JP2023050471A - Method for recovering and reusing acrylic acid production process wastewater - Google Patents

Abstract

To provide a method for further increasing the yield of a product without increasing utility such as steam and electricity.SOLUTION: Provided is a method for recovering and reusing acrylic acid production process wastewater, comprising recovering wastewater generated to drive a decompression device used in an acrylic acid production process and reusing the same for the same and/or a separate acrylic acid production process and a production process of at least one selected from an acrylic acid ester, an acrylic acid metal salt, and an acrylic acid-based (co)polymer which uses the acrylic acid as a raw material.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a method for recovering and reusing wastewater discharged from a decompression device of a distillation column used in an acrylic acid production process, particularly a purification process.

The production process of acrylic acid consists of a catalytic gas-phase oxidation reaction process for propylene or the like and a distillation process for the reaction product obtained in the reaction process. In addition, the distillation process can obtain a product by distilling using one or more distillation columns, focusing on the difference in physical properties (especially the boiling point) between the target substance (product) and impurities in the reaction product. Common. Furthermore, depending on the purpose, chemical treatments are performed to obtain high-purity products.

Distillation in the above distillation column is usually carried out by heating the reaction product and the like, so polymerization of acrylic acid easily occurs. Therefore, as a measure to prevent polymerization in the distillation column, a polymerization inhibitor such as methoxyphenol and molecular oxygen are added, and a decompression device such as a steam ejector is used to reduce the temperature in the distillation column. method is adopted.

In Patent Document 1, for the purpose of improving the yield of (meth)acrylic acid, in the production process of (meth)acrylic acid, a waste liquid containing (meth)acrylic acid generated at a vacuum source in a preliminary purification step and/or a purification step is used to prepare a polymerization inhibitor solution, and a technique of supplying this to the steps subsequent to the collection step is disclosed.

Japanese Patent Application Laid-Open No. 2005-232007

In the above Patent Document 1, a waste liquid containing (meth)acrylic acid generated in a vacuum source in a preliminary purification step and/or a purification step is used to prepare a polymerization inhibitor solution, but the waste liquid is often water. On the other hand, some polymerization inhibitors are water-insoluble. Therefore, the range of use is limited, and it is not necessarily satisfactory from the viewpoint of improving the yield of the product.

The present invention has been made in view of the above-mentioned problems existing in the prior art, and its object is to provide a method for further improving the product yield without increasing utilities such as steam and electric power. .

Therefore, in view of the above problems, the present inventors have found that waste water discharged from a pressure reducing device such as a steam ejector can be recovered and reused in the manufacturing process of the same product and / or other products, and completed the present invention. let me

That is, the present invention provides wastewater generated for driving a decompression device used in an acrylic acid production process, in the same and/or another acrylic acid production process, and an acrylic acid ester using the acrylic acid as a raw material, It is a method of recovering and reusing in at least one manufacturing process selected from the group consisting of metal acrylates and acrylic acid-based (co)polymers.

According to the present invention, the product yield can be further improved without increasing utilities such as steam and electric power.

The present invention relates to the handling of waste water generated during production of acrylic acid.

Specifically, the present invention uses wastewater generated for driving a decompression device used in an acrylic acid production process for the same and/or another acrylic acid production process and an acrylic acid using the acrylic acid as a raw material It is to be recovered and reused in at least one manufacturing process selected from the group consisting of acid esters, acrylic acid metal salts, and acrylic acid-based (co)polymers.

As the production process of acrylic acid, any process may be used as long as vacuum distillation is performed in part or all of the distillation process, and the type of raw material and production process is not limited. That is, in the process for producing acrylic acid, propane, propylene, or acrolein is used as a raw material for a catalytic gas-phase oxidation reaction, the generated acrylic acid-containing gas is collected with a solvent such as water, and the obtained acrylic acid-containing solution is extracted from the acrylic acid-containing solution. A common manufacturing process is to separate low boiling point compounds, high boiling point compounds, etc. contained in the solution by distillation, add an aldehyde treating agent to the resulting crude acrylic acid, and then perform vacuum distillation to obtain high-purity acrylic acid. .

The "depressurizing device" used in the above acrylic acid production process is not particularly limited as long as it is a device for reducing the pressure in the distillation column, but preferably a steam ejector, a liquid-driven ejector, or a liquid-ring vacuum pump. etc. Among them, a steam ejector is preferable from the viewpoint of operability, degree of vacuum, and ease of maintenance.

Apparatus types of the "distillation column" include a plate column, a packed column, or a combination thereof (packing and trays, multiple types of trays, multiple types of packing), and the like. In addition to the most general-purpose sieve trays, the types of trays include dual float trays with no downcomers and few liquid or gas retention areas, disk and donut trays, and turbo grid trays. is not limited to

The plate column, which is one of the above-mentioned "distillation columns", has the advantage of being less likely to be clogged with polymers, but on the other hand, it has the disadvantage of poor gas-liquid contact due to its simple structure, resulting in low separation efficiency. have. Therefore, when a plate column is used, it is preferable to use a multi-stage distillation column having a plurality of plates. The number of stages is usually 1 or more, preferably 3 or more, more preferably 5 or more, from the viewpoint of obtaining the number of theoretical stages necessary for distillation separation. In addition, when the number of stages increases, the gas tends to gather in the central part and the liquid tends to gather on the outside, resulting in deterioration of gas-liquid contact. From the above viewpoints, the upper limit of the number of stages is usually 20 stages or less, preferably 15 stages or less, more preferably 10 stages or less.

The packings used in the packed column, which is one of the above-mentioned "distillation columns", are roughly classified into regular packings and random packings. Specific examples of the structured packing include gauze-type structured packing such as Sulzer Packing (manufactured by Sulzer Chemtech) and Technopack (manufactured by Sanrei Techno), Merapack (manufactured by Sulzer Chemtech), and Technopack ( Sanrei Techno Co., Ltd.), sheet-type structured packing such as MC Pack (Mitsubishi Kagaku Engineering Co., Ltd.), grid-type structured packing such as Flexigrid (Coke Glitch Co., Ltd.), etc. Woven Good Roll Packing (manufactured by Totokenji Co., Ltd.), Super H Pack (manufactured by Nagaoka Co., Ltd.) in which a large number of metal wires are arranged vertically, and the like are also mentioned. Examples of the random packing include Cascade Miniring, IMTP, Interox (manufactured by Cork Glitch), Terralet (manufactured by Tsukishima Kankyo Engineering), and Flexiring (manufactured by JGC).

In order to prevent polymerization of acrylic acids in the distillation column, a polymerization inhibitor or a polymerization inhibitor solution is supplied from the feed liquid, the reflux liquid, and the column in the middle section of the column. Specific examples of the polymerization inhibitor include phenol compounds such as hydroquinone and methoquinone, copper or manganese complexes of dialkyldithiocarbamates such as 2,2-dibutyldithiocarbamic acid, and 4-hydroxy-2,2,6,6-tetramethyl. Examples include nitroxyl radical compounds such as pyridyl oxide, phenothiazine, and the like. Similarly, an oxygen-containing gas such as air or nitrogen-diluted air is supplied.

From the viewpoint of suppressing polymerization caused by the generation of radicals, the bottom temperature of the distillation column is preferably as low as possible, more preferably below the boiling point of acrylic acid under normal pressure, and is 10° C. or higher than the boiling point. Lower is more preferred. Therefore, the bottom temperature is preferably 100°C or lower, more preferably 90°C or lower.

On the other hand, the gaseous component distilled from the top of the distillation column is condensed and liquefied in the condenser and then transferred to the storage tank. Part or all of the condensate transferred to the storage tank is circulated to the distillation column as a reflux liquid. The condenser is generally air-cooled or water-cooled, and can be cooled to a temperature close to that of the outside air, rivers, seawater, etc., to which heat is directly or indirectly released.

In the present invention, a steam ejector, a liquid-driven ejector, a liquid ring vacuum pump, or the like is used as the "decompression device". Among them, an ejector, which is a type of pump that ejects high-pressure steam or water from a nozzle and discharges surrounding water, air, or steam, is preferably used. The ejector is classified into a water ejector, a steam ejector, an air ejector, etc., depending on the type of fluid to be ejected. , steam ejectors are particularly preferred.

The main part of the steam ejector consists of a nozzle and a diffuser. In order to efficiently obtain a high vacuum, it is necessary that the mixture of the driving steam from the nozzle and the intake gas has a speed of sound or higher at the inlet of the diffuser. The degree of vacuum obtained by a single-stage ejector is usually about 100 mmHg (about 13.3 kPa) when the outlet is at atmospheric pressure. be done.

The operating conditions and the like of the decompression device may be appropriately set according to the degree of decompression in the installed distillation column, the production volume, and the like. Therefore, the amount of wastewater generated for driving the decompression device may be appropriately set according to the operating conditions of the decompression device, the operating conditions of the recovery/reuse destination, the production volume, and the like. There are no particular restrictions on the reuse thereof, and examples thereof include use as a solvent for collecting generated gas, a solvent for azeotropic dehydration, a mother liquor of a polymerization inhibitor, and as a raw material.

For example, acrylic acid is contained as an active ingredient in the wastewater generated for driving a decompression device used in the production process of acrylic acid. Therefore, it can be used as a solvent for collecting acrylic acid-containing gas in the same and / or another acrylic acid production process, mixed with the distillate component of the azeotropic dehydration tower of the acrylic acid-containing solution and recovered, or can be used as a mother liquor for polymerization inhibitors. It can also be used as a raw material for acrylic acid metal salts, water-soluble polyacrylic acid (salts), and acrylic acid-based (co)polymers.

As for the collection and reuse of the above-mentioned "wastewater", "same and/or different acrylic acid production process" means the same production process or a different production process if there are multiple acrylic acid production processes. means either one or both of

Acrylic acid ester, which is one of the destinations for recovery and reuse of the above "wastewater", is not particularly limited as long as it is an ester derived from acrylic acid, but is a dehydrated ester with an aliphatic alcohol having 1 to 12 carbon atoms, or Addition products with alkylene oxides having 2 to 6 carbon atoms are preferred.

Specific examples of the dehydrated esters include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isobutyl acrylate, t-butyl acrylate, isononyl acrylate, methoxyethyl acrylate, trimethylolpropane triacrylate, isobornyl acrylate and the like. Moreover, as the addition reaction product, specifically, hydroxyethyl acrylate, hydroxypropyl acrylate, and the like can be mentioned.

The metal salt of acrylic acid, which is one of the destinations for recovery and reuse of the "wastewater", is not particularly limited as long as it is a metal salt derived from acrylic acid. Specific examples include potassium acrylate and zinc acrylate.

The above-mentioned "acrylic acid-based (co)polymer using acrylic acid as a raw material" is a polymer obtained by polymerizing acrylic acid as a monomer (homopolymer), and a polymer obtained by polymerizing acrylic acid and a monomer other than acrylic acid. (copolymer).

In the present invention, the above-mentioned "acrylic acid-based (co)polymer" also includes a polymer of a salt (acrylic acid salt) obtained by neutralizing part or all of acrylic acid, and the polymer is referred to as "poly acrylic acid (salt)”. Specific examples of the "polyacrylic acid (salt)" include water-soluble polyacrylic acid (salt), water-absorbing resin (water-absorbing polyacrylic acid (salt)), and the like.

The acrylate is preferably a monovalent salt, more preferably an alkali metal salt, an ammonium salt, or the like. The alkali metal salt preferably includes sodium salt and potassium salt.

The water-soluble polyacrylic acid (salt) is a polymer that is substantially 100% soluble in water. The water-absorbing resin (water-absorbing polyacrylic acid (salt)) is a polyacrylic acid (salt) having a crosslinked structure exhibiting water-swelling properties, and is 3 times or more its own weight, preferably 10 to 1000 times pure water. Alternatively, it is a polymer that absorbs physiological saline and forms a substantially water-insoluble hydrogel (the water-soluble component content is 25% by mass or less, more preferably 10% by mass or less).

The above polyacrylic acid (salt) may be copolymerized with other monomers or crosslinked with 0.001 to 5 mol% of a crosslinking agent, and may be added to hydrophilic polymers such as starch and polyvinyl alcohol. You may carry out graft polymerization. In addition, the polyacrylic acid (salt) is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, based on the total polymer, acrylic acid and / or its salt, included.

Examples of the polyacrylic acid (salt) in the present invention include, in addition to the above, acrylic acid/maleic acid copolymers, acrylic acid/sulfonic acid monomer copolymers, and the like.

Example 1
Gas phase acrylic acid was obtained by catalytic gas-phase oxidation of a raw material gas containing propylene. For the gaseous acrylic acid, a reaction product containing acrylic acid was collected using water as a collecting solvent, and hydroquinone was added as a polymerization inhibitor to obtain an acrylic acid aqueous solution.

The acrylic acid aqueous solution was separated into acrylic acid and low boiling point compounds containing water and toluene in an azeotropic dehydration tower using toluene as a solvent for azeotropic dehydration. Acrylic acid was withdrawn from the bottom of the azeotropic separation column.

Subsequently, the acrylic acid extracted from the bottom of the azeotropic separation column was introduced into the high-boiling compound separation column to obtain crude acrylic acid from the top of the column, and a high-boiling compound containing a polymerization inhibitor was extracted from the bottom of the column.

An 80% by mass aqueous solution of hydrazine hydrate was added as an aldehyde treating agent to the crude acrylic acid obtained above, introduced into a flash distillation column, and distilled to obtain high-purity acrylic acid from the top of the distillation column. . A steam ejector was used as a decompression device for the distillation column, and the operating conditions of the steam ejector were set so that the pressure at the top of the distillation column was 50 hPa.

Since the waste water generated for driving the steam ejector contained acrylic acid, it was recovered and reused as the collecting solvent. As a result, the yield was improved by the amount of recovery of the acrylic acid in the waste water.

Example 2
The same operation as in Example 1 was carried out, except that the wastewater generated for driving the steam ejector was recovered to the condensation section of the distillate gas of the azeotropic dehydration tower. Also in Example 2, the yield was improved as much as the acrylic acid in the waste water was recovered.

Example 3
The same operation as in Example 1 was performed, except that the waste water generated for driving the steam ejector was used as the raw material for the water absorbent resin. Also in Example 3, the yield was improved as much as the acrylic acid in the waste water was recovered.

Example 4
The same operation as in Example 1 was performed, except that the waste water generated for driving the steam ejector was used as a raw material for butyl acrylate. Also in Example 4, the yield was improved as much as the acrylic acid in the waste water was recovered.

Example 5
The same operation as in Example 1 was performed, except that the waste water generated for driving the steam ejector was used as the raw material for hydroxyethyl acrylate. Also in Example 5, the yield was improved as much as the acrylic acid in the waste water was recovered.

Example 6
The same operation as in Example 1 was performed, except that the waste water generated for driving the steam ejector was used as a raw material for water-soluble polyacrylic acid (salt). Also in Example 6, the yield was improved as much as the acrylic acid in the waste water was recovered.

Example 7
The same operation as in Example 1 was performed, except that the waste water generated for driving the steam ejector was used as a raw material for potassium acrylate. Also in Example 7, the yield was improved as much as the acrylic acid in the waste water was recovered.

ADVANTAGE OF THE INVENTION According to this invention, a product yield can be improved, without increasing utilities, such as steam and electric power.

Claims (8)

Wastewater generated for driving a pressure reduction device used in the acrylic acid production process is used for the same and / or another acrylic acid production process, and acrylic acid esters, acrylic acid metal salts, acrylic acid metal salts, and an acrylic acid-based (co)polymer. 2. The method of claim 1, wherein said pressure reducing device is at least one device selected from the group consisting of a steam ejector, a liquid driven ejector and a liquid ring vacuum pump. 3. The method according to claim 1, wherein the acrylic acid ester is a dehydrated ester of acrylic acid and a linear or branched aliphatic alcohol having 1 to 12 carbon atoms. The dehydrated ester is methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isobutyl acrylate, t-butyl acrylate, isononyl acrylate, methoxyethyl acrylate, trimethylolpropane triacrylate. , and at least one selected from isobornyl acrylate, the method according to claim 3. The method according to any one of claims 1 to 4, wherein the acrylic acid ester is a hydroxyalkyl acrylate which is an addition product of acrylic acid and an alkylene oxide having 2 to 6 carbon atoms. 6. The method of claim 5, wherein said hydroxyalkyl acrylate is hydroxyethyl acrylate and/or hydroxypropyl acrylate. The method according to any one of claims 1 to 6, wherein the metal acrylate is potassium acrylate and/or zinc acrylate. The acrylic acid-based (co)polymer is a water-soluble polyacrylic acid (salt) and/or a water-absorbing resin (water-absorbing polyacrylic acid (salt)) according to any one of claims 1 to 7. the method of.