JPS6314752A - Purification of methacrylic acid - Google Patents

Abstract

PURPOSE:To obtain the titled compound having high purity, excellent polymerizability and reduced coloring of the formed polymer, by using a specific extracting solvent and treating the titled compound with a hydrazine in obtaining the titled compound by catalytic vapor-phase oxidation of isobutylene, etc. CONSTITUTION:Isobutylene, tert-butanol, methacrolein, or isobutyl aldehyde is catalytically oxidized in the vapor phase and the resultant methacrylic acid (MAA)-containing reaction product gas is cooled and condensed to give an aqueous solution of the MAA. Light-boiling substances contained in the above- mentioned aqueous solution are then removed by distillation or stripping and the MAA is extracted from the resultant aqueous solution or the MAA using a 6-20C aliphatic chain saturated hydrocarbon as an extracting extracting solvent. The resultant MAA-containing solution is then treated in steps of separating the solvent, the light-boiling substance and heavy substances, redistilling and purifying the resultant product. In the steps, 0.001-1wt%, particularly 0.01-0.5wt% hydrazine, e.g. hydrazine hydrate or phenylhydrazine, is added to any step thereof (preferably the redistillation and purification step).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for purifying methacrylic acid (hereinafter referred to as MAA). Specifically, the present invention relates to inbutylene,
Cooling of the MAA-containing reaction product gas discharged from the oxidation reactor in a process for producing MAA by the 111 oxidation reaction of tertiary-butanol, methacrolein or isobutyraldehyde (hereinafter referred to as Class 04). From the crude MAA aqueous solution obtained by the condensation operation,
This invention relates to a method for industrially purifying and obtaining MAA of high purity and high quality.

[Conventional technology and problems]

The production of MAA by catalytic gas phase oxidation of the C4 group in one or more stages of reaction is well known in many documents related to the development of oxidation catalysts and process development. However, many years were required before MAA could be produced industrially by catalytic gas phase oxidation reaction. The reason for this is that there are many various by-products in the reaction product gas, and some of these by-products accompany the crude MAA solution, causing various troubles in the MAA purification process. This may have led to a decline in the quality of the MAA product. In other words, in addition to MAA, the reaction product gas contains substances with relatively low boiling points such as methacrolein, acrolein, acrylic acid, acetic acid, acetaldehyde, protoanemonin, and carbon oxides, as well as maleic acid and terephthalic acid. , aromatic carboxylic acids such as toluic acid, benzoic acid, and tar-like substances are present in small amounts. and tar-like substances) are the subsequent M
It has been found that these impurities cause various troubles in the AA purification process and that it is difficult to obtain high quality methacrylic acid.

In order to solve the above-mentioned problems, MAA is extracted from an aqueous MAA solution containing acetic acid and acrylic acid as by-products using an aliphatic or alicyclic hydrocarbon having 5 to 7 carbon atoms, and then distilled to obtain υ high purity. How to obtain MAA of
3112), an aqueous MAA solution in an organic solvent mixture consisting of at least one acetate ester of an aliphatic alcohol having 2 to 4 carbon atoms and at least one hydrocarbon selected from hexane, heptane, and benzene. From MA
After extracting A, the extract is dehydrated and distilled, and then MAAtl is produced by distillation (Japanese Patent Application Laid-Open No. 51-10191
(Refer to Publication No. 3), MAA-containing substances found in gas phase catalytic oxidation reactions of compounds having 4 carbon atoms are combined with sulfonic acid group-containing compounds, carbonyl group-containing compounds other than formaldehyde, and primary and/or secondary amines. A method (see Japanese Patent Application Laid-Open No. 59-4'8439) has been proposed. However, among the above methods, JP-A-49-1
According to the studies of the present inventors, the methods of JP-A-3112 and JP-A-51-101913 contain isobutylene,
High-quality MAA that does not cause deterioration in polymerization performance or coloring due to insufficient removal of various by-products generated during MAA production by catalytic gas-phase oxidation reaction of tertiary-butanol, methacrolein, or isobutyraldehyde.
It was difficult to obtain

Furthermore, the method disclosed in JP-A-59-48439 uses two types of compounds in combination, and also requires consideration of conditions such as treatment time and temperature, which complicates the process and increases costs. Furthermore, according to studies conducted by the present inventors, the quality of the obtained MAA was improved by the above-mentioned treatment, but it was not necessarily at a sufficient level.

Furthermore, as disclosed in JP-A-60-252446, isobutylene, tertiary-butanol,
In the process of producing MAA by catalytic gas phase oxidation of methacrolein or isobutyraldehyde, an aqueous bisulfite solution is added and mixed to the extract containing the extraction solvent and MAA obtained from the extraction step, and further a solvent separation step, By adding and mixing a hydrazine compound to the MAA-containing solution in at least one of the light boiling point separation step and redistillation purification step, high purity MAA can be obtained, and MAA with low polymerization performance and coloring degree can be obtained. It is proposed that it can be done. However, since this method involves a step of adding an aqueous bisulfite solution, it is unavoidable that a new dehydration step is required and the wastewater treatment is costly and complicated.

[Means for solving problems]

Thus, in the process of producing MAA by catalytic gas phase oxidation of isobutylene, tertiary-butanol, methacrolein, or isobutyraldehyde, the present invention efficiently removes generated by-products and stabilizes the ffff process without troubles caused by polymerization. High quality M through continuous operation
The purpose is to provide a method to earn AA. More specifically, identifying the extraction solvent used in the extraction process,
Furthermore, by treating the MAA that can be found with a small amount of hydrazine compounds, MAAI with high purity and excellent polymerization ability and greatly improved coloration of the resulting polymer can be obtained.
provide a way to benefit.

That is, the present invention is specified as follows.

(1) Obtained by cooling and condensing the methacrylic acid-containing reaction product gas discharged from the oxidation reactor in the process of producing methacrylic acid by catalytic gas phase oxidation of inbutylene, tertiary-butanol, methacrolein, or inbutyraldehyde. When a methacrylic acid aqueous solution is purified by first removing light-boiling substances contained in the aqueous solution by distillation or dispersion operation and then by redistillation purification process, an extraction solvent having 6 to 20 carbon atoms, preferably 6 to 1 carbon atoms is used as an extraction solvent.
Methacrylic acid is extracted from the methacrylic acid aqueous solution using the aliphatic chain saturated hydrocarbon of step 2, and a solvent separation step,
A method for purifying methacrylic acid, comprising adding and mixing a hydrazine compound to a methacrylic 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 (11) above, wherein the hydrazine compound is at least one selected from those having the following general formula.

(In the formula, R11 is a hydrogen atom, an alkyl group of CI~,
Indicates a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group. ) By adopting the present invention, troubles in the separation and purification process of MAA, especially the generation of polymer products and precipitation of scale in the distillation column, can be greatly reduced, and the quality of the MAA observed can also be improved by polymerization performance. We were able to obtain a product with a very low content of protoanemonin, maleic acid, etc. Furthermore, the coloring properties of methacrylic acid ester polymers synthesized and purified using this purified MAA were also improved over time.

Hereinafter, aspects of the method of the present invention will be described in detail.

When isobutylene, tertiary-butanol, methacrolein, or isobutyraldehyde is subjected to a single-stage or multi-stage oxidation reaction using an oxidation catalyst mainly composed of molybdenum oxide or its composite oxide, a reaction product mainly composed of MAA can be obtained. . And MAA is usually
It is collected by cooling and condensing as an aqueous solution. This aqueous solution contains a small amount of light-boiling substances such as methacrolein and acetone, so it is subjected to a dispersion process such as distillation.
These light boiling substances are removed. Next, this crude MAA
The aqueous solution is subjected to an extraction operation using an extraction solvent containing at least one of the aliphatic chain saturated hydrocarbons having 6 to 20 carbon atoms specified in the present invention, and the extract containing MAA is It can be grown. The number of carbon atoms specified by the present invention is 6.
~20° In particular, the aliphatic chain saturated hydrocarbon of 6 to 12 is specifically hexane, heptane, octane, nonane,
Examples include decane and dodecane, but these may have branches and may be heated at °C, and may also be a mixture of these hydrocarbons. These extract and separate MAA well,
Moreover, the amount of impurities such as aldehydes extracted is small.

In the present invention, a conventional extraction device is used,
Normal extraction conditions apply. In other words, better results can be obtained.

The location where the hydrazine compound is added is not particularly limited as long as it is intended for the MAA-containing liquid as mentioned above, and it is effective even if it is added at any step in the distillation column for extraction liquid, extractant separation, and light boiling separation. However, it is particularly preferable to add it to the distillate of a high-boiling separation column and redistill it.

The hydrazine compound used in the present invention is a hydrogen atom, an alkyl group having CI to 3, 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, p-nitrophenylhydrazine, 2,4-dinitrophenylhydrazine, etc. are effective.

These hydrazine compounds may be added singly or as a mixture of two or more. Further, the amount added is 0,001 to 1% by weight, preferably 0% to the MAA to be treated.
．． The range is 0.01 to 0.5% by weight.

The process of the invention is carried out in the presence of conventionally known polymerization inhibitors such as hydroquinone, methoxyhydroquinone, methylene blue, phenothiazines, salicylates, dialkyldithiocarbamates, and molecular oxygen.

〔Effect of the invention〕

Although the cause of the phase opening effect due to the use of the extraction solvent and the hydrazine treatment specified in the present invention is not clear, MAA observed in the catalytic gas phase oxidation of isobutylene, tert-butanol, methacrolein, or isobutyraldehyde is It is believed that there are very small amounts of specific by-products, and these by-products have a negative effect on the polymerizability during purification and the quality of the obtained MAA. It is assumed that these by-products can be separated and removed using the specified extraction solvent and extraction conditions, thus solving the above-mentioned problems.

As an effect of the invention, it has become possible to operate for a long period of time without polymerization troubles in MAA and N yarn spinning, which is a great advantage in terms of stable operation. In addition, the hue stability of methacrylic esters synthesized using purified MAA is improved.
It has a great advantage in that it improves the quality of MAA obtained by catalytic gas phase oxidation. Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 Using a molybdenum-based composite oxide as a catalyst for the first stage reaction,
Using a molybdenum-phosphorus heteropolyacid-based catalyst as a catalyst for the subsequent reaction, isobutylene is subjected to a catalytic gas phase oxidation reaction with air in the presence of water vapor, and the resulting reaction product gas is cooled using hydroquinone as a polymerization inhibitor. It was condensed to obtain an aqueous solution containing methacrylic acid. Light boiling substances such as methacrolein were removed by distillation from the resulting aqueous solution, resulting in 24% by weight of methacrylic acid, 3.6% by weight of acetic acid, 1.4% by weight of phthalic acids (o-1m-1p-), and 0.5% by weight of maleic acid. 20 kg/Hr of an aqueous solution containing 8% by weight, 1.0% by weight of a tar-like substance, and 100 ppm of glotoanemonin (hereinafter referred to as PAN) was obtained.

This aqueous solution was supplied from the upper part of the extraction column, and n-hebutane was supplied from the lower part of the extraction column at a rate of 26 kg/Hr to perform extraction continuously in countercurrent. The extraction operation was performed at room temperature and pressure. The extraction column is a rotating disk base with an inner diameter of 70mm and a total height of 1800mm. After the extraction has sufficiently reached extraction equilibrium, the extract (organic layer) is poured into the upper part of the extraction column at a rate of 30.9 kg/l.
- Ir and the raffinate liquid (aqueous layer) from the bottom of the extraction column at 15.1
It was obtained at the rate of kg/Hr. No scum was observed at the interface between the two layers of the extraction tower. PAN in the extract was 30 ppm.

The obtained organic layer was supplied to the 15th stage of a solvent separation column (inner diameter 6B, 30 sheath trays, manufactured by 5TJS304) and distilled at a column top pressure of 105 yn + IT g s reflux ratio of 1.0. The solvent distilled from the top of the column was reused in the extraction column.

As the bottoms, 99.7 Irff1:it% methacrylic acid was obtained. This bottoms is further processed into a light boiling point separation column (inner diameter 6B1, 30 sheath trays, SUS 304
The mixture was supplied to the bottom of a 15th column (manufactured by 5US304) at a top pressure of 35 mmHg and a reflux ratio of 15%, and distilled at a top pressure of 35 mmHg and a reflux ratio of 0.5.

An aqueous solution of 80 g of hydrazine Hitlerd was added to the distilled methacrylic acid solution at a concentration of 0.03% by weight based on the methacrylic acid, and this was added to the distilled methacrylic acid solution in a purification column (inner diameter 6B, sieve tray 1).
5 stages, made of SUS 304), and the top pressure is 35.
Distillation was performed at mmHg and a reflux ratio of 2.0 to obtain purified methacrylic acid. Analysis by gas chromatography showed that the purity of the product was greater than 99.9% by weight, and the amount of total aldehyde determined by the 2,4-dinitrophenylhydrazine method was a trace value. Using this purified methacrylic acid, an esterification reaction is carried out by adding ethylene oxide under an iron methacrylate catalyst, and 2-hydroxyethyl methacrylate (hereinafter referred to as HEMA), which is purified by distillation, is produced in a butanol solvent. , 2'-Azobisbutyronitrile as a polymerization initiator, solution polymerization was carried out at 95°C for 5 hours, and the coloring degree of the obtained polymer was tested at 50°C over time, and the results shown in Table 1 were obtained. .

Incidentally, no troubles due to polymers etc. occurred in the solvent separation column, light boiling point separation column, heavy substance separation column and redistillation purification column during continuous operation for 60 days.

Example 2 The same aqueous methacrylic acid solution used in Example 1 was used, except that the extraction solvent was changed to n-hexane, and 0.05% by weight of hydrazine hydrogen chloride was added to the methacrylic acid. Purification was carried out using the same equipment and method.

No trouble due to polymerization occurred during continuous operation of the solvent separation column, light boiling point separation column, heavy substance separation column, and redistillation purification column for 60 days. Using the obtained purified methacrylic acid, a hue change test of a HEMA polymer was conducted in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Example 3 The same aqueous methacrylic acid solution used in Example 1 was used, except that the extraction solvent was changed to n-octane, and 0.05% by weight of hydrazine hydrogen chloride was added to the methacrylic acid.
Purification was carried out using the same equipment and method as in Example 1.

During 60 days of continuous operation, no troubles due to polymerization occurred in the solvent separation column, the light boiling point separation column, and the product separation column and redistillation column. Using the obtained purified methacrylic acid, a hue change test of a HEMA polymer was conducted in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Comparative Example 1 The same aqueous methacrylic acid solution used in Example 1 was treated with the same equipment and method as in Example 1. However, 8
No aqueous solution of hydrazine hittride was added.

No troubles due to polymerization occurred in the solvent separation column, light boiling point separation column, heavy substance separation column and redistillation purification column during continuous operation for 60 days. Using the purified methacrylic acid obtained, a hue change test of a HEMA polymer was carried out in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Comparative Example 2 Same as in Example 1 except that the same aqueous methacrylic acid solution used in Example 1 was used, except that the extraction solvent was changed to toluene, and 0.1% by weight of hydrazine hydrogen hydride was added to the methacrylic acid. Purification was carried out using equipment and methods.

Polymerization occurred in each reboiler of the solvent separation column, light boiling point separation column, and heavy substance separation column, and the purification operation had to be stopped after 10 hours. Using the obtained purified methacrylic acid, a hue change test of IIEMA polymer was carried out in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Comparative Example 3 The same methacrylic acid aqueous solution used in Example 1 was used, except that the extraction solvent was changed to toluene, and the 80% hydrazine hydrogen hydride aqueous solution was not added.

Purification was carried out using the same equipment and method as in Example 1. Polymerization occurred in each reboiler of the solvent separation column, light boiling point separation column, and heavy substance separation column, and the purification operation had to be stopped after 10 hours. Using the obtained purified methacrylic acid, a hue change test of a HEMA polymer was conducted in the same manner as in Example 1, and the results shown in Table 1 were obtained.

Table 1 HEMA polymer hue change (50”C) Note 1) After 21 days APHA 100 or less Good 100-200 OK 200 or more Not applicable Patent applicant Representative of Nippon Shokubai Chemical Co., Ltd.
Tsuyoshi Yamaguchi.

Claims (2)

[Claims] (1) In the process of producing methacrylic acid by catalytic gas phase oxidation of isobutylene, tert-butanol, methacrolein or isobutyraldehyde, it is obtained by cooling and condensing the methacrylic acid-containing reaction product gas discharged from the oxidation reactor. First, light boiling substances contained in the methacrylic acid aqueous solution are removed by distillation or dispersion operation, and then the obtained methacrylic acid aqueous solution is subjected to an extraction process, a solvent separation process, a light boiling point separation process, and a heavy substance separation process. When processing and refining in the redistillation refining step, methacrylic acid is extracted from the methacrylic acid aqueous solution using an aliphatic chain saturated hydrocarbon having 6 to 20 carbon atoms as an extraction solvent, and a further solvent separation step is performed to remove light boiling point substances. A method for purifying methacrylic acid, which comprises adding and mixing a hydrazine compound to a methacrylic acid-containing solution in at least one of a separation step, a heavy substance separation step, and a redistillation purification step. (2) The method according to claim (1), 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 R_2 represent a hydrogen atom, an alkyl group of C_1_ to_3, a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group.)