JPH0621104B2 - Extraction and separation of methacrylic acid - Google Patents

Description

The present invention relates to an aqueous solution of a reaction product obtained when methacrylic acid is produced from isobutylene, t-butanol, isobutyraldehyde or methacrolein by gas phase catalytic oxidation. The present invention relates to a method for removing a polymer production promoting substance and a non-volatile high-boiling substance and selectively separating and recovering methacrylic acid.

(Prior Art) Methacrylic acid obtained by vapor-phase catalytic oxidation of isobutylene, t-butanol, isobutyraldehyde, or methacrolein is usually obtained by quenching a reaction product gas produced by a vapor-phase catalytic oxidation reaction or contacting with water. To make an aqueous solution of methacrylic acid, and then separate low-boiling substances such as acetone and methacrolein by distillation, extract with a sparingly water-soluble organic solvent to remove most of water and acetic acid, and then distill organically. Separates the solvent and methacrylic acid. At this time, aromatic solvents (Japanese Patent Publication No.
21018), aliphatic / alicyclic hydrocarbons (Japanese Patent Publication No. 56)
-52007), mixed solvents of esters and hydrocarbons (Japanese Patent Publication No. 49-41413, Japanese Patent Publication No. 55-27894, Japanese Patent Publication No. 58-29935), mixed solvents of ketones and hydrocarbons (Japanese Patent Publication No. 55- 34784) and the like.

(Problems to be Solved by the Invention) In the aqueous oxidation product solution containing methacrylic acid as a main component, which is obtained by quenching the gas-phase catalytic oxidation reaction product gas or contacting with water, a polymer formation promoting substance (hereinafter Polymer factor substances), various polymers derived from methacrolein and methacrylic acid, and non-volatile high-boiling substances in the form of polymer tar (collectively abbreviated as non-volatile substances below) are dissolved. Due to the substance, if an extraction solvent with a high methacrylic acid extraction capacity is used during the extraction operation of methacrylic acid, a large amount of insoluble solid substance (abbreviated as scum below) will accumulate in the extraction tower and interface control section, and it will be stable. It will make long-term driving difficult. Further, the problems of the dissolved polymer factor substance and the non-volatile generating substance have an adverse effect on the subsequent distillation step. That is, the dissolved polymer factor substance and the non-volatile substance extracted together with methacrylic acid accelerate the polymerization of methacrylic acid in the distillation column, and the non-volatile substance is accumulated in the distillation column and / or the reboiler as the distillation proceeds. It accumulates or deposits inside, resulting in impaired normal operation of the distillation column for a long period of time. No effective method for solving these problems has been proposed yet.

(Means for Solving Problems) As a result of intensive investigations by the present inventors to solve such problems, as a result of quenching the gas-phase catalytic oxidation reaction product gas or contacting with water, an aqueous methacrylic acid solution was obtained. , Methacrylic acid is selectively extracted by using a mixed solvent in which specific aromatic hydrocarbons and aliphatic hydrocarbons are mixed at a predetermined ratio, while the polymer factor substance and the non-volatile substance are left in the extraction residual water phase. As a result, a method for separating and recovering methacrylic acid, which is excellent in economic efficiency while preventing accumulation and deposition of scum and non-volatile substances in the extraction step and the distillation step, has been completed.

That is, the present invention is obtained by vapor-phase catalytic oxidation of isobutylene, t-butanol, isobutyraldehyde or methacrolein, and quenching the produced gas or contacting with water. 20-70% by weight of an aromatic hydrocarbon selected from benzene, toluene and xylene from an aqueous solution of methacrylic acid containing 20-45% by weight of methacrylic acid, 0.5-5% by weight of a polymer formation promoting substance and 0.5-5% by weight of a non-volatile high boiling point substance. %
Methacrylic acid is characterized by selectively extracting methacrylic acid using a mixed solvent containing the aromatic hydrocarbon and an aliphatic hydrocarbon selected from n-hexane, n-heptane, and n-octane. Regarding the extraction and separation method of.

Gas phase catalytic reaction of isobutylene, t-butanol, isobutyraldehyde or methacrolein The methacrylic acid aqueous solution obtained by quenching the product gas or contacting with water is usually 20 to 45% by weight of methacrylic acid and 1 to 10% by weight of acetic acid. , Acrylic acid 0.1-1% by weight, methacrolein 1
.About.6 wt%, acetone 0.02 to 5 wt%, polymer factor substance and non-volatile substance 0.5 to 5 wt%. This methacrylic acid aqueous solution may be sent to the extraction step as it is, or may be sent to the extraction step after removing low-boiling substances such as acetone and methacrolein.

In the present invention, a mixed solvent of aromatic hydrocarbons and aliphatic hydrocarbons is used as the extraction solution of methacrylic acid.
The aromatic hydrocarbon in this case is selected from three kinds of benzene, toluene and xylene, and may be used alone or in combination of two or more kinds.

Also, aliphatic hydrocarbons include n-hexane, n-heptane,
It is selected from three types of n-octane, and one type may be used, or two or more types may be used in combination.

Further, the mixing ratio of these aromatic hydrocarbons and aliphatic hydrocarbons is such that the concentration of aromatic hydrocarbons in the mixed solvent is 20 to 7
The ratio is 0% by weight, but especially when aromatic hydrocarbon is 4%.
A mixed solvent containing 0 to 60% by weight is preferable.

When an aromatic hydrocarbon is used alone as a methacrylic acid extraction solvent, the extraction power of methacrylic acid is strong and preferable,
At the same time, the extracting ability of the polymer factor substance and the non-volatile substance becomes relatively strong, resulting in an inconvenient result.

Further, when the aliphatic hydrocarbon is used as a single group, the extraction power of methacrylic acid is extremely weak, and therefore the economical efficiency of the process is considerably deteriorated.

However, when the mixed solvent of the present invention is used, the extraction rate of methacrylic acid can be kept sufficiently high at an economical solvent usage rate, and the extraction rates of polymer factor substances and non-volatile substances that cause various troubles. Can be kept as low as necessary.

Further, there is a correlation between the extraction rate of methacrylic acid and the amount of scum generated at the interface of the extraction tower, and if the extraction rate of methacrylic acid is too high, the amount of column generation will increase.

The reason for this is that if the extraction rate of methacrylic acid is too high,
It can be considered that since most of the components that make up the scum are extracted by the extraction solvent, the scum does not dissolve in the aqueous phase of the extraction column and precipitates without being completely dissolved, which accumulates at the interface.

The amount of scum generated is also significantly reduced by using the mixed solvent of the present invention as compared with the conventional one.

As the extraction method, any method such as batch extraction and continuous countercurrent extraction can be adopted, but continuous countercurrent extraction is industrially advantageous.

The extraction temperature is usually 10 to 50 ° C., and there is no problem at around normal temperature.

A packed column, a perforated plate column, a rotary disc extraction column and the like can be used as the extraction device, and among them, the rotary disc extraction column is considered to be particularly suitable.

The thus obtained methacrylic acid extract has a remarkably small amount of polymer factor substances and non-volatile substances.

This extract is then sent to a solvent separation column, where the solvent, acetic acid and other low boiling point components are separated from the column top, and crude methacrylic acid is obtained from the column bottom. Since the solvent separation column is usually operated at a high temperature, a polymerization inhibitor for methacrylic acid is usually added. As described above, in the case of the present invention, the content of the limmer factor substance and the non-volatile substance in the extract is remarkably low, so that almost no polymer formation is observed in the distillation column, and therefore the concentration of the non-volatile substance in the crude methacrylic acid is reduced. It can be kept sufficiently low, which makes it possible to prevent the accumulation or deposition of non-volatile substances in the distillation column and / or the reboiler.

The crude methacrylic acid obtained is usually further purified to industrial methacrylic acid or esterified with methanol to methyl methacrylate.

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

A methacrylic acid aqueous solution obtained by quenching a gas-phase catalytic oxidation reaction product gas such as isobutylene or t-butanol after removing low-boiling components such as methacrolein is fed into a methacrylic acid extraction column 2 through a pipe 1. To do. On the other hand, from tube 3,
The methacrylic acid is extracted by feeding the mixed solvent according to the present invention. Methacrylic acid is extracted with a mixed solvent and pipe 4
And enters the next solvent separation tower 6.

On the other hand, almost all polymer factor substances and non-volatile substances are discharged from the pipe 5 together with water. In the tower 6, a pipe 7 in which low boiling point components such as solvent, water and acetic acid are separated from the top of the tower 7
Pass through Decanter 8. Here, the water phase and the oil phase are separated, and the water phase is withdrawn through the pipe 9. Oil phase is partly pipe 1
It is used as the reflux of the tower 6 through 0, and the others through the tube 3 and the tower 2
It is sent to the bottom of the column and recycled as a solvent.

From the bottom of the tower 6, crude methacrylic acid containing almost no non-volatile substance such as a polymer is recovered through a pipe 11.

(Example) Next, an Example is given and this invention is demonstrated more concretely.

Example 1 Methacrolein was subjected to gas-phase catalytic oxidation in the presence of air and water vapor using a phosphorus-molybdenum-based oxidation catalyst, and the resulting oxidation reaction product was quenched and recovered, and then an aldehyde having a low boiling point, The ketones were removed by distillation and methacrylic acid 3
0.0 wt%, acetic acid 5.2 wt%, acrylic acid 0.4 wt%,
Polymer factor substances and non-volatile substances 2.2 wt%, water 6
An aqueous methacrylic acid solution containing 0.5 wt% and 1.7 wt% was obtained. This aqueous solution was fed into the methacrylic acid extraction column shown in FIG. 1 through pipe 1 at a flow rate of 3.0 kg / HR. The methacrylic acid extraction column is a rotating disc extraction column having an inner diameter of 50 mm and 86 discs, and operated at a rotation speed of 700 rpm at room temperature. As the extraction solvent, toluene 50 wt%, n-heptane 50 wt
% Mixed solvent, and the mixture was fed into the lower part of the extraction column through the pipe 3 at a flow rate of 3.0 kg / HR. The composition of the extract in steady operation was 22.5 wt% of methacrylic acid, 1.2 wt% of acetic acid, 0.23 wt% of acrylic acid, polymer factor substances and non-volatile substances.
02 wt% and others 76.05 wt% and the flow rate is 3.
It was 95 Kg / HR. The composition of the raffinate discharged from the pipe 5 is 0.40 wt% methacrylic acid, 5.2 wt% acetic acid, 0.2 wt% acrylic acid, 3.4 wt% polymer factor substances and non-volatile substances, and 90.8 wt% for others. %, And the flow rate was 2.1 Kg / HR.

In this case, the extraction rate of methacrylic acid was 99.1%, which was a practically satisfactory value, and the extraction rate of the polymer factor substance and the non-volatile substance was 1.1%, which was a sufficiently low value. The obtained extract was sent to the solvent separation tower 6 through the pipe 4.

As the solvent separation column, a packed column having an inner diameter of 72 m and a Goodroll packing 2.4 m was used. It was operated at a reflux ratio of 1.0 at an operating pressure of 50 toor. The solvent and other low-boiling components were recovered from the top of the column and recycled to the super-extraction column 2 through the pipe 3. From the bottom of the column, crude methacrylic acid was obtained from the tube 11, and its composition was 98.75% by weight of methacrylic acid, 0.9% by weight of acrylic acid, 0.15% by weight of polymer factor substances and non-volatile substances, and others.
It was 2 wt%.

This liquid was transparent, solid fine particles such as polymer were not observed at all, and it was a very good liquid property. The combined operation of the extraction column and the distillation column was carried out for 5 days, but the scum at the interface of the extraction column after the operation was small with a thickness of 2 to 3 mm, and stains due to the adherence of solid substances such as polymers to the inner surface of the distillation column reboiler were observed. There wasn't.

Example 2 Benzene 50 wt% and n-heptane 50 wt as extraction solvents
% Of the mixed solvent was used, and the extraction column and the solvent separation column were operated under exactly the same conditions as in Example 1 except for the above. The composition of the obtained extract solution was 22.6 wt% methacrylic acid, 1.3 wt% acetic acid, 0.25 wt% acrylic acid, 0.03 wt% polymer factor substances and non-volatile substances, and 75.8 wt% other, and the flow rate was 3. It was 95 Kg / HR. Oil residual liquid composition is methacrylic acid 0.35 wt%, polymer factor substances and non-volatile substances 3.
4wt%, others 96.25wt% and its flow rate is 2.0
It was 5 Kg / HR. In this case, the extraction rate of methacrylic acid is 99.
2%, the extraction rate of the polymer factor substance and the non-volatile substance was 1.7%, which were sufficiently satisfactory values.

The extract is continuously sent to the solvent separation tower, and from the bottom of the tower, methacrylic acid 98.7 wt%, acrylic acid 0.9 wt%, polymer factor substances and non-volatile substances 0.2 wt%, other 0.2 wt%
Of crude methacrylic acid was obtained. The liquid properties were similar to those in Example 1 and were very good.

After operating for 5 days, the scum thickness at the extraction tower interface was 2 to 3 mm, and the operation could be performed without any trouble.

In addition, solid matters such as polymers were not adhered to the inner surface of the distillation tower reboiler and the inside of the tower, and the operation was satisfactory.

Example 3 Xylene 50 wt% and n-hexane 50 wt% as extraction solvents
When the operation was performed in the same manner as in Example 1 except that the mixed solvent of 1% was used, the same satisfactory result as in Example 1 was obtained.

Example 4 Toluene 50 wt% and n-octane 50 wt% as extraction solvents
When the operation was performed in the same manner as in Example 1 except that the mixed solvent of 1% was used, the same satisfactory result as in Example 1 was obtained.

Example 5 Vapor Phase Catalytic Oxidation of Methacrolein An aqueous solution of methacrylic acid obtained by quenching the vapor phase catalytic oxidation of isobutylene, t-butanol or isobutyraldehyde was used in place of the aqueous solution of methacrylic acid obtained by quenching the product gas. When the operation was carried out in the same manner as in Example 1, satisfactory results were obtained as in Example 1 in all cases.

Comparative Example 1 Toluene was used as an extraction solvent, and the extraction column and the solvent separation column were operated under exactly the same conditions as in Example 1. The composition of the resulting extract is 22.6 wt% methacrylic acid, 1.5 wt% acetic acid, 0.3 wt% acrylic acid, 0.15 wt% polymer and non-volatile matter, and 75.45 wt% other.
And the flow rate was 3.97 Kg / HR. The composition of the raffinate was 0.25 wt% of methacrylic acid, 3.2 wt% of the polymer factor substance and non-volatile substance, and 96.55 wt% of others, and the flow rate was 2.0 Kg / HR.

In this case, the extraction rate of methacrylic acid was as good as 99.5%, but the extraction rates of the polymer factor substance and the non-volatile substance were too high at 8.5%. There were many scums at the interface of the extraction tower, and small-sized scums sometimes mixed with the extraction liquid and accompanied. This extract is subsequently sent to the solvent separation tower,
Methacrylic acid 97.6 wt%, acrylic acid 1.
3wt%, polymer factor substances and non-volatile substances 0.85wt
%, And other crude methacrylic acid having a composition of 0.25 wt% was obtained.

A small amount of white fine particles were present in this crude methacrylic acid. The operation was carried out for 5 days, but the thickness of the scum layer at the interface of the extraction tower was 5 to 10 mm, which was considerably larger than that in Example 1. In addition, a thin film-like white deposit (polymer of methacrylic acid was the main component) was found on the inner surface of the distillation column reboiler, which reduced the heat transfer ability.

Comparative Example 2 n-heptane was used as the extraction solvent, and the others were used in Example 1.
The operation was carried out under exactly the same conditions as above.

The composition of the obtained extract was 22.1 wt% methacrylic acid, 0.8 wt% acetic acid, 0.15 wt% acrylic acid, 0.01 wt% polymer factor substances and non-volatile substances, and other 76.94%.
It was wt% and the flow rate was 3.90 Kg / HR. The composition of the raffinate was 1.70 wt% of methacrylic acid, 3.30 wt% of polymer factor substances and non-volatile substances, and 95.0 wt% of others, and the flow rate was 2.15 Kg / HR. In this case, the extraction ratio of the polymer-causing substance and the non-volatile substance was low at 0.5%, which was preferable, but the extraction ratio of methacrylic acid as the main component was 96.0%, which was too low. I knew it wouldn't happen.

Next, in order to improve the extraction rate of methacrylic acid, only the flow rate of n-heptane was doubled to 6.0 kg / HR, and the others were operated as they were. The composition of the obtained extract was 12.8 methacrylic acid.
wt%, acetic acid 0.56 wt%, acrylic acid 0.1 wt%, polymer factor substances and non-volatile substances 0.01 wt%, others 8
The flow rate was 6.53 wt% and the flow rate was 6.94 Kg / HR.

The composition of the raffinate is 0.43 wt% methacrylic acid, 3.2 wt% polymer factor substances and non-volatile substances, and 96.37 other.
%, And the flow rate was 2.1 Kg / H. In this case, the extraction rate of methacrylic acid is 99.0%, and the extraction rate of polymer factor substances and non-volatile substances is 1.0%, which is satisfactory, but the amount of extraction solvent used is twice as large, which is also practical. It was proved to lack sex.

(Effects of the Invention) As described above, when methacrylic acid is extracted from an aqueous methacrylic acid solution using the mixed solvent according to the present invention, methacrylic acid can be highly selectively and economically extracted, and further extraction and distillation can be performed. In the process, accumulation and deposition of non-volatile substances such as polymers can be prevented, and stable operation for a long period of time becomes possible.

[Brief description of drawings]

FIG. 1 is a flow sheet showing one embodiment of the method of the present invention. 2 ... Methacrylic acid extraction tower 6 ... Solvent separation tower 8 ... Decanter (phase separator)

Claims (1)

[Claims] 1. Methacrylic acid 20 to 45% by weight, which is obtained by subjecting isobutylene, t-butanol, isobutyraldehyde or methacrolein to vapor-phase catalytic oxidation and quenching the produced gas or contacting with water to accelerate polymer production. Substances and non-volatile high-boiling substances, methacrylic acid aqueous solutions containing 0.5 to 5% by weight, benzene, toluene,
Using 20 to 70% by weight of an aromatic hydrocarbon selected from xylene, a mixed solvent of the aromatic hydrocarbon and an aliphatic hydrocarbon selected from n-hexane, n-heptane, and n-octane, A method for extracting and separating methacrylic acid, which comprises selectively extracting methacrylic acid.