JPH0324459B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention uses methacrylic acid (hereinafter referred to as MAA).
This invention relates to a method for refining. More specifically, the present invention is directed to the catalytic gas phase oxidation reaction of isobutylene, tert-butanol, methacrolein or isobutyraldehyde (hereinafter referred to as _C4 ).
A method for industrially purifying and obtaining high-purity and high-quality MAA from a crude MAA aqueous solution obtained by cooling and condensing the MAA-containing reaction product gas discharged from an oxidation reactor in the process of manufacturing MAA. Regarding. [Prior art and problems] It is known from many documents related to the development of oxidation catalysts and processes that MAA can be produced by catalytic gas phase oxidation of the above _C4 group in one or more stages of reaction. It is. However, it took many years 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 are mixed into the crude MAA solution, causing various troubles in the MAA purification process. This caused a decline in the quality of the product MAA. In other words, in the reaction product gas,
In addition to MAA, methacrolein, acrolein,
Substances with relatively low boiling points such as acrylic acid, acetic acid, acetaldehyde, protoanemonin, and carbon oxides, aromatic carboxylic acids such as maleic acid, terephthalic acid, toluic acid, benzoic acid, and tar-like substances are present in small amounts. Among these, by-products with relatively high boiling points (aromatic compounds and tar-like substances) that dissolve in the crude MAA solution can cause various troubles in the subsequent MAA purification process. Furthermore, it has been found that these impurities make it difficult to obtain high quality methacrylic acid. In order to solve the above-mentioned problems, aliphatic or alicyclic hydrocarbons having 5 to 7 carbon atoms were used as by-products from MAA aqueous solutions containing acetic acid and acrylic acid.
MAA is extracted and further distilled to obtain high purity
A method for obtaining MAA (see JP-A-49-13112), from 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. A method of extracting MAA from an aqueous MAA solution using an organic solvent mixture of MAA-containing substances obtained by phase contact oxidation reaction,
A method of treatment with a sulfonic acid group-containing compound, a carbonyl group-containing compound other than formaldehyde, and primary and/or secondary amines has been proposed (see JP-A-59-48439). However, among the above-mentioned methods, the methods of JP-A-49-13112 and JP-A-51-101913,
According to studies by the present inventors, by catalytic gas phase oxidation reaction of isobutylene, tert-butanol, methacrolein or isobutyraldehyde.
It has been difficult to obtain high-quality MAA that does not cause deterioration in polymerization performance or coloration due to insufficient removal of various by-products generated during the production of MAA. Furthermore, the method disclosed in JP-A-59-48439 uses two types of compounds in combination, and it is also necessary to consider conditions such as treatment time and temperature, which has the disadvantage of complicating the process and increasing costs. Furthermore, according to studies by the present inventors, the quality of the obtained MAA was improved by the above-mentioned treatment, but was not necessarily at a sufficient level. Furthermore, as disclosed in JP-A No. 60-252446, in the process of producing MAA by catalytic gas phase oxidation of isobutylene, tert-butanol, methacrolein, or isobutyraldehyde, an extraction solvent obtained from the extraction step is used. and
A bisulfite aqueous solution is added and mixed to the extract containing MAA, and at least one of the solvent separation step, light boiling point separation step, and redistillation purification step is performed.
High purity MAA is obtained by adding and mixing a hydrazine compound to the MAA-containing solution in two steps.
It has also been proposed that MAA with low polymerization performance and low degree of coloration can be obtained. 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 expensive and complicated. [Means for Solving the Problems] Thus, the present invention efficiently removes generated by-products in the process of producing MAA by catalytic gas phase oxidation of isobutylene, tert-butanol, methacrolein or isobutyraldehyde, The purpose of the present invention is to provide a method for obtaining high-quality MAA through stable continuous operation of the purification process without troubles caused by polymerization. More specifically, by specifying the extraction solvent used in the extraction process and further treating the obtained MAA with a small amount of hydrazine compounds, we have achieved high purity and excellent polymerization ability, and the resulting polymer has extremely high coloration. Provide an improved way to obtain MAA. 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 isobutylene, tert-butanol, methacrolein, or isobutyraldehyde. A methacrylic acid aqueous solution is first removed by distillation or dispersion operation to remove light boiling substances contained in the aqueous solution, and then the obtained methacrylic acid aqueous solution is subjected to an extraction step, a solvent separation step, a light boiling point separation step,
When processing and refining in the heavy substance separation process and redistillation purification process, carbon atoms with 6 to 6 carbon atoms are used as extraction solvents.
Methacrylic acid is extracted from the methacrylic acid aqueous solution using a 20, preferably 6 to 12 aliphatic chain saturated hydrocarbon, and further a solvent separation step, a light boiling point separation step, a heavy material separation step and a re-evaporation purification step are carried out. A method for purifying methacrylic acid, which comprises adding and mixing a hydrazine compound to a methacrylic acid-containing solution in at least one step. (2) The method according to (1) above, wherein the hydrazine compound is at least one selected from those having the following general formula. (In the formula, R ₁ and R ₂ represent a hydrogen atom, a C _1-3 alkyl group, a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group.) By adopting the present invention, MAA separation of,
Trouble in the purification process, especially the generation of polymer products and scale precipitation in the distillation column, is greatly reduced, and the quality of the obtained MAA is good, with good polymerization performance and low content of protoanemonin, maleic acid, etc. I was able to get very few products. 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-tert-butanol, methacrolein or isobutyraldehyde is subjected to a single-stage oxidation 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. . Then, MAA is usually collected by cooling and condensing as an aqueous MAA solution. Since this aqueous solution contains a small amount of light-boiling substances such as methacrolein and acetone, it is subjected to a dispersion process such as distillation to remove these light-boiling substances. Then,
This crude MAA aqueous solution is subjected to an extraction operation using an extraction solvent containing at least one kind of aliphatic chain saturated hydrocarbons having 6 to 20 carbon atoms specified in the present invention, and the MAA An extract containing . Here, the aliphatic chain saturated hydrocarbon having 6 to 20 carbon atoms, particularly 6 to 12 carbon atoms, specified by the present invention specifically includes hexane, heptane, octane, nonane, decane, dodecane, etc. It may be branched, or it may be a mixture of these hydrocarbons. These extract and separate MAA well, and extract only a small amount of impurities such as aldehydes. In the present invention, a conventional extraction device is used, and conventional extraction conditions are applied, that is, a conventional countercurrent contact type device is used, the temperature range is from room temperature to 70°C, and the extractant ratio is in the range of 0.5 to 1.5. Good results can be obtained by operating with . The location where the hydrazine compound is added is as described above.
It is not particularly limited as long as it is intended for MAA-containing liquids, and it can be added at any stage of the distillation column for extraction liquid, extractant separation, and low-boiling separation, but it is especially effective for high-boiling separation. Preferably, it is added to the column distillate and redistilled. The hydrazine compound used in the present invention has the following general formula.

〔Effect of the invention〕

Although the cause of the mutual effect caused by the use of the extraction solvent specified in the present invention and the hydrazine treatment is not clear, MAA obtained by catalytic gas phase oxidation of isobutylene, tert-butanol, methacrolein, or isobutyraldehyde It is believed that there are trace amounts of unique by-products, and these by-products adversely affect 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 a result of the invention, it has become possible to operate the MAA refining system for a long period of time without polymerization troubles, which is a great advantage in terms of stable operation. In addition, improved hue stability of methacrylic acid esters synthesized using purified MAA was obtained using catalytic gas phase oxidation method.
It has great merit in that it improves the quality of MAA. Examples of the present invention will be shown below, but the present invention is not limited thereto. Example 1 A molybdenum-based composite oxide was used as a catalyst for the first reaction, and molybdenum was used as a catalyst for the second reaction.
Using a catalyst based on a phosphorous heteropolyacid, 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 and condensed using hydroquinone as a polymerization inhibitor to form an aqueous solution containing methacrylic acid. I got it. Light boiling substances such as methacrolein were removed by distillation from the resulting aqueous solution, and 24% by weight of methacrylic acid, 3.6% by weight of acetic acid,
20 kg/hr of an aqueous solution containing 1.4% by weight of phthalic acids (o-, m-, p-), 0.8% by weight of maleic acid, 1.0% by weight of tar-like substances, and 100ppm of protoanemonin (hereinafter referred to as PAN) was obtained. This aqueous solution was supplied from the upper part of the extraction column, and n-heptane 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 tower has an inner diameter of 70 mm and a total height of 1800 mm.
mm rotating disk tower. After the extraction sufficiently reached extraction equilibrium, an extract (organic layer) was obtained from the upper part of the extraction column at a rate of 30.9 Kg/Hr, and a raffinate solution (aqueous layer) was obtained from the lower part of the extraction column at a rate of 15.1 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 6 ^B , 30 sieve trays, made of SUS304) and distilled at a column top pressure of 105 mmHg and a reflux ratio of 1.0. The solvent distilled from the top of the column was reused in the extraction column. 99.7% by weight of methacrylic acid was obtained as bottom liquid. This bottoms was further fed to the 15th stage of a light boiling point separation column (inner diameter 6 ^B , 40 sieve trays, made of SUS304) and distilled at a column top pressure of 35 mmHg and a reflux ratio of 15. The bottoms are collected in a heavy matter separation column (inner diameter 6 ^B , sieve tray).
15 stages, made of SUS304) is supplied to the bottom of the tower, and the top pressure is 35 mm.
Hg was distilled at a reflux ratio of 0.5. Hydrazine hydrate 80 in distilled methacrylic acid solution
% aqueous solution was added to methacrylic acid at a concentration of 0.03% by weight, and this was supplied to the bottom of a purification tower (inner diameter 6 ^B , 15 sieve trays, made of SUS304), and the top pressure was 35 mmHg and the reflux ratio was 2.0. Distillation yielded purified methacrylic acid. When analyzed by gas chromatography, the purity of the product was over 99.9% by weight, with a purity of 2.4% by weight.
- The total aldehyde content determined by the dinitrophenylhydrazine method was a trace measurement. 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) obtained by distillation is purified in a butanol kiln medium. Using 2,2'-azobisbutyronitrile as a polymerization initiator, solution polymerization was carried out at 95℃ for 5 hours, and the coloring degree of the obtained polymer was tested at 50℃ with the results shown in Table 1. I got it. The solvent separation column, light boiling point separation column, heavy substance separation column and redistillation purification column did not experience any trouble due to polymers during 60 days of continuous operation. 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 hydrate was added to the methacrylic acid. Purification was carried out using equipment and methods. The solvent separation column, light boiling point separation column, heavy substance separation column and redistillation purification column are all in continuous operation for 60 days.
No troubles due to polymerization occurred. 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 hydrate was added to the methacrylic acid. Purification was carried out using the same equipment and method. The solvent separation column, light boiling point separation column, heavy substance separation column and redistillation purification column are all in continuous operation for 60 days.
No troubles due to polymerization occurred. 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, an 80% aqueous hydrazine hydrate solution was not 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. In the same manner as in Example 1 using the purified methacrylic acid obtained.
When we conducted a hue change test on HEMA polymers, we obtained the results shown in Table 1. Comparative Example 2 The same equipment and equipment as in Example 1 were used, except that the same aqueous methacrylic acid solution used in Example 1 was used, the extraction solvent was changed to toluene, and 0.1% by weight of hydrazine hydrate was added to the methacrylic acid. It was purified by the following method. Polymerization occurred in the reboilers of the solvent separation column, light boiling point separation column, and heavy substance separation column, and purification operations had to be stopped after 10 hours. Using the obtained purified methacrylic acid, in the same manner as in Example 1,
When we conducted a hue change test on HEMA polymers, we obtained the results shown in Table 1. 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 hydrate aqueous solution was not added.
Purification was carried out using the same equipment and method as in Example 1. Polymerization occurs in the reboilers of the solvent separation tower, light boiling point separation tower, and heavy material separation tower, and purification operations are carried out.
It had to be stopped after 10 hours. Using the obtained purified methacrylic acid, the same procedure as in Example 1 was carried out.
When we conducted a hue change test on HEMA polymers, we obtained the results shown in Table 1.

【table】

Claims (1)

[Scope of Claims] 1. In a process for producing methacrylic acid by catalytic gas phase oxidation of isobutylene, tert-butanol, methacrolein or isobutyraldehyde, a process for producing methacrylic acid by cooling and condensing the methacrylic acid-containing reaction product gas discharged from an oxidation reactor. The obtained methacrylic acid aqueous solution is first removed by distillation or dispersion operation to remove the light boiling point substances contained in the aqueous solution, and then the obtained methacrylic acid aqueous solution is subjected to an extraction step, a solvent separation step, a light boiling point separation step, When processing and refining in the heavy substance separation process and redistillation generation process,
After extracting methacrylic acid from the methacrylic acid aqueous solution using an aliphatic chain saturated hydrocarbon having 6 to 12 carbon atoms as an extraction solvent, and further purifying it in a solvent separation step, a light boiling point separation step, and a heavy substance separation step. A method for purifying methacrylic acid, which comprises adding and mixing a hydrazine compound to a methacrylic acid-containing solution in 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. (In the formula, R1 and R2 represent a hydrogen atom, a C1-3 alkyl group, a phenyl group, a phenyl group having a substituent, or an alicyclic hydrocarbon group.)