Pretreatment process of nitrile latex wastewater

Abstract

The present invention belongs to the technical field of chemical wastewater treatment, and specifically relates to a pretreatment process for nitrile-containing latex wastewater, comprising the following steps: (1) homogenization adjustment: adjusting the pH value of the wastewater to above 10 to obtain alkaline wastewater; (2) ultrasonic treatment: hydrolyzing acrylonitrile in the alkaline wastewater into acrylamide using ultrasonic waves to obtain nitrile-free wastewater; (3) polymerization reaction and latex coagulation flotation: adjusting the pH value of the nitrile-free wastewater to 6-8, adding an initiator to cause acrylamide to undergo polymerization reaction to obtain polyacrylamide, adding a coagulant, and performing solid-liquid separation to obtain clarified wastewater; (4) ultraviolet light catalytic oxidation treatment: controlling the pH value of the clarified wastewater to 2-6, adding an iron salt and an oxidant, and then using ultraviolet light catalysis. The pretreatment process for nitrile-containing latex wastewater of the present invention can completely remove pollutants, improve wastewater quality, reduce the amount of hazardous waste generated, and significantly improve the biodegradability of wastewater. It is simple to operate, has low operating costs, and can be used for industrial treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical wastewater treatment, and particularly relates to a pretreatment process for nitrile latex wastewater. Background Art

[0002] Nitrile-butadiene rubber, abbreviated as NBR, is a copolymer made by emulsion polymerization of butadiene and acrylonitrile, followed by coagulation, water washing, and dehydration drying. NBR has excellent oil resistance, heat resistance, and mechanical properties, and is widely used in the automotive, aerospace, oil extraction, chemical, textile, wire and cable, printing, and food packaging industries. In the NBR synthesis process, butadiene and acrylonitrile are used as raw materials, and various additives such as initiators, emulsifiers, electrolytes, regulators, dispersants, and terminators are added. Therefore, the production wastewater contains incompletely recovered butadiene and acrylonitrile monomers and various additives, resulting in complex water quality and a COD content of approximately 1300 mg / L. The oligomers are high in content, highly toxic, and difficult to biodegrade, making them difficult to treat. If they are directly fed into the biochemical treatment system without pretreatment, they will have a serious impact on the sewage field and even cause environmental pollution.

[0003] Currently, there are few reports on the treatment of nitrile latex wastewater generated during NBR production. The existing process involves flotation to remove suspended particles from the NBR wastewater before mixing it with other wastewaters. Some technologies also target specific components in the wastewater.

[0004] Chinese patent CN104556538A discloses a method for treating low-concentration acrylonitrile: under polymerization conditions, nitrile-containing latex wastewater is mixed with a polymerization initiator to induce a polymerization reaction between acrylonitrile and oligomers. The wastewater is then subjected to magnetic flocculation and finally biochemical treatment using an activated sludge process. The resulting wastewater is essentially free of acrylonitrile residue, with a COD value of less than 50 mg / L and an ammonia nitrogen content of less than 5 mg / L. However, practical applications have revealed that this method suffers from incomplete sodium persulfate coagulation of polyacrylonitrile, with residual acrylonitrile remaining at a concentration of 8 to 19 mg / L throughout the entire treatment process. This not only affects the stable operation of the biochemical system but also causes secondary environmental pollution.

[0005] Chinese patent CN104556539B discloses a treatment method: NBR wastewater is mixed with an excess of sulfite to convert acrylonitrile in the wastewater into the non-volatile sodium cyanoethylsulfonate. H₂O₂ and ferrous sulfate solution are then added to the water for Fenton reagent advanced oxidation treatment. After solid-liquid separation, the supernatant is mixed with activated sludge for biochemical treatment. This method reduces the acrylonitrile content in the water, achieving a COD value of less than 50 mg / L and an ammonia nitrogen content of less than 5 mg / L. Practical applications have shown that while this method fails to detect acrylonitrile in the water, the biotoxic -CN is still present. The B / C ratio for various concentrations of sodium cyanoethylsulfonate ranges from 0.1 to 0.23, significantly reducing the wastewater's treatment difficulty and biodegradability. Furthermore, Fenton reagent treatment of the wastewater produces a large amount of iron sludge, causing secondary environmental pollution.

[0006] In the article "Technology and Equipment Improvement for Nitrile Rubber Wastewater Treatment," Zhang Jieliang, published in the September 2012 issue of Gansu Science and Technology, noted that a combined "coagulation-sedimentation-microelectrolysis-catalytic oxidation-neutralization" process was used to treat the wastewater from the latex coagulation unit of the nitrile rubber plant at the Lanzhou Petrochemical Company's rubber plant. The treatment achieved a 70% or higher removal rate for pulverized powder, 30% or higher for COD, and 80% or higher for SS. The core of this process is the Fe / C microelectrolysis-Fenton combination. However, due to the varying water composition and production processes of nitrile rubber, the presence of solid rubber residue, latex, and suspended impurities in the water, as well as foam entrainment during aeration, can lead to clogging of the microelectrolysis reactor packing, affecting the long-term operation of the unit. This process has certain limitations in its widespread application.

[0007] In summary, most of the existing nitrile latex wastewater treatment processes and technologies have disadvantages such as complex processes, poor effluent quality, harsh and difficult to control reaction conditions in the treatment units, etc., which result in low wastewater treatment efficiency, high investment costs, and difficulty in industrialization. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a pretreatment process for nitrile latex wastewater, which can completely remove pollutants, improve the water quality of wastewater, reduce the amount of hazardous waste generated, and significantly improve the biodegradability of wastewater. The process is simple to operate, has low operating costs, and can be used for industrial treatment.

[0009] The pretreatment process of nitrile-containing latex wastewater of the present invention comprises the following steps:

[0010] (1) Homogenization adjustment: Adjust the pH value of the wastewater to above 10 to obtain alkaline wastewater.

[0011] An alkaline substance is added to the nitrile latex wastewater to adjust the pH to be greater than 10, preferably 10.5-12.5. The wastewater enters a homogenization tank for homogenization adjustment to prepare for the alkaline hydrolysis of acrylonitrile. The size of the homogenization tank is determined according to the amount of water to be treated, and the hydraulic retention time is 2-6 hours, preferably 3-5 hours. The added alkaline substance can be sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.

[0012] (2) Ultrasonic treatment: Use ultrasonic waves to hydrolyze acrylonitrile in alkaline wastewater into acrylamide to obtain nitrile-free wastewater.

[0013] Preferably, the ultrasonic treatment process parameters are: frequency of 10-100 kHz, more preferably 20-80 kHz; power of 10-500 W, more preferably 50-450 W; time of 5-60 min, more preferably 10-50 min; temperature of 50-60°C.

[0014] Ultrasonic waves are high-frequency mechanical waves characterized by short wavelength, concentrated energy, and linear propagation. Ultrasonic treatment technology, which integrates advanced oxidation, pyrolysis, and supercritical oxidation techniques, can transform organic matter in water into CO2, H2O, inorganic ions, or less toxic and more biodegradable organic matter. This makes it significantly superior in treating difficult-to-biodegrade organic pollutants.

[0015] In the present invention, cavitation bubbles are generated by ultrasonic irradiation, and ·OH and ·H free radicals are generated by the decomposition of water vapor entering the cavitation bubbles to attack residual acrylonitrile, causing it to hydrolyze in an alkaline environment to produce acrylamide, thereby achieving the purpose of eliminating acrylonitrile and preventing organic matter containing -CN from generating secondary pollution in the subsequent advanced oxidation stage and generating highly toxic hydrocyanic acid.

[0016] In addition, the latex particles suspended in the water vibrate together with the rubber production wastewater containing acrylonitrile in the ultrasonic field and produce a "displacement effect". Due to the existence of the "displacement effect", the latex particles continue to move toward the antinode or node of the ultrasonic wave, and the latex particles collide and adhere to each other, increasing their volume and weight, and finally separating and floating, thereby improving the removal effect of COD and turbidity in sewage.

[0017] Ultrasonic treatment can be achieved using an ultrasonic reactor. This is a pipe-type device equipped with internal baffles to extend the hydraulic retention time of the ultrasonic process section. An ultrasonic generator and transducer are installed on the outer wall of the pipe. Online acrylonitrile concentration monitors are installed at the inlet and outlet of the ultrasonic device. When the outlet monitoring value shows that the acrylonitrile concentration has dropped to 0, it indicates that the acrylonitrile in the water has been completely hydrolyzed to acrylamide, and the wastewater enters the next process for further treatment. If the monitoring shows that the wastewater contains acrylonitrile, it returns to the inlet of the ultrasonic device for further hydrolysis to ensure that the acrylonitrile is completely hydrolyzed to acrylamide.

[0018] (3) Polymerization reaction and latex coagulation flotation: Adjust the pH value of the nitrile-free wastewater to 6~8, add an initiator to make acrylamide undergo polymerization reaction to obtain polyacrylamide, add a coagulant, and obtain clarified wastewater after solid-liquid separation.

[0019] Preferably, the initiator is one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and azobisisobutyl ether hydrochloride; the amount of the initiator added is 50-500 mg / L, preferably 100-450 mg / L;

[0020] The polymerization temperature is 40-70° C., preferably 45-65° C.; the polymerization time is 1-4 h, preferably 1.5-3.5 h.

[0021] Preferably, the amount of coagulant added is 50-300 mg / L, preferably 60-250 mg / L.

[0022] The coagulant is a conventional water treatment coagulant, preferably one or more of polyaluminium chloride, polyferric sulfate and polyaluminium ferric sulfate.

[0023] After acrylonitrile in nitrile-containing latex wastewater is hydrolyzed to form acrylamide, it enters a latex coagulation and flotation unit, where acid is added to adjust the pH to a neutral pH of 6-8. Simultaneously, an initiator is added to initiate a free radical chain polymerization reaction using compounds such as persulfate, causing the acrylamide to polymerize into polyacrylamide, or PAM for short. PAM is a linear organic macromolecular polymer that can adsorb suspended particles in water, acting as a bridge between particles, causing fine particles to form relatively large flocs and accelerating the rate of precipitation. Due to its excellent flocculation effect, polyacrylamide is widely used as a flocculant in water treatment and sewage treatment. In the present invention, during the process of acrylamide polymerization to form PAM, the latex particles gradually grow larger, encapsulating the colloid particles and suspended impurities in the water. After the addition of a coagulant, the latex particles form large flocs, which are then separated by dissolved air flotation to achieve solid-liquid separation.

[0024] (4) Ultraviolet photocatalytic oxidation treatment: Control the pH value of clarified wastewater to 2~6, add iron salt and oxidant, and then use ultraviolet photocatalysis to obtain pretreated wastewater.

[0025] Preferably, the iron salt is one of a ferric salt or a divalent iron salt, and more preferably, the iron salt is one or more of ferric sulfate, ferric chloride, ferrous sulfate, and ferrous chloride; the amount of the iron salt added is 20-200 mg / L based on the mass of the iron element, and more preferably 25-150 mg / L.

[0026] Preferably, the oxidant is hydrogen peroxide, and the amount of hydrogen peroxide added is 500-10000 mg / L, which can be adjusted according to the quality of the incoming water, and is more preferably 1000-8000 mg / L.

[0027] Preferably, the ultraviolet photocatalytic oxidation time is 0.5 to 6 hours, more preferably 40 minutes to 5.5 hours.

[0028] The most potent and effective oxidant for recalcitrant organic matter is the hydroxyl radical •OH. The optimal method for generating •OH is the Fenton reagent, which involves the use of hydrogen peroxide under acidic conditions, catalyzed by ferrous iron, to generate •OH. While the Fenton reagent is highly effective in removing COD from synthetic rubber wastewater, it also produces a large amount of iron oxide precipitate, leading to high treatment costs. Therefore, to improve the efficiency of the Fenton reaction and significantly reduce sludge production, photocatalytic Fenton reaction is an effective and cost-effective method.

[0029] More preferably, unlike the conventional Fenton reaction which uses divalent iron salt as catalyst, the photo-promoted Fenton reaction in the present invention uses trivalent iron salt as catalyst. Under acidic conditions, with hydrogen peroxide as oxidant, ultraviolet light efficiently catalyzes the decomposition of hydrogen peroxide to produce •OH. Fe 3+ Under ultraviolet light conditions, it can be hydrolyzed to generate hydroxyl radical Fe(OH) under acidic conditions. 2+ , Fe(OH) 2+ Under the action of ultraviolet light, it can be converted into Fe 2+ , and simultaneously produces •OH. Fe 2+ The OH produced by these reactions reacts with H₂O₂ to form a Fenton reaction. This reaction can then react with organic matter to reduce COD, lower the biotoxicity of pollutants, and improve the biodegradability of wastewater. The use of ultraviolet light in this process significantly reduces the amount of iron ions used, thereby reducing the amount of iron sludge produced and lowering the cost of hazardous waste disposal.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The acrylonitrile contained in the wastewater is converted into acrylamide with good biodegradability through ultrasonic treatment in an alkaline environment, which triggers the polymerization of acrylamide to form polyacrylamide. Polyacrylamide is used as a common water treatment flocculant and is discharged with the scum in the latex coagulation flotation unit, thereby improving the sewage purification effect and reducing the operating cost.

[0032] 2. The introduction of ultrasonic treatment units can completely convert residual acrylonitrile in the wastewater into acrylamide, and make residual latex, tiny coke residues suspended in the water and other impurities vibrate and collide under the action of the sound field, increasing their volume and facilitating solid-liquid separation, which is conducive to converting them into flocs in the subsequent treatment and more thorough discharge in the dissolved air flotation treatment;

[0033] 3. It can eliminate toxic nitrile substances and macromolecular organic polymers that are difficult to biodegrade. The pollutants are removed completely without secondary pollution, avoiding the generation of highly toxic HCN under acidic conditions in the advanced oxidation stage of subsequent treatment. The COD removal rate is greater than 30%, and the B / C value is greater than 0.4. It significantly improves the biodegradability of wastewater and creates good conditions for subsequent domestic treatment.

[0034] 4. It reduces the amount of hazardous waste generated, is easy to operate, and can be used for industrial management. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 , a schematic diagram of a process flow for pretreatment of nitrile-containing latex wastewater according to the present invention;

[0036] In the figure: 1. Homogenizing tank; 2. Ultrasonic reactor; 3. PAM polymerization reactor; 4. Dissolved air flotation tank; 5. High-efficiency sedimentation tank; 6. Ultraviolet photocatalytic device; 7. Ultrasonic generator; 8. Automatic control system; 8-1. First valve; 8-2. Second valve; 9. Acrylonitrile concentration detector. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments.

[0038] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation for the convenience of expression and do not represent a sequential relationship.

[0039] like Figure 1 As shown, the pretreatment process of nitrile latex wastewater according to the present invention is as follows, and the specific process parameters are shown in Examples 1 to 5.

[0040] (1) Homogenization adjustment: pH adjustment reagent is added to the wastewater containing nitrile latex to adjust the pH value to 10.5~12.5. The wastewater enters the homogenization tank 1 for homogenization adjustment. The hydraulic retention time is 2~6h to obtain alkaline wastewater, which is prepared for the alkaline hydrolysis of acrylonitrile.

[0041] (2) Ultrasonic treatment: The homogenized alkaline wastewater enters the ultrasonic reactor 2. A baffle is installed inside the first ultrasonic reactor 2 to extend the wastewater's residence time in the pipe. When the alkaline wastewater fills the pipe, the ultrasonic generator 7 is turned on. The ultrasonic transducer on the pipe wall transmits ultrasonic energy to the alkaline wastewater, promoting the hydrolysis of acrylonitrile to acrylamide in the alkaline environment. The ultrasonic frequency is 10-100kHz, the power is 10-500W, the reaction time is 5-60min, and the reaction temperature is 50-60°C. At the same time, the latex suspended in the water vibrates and collides under the action of the acoustic field, and the particle size gradually increases.

[0042] The wastewater after ultrasonic treatment is analyzed for acrylonitrile concentration by an acrylonitrile concentration detector 9. If the measured result is 0 mg / L, the acrylonitrile is completely hydrolyzed, and the signal is returned to the automatic control system 8. The control system opens valve 8-1, allowing the wastewater after acrylonitrile removal to enter the PAM polymerization reactor 3. If the monitored acrylonitrile concentration is greater than 0 mg / L, valve 8-2 is opened, and the wastewater returns to the inlet of the ultrasonic reactor for further ultrasonic treatment, and finally nitrile-free wastewater is obtained.

[0043] (3) Polymerization reaction and latex coagulation flotation: Nitrile-free wastewater is discharged into the PAM polymerization reactor 3. H2SO4 is added through the pipeline mixer during pipeline transportation to adjust the pH to neutral, about 6~8. The initiator is added in an amount of 50~500 mg / L; the polymerization temperature is controlled at 40~70℃ and the polymerization time is 1~4h to allow the hydrolyzed acrylamide to undergo polymerization reaction to generate polyacrylamide. During the reaction, the latex particles and impurities in the water are wrapped, the latex is destabilized, and the solid-liquid separation is facilitated to obtain flotation feed water.

[0044] The flotation water enters the mixing zone, where a coagulant is added at a rate of 50-300 mg / L. The water then enters the dissolved air flotation tank 4, where the polyacrylamide generated by polymerization is used as a flocculant to cause the latex and impurities suspended in the water to float to form scum, thereby achieving solid-liquid separation.

[0045] (4) Ultraviolet photocatalytic oxidation treatment: To ensure the treatment effect of the ultraviolet photocatalytic oxidation unit, as a safeguard measure, the effluent from the flotation tank enters the high-efficiency sedimentation tank 5 to further remove suspended matter and impurities, and the supernatant enters the ultraviolet photocatalytic device 6, where the pH is controlled at 2-6, and iron salt is added. The amount of iron salt added is 20-200 mg / L based on the mass of the iron element;

[0046] Hydrogen peroxide was added as an oxidant with a concentration of 27.5% and an addition amount of 500~10000 mg / L. A homogeneous oxidation reaction was used to deeply oxidize the refractory organic matter in the water. At the same time, an ultraviolet photocatalytic device 6 was used for catalysis with an ultraviolet light intensity of 15 kW·m -3 The time of ultraviolet catalytic oxidation is 0.5 to 6 hours. The process parameters and water quality parameters of each step in Examples 1 to 5 are shown in Tables 1 to 5.

[0047] Example 1

[0048] The indicators of a certain nitrile and latex wastewater are: COD is 2111mg / L, acrylonitrile content is 500mg / L, turbidity is 15NTU, and 150m 3 / h flow rate into Figure 1 The process flow shown is:

[0049] Table 1 Process and water quality parameters of Example 1

[0050]

[0051] Example 2

[0052] The indicators of a certain nitrile and latex wastewater are: COD 3200 mg / L, acrylonitrile content 1000 mg / L, turbidity 20 NTU, and 150 m 3 / h flow rate into Figure 1 The process flow shown is:

[0053] Table 2 Process and water quality parameters of Example 2

[0054]

[0055] Example 3

[0056] The indicators of a certain nitrile and latex wastewater are: COD is 1270 mg / L, acrylonitrile content is 250 mg / L, turbidity is 13 NTU, and 100 m 3 / h flow rate into Figure 1 The process flow shown is:

[0057] Table 3 Process and water quality parameters of Example 3

[0058]

[0059] Example 4

[0060] The indicators of a certain nitrile and latex wastewater are: COD is 1680 mg / L, acrylonitrile content is 400 mg / L, turbidity is 13 NTU, and 100 m 3 / h flow rate into Figure 1 The process flow shown is:

[0061] Table 4 Process and water quality parameters of Example 4

[0062]

[0063] Example 5

[0064] The indicators of a certain nitrile and latex wastewater are: COD 2830mg / L, acrylonitrile content 700mg / L, turbidity 17NTU, and 150m 3 / h flow rate into Figure 1 The process flow shown is:

[0065] Table 5 Process and water quality parameters of Example 5

[0066]

[0067] It can be seen from the water quality indicators after pretreatment in Tables 1 to 5 that the COD removal rate can reach up to 83% and the B / C value can reach above 0.4, which proves that the pretreatment process for nitrile latex wastewater containing the present invention can effectively reduce biological toxicity and improve biodegradability. After ultraviolet photocatalytic oxidation treatment, the difficult-to-degrade organic matter in the water is decomposed into small molecular organic matter that is easily biodegradable, creating good conditions for subsequent biochemical treatment and facilitating the stable operation of the sewage treatment plant.

Claims

1. A pretreatment process for nitrile latex wastewater, characterized in that, The following steps are involved: (1) Homogenization adjustment: adjust the pH value of the wastewater to above 10 to obtain alkaline wastewater; (2) Ultrasonic treatment: Use ultrasonic waves to hydrolyze acrylonitrile in alkaline wastewater into acrylamide to obtain nitrile-free wastewater; (3) Polymerization reaction and latex coagulation flotation: adjust the pH value of the nitrile-free wastewater to 6-8, add an initiator to polymerize acrylamide to obtain polyacrylamide, add a coagulant, and obtain clarified wastewater after solid-liquid separation; (4) Ultraviolet photocatalytic oxidation treatment: Control the pH value of clarified wastewater to 2~6, add iron salt and oxidant, and then use ultraviolet photocatalysis to complete the wastewater pretreatment process.

2. The pretreatment process for nitrile latex wastewater according to claim 1, wherein Ultrasonic treatment process parameters: frequency is 10~100kHz, power is 10~500W, time is 5~60min, and temperature is 50~60℃.

3. The pretreatment process for nitrile latex wastewater according to claim 1, wherein The initiator is one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and azobisisobutyl ether hydrochloride, and the amount of the initiator added is 50-500 mg / L.

4. The pretreatment process for nitrile latex wastewater according to claim 1, wherein The polymerization temperature is 40~70℃, and the polymerization time is 1~4h.

5. The pretreatment process for nitrile latex wastewater according to claim 1, wherein The amount of coagulant added is 50~300mg / L.

6. The pretreatment process for nitrile latex wastewater according to claim 1, wherein The iron salt is one of a trivalent iron salt or a divalent iron salt, and the amount of the iron salt added is 20-200 mg / L based on the mass of the iron element.

7. The pretreatment process for nitrile latex wastewater according to claim 6, wherein The iron salt is one or more of ferric sulfate and ferric chloride.

8. The pretreatment process for nitrile latex wastewater according to claim 6, wherein The iron salt is one or more of ferrous sulfate and ferrous chloride.

9. The pretreatment process for nitrile latex wastewater according to claim 1, wherein The oxidant is hydrogen peroxide, and the amount of hydrogen peroxide added is 500~10000mg / L.

10. The pretreatment process for nitrile latex wastewater according to claim 1, wherein The ultraviolet photocatalytic oxidation time is 0.5~6h.

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