JP2001121138A - Method for treating waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of reducing the consumption of a heating source, such as steam, to be freshly used in distillation operation and separating the cyanide, chemical oxygen demand(COD) materials and total nitrogen in the waste water in the preparation of acrylonitrile or methacrylonitrile by ammoxidation of propane, propylene or isobutyrene. SOLUTION: The waste water is separated to the waste water reduced in the cyanide, COD materials and total nitrogen and the condensate containing a high concentration of the cyanide compound, COD materials and total nitrogen by carrying out the distillation operation at a temperature higher than the temperature of the waste water using a multistage distillation column as a distillation column and under conditions under which the quantity of heat to be freshly used for the distillation operation is little. The high boiling components of the waste water are otherwise removed by the distillation operation using >=2 columns of the multistage distillation columns and thereafter the removal of the low b.p. components is carried out by the distillation operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating wastewater in the production of acrylonitrile or methacrylonitrile by the ammoxidation of propane, propylene or isobutylene.

[0002]

2. Description of the Related Art In a process for producing acrylonitrile or methacrylonitrile by ammoxidation of propane, propylene or isobutylene, a reaction product is treated by the following method. That is, this reaction product is usually introduced into an absorption tower after cooling and washing, and acrylonitrile, methacrylonitrile, acetonitrile, hydrogen cyanide and other reaction by-products are absorbed by a large amount of water. This absorbed water is supplied to a water extraction distillation column called a recovery column (1), and acrylonitrile, methacrylonitrile and hydrogen cyanide are distilled off at the top, and a large amount of water and acetonitrile, a small amount of hydrogen cyanide and other reaction by-products are removed. It is withdrawn from the bottom as bottoms.

[0003] The bottom liquid is supplied to a distillation column called a stripping column (2), and acetonitrile and water containing hydrogen cyanide are distilled off from the top of the column.
From the side stream or the bottom of the column as the absorption water of the absorption tower and the extraction water of the recovery tower (1). The remaining water is discharged out of the system as wastewater from the bottom of the tower. However, wastewater discharged by such a method usually contains a large amount of cyanide, a chemical oxygen demand substance and total nitrogen, and cannot be discharged to public water as it is.

[0004] As a method of treating wastewater containing a large amount of cyanide, a chemical oxygen demanding substance and a large amount of total nitrogen generated from such an acrylonitrile or methacrylonitrile production process, an oxidative combustion method is conventionally known. However,
The oxidative combustion method has the drawback that a large amount of fuel is required because the wastewater is spray-combusted as it is, and the combustion equipment becomes very large.

Another method for treating the wastewater is disclosed in
In the method proposed in 79165, in which the wastewater is heated and then flashed to reduce the amount of cyanide in the wastewater, cyanide remains in the obtained wastewater, and there is no description about the concentration of the chemical oxygen demanding substance. unacceptable.

Further, in the method proposed in Japanese Patent Application Laid-Open No. 53-136356, in which the wastewater is subjected to a high-temperature treatment and then separated into steam and liquid, the obtained steam distillate has a reduced cyanide content, but has a chemical oxygen demanding substance. Is still high and the total nitrogen concentration in the wastewater is not described at all.

Japanese Patent Application Laid-Open No. Sho 50-156263 and Japanese Patent Publication No. Sho 5
In the method proposed in Japanese Patent Publication No. 3-46383 and Japanese Patent Publication No. 04-56679, in which an alkali or an organic amide is added to the wastewater to obtain a distillate in which cyanide and chemical oxygen demanding substances are reduced, cyanide can be certainly reduced and Although the concentration of the chemical oxygen demanding substance can be reduced to some extent, the cost of using the additive is required, and the relatively stable chemical oxygen demanding substance does not react and is partially distilled off to the distillate side. Reduction of chemical oxygen demanding substances is not always complete.

Further, there is no description about the total nitrogen concentration in the wastewater. On the contrary, in this method, ammonia is generated due to hydrolysis of organic substances in the wastewater, particularly nitrile compounds, and decomposition of ammonium organic acid by addition of alkali and the like. ,
The total nitrogen concentration in the wastewater increases as compared with the case where no alkali or the like is added. In the method proposed in Japanese Patent Publication No. 51-40388, in which a column is added to the bottom of a stripping tower to remove low-boiling substances in wastewater before being extracted as wastewater, the removed low-boiling substances are not extracted to the outside of the system, but acrylonitrile is used. Alternatively, the process returns to the production process of methacrylonitrile. Therefore, a method of removing the low-boiling substance by accumulation in the production process or by some means is required.

In the method proposed in Japanese Patent Publication No. 51-40388, simple distillation is performed by further adding an organic amine to the wastewater extracted from the bottom of the stripping tower. It has the disadvantage that the total nitrogen concentration in the effluent increases compared to the wastewater withdrawn from the bottom of the stripping tower.

[0010] Similarly, as a method of using an additive, the use of ozone is proposed in Japanese Patent Application Laid-Open No. 06-154771, but in order to introduce a large amount of wastewater into a continuous process, more ozone than the amount required for the oxidation treatment is required. It has the disadvantage of requiring high costs for generating large amounts of ozone.
No description is found for the total nitrogen concentration in the wastewater.

Japanese Patent Application Laid-Open Nos. 50-156263 and 5
3-136356, JP-A-53-46383 and DD
The method proposed in 138196 requires some form of heating source when performing wastewater treatment.

In particular, a distillate in which cyanide and a chemical oxygen demanding substance are reduced by a method in which a simple distillation operation is performed several times, for example, a simple distillation operation two or more times proposed in JP-A-50-156263. Is not economical because the vapor required for evaporating the liquid is required for the number of simple distillations.

In the case of performing multi-stage distillation under low pressure or normal pressure as proposed in DD138196, the temperature of the vapor or liquid extracted from the multi-stage distillation column is low. It cannot be reused as a heat source in the acrylonitrile or methacrylonitrile production process requiring a temperature equal to or higher than the temperature. As a result, since all the heat sources required for the multi-stage distillation are newly required, this heat source cost is newly required for the wastewater treatment cost, which is not economical.

[0014]

SUMMARY OF THE INVENTION The present invention relates to propane,
After removing the reaction product from the ammoxidation of propylene or isobutylene in the recovery tower (1), acrylonitrile or methacrylonitrile and most of the hydrogen cyanide are removed, the liquid extracted from the bottom of the recovery tower (1) is further discharged to the dispersion tower (2). ) To distill acetonitrile and a small amount of hydrogen cyanide by distillation, and then, in extracting the liquid at the bottom of the stripping tower (2) as wastewater, reduce the amount of a heating source such as steam newly used in the distillation operation, It is another object of the present invention to provide a method for separating cyanide, a chemical oxygen demanding substance and total nitrogen in the wastewater, and in particular, a method for obtaining wastewater in which cyanide, a chemical oxygen demanding substance and total nitrogen are reduced.

[0015]

SUMMARY OF THE INVENTION In view of these circumstances, the present inventors have found that effective treatment of wastewater containing a large amount of cyanide, a chemical oxygen demanding substance, and total nitrogen generated from an acrylonitrile or methacrylonitrile production process. As a result of intensive studies on economical and economical methods, the steam generated when the wastewater is heated and concentrated contains high-boiling cyanide, chemical oxygen demanding substances and total nitrogen, low-boiling cyanide, Was found to contain a high oxygen demanding substance and total nitrogen substances, and the wastewater was subjected to a distillation separation operation using a multi-stage distillation column to obtain a high boiling point cyanide, a chemical oxygen demanding substance and total nitrogen, and a low boiling point. It was found that by removing cyanide, chemical oxygen demanding substances and total nitrogen, wastewater with reduced cyanide, chemical oxygen demanding substances and total nitrogen could be obtained.

Even when an alkali is added at the time of heating and concentrating, relatively stable high-boiling organic substances are present in the generated steam, and the generated steam is further separated by distillation to further increase the cyanide and chemical properties. It has been found that wastewater with reduced oxygen demand and total nitrogen can be obtained.

Further, by using a multi-stage distillation column as the distillation equipment used for the distillation separation, multi-stage distillation can be performed with a smaller amount of steam than when a known simple distillation operation is performed twice or more, and the separation and separation of high boiling components can be performed. When performing the distillation, the distillation operation is usually performed at a temperature lower than the temperature of the wastewater withdrawal liquid.By operating the distillation equipment at a temperature higher than the wastewater withdrawal temperature, the steam withdrawn from the distillation equipment is removed. It has also been found that the liquid can be reused as a heat source in the acrylonitrile or methacrylonitrile production process, and the amount of newly used vapor can be significantly reduced.

That is, according to the present invention, the reaction product obtained by the ammoxidation of propane, propylene or isobutylene is removed from the acrylonitrile or methacrylonitrile and most of the hydrogen cyanide in the recovery tower (1), and then the recovery tower (1) is installed. Separation liquid from bottom is further stripped off (2)
Distill acetonitrile and a small amount of hydrogen cyanide by distillation at

Next, when the liquid at the bottom of the stripping tower (2) is extracted as wastewater, a multistage distillation column is used as the distillation column (3), and a distillation operation is performed at a temperature higher than the temperature at which the wastewater is extracted. The lower boiling component is removed from the bottom, the high boiling component is removed from the bottom, and part or all of the vapor or liquid extracted from the distillation column (3) is collected in the recovery column (1) and / or the stripping column (2). By using it as a heat source,

Stripping tower (2) Cyan, compared to the liquid at the bottom of the tower
A method for treating acrylonitrile or methacrylonitrile production wastewater, characterized in that wastewater with reduced chemical oxygen demand and total nitrogen is obtained as liquid or steam from the side of the distillation column (3).

Alternatively, using a multi-stage distillation column of two or more columns, a distillation operation is first performed in the first multi-stage distillation column at a temperature higher than the temperature at which the wastewater is withdrawn, and the wastewater is discharged from the bottom of the first multi-stage distillation column. Of the high-boiling components of the wastewater, the low-boiling components of the wastewater extracted from the top of the first distillation column are removed in the second and subsequent multistage distillation columns, and the high-boiling components are removed from the two or more multistage distillation columns. Recovery tower (1) for part or all of the vapor or liquid to be collected
And / or by utilizing as a heat source of the stripping tower (2),

Stripping tower (2) Cyan, compared to the liquid at the bottom of the tower
A method for treating acrylonitrile or methacrylonitrile wastewater, which comprises obtaining a wastewater with reduced chemical oxygen demand and total nitrogen.

In the present invention, most of the hydrogen cyanide after removing most of the hydrogen cyanide means about 90.0 to 99.9% by weight of the hydrogen cyanide in the reaction product. The small amount of hydrogen cyanide obtained by distilling a small amount of hydrogen cyanide of the present invention is the remaining hydrogen cyanide excluding most of the hydrogen cyanide.

In the present invention, the low-boiling components cyan, chemical oxygen demanding substances and total nitrogen which are removed by distillation are as follows:
A substance produced and / or added in an ammoxidation reaction of propane, propylene or isobutylene or an acrylonitrile or methacrylonitrile production process after the reaction, and having a lower boiling point than water under the operating pressure of the multi-stage distillation column used in the present invention. Indicates a substance.

For example, hydrogen cyanide, acrylonitrile,
Examples include methacrylonitrile, acetonitrile and / or ammonia. Of these, ammonia is often generated by decomposition of ammonium organic acid contained in wastewater extracted from the bottom of the stripping tower (2) or by hydrolysis of a nitrile compound. ) The amount of low boiling components containing ammonium organic acid and / or nitrile compounds in the wastewater withdrawn from the bottom varies depending on the ammoxidation reaction conditions, unreacted ammonia removal conditions, and the operating conditions of the recovery tower and / or the stripping tower. I do.

In the present invention, the high-boiling cyanide, the chemical oxygen-requiring substance and the total nitrogen which are removed by distillation are, like the low-boiling components, the ammoxidation reaction of propane, propylene or isobutylene or acrylonitrile after the reaction. Or a substance which is produced and / or added in a methacrylonitrile production process and has a higher boiling point than water under the operating pressure of the multistage distillation column used in the present invention.

For example, organic acids such as cyanide, acetic acid or acrylic acid, nitrile compounds such as succinonitrile and fumaronitrile, and / or compounds of pyridines can be mentioned. However, some of the substances in the wastewater extracted from the bottom of the stripping tower (2) form an azeotropic composition, such as 3-cyanopyridine. Such a substance is removed as a low-boiling component even if the substance has a higher boiling point than water under the operating pressure of the multi-stage distillation column.

Stripping tower (2) The amount of each of the low-boiling components and / or high-boiling components contained in the wastewater withdrawn from the bottom of the tower is determined by the conditions of the ammoxidation reaction,
It depends on the conditions for removing unreacted ammonia after the reaction and the operating conditions of the acrylonitrile or methacrylonitrile production process.

The type of the multi-stage distillation column used in the wastewater distillation operation in the present invention is not particularly limited, and may be any type such as a tray column or a packed column generally used for a distillation column. When the multistage distillation column used in the present invention is a tray column, the actual number of plates in the distillation column is not particularly limited,
Preferably, the number of actual stages should be 1 or more and 100 or less,
It is particularly preferable that the number be 5 to 70 steps.

When the multistage distillation column used in the present invention is a packed column, the packed bed height in the distillation column is not particularly limited, but preferably the total packed bed height is 0.5 m or more and 70 m or more.
It is sufficient if it is not more than 5 m, particularly preferably not less than 5 m and not more than 50 m. Further, if the design of the distillation column is hindered, the multi-stage distillation column may be divided into two columns.

The type of heat exchanger used for condensing the vapor at the top of the multistage distillation column used in the distillation operation of the wastewater in the present invention is not particularly limited, and a partial condenser is used to extract a part of the vapor as steam. Is also good.

When the overhead vapor of the multistage distillation column is used as a heating source for the recovery tower (1) and / or the stripping tower (2), the recovery tower (1) and / or the stripping tower (2)
Into the heat exchanger at the bottom of the column. In the case where the wastewater obtained by the distillation operation of the wastewater according to the present invention, in which cyan, chemical oxygen demand substances and total nitrogen are reduced, is extracted with steam, this steam is also heated in the recovery tower (1) or the stripping tower (2). As a source, it may be introduced into a heat exchanger at the bottom of the recovery tower (1) or the stripping tower (2).

The operating pressure of the multistage distillation column used in the distillation operation of the wastewater in the present invention is not particularly limited, and the distillation operation is performed at a temperature higher than the temperature of the liquid extracted from the bottom of the stripping column (2). Any operating pressure can be used. In particular, when the steam extracted from the multi-stage distillation column used in the present invention is used as a heat source of the recovery column (1) and / or the stripping column (2), the operating pressure of the multi-stage distillation column used in the present invention is recovered. It is determined by the operating conditions of the tower (1) and / or the stripping tower (2) and the surface of the heat exchanger used for heat exchange.

The heating heat exchanger used in the recovery tower (1) or the stripping tower (2) is often made of carbon steel. In this case, since the vapor and liquid extracted from the multi-stage distillation column used in the present invention are corrosive to carbon steel, the vapor and / or liquid is removed using an existing heat exchanger. The method used as a heating source for the recovery tower (1) or the stripping tower (2) cannot be adopted. Therefore, the present inventors added alkali to the steam and / or liquid as a measure to prevent corrosion of carbon steel contacted with these steams,
It has been found that corrosion of carbon steel does not progress by increasing the pH of the steam to 8 to 14, preferably 9 to 11.

It has also been found that when adding alkali to steam, ammonia gas is an effective means in consideration of diffusion of steam into steam. As a method for injecting ammonia gas, the ammonia gas may be injected into the top of the main body of the multi-stage distillation column in a liquid or gas state, or may be directly injected into the top steam pipe in a gas state. In order to check the pH of the steam, a method is generally used in which the pH of the steam condensate after introduction into the bottom heat exchanger of the recovery tower (1) or the stripping tower (2) is measured.
The stainless steel and carbon steel in the present invention may be any stainless steel and carbon steel described in Japanese Industrial Standards (JIS).

In the present invention, the treatment of the liquid containing low-boiling point cyan, a chemical oxygen-requiring substance and total nitrogen which is removed by the distillation operation of the wastewater is not particularly limited. Or a method of recovering cyan.

The type of the heat exchanger for heating the bottom of the multistage distillation column used in the present invention is not particularly limited, and generally a multitubular heat exchanger is used. For the purpose of preventing the heat exchanger from being clogged by contamination, an alkali may be added to the bottom of the multistage distillation column used in the present invention before the bottom liquid is introduced into the heat exchanger or to the bottom of the column. However, in this case, the nitrile compounds contained in the wastewater may hydrolyze at the bottom of the tower and generate ammonia, so that the total nitrogen in the wastewater, which has reduced cyanide, chemical oxygen demand substances and total nitrogen, may increase. There is. Further, a method may be adopted in which steam is directly supplied to the bottom of the distillation column as a heat source without installing a heat exchanger at the bottom of the distillation column used in the present invention.

In the present invention, there is no particular limitation on the treatment of the liquid containing high-boiling cyanide, a chemical oxygen-requiring substance and total nitrogen, which is removed by the distillation operation of the wastewater. Or a method of incineration after mixing with waste ammonium sulfate.

In the present invention, the location of the wastewater supply to the multi-stage distillation column and the location of the wastewater from which the cyanide, the chemical oxygen demanding substance and the total nitrogen are reduced are not particularly limited. The number of each stage is determined according to the required condition of the wastewater. Furthermore, the wastewater obtained by the multistage distillation operation, in which the amount of cyanogen, the chemical oxygen-requiring substance and the total nitrogen is reduced, may be further subjected to treatment such as biological treatment in view of the regulation value of the wastewater.

A method for treating a wastewater containing a large amount of a cyanide compound, a chemical oxygen-requiring substance and a large amount of total nitrogen generated from an acrylonitrile or methacrylonitrile production process will be described in detail with reference to FIGS. 1, 2 and 3. I do.

The reaction product obtained by the ammoxidation reaction of propane, propylene or isobutylene is supplied to the recovery column 1 through the conduit 3 after removing unreacted ammonia and non-condensable gas contained in the reaction product. Is done. In the acrylonitrile recovery column 1, by performing water extraction distillation, acrylonitrile and hydrogen cyanide are distilled out through the conduit 4 at the top of the recovery column 1 and led to the next purification step. Recovery tower 1 Bottom liquid is passed through conduit 5 and stripping tower 2
Sent to

The bottom liquid contains a large amount of water and acetonitrile, a small amount of hydrogen cyanide and other reaction by-products. In the stripping tower 2, acetonitrile and water containing hydrogen cyanide are distilled from the top of the tower through a conduit 6. A part of the remaining water is withdrawn from the side stream of the distillation column or the bottom through the conduit 7 as the absorption water of the absorption column and the extraction water of the extraction distillation column.

Further, the remaining water is discharged out of the system as waste water from the bottom of the tower through a conduit 8. This wastewater is withdrawn at a temperature higher than 100 ° C. The wastewater withdrawn through conduit 8 contains cyanide, chemical oxygen demands and total nitrogen. The wastewater is passed through a conduit 8 to a distillation column 9
Where the low-boiling components cyan, chemical oxygen demanding substances and total nitrogen contained in the wastewater are withdrawn from the top of the distillation column 9 with steam through a conduit 10 and a part or all of the steam is removed. After the condensation, a part of the condensate is supplied as a reflux liquid of the distillation column 9 through the conduit 11, and the remainder is discharged out of the system through the conduit 12.

The high-boiling components cyanide, chemical oxygen demanding substances and total nitrogen are withdrawn from the bottom of the distillation column 9 through a conduit 13. Cyan, chemical oxygen demanding substances and waste water having a reduced total nitrogen are discharged from a side of the distillation column 9 into a conduit 1.
Get through 4. The wastewater extracted from the distillation column 9 from which cyan, chemical oxygen demand substances and total nitrogen are reduced may be liquid or steam, and in the case of steam, it is condensed to wastewater.

At this time, part or all of the extracted vapor or liquid or the vapor distilled at the top of the distillation column 9 is recovered.
And / or used as a heat source for heating the stripping tower 2. For example, this means that the heating heat exchanger at the bottom of the recovery tower 1 and / or the stripping tower 2 is used to supply steam at the top of the distillation tower 9 as a heat exchanger for vapor condensation at the top of the distillation tower 9. Can be achieved.

As a result, although the amount of heat required for the multi-stage distillation operation of the wastewater is required, the amount of heat of the re-used heating source is reduced from the amount of heat required for the recovery tower 1 and / or the stripping tower 2. The sum of the amount of heat used in the recovery tower 1 and / or the stripping tower 2 and the amount of heat used in the multi-stage distillation of the wastewater can be significantly reduced as compared with the case where each is heated alone. This example is shown in FIG. Recovery tower 1
And / or a distillation tower 9 as a heat source for heating the stripping tower 2
The method of utilizing the vapor or liquid extracted from the liquid may be another method, for example, may be used as a heating source of the liquid supplied to the recovery tower 1.

Alternatively, as shown in FIG. 3, the distillation column may be divided into two or more columns. That is, the wastewater extracted from the stripping tower 2 through the conduit 8 is guided to the wastewater high-boiling separation distillation tower 15,
Here, wastewater containing low-boiling components cyan, a chemical oxygen demanding substance, and total nitrogen contained in the wastewater is withdrawn from the top of the distillation column 15 with steam through a conduit 16. After condensing the vapor, a part of the condensate is supplied as a reflux of the distillation column 15 through a conduit 17, and the remainder is supplied through a conduit 18 to the distillation column 2.
Sent to 0.

The high-boiling components cyanide, chemical oxygen demanding substances and total nitrogen are withdrawn from the bottom of the distillation column 15 through a conduit 19. The high-boiling cyanide, chemical oxygen demand and total nitrogen-depleted wastewater supplied through conduit 18 are then removed in low-boiling wastewater distillation column 20 to remove low-boiling cyanide, chemical oxygen demand and total nitrogen. After the vapor is removed from the top of the column with vapor through a conduit 21 and a part or all of the vapor is condensed, a part of the condensate is supplied as a reflux liquid of the distillation column 20 through a conduit 22, and the rest is withdrawn through a conduit 23.

[0049] As a result, wastewater having a reduced cyanide content, chemical oxygen demand and total nitrogen content is withdrawn from the bottom of distillation column 20 through conduit 24. Part or all of the vapor or liquid extracted from the distillation tower 15 or the distillation tower 20 is used as a heat source for heating the recovery tower 1 or the stripping tower 2.
The method used as a heat source for heating the recovery tower 1 or the stripping tower 2 may be the same as the method described in the description of FIG. 1 or FIG.

The wastewater extracted from the bottom of the stripping tower 2 according to the present invention contains cyan, a chemical oxygen demanding substance and total nitrogen, and their respective concentrations are not particularly limited. Further, the wastewater is distilled from distillation column 9 or distillation column 1
Before feeding to 5, an alkali or organic amide may be added to the wastewater.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to examples, but the contents of the present invention are not limited to these examples. The analysis of cyanide, chemical oxygen demanding substances and total nitrogen substances in the wastewater was performed as follows.

(1) Cyan density: JIS K0102-
Total cyan (p) in the cyan compound measurement method described in 1993
(Hydrogen cyanide generated below H2). (2) Chemical oxygen demand substance concentration; JIS K0102-
It was measured according to the method for measuring oxygen consumption (COD _Mn ) by potassium permanganate at 100 ° C. described in 1993. (3) Total nitrogen substance concentration; JIS K0102-1993
It measured according to the sum total method in the total nitrogen measurement method described.

[0053]

Example 1 A reaction product obtained by the ammoxidation of propylene was subjected to water extraction distillation to remove acrylonitrile or methacrylonitrile and most of hydrogen cyanide, and then acetonitrile and a small amount of hydrogen cyanide were distilled off. The following operation was performed using the wastewater extracted from the bottom of the stripping tower as a raw material. At this time, each concentration of the wastewater is 76 ppm of cyanide and 1180 of chemical oxygen demanding substance.
0 ppm and total nitrogen 2490 ppm.

As the distillation column, a distillation apparatus having a diameter of 400 mm, a perforated plate system having a total of 10 stages was used, the wastewater was supplied to the bottom of the column, the pressure at the top was controlled at 0.25 MPa, and a low-boiling cyanide was supplied from the top of the column. The wastewater containing the chemical oxygen demanding substance and the total nitrogen is withdrawn in an amount of 5% of the feed amount, and the wastewater containing the high boiling point cyanide, the chemical oxygen demanding substance and the total nitrogen is discharged from the bottom of the column at 10% of the feed rate. Withdrawal, from the bottom five positions, wastewater with reduced cyanide, chemical oxygen demand, and total nitrogen was obtained in an amount of 85% of the supplied amount.

At this time, the temperature at the top of the tower is 125 ° C. to 126 ° C.
° C, which was higher than the bottom temperature of the stripping tower, which was sufficient for use as a heat source for the stripping tower. After a continuous operation of about 30 hours under these conditions, each concentration of the obtained wastewater is 1.5 ppm of cyanide and 66
It was 0 ppm and the total nitrogen concentration was 315 ppm.

[0056]

Example 2 The following operation was further performed using the same wastewater raw material as in Example 1. As a first operation, a high-boiling separation operation of the wastewater was performed. The diameter of wastewater high boiling separation distillation column is 40
The wastewater was supplied to the bottom of the column using a 0 mm, perforated plate type distillation apparatus having a total of 10 stages, and the pressure at the top was controlled at 0.25 MPa. Waste water containing low-boiling point cyanide, chemical oxygen demanding substances and total nitrogen is withdrawn from the top of the column in an amount of 90% of the supply amount, and wastewater containing high boiling point cyanide, chemical oxygen demanding substances and total nitrogen is taken from the bottom of the tower Was extracted at 10% of the supply amount.

At this time, the temperature at the top of the tower was 126 ° C.
This temperature was higher than the bottom temperature of the stripping tower, which was sufficient when used as a heat source for the stripping tower. About 3
After the continuous operation for 0 hours, the concentration of each of the distillate wastewater obtained from the top of the tower was 62 ppm for cyanide, and 9
It was 90 ppm and the total nitrogen concentration was 470 ppm.

Next, as a second operation, a low-boiling separation operation was carried out using the liquid extracted at the top of the high-boiling separation distillation column obtained in the first operation as a raw material liquid. As a low-boiling wastewater distillation column, a distillation apparatus having a diameter of 40 mm and a perforated plate system having a total of 25 stages was used. The raw material liquid was supplied to the top of the column, and 10% of the vapor was supplied from the bottom of the column to the vapor.

The top pressure was controlled at atmospheric pressure, wastewater containing low boiling point cyan, chemical oxygen demanding substances and total nitrogen was withdrawn from the top of the column in an amount of 5% of the feed amount of raw material, and the remaining wastewater was collected at the bottom of the column. Extracted from After the continuous operation for about 10 hours under these conditions, each concentration of the wastewater obtained from the bottom of the column is 0.1% of cyan.
6 ppm, 580 ppm of chemical oxygen demanding substance and 171 ppm of total nitrogen concentration.

[0060]

Comparative Example 1 The wastewater raw material used in Example 1 was supplied to the flask by a simple distillation apparatus using a 1 L flask, the wastewater was supplied to the flask, the pressure was controlled at atmospheric pressure, and the amount of wastewater was 85% of the supplied amount. Distilled at. After continuous operation for about 30 hours under these conditions,
The respective concentrations of the obtained distillate wastewater were 23.9 ppm of cyan, 1800 ppm of chemical oxygen demanding substances, and 33% of total nitrogen.
It was 40 ppm.

[0061]

Comparative Example 2 The wastewater raw material used in Example 1 was replaced with Comparative Example 1.
Caustic soda was added to the flask to adjust the pH of the liquid in the flask to 11 using the same apparatus as in the above. When the operating conditions and the distilling rate were the same as in Comparative Example 1, the resulting distillate wastewater had a cyanide concentration of 0.5 ppm and a chemical oxygen demanding substance concentration of 77.
It was 0 ppm and the total nitrogen concentration was 5120 ppm.

[0062]

According to the treatment method of the present invention, in the production of acrylonitrile and methacrylonitrile by the ammoxidation oxidation of propane, propylene or isobutylene, the amount of a heating source such as steam newly used in a distillation operation is reduced. A method for reducing and separating cyanide, chemical oxygen demanding substances and total nitrogen in the wastewater,
In particular, it is possible to provide a method for obtaining wastewater in which cyanide, a chemical oxygen demanding substance and total nitrogen are reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of an example of a processing method of the present invention.

FIG. 2 is a diagram showing a flow of an example of a processing method of the present invention.

FIG. 3 is a diagram showing a flow of an example of a processing method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Recovery tower 2 Stripping tower 3 Conduit for reaction product-containing liquid 4 Conduit for acrylonitrile and hydrogen cyanide 5 Conduit for bottom liquid of the recovery tower 6 Acetonitrile and water containing hydrogen cyanide 7 Conduit for absorption water and extraction water 8 Conduit for wastewater Reference Signs List 9 Distillation column 10 Low-boiling-point conduit for cyanide, chemical oxygen-requiring substance and vapor containing total nitrogen 11 Reflux liquid conduit to distillation column 12 Condensate withdrawal conduit 13 High-boiling-point cyanide, chemical-oxygen-requiring substance And a conduit for withdrawing a liquid containing total nitrogen 14 A conduit for wastewater in which cyanide, a chemical oxygen-requiring substance and total nitrogen are reduced 15 A wastewater high-boiling separation distillation column 16 A low-boiling point containing cyanogen, a chemical oxygen-requiring substance and total nitrogen Vapor conduit 17 Reflux liquid conduit to distillation column 15 Condensate withdrawal conduit 19 High-boiling cyanide, chemical oxygen demanding substance And a line for extracting liquid containing total nitrogen 20 wastewater low-boiling separation distillation column 21 a line for vapor containing low-boiling point cyan, a chemical oxygen demanding substance and total nitrogen 22 a reflux liquid line to distillation column 20 23 withdrawing condensate Conduit 24 Wastewater conduit with reduced cyanide, chemical oxygen demand and total nitrogen

Claims (12)

[Claims] 1. A reaction product obtained by ammoxidation of propane, propylene or isobutylene is used to remove acrylonitrile or methacrylonitrile and most of hydrogen cyanide in a recovery tower (1). Acetonitrile and a small amount of hydrogen cyanide are further distilled off by distilling the discharged liquid in a stripping tower (2), and then a multi-stage distillation column is used as a distillation tower (3) when the liquid at the bottom of the stripping tower (2) is extracted as wastewater. A distillation operation is performed at a temperature higher than the temperature at which the wastewater is withdrawn to remove low-boiling components from the top of the column, high-boiling components from the bottom of the column, and to remove steam or liquid extracted from the distillation column (3). By using a part or the whole as a heat source of the recovery tower (1) and / or the stripping tower (2), the cyanide and the chemical liquid are compared with the liquid at the bottom of the stripping tower (2). A method for treating acrylonitrile or methacrylonitrile wastewater, characterized in that wastewater with reduced oxygen demand and total nitrogen is obtained as liquid or steam from the side of the distillation column (3). 2. The processing method according to claim 1, wherein a material used for said distillation column (3) is stainless steel. 3. The processing method according to claim 2, wherein the material used in the place where the vapor and liquid extracted from the distillation column (3) come into contact is stainless steel. 4. When carbon steel is used at a place where the vapor and / or liquid extracted from the distillation column (3) comes into contact, the vapor and / or liquid extracted from the distillation column (3) contains carbon steel. 3. The treatment method according to claim 2, wherein a base is added upstream of a portion where the steel is used, and the pH of the vapor and / or the liquid is adjusted to 8 or more and 14 or less. 5. The processing method according to claim 4, wherein the pH of the vapor and / or the liquid is adjusted to 9 or more and 11 or less. 6. The processing method according to claim 4, wherein the base added to the vapor is ammonia gas. 7. A reaction product obtained by ammoxidation of propane, propylene or isobutylene is extracted from the bottom of the recovery tower (1) after removing acrylonitrile or methacrylonitrile and most of hydrogen cyanide in the recovery tower (1). The liquid is further distilled in a stripping tower (2) to distill acetonitrile and a small amount of hydrogen cyanide, and then, when the liquid at the bottom of the stripping tower (2) is extracted as wastewater, two or more multi-stage distillation columns are used. The first multi-stage distillation column performs a distillation operation at a temperature higher than the temperature at which the waste water is withdrawn, removes the high-boiling components of the waste water from the bottom of the first multi-stage distillation column, and further performs multi-stage distillation of the second and subsequent columns. In the distillation column, the first
Remove low-boiling components of wastewater extracted from the top of the distillation column,
In addition, by using part or all of the vapor or liquid extracted from the two or more multistage distillation columns as a heat source for the recovery tower (1) and / or the stripping tower (2), the bottom of the stripping tower (2) A method for treating acrylonitrile or methacrylonitrile wastewater, comprising obtaining wastewater with a reduced amount of cyanide, chemical oxygen demanding substances and total nitrogen as compared to the liquid of the above. 8. The processing method according to claim 7, wherein the material used for the multi-stage distillation column is stainless steel. 9. The processing method according to claim 8, wherein a material used for a place where the vapor and the liquid extracted from the multi-stage distillation column come into contact with each other is stainless steel. 10. When carbon steel is used in a place where steam and / or liquid extracted from the multi-stage distillation column comes into contact, carbon steel is used for steam and / or liquid extracted from the multi-stage distillation column. 9. The processing method according to claim 8, wherein a base is added upstream of a certain point, and the pH of the vapor and / or the liquid is adjusted to 8 or more and 14 or less. 11. The processing method according to claim 10, wherein the pH of the vapor and / or the liquid is adjusted to 9 or more and 11 or less. 12. The method according to claim 10, wherein the base added to the vapor is ammonia gas.