JPS63198648A - Treating method of distillation residue of methacrylic acid - Google Patents

Abstract

PURPOSE:To readily and efficiently recover methacrylic acid as methyl methacrylate, by adding specific amounts of methanol and sulfuric acid to a distillation residue containing methacrylic acid as a main component and carrying out steam distillation while esterifying the mixture. CONSTITUTION:Isobutylene, tert, butanol, methacrolein, etc., is catalytically oxidized by molecular O2 in the presence of steam and methacrylic acid water solution obtained by cooling the oxidation product is subjected to extraction of methacrylic acid by a solvent, recovery of the solvent and removal of light boiling point component and 1-5 times mole of methanol based on methacrylic acid and sulfuric acid in an amount of >=2wt.% based on a distillation residue obtained by distillation separation of the methacrylic acid is added to the distillation residue and the mixture is subjected to steam distillation while carry out esterification reaction and the remaining methacrylic acid is distilled off and recovered as methyl methacrylate. The above-mentioned method is excellent as a continuous treating method of the distillation residue which is carried out in a large scale.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating methacrylic acid distillation bottom liquid. More specifically, the present invention relates to a treatment method for effectively recovering methacrylic acid as methyl methacrylate from a still residue containing methacrylic acid as a main component.

[Prior art and problems to be solved by the invention] Isobutylene, tertiary butanol, methacrolein or isobutyraldehyde is catalytically oxidized with molecular oxygen in the presence of water vapor in one or two steps. The methacrylic acid obtained can be made into a highly pure product by conventional purification methods such as extraction and distillation. However, in order to finally obtain methacrylic acid, it is necessary to remove low-boiling components such as aldehydes and ketones from an aqueous methacrylic acid solution, recover the solvent after extraction, separate acids with lower boiling points than methacrylic acid, and It is exposed to heating conditions many times, such as during the separation process of boiling point components. Therefore, each process is carried out in the presence of conventionally known polymerization stoppers such as phenothiazine, benzophenothiazine, hydroquinone, hydroquinone monomethyl ether, methylene blue, and molecular oxygen, but the polymerization of methacrylic acid, etc. is completely inhibited. It is not possible to do so, and polymers such as methacrylic acid and polymerization inhibitors are accumulated with each step, and the amount in the final step is not negligible. Therefore, in addition to the high-boiling point impurities generated by the reaction, a considerable amount of polymers and polymerization inhibitors are present in the bottom liquid after rectifying methacrylic acid, so the distillation rate of methacrylic acid is If the (distillation amount/supply amount) is too high, the purity of methacrylic acid will decrease and the viscosity of the bottom liquid will increase, which will deteriorate the thermal efficiency of the reboiler and further promote the polymerization of methacrylic acid, etc. becomes. Therefore, the distillation rate of methacrylic acid is inevitably kept below a certain range, and a considerable amount of methacrylic acid is discharged together with high-boiling components including polymers as bottom liquid from the tank. Therefore, if the residual liquid from the can is disposed of or incinerated, it will lead to a loss of methacrylic acid, which will lead to a worsening of the unit consumption and an increase in costs, so some method must be used to recover the methacrylic acid.

In the production process of methyl methacrylate using the acetone cyanohydrin method, various methods have been proposed as methods for recovering methacrylic acid remaining in the final still residue.

That is, the remaining liquid in the can is cooled to crystallize methacrylic acid,
A method for obtaining high-purity methacrylic acid by centrifugation (Japanese Patent Publication No. 42-1530), in which the remaining liquid in the tank is treated with methanol and water or a solution containing methanol and water, the polymer is precipitated and separated, and the remaining liquid is converted into an ester. Method of recycling to chemical process (Special Publication No. 47-35886)
, and a method of steam distilling the bottom liquid in the presence of a non-volatile inorganic acid (Japanese Patent Publication No. 35726/1983).

However, in the case of methacrylic acid produced by the oxidation reaction of hydrocarbons, etc., which is the object of the present invention, the impurities produced are markedly different from those of conventional methods, and as a result, the composition of the final can residue is also inevitably very different. come. Therefore, in the above crystallization method, many impurities precipitate together with methacrylic acid, and even if it could be carried out, the process would be complicated, such as requiring recrystallization, and would not be economical. Further, the method of adding water and methanol to precipitate and separate the polymer cannot be applied to the bottom liquid of the present invention because the polymer of methacrylic acid is soluble in methanol and cannot be separated from other impurities.

Furthermore, simple steam distillation in the presence of an inorganic acid cannot be expected to distill methacrylic acid because methacrylic acid is the main component, unlike the aceto/cyanhydrin method in which methacrylic acid is esterified. As described above, the methods that have been effectively carried out in the past can hardly be adopted for recovery of methacrylic acid through an oxidation reaction process.

On the other hand, as a general treatment method for the bottom liquid under the oxidation reaction process, methacrylic acid is recovered by reevaporation of the bottom liquid in an evaporator or the like, or methacrylic acid is recovered by organic solvent extraction. has been considered. However, the former has problems such as poor recovery rate and operational problems due to polymerization of methacrylic acid, while the latter produces a large amount of floating rings due to the extraction solvent, causing emulsification and flooding of the extraction tower. cannot be said to be an effective method.

[Means to solve the problem]

The present inventors focused on the above-mentioned problems, and as a result of intensive study on a method for effectively recovering methacrylic acid from the polymer after distillation and separation of methacrylic acid and from the bottom liquid containing high-boiling components, the present invention was developed. The present invention has been completed based on the discovery that a method of recovering methyl methacrylate from the remaining liquid containing specific impurities is superior.

That is, the present invention provides isobutylene, tertiary butanol,
Catalytic oxidation of methacrolein or isobutyraldehyde with a gas containing molecular oxygen in the presence of water vapor,
The methacrylic acid aqueous solution obtained by cooling this oxidation product is extracted from the methacrylic acid with a solvent, the solvent is recovered, and the low-boiling point components are removed.The methacrylic acid is distilled and separated from the crude methacrylic acid, which remains in the bottom liquid. To recover methacrylic acid, the molar ratio of methanol to methacrylic acid is 1 to 5 times the molar ratio, the amount of sulfuric acid is at least 2 parts by weight of the bottom liquid, and the bottom liquid is steam distilled while esterifying the bottom liquid.
An object of the present invention is to provide a method for treating methacrylic acid distillation bottom liquid, which is characterized by distillation and recovery as methyl methacrylate.

[Detailed description of the invention]

The bottom liquid targeted by the method of the present invention is obtained by catalytically oxidizing isobutylene, tertiary butanol, methacrolein, or isobutyraldehyde with a gas containing molecular oxygen in the presence of water vapor, and cooling the oxidized product. The methacrylic acid aqueous solution obtained by this process is the bottom liquid obtained by distilling and separating methacrylic acid from crude methacrylic acid, which has been subjected to conventional extraction of methacrylic acid with a solvent, recovery of the solvent, removal of light boiling point components, etc. 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 point substance, and 1 to 10 parts by weight of a polymer. The high-boiling components in the bottom liquid are acids such as maleic acid, citraconic acid, benzoic acid, toluic acid, and trimellitic acid, aldehydes such as benzaldehyde and tolualdehyde, and phenothiazine, hydroquinone, and hydroquinone added as polymerization inhibitors. Monomethyl ether, etc., and polymers include methacrylic acid and methacrolein.

Although the method of the present invention can also be applied to the batch processing of small amounts of can residual liquid, it is generally possible to treat can residual liquid discharged in the methacrylic acid manufacturing process that is carried out on a large scale industrially.
This method is particularly suitable for continuous processing.

In the resulting reaction product, methacrylic acid and high-boiling point impurities such as maleic acid, citraconic acid, benzoic acid, toluic acid, and trimellitic acid are unreacted in the respective ester pools due to the esterification reaction with methanol. Acids, methanol, and reaction product water coexist. Since the acid esterification reaction is an equilibrium reaction, it is impossible to esterify most of the active ingredient methacrylic acid into methyl methacrylate in a simple esterification reaction, but steam distillation during the above esterification reaction Only the methyl methacrylate produced by this process is distilled and recovered together with methanol and water. Therefore, since almost no methyl methacrylate remains in the system, the equilibrium reaction proceeds preferentially toward the target product, improving the recovery rate of methacrylic acid as methyl methacrylate. At this time, some of the other acids, which are originally high-boiling components, are esterified, but their vapor pressure is lower than that of methyl methacrylate, and only a small amount is distilled out under the same conditions. Therefore, the equilibrium state within the reaction system hardly changes and methanol is effectively consumed for the desired reaction. By performing steam distillation while esterifying in this way, methacrylic acid can be recovered as methyl methacrylate without distilling out most of the impurity components that were present in the bottom liquid and were difficult to separate from methacrylic acid. can. Furthermore, since methyl methacrylate is distilled out of the system at the same time as esterification, the residence time in the reaction system where sulfuric acid is present is short, and polymerization loss can be minimized.

The methanol used in the present invention may be used in a molar amount of 1 to 5 times, preferably 1.2 to 2 times, the amount of methacrylic acid in the bottom liquid, although it depends on the composition of the bottom liquid. High esterification conversions can be achieved at low molar ratios. In this esterification reaction, if the amount of methanol is less than 1 mole, a high esterification conversion rate cannot be expected, and if it exceeds 5 moles, the recovered methyl methacrylate will be diluted and will not be used. Easy to attract profits.

The amount of sulfuric acid used in the present invention must be at least 2 parts by weight based on the remaining liquid in the can. If the amount of sulfuric acid used is less than 2% by weight, the amount of high-boiling components accumulated in the sulfuric acid layer increases, the sulfuric acid concentration decreases, the esterification reaction rate slows down, and solids may precipitate in the sulfuric acid layer. be.

In continuous industrial operations, a predetermined amount of sulfuric acid catalyst is continuously supplied and, after remaining in the reaction system for 30 minutes to 2 hours, is continuously extracted together with non-volatile impurities as waste sulfuric acid.

In the present invention, a considerable amount of water or steam necessary for steam distillation is supplied as reaction product water; It is appropriately selected depending on the composition and the like.

Usually, a ratio of 20 to 50 weight ratio is adopted for the methacrylic acid in the can residual liquid.

Although the method of the present invention can be carried out under normal pressure, reduced pressure, or increased pressure, it is usually carried out at normal pressure to slightly increased pressure at the boiling point temperature of the reaction system.

The steam distillate contains, in addition to methyl methacrylate and water, an excess amount of methanol and a small amount of methacrylic acid, but almost no substances that are difficult to separate from methyl methacrylate are distilled out.

This distillate is fed to a suitable point in the process of producing methyl methacrylate from methacrylic acid, for example in a process using isobutylene as a raw material, to the product stream from an esterification column packed with a strongly acidic cation exchange resin as a catalyst. By doing so, methyl methacrylate, methanol and water can be separated and purified.

〔Effect of the invention〕

According to the treatment method of the present invention, methacrylic acid, which has conventionally been discarded or incinerated together with high-boiling components and polymers as can residual liquid, can be easily and efficiently recovered as methyl methacrylate.

〔Example〕

The present invention will be specifically explained below with reference to Examples. The bottom liquid used in the examples is a bottom liquid obtained by precision distillation of crude methacrylic acid obtained by catalytic oxidation reaction of isobutylene, and its composition is as follows.

Weight ratio Methacrylic acid 94.34 Benzoic acid 0.83 Para-toluic acid 0.34 Other volatile components 0.20 Polymerization inhibitor 2.98 Non-volatile components 1.31 Example 1 1. A 6 ktz/hr raw material mixed with 3 times the molar amount of methanol and sulfuric acid with a weight of 2 times the amount of the remaining liquid from the tank were supplied to the reaction tank, and at the same time 1 portion of water was added.
500g/hr was supplied. Reactive distillation was carried out at a reaction temperature of 106.50, during which the composition of the distillate was monitored, and when the reactive distillation reached a stable state, the distillate was sampled over a period of 1 hour, and the results are shown in Table 1.

Table 1 Table 1 shows that 93 tons of methacrylic acid in the can residual liquid was recovered as methyl methacrylate substantially free of harmful impurities.

Example 2 Raw material supply port at the bottom of the reaction tank, middle side wall (filling liquid volume 401
! 1001 equipped with a catalyst extraction port at the top and a distillation column at the top.
1 for the methacrylic acid in the bottom liquid of the reactor.
．． A raw material prepared by mixing 4 times the molar amount of methanol and sulfuric acid in a 4 weight range with respect to the remaining liquid in the tank was continuously supplied at a rate of 61.2 kg/hr, and at the same time, the temperature was 115' while supplying 1.0 kg Ar of steam. Reactive distillation was carried out with O. When the sulfuric acid catalyst overflows and is continuously extracted from the outlet on the side wall in the middle of the reaction tank and the system becomes stable, the distillate is heated for 1 hour and 30 minutes.
The results are shown in Table 2.

The distillate in this experiment was separated into two layers.

Claims (1)

[Claims] (1) A methacrylic acid aqueous solution obtained by catalytically oxidizing isobutylene, tertiary butanol, methacrolein, or isobutyraldehyde with a gas containing molecular oxygen in the presence of water vapor and cooling the oxidation product is used as a solvent. When recovering the methacrylic acid remaining in the bottom liquid from the distillation of crude methacrylic acid after extraction of methacrylic acid, recovery of the solvent, and removal of light boiling point components, the molar molar ratio of methanol to methacrylic acid is 1~
A distillation still bottom liquid of methacrylic acid, characterized in that the bottom liquid is steam distilled while esterifying the bottom liquid with a sulfuric acid amount of 5 times the molar amount and 2% by weight or more of the bottom liquid, and is distilled and recovered as methyl methacrylate. processing method.