Method for purifying wastewater

Abstract

A method for purifying wastewater is provided. The purification method includes: feeding a first mixed material stream in which wastewater containing water, a nitrile monomer, and ammonia is mixed with an acid component into a first tower; recovering the nitrile monomer from the upper discharge material stream from the first tower; feeding a second mixed material stream in which the lower discharge material stream from the first tower is mixed with an alkali component into a second tower; and recovering ammonia from the upper discharge material stream from the second tower and separating the purified wastewater.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0158785, filed on November 17, 2021, the entire contents of which are incorporated herein by reference as part of this specification. Technical Field

[0004] The present invention relates to a method for purifying wastewater, and more particularly, to a method for recovering reusable components from wastewater and reducing the total nitrogen content in the wastewater transported to a wastewater tank in a purification step at the backend of a polymerization reaction using a nitrile-based monomer. Background Art

[0005] Generally, nitrile-based rubber can be obtained by manufacturing a homopolymer or copolymer latex containing units from a nitrile-based monomer using the nitrile-based monomer. Examples of nitrile-based rubber may include acrylonitrile-butadiene copolymer latex manufactured by copolymerizing acrylonitrile and 1,3-butadiene.

[0006] Nitrile-based rubber can be manufactured by emulsion polymerization, and emulsion polymerization may be a method of polymerizing monomers in a solution state using a medium. Emulsion polymerization of nitrile-based rubber can be carried out as follows, for example, using water as a medium, and polymerizing by separately adding a nitrile-based monomer or also adding additional monomers for copolymerization with the nitrile-based monomer, thereby manufacturing a homopolymer or copolymer latex containing units from the nitrile-based monomer.

[0007] After polymerization is completed, the homopolymer or copolymer latex containing units from the nitrile-based monomer is transported to a discharge tank, and unreacted substances and water can be evaporated to the upper part in the discharge tank and transported to a wastewater tank.

[0008] Meanwhile, in the discharge tank, ammonia is added to adjust the pH of the latex, and ammonia can be partially evaporated to the upper part together with water and transported to the wastewater tank. In this case, in the wastewater tank, 2 moles of unreacted nitrile-based monomer and 1 mole of ammonia react to produce a trimer, resulting in a loss of the nitrile-based monomer.

[0009] In addition, the wastewater remaining after recovering the nitrile-based monomer from the wastewater is transported to a wastewater treatment plant. Herein, since the total nitrogen (TN) content in the wastewater transported to the wastewater treatment plant is very high, a large amount of funds should be invested in the wastewater treatment plant to treat the wastewater, and under more stringent environmental regulations, there will be a large loss in the price competitiveness of latex products. Summary of the Invention

[0010] Technical problem

[0011] An object of the present invention is to provide a method that can prevent losses in the recovery of unreacted nitrile monomers in the manufacturing process of a homopolymer or copolymer latex containing units from nitrile monomers, and minimize the total nitrogen content in the wastewater sent to a wastewater treatment plant, so as to solve the problems mentioned in the background art.

[0012] Technical solution

[0013] In a general aspect, a method for purifying wastewater includes: feeding a first mixed material stream in which wastewater containing water, a nitrile monomer, and ammonia is mixed with an acid component into a first tower; recovering the nitrile monomer from the material stream discharged from the upper part of the first tower; feeding a second mixed material stream in which the material stream discharged from the lower part of the first tower is mixed with a base component into a second tower; and recovering ammonia from the material stream discharged from the upper part of the second tower, and separating the purified wastewater.

[0014] Advantageous effects

[0015] According to the method for purifying wastewater of the present invention, in the manufacturing process of a homopolymer or copolymer latex containing units from nitrile monomers, the loss of unreacted nitrile monomers can be minimized, and the nitrile monomer can be recovered and reused, thereby improving cost competitiveness.

[0016] In addition, ammonia can be recovered and reused from the wastewater from which unreacted nitrile monomers have been recovered, and the total nitrogen content in the purified wastewater sent to the wastewater treatment plant is effectively reduced, thereby reducing the input cost in the wastewater treatment plant for wastewater treatment, and under more stringent environmental regulations, the price competitiveness of latex products can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 and Figure 2 are respectively process flow diagrams of the method for purifying wastewater in exemplary embodiments according to the present invention.

[0018] Figure 3 is a process flow diagram of the method for purifying wastewater in a comparative example. DETAILED DESCRIPTION

[0019] The terms and words used in the description and claims of the present invention should not be construed restrictively as having a general or dictionary meaning, but should be interpreted as having a meaning and concept consistent with the technical idea of the present invention based on the principle that the inventors can appropriately define the terms so as to describe their own invention in the best way.

[0020] The term "material stream" in the present invention may refer to the fluid flow in a process, or may refer to the fluid itself flowing in a pipeline. Specifically, the material stream may refer to both the fluid itself and the fluid flow flowing in the pipeline connecting each device. In addition, the fluid may include any one or more components of gas, liquid, and solid.

[0021] Hereinafter, reference will be made to Figure 1 and Figure 2 to describe the present invention in more detail for better understanding of the present invention.

[0022] According to the present invention, a method for purifying wastewater is provided. More specifically, the method for purifying wastewater may include: supplying a first mixed material stream in which wastewater containing water, a nitrile monomer, and ammonia is mixed with an acid component to a first tower 20; recovering the nitrile monomer from the material stream discharged from the upper part of the first tower 20; supplying a second mixed material stream in which the material stream discharged from the lower part of the first tower 20 is mixed with an alkali component to a second tower 30; and recovering ammonia from the material stream discharged from the upper part of the second tower 30, and separating the purified wastewater.

[0023] According to an exemplary embodiment of the present invention, the wastewater may be generated from a manufacturing process of a homopolymer or copolymer latex containing units from a nitrile monomer. Specifically, the manufacturing process of the homopolymer or copolymer latex containing units from a nitrile monomer may include a polymerization step and a purification step.

[0024] The polymerization step may be carried out by emulsion polymerization. In emulsion polymerization, water may be used as a medium, and the polymerization may be carried out by separately adding a nitrile monomer or further adding an additional monomer for copolymerization with the nitrile monomer. For example, the additional monomer may include a conjugated diene monomer.

[0025] The nitrile monomer may include one or more selected from acrylonitrile, methacrylonitrile, fumaronitrile, α-chloronitrile, and α-cyanoethyl acrylonitrile. As a specific example, the nitrile monomer may be acrylonitrile.

[0026] The conjugated diene monomer may include one or more selected from 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and isoprene. As a specific example, the conjugated diene monomer may be 1,3-butadiene.

[0027] The purification step may be a step of separating unreacted substances and water from a homopolymer or copolymer latex containing units from a nitrile monomer after polymerization. Specifically, the homopolymer or copolymer latex containing units from a nitrile monomer after polymerization is transported to a discharge tank, and in the discharge tank, the unreacted substances and water can be evaporated to the upper part and transported to a wastewater tank 10.

[0028] In the discharge tank, ammonia should be added to adjust the pH of the latex. However, during the process of evaporating unreacted substances and water in the discharge tank and transporting them to the wastewater tank 10, a part of ammonia is evaporated together with water and introduced into the wastewater tank 10, such that in the wastewater tank 10, 2 moles of unreacted nitrile monomer react with 1 mole of ammonia to produce a trimer called 3,3 - iminodipropionitrile, resulting in the loss of nitrile monomer.

[0029] In addition, the wastewater remaining after recovering the nitrile monomer from the wastewater tank is transported to a wastewater treatment plant. Since the total nitrogen content in the wastewater transported to the wastewater treatment plant is very high, a large amount of funds should be invested in the wastewater treatment plant to treat the wastewater, and under stricter environmental regulations, the price competitiveness of latex products decreases.

[0030] For this reason, the present invention aims to provide a method for minimizing the loss of unreacted nitrile monomer and the total nitrogen content in wastewater, so as to reduce the cost for wastewater treatment and improve the price competitiveness of latex products.

[0031] According to an exemplary embodiment of the present invention, wastewater containing water, a nitrile monomer, and ammonia can be supplied to the wastewater tank 10 through a wastewater transport pipeline 11. In addition, an acid component can be added to the wastewater tank 10 through an acid component transport pipeline 12. The acid component is not particularly limited. For example, it may include one or more selected from acetic acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, and cyanic acid. As a specific example, the acid component may be acetic acid.

[0032] A first mixed material stream in which the wastewater containing water, a nitrile monomer, and ammonia is mixed with the acid component can be discharged from the wastewater tank 10, and the first mixed material stream can be supplied to a first tower 20.

[0033] The first mixed material stream may be in a state where the wastewater is mixed with the acid component, such that the pH of the wastewater is reduced. For example, the pH of the first mixed material stream may be 1.5 or more, 2.5 or more, or 3.5 or more and 4.5 or less, 5 or less, or 5.5 or less. By adjusting the pH of the first mixed material stream to the above range, ammonia (NH3) in the first mixed material stream is converted into an ammonium salt (NH 4+ ) to prevent the formation of a trimer due to the side reaction between the nitrile monomer and ammonia, thereby reducing the loss of the nitrile monomer.

[0034] According to an exemplary embodiment of the present invention, the first mixed material stream is supplied to the first tower 20, and the nitrile monomer contained in the first mixed material stream can be recovered in the first tower 20, and the remaining components can be supplied to the second tower 30.

[0035] In the first tower 20, the components of the first mixed material stream can be separated by distillation, and the nitrile monomer can be recovered from the upper discharge material stream from the first tower 20. Specifically, the upper discharge material stream from the first tower 20 can be condensed in the condenser 21 and then supplied to the decanter 22. The flare gas is discharged from the decanter 22, and the condensed upper discharge material stream from the first tower 20 can be separated into an aqueous layer and an organic layer. The components of the aqueous layer separated in the decanter 22 can be transported to the wastewater tank 10, and the organic layer components containing the nitrile monomer can be recovered and reused in the polymerization step of the manufacturing process of the homopolymer or copolymer latex containing the unit from the nitrile monomer.

[0036] A part of the lower discharge material stream from the first tower 20 can be heated in the general reboiler 23 and then refluxed to the first tower 20.

[0037] Since the nitrile monomer in the wastewater is recovered in the first tower 20, the total nitrogen content in the wastewater can be reduced. For example, the ratio of the total nitrogen content in the lower discharge material stream from the first tower 20 to the total nitrogen content in the wastewater can be 0.25 or more, 0.3 or more, or 0.35 or more and 0.5 or less or 0.55 or less.

[0038] The operating temperature of the first tower 20 can be 80 °C or more, 90 °C or more, or 95 °C or more and 100 °C or less, 110 °C or less, or 130 °C or less. When the operating temperature of the first tower is higher than 130 °C, the generation of polymers is accelerated by the self-polymerization of acrylonitrile, and thus, fouling may occur in the device, making it impossible to carry out the process operation.

[0039] In addition, the operating pressure of the first tower 20 can be 0.5 bar or more, 0.7 bar or more, or 0.9 bar or more and 1.5 bar or less, 2 bar or less, or 3 bar or less. By controlling the operating conditions of the first tower 20 to the above range, the nitrile monomer can be effectively separated to the upper part.

[0040] According to an exemplary embodiment of the present invention, the lower discharge material stream from the first tower 20 can be supplied to the second tower 30. Specifically, the lower discharge material stream from the first tower can contain the remaining components after recovering the nitrile monomer from the wastewater, such as water and ammonium salts.

[0041] The lower discharge stream from the first column 20 can be mixed with an alkali component to form a second mixed material stream before being supplied to the second column 30, and the second mixed material stream can be supplied to the second column 30.

[0042] In the region where the lower discharge stream from the first column 20 is mixed with the alkali component to form a second mixed material stream, a line mixer 50 can be provided. Specifically, the lower discharge stream from the first column 20 is transported through a line connecting the first column 20 to the second column 30, and an alkali component supply line 40 for transporting the alkali component can be joined at any point on the line connecting the first column 20 to the second column 30. Herein, the line mixer 50 is provided in the region where the line connecting the first column 20 to the second column 30 and the alkali component supply line 40 are joined to form a second mixed material stream. Thus, the lower discharge stream from the first column 20 and the alkali component can be effectively mixed in a short time by forming a vortex, and a mixing device that does not require a separate working space is not needed. In addition, the lower discharge stream from the first column 20 and the alkali component are effectively mixed by the line mixer 50, so that most of the ammonium salts are converted into ammonia before the second mixed material stream is supplied to the second column 30.

[0043] There is no particular limitation on the alkali component. For example, it can include one or more selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, and barium hydroxide. As a specific example, the alkali component can be sodium hydroxide.

[0044] Since the second mixed material stream is mixed with the alkali component from the lower discharge stream of the first column 20, it can be in a state of increased pH. For example, the pH of the second mixed material stream can be 8 or more, 8.5 or more, or 9 or more and 12 or less, 12.5 or less, 13 or less, or 13.5 or less. By adjusting the pH of the second mixed material stream to the above range, ammonium salts (NH4 + ) in the second mixed material stream are converted into ammonia (NH3), and the ammonia can be recovered and reused in the second column 30.

[0045] According to an exemplary embodiment of the present invention, the second mixed material stream can be supplied to a distributor installed at the upper part of the second column 30. In the second column 30, ammonia and water in the second mixed material stream can be separated by distillation. Specifically, in the second column 30, ammonia is recovered from the upper discharge stream, and the purified wastewater can be separated as the lower discharge stream.

[0046] The steam supply unit 33 can be arranged at the lower part of the second tower 30. Specifically, as a means for supplying heat to the second tower 30, steam can be supplied by the steam supply unit 33 arranged in the lower part of the second tower 30 without installing a general reboiler. Therefore, there is no need to install a reboiler at the lower part of the second tower 30, and scaling caused by partial precipitation of salts inside or outside the tubes of the reboiler can be prevented when the reboiler is installed.

[0047] The steam supply unit 33 can include a steam delivery pipe for delivering steam to the second tower 30 and one or more nozzles arranged in the steam delivery pipe and injecting the steam into the second tower 30.

[0048] The nozzle can be formed to inject steam downward. Specifically, the nozzle is installed at the lower part of the steam delivery pipe and can inject steam downward. By directly injecting steam downward inside the second tower 30, the steam can be evenly dispersed and mixed with the wastewater inside the second tower 30 to improve the separation efficiency of ammonia in the second tower 30, thereby reducing the total nitrogen content in the purified wastewater.

[0049] The ratio of the flow rate of the steam added to the steam supply unit 33 to the flow rate of the second mixed material flow supplied to the second tower 30 can be, for example, 0.01 or more, 0.05 or more, or 0.1 or more and 0.3 or less, 1 or less, 2 or less, 5 or less, or 10 or less. Within this range, the volatility of ammonia is adjusted to improve the separation efficiency, thereby reducing the total nitrogen content in the purified wastewater.

[0050] The operating temperature of the second tower 30 can be 80 °C or more, 90 °C or more, 95 °C or more, or 99 °C or more and 100 °C or less, 105 °C or less, 110 °C or less, or 130 °C or less. When the operating temperature of the second tower 30 is higher than 130 °C, the capacity of the heat exchanger required to transport the discharge material flow from the lower part of the second tower 30 to the wastewater treatment plant increases, which is disadvantageous in terms of capital investment cost and operating cost.

[0051] In addition, the operating pressure of the second tower 30 can be 0.5 bar or more, 0.7 bar or more, or 0.9 bar or more and 1.5 bar or less, 2 bar or less, or 3 bar or less. By controlling the operating conditions of the second tower 30 within the above range, the separation efficiency of ammonia can be improved to reduce the total nitrogen content in the purified wastewater.

[0052] The packing height of the second tower can refer to the height of the packing material cluster where gas-liquid contact occurs in the second tower 30, and this packing height can be, for example, 2 m or more, 4 m or more, 6 m or more, or 10 m or more and 15 m or less, 20 m or less, or 25 m or less.

[0053] When the filling height is at least 2 m or more, the effect of reducing the total nitrogen content in the wastewater can be obtained. When the filling height is higher than 25 m, compared with the filling height below 25 m, the difference in the reduction amount of the total nitrogen content is not significant, but the equipment cost for the tower and the tower structure increases accordingly.

[0054] Through the steam injection of the steam supply unit 33, ammonia can volatilize to the upper part of the tower. The volatilized ammonia is discharged as the upper discharge material flow from the second tower 30, and the upper discharge material flow from the second tower 30 can be condensed in the condenser 31 and then supplied to the reflux drum 32.

[0055] The flare gas is discharged to the upper part of the reflux drum 32. A part of the lower discharge material flow containing ammonia is refluxed to the second tower 30, and the remaining part can be recovered and reused for the pH adjustment of the latex. Herein, a part of the lower discharge material flow of the reflux drum 32 is refluxed, thereby increasing the concentration of ammonia in the recovered ammonia. Therefore, the process formula can be easily controlled when reused.

[0056] Through the lower discharge material flow from the second tower 30, the remaining purified wastewater from which the nitrile monomer and ammonia have been separated can be discharged, and it can be transported to the wastewater treatment plant. Herein, the ratio of the total nitrogen content in the lower discharge material flow from the second tower 30 to the total nitrogen content in the wastewater can be 0.01 or more, 0.05 or more, or 0.08 or more and 0.11 or less, 0.13 or less, or 0.15 or less. Specifically, when the wastewater generated in the manufacturing process of the homopolymer or copolymer latex containing the unit of the nitrile monomer is purified by the wastewater purification method according to the present invention, while reducing the loss of the nitrile monomer in the wastewater, recovery and reuse are feasible, ammonia can be recovered and reused, and the total nitrogen content in the wastewater when the wastewater is transported to the wastewater treatment plant can be effectively reduced.

[0057] According to an exemplary embodiment of the present invention, in the wastewater purification method, if necessary, equipment such as distillation towers, condensers, reboilers, valves, pumps, separators, and mixers can be further installed.

[0058] In the above, the wastewater purification method according to the present invention has been described and illustrated, but the description and illustration are for understanding only the core composition of the present invention, and processes and devices that have not been separately described and illustrated in addition to the processes and devices described and illustrated above can also be appropriately applied and used to implement the wastewater purification method according to the present invention.

[0059] Hereinafter, the present invention will be described in more detail by way of examples. However, to illustrate the present invention, the following examples are provided, and it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0060] Example

[0061] Example 1

[0062] According to Figure 1 the process flow chart shown in, the wastewater discharged from the manufacturing process of acrylonitrile-butadiene copolymer latex is purified.

[0063] Specifically, wastewater containing water, acrylonitrile monomer and ammonia and having a pH of 8 is supplied to a wastewater tank 10 through a wastewater transfer pipeline 11, acetic acid is added to the wastewater tank 10 through an acid component transfer pipeline 12, and the first mixed material stream discharged from the wastewater tank 10 is supplied to a first tower 20. At this time, it is confirmed that the total nitrogen content of the wastewater is 6000 ppm, the pH of the first mixed material stream is 5.5, and the total nitrogen content is measured using a commercial total nitrogen (TN) measuring device.

[0064] The upper discharge material stream from the first tower 20 is condensed in a condenser 21 and supplied to a decanter 22, the flare gas is discharged from the decanter 22, separated into a water layer and an organic layer, the acrylonitrile monomer is recovered and reused from the organic layer components, and the water layer components are transferred to the wastewater tank 10. In addition, a part of the lower discharge material stream from the first tower 20 is heated by a reboiler 23 and refluxed, and the remaining part is mixed with sodium hydroxide conveyed through an alkali component transfer pipeline 40 to form a second mixed material stream, and then supplied to a second tower 30. At this time, the operating temperature of the first tower 20 is 95 °C, and the operating pressure is adjusted to 1 bar. In addition, it is confirmed that the total nitrogen content of the lower discharge material stream from the first tower 20 is 3,000 ppm, and the pH of the second mixed material stream is 10.

[0065] In the second tower 30, when the ratio of the flow rate of the steam supplied through the steam supply unit 33 formed to jet steam upward to the flow rate of the second mixed material stream supplied to the second tower 30 is adjusted to 0.1, the components of the second mixed material stream are separated simultaneously. The upper discharge material stream from the second tower 30 is condensed in the condenser 31 and then supplied to the reflux drum 32. The flare gas is discharged from the reflux drum 32. A part of the lower discharge material stream is refluxed, and ammonia is recovered from the remaining part and reused. In addition, the lower discharge material stream from the second tower 30 is conveyed as purified wastewater to the wastewater treatment plant. At this time, the operating temperature of the second tower 30 is 99 °C, its operating pressure is adjusted to 1 bar, and the packing height is adjusted to 10 m. In addition, the total nitrogen content in the purified wastewater conveyed to the wastewater treatment plant is determined to be 500 ppm. In addition, the acrylonitrile recovery rate calculated from the ratio of the content of the acrylonitrile monomer recovered in the first tower 20 to the content of the acrylonitrile monomer contained in the wastewater tank supplied to the wastewater tank 10 is confirmed to be 99.9%.

[0066] Example 2

[0067] According to Figure 2 the process flow chart shown in, the wastewater discharged from the manufacturing process of acrylonitrile-butadiene copolymer latex is purified.

[0068] Specifically, except that a pipeline mixer 50 is used when mixing the lower discharge material stream from the first tower 20 with sodium hydroxide, the process is carried out in the same manner as in Example 1. In this case, the total nitrogen content in the purified wastewater conveyed to the wastewater treatment plant is confirmed to be 300 ppm. In addition, the acrylonitrile recovery rate is confirmed to be 99.9%.

[0069] Therefore, by installing the pipeline mixer 50 in the mixing of the lower discharge material stream from the first tower 20 with sodium hydroxide, the conversion rate of ammonium salt in the lower discharge material stream from the first tower 20 to ammonia is increased, so as to increase the amount of ammonia recovered in the second tower 30. Therefore, it is confirmed that the total nitrogen content in the purified wastewater conveyed to the wastewater treatment plant is reduced compared with Example 1.

[0070] Example 3

[0071] Except that the steam supply unit 33 is formed so that the steam jets downward in the second tower 30, the process is carried out in the same manner as in Example 1. In this case, the total nitrogen content in the purified wastewater conveyed to the wastewater treatment plant is confirmed to be 300 ppm. In addition, the acrylonitrile recovery rate is confirmed to be 99.9%.

[0072] Therefore, when steam is jetted downward through the steam supply unit 33 in the second tower 30, it is confirmed that the dispersion and mixing efficiency of the wastewater in the second tower 30 is improved compared with that in Example 1, thereby showing the effect of reducing the total nitrogen content in the purified wastewater.

[0073] Example 4

[0074] According to Figure 2 the process flow chart shown in

[0075] purify the wastewater discharged from the manufacturing process of acrylonitrile-butadiene copolymer latex. Specifically, except that a pipeline mixer 50 is used when the material flow discharged from the lower part of the first tower 20 is mixed with sodium hydroxide, and the steam supply unit 33 is formed such that steam is jetted downward in the second tower 30, the process is carried out in the same manner as in Example 1. In this case, the total nitrogen content in the purified wastewater delivered to the wastewater treatment plant is confirmed to be 100 ppm. In addition, the recovery rate of acrylonitrile is confirmed to be 99.9%.

[0076] Therefore, by installing the pipeline mixer 50, the total nitrogen content in the purified wastewater is reduced, and by jetting steam downward through the steam supply unit 33, the separation, dispersion and mixing efficiency of the wastewater in the second tower 30 is improved, and the pH of the second mixed material flow is made consistent by the pipeline mixer to improve the conversion efficiency of ammonium salt to ammonia, so as to more effectively reduce the remaining nitrogen content in the purified wastewater.

[0077] Example 5

[0078] The process is carried out in the same manner as in Example 4 except that the pH of the first mixed material flow is controlled to be 5.5. In this case, the recovery rate of acrylonitrile is confirmed to be 99.9%.

[0079] Example 6

[0080] The process is carried out in the same manner as in Example 4 except that the pH of the first mixed material flow is controlled to be 6. In this case, the recovery rate of acrylonitrile is confirmed to be 90%.

[0081] Example 7

[0082] The process is carried out in the same manner as in Example 4 except that the pH of the first mixed material flow is controlled to be 6.5. In this case, the recovery rate of acrylonitrile is confirmed to be 60%.

[0083] Example 8

[0084] The process is carried out in the same manner as in Example 4 except that the pH of the first mixed material flow is controlled to be 7. In this case, the recovery rate of acrylonitrile is confirmed to be 30%.

[0085] Referring to Examples 4 to 8, it was confirmed that the recovery rate of acrylonitrile was high when the pH of the first mixed material flow supplied to the first tower 20 was controlled to be 5.5 or less, as compared with the case when the pH of the first mixed material flow supplied to the first tower 20 was greater than 5.5.

[0086] Example 9

[0087] The process was carried out in the same manner as in Example 4, except that the pH of the second mixed material flow at the rear end of the pipeline mixer was controlled to be 8. In this case, the total nitrogen content in the purified wastewater was confirmed to be 200 ppm.

[0088] Example 10

[0089] The process was carried out in the same manner as in Example 4, except that the pH of the second mixed material flow at the rear end of the pipeline mixer was controlled to be 9. In this case, the total nitrogen content in the purified wastewater was confirmed to be 150 ppm.

[0090] Example 11

[0091] The process was carried out in the same manner as in Example 4, except that the pH of the second mixed material flow at the rear end of the pipeline mixer was controlled to be 11. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0092] Example 12

[0093] The process was carried out in the same manner as in Example 4, except that the pH of the second mixed material flow at the rear end of the pipeline mixer was controlled to be 12. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0094] Referring to Example 4 and Examples 9 to 12, it was confirmed that when the pH value of the second mixed material flow at the rear end of the pipeline mixer was 10 or more, the efficiency of removing nitrogen from the wastewater was high.

[0095] Example 13

[0096] The process was carried out in the same manner as in Example 4, except that the packing height of the second tower 30 was controlled to be 3 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 500 ppm.

[0097] Example 14

[0098] The process was carried out in the same manner as in Example 4, except that the packing height of the second tower 30 was controlled to be 5 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 200 ppm.

[0099] Example 15

[0100] The process was carried out in the same manner as in Example 4, except that the packed height of the second tower 30 was controlled to be 15 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0101] Example 16

[0102] The process was carried out in the same manner as in Example 4, except that the packed height of the second tower 30 was controlled to be 20 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0103] Referring to Example 4 and Examples 13 to 16, it was confirmed that when the packed height of the second tower 30 was controlled within 10 m to 20 m, the efficiency of removing nitrogen from the wastewater was high.

[0104] Example 17

[0105] The process was carried out in the same manner as in Example 4, except that the ratio of the flow rate of the supplied steam to the flow rate of the second mixed material flow supplied to the second tower 30 was controlled to be 0.03. In this case, the total nitrogen content in the purified wastewater was confirmed to be 1000 ppm.

[0106] Example 18

[0107] The process was carried out in the same manner as in Example 4, except that the ratio of the flow rate of the supplied steam to the flow rate of the second mixed material flow supplied to the second tower 30 was controlled to be 0.05. In this case, the total nitrogen content in the purified wastewater was confirmed to be 300 ppm.

[0108] Example 19

[0109] The process was carried out in the same manner as in Example 4, except that the ratio of the flow rate of the supplied steam to the flow rate of the second mixed material flow supplied to the second tower 30 was controlled to be 0.2. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0110] Example 20

[0111] The process was carried out in the same manner as in Example 4, except that the ratio of the flow rate of the supplied steam to the flow rate of the second mixed material flow supplied to the second tower 30 was controlled to be 0.3. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0112] Referring to Example 4 and Examples 17 to 20, it was confirmed that when the ratio of the flow rate of the supplied steam to the flow rate of the second mixed material flow supplied to the second tower 30 was controlled within 0.1 to 0.3, the efficiency of removing nitrogen from the wastewater was high.

[0113] Example 21

[0114] The process was carried out in the same manner as in Example 4, except that the operating temperature of the first column 20 was adjusted to 80°C. In this case, the recovery rate of acrylonitrile was confirmed to be 70%.

[0115] Example 22

[0116] The process was carried out in the same manner as in Example 4, except that the operating temperature of the first column 20 was adjusted to 85°C. In this case, the recovery rate of acrylonitrile was confirmed to be 90%.

[0117] Example 23

[0118] The process was carried out in the same manner as in Example 4, except that the operating temperature of the first column 20 was adjusted to 90°C. In this case, the recovery rate of acrylonitrile was confirmed to be 98%.

[0119] Example 24

[0120] The process was carried out in the same manner as in Example 4, except that the operating temperature of the first column 20 was adjusted to 100°C. In this case, the recovery rate of acrylonitrile was confirmed to be 99.9%.

[0121] Referring to Example 4 and Examples 21 to 24, it was confirmed that when the operating temperature of the first column 20 was 90°C or higher, the recovery rate of acrylonitrile was high.

[0122] Example 25

[0123] The process was carried out in the same manner as in Example 4, except that the operating temperature of the second column 30 was adjusted to 80°C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 1000 ppm.

[0124] Example 26

[0125] The process was carried out in the same manner as in Example 4, except that the operating temperature of the second column 30 was adjusted to 85°C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 500 ppm.

[0126] Example 27

[0127] The process was carried out in the same manner as in Example 4, except that the operating temperature of the second column 30 was adjusted to 90°C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 300 ppm.

[0128] Example 28

[0129] The process was carried out in the same manner as in Example 4, except that the operating temperature of the second column 30 was adjusted to 105°C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

[0130] Referring to Example 4 and Examples 25 to 28, it was confirmed that when the operating temperature of the second column 30 was controlled above 95°C, the efficiency of nitrogen removal from the wastewater was high.

[0131] Comparative Example

[0132] Comparative Example 1

[0133] According to Figure 3 the process flow chart shown in, the wastewater discharged from the manufacturing process of acrylonitrile-butadiene copolymer latex was purified.

[0134] Specifically, the wastewater containing water, acrylonitrile monomer and ammonia and having a pH of 8 was supplied to the wastewater tank 10 through the wastewater transfer pipeline 11, and the wastewater was discharged from the wastewater tank 10 and supplied to the first column 20. At this time, the total nitrogen content of the wastewater was confirmed to be 6,000 ppm.

[0135] The upper discharge material flow from the first column 20 was condensed in the condenser 21 and supplied to the decanter 22. The flare gas was discharged from the decanter 22, separated into a water layer and an organic layer. The acrylonitrile monomer was recovered and reused from the organic layer components, and the water layer components were transported to the wastewater tank 10. In addition, a part of the lower discharge material flow from the first column 20 was heated using the reboiler 23 and then refluxed, and the remaining part was transported to the wastewater treatment plant as purified wastewater. At this time, the operating temperature of the first column 20 was 95°C, and its operating pressure was adjusted to 1 bar. In addition, the total nitrogen content in the purified wastewater transported to the wastewater treatment plant was confirmed to be 3,000 ppm. In addition, the recovery rate of acrylonitrile was confirmed to be 30%.

Claims

1. A method for purifying wastewater, comprising: feeding a first mixed material stream in which wastewater containing water, a nitrile monomer, and ammonia is mixed with an acid component into a first tower; recovering the nitrile monomer from the material stream discharged from the upper part of the first tower; feeding a second mixed material stream in which the material stream discharged from the lower part of the first tower is mixed with an alkali component into a second tower; and recovering ammonia from the material stream discharged from the upper part of the second tower and separating the purified wastewater, wherein the pH of the first mixed material stream is 1.5 to 5.

5.

2. The purification method of wastewater according to claim 1, wherein, The acid component includes one or more selected from acetic acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, and cyanic acid.

3. The wastewater purification method according to claim 1, wherein, The pH of the second mixed material stream is 8 to 13.

5.

4. The wastewater purification method according to claim 1, wherein, The alkali component includes one or more selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, and barium hydroxide.

5. The purification method of wastewater according to claim 1, wherein, including a pipeline mixer, which is arranged in the area where the material stream discharged from the lower part of the first tower is mixed with the alkali component to form the second mixed material stream.

6. The purification method of wastewater according to claim 1, wherein, The second tower includes a steam supply unit arranged at the lower part.

7. The purification method of wastewater according to claim 6, wherein, The steam supply unit includes a steam delivery pipe for delivering steam to the second tower and one or more nozzles arranged in the steam delivery pipe and spraying steam into the second tower, and the nozzles are formed to spray steam downward.

8. The purification method of wastewater according to claim 6, wherein, The ratio of the flow rate of the steam added to the steam supply unit to the flow rate of the second mixed material stream supplied to the second tower is 0.01 to 10.

9. The purification method of wastewater according to claim 1, wherein, The operating temperature of the first tower is 80°C to 130°C, and the operating pressure of the first tower is 0.5 bar to 3 bar.

10. The wastewater purification method according to claim 1, wherein, The operating temperature of the second tower is 80°C to 130°C, and the operating pressure of the second tower is 0.5 bar to 3 bar.

11. The wastewater purification method according to claim 1, wherein, The filling height of the second tower is 2 m to 25 m.

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