Patent ID: 12215042

DETAILED DESCRIPTION

The terms and words used in the description and claims of the present invention are not to be construed limitedly as having general or dictionary meanings but are to be construed as having meanings and concepts meeting the technical ideas of the present invention, based on a principle that the inventors are able to appropriately define the concepts of terms in order to describe their own inventions in the best mode.

The term “stream” in the present disclosure may refer to a fluid flow in a process, or may refer to a fluid itself flowing in a pipe. Specifically, the stream may refer to both a fluid itself flowing in a pipe connecting each device and a fluid flow. In addition, the fluid may include any one or more components of gas, liquid, and solid.

Hereinafter, the present disclosure will be described in more detail with reference to theFIGS.1and2, for better understanding of the present disclosure.

According to the present disclosure, a wastewater purification method is provided. More specifically, the wastewater purification method may include: supplying a first mixed stream, in which an acid component and wastewater including water, a nitrile-based monomer, and ammonia are mixed, to a first column20; recovering the nitrile-based monomer from an upper discharge stream from the first column20; supplying a second mixed stream, in which a lower discharge stream from the first column20and a base component are mixed, to a second column30; and recovering the ammonia from an upper discharge stream from the second column30and separating purified wastewater.

According to an exemplary embodiment of the present invention, the wastewater may be produced from a manufacturing process of a homopolymer or copolymer latex including a nitrile-based monomer-derived unit. Specifically, the manufacturing process of a homopolymer or copolymer latex including a nitrile-based monomer-derived unit may include a polymerization step and a purification step.

The polymerization step may be performed by emulsion polymerization. In the emulsion polymerization, water may be used as a medium, and polymerization may be performed by adding a nitrile-based monomer alone or further adding an additional monomer for copolymerization with the nitrile-based monomer. For example, the additional monomer may include a conjugated diene-based monomer.

The nitrile-based monomer may include one or more selected from the group consisting of acrylonitrile, methacrylonitrile, fumaronitrile, α-chloronitrile, and α-cyanoethyl acrylonitrile. As a specific example, the nitrile-based monomer may be acrylonitrile.

The conjugated diene-based monomer may include one or more selected from the group consisting of 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-based monomer may be 1,3-butadiene.

The purification step may be a step of separating an unreacted material and water from the homopolymer or copolymer latex including the nitrile-based monomer-derived unit after the polymerization is completed. Specifically, the homopolymer or copolymer latex including the nitrile-based monomer-derived unit after the polymerization is completed is transferred to a blowdown tank, and in the blowdown tank, the unreacted material and water may be vaporized to the upper portion and transferred to a wastewater tank10.

In the blowdown tank, ammonia should be added for adjusting the pH of latex. However, in the process of vaporizing the unreacted material and water and transferring them to the wastewater tank10in the blowdown tank, a part of ammonia is vaporized with water and introduced to the wastewater tank10. Thus in the wastewater tank10, 2 mol of an unreacted nitrile-based monomer and 1 mol of ammonia react to produce a trimer referred to as 3,3-iminodipropionitrile, resulting in a loss of the nitrile-based monomer.

In addition, remaining wastewater after recovering the nitrile-based monomer from the wastewater tank is transferred to a wastewater treatment plant. Since a total nitrogen content in the wastewater transferred to the wastewater treatment plant is very high, a lot of money should be invested in the wastewater treatment plant for treating the wastewater, and in the midst of stricter environmental regulations, the price competitiveness of a latex product is decreased.

For this, the present disclosure was intended to provide a method for minimizing the loss of an unreacted nitrile-based monomer and a total nitrogen content in wastewater to reduce costs for a wastewater treatment and improve the price competitiveness of a latex product.

According to an exemplary embodiment of the present invention, the wastewater tank10may be supplied with wastewater including water, a nitrile-based monomer, and ammonia through a wastewater transfer line11. In addition, an acid component may be added to the wastewater tank10through an acid component transfer line12. The acid component is not particularly limited, and for example, may include one or more selected from the group consisting of acetic acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, and cyanic acid. As a specific example, the acid component may be acetic acid.

From the wastewater tank10, a first mixed stream, in which the acid component and the wastewater including water, a nitrile-based monomer, and ammonia are mixed, may be discharged, and the first mixed stream may be supplied to a first column20.

The first mixed stream may be in a state in which the wastewater is mixed with the acid component so that the pH of the wastewater is lowered. For example, the pH of the first mixed 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 stream to the above range, ammonia (NH3) in the first mixed stream is converted into an ammonium salt (NH4+) to prevent formation of a trimer due to a side reaction of the nitrile-based monomer and ammonia, thereby decreasing the loss of the nitrile-based monomer.

According to an exemplary embodiment of the present invention, the first mixed stream is supplied to the first column20, the nitrile-based monomer included in the first mixed stream may be recovered in the first column20, and the remaining components may be supplied to a second column30.

In the first column20, the components of the first mixed stream are separated by distillation, and the nitrile-based monomer may be recovered from an upper discharge stream from the first column20. Specifically, the upper discharge stream from the first column20may be condensed in a condenser21and then supplied to a decanter22. From the decanter22, flare gas is discharged, and the condensed upper discharge stream from the first column20may be separated into a water layer and an organic layer. The water layer components separated in the decanter22may be transferred to the wastewater tank10, and the organic layer components including the nitrile-based monomer may be recovered and reused in a polymerization step of a manufacturing process of a homopolymer or copolymer latex including the nitrile-based monomer-derived unit.

A part of the lower discharge stream from the first column20may be heated in a common reboiler23and then refluxed to the first column20.

Since the nitrile-based monomer in the wastewater is recovered in the first column20, the total nitrogen content in the wastewater may be decreased. For example, a ratio of a total nitrogen content in the lower discharge stream from the first column20to a total nitrogen content in the wastewater may be 0.25 or more, 0.3 or more, or 0.35 or more and 0.5 or less or 0.55 or less.

An operating temperature of the first column20may be 80° C. or higher, 90° C. or higher, or 95° C. or higher and 100° C. or lower, 110° C. or lower, or 130° C. or lower. When the operating temperature of the first column is higher than 130° C., polymer production is accelerated by self-polymerization of acrylonitrile, and thus, fouling in a device may be caused to make process operation impossible.

In addition, an operating pressure of the first column20may 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 column20to the above ranges, the nitrile-based monomer may be effectively separated to the upper portion.

According to an exemplary embodiment of the present invention, the lower discharge stream from the first column20may be supplied to the second column30. Specifically, the lower discharge stream from the first column may include the remaining components after the nitrile-based monomer is recovered from the wastewater, for example, water and an ammonium salt.

The lower discharge stream from the first column20may be mixed with a base component before being supplied to the second column30to form a second mixed stream, and the second mixed stream may be supplied to the second column30.

Referring now toFIG.2, in an area in which the lower discharge stream from the first column20and the base component are mixed to form the second mixed stream, a line mixer50may be provided. Specifically, the lower discharge stream from the first column20is transferred through a line which connects the first column20to the second column30, and a base component transfer line40which transfers the base component may be joined at an arbitrary point of a line connecting the first column20to the second column30. Here, the line mixer50is provided in an area in which the line connecting the first column20to the second column30and the base component transfer line40are joined to form the second mixed stream, whereby the lower discharge stream from the first column20and the base component may be effectively mixed in a short time by vortex formation, and a mixing device occupying a separate work space is not required. In addition, the lower discharge stream from the first column20and the base component are effectively mixed by the line mixer50, thereby converting most of the ammonium salt into ammonia before the second mixed stream is supplied to the second column30.

The base component is not particularly limited, and for example, may include one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, and barium hydroxide. As a specific example, the base component may be sodium hydroxide.

The second mixed stream may be in a state of having an increased pH since the lower discharge stream from the first column20is mixed with the base component. For example, the pH of the second mixed stream may 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 stream to the above range, an ammonium salt (NH4+) in the second mixed stream is converted into ammonia (NH3), and the ammonia may be recovered in the second column30and reused.

According to an exemplary embodiment of the present invention, the second mixed stream may be supplied to a dispenser installed in the upper portion of the second column30. In the second column30, ammonia and water in the second mixed stream may be separated by distillation. Specifically, ammonia is recovered from an upper discharge stream, and purified wastewater may be separated as a lower discharge stream, in the second column30.

A steam supply unit33may be provided in a lower portion of the second column30. Specifically, steam may be supplied by the steam supply unit33provided in a lower portion of the second column30, without installing a common reboiler, as a means for supplying heat to the second column30. Thus, it is not necessary to install a reboiler in the lower portion of the second column30and fouling, which occurs by partial precipitation of salts in or outside a pipe of the reboiler when the reboiler is installed, may be prevented.

The steam supply unit33may include a steam transfer pipe which transfers steam to the second column30and one or more spray nozzles, each of which is provided in the steam transfer pipe and sprays steam into the second column30.

Each of the one or more spray nozzles may be configured to spray steam downwards. Specifically, the spray nozzles are each installed in a lower portion of the steam transfer pipe and may each spray steam downwards. By directly spraying steam downwards inside the second column30, the steam may be evenly dispersed in and mixed with wastewater inside the second column30to improve the separation efficiency of ammonia in the second column30to lower the total nitrogen content in the purified wastewater.

A ratio of a flow rate of steam added to the steam supply unit33to a flow rate of the second mixed stream supplied to the second column30may 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 the range, a volatilization degree of ammonia is adjusted to increase separation efficiency, thereby lowering the total nitrogen content in the purified wastewater.

An operating temperature of the second column30may be 80° C. or higher, 90° C. or higher, 95° C. or higher, or 99° C. or higher and 100° C. or lower, 105° C. or lower, 110° C. or lower, or 130° C. or lower. When the operating temperature of the second column30is higher than 130° C., the capacity of a heat exchanger required to transfer the lower discharge stream from the second column30to the wastewater treatment plant is increased, which is unfavorable in terms of facility investment costs and operating costs.

In addition, an operating pressure of the second column30may 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 column30to the above range, the separation efficiency of ammonia may be increased to lower the total nitrogen content in the purified wastewater.

A packing height of the second column may refer to a height of a packing material cluster where a gas-liquid contact occurs in the second column30. The packing height may be, for example, 2 m or higher, 4 m or higher, 6 m or higher, or 10 m or higher and 15 m or less, 20 m or less, or 25 m or less.

When the packing height is at least 2 m or higher, an effect of reducing the total nitrogen content in wastewater may be obtained. When the packing height is higher than 25 m, a difference in the total nitrogen content reduction amount is not large as compared with the packing height of 25 m or lower, but equipment costs for columns and column structures therefor are increased.

By steam spraying through the steam supply unit33, ammonia may be volatilized to the upper portion in the column. The volatilized ammonia is discharged as the upper discharge stream from the second column30, and the upper discharge stream from the second column30may be condensed in a condenser31and then supplied to a reflux tank32.

Flare gas is discharged to the upper portion in the reflux tank32, a part of the lower discharge stream including ammonia is refluxed to the second column30, and the remaining may be recovered and reused for pH adjustment of latex. Here, a part of the lower discharge stream of the reflux tank32is refluxed, thereby increasing the concentration of ammonia in recovered ammonia, and thus, it may be easy to control a process recipe when reused.

Through lower discharge stream from the second column30, remaining purified wastewater from which the nitrile-based monomer and ammonia have been separated may be discharged, which may be transferred to the wastewater treatment plant. Here, a ratio of the total nitrogen content in the lower discharge stream from the second column30to the total nitrogen content in wastewater may 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 wastewater produced in the manufacturing process of a homopolymer or copolymer latex including the nitrile-based monomer-derived unit is purified by the wastewater purification method according to the present disclosure, recovery and reuse are possible while decreasing the loss of the nitrile-based monomer in wastewater, ammonia may be recovered and reused, and the total nitrogen content in wastewater when the wastewater is transferred to the wastewater treatment plant may be effectively decreased.

According to an exemplary embodiment of the present invention, in the wastewater purification method, if necessary, devices such as a distillation tower, a condenser, a reboiler, a valve, a pump, a separator, a mixer, and the like may be further installed.

Hereinabove, the wastewater purification method according to the present disclosure has been described and illustrated in the drawings, but the description and the illustration in the drawings are the description and the illustration of only core constitutions for understanding of the present disclosure, and in addition to the process and devices described above and illustrated in the drawings, the process and the devices which are not described and illustrated separately may be appropriately applied and used for carrying out the wastewater purification method according to the present disclosure.

Hereinafter, the present disclosure will be described in more detail by the Examples. However, the following Examples are provided for illustrating the present invention, and it is apparent to a person skilled in the art that various modifications and alterations may be made without departing from the scope and spirit of the present invention and the scope of the present invention is not limited thereto.

EXAMPLES

Example 1

According to the process diagram illustrated inFIG.1, wastewater discharged from a manufacturing process of an acrylonitrile-butadiene copolymer latex was purified.

Specifically, wastewater, which included water, an acrylonitrile monomer, and ammonia and had a pH of 8, was supplied to a wastewater tank10through a wastewater transfer line11, acetic acid was added to the wastewater tank10through an acid component transfer line12, and a first mixed stream discharged from the wastewater tank10was supplied to a first column20. At this time, it was confirmed that the total nitrogen content of the wastewater was 6,000 ppm and the pH of the first mixed stream was 5.5, and total nitrogen content was measured using a commercialized total nitrogen (TN) measuring device.

The upper discharge stream from the first column20was condensed in a condenser21and supplied to a decanter22, flare gas was discharged from the decanter22, separation into a water layer and an organic layer was performed, an acrylonitrile monomer was recovered from the organic layer component and reused, and a water layer component was transferred to the wastewater tank10. In addition, a part of the lower discharge stream from the first column20was heated using a reboiler23and refluxed, and the rest was mixed with sodium hydroxide transferred through a base component transfer line40to form a second mixed stream and then supplied to a second column30. At this time, the operating temperature of the first column20was 95° C., and the operating pressure was adjusted to 1 bar.

In addition, it was confirmed that the total nitrogen content of the lower discharge stream from the first column20was 3,000 ppm, and the pH of the second mixed stream was 10.

In the second column30, the components of the second mixed stream were separated while a ratio of the flow rate of steam supplied to the flow rate of the second mixed stream supplied to the second column30by the steam supply unit33configured to spray steam upwards was adjusted to 0.1. The upper discharge stream from the second column30was condensed in a condenser31and then supplied to a reflux tank32, flare gas was discharged from the reflux tank32, a part of the lower discharge stream was refluxed, and ammonia was recovered from the remaining and reused. In addition, the lower discharge stream from the second column30was transferred to a wastewater treatment plant as purified wastewater. At this time, the operating temperature of the second column30was 99° C., the operating pressure thereof was adjusted to 1 bar, and a packing height was adjusted to 10 m. In addition, the total nitrogen content in the purified wastewater transferred to the wastewater treatment plant was confirmed to be 500 ppm. In addition, a recovery rate of acrylonitrile which was calculated from a ratio of the content of the acrylonitrile monomer recovered in the first column20to the content of the acrylonitrile monomer included in wastewater tank supplied to the wastewater tank10was confirmed to be 99.9%.

Example 2

According to the process diagram illustrated inFIG.2, wastewater discharged from the manufacturing process of an acrylonitrile-butadiene copolymer latex was purified.

Specifically, the process was performed in the same manner as in Example 1, except that a line mixer50was used when the lower discharge stream from the first column20and sodium hydroxide were mixed. In this case, the total nitrogen content in the purified wastewater transferred to the wastewater treatment plant was confirmed to be 300 ppm. In addition, the recovery rate of acrylonitrile was confirmed to be 99.9%.

Thus, by installing the line mixer50in mixing the lower discharge stream from the first column20with caustic soda, the conversion rate of an ammonium salt in the lower discharge stream from the first column20into ammonia was increased to increase the amount of ammonia recovered in the second column30, and thus, it was confirmed that the total nitrogen content in purified wastewater transferred to the wastewater treatment plant was decreased as compared with Example 1.

Example 3

The process was performed in the same manner as in Example 1, except that a steam supply unit33was configured so that steam was sprayed downwards in the second column30. In this case, the total nitrogen content in the purified wastewater transferred to the wastewater treatment plant was confirmed to be 300 ppm. In addition, the recovery rate of acrylonitrile was confirmed to be 99.9%.

Thus, when steam was sprayed downwards by the steam supply unit33in the second column30, it was confirmed that the dispersion and mixing efficiencies of wastewater in the second column30were increased to show an effect of decreasing the total nitrogen content in purified wastewater as compared with Example 1.

Example 4

According to the process diagram illustrated inFIG.2, wastewater discharged from the manufacturing process of an acrylonitrile-butadiene copolymer latex was purified.

Specifically, the process was performed in the same manner as in Example 1, except that a line mixer50was used when the lower discharge stream from the first column20and sodium hydroxide were mixed, and a steam supply unit33was configured so that steam was sprayed downwards in the second column30. In this case, the total nitrogen content in the purified wastewater transferred to the wastewater treatment plant was confirmed to be 100 ppm. In addition, the recovery rate of acrylonitrile was confirmed to be 99.9%.

Thus, the total nitrogen content in the purified wastewater was decreased by installing the line mixer50and also steam was sprayed downwards by the steam supply unit33, thereby increasing the separation dispersion and mixing efficiencies of wastewater in the second column30, and the pH of the second mixed stream was made uniform by the line mixer to increase the conversion efficiency of an ammonium salt into thereby ammonia, more effectively decreasing the nitrogen content remaining in the purified wastewater.

Example 5

The process was performed in the same manner as in Example 4, except that the pH of the first mixed stream was controlled to 5.5. In this case, the recovery rate of acrylonitrile was confirmed to be 99.9%.

Example 6

The process was performed in the same manner as in Example 4, except that the pH of the first mixed stream was controlled to 6. In this case, the recovery rate of acrylonitrile was confirmed to be 90%.

Example 7

The process was performed in the same manner as in Example 4, except that the pH of the first mixed stream was controlled to 6.5. In this case, the recovery rate of acrylonitrile was confirmed to be 60%.

Example 8

The process was performed in the same manner as in Example 4, except that the pH of the first mixed stream was controlled to 7. In this case, the recovery rate of acrylonitrile was confirmed to be 30%.

Referring to Examples 4 to 8, it was confirmed that when the pH of the first mixed stream supplied to the first column20was controlled to 5.5 or less, the recovery rate of acrylonitrile was high, as compared with the case when the pH of the first mixed stream supplied to the first column20was more than 5.5.

Example 9

The process was performed in the same manner as in Example 4, except that the pH of the second mixed stream at the rear end of the line mixer was controlled to 8. In this case, the total nitrogen content in the purified wastewater was confirmed to be 200 ppm.

Example 10

The process was performed in the same manner as in Example 4, except that the pH of the second mixed stream at the rear end of the line mixer was controlled to 9. In this case, the total nitrogen content in the purified wastewater was confirmed to be 150 ppm.

Example 11

The process was performed in the same manner as in Example 4, except that the pH of the second mixed stream at the rear end of the line mixer was controlled to 11. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Example 12

The process was performed in the same manner as in Example 4, except that the pH of the second mixed stream at the rear end of the line mixer was controlled to 12. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Referring to Examples 4 and 9 to 12, it was confirmed that when the pH of the second mixed stream at the rear end of the line mixer was 10 or more, the efficiency of removing nitrogen in wastewater was high.

Example 13

The process was performed in the same manner as in Example 4, except that the packing height of the second column30was controlled to 3 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 500 ppm.

Example 14

The process was performed in the same manner as in Example 4, except that the packing height of the second column30was controlled to 5 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 200 ppm.

Example 15

The process was performed in the same manner as in Example 4, except that the packing height of the second column30was controlled to 15 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Example 16

The process was performed in the same manner as in Example 4, except that the packing height of the second column30was controlled to 20 m. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Referring to Examples 4 and 13 to 16, it was confirmed that when the packing height of the second column30was controlled to 10 m to 20 m, the efficiency of removing nitrogen in wastewater was high.

Example 17

The process was performed in the same manner as in Example 4, except that a ratio of the flow rate of steam supplied to the flow rate of the second mixed stream supplied to the second column30was controlled to 0.03. In this case, the total nitrogen content in the purified wastewater was confirmed to be 1000 ppm.

Example 18

The process was performed in the same manner as in Example 4, except that a ratio of the flow rate of steam supplied to the flow rate of the second mixed stream supplied to the second column30was controlled to 0.05. In this case, the total nitrogen content in the purified wastewater was confirmed to be 300 ppm.

Example 19

The process was performed in the same manner as in Example 4, except that a ratio of the flow rate of steam supplied to the flow rate of the second mixed stream supplied to the second column30was controlled to 0.2. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Example 20

The process was performed in the same manner as in Example 4, except that a ratio of the flow rate of steam supplied to the flow rate of the second mixed stream supplied to the second column30was controlled to 0.3. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Referring to Examples 4 and 17 to 20, it was confirmed that when the ratio of the flow rate of steam supplied to the flow rate of the second mixed stream supplied to the second column30was controlled to 0.1 to 0.3, the efficiency of removing nitrogen in wastewater was high.

Example 21

The process was performed in the same manner as in Example 4, except that the operating temperature of the first column20was adjusted to 80° C. In this case, the recovery rate of acrylonitrile was confirmed to be 70%.

Example 22

The process was performed in the same manner as in Example 4, except that the operating temperature of the first column20was adjusted to 85° C. In this case, the recovery rate of acrylonitrile was confirmed to be 90%.

Example 23

The process was performed in the same manner as in Example 4, except that the operating temperature of the first column20was adjusted to 90° C. In this case, the recovery rate of acrylonitrile was confirmed to be 98%.

Example 24

The process was performed in the same manner as in Example 4, except that the operating temperature of the first column20was adjusted to 100° C. In this case, the recovery rate of acrylonitrile was confirmed to be 99.9%. Referring to Examples 4 and 21 to 24, it was confirmed that when the operating temperature of the first column20was 90° C. or higher, the acrylonitrile recovery rate was high.

Example 25

The process was performed in the same manner as in Example 4, except that the operating temperature of the second column30was adjusted to 80° C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 1000 ppm.

Example 26

The process was performed in the same manner as in Example 4, except that the operating temperature of the second column30was adjusted to 85° C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 500 ppm.

Example 27

The process was performed in the same manner as in Example 4, except that the operating temperature of the second column30was adjusted to 90° C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 300 ppm.

Example 28

The process was performed in the same manner as in Example 4, except that the operating temperature of the second column30was adjusted to 105° C. In this case, the total nitrogen content in the purified wastewater was confirmed to be 100 ppm.

Referring to Examples 4 and 25 to 28, it was confirmed that when the operating temperature of the second column30was controlled to 95° C. or higher, the efficiency of removing nitrogen in wastewater was high.

COMPARATIVE EXAMPLES

Comparative Example 1

According to the process diagram illustrated inFIG.3, wastewater discharged from the manufacturing process of an acrylonitrile-butadiene copolymer latex was purified.

Specifically, wastewater which included water, an acrylonitrile monomer, and ammonia and had a pH of 8 was supplied to the wastewater tank10through the wastewater transfer line11, and the wastewater was discharged from the wastewater tank10and supplied to the first column20. At this time, the total nitrogen content of the wastewater was confirmed to be 6,000 ppm.

The upper discharge stream from the first column20was condensed in the condenser21and supplied to the decanter22, flare gas was discharged from the decanter22, separation into a water layer and an organic layer was performed, an acrylonitrile monomer was recovered from the organic layer component and reused, and a water layer component was transferred to the wastewater tank10. In addition, a part of the lower discharge stream from the first column20was heated using the reboiler23and then refluxed, and the rest was transferred to the wastewater treatment plant as purified wastewater. At this time, the operating temperature of the first column20was 95° C., and the operating pressure thereof was adjusted to 1 bar. In addition, the total nitrogen content in the purified wastewater transferred to the wastewater treatment plant was confirmed to be 3000 ppm. In addition, the recovery rate of acrylonitrile was confirmed to be 30%.