JPH0621103B2 - 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 methacrylic 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 conventional purification means such as extraction and distillation. It can be a pure product.

However, until methacrylic acid is finally obtained, removal of light-boiling components such as aldehydes and ketones from methacrylic acid aqueous solution, recovery of solvent after extraction treatment, separation of acids having a lower boiling point than methacrylic acid, and high-boiling components 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. This cannot be done, and the polymer such as methacrylic acid and the polymerization inhibitor are gradually accumulated with each step, and the amount becomes nonnegligible in the final step.

Therefore, in the bottom liquid after the methacrylic acid has been distilled off by rectification, a considerable amount of a polymer and a polymerization inhibitor are present in addition to the high-boiling-point impurities generated by the reaction. If the amount of distillate / supply is too high, the liquid viscosity of the can portion rises, the thermal efficiency of the reboiler deteriorates, and the polymerization of methacrylic acid and 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. Therefore, if the residual liquid in the can is discarded or incinerated, loss of methacrylic acid is caused, which leads to deterioration of the basic unit and increase in cost. Therefore, recovery of methacrylic acid must be done by some method.

Heretofore, as a general method, recovery of methacrylic acid by re-evaporation of a bottom liquid in an evaporator or recovery of methacrylic acid by extraction with an organic solvent has been considered. However, the former has problems such as poor recovery rate and operational problems due to polymerization of methacrylic acid, and the latter causes a large amount of sludge to be generated by the extraction solvent, resulting in emulsification and flooding of the extraction tower. However, none of them are effective methods.

[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 problems]

The present inventors focused their attention on this point, and as a result of earnest research on a method for effectively recovering methacrylic acid from a bottoms solution containing a polymer and a high-boiling component after methacrylic acid was separated by distillation, as a result, When added to the bottom liquid, most of the high-boiling components such as high-boiling aldehydes, polymers, and polymerization inhibitors are selectively separated into two layers from the aqueous methacrylic acid solution, and methacrylic acid can be recovered easily and efficiently. The present invention has been completed based on the findings and the findings.

Methacrylic acid recovery method of the present invention is methacrylic acid 60-9
5 parts by weight, high boiling substance 3 to 30 parts by weight and polymer 2-1
Water was added to 0 parts by weight of the bottoms obtained by distillation to separate methacrylic acid, and two layers were separated into a layer of the polymer and the high boiling point component and a methacrylic acid aqueous solution layer. It is characterized by being extracted with a solvent and recovered.

As a method for separating methacrylic acid from the separated methacrylic acid aqueous solution, distillation, extraction, a method such as semipermeable membrane can be applied, but since this methacrylic acid aqueous solution contains a small amount of hydrophilic high-boiling point component, The method of extracting methacrylic acid with a specific organic solvent is the most effective for recovering methacrylic acid from here with high purity and at low cost.

As the bottoms solution targeted by the method of the present invention, bottoms solutions obtained by distilling methacrylic acid obtained by various known methods can be used. For example, isobutylene, tert-butanol, methacrolein or isobutyraldehyde is catalytically oxidized with a gas containing molecular oxygen in the presence of water vapor, and the methacrylic acid aqueous solution obtained by cooling the oxidation product is treated with a methacrylic acid by a solvent. It is a bottom liquid obtained by acid extraction, solvent recovery, and methacrylic acid distillation separation.

The composition of the bottom liquid is usually 60 to 95 parts by weight of methacrylic acid, 3 to 30 parts by weight of a high-boiling substance, and 2 to 10 parts by weight of a polymer. In the present invention, the bottom solution of this structure is used. The high-boiling 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 added as a polymerization inhibitor, and the polymer is a polymer of methacrylic acid.

In the present invention, the amount of water to be added to the bottom liquor varies depending on the composition of the bottom liquor, but is usually 2 to 6 times the weight (weight) of the bottom liquor. When the amount is less than 2 times the weight (weight) or when the amount is more than 6 times the weight (weight), the two layers are not separated as a homogeneous solution and the object of the present invention cannot be achieved.

In the present invention, the organic solvent used to extract methacrylic acid is a water-insoluble organic solvent having a lower boiling point than methacrylic acid, for example, aliphatic hydrocarbons, alicyclic hydrocarbons,
Aromatic hydrocarbons, acetic acid esters or ethers can be used, and particularly preferably n-pentane, n-heptane, n
-Hexane and n-octane, cyclohexane, toluene, ethylbenzene, xylene and the like can be mentioned.

Most of the water and hydrophilic high-boiling point components are separated as a raffinate by extracting methacrylic acid with the above organic solvent from the methacrylic acid aqueous solution obtained by separating the two layers by adding water to the bottom liquid. It can be removed and treated by a wastewater treatment facility.

On the other hand, the organic solvent solution of methacrylic acid obtained as the extract can be recovered at low cost by separating the organic solvent by distillation.

〔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 Methacrylic acid 93.84%, polymer and high boiling point component 6.16
% Of methacrylic acid rectification column containing 75% of water was added to 75 kg of water, and the mixture was sufficiently stirred and allowed to stand.
94.73 kg of upper layer liquid having a composition of 4%, high boiling point component 0.48%, and water 76.98%, methacrylic acid 40.04%, high boiling point component
A layer-separated solution was obtained with 5.27 kg of a lower layer liquid having a composition of 20.49% and water 39.47%. The recovery rate of methacrylic acid is 91.0%,
The removal rate of high-boiling components was 70.1%.

2.0 kg of upper layer liquid to the top of a rotating disk extraction tower with 20 actual stages
/ N-hexane at a flow rate of 2.0 kg / hr. Both of them are brought into countercurrent contact and from the top of the column, methacrylic acid 18.00%, n-hexane 81.91%, high boiling point component.
Extraction liquid 2.44 kg / hr of 120 ppm and water 820 ppm is passed from the bottom of the tower to 0.72% of methacrylic acid, 0.60% of high boiling point component and 98.68 of water.
% Raffinate was obtained at 1.56 kg / hr. The recovery rate of methacrylic acid is
The removal rate of high-boiling components was 97.5% and 96.9%. The final methacrylic acid recovery rate through both steps was 88.7%, and the high boiling point component removal rate was 99.1%.

Examples 2 to 5 The results obtained by carrying out the same treatment as in Example 1 using the two types of bottom liquids shown in Table 1 as raw materials and changing the addition amount of water and the type and addition amount of solvent are shown in Example 1. The results are shown in Table-1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Koshibe 1-3-16 Shinhiodai, Sakai City, Osaka Prefecture

Claims (2)

[Claims] 1. Methacrylic acid 60 to 95 parts by weight, high boiling point material 3 to 30 parts by weight and polymer 2 to 10 parts by weight,
Water is added to the bottom liquid obtained by distilling and separating methacrylic acid, and two layers are separated into a polymer layer and a high boiling point component layer and a methacrylic acid aqueous solution layer, and methacrylic acid is extracted from the methacrylic acid aqueous solution with an organic solvent and recovered. A method for recovering methacrylic acid, which comprises: 2. The organic solvent is n-pentane, n-hexane,
A process according to claim 1 which is n-heptane, n-octane, cyclohexane, toluene, ethylbenzene or xylene.