JP3246216B2 - Method for separating methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for separating methacrylic acid, and more particularly to a method for separating methacrylic acid from a reaction product gas obtained by subjecting isobutylene or the like to catalytic gas phase oxidation.

[0002]

2. Description of the Related Art Isobutylene, t-butyl alcohol,
In the method for producing methacrylic acid by catalytic gas-phase oxidation of methacrolein or the like, the reaction product gas is cooled and collected as an aqueous solution, methacrylic acid is extracted from the aqueous methacrylic acid solution using an organic solvent, and then distilled or the like. A purification method is generally used.

[0003] In addition to methacrylic acid, various by-products such as aromatic carboxylic acids such as terephthalic acid, maleic acids, aldehydes, and polymers are present in the reaction product gas. Suspending in an aqueous solution obtained by cooling the produced gas, depositing as a scum on the interface at the time of extraction to make separation difficult, and promoting the polymerization of methacrylic acid during purification of methacrylic acid, Hinders the separation operation.

Various proposals have been made to solve these problems. A method of selectively condensing and adhering high-boiling impurities before quenching the reaction product gas (JP-A-58-52).
No. 239), the reaction product gas is condensed in multiple stages, and in the first stage substantially all of the high-boiling by-products are condensed and separated from methacrolein and methacrylic acid, and methacrylic acid in the condensate is extracted with a hydrocarbon solvent. , Collection method (Japanese Patent Publication No. 3-331)
No. 43), when extracting and separating from an aqueous methacrylic acid solution,
A method of preliminarily contacting with a solvent to precipitate a polymer, separating the polymer, and extracting the polymer (JP-B-60-16927);
A method for preventing the generation of scum in the extraction step by adding bisulfite to a methacrylic acid aqueous solution (Japanese Patent Publication No. Sho 62-45)
No. 218) is known.

Also, a method using an aromatic hydrocarbon such as benzene, toluene and xylene, an aliphatic saturated hydrocarbon such as hexane and heptane, and an alicyclic hydrocarbon such as cyclohexane as an extraction solvent for methacrylic acid (Japanese Patent Publication No. 55 (1985)). -16
495), a method using an ester of xylene or the like and methacrylic acid (JP-B-49-41413, JP-B-62-1).
No. 5542), a method using xylene or the like and hexane, heptane or the like (Japanese Patent Application Laid-Open No. 63-212249), a method using an aromatic hydrocarbon such as xylene or an acetate (Japanese Patent Publication No. 62-45218), isopropyl acetate, or the like. A method using methyl ethyl ketone, diisopropyl ether or the like (Japanese Patent Publication No. 3-33143) is known.

[0006]

However, in the conventional method, it is difficult to treat the separated high-boiling impurities,
An extraction solvent with a low extraction capacity must be used to avoid the effects of high boiling impurities, or the extraction and separation operation is complicated due to the high extraction capacity but accompanied by water, and the drainage load is high. However, it is not always satisfactory industrially. An object of the present invention is to solve the above conventional problems and to provide an efficient method for separating methacrylic acid.

[0007]

That is, the present invention relates to isobutylene, tert-butyl alcohol, methacrolein,
In a method of condensing a reaction product gas obtained by subjecting tert-butyl methyl ether to gas-phase catalytic oxidation and extracting and separating methacrylic acid from an aqueous methacrylic acid solution obtained, the reaction product gas is condensed using a two- or three-stage condenser. Cooling, condensing,
In a first condenser having a condensation temperature of 70 to 80 ° C, a part of methacrylic acid and substantially all of by-products having a boiling point equal to or higher than methacrylic acid are collected, and the remaining methacrylic acid is removed from the second condenser and thereafter. Collected together with water, the condensate of the first condenser is distilled to distill methacrylic acid together with water to separate high-boiling by-products, and the obtained methacrylic acid-containing distillate is separated from the second condenser and thereafter. Combining with the obtained aqueous methacrylic acid solution, separation of methacrylic acid characterized by extracting methacrylic acid from the aqueous methacrylic acid solution using methyl methacrylate alone or a mixed solvent of methyl methacrylate and n-heptane as an extraction solvent A method of isobutylene, tert-butyl alcohol, methacrolein, tert.
In a method of condensing a reaction product gas obtained by subjecting butyl methyl ether to gas phase catalytic oxidation and extracting and separating methacrylic acid from an aqueous methacrylic acid solution obtained, the reaction product gas is cooled using a two- or three-stage condenser. Condensing and collecting in the first condenser substantially all of the by-products having a boiling point of less than 15% of methacrylic acid and more than methacrylic acid;
The remaining methacrylic acid is collected together with water after the second condenser, and the condensate of the first condenser is distilled to distill methacrylic acid together with water to separate high-boiling by-products and obtain the obtained methacrylic acid. The containing distillate is combined with the aqueous methacrylic acid solution obtained in the second condenser or later, and methacrylic acid is extracted from the aqueous methacrylic acid solution using methyl methacrylate alone or a mixed solvent of methyl methacrylate and n-heptane as an extraction solvent. It is intended to provide a method for separating methacrylic acid, which is characterized by extraction.

As a raw material gas for producing methacrylic acid in the present invention, isobutylene, tert-butyl alcohol, methacrolein, tert-butyl methyl ether and a mixture thereof are used.

The present invention will be described in detail with reference to FIG. 1 showing an embodiment of the present invention. A gas containing isobutylene and molecular oxygen is introduced into the reaction section A from the raw material supply line 1. The reaction section is usually constituted by a two-stage reactor, and a Mo-Bi catalyst is used in the first reactor, and isobutylene is mainly oxidized to methacrolein. This reaction gas is introduced into the second reactor, where methacrolein is oxidized to methacrylic acid using a Mo-based heteropolyacid catalyst. The amount of molecular oxygen used is usually about 0.5 to 2 with respect to isobutylene.
The reaction is performed in a range of 0 mole times. The source gas may contain an inert gas such as nitrogen or carbon dioxide. Usually, the reaction is carried out under normal pressure at 250 to 450 ° C.,
The supply is performed at で 5000 hr ⁻¹ (STP). The reaction is not particularly limited to a fixed bed, fluidized bed or the like.

The reaction product gas is introduced into the first condenser B,
The condensate is cooled and circulated to contact the reaction product gas for about 65
Cooling to ~ 85 ° C, preferably about 70-80 ° C, collects a portion of methacrylic acid and substantially all by-products having a boiling point equal to or higher than methacrylic acid. The uncondensed gas is cooled and circulated in the second condenser C to circulate the condensed liquid so as to come into contact with the gas for about 30 to 55
C., preferably to about 35-50.degree. C., to collect substantially all of methacrylic acid, water, and by-product acrylic acid, acetic acid and the like.

The condensate in the first condenser B is usually obtained by filtering and removing a slurry component (such as terephthalic acid) and then distilling it in a high-boiling substance separation column H to remove methacrylic acid, water and the like contained in the condensate. Distill and collect. The distillate is combined with the condensate of the second condenser C for further processing. The bottom liquid which is a high-boiling substance is discarded from the high-boiling substance discharge line 9.

A gas mainly composed of methacrolein and an inert gas which is not condensed in the condenser is collected in a methacrolein recovery section D.
And then absorb into an aqueous solution containing methacrylic acid, and then introduce an oxygen-containing gas to diffuse and separate methacrolein. This methacrolein is circulated to the reaction part A and recovered. The gas discharged at the time of absorption of methacrolein is washed, if necessary, with methacrylic acid, and then discarded through an exhaust gas treatment step (not shown), or a part of the gas is collected in the reaction section. The acid concentration of the absorption solution of methacrolein is about 5 to 35 wt%, preferably about 10 to 30 wt% in terms of methacrylic acid.
%. The supply temperature of the absorbing liquid is about 0 to 15 ° C, preferably about 0 to 10 ° C.

The condensate of the second condenser contains some methacrolein. This condensate is combined with the distillate from the high-boiling point separation tower H and the liquid in the excess methacrolein recovery section, and introduced into the methacrolein separation tower E, where methacrolein is separated by distillation, and methacrolein is recovered. Collected in section D.

The aqueous solution containing methacrylic acid which has been demethacrolein is supplied to a methacrylic acid extraction tower F, and methyl methacrylate alone or methyl methacrylate and n
-Extract methacrylic acid using a mixed solvent of heptane. The aqueous solution after extraction is sent from the extraction residual water discharge line 7 to a wastewater treatment step. The extraction solvent is distilled off the extraction solvent, water, acetic acid, acrylic acid and the like in the extraction solvent recovery column G, circulated to the methacrylic acid extraction column F and reused. Crude methacrylic acid is separated from line 8 at the bottom of the extraction solvent recovery tower, which is usually further purified to obtain a product methacrylic acid and esterified to produce methyl methacrylate.

Table 1 shows the physical properties such as the distribution coefficient of methacrylic acid in various extraction solvents. Aromatic hydrocarbons such as xylene and n-heptane and aliphatic hydrocarbons have good liquid separation properties, but have low methacrylic acid extraction performance. If a crude methacrylic acid aqueous solution contains a large amount of high boiling point impurities and the like, a solvent having high extraction performance is used to extract a large amount of impurities, and the liquid separation property is deteriorated. Therefore, a hydrocarbon solvent is used. In the present invention, a solvent having high extraction performance can be used because the high boiling point impurities have been removed in advance.

In the extraction solvent recovery column, acrylic acid and acetic acid are distilled off together with the solvent without accompanying methacrylic acid to the top liquid, so that acrylic acid is not released into methacrylic acid in the bottom liquid. Has a boiling point of methacrylic acid (boiling point: 161
C.) and acrylic acid (boiling point: 141.degree. C.). For example, when xylene (boiling point: 140 ° C.) is present, methacrylic acid is entrained in the overhead liquid, and methacrylic acid in the extraction residual water increases, which is not preferable. Aromatic hydrocarbons, which have been conventionally used to address problems during extraction, need not be used by removing high boiling impurities in advance.

[0017]

[Table 1] MAA: Methacrylic acid MEK: Methyl ethyl ketone MIBK: Methyl isobutyl ketone XY: Xylene MMA: Methyl methacrylate * MAA distribution coefficient Measured by mixing equal weights of an extraction solvent and a 0.2% by weight MAA aqueous solution at 25 ° C.

Aliphatic ketones have high extraction performance, but have high compatibility with oil and water, and the oil phase and the water phase after separation have increased amounts of water and oil, respectively, and require energy to separate them.
Not preferred. Esters such as isopropyl acetate and butyl acetate have high extraction performance, but partially hydrolyze during the extraction or recovery operation to produce acetic acid, isopropyl alcohol, butyl alcohol, etc. Further, it is not preferable because it is mixed with methacrylic acid or methyl methacrylate. Naturally, those having a boiling point close to the boiling point of methacrylic acid are not preferred because separation of the solvent and methacrylic acid becomes difficult.

As a solvent, methyl methacrylate has a high extraction performance of methacrylic acid, has a good boiling point for separating methacrylic acid and acrylic acid, and even if a part thereof is hydrolyzed to form methacrylic acid and methyl alcohol, Normal,
At the same time, methyl methacrylate is produced from methacrylic acid and methyl alcohol, separation is easy, and there is no problem such as contamination of impurities.

When methyl methacrylate alone is used as the solvent, the entrainment of water is slightly increased, and the separation energy in the extraction solvent recovery tower is correspondingly increased. Therefore, a mixed solvent to which n-heptane is added is used. More preferably.
Usually, the content of n-heptane in the mixed solvent is about 5 to 40 wt.
%. If the amount of n-heptane is too large, the extraction performance will be low. If the amount is too small, the effect of suppressing the entrainment of water will be reduced.

When methyl methacrylate is used as a solvent, a large amount of acetic acid produced as a by-product from a methacrylic acid-containing aqueous solution is extracted, so that acetic acid can be economically recovered from the extract. In this case, first, the extraction solvent, methyl methacrylate or methyl methacrylate and n-heptane, is distilled off from the extract in the extraction solvent recovery tower, and then the bottom liquid is introduced into the acetic acid recovery tower, and acetic acid is distilled off and recovered. I do. The acrylic acid tower is distilled off from the bottom liquid of the acetic acid recovery tower in the methacrylic acid recovery tower, and crude methacrylic acid is obtained from the tower bottom.

[0022]

The method of the present invention is a combination of a method for separating a specific high-boiling substance and a specific extraction solvent. With this combination, troubles due to high-boiling impurities are smaller than those of the conventional method, and the separation operation is improved. Was stabilized, and methacrylic acid could be separated efficiently.

[0023]

【Example】

Example 1 An oxidation reaction of isobutylene was performed according to the flow shown in FIG.
Methacrylic acid was separated from the reaction product gas. Table 2 shows the conditions of each apparatus, and Table 3 shows the flow rates (unit: kg / hr) of each component of the main line.

The reaction product gas is introduced into the first condenser B, and the condensate is cooled and circulated to be brought into contact with the reaction product gas and cooled to partially convert methacrylic acid and by-products having a boiling point higher than methacrylic acid. Total amount was collected. The uncondensed gas was cooled in the second condenser C, circulated and contacted with the gas to be cooled, and methacrylic acid, water, and by-product acrylic acid, acetic acid, and the like were substantially all collected. The condensate in the first condenser was filtered and removed of the slurry component, and then distilled in a high-boiling-point separation column H to distill and collect methacrylic acid, water and the like contained in the condensation. The bottom liquid was withdrawn from the high boiling point discharge line 9.

A gas mainly composed of methacrolein and an inert gas which is not condensed in the condenser is collected in a methacrolein recovery section D.
And absorbed and diffused in an aqueous solution containing methacrylic acid to separate methacrolein, which was circulated to the reaction section. The gas discharged during the absorption of methacrolein burned organic matter in an exhaust gas combustion facility, and a part of the gas was recovered in a reaction section.

The condensate of the second condenser contains some methacrolein. This condensate is combined with the distillate from the high boiling point separation tower H and the liquid in the excess methacrolein recovery section, and introduced into the methacrolein separation tower E, where it is distilled to separate methacrolein. It was collected in the collection section D.

The methacrylic acid-containing aqueous solution that had been demethacrolein was supplied to a methacrylic acid extraction tower F, and methacrylic acid was extracted using only methyl methacrylate as an extraction solvent. The aqueous solution after extraction was extracted from the extraction residual water discharge line 7 and used as drainage. The extraction solvent was distilled off the extraction solvent, water, acetic acid, acrylic acid and the like in the extraction solvent recovery column G, circulated to the methacrylic acid extraction column F and reused. Crude methacrylic acid was obtained from the bottom of the extraction solvent recovery tower.

According to this method, a high-boiling substance was not attached and did not hinder the separation operation, and continuous operation was possible for one year. In addition. Similar results were obtained when using a mixed solvent of methyl methacrylate and n-heptane as the extraction solvent.

[0029]

[Table 2]

[0030]

[Table 3]

Comparative Example 1 Isobutylene was oxidized according to the flow shown in FIG.
Methacrylic acid was separated from the reaction product gas. Table 4 shows the conditions of each apparatus, and Table 5 shows the flow rate (unit: kg / hr) of each component of the main line.

The reaction product gas is introduced into the first condenser B,
The condensed liquid was cooled and circulated to contact the reaction product gas and cooled to collect a part of methacrylic acid and substantially all by-products having a boiling point higher than methacrylic acid. The uncondensed gas was cooled in the second condenser C, circulated and contacted with the gas to be cooled, and substantially all of methacrylic acid, water, and by-product acrylic acid and acetic acid were collected. The condensate of the second condenser was collected in the first condenser.

A gas mainly composed of methacrolein and an inert gas which is not condensed in the condenser is collected in a methacrolein recovery section D.
And absorbed and diffused in an aqueous solution containing methacrylic acid to separate methacrolein, which was circulated to the reaction section. The gas discharged during the absorption of methacrolein burned organic matter in an exhaust gas combustion facility, and a part of the gas was recovered in a reaction section. The condensate in the methacrolein recovery section was recovered in the first condenser.

The condensate of the first condenser contains some methacrolein. This condensate is separated into methacrolein separation column E
, And methacrolein was separated by distillation, and the methacrolein was collected in the methacrolein collecting part D.

After removing the methacrylic acid-containing aqueous solution from the demethacrolein, the slurry component was filtered and removed, and then supplied to a methacrylic acid extraction tower F, where methacrylic acid was extracted using a mixed solvent of methyl methacrylate and xylene as an extraction solvent. The aqueous solution after extraction was extracted from the extraction residual water discharge line 7 and used as drainage. The extraction solvent was distilled off the extraction solvent, water, acetic acid, acrylic acid and the like in the extraction solvent recovery column G, circulated to the methacrylic acid extraction column F and reused. Crude methacrylic acid was obtained from the bottom of the extraction solvent recovery tower.

In this method, a high-boiling substance adheres and the separation operation is hindered. For example, the methacrylic acid extraction column needs to be washed about once every three months.

[0037]

[Table 4]

[0038]

[Table 5]

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an example of an embodiment of the present invention.

FIG. 2 is a flow sheet in a comparative example.

[Explanation of symbols]

 A reaction section B first condenser C second condenser D methacrolein recovery section E methacrolein separation tower F methacrylic acid extraction tower G extraction solvent recovery tower H high boiling matter separation tower 1 raw material gas supply line 7 extraction residual water discharge line 8 Methacrylic acid discharge line 9 High boiling matter discharge line

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-87241 (JP, A) JP-A-62-145044 (JP, A) JP-A-60-152438 (JP, A) JP-A-60-87 69053 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C07C 57/07 C07C 57/05

Claims (4)

(57) [Claims] 1. A method for condensing a reaction product gas obtained by subjecting isobutylene, tert-butyl alcohol, methacrolein, and tert-butyl methyl ether to gas-phase oxidation, and extracting and separating methacrylic acid from the obtained aqueous methacrylic acid solution. The reaction product gas is cooled and condensed using a two- or three-stage condenser, and a part of methacrylic acid and a by-product having a boiling point equal to or higher than methacrylic acid in a first condenser having a condensation temperature of 70 to 80 ° C. Substantially the entire amount is collected, the remaining methacrylic acid is collected together with water after the second condenser, and the condensate of the first condenser is distilled to distill methacrylic acid together with water to form a high-boiling by-product. And the obtained methacrylic acid-containing distillate is combined with the aqueous methacrylic acid solution obtained in the second condenser and thereafter, and methyl methacrylate alone is used as an extraction solvent from the aqueous methacrylic acid solution. And methyl methacrylate n-
A method for separating methacrylic acid, comprising extracting methacrylic acid using a mixed solvent of heptane. 2. A method for condensing a reaction product gas obtained by subjecting isobutylene, tert-butyl alcohol, methacrolein, and tert-butyl methyl ether to gas-phase catalytic oxidation and extracting and separating methacrylic acid from the obtained aqueous methacrylic acid solution. The reaction product gas is cooled and condensed using a two- or three-stage condenser, and substantially the entire amount of by-products having a boiling point of less than 15% of methacrylic acid and more than methacrylic acid is collected in the first condenser. The remaining methacrylic acid is collected together with water after the second condenser, and the condensate of the first condenser is distilled to distill methacrylic acid together with water to separate high-boiling by-products. The acid-containing distillate is combined with the aqueous methacrylic acid solution obtained in the second condenser or later, and methyl methacrylate alone or methyl methacrylate is used as an extraction solvent from the aqueous methacrylic acid solution. The method of separating methacrylic acid and extracting methacrylic acid using a mixed solvent of n- heptane. 3. A process for separating methyl methacrylate and n- methacrylate according to claim 1 or 2, wherein n- heptane content in the mixed solvent is 5 to 40 wt% heptane. Wherein the slurry is filtered fraction of the condensate in the first condenser, after separation, according to claim 1 or 2 process for separating methacrylic acid according to the distillation.