

[0035] The treatment method also includes settling and overflowing the waste liquid after mixing and filtration. The settling and overflowing time is less than 6.5 hours, and the flow rate of the waste liquid is greater than 1.0 m / s. Specifically, a raw liquid storage tank is used to settling and overflow the waste liquid after mixing and filtration. In this embodiment, it is preferable to use at least two continuously arranged raw liquid storage tanks for settling and overflowing the waste liquid. An overflow pipe is used between adjacent raw liquid storage tanks for overflow, and the height of the overflow pipe is sufficient to allow the raw liquid storage tank to hold 80% of the material. In this embodiment, it is more preferable to use a method in which the volume of the raw liquid storage tank gradually decreases along the settling and overflowing path to settling and overflow the waste liquid. In this embodiment, the two raw liquid storage tanks are raw liquid storage tank E and raw liquid storage tank F. The volume of raw liquid storage tank E is 300m³, and the volume of raw liquid storage tank F is 160m³. The overflow method is from raw liquid storage tank E to raw liquid storage tank F. The residence time of waste liquid in raw liquid storage tank E is 3.84 hours, the residence time of waste liquid in raw liquid storage tank F is 2.05 hours, the total settling and overflow time of waste liquid is 5.89 hours, and the flow velocity of waste liquid is 1.224m / s.

[0036] After running for 8000 hours, observe the bottom accumulation in the raw liquid storage tank: there is basically no material accumulation at the bottom center of the raw liquid storage tank, and the material mainly accumulates at the bottom of the raw liquid storage tank near the wall.

[0037] Example 3: Figure 1 As shown, a treatment apparatus for treating waste liquid in the production process of polyvinyl alcohol according to the present invention includes a sedimentation tank 1 for sedimentation treatment of the waste liquid; and a filter 2 for filtration treatment of the waste liquid, the inlet end of the filter 2 being connected to the outlet of the sedimentation tank 1. The treatment apparatus also includes a raw liquid storage tank for settling and overflow treatment of the waste liquid, the inlet end of the raw liquid storage tank being connected to the waste liquid discharge end of the polyvinyl alcohol production process. In this embodiment, the inlet end of the raw liquid storage tank is connected to the liquid outlet of the filter 2. At least two raw liquid storage tanks are provided, and adjacent raw liquid storage tanks are connected by an overflow pipe 4. In this embodiment, two raw liquid storage tanks are provided, namely a first raw liquid storage tank 3 and a second raw liquid storage tank 5, and the two raw liquid storage tanks are connected by an overflow pipe 4. The height of the overflow pipe 4 is sufficient to ensure that the raw liquid storage tank can hold 80% of the material. In this embodiment, the volume of all raw liquid storage tanks gradually decreases along the settling and overflow path. In this embodiment, the volume of the first raw liquid storage tank 3 is greater than the volume of the second raw liquid storage tank 5.

[0038] Example 4: Application of the treatment device in the treatment of waste liquid during the production of polyvinyl alcohol.

[0039] Example 1, Example 2, and Comparative Example 1 all involved treating waste liquid from the same polyvinyl alcohol production process. After 8000 hours of operation, the accumulation of material at the bottom of the raw material storage tank was observed. It was found that a large amount of material was separated in Example 1 and Example 2, while less material was separated in Comparative Example 1. In the subsequent recycling of waste liquid, the heat exchanger blockage caused by the waste liquid treated in Example 1 and Example 2 was significantly less than that caused by the waste liquid treated in Comparative Example 1.

[0040] Compared with existing technologies, this solution for treating wastewater from polyvinyl alcohol production eliminates the need for additional materials, allowing for the separation and precipitation of large amounts of solids in the wastewater. This reduces treatment costs and prevents heat exchanger blockage, ensuring heat exchange efficiency and ultimately improving production efficiency. Furthermore, the wastewater treated with this solution exhibits lower COD, reducing the complexity of subsequent processing steps.

[0041] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics in the solutions is not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for treating waste liquid in the production process of polyvinyl alcohol, comprising precipitation treatment of the waste liquid, characterized in that: The waste liquid after precipitation treatment is mixed and filtered with the liquid containing methanol and methyl acetate discharged during the production of polyvinyl alcohol; the waste liquid after mixed filtration treatment is also subjected to sedimentation and overflow treatment, wherein the sedimentation and overflow time of the waste liquid is greater than 6.5 hours and the flow rate of the waste liquid is less than 1.0 m / s.

2. The method for treating waste liquid in the production process of polyvinyl alcohol according to claim 1, characterized in that: The sedimentation and overflow treatment of the waste liquid is carried out in the original liquid storage tank.

3. The method for treating waste liquid in the production process of polyvinyl alcohol according to claim 2, characterized in that: The sedimentation and overflow treatment of the waste liquid is carried out in at least two consecutive raw liquid storage tanks.

4. The method for treating waste liquid in the production process of polyvinyl alcohol according to claim 3, characterized in that: Overflow pipes are used to overflow between adjacent raw material storage tanks.

5. The method for treating waste liquid in the production process of polyvinyl alcohol according to claim 4, characterized in that: Waste liquid is treated by gradually reducing the volume of the raw liquid storage tank along the sedimentation overflow path.

6. The method for treating waste liquid in the production process of polyvinyl alcohol according to claim 5, characterized in that: The liquid containing methanol and methyl acetate is the condensate evaporated from the dryer during the production of polyvinyl alcohol.

7. A treatment apparatus for treating waste liquid in the polyvinyl alcohol production process according to any one of claims 1 to 6, characterized in that: It includes a raw liquid storage tank for settling and overflow treatment of waste liquid, wherein the inlet end of the raw liquid storage tank is connected to the waste liquid discharge end of the polyvinyl alcohol production process.

8. The processing apparatus according to claim 7, characterized in that: At least two raw liquid storage tanks are provided, and adjacent raw liquid storage tanks are connected by an overflow pipe.

9. The processing apparatus according to claim 8, characterized in that: The volume of all the aforementioned raw material storage tanks is set to gradually decrease along the sedimentation overflow path.

10. The application of the treatment apparatus according to any one of claims 7-9 in the treatment of waste liquid during the production of polyvinyl alcohol.

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