JPS60147288A - Treatment of waste water from ammoxidation process - Google Patents

Abstract

PURPOSE:To reduce the amount of caustic soda to be used, by concentrating alkaline waste water containing a cyanide compound under heating while adding the concentrate to waste water containing ammonium sulfate and an org. compound to convert ammonium sulfate to sodium sulfate and an ammonium salt. CONSTITUTION:Waste water containing a cyanide compound and a COD component discharged from the tower bottom of an acrylonitrile recovery tower 1 is supplied to a concn. boiler 2 through a conduit 11 but caustic soda is supplied from a conduit 12 on the way of said conduit 11 to adjust the pH of the waste water to 9 or more. A black conc. solution is discharged from the bottom of the concn. boiler 2 through a conduit 14. On the other hand, unreacted ammonia in the reaction gas flowed out of a reactor for the ammoxidation of propylene is brought into contact with an ammonium sulfate solution to form a raw ammonium sulfate solution which is, in turn, subjected to wet oxidation to deposit and recover ammonium sulfate. Several - several tens % of the ammonium sulfate mother liquid after recovery is taken out of the system as a discharged mother liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater discharged from an olefin ammoxidation process.

Specifically, the present invention relates to a method for treating wastewater containing cyanide compounds and COD components discharged from an olefin ammoxidation process, and wastewater containing ammonium sulfate and organic compounds.

A method for producing unsaturated nitrites such as acrylonitrile and methacrylonitrile by air oxidizing olefins such as propylene and imbutylene and ammonia in the presence of a catalyst is called an ammoxidation reaction. From this ammoxidation step, cyanide and CO
When component D is contained, wastewater containing 6-water, ammonium sulfate, and organic compounds is discharged, but these wastewaters cannot be discharged as they are, and are appropriately treated separately. That is, the reaction residue obtained from this olefin ammoxidation reaction contains the main products, unsaturated nitrile, hydrogen cyanide, unreacted ammonia, acetonate, water, non-condensable gases, and various other organic compounds. , subjected to a purification process.

First, it is rapidly cooled in a quench tower, and in order to remove unreacted ammonia, it is brought into contact with a sulfuric acid solution to convert unreacted ammonia into ammonium sulfate, which is recovered as highly concentrated ammonium sulfate water. Ammonium sulfate is usually wet-oxidized to oxidatively decompose the organic compounds contained therein, but complete oxidation is impossible. Therefore, when concentrating the oxidized waste liquid and crystallizing ammonium sulfate, unoxidized organic compounds become tar and remain in the ammonium sulfate mother liquor, making the ammonium sulfate separation operation difficult and contaminating the crystallized ammonium sulfate. A portion of the ammonium sulfate mother liquor saturated with ammonium sulfate and contaminated with tar is discharged from the system. However, the woman said that the discharged mother liquor containing ammonium sulfate and tar cannot be discharged into public waters, and that there is a method for directly incinerating the discharged mother liquor and then carrying out flue gas desulfurization. A method in which ammonium sulfate is fixed in the form of sodium chloride (mirabilite) with caustic soda or soda carbonate, and then incinerated at a temperature below the melting point of sodium sulfate; A method in which the discharged mother liquor is recycled to the wet oxidation process by
It is processed by a known method such as. However, in method Q), when the oxidation rate is lower than 7S%, tar accumulates during circulation, and in order to remove this tar, a portion of the ammonium sulfate mother liquor must be discharged out of the system again.

Therefore, the known methods (1) and (2) have been adopted as treatment methods, and an effective and economical treatment method for the discharged mother liquor is strongly desired.

On the other hand, the reaction gas from which unreacted ammonia has been removed is then brought into contact with water in an unsaturated nitrile absorption unit, and non-condensable gas is discharged to the outside of the fiber, forming vesicles. '7
7 (ts hydrogen・7′″!) = ) IJ.

and other organic compounds are absorbed by water.

The reaction product absorbed in water is then fed to an unsaturated nitrile recovery column, and the unsaturated nitrile and most of the hydrogen cyanide are distilled out from the top of the column by water extractive distillation and sent to the next l* production step. Hydrogen cyanide (acetonyl) and pinky are extracted from the side stream of the unsaturated nitrile recovery column,
It is purified in an acetonitrile distillation column. A small amount of hydrogen cyanide and water containing organic compounds are discharged from the bottom of the unsaturated nitrile recovery column. A part of this water can be reused as quenching water in the quenching tower, but the rest is discharged outside the system as one-shot water. However, such wastewater usually contains several hundred ppm of cyanide, several φ of C0D components, and several units of total carbon l,, f (hereinafter abbreviated as T-C), and is not directly discharged into public waters. I can't. Such cyanide and CO
As a method for treating wastewater containing component D (FL), a method of treating the wastewater at a high temperature of 100~/gθ°C (% Kaishos, ?-/, ?A, ?sA),
A method of adding all alkali to the folding water, heating and concentrating it, and then adding alkali to the distilled steam and treating it in a pan (Japanese Patent Application Laid-open No. 1973-//q'1g!i) It is known that ■
In this method, if the heating time is not increased at high temperature, the cyanide content can be reduced, but the COD content is still large. Furthermore, the method (b) has problems such as &J, requiring two stages of processing in one piece, which is complicated, and also having an excessively large amount of COD components. Therefore, the distillate vapor obtained through these treatments cannot be discharged into public water bodies, and must be treated by known methods such as incineration or activated sludge treatment. However, in the case of incineration, the supply of distilled steam lowers the furnace temperature, so the supply of fuel must be increased, which leads to an increase in nitrogen oxides (hereinafter abbreviated as NOX). In addition, in the case of activated sludge treatment 1', it is necessary to reduce the load on the activated sludge as much as possible, and the cyanide concentration is preferably 10 ppm or less, more preferably 1/ppm.
Hereinafter, CO] component concentration is preferably SOθppn1 or less, more preferably 30 ppm or less, T-0 is preferably 1θ, OS% or less, more preferably 0.0 J
% or less, 1) H is better than 4/2, is it better to go down g~? There is a necessary chivalry to do so.

In view of these circumstances, the present inventors have been conducting intensive studies on an effective and economical method for treating wastewater containing cyanide compounds and COD components, as well as wastewater containing ammonium sulfate and organic compounds. As a result, it was discovered that ammonium sulfate could be converted to pyrochloride by adding caustic soda to wastewater containing cyanide compounds and COD components, and adding the concentrate obtained by heating and braiding to wastewater containing ammonium sulfate and organic compounds. We have arrived at the present invention.

That is, the present invention is useful for treating wastewater containing cyanide compounds and COD components discharged from an ammoxidation process, as well as wastewater containing ammonium sulfate and organic compounds, and for treating wastewater containing cyanide compounds and COD components. After adding sodium chloride/I and soda to keep the waste water alkaline, it is heated and concentrated to remove cyanide and 00
The distillate vapor with a reduced content of the D component is separated into a concentrated liquid containing a high concentration of cyanide and COD components, and the concentrated liquid is mixed with the ammonium sulfate and the concentrated liquid.

The gist of this method is to add it to wastewater containing organic compounds, convert ammonium sulfate into sodium sulfate and ammonium salt, remove ammonium f-/I as necessary, and then incinerate it.

An example of a method for treating wastewater discharged during the production of acrylonitrile by a propylene ammoxidation method will be described in detail below using figures.

Unreacted ammonia and non-condensable gas are removed from the reaction gas obtained by the ammoxylation reaction of propylene, and the reaction product is supplied to the acrylonitrile recovery column/through the isotube g. In the acrylonitrile recovery column/, acrylonitrile and most of the hydrogen cyanide are distilled out from the top of the column through a special pipe 9 by extractive distillation of water.
It is sent to the next refining process. Acetonitrile and a small amount of hydrogen cyanide are extracted from the side stream 10 of the acrylonitrile recovery column 1 and purified. M wastewater containing cyanide compounds and COD components is discharged from the bottom of the acrylonitrile recovery tower. The wastewater has a cyanide concentration of approximately 50
OpJ river, COD component concentration approximately 3%, T-C approximately 1qb.

1) It is a black liquid of H5-A. The wastewater is transferred to conduit l/f:
11 is supplied to the condensing can, and soda 171 is supplied from an intermediate conduit. Addition of caustic soda
If is the pH of the wastewater after addition, preferably t or more -1-1
More preferably, it is set to 72 or more. In the case of canned fish, the temperature is IOθ℃, the pressure is normal pressure, and the cocoon shrinkage rate is 10-20.
Although it is operated under twice the conditions, the more the lachrymal material is sold, the less the solution after nitrification becomes.I! Iν is preferable because it can reduce the amount of fuel used in the reactor. Dark i? The distilled steam that is distilled from the I can is incinerated in a combustion furnace (not shown), or MY heat output steam cyanide concentration, COD component concentration, 1:hi']' If -C is low, it is best to cool it and treat it with active slurry. in this case,
Since the temperature of the distilled steam is about 100°C, it is heated and pressurized by the Stinim compressor 7, and is effectively used as a heating tank for the distillation column, especially the reboiler 3 of the boiler and compressor, and is then treated with activated sludge. . Such activated sludge treatment of distillate vapor can reduce the amount of fuel used in the incinerator and reduce the generation of N and OX.

Still, T-0 about 10φ from the bottom of the compact can, PHA~
10 black concentrated liquid is discharged through dedicated pipe /4'7'
1 degree.

On the other hand, unreacted ammonia in the reaction gas flowing out from the reactor due to the ammoxidation reaction of propylene was brought into contact with a sulfuric acid solution to convert the ammonia into ammonium sulfate (IliC ammonium stock solution was obtained by converting ammonium sulfate to ammonium sulfate 30-1' 0%). , Contains / ~ 2% as T-C of organic compounds.Wet oxidation of the nuclear liquid 1.After crystallizing and recovering ammonium sulfate, the number φ to the number φ of the ammonium sulfate matrix is discharged outside the system as a mother liquor. This discharged mother liquor is supplied to the Glauber's nitrification 4+,!!Itl through the 2s pipe 73' and the above-mentioned special pipe/g. , the caustic soda added in the insulator tube exists as sodium carboxylate!
In the mirabilite nitrification tank Hironaka, the reaction shown by the following formula (1) occurs, and mirabilite nitrification progresses.

,2FCOONa+tN)l,)2So4-N
a25o4 + , 2FCOONH4... (I)
One inch of addition of the powder in the pestle is 2 moles of sodium ions in the concentrate per 1 mole of sulfate ions in ammonium sulfate, 1.1-hi,
Preferably, t L < is adjusted to 2 to 3 mol.

In carrying out the present invention, if there is an excess of concentrated liquid, the excess can be incinerated in the incinerator 3-, or if by mistake there is a shortage of M liquid, new caustic soda can be cooled. . In the latter case, the ammonia is recovered from the exclusive tank/miyori for safety reasons, and 4 g/q of fluorine nitrification liquid is extracted from the bottom of the fluorine nitrification tank and incinerated in the incinerator S. The amount of oxides (hereinafter abbreviated as s'ox) and NOx generation IA are the same as in the case of conventional new sodium nitride solution made by cooling and flinting caustic soda, despite the presence of ammonium salts. Increase compared to 1-, ``・6J''
The ammonia decomposes in the sintered grade 1 and generates ammonia, and this ammonia suppresses the generation of NOx because the denitrification reaction occurs. be noticed.

As described in detail above, the method of the present invention can reduce smudges by (1) eliminating the use of caustic soda used in glauber's glass.

(II) Contains sodium carboxylate in mirabilization. By using Ff'k ifj+, the generation of ammonia is almost eliminated, and ammonia recovery Ff'k ifj+
And Anmoev 111g useful! Convexity becomes unnecessary.

Even if one tank of mirabilite containing ammonium fr! is incinerated in an incinerator, NOX and SOX will be emitted.

The amount increases by 4.

(Vl The tar melts due to the alkaline solution, and there is no blockage in the tube when both liquids are removed.)

() Hydrogen cyanide of distillate vapor, COD component Oshibi T-
It is possible to reduce the concentration of C, and by applying activated sludge treatment, it is possible to reduce the combustion amount for boiler heating, thereby reducing NOX.
The amount of steam generated can be reduced. The distilled steam can be used in conjunction with the heating section of the reboiler to reduce the amount of steam used for heating.

As such, the method of the present invention is a very significant method from an industrial perspective, particularly as a countermeasure against pollution.

The present invention will be described in more detail below with reference to Examples, but the present invention does not exceed the gist thereof and is not limited to the following Examples.Example/Acrylonitrile recovery tower Concentration of the cyanide water system discharged from the bottom of the tower: 32'Oppm, COD component concentration: 1,j4'
,2,? To wastewater λ containing θθθppm, T-〇80〇, l/-g cylindrical soda 6λ, 3 Kq at T/11
/H is added (at a temperature of 103~ in a 5 Am can λ).
101. The mixture was heated and condensed at 6°C, and distilled vapor/g was distilled from the top of the can, and 11 g of distilled liquid was obtained from the can. The properties of the distilled vapor and concentrated liquid are shown in Table/. The distillate steam was combusted in a boiler 11 thermal combustion furnace. Concentration 1'ik t) j Extraction (-7), 14 Bone occlusion (・-
1. It did not occur at all.

Next, 4'J (mother liquor? 90 Kg/H) containing tar (as T, -C) and the above-mentioned (Me: & Ain solution +/T/ +A to H and @1fc
'% caustic soda/ff' 7.5 K, 7/11 was added, and the tank bottom temperature at 1,13 Q) B゛7 o
Glauber's nitrification was performed at ℃.

The distillation rate of ammonia is 70%.
The nitrified liquid is sent to the incinerator S and incinerated, and the SOX and NOX generation in the gas is below /θppm, /0~20ppu+/r.

Execution 11.2 Same as in Execution 1'zil / To the waste water of g.
a! M? +The properties of the liquid are shown in Table/.

Steam compression of air into distillate 4. ') At p, the load temperature is 1 pressure -j
2. Adding source of the reboiler 3 for heating the V-bulk can and 1. After using it for 7 days, it is cooled and processed into a sludge treatment facility. did. Due to stiffness, the boiler heating combustion furnace NOx Q raw 14:r
J: o,;n+M”/T=distillate steam was reduced, and /6 air of the dead concentrator reboiler was also not reduced.Furthermore, (b”
No blockage of fat (1-12 cm) of 1-liquid solution occurred.

Next, the concentrated solution HgAT/H was added to the ammonium sulfate-containing discharged mother liquor similar to that in Example, and the same as in Example was used to perform mirabilite nitrification and incineration of the mirabilite nitrification solution, resulting in the distillation of ammonia. The rate decreased to 2%, and the amount of generated SO,
Met.

Hs soft example/1i? , except that no caustic soda was added to the water'
- Same as J θ 1 Example / (Concentrate by heating using the method described above, distilled vapor / E T / H 1 condensate 2 T / H is I #. The properties of distilled steam and condensate are 7.

When distilled steam is burned in a combustion furnace for boiler heating, the amount of NOx generated is O1λNM3/T-distilled steam increases by 17. The concentrated liquid was directly incinerated in the incinerator S7.
7j The condensate extraction conduit/conduit was frequently clogged, so the conduit was cleaned frequently.

Next, 11 g of ammonium sulfate-containing discharged mother liquor was added to the discharged mother liquor of 91 /, and 1 g was added to the mother liquor containing ammonium sulfate. Soda, 2 liters of OK9/H were added, and the mirabilite nitrification and incineration of the mirabilite solution were carried out in the same manner as in Example/P, and the distillation rate of ammonia was 94.
1. Also, generation of SOX and NOX. ；Each/
Oppm or less, it was 10 to 10 ppm.

[Brief explanation of drawings]

Figure / is a process diagram showing the ammoxidation (H) wastewater treatment method of the present invention.
・・Zoboiler ・Da・・Brown nitrification tank S・・Incinerator 6
...Combustion furnace or activated sludge treatment equipment 61 Applicant: Mitsubishi Chemical Industries, Ltd. Representative: Chief Patent Attorney (7 persons) Continued from page 1 ■ Int, C1, 4 identification symbol Organized within the agency Number C02F
CDV 6923-4DO Inventor Yasuhiro Kajiwara Shiodori, Kurashiki City. Inside

Claims (1)

[Claims] (1) Wastewater containing cyanide compounds and COD components discharged from the ammoxidation process, and wastewater containing said cyanide compounds and COD components during the treatment of one-shot water containing ammonium sulfate and organic compounds. After cooling the caustic soda to keep the waste water alkaline, the waste water is heated and concentrated to produce distilled vapor with a reduced content of cyanide compounds and COD components and a concentrated liquid containing high concentrations of cyanide compounds and COD components. Separation 1 ~, adding the concentrated liquid to the wastewater containing the ammonium sulfate and organic compounds,
A method for treating wastewater from an ammoxidation process, which comprises converting ammonium sulfate into (jltf f!) sodium and ammonium salts, removing ammonia as necessary, and then incinerating.