JPH0739367B2 - Methacrylic acid recovery method - Google Patents

Description

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

[Conventional technology]

Methacrylic acid obtained by catalytic oxidation of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with molecular oxygen in the presence of steam in a one-step or two-step reaction can be highly purified by ordinary purification means such as extraction and distillation. It can be a pure product. However, until methacrylic acid is finally obtained, the light boiling point components such as aldehydes and ketones are removed from the methacrylic acid aqueous solution, the solvent is recovered after the extraction treatment, the acid having a lower boiling point than methacrylic acid is separated, and the high boiling point component is removed. And is repeatedly exposed to heating conditions. Therefore, the treatment of each step is carried out in the presence of a conventionally known polymerization inhibitor such as phenothiazine, benzophenothiazine, hydroquinone, methoxyhydroquinone, methylene blue and molecular oxygen, but it is not possible to completely suppress the polymerization of methacrylic acid or the like. The polymer such as methacrylic acid gradually accumulates each time the process goes through, and the amount is not negligible in the final process. Therefore, since a considerable amount of polymer is present in the high boiling point component after methacrylic acid is distilled off,
If the distillation rate of methacrylic acid (distilled amount / supplied amount) is too high, the liquid viscosity of the can portion rises, the thermal efficiency of the reboiler deteriorates, and further the polymerization of methacrylic acid or the like is promoted. Therefore, the distillation rate of methacrylic acid is necessarily suppressed below a certain range, and a considerable amount of methacrylic acid is discharged together with the high boiling point component containing the polymer as a bottom liquid.

[Problems to be Solved by the Invention]

Therefore, an object of the present invention is to provide a method for easily and efficiently recovering methacrylic acid from a bottom liquid of a methacrylic acid distillation.

[Means for Solving the Problems]

Focusing on this point, the present inventors have earnestly studied about a method for effectively recovering methacrylic acid from a methacrylic acid containing a polymer and a high-boiling point component, and as a result, an aliphatic, alicyclic or aromatic hydrocarbon has been obtained. It was found that when a specific amount of the above was added to the bottom liquid, a polymer such as methacrylic acid and a part of the high boiling point component were selectively deposited, and the present invention was completed based on this finding.

The method for recovering methacrylic acid of the present invention is carried out by distilling and separating methacrylic acid, which is 60 to 95 parts by weight of methacrylic acid and 3 to 3 high-boiling components.
To the bottom liquid consisting of 30 parts by weight and the polymer 2 to 10 parts by weight, 1 to 4 times the weight of the bottom liquid is added an organic solvent selected from aliphatic hydrocarbons, alicyclic hydrocarbons or aromatic hydrocarbons. Add
The polymerized product and high-boiling-point components that precipitate are removed by filtration, and methacrylic acid is recovered from the organic solvent layer.

As the bottom liquid, the bottom liquid obtained by distilling methacrylic acid obtained by various known methods can be used.
For example, isobutylene, tertiary butanol, methacrolein, or isobutyraldehyde is catalytically oxidized by a gas containing molecular oxygen in the presence of steam, and the oxidation product is cooled to obtain an aqueous methacrylic acid solution. It is a bottom liquid obtained by extracting methacrylic acid, recovering the solvent, and separating methacrylic acid by distillation.

The composition of the bottom liquid is 60 to 95 parts by weight of methacrylic acid and 3 high boiling substances.
-30 parts by weight and 2-10 parts by weight of polymer. The high-boiling components in the bottom liquid are high-boiling acids such as citraconic acid, maleic acid and terephthalic acid, and hydroquinone added as a polymerization inhibitor, and the polymer is a polymer of methacrylic acid.

The organic solvent used in the present invention is n-pentane,
It is selected from aliphatic hydrocarbons such as n-hexane, n-heptane and n-octane, alicyclic hydrocarbons such as cyclohexane and aromatic hydrocarbons such as ethylbenzene, xylene and toluene. The amount of the organic solvent added varies depending on the type of solvent and the composition of the bottom liquid, but is 1 to 4 relative to the bottom liquid.
Double amount (weight) is adopted. If the amount is less than 1 time (weight), precipitation of the polymer and high-boiling point components is not sufficient and the original purpose cannot be achieved. If more than 4 times (weight) is used, go to the previous step. The energy cost for separating and recovering the solvent when returned is increased, which is not preferable.

There is no particular limitation on the filter used for the excess of the polymer and the high boiling point component which are precipitated by adding the organic solvent to the bottom liquid, but a cartridge filter, a pressure leaf filter, etc. are generally used.

The organic layer after separating the polymer and the high boiling point component is returned to the previous step of liquid-liquid extraction from the aqueous solution of methacrylic acid or the solvent recovery step from the extraction phase to recover methacrylic acid. In some cases, it is also possible to distill the organic layer alone to separate it from the solvent and recover methacrylic acid.

〔The invention's effect〕

According to the method of the present invention, methacrylic acid, which has been conventionally discarded or incinerated together with a high boiling point component and a polymer as a bottom liquid, can be easily and efficiently recovered.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 10 kg of a bottom liquid in a methacrylic acid rectification column consisting of 84.5 parts by weight of methacrylic acid, 10.3 parts by weight of a high boiling point component and 5.2 parts by weight of a polymer.
20 kg of n-hexane was added to the above and sufficiently stirred, and when the polymer was completely precipitated, treatment was carried out through a 0.1 m ² cartridge filter. 28.8 parts by weight of methacrylic acid in the obtained n-hexane solution, 2.2 parts by weight of a high boiling point component,
With 0.1 part by weight of the polymer, the recovery of methacrylic acid was 98.0%, the removal of the polymer was 94.2%, and the removal of high boiling point components was 60.1%.

Examples 2 and 3 The bottom liquid having the composition shown in Table 1 was treated with n-hexane in the same manner as in Example 1. The results are shown in Table-1.

Examples 4 and 6 Table 2 shows the results of the same treatment as in Example 1 except that the amount of the solvent added to the bottom liquid was changed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuharu Yoguchi 4-10-11 Kamo, Takaishi-shi, Osaka (56) References JP-A-60-69053 (JP, A) JP-A-60-104034 (JP, A)

Claims (2)

[Claims] 1. Methacrylic acid 60 to 95 parts by weight, high boiling point component 3 to 30 parts by weight and polymer 2 obtained by distilling and separating methacrylic acid.
To 10 parts by weight of bottom liquid, 1 to 4 times the weight of the bottom liquid by weight of an organic solvent selected from aliphatic hydrocarbons, alicyclic hydrocarbons or aromatic hydrocarbons is added to deposit a polymer. And a method for recovering methacrylic acid, characterized in that methacrylic acid is recovered from the organic solvent layer by filtering out and removing high-boiling components. 2. The method according to claim 1, wherein the organic solvent is n-pentane, n-hexane, n-heptane, n-octane, cyclohexane, toluene, ethylbenzene or xylene.