JPS6296447A - Recovery of methacrylic acid - Google Patents

Abstract

PURPOSE:A reaction mixture produced by a vapor-phase catalytic oxidization reaction of isobutylene, etc., is extracted with a hydrocarbon solvent to extract a part of methacrylic acid and acetic acid, methacrylic acid is separated and acetic acid is recovered from the extract and the acetic acid is used in the recovery of methacrolein. CONSTITUTION:Isobutylene, t-butanol, isobutylaldehyde or methacrolein is subjected to vapor-phase catalytic oxidization (2,4) and the reaction product gas is quenched or made to contact (6,8) with water. The obtained aqueous solution of methacrylic acid containing acetic acid as an impurity is introduced to a methacrolein stripper 27 and an extraction column 34 and a part of methacrylic acid and acetic acid is extracted with a hydrocarbon solvent 43. The extract liquid is distilled (36) and methacrylic acid is recovered (39). The column top liquid is washed (41) with water and an aqueous solution of acetic acid 44 is separated from the solvent. The aqueous solution is introduced to an acetic acid absorption column 15 to effect the absorption of acetic acid in off gas discharged from a methacrylein absorption column 12 and, at the same time, water is dissipated to effect the concentration of the solution. The concentrated solution is used as an absorbent of methacrolein in the absorption column 12.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to the production of methacrylic acid from isobutylene, t-butanol, inbutyraldehyde, or methacrolein by gas phase catalytic oxidation from an aqueous solution of a reaction product obtained by gas phase catalytic oxidation. While advantageously recovering the main product methacrylic acid,
This invention relates to a method for economically recovering and utilizing by-product acetic acid.

(Prior art) Methacrylic acid obtained by gas phase catalytic oxidation of isobutylene, t-butanol, imbutyraldehyde or methacrolein is usually obtained by quenching the reaction product gas produced by gas phase catalytic oxidation reaction or adding it to water. Contact to form an aqueous solution of methacrylic acid.

Next, it is distilled to separate low-boiling substances such as acetone and methacrolein, and then extracted with an organic solvent that is sparingly soluble in water to separate water and methacrylic acid, followed by further distillation.

Therefore, the extraction solvent and methacrylic acid are separated and purified. In addition, the reaction product gas produced by the gas phase catalytic oxidation reaction contains a considerable amount of produced methacrolein or unreacted methacrolein, and the off-gas after obtaining the methacrylic acid aqueous solution in the Kuenna tower or absorption tower. It is essential to efficiently recover the amount of methacrolein. There are two methods: one is to recover methacrolein, and the other is to absorb methacrolein into acetic acid (Special Publication Sho S8-+19x2).

(Problems to be Solved by the Invention) An aqueous solution of an oxidation product containing methacrylic acid as a main component obtained by quenching the gas produced by a gas-phase catalytic oxidation reaction or contacting it with water contains a polymer production promoting substance (hereinafter referred to as If an organic solvent with a high extraction ability that can extract acetic acid as well as methacrylic acid at a high rate is used in the methacrylic acid extraction process, the extraction column A large amount of polymers accumulates in the interior and interface control parts, making long-term continuous operation extremely difficult. Moreover, the problem of dissolved polymers or polymeric agents goes beyond just the extraction process. In the next distillation process, the dissolved polymers or polymer factor substances extracted together with methacrylic acid accumulate or deposit in the column and/or reboiler as the solvent separation or acetic acid separation progresses, resulting in long-term continuation. This can easily interfere with driving.

Also, it is known that acetic acid can be used as an absorption solvent when recovering methacrolein, but isobutylene,
When producing methacrylic acid through the gas phase catalytic oxidation reaction of butanol, imbutyraldehyde or methacrolein, all of the acetic acid by-produced is effectively utilized to quench the gas produced by the gas phase catalytic oxidation reaction or bring it into contact with water. No sufficiently economical process has yet been proposed for efficiently recovering methacrolein from methacrolein-containing off-gas generated when obtaining aqueous methacrylic acid.

(Means for Solving the Problem) As a result of intensive studies to solve the problem, the present inventors found that the gas produced by the gas phase catalytic oxidation reaction was quenched or brought into contact with water. By selectively extracting methacrylic acid from an aqueous methacrylic acid solution, dissolved polymers or polymer-factor substances are left in the raffinate aqueous phase, thereby preventing polymer accumulation in the extraction and distillation steps;
In addition, we have completed an innovative and economical method to efficiently collect and concentrate a small amount of acetic acid, which is extracted together with methacrylic acid, and use it to recover methacrolein.

That is, 1 the present invention is directed to producing hydrocarbons from a methacrylic acid aqueous solution containing acetic acid as an impurity obtained by quenching a gas produced by a gas phase catalytic oxidation reaction of isobutylene, t-butanol, imbutyraldehyde, or methacrolein or by contacting it with water. Extract methacrylic acid and acetic acid using a solvent
Next, the solvent and acetic acid were distilled off to separate methacrylic acid, and then the acetic acid was extracted from the acetic acid-containing solvent with water, and the resulting acetic acid aqueous solution was quenched with the gas produced by the gas-phase catalytic oxidation reaction or brought into contact with water. It is used as a solvent to absorb acetic acid from the off-gas after absorbing and removing methacrolein in the methacrolein-containing gas obtained during the process, and at the same time absorbs the acetic acid in the off-gas and simultaneously diffuses water into the off-gas to concentrate the acetic acid aqueous solution. The present invention relates to a method for recovering methacrylic acid, characterized in that the methacrylic acid is then used as an absorption solvent for methacrolein in the methacrolein-containing gas.

The methacrylic acid aqueous solution obtained by quenching the gas phase catalytic oxidation reaction product gas of isobutylene, t-getanol, imbutyraldehyde, or methacrolein or by contacting it with water usually contains 1% methacrylic acid, 20 to 45% by weight qb% acetic acid, 1%
~5% by weight, methacrolein 1-6% by weight, acetone 0
．． 02-5% by weight.

It has a polymer and a polymer factor of 0.5 to 4 weight range.

In addition, when the gas phase catalytic oxidation reaction product gas is brought into contact with water to absorb and recover methacrylic acid, acetic acid, etc., pure water may be used as the water.

An aqueous solution containing methacrylic acid or acetic acid, such as an absorption tower bottom aqueous solution obtained by absorbing methacrylic acid or acetic acid from the gas, may be used.

The methacrylic acid aqueous solution may be sent as it is to an extraction step using a hydrocarbon non-solvent, but it is better to use acetone.

It may be sent to the extraction step after removing low-boiling substances such as methacrolein.

Examples of hydrocarbon solvents include aliphatic, alicyclic or aromatic hydrocarbons, such as hexane.

Examples include heftane, octane, cyclohexane, benzene, toluene, and xylene. These can be used alone, for example, n-hebutane alone, toluene alone, or mixed together, such as n-heptane-toluene mixture, n-hebutane-toluene.
benzene mixture, ) luene-n-hexane mixture,
It can be used in the form of a toluene-cyclohexane mixture.

These hydrocarbon solvents have a relatively low ability to extract acetic acid; only a portion of the acetic acid is extracted during the extraction process, and most of the acetic acid remains in the raffinate aqueous phase, and most of the dissolved polymers and polymer-related substances are also extracted. It remains in the residual water phase.

The hydrocarbon solvent is usually a methacrylic acid aqueous solution of 50 to 3
It is preferable to use 00% by weight.

The hydrocarbon solvent from which methacrylic acid and a portion of acetic acid have been extracted is then distilled to remove the solvent and acetic acid, thereby separating methacrylic acid. At this time, acetic acid and the solvent may be distilled out azeotropically from the beginning of the distillation, or when a mixed solvent is used, only one type of solvent is distilled out at first, and then acetic acid and the solvent are distilled out azeotropically. Sometimes it is distilled out.

When extracting acetic acid from a solvent containing acetic acid with water, it is preferable to use 2 to 50% by weight of water based on the solvent.

The acetic acid concentration in the obtained acetic acid aqueous solution is usually 5 to 60% by weight.
That's about it.

This acetic acid aqueous solution is used to quench the vapor phase catalytic oxidation reaction product gas or to absorb and remove methacrolein in the methacrolein-containing gas obtained when it is brought into contact with water. When absorbing the acetic acid in the acetic acid solution, the water in the acetic acid aqueous solution is simultaneously released into the off-gas, and a highly concentrated acetic acid aqueous solution is obtained from the bottom of the absorption tower. The concentrated acetic acid aqueous solution thus obtained contains 40 to 80% by weight of acetic acid.

The absorption temperature of acetic acid is preferably 10 to 30°C. In order to promote water dissipation in the acetic acid aqueous solution, the acetic acid aqueous solution supplied to the acetic acid absorption tower may be heated to 30 to 80°C before being supplied.

The resulting highly concentrated acetic acid aqueous solution is a methacrolein-containing gas (usually methacrolein-containing gas obtained by quenching gas phase catalytic oxidation reaction product gas or contacting it with water).
It is used as a solvent to absorb and recover methacrolein (containing 5-4.01%). As a result, almost the entire amount of methacrolein in the methacrolein-containing gas is recovered into the acetic acid aqueous solution. The methacrolein thus recovered is sent to, for example, a methacrolein recovery distillation column, and separated from the aqueous acetic acid solution by a conventional method.

The separated methacrolein may be recycled to the methacrolein oxidation process (gas phase catalytic oxidation reaction process) for further oxidation to produce methacrylic acid, or it may be sent to another process for another use.

In addition, most of the bottom liquid of the methacrolein recovery distillation column is recycled to the methacrolein absorption column that recovers methacrolein from the methacrolein-containing gas, and a portion is reused after separating the accumulated high boiling point substances. I can do it.

Next, an example of the present invention will be specifically explained with reference to FIG.

An oxidizing raw material such as isobutylene or t-butanol and a mixed raw material gas such as air, steam, or inert gas are introduced into the first stage reactor 2 through a line 1 to obtain the main product methacrolein. The reaction product gas exits from line 3, is added with recovered methacrolein from rye/46, and secondary air, secondary steam, etc. added from line 47 as necessary, and is then transferred from line 48 to the second stage reactor. Introduced in 4. When isobutyraldehyde is used, only the second stage reactor 4 is used and the oxidation reaction is carried out in a conventional manner. The first stage reactor output gas containing methacrylic acid as the main product is sent to the first quench column 6 through line 5. The gas is introduced into the output gas line 7 and the second quench tower 8 to quench the gas, and the quench liquid is extracted from the line 26 and the methacrolein-containing gas is extracted from the line 11. 10 is the second
Quench 10 - This is a circulating liquid cooler for column 8, and the condensate from the second quench column is introduced into the top of the first quench column from line 9.

The methacrolein-containing gas in line 11 is introduced into methacrolein absorption tower 12, and methacrolein is absorbed by aqueous acetic acid solution in lines 25 and 14. A gas containing acetic acid vapor is introduced from line 13 into acetic acid absorption tower 15 . A dilute aqueous acid solution is introduced into the column 15 from the solvent washing base 41 through the line 44, where absorption of acetic acid and dissipation of water are performed, and concentrated aqueous acetic acid is taken out from the line 14.
It is introduced into the methacrolein absorption tower 12. Off-gas containing dissipated water vapor is discharged from the line 16.

The methacrolein absorption liquid is supplied to a methacrolein recovery distillation column 18 through a line 17, and methacrolein is recovered from the top of the column through a line 19 and a decanter 20% line 22. Line 21j is a line for refluxing a part of distilled methacrolein to column 1B, and line 2S is a line for extracting the distilled water phase, and since it contains some methacrolein, it is necessary to recover methacrolein. is desirable. tower 18
The bottom liquid passes through line 25 to methacrolein absorption tower 12.
A portion is withdrawn from line 24 and the high-boiling components are recycled to group 12 after separation.

The quench liquid obtained in the quench tower 6 is supplied to a methacrolein stripper 27 via a line 26, and low-boiling components such as methacrolein and acetone are removed through a line 28. It is extracted from line 30 via decanter 29 and recycled together with recovered methacrolein from line 22 via line 46 to second stage reactor 4. A portion of the distilled methacrolein is refluxed to column 27 via line 32. It is preferable that the distillate water phase in the decanter 29 is drawn out through the line 31 and combined with the distillate water phase in the line 25 to recover methacrolein.

The bottom liquid of methacrolein stripper 27 is in line 3.
3 into the methacrylic acid extraction column 54.

Methacrylic acid is extracted with a hydrocarbon solvent supplied from line 43.

The solvents used were n-hebutane alone, toluene alone, and n-hebutane alone.
- such as hebutane-toluene mixture, n-heptane-benzene mixture, toluene-n-hexane mixture, toluene-cyclohexane mixture.

Aliphatic, cycloaliphatic or aromatic hydrocarbons are used alone or in mixtures. Such a solvent system can selectively extract methacrylic acid, leaving most of the polymeric substances and dissolved polymers in the raffinate aqueous phase.

The amount of acetic acid required for extraction varies depending on the catalyst used in each reactor 2, 4 or the reaction conditions. If it is necessary to increase the acetic acid extraction rate, this can be done by increasing the mixing ratio of benzene, toluene, etc.

The raffinate aqueous phase is extracted through line 45 and sent to the wastewater treatment process, and the methacrylic acid extract is extracted through line 35 to distillation column 56.
The methacrylic acid is recovered from the column bottom line 59. From the top line 57 and line 40, acetic acid and the solvent are separated as a distillate and introduced into the solvent washing group 41. A portion of the distillate is refluxed to column 36 via line 38.

Although Fig. 1 shows an example in which desolvation and acetic acid removal are performed simultaneously in the column 36, it is also possible to separate the mixture of the high boiling point solvent and acetic acid by distillation after separating the low boiling point solvent in two stages. It is.

Water is supplied to the solvent washing base 41 from a line 42 and separated into a solvent and an acetic acid aqueous solution. The washed solvent is sent to the methacrylic acid extraction tower 34 via line 43, and the acetic acid aqueous solution is sent to line 44.
The acetic acid is then introduced into the acetic acid absorption tower 15.

Next, another specific example of the present invention will be explained with reference to FIG.

Raw material gas is introduced into the first stage reactor 102 through line 101, and reaction product gas containing methacrolein is extracted through line 103. For the second stage reactor 104,
Methacrolein recovered in a later step is introduced through line 146, a mixed gas of air, steam, inert gas, etc. is introduced through line 147, and the reaction product gas is extracted through line 105.

Line 148 along with the reaction product gas from the first stage reactor.
It is introduced into the first quench tower B. After that, the process is the same as in FIG. Note that the methacrolein recovered from the line 22 is supplied to the second stage reactor 104 via the line/146.

Note that FIGS. 1 and 2 illustrate some specific examples of the present invention, and the present invention is not limited to the examples shown in both figures.

(Example) Next, the present invention will be explained by examples.

Example 1 Methacrolein 2.42 Kp/H, 2 gas 9.B
sN, //H1 nitrogen 6.58NffI'/H, water vapor 2
・A mixed gas consisting of 62 Kp/H was supplied to obtain the oxidized gas of methacrolein, which was introduced into the quench tower 6 in Figure 1, and operated at a bottom temperature of tower 6 of 40°C and a temperature of tower 8 of 10°C. A crude aqueous solution of methacrylic acid (4,6a Kp/H) containing 40.4 wt% methacrylic acid, 3.16 wt% acetic acid, 1.09 wt% methacrolein, and 0 swt% acetone was obtained from line 26.

On the other hand, the gas leaving the Ente tower 8 (methacrolein at 1.0
(contains 7 vol%) (17,11JTr?/H) is a methacrolein absorption tower 12. which absorbs methacrolein at 10°C. The mixture was then introduced into an acetic acid absorption tower 15 which absorbs acetic acid and simultaneously releases water at 12°C.

From line 25, acetic acid 7 is used as methacrolein absorption solvent.
A mixed solution of 5 wt% water, 20 wt% water, and methacrylic acid swt-11KJ1/H was supplied to the top of column 12.

An absorption rate of methacrolein of 99.5% was obtained. Acetic acid equivalent to 2.4% of the acetic acid in the absorption solvent is released from line 13 to acetic acid absorption tower 15, and from line 17 70.64% of acetic acid is released.
wbchi, water 19.30 wbchi, methacrylic acid 4.8
3wt%, methacrolein5. o1wt%1 acetone 0
．． 25wt%7 methacrolein absorption liquid 11.40,
/ Obtained H.

A seed acetic acid aqueous solution containing 0.3 wb % of acetic acid as an acetic acid absorption solvent is supplied from a line 44 to the acetic acid absorption tower 15.
s Kp/'' was supplied. The absorption rate of acetic acid was 82%.

The water dissipation rate to line 16 was 42%, and the concentrated acetic acid solution o containing 55.5% acetic acid as the acetic acid absorption column bottom liquid,
39 Kp/1'' was obtained from line 14 and fed to absorption tower 12.

Methacrolein absorption liquid 11.40 Kp/HhaJ Supplied to tacrolein recovery tower 18, top pressure 300 mmH
It was distilled with From line 22, acetone 4.2W 7chi,
Methacrolein 0.608K containing 2.8wt% water
P/H and from line 25 methacrolein 5.2
wt H, a distillate water phase o containing 1.7wt9I+ acetone,
11/+Kp/H was obtained. From line 21, 0.184//H of distilled methacrolein was introduced as reflux.

The bottom liquid of the quench tower 6 was treated to remove methacrolein in the tower 27, resulting in 59.8% methacrylic acid and 5.46% acetic acid.
A methacrylic acid aqueous solution containing 4.
65KJl/H was obtained. At the same time, line 30 color acetone 1
6.4. yt%, water 3. From line 61, a distillate aqueous phase containing 6.8 wt% acetone and 4.70 wt% methacrolein (0.0085 Kr/'H) was obtained from line 10. 0.39 Kp/H of distilled methacrolein was introduced as reflux.

Methacrolein stripper 27 bottom liquid s, 6aK
y/H to 50m1TlφX42 stage rotating disk extraction tower 34
50wt% of n-heptane is supplied to the top of the column, and 50wt% of n-heptane is supplied to the bottom of the column.
,) A mixed solvent of 50 wt% toluene was introduced at a rate of 5.4 KP/H, and 20.7 wt% of methacrylic acid and 0.7 wt% of acetic acid were introduced.
An extract of 6.89 KP/H containing 87 Wt was obtained.

The inside of the extraction tower remains intact even after 5 days of continuous operation.

No accumulation of polymers was observed.

The extracted liquid 1.0 TKP/H was supplied to an Aldershaw type distillation column 36 having a diameter of 50 mm and 20 stages, and the top pressure was adjusted to 50 TKP/H.
mmHf, distilled at a reflux ratio of 0.6, and the distillate was a mixed solution of 1.09 wt% acetic acid, 0.26 wt% water, 49.6 wt% n-butane, and 49.3 wt% toluene.
．． To 799? /H as tower bottom liquid, acetic acid o, o2wt%
0.209 Ky/H of methacrylic acid was obtained. Phenothiazine was added as a polymerization inhibitor to the reflux liquid, and air was blown into the bottom of the column. During continuous operation for 20 days, no accumulation of polymers was observed in the tower.

The above distillate 6.OKp/H consisting of n-hebutane, toluene, acetic acid and water was passed through line 40 to a 50 mmφX
P/H was introduced into the lower part of a 42-stage rotating disk extraction tower 41, and water 0.318% was introduced into the top of the tower through a line 42.
Acetic acid in the solvent was extracted with water to obtain a 15 wt aqueous acetic acid solution of 0.4 s 5 Kp/H as a column bottom liquid. The acetic acid aqueous solution was introduced into the top of the acetic acid absorption tower 15, and water was removed at the same time as acetic acid recovery.

The top liquid raffinate solvent of the column 41 is substantially a mixture of n-hebutane and toluene, and can be recycled to the methacrylic acid extraction column 34.

(Effect of the invention) As described in 2 below, methacrylic acid is selectively extracted from an aqueous methacrylic acid solution using a hydrocarbon solvent, and at the same time, a portion of acetic acid is extracted, and the solvent and acetic acid are distilled by distillation of the extract. A mixed solution is distilled out, and acetic acid is extracted from the distillate with water to obtain an acetic acid aqueous solution, which is introduced into the acetic acid absorption column top of a methacrolein absorption system to absorb acetic acid and dissipate water. This makes it possible to concentrate the aqueous acetic acid solution, thereby increasing the absorption efficiency of methacrolein, and to recover and produce methacrylic acid stably for a long period of time without the accumulation of polymers in the methacrylic acid extraction process and the acetic acid separation and distillation process. It has become possible.

The present invention is a very economical process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are flown-1 showing an embodiment of the method of the present invention.

Claims (1)

[Claims] (1) Using a hydrocarbon solvent from an aqueous methacrylic acid solution containing acetic acid as an impurity, which is obtained by quenching the gas produced by the gas-phase catalytic oxidation reaction of isobutylene, t-butanol, isobutyraldehyde, or methacrolein or by contacting it with water. methacrylic acid and acetic acid are extracted by distillation, the solvent and acetic acid are distilled off to separate methacrylic acid, the acetic acid is extracted from the acetic acid-containing solvent with water, and the resulting acetic acid aqueous solution is subjected to gas phase catalytic oxidation. It is used as a solvent to absorb acetic acid from the off-gas after absorbing and removing methacrolein in the methacrolein-containing gas obtained when the reaction product gas is quenched or brought into contact with water. A method for recovering methacrylic acid, comprising concentrating an acetic acid aqueous solution by dissipating it into the off-gas, and then using it as an absorption solvent for methacrolein in the methacrolein-containing gas.