JPH0813779B2 - Method for recovering methacrylic acid as methyl methacrylate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering methacrylic acid as methyl methacrylate. More specifically, it relates to a method for recovering methacrylic acid from a bottom liquid obtained by distilling and separating methacrylic acid and a bottom liquid after distilling and separating methyl methacrylate.

[Conventional technology]

Examples of the industrial production method of methacrylic acid include catalytic air oxidation of isobutylene, tertiary butanol or methacrolein, rapid cooling of reaction product gas, extraction of methacrylic acid, separation of extractant and methacrylic acid, and purification of methacrylic acid. There is known a method of obtaining high-purity methacrylic acid through steps such as the above.

Methyl methacrylate is esterified with methacrylic acid and methanol in the presence of an acid catalyst to give methanol, water,
There have been proposed various methods for producing impurities by separating and purifying impurities and the like by an ordinary purifying means such as extraction and distillation. By the way, in order to produce methacrylic acid or methyl methacrylate with sufficient quality to be accepted in the market and at low cost, a polymerization inhibitor, methacrylic acid or methacrylic acid, which is gradually concentrated after each step such as extraction and distillation, is produced. Methacrylic acid and methyl methacrylate must be efficiently recovered from bottoms of a distillation column containing a polymer of methyl acid and other high boiling impurities.

That is, since the bottom liquid after rectifying and distilling out methacrylic acid contains a considerable amount of a polymer and a polymerization inhibitor in addition to the high-boiling point impurities generated by the reaction, the distillation rate of methacrylic acid (distillation If the amount (supply amount / supply amount) is too high, the quality of the methacrylic acid product may be deteriorated, and the thermal efficiency of the reboiler may be deteriorated and further the polymerization of methacrylic acid may be promoted. Therefore, by controlling the distillation rate of methacrylic acid within a certain range, a considerable amount of methacrylic acid is contained in the bottoms of the bottom together with the high-boiling component. Therefore,
If the residual liquid in the can is discarded or incinerated, methacrylic acid will be lost and the cost will increase. Therefore, methacrylic acid must be recovered by some method. The same can be said for the bottom liquid after the rectification of methyl methacrylate.

Conventionally considered as a method for recovering methacrylic acid from a bottom liquid is a method of further evaporating methacrylic acid using an evaporator or the like, or a method of extracting methacrylic acid using an organic solvent.

[Problems to be Solved by the Invention]

However, in the former method, that is, in the evaporation method using an evaporator or the like,
Polymerization of methacrylic acid occurs during the operation, so that the evaporation operation does not proceed smoothly and the recovery rate of methacrylic acid is not good. On the other hand, in the latter method, that is, the solvent extraction method, a large amount of slag is generated during the extraction operation, which causes emulsification and phase separation does not proceed smoothly. It is easy to become.

That is, none of the conventionally conceived methods is a preferable method.

[Means for solving the problem]

As a result of intensive studies to solve such problems, the present inventors have found that a bottom liquid containing a polymerization inhibitor, a polymerized product and other high-boiling impurities after distilling and separating methacrylic acid and methyl methacrylate. The present invention has been completed by combining the residual liquid after distilling and separating the product with ester, esterifying it with methanol using sulfuric acid as a catalyst, and recovering it efficiently, and completed the present invention.

That is, the present invention is to separate impurities by extraction or distillation from an aqueous solution of methacrylic acid obtained by vapor-phase catalytic oxidation of isobutylene, tertiary butanol or methacrolein, and obtain crude methacrylic acid in a methacrylic acid rectification column. Separation into purified methacrylic acid and bottom liquid, and subjecting the purified methacrylic acid together with methanol to the first esterification with a cation exchange resin as a catalyst to recover unreacted methacrylic acid in the esterification reaction liquid. It is separated by distillation in a tower and recovered as a bottom liquid, methanol is collected from the distillate of the recovery tower,
Methyl methacrylate obtained by separating water and low-boiling impurities is refined in a methyl methacrylate rectification tower, and when a methyl methacrylate product is obtained from the top of the rectification tower, it is recovered as a bottom liquid in the methacrylic acid recovery tower. Methacrylic acid is circulated to the methacrylic acid rectification column, and the bottom liquid of the methacrylic acid rectification column is subjected to the second esterification using sulfuric acid as a catalyst together with the bottom liquid of the methyl methacrylate rectification column. A method of circulating both the esterification reaction solution and the first esterification reaction solution in the methacrylic acid recovery tower, wherein the second esterification is carried out at a molar ratio of methanol to methacrylic acid of 1.0 to 3.
0, a method for recovering methacrylic acid as methyl methacrylate, which is carried out by reactive distillation under conditions that the amount of sulfuric acid used relative to methacrylic acid is 1.0 to 5.0% by weight and the residence time in the reactor is 0.1 to 2 hours. .

The bottom product of the recovery method according to the present invention is a bottom product obtained by distilling methacrylic acid and a bottom product obtained by distilling methyl methacrylate. For example, extraction of methacrylic acid with a solvent from an aqueous solution of methacrylic acid obtained by catalytically oxidizing isobutylene, tertiary butanol or methacrolein with a gas containing molecular oxygen in the presence of steam and cooling the oxidation product, An example of a bottom liquid obtained by recovering the solvent and distilling and separating methacrylic acid is mentioned. The composition of the bottom liquid is usually 60 to 95% by weight of methacrylic acid and 3 to 30% by weight of high boiling substances.
And 2 to 10% by weight of the polymer. The high boiling point components in the bottom liquid are citraconic acid, maleic acid, terephthalic acid, trimellitic acid and other acids, P-tolualdehyde, aldehydes such as benzaldehyde, and hydroquinone and phenothiazine added as polymerization inhibitors, The polymer is a polymer of methacrylic acid. As the methyl methacrylate distillation bottoms, methacrylic acid and methanol are esterified using a cation exchange resin as a catalyst, and an esterification reaction liquid containing water, methanol, methacrylic acid and other impurities in addition to methyl methacrylate is used. Examples thereof include a residual liquid of a distillation bottom of methyl methacrylate after separating water, methanol and methacrylic acid by operations such as extraction and distillation. The composition of this bottom liquid is usually 85
~ 98% by weight, high boiling point substances 1 to 10% by weight and polymers 1 to 5
% By weight. The high-boiling components in the bottom liquid are acids such as methacrylic acid and phenothiazine added as a polymerization inhibitor, and the polymer is a polymer of methyl methacrylate.

In the present invention, as the treatment of the above two types of bottom liquid, a method of carrying out esterification by reactive distillation and then returning to the methacrylic acid recovery column in the system is employed instead of performing ordinary separation, that is, distillation or extraction.

At this time, it is not necessary to treat the two types of bottom liquid separately, but they can be treated together. Further, after the bottoms of the bottom is esterified, it can be treated by a separation device provided in the system in the first place, so that the equipment for recovering the necessary components from the bottoms of the bottom can be very small. The only major equipment required is a reactor for esterification.

The esterification of the bottom liquid is carried out by mixing two types of bottom liquid with methanol and using sulfuric acid as a catalyst.

By adopting such an esterification method, it was difficult to separate methacrylic acid from a high-boiling point component composed of a type such as maleic acid and aldehydes such as benzaldehyde by a normal distillation operation. Then, the separation of methyl methacrylate obtained by esterifying methacrylic acid and the high boiling point component can be easily achieved, and therefore methacrylic acid can be recovered in high yield as methyl methacrylate.

Furthermore, since the sulfuric acid used as the esterification catalyst partially reacts with methanol used as the esterification raw material and exists in the form of sulfuric acid methyl ester and has a function as a solvent having a high boiling point component and a polymer, The precipitation of the substance is suppressed, and the high boiling point component and the polymer are separated and discharged into the waste sulfuric acid. Therefore, this method enables stable operation and has a high recovery rate and is excellent in economic efficiency, as compared with the recovery method in which methacrylic acid and methyl methacrylate in the bottom liquid are re-concentrated with an ordinary evaporator or the like.

In the present invention, when esterifying methacrylic acid contained in the bottom liquid, methanol is added in an amount of 1.0 to 3.0 mol per 1 mol of methacrylic acid, and sulfuric acid is added in an amount of 1.0 to 5.0 wt% relative to methacrylic acid. used. The residence time of the reaction solution in the esterification reactor is in the range of 0.1 to 2 hours. If the molar ratio of methanol to methacrylic acid is less than 1.0, the yield of methyl methacrylate decreases. Further, when the molar ratio exceeds 3.0, the yield of methyl methacrylate is improved, but the effect is not remarkable, rather the industrially advantageous conditions such as an increase in the amount of dimethyl ether by-product and a loss of methanol. It can not be said. On the other hand, when the amount of sulfuric acid used is 1.0% by weight or less with respect to methacrylic acid, the yield of methyl methacrylate decreases,
Moreover, precipitation of the polymer and blockage of the pipe due to the increase in the concentration of the high boiling point component, the polymer, etc. in the waste sulfuric acid cause operational problems, which is not preferable. On the other hand, when the amount of sulfuric acid used exceeds 5.0% by weight with respect to methacrylic acid, the cost burden for neutralizing the waste sulfuric acid increases, which is not an industrially advantageous condition. Further, when the residence time in the reactor is 0.1 hour or less, the yield of methyl methacrylate decreases.
When the residence time in the reactor exceeds 2 hours, the yield of methyl methacrylate is not significantly improved and the reactor volume increases, which increases the facility cost and is industrially disadvantageous.

 The present invention will be specifically described with reference to the drawings.

FIG. 1 is a flow chart according to an embodiment of the present invention.
The reaction product gas obtained by vapor-phase catalytic oxidation of isobutylene, tertiary butanol or methacrolein is cooled and condensed, and the crude methacrylic acid after the impurities are extracted and distilled from the obtained methacrylic acid aqueous solution is removed. Line 10
And is supplied to the methacrylic acid rectification column 1. The top liquid is supplied via line 12 to the first esterification reactor 2 using cation exchange resin as catalyst together with methanol from line 14, and the bottom liquid is supplied via line 13 as sulfuric acid as second ester. It is led to the chemical reaction reactor 8. The first esterification reaction liquid is supplied via line 15 to the methacrylic acid recovery column 3 from line 16 together with the second esterification reaction liquid from line 29.
The top liquid of the recovery column is supplied to the methanol extraction column 4 via line 17, and the bottom liquid containing methacrylic acid as the main component is supplied to line 11.
It is recycled to the methacrylic acid rectification column. In the methanol extraction tower 4, the extraction water is supplied from the line 18, and the extraction liquid containing methanol as a main component is withdrawn from the bottom of the tower,
It is supplied to the methanol recovery tower 7 via 20.

On the other hand, the oil residual liquid containing methyl methacrylate as a main component is supplied to the low boiling point separation column 5 through the line 19 from the column top, and the low boiling point product is withdrawn from the system through the line 21 to the outside of the system. The bottom liquid is supplied to the methyl methacrylate rectification column 6 via a line 22, and the product methyl methacrylate is obtained from the top of the column via a line 23. The bottom liquid is supplied to the second esterification reactor via line 24. In the methanol recovery tower, methanol is recovered from the top of the tower via the line 25 and recycled to the first and second esterification reactors via the methanol storage tank 9. The bottom liquid is discharged to the outside of the system via line 26. In the second esterification reactor 8, the methacrylic acid rectification column bottom liquid from line 13,
Methyl methacrylate rectification column bottoms from line 24, sulfuric acid from line 27 and methanol from line 28 are fed. The reaction liquid containing methyl methacrylate as the main component, which has been reactively distilled in the second esterification reactor, is supplied to the methacrylic acid recovery column via line 29, and the waste sulfuric acid is withdrawn from line 30.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

The reaction product gas obtained by vapor-phase catalytic oxidation of isobutylene was cooled and condensed, and impurities were extracted and distilled from the obtained aqueous solution of methacrylic acid to remove crude methacrylic acid as a raw material. Methacrylic acid and methyl methacrylate were recovered according to the flow shown. Table 1 shows the outline of each device and its operating conditions, and Table 2 shows the results of implementation.

[Effects of the Invention] According to the present invention, it has become possible to recover methacrylic acid contained in the bottom liquid of a distillation column can as methyl methacrylate efficiently, economically and stably by an extremely simple operation.

[Brief description of drawings]

 FIG. 1 is a flow chart according to an embodiment of the present invention. 1 ... Methacrylic acid rectification column, 2 ... First esterification reactor, 3 ... Methacrylic acid recovery column, 4 ... Methanol extraction column, 5 ... Low boiling separation column, 6 ... Methyl methacrylate rectification column Tower, 7 ... Methanol recovery tower, 8 ... Second esterification reactor, 9 ... Methanol storage tank, 10-30 ... Each line.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C07B 61/00 300 (72) Inventor Morimasa Kuragano 2-2-1-1-418 (Shinkaidaidai, Sakai City, Osaka Prefecture) 72) Inventor Minoru Koshibe 1-3-16 Shinhiodai, Sakai City, Osaka Prefecture (56) References JP49-45020 (JP, A) JP60-6636 (JP, A)

Claims (1)

[Claims] 1. An impurity is extracted or separated from an aqueous solution of methacrylic acid obtained by vapor phase catalytic oxidation of isobutylene, tertiary butanol or methacrolein, and crude methacrylic acid obtained is separated in a methacrylic acid rectification column. Separation into purified methacrylic acid and bottom liquid, and subjecting the purified methacrylic acid together with methanol to the first esterification with a cation exchange resin as a catalyst to recover unreacted methacrylic acid in the esterification reaction liquid. Methyl methacrylate obtained by separating methanol, water, and low-boiling-point impurities from the distillate of the recovery tower by distilling and separating it in the tower is purified in a methyl methacrylate rectification tower, and the rectification tower When obtaining a methyl methacrylate product from the top of the tower, methacrylic acid recovered as a bottom liquid in the methacrylic acid recovery tower is circulated to the methacrylic acid rectification tower, The bottom liquid of the methacrylic acid rectification column is subjected to the second esterification using sulfuric acid as a catalyst together with the bottom liquid of the methyl methacrylate rectification column to obtain a second esterification reaction liquid and a first esterification reaction liquid. In the methacrylic acid recovery tower, wherein the second esterification is carried out by using a methanol molar ratio of methacrylic acid of 1.0 to 3.0, a sulfuric acid usage of methacrylic acid of 1.0 to 5.0% by weight, and a reactor residence time. The method for recovering methacrylic acid as methyl methacrylate is characterized by performing reactive distillation under the condition of 0.1 to 2 hours.