JPH11269119A - Recovery of methacrolein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain methacrolein containing reduced amounts of impurities such as a variety of organic acids, aldehydes, ketones and the like as the by- products in a vapor-phase catalytic oxidation in which isobutylene and/or tertiary butanol are catalytically oxidized with molecular oxygen in the vapor phase, moisture and high-boiling substances are condensed and separated from the resultant reaction mixture and the remaining methacrolein gas is brought into contact with water or an organic acid aqueous solution, the resultant methacrolein-absorbing solution is fractionated by distillation into a still bottom fraction and a distillate fraction where the still bottom fraction is cycled as an absorbing agent for the methacrolein gas, while the distillate is phase- separated into the methacrolein phase and the aqueous phase and the methacrolein is recovered. SOLUTION: After methacrolein is phase-separated, the methacrolein is brought into contact with water and the water is separated again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering methacrolein from a reaction product gas obtained by subjecting isobutylene and / or tertiary butyl alcohol to gas-phase catalytic oxidation in the presence of molecular oxygen.

[0002]

2. Description of the Related Art When gas-phase catalytic oxidation of isobutylene and / or tertiary butyl alcohol in the presence of molecular oxygen, a reaction containing methacrylic acid, methacrolein, carbon monoxide, carbon dioxide, water, oxygen, nitrogen, etc. A product gas is obtained. Usually, the obtained reaction product gas is quenched and separated into a condensate such as methacrylic acid and water and a non-condensable gas such as most of methacrolein, nitrogen and oxygen.

[0003] As a method for efficiently separating and recovering methacrolein from the non-condensable gas thus separated, methacrolein is absorbed using an absorbent, and the absorbed liquid is separated by an operation such as distillation or stripping. A method for recovering methacrolein is known. Examples of the methacrolein absorbent used at this time include water (JP-A-53-144515) and acetic acid (JP-A-54-48).
706) and a methacrylic acid aqueous solution from which methacrolein has been removed (JP-A-54-52027). The absorbent used for the recovery of methacrolein and separated by distillation, stripping, etc., is recycled as an absorbent for the absorption of methacrolein in consideration of economic efficiency when industrially implemented. Is done.

[0004]

However, impurities such as various organic acids, aldehydes and ketones which are by-produced in the gas phase catalytic oxidation reaction accumulate in the circulating absorbent. In particular, when water or an aqueous solution is used as the absorbent, it is inevitable that these water-soluble impurities accumulate, and these impurities are mixed in the methacrolein absorbing solution. When distillation is performed to separate the absorbent from the methacrolein absorbent, the resulting distillate is an azeotropic mixture of methacrolein and water. This distillate contains impurities distilled together with water.Even if the distillate is cooled and the aqueous phase is separated by a decanter, the impurities are distributed to the methacrolein phase. It has been difficult to sufficiently reduce the impurities of.

Accordingly, an object of the present invention is to provide methacrolein obtained by subjecting isobutylene and / or tertiary butyl alcohol to gas-phase catalytic oxidation in the presence of molecular oxygen and condensing and separating water and high-boiling substances from the resulting reaction product gas. Contact the gas containing water or organic acid aqueous solution as an absorbent,
The obtained methacrolein-absorbed liquid is separated into a bottom liquid and a distillate by distillation, and the bottom liquid is recycled and reused as an absorbent for methacrolein-containing gas, and the distillate is separated into a methacrolein phase and an aqueous phase. In a method of recovering methacrolein by performing the method, it is to obtain methacrolein with few impurities such as various organic acids, aldehydes, and ketones by-produced by gas phase catalytic oxidation.

[0006]

DISCLOSURE OF THE INVENTION The present inventors distilled a methacrolein-absorbing solution to distill it as an azeotropic mixture of methacrolein and water, and obtained a methacrolein obtained by phase-separating the distillate. It has been found that the content of various organic acids, aldehydes, ketones, etc. contained in methacrolein can be effectively reduced by bringing impurities into contact with water to extract and remove impurities, thereby completing the present invention.

That is, the present invention relates to isobutylene and / or
Alternatively, tertiary butyl alcohol is subjected to gas-phase catalytic oxidation in the presence of molecular oxygen, and water and a high boiling point substance are condensed and separated from the resulting reaction gas into a methacrolein-containing gas, and water or an organic acid aqueous solution as an absorbent is used. And the resulting methacrolein-absorbed solution is separated into a bottoms and a distillate by distillation, and the bottoms are recycled and reused as an absorbent for a methacrolein-containing gas, and the distillate is a methacrolein phase and water. A method for recovering methacrolein by separating phases into phases, wherein methacrolein is brought into contact with water after phase separation of methacrolein, and water is separated again.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a reaction product gas obtained by subjecting isobutylene and / or tertiary butyl alcohol to gas-phase catalytic oxidation in the presence of molecular oxygen is led to a condenser. In the condenser, water and high-boiling substances in the reaction product gas are condensed and withdrawn from the bottom of the column, and the remaining gas containing methacrolein is withdrawn from the top of the condenser.

The obtained methacrolein-containing gas is led to a methacrolein absorption tower, and is brought into contact with water or an organic acid aqueous solution as an absorbent. The method of contact is not particularly limited, but countercurrent contact is preferred in terms of absorption efficiency. In particular,
A method may be exemplified in which a methacrolein-containing gas supplied from the bottom of the column and an absorbent supplied from the top of the column are brought into countercurrent contact to absorb methacrolein, and a methacrolein-absorbed liquid is obtained from the bottom of the column.

The absorbent supplied to the methacrolein absorption tower is water or an organic acid aqueous solution at the beginning of the treatment, but it is mainly a bottom liquid of a methacrolein recovery tower described later during continuous operation. Includes impurities such as various organic acids, aldehydes and ketones by-produced in the reaction. Examples of the organic acid aqueous solution that can be used as the adsorbent include an acetic acid aqueous solution, a methacrylic acid aqueous solution, and the like.

The methacrolein-absorbed liquid thus obtained from the bottom of the column is led to a methacrolein recovery tower, and an azeotropic mixture of methacrolein and water is distilled off from the top as a distillate by a known distillation operation. Let it. The bottoms obtained from the bottom of the column are recycled as an absorbent for the gas containing methacrolein. At this time, the operating pressure may be either reduced pressure or atmospheric pressure, but the operating temperature is usually 100 ° C or lower, preferably 80 ° C or lower in the stage where methacrolein is present.

The azeotropic mixture of methacrolein and water thus obtained is appropriately cooled in a condenser or the like, and separated into a water phase and a methacrolein phase by a decanter. The liquid temperature at the time of decantation is preferably lower as the amount of water dissolved in the methacrolein phase becomes smaller.
Or less, preferably 10 ° C. or less. The upper phase methacrolein phase may be extracted as it is, or a part thereof may be refluxed to the top of the methacrolein recovery tower. The lower aqueous phase is preferably circulated to the recovery system and reused, but may be taken out of the system.

The thus obtained methacrolein (hereinafter referred to as crude methacrolein) is brought into contact with water as an extractant to extract and remove water-soluble impurities contained in the crude methacrolein. The method of the extraction operation is not particularly limited, and may be a continuous type or a batch type. Specifically, for example, a method using a mixer-settler type extractor, a perforated plate type extractor, a stirrer type step extractor, a separating funnel and the like can be mentioned. The operation temperature of the extraction operation is not particularly limited, but a temperature lower than the liquid temperature at the time of the decantation is preferable in order to reduce the amount of water dissolved in methacrolein.

The water to be brought into contact with the extractant is preferably water which does not substantially contain impurities such as the above-mentioned various organic acids, aldehydes and ketones. However, the impurities in the crude methacrolein can be reduced by the extraction operation. If so, these impurities may be contained in trace amounts. If a large amount of water is used as the extractant, methacrolein with few impurities can be obtained, but in that case, the amount of methacrolein dissolved in the water side increases, and extra energy is required to recover the dissolved methacrolein Therefore, it is desirable to minimize the amount of water. Specifically, methacrolein 1
Water is usually used in an amount of 10 to 200 parts by weight, preferably 20 to 100 parts by weight, based on 00 parts by weight.

Next, the present invention will be described with reference to FIG.
The process for implementing the method of the present invention is not limited to the process of FIG. From a reaction product gas obtained by subjecting isobutylene and / or tertiary butyl alcohol to gas-phase catalytic oxidation in the presence of molecular oxygen, to a methacrolein-containing gas obtained by condensing and separating water and a high-boiling substance, water or an organic acid aqueous solution is used. The methacrolein absorbing solution obtained by contacting
It is introduced into the methacrolein recovery tower 2 from the line 1 to obtain an azeotropic mixture of methacrolein and water.

The azeotrope passes through line 3 and passes through heat exchanger 6
After being condensed, the mixture is introduced into the decanter 7. An aqueous solution substantially free of methacrolein is taken out from the lower portion of the methacrolein recovery tower 2 and is recycled to the methacrolein absorption tower as a methacrolein absorbent through a line 5. In the decanter 7, the condensate is separated into two phases, and the aqueous phase is mixed with the methacrolein absorbing solution 1 from the line 10 and recycled to the methacrolein recovery tower. On the other hand, a part of the methacrolein phase, which is the upper phase of the decanter 7, is refluxed to the top of the methacrolein recovery tower by the line 8,
The remainder is introduced into the extraction column 11 through the line 9.

In the extraction column 11, water as an extracting agent is supplied from a line 12, methacrolein from which water-soluble impurities have been removed from a line 13 above the extraction column 11, and an aqueous phase from a line below the extraction column 11. Obtained respectively. A part of the aqueous phase obtained from the lower part of the extraction tower 11 is recycled to the methacrolein recovery tower through a line 14, and the rest is extracted out of the system through a line 15. Note that methacrolein is slightly dissolved in the aqueous phase extracted from the line 15,
An operation for collecting methacrolein can be performed as necessary.

The present invention solves the problem of impurity distribution in methacrolein due to the accumulation of impurities in a methacrolein-absorbing solution in a circulation process in which a methacrolein absorbent is recycled and reused. The problem is solved by combining an independent unit operation of washing with water having no or little impurities with a circulation process.

[0019]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The composition analysis in the examples was all performed by gas chromatography.

Example 1 A reaction product gas obtained by subjecting tertiary butyl alcohol to gas-phase catalytic oxidation in the presence of molecular oxygen was first directly mixed with a methacrylic acid aqueous solution previously condensed and accumulated in a quenching tower. The mixture was brought into contact to condense and remove high-boiling substances, acids, water, etc., to obtain a 28 ° C. mixed gas containing methacrolein and a non-condensable gas from the top of the quenching tower. This mixed gas was supplied to a packed-type methacrolein absorption tower having an inner diameter of 25 mm, and cooled to 10 ° C. from the top of the methacrolein absorption tower to 6% by weight of methacrylic acid, 4% by weight of acetic acid, 87% by weight of water, and 3
An aqueous solution containing weight% was supplied as methacrolein absorbent. From the bottom of the methacrolein absorption tower, methacrolein containing 3.1 wt% of methacrolein, 6.0 wt% of methacrylic acid, 3.9 wt% of acetic acid, and about 3 wt% of other organic acids, ketones and aldehydes A liquid was obtained.

The methacrolein-absorbed liquid thus obtained is distilled using an Oldershaw type continuous distillation column.
Separation and recovery of methacrolein were performed. The Oldershaw type continuous distillation column has an inner diameter of 36 mm in 10 stages and an inner diameter of 55 mm.
Is a total of 30 stages, and a raw material supply port is provided at the 10th stage from the top of the tower. The reboiler of the Oldershaw type continuous distillation column is of a natural circulation type, and has a structure in which the bottom liquid can be withdrawn by overflow. The Oldershaw type continuous distillation column is
It has a glass decanter for phase separation of the condensate. The decanter is equipped with a jacket and has an internal volume of 1
The upper phase (metacrolein phase), which has overflowed, is distributed to a reflux line to the top of the column and a line for taking out methacrolein by a magnet-type reflux device.

The above-mentioned methacrolein absorbing solution is supplied at an average of 10 kg / h from the raw material supply port of the Oldershaw type continuous distillation column, and the column bottom temperature is 102 ° C. and the column top temperature is 62 ° C. under atmospheric pressure.
Distillation was carried out. The bottoms overflowed at 9570 g / h from the bottom of the column, and an azeotropic mixture of water and methacrolein was continuously distilled off from the top of the column. The azeotropic mixture is condensed, and the phases are separated by a decanter adjusted to a liquid temperature of 10 ° C., the aqueous phase is continuously withdrawn at 70 g / h outside the system, the methacrolein phase is withdrawn at 360 g / h, and The rain phase was refluxed at a reflux ratio of 1.3 to the top of the Oldershaw-type continuous distillation column, and the remainder was taken out of the system as a product.

When the crude methacrolein thus obtained was analyzed, 92.6 wt% of methacrolein, 2.6 wt% of water, 2.1 wt% of acetone, 0.5 wt% of acrolein, and other organic It contained 2.2% by weight of impurities such as acids and aldehydes.

25 parts by weight of pure water was added to 100 parts by weight of the crude methacrolein, and a batch extraction operation using a separating funnel was performed three times while maintaining the liquid temperature at 5 ° C. When the obtained product methacrolein was analyzed, it contained 0.35% by weight of acetone and 0.60% by weight of impurities such as other organic acids and aldehydes in addition to water.

Example 2 The methacrolein phase extracted from the decanter obtained in the same manner as in Example 1 was subjected to a continuous extraction operation using a glass-type stirring type continuous extraction column. The extraction tower has an inner diameter of 36 mm, a height of 800 mm, and two stages.
0, having a sedimentation section at the top and bottom of the tower, a stirrer inside the tower, and a brine trace outside the tower for cooling. In the extraction operation, while stirring the inside of the extraction tower, the methacrolein-absorbed liquid was supplied at 500 g / h from the light liquid feed port provided in the settling section at the bottom of the tower, and purified from the heavy liquid feed port provided in the settling section at the top of the tower. 400 water
g / h were continuously supplied, and the reaction was continuously performed while maintaining the liquid temperature in the column at 5 ° C. About 475 g / h of the methacrolein phase from the top of the column and about 425 g of the aqueous phase from the bottom of the column.
g / h. When the obtained product methacrolein was analyzed, it contained, in addition to water, 0.08% by weight of acetone and 0.11% by weight of other impurities such as organic acids and aldehydes.

[0026]

According to the present invention, isobutylene and / or
Alternatively, the reaction product gas obtained by subjecting tertiary butyl alcohol to gas-phase catalytic oxidation in the presence of molecular oxygen can be used as a source of a gas containing a small amount of impurities such as various organic acids, aldehydes, and ketones by-produced in the gas-phase catalytic oxidation reaction. You can get rain.

[Brief description of the drawings]

FIG. 1 is an example of an embodiment according to the present invention.

[Explanation of symbols]

1, 3, 5, 8, 9, 10, 12, 13, 14, 15:
Line 2: Methacrolein recovery tower 4: Reboiler 6: Heat exchanger 7: Decanter 11: Extraction tower

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C07B 61/00 300 C07B 61/00 300

Claims (1)

[Claims] 1. A gas phase catalytic oxidation of isobutylene and / or tertiary butyl alcohol in the presence of molecular oxygen,
Water or an organic acid aqueous solution as an absorbent is brought into contact with a methacrolein-containing gas obtained by condensing and separating water and a high-boiling substance from the obtained reaction product gas, and the resulting methacrolein-absorbed solution is subjected to distillation by distillation and a distillate. The distillate is separated into a methacrolein phase and an aqueous phase to recover methacrolein, and the methacrolein is phase-separated. A method for recovering methacrolein, comprising bringing methacrolein into contact with water and separating water again.