JPS61218556A - Purification of acrylic acid - Google Patents

Abstract

PURPOSE:To remove impurities having polymerization-suppressing or polymerization-inhibiting action from crude acrylic acid produced by the catalytic vapor-phase oxidation of propylene, etc., by treating the crude acrylic acid with an aqueous solution of a bisulfite and then with a hydrazine. CONSTITUTION:A reaction product gas obtained by the catalytic vapor-phase oxidation of propylene or acrolein is cooled and condensed to obtain an aqueous solution of acrylic acid, which is distilled or evaporated to remove the components having low-boiling point. The aqueous solution of acrylic acid to be extracted and/or the acrylic acid solution obtained from the extraction process and containing extraction solvent are mixed with an aqueous solution containing a bisulfite in an amount of 0.5-15wt%, especially 1-10% based on the acrylic acid. Acrylic acid having high purity and quality is produced by adding 0.001-1%, especially 0.01-0.5% hydrazine compound to the separated and recovered acrylic acid solution in either of the following solvent-separation, low-boiling component separation, high-boiling component separation and redistillation processes (preferably added to the distillate after the separation of the high-boiling component).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for purifying acrylic acid. Specifically, the present invention is a process for producing acrylic acid by catalytic gas phase oxidation reaction of propylene or acrolein, from an aqueous acrylic acid solution found by cooling and condensing the acrylic acid-containing reaction product gas discharged from an oxidation reactor.
4. It relates to a method for industrially efficiently purifying and obtaining high-purity and high-quality acrylic acid without any trouble.

[Prior art]

Scales in which acrylic acid is produced by catalytic gas phase oxidation of compounds having three carbon atoms, such as propylene and acrolein, have been known in recent years from numerous documents relating to the development of oxidation catalysts and process developments. However, in the process of separating and refining high-purity acrylic acid from the aqueous acrylic acid solution,
It is true that we encounter various difficulties. The reason for this is that even though the catalyst performance is at a high level, various by-products are present in the reaction products. This is because it is extremely difficult to separate and remove these by-products from the intended acrylic acid, and various problems in the acrylic acid purification process have not yet been solved. In addition to acrylic acid, the reaction product gas contains acrolein, propionic acid, acetic acid,
Substances with relatively low boiling points such as formic acid, acetaldehyde, formaldehyde, and carbon oxides, maleic acid, furfural, protoanemonin, aromatic carboxylic acids such as benzoic acid and phthalic acids, and tar-like substances are present in small amounts. Of these, by-products with relatively high boiling points (aromatic compounds and tar-like substances) that dissolve in the crude acrylic acid aqueous solution have caused various troubles in the subsequent acrylic acid purification process. Furthermore, it has been found that these impurities make it difficult to obtain high quality acrylic acid.

In order to overcome the above-mentioned difficulties, the present inventors investigated a method for purifying acrylic acid characterized by bringing bisulfite into contact with an aqueous solution of acrylic acid produced by the oxidation reaction, and published this method in JP-A No. 59 In the invention of No.-10546, it was established and proposed as a method for purifying acrylic acid. The present invention relates to an improved method of this proposal. As mentioned above, in addition to the main product acrylic acid, many by-products are produced by the oxidation reaction, and these are the cause of trouble in the separation and purification process of acrylic acid. The invention of No. 59-10546 adds bisulfite to an acrylic acid aqueous solution, and converts by-product impurities contained in the acrylic acid aqueous solution, especially tar-like substances mainly composed of high-boiling aldehydes, into bisulfite. The gist of this method is to purify diacrylic acid by reacting and leaving these reactants in the aqueous layer.

By adopting this proposed method, troubles in the purification process were resolved and it became possible to obtain highly pure acrylic acid.

[Problem that the invention seeks to solve]

However, in recent years, there has been a wide range of development in the fields of application of acrylic acid, particularly in various application areas, and the demands for higher purity and higher quality of raw material monomers and their esters are increasing. Under such circumstances, it has been found that the acrylic acid obtained by the above method or the esters obtained by synthesizing various esters using this acrylic acid are still not fully satisfactory in terms of quality. did.

In other words, the purified acrylic acid obtained by the method proposed above still contains trace amounts of impurities that are difficult to completely remove by distillation, and these impurities may cause acrylic acid to be homopolymerized or copolymerized with it. When copolymerizing with a monomer, the induction time of the polymerization reaction is lengthened,
It has also been found that it has the disadvantage of acting as a chain terminator, which causes the formation of low polymerization degree polymers.

: A last resort to solve the problem] As a result of intensive studies to overcome the above-mentioned drawbacks, the present inventors have found that trace amounts of impurities contained in acrylic acid produced by the oxidation reaction have a polymerization inhibiting effect or They discovered that acrylic acid is a causative substance that has an inhibiting effect, found an effective method for its removal, and thus established a new industrially highly efficient purification method for acrylic acid.

The present invention is characterized in that impurities in crude acrylic acid found in the catalytic gas phase oxidation reaction of propylene and acrolein are treated with an aqueous bisulfite solution in the purification process, and then further treated with a hydrazine compound. A method for purifying acrylic acid is provided.

That is, the present invention is specified as follows.

(1) In the process of producing acrylic acid by catalytic gas phase oxidation of propylene or acrolein, the aqueous acrylic acid solution produced by cooling and condensing the acrylic acid-containing reaction product gas discharged from the oxidation reactor is first included in the aqueous solution. The light boiling point substances that are present are removed by distillation or dispersion operation, and then the acrylic acid from the resulting aqueous acrylic acid solution is sequentially processed through an extraction process, a solvent separation process, a light boiling point separation process, a heavy substance separation process, and a redistillation purification process. When separating and purifying the acrylic acid aqueous solution supplied to the extraction step and/or the extract containing the extraction solvent and acrylic acid seen from the step, an aqueous bisulfite solution is added and mixed, and further a solvent separation step, A method for purifying acrylic acid, comprising adding and mixing a hydrazine compound to an acrylic acid-containing solution in at least one of a light boiling point separation step, a heavy substance separation step, and a redistillation purification step.

(2) The method according to (1) above, wherein the bisulfite is at least one selected from the group consisting of alkali metal salts and ammonium salts.

(3) The method according to (1) or (2) above, wherein the hydrazine compound is at least one selected from those having the following general formula.

(In the formula, R1 and stone represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group.) [Function] Adopting the present invention This greatly reduces troubles in the separation and purification process of acrylic acid, especially the generation of polymer products and scale precipitation in the distillation column.In addition, the quality of the acrylic acid observed is excellent in polymerization performance. It becomes possible to obtain highly pure and high quality products with extremely low contents of aldehydes and ketones such as acrone, protoanemonin, and furfural, and maleic acid.

Next, the present invention will be explained in more detail.

When propylene or acrolein is subjected to a single-stage or multi-stage oxidation reaction using an oxidation catalyst prepared based on molybdenum oxide or its composite oxide, a reaction product containing acrylic acid as a main component is obtained. The acrylic acid is then collected, usually as a condensed aqueous solution containing acrylic acid. This aqueous acrylic acid solution is then subjected to distillation or dispersion operations to remove light boiling point substances, and then extracted with a specific organic solvent to obtain an extract containing acrylic acid.

Extraction solvents specified by the present invention include those that are substantially insoluble in water and form an azeotropic composition with water, specifically aromatic hydrocarbons such as benzene, toluene, xylenes, ethylbenzene, and acetic acid. Acetic esters such as inpropyl and isobutyl acetate, hydrocarbons such as n-hexane and n-heptane, and ketones such as methyl isobutyl ketone are used.

Regarding extraction equipment, extraction conditions, etc., conventional methods and equipment can be used as appropriate.

In the method of the present invention, as the first operation in these steps, an aqueous bisulfite solution is added to an aqueous solution or extract containing acrylic acid, and after thorough mixing and contact, the two layers are separated, and the organic layer seen is separated. is subjected to a subsequent distillation purification operation.

The bisulfite used in the present invention is selected from alkali metal salts such as sodium, potassium, and cesium, and ammonium salts, and sodium salts, potassium salts, and ammonium salts are particularly preferably used. These are used in the form of saturated aqueous solutions with concentrations of 10% by weight or more,
The amount used is in the range of 0.5 to 15% by weight, preferably 1 to 10% by weight based on the target acrylic acid. In order to separate and recover acrylic acid from crude acrylic acid treated with an aqueous solution of bisulfite, it is sufficient to make the extraction solvent coexist and perform two-layer separation.In particular, the presence of a water-insoluble organic solvent is essential; After layer separation, the solvent layer is determined so that most of the acrylic acid remains in the oil layer, and the bisulfite is added so that the proportion of acrylic acid that migrates to the aqueous layer is 10% by weight or less, preferably 5% by weight or less. It is necessary to determine the amount of water added accordingly.

Therefore, for this purpose, the amount of organic solvent should be 10 to 5
It must be present in an amount of 0% by weight, preferably 20 to 40% by weight.

The easiest way to carry out the method of the present invention is to mix and contact an aqueous bisulfite solution with an acrylic acid-containing extract. In this case, after thoroughly mixing both solutions in a line mixer or continuous or semi-continuous stirring tank, the two solutions are separated by being sent to a two-layer separation tank, or a continuous extraction device is used. is preferred. Furthermore, this aqueous layer can be recycled into the stirring tank. The contact time between both liquids varies depending on the mixing method, but is usually 0.1 to 1 hour. Further, the contact temperature does not require a particularly high temperature, and is usually in the range of room temperature to 60°C.

The method of adding the hydrazine compound is not particularly limited as long as the acrylic acid-containing liquid has been treated with an aqueous bisulfite solution.

Effects can be obtained by adding it to any step of the extraction liquid, extractant separation, light-boiling separation, or high-boiling distillation column, but it is especially effective when added to the distillate of the high-boiling separation column for repurification distillation. is excellent and preferable.

In the hydrazine compounds used in the present invention, 2 below represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group. ) Among these hydrazine compounds, monosubstituted hydrazines give particularly preferable results. Specifically, hydrazine hydrazine, phenylhydrazine, and p-nitrophenylhydrazine y,z,4-dinitrophenylhydrazine are effective.

These hydrazine compounds may be added singly or as a mixture of two or more.

Also, the amount added is 0.001 per acrylic acid to be treated.
-1% by weight, preferably 0.01-0.5% by weight.

The method of the present invention uses conventionally known polymerization inhibitors such as hydroquinone, methoxynohydroquinone, methylene blue,
It is carried out in the presence of phenothiazines, salicylates, dialkyldithiocarbamates and molecular oxygen.

Hereinafter, the present invention will be explained in more detail by giving examples.

Example 1 Using a molybdenum-based composite oxide as a catalyst for the first stage reaction,
Using a catalyst based on a molybdenum-vanadium complex oxide as a catalyst for the subsequent reaction, propylene is subjected to a catalytic gas phase oxidation reaction with air in the presence of water vapor, and the resulting reaction gas is cooled and condensed to inhibit polymerization. An aqueous solution containing acrylic acid containing hydroquinone as an agent was obtained. Light boiling substances such as acrolein were removed by distillation from the resulting aqueous solution, resulting in 24% by weight of acrylic acid, 0.8% by weight of acetic acid, 0.5% by weight of phthalic acids (ortho, meta, para), and 0.8% by weight of maleic acid. %, a tar-like substance of 1.0% by weight, and 20 kg/Hr of an aqueous solution containing 65 ppm of protoanemonin (hereinafter abbreviated as PAN) was obtained.

This aqueous solution was supplied from the upper part of the extraction column, and isobutyl acetate was supplied from the lower part of the extraction column at a rate of 20 kg/Hr to perform extraction continuously in countercurrent. The extraction operation was performed at room temperature and pressure. The extraction tower is a rotating disk tower with an inner diameter of 70mm and a total height of 1800m. After the extraction has sufficiently reached extraction equilibrium,
26.9 kg/26.9 kg of extract (organic layer) from the top of the extraction tower
Hr, extract the raffinate (aqueous layer) from the bottom of the extraction tower at 13.1
Each was obtained at the rate of kg/Hr. P in the extract
AN was 47 ppm.

The resulting extract was mixed with a 30% by weight aqueous sodium bisulfite solution at a rate of 0.086 ky/Hr using a line mixer, and then supplied to a stirring tank for a contact time of 0.5 hours. Organic layer 26.9 kg in layer separation tank
/Hr and the aqueous layer was separated into 0.096 kg7Hr. The obtained organic layer was distilled using a solvent separation column. The solvent distilled from the top of the column was reused in the extraction column. 96.0 for bottom liquid
- of acrylic acid was obtained. This bottoms liquid was further distilled in a light boiling point separation column, and the bottoms liquid was supplied to the bottom of a heavy substance separation column and distilled. To the acrylic acid distilled from the top of the column, add an 80% aqueous solution of human 2-Zinhthard to the acrylic acid.
．． 0.7% by weight was added to the bottom of the purification column, and purified acrylic acid was obtained by distillation. When analyzed by gas chromatography, the purity of the product was 99.9% by weight.
That was it.

Using the purified acrylic acid found, an esterification reaction with n-butanol (using a sulfuric acid catalyst and benzene dichloromethane) was carried out to produce n-butyl acrylate (hereinafter referred to as
AB) in xylene solvent as a polymerization initiator, 2
,2'-azo, bisbutyronitrile (hereinafter referred to as human IBN)
Solution polymerization was carried out at 115° C. for 5 hours using the following methods: The change in hue of the obtained polymer over time was tested at 50° C., and the results shown in Table 1 were obtained.

Comparative Example 1 The same aqueous acrylic acid solution obtained in Example 1 from which light boilers had been removed was purified using the same apparatus and method as used in Example 1. However, hydrazine hydrate was not added.

When the hue change test of the AB polymer was carried out in the same manner as in Example 1 using the purified acrylic acid obtained, the results shown in Table 1 were obtained.

Example 2 Using the purified acrylic acid obtained in Example 1, esterification reaction was carried out by adding ethylene oxide under the catalyst of iron acrylate, followed by distillation purification to obtain 2-human xyethyl acrylate (hereinafter referred to as , HgA) in a butanol solvent with AIBN as a polymerization initiator at 95°C for 50 minutes.
Time-solution polymerization was carried out, and the results shown in Table 1 were obtained in the hue change test of the obtained polymer.

Comparative Example 2 A color change test of the HEA polymer obtained in the same manner as in Example 2 using the purified acrylic acid obtained in Comparative Example 1 yielded the results shown in Table 1.

Comparative Example 3 The same aqueous acrylic acid solution from which light boilers had been removed as in Example 1 was purified using the same equipment and method as used in Example 1 without adding sodium bisulfite. As a result, solid matter precipitated in each column of the solvent separation column, light boiling point separation column, and heavy substance separation column, and polymerization occurred in the reboiler, making it necessary to stop the purification operation after 10 hours.

In addition, a hue change test of the HEA polymer obtained in the same manner as in Example 2 using the purified acrylic acid obtained gave the results shown in Table 1.

Patent applicant Nippon Shokubai Kagaku Kogyo Co., Ltd., 97
゛＼

Claims (3)

[Claims] (1) In the process of producing acrylic acid by catalytic gas phase oxidation of propylene or acrolein, an acrylic acid aqueous solution obtained by cooling and condensing the acrylic acid-containing reaction product gas discharged from the oxidation reactor is first Light boiling point substances contained in the aqueous solution are removed by distillation or dispersion operation, and then acrylic acid is extracted from the resulting acrylic acid aqueous solution through an extraction process, a solvent separation process, a light boiling point separation process, a heavy substance separation process and redistillation. When sequentially treating and separating and purifying in the purification process, an aqueous bisulfite solution is added to and mixed with the acrylic acid aqueous solution supplied to the extraction process and/or the extract containing the extraction solvent and acrylic acid obtained from the process, A method for purifying acrylic acid, further comprising adding and mixing a hydrazine compound to the acrylic acid-containing solution in at least one of a solvent separation step, a light boiling point separation step, a heavy substance separation step, and a redistillation purification step. . (2) The method according to claim (1), wherein the bisulfite is at least one selected from the group consisting of alkali metal salts and ammonium salts. (3) The method according to claim (1) or (2), wherein the hydrazine compound is at least one selected from those having the following general formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_1 and B_2 represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group)