JPH022874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing methyl methacrylate via acetone cyanohydrin.

Methyl methacrylate (MMA) is produced by a method in which acetone cyanohydrin (ACH), obtained by reacting hydrocyanic acid and acetone, is reacted with methanol in the presence of concentrated sulfuric acid. However, this method involves the production of large amounts of waste sulfuric acid and acidic ammonium sulfate, and the raw hydrocyanic acid is ultimately recovered in the form of ammonium sulfate. Moreover, the amount is more than 2 tons of ammonium sulfate per 1 ton of MMA, which is a drawback of the ACH method for producing MMA. The present invention solves the above-mentioned drawbacks, and relates to a method for producing MMA using the ACH method, which recovers hydrocyanic acid in its original form and does not involve the by-product of ammonium sulfate.
Acetone cyanohydrin obtained by reacting hydrocyanic acid and acetone is hydrated to produce α-hydroxyisobutyric acid amide, which is then reacted with carbon monoxide and methanol to produce methyl α-hydroxyisobutyrate and formamide. Then, methyl α-hydroxyisobutyrate and formamide are separated, methyl α-hydroxyisobutyrate is dehydrated to form methyl methacrylate, and formamide is dehydrated to form hydrocyanic acid, which is then reacted with acetone again for recycling. .

In the present invention, by the reaction of hydrocyanic acid and acetone
ACH can be produced by generally known means. That is, using small amounts of alkali and amines as catalysts, hydrocyanic acid and acetone are mixed in a liquid phase under normal pressure, and the reaction is carried out while stirring and cooling.
The reaction proceeds quantitatively and ACH is obtained in high yield.

The subsequent hydration reaction of ACH proceeds in the presence of a strong acid such as sulfuric acid, but in order to economically separate the acid, it is reacted with water and a solvent using a metal catalyst or an alkali catalyst.

As the metal catalyst, copper, copper oxide, nickel, manganese oxide, etc. can generally be used, and manganese oxide is particularly preferred. In addition, the coexistence of a solvent is also effective in this reaction, and hydrophilic solvents such as acetone and methanol are suitable, with acetone being particularly preferred. The reaction may be carried out in a gas phase or a liquid phase, preferably in a liquid phase. The reaction type may be either a batch type or a flow type, but industrially it is appropriate to use a flow reactor having a fixed catalyst bed. The reaction pressure may be normal pressure or increased pressure, and the reaction temperature is 20℃~200℃.
It can be carried out in the range of ℃. In addition, α-
It is also possible to obtain hydroxyisobutyric acid amide.

The α-hydroxyisobutyric acid amide thus obtained is reacted with methanol and carbon monoxide to form methyl α-hydroxyisobutyrate. Various gases containing carbon monoxide can be used as carbon monoxide, but the higher the purity, the faster and more efficient the reaction. As methanol, ordinary industrial methanol is sufficient. The reaction conditions are such that the pressure is 10 to 500 Kg/cm 2 , preferably 30 to 500 Kg/cm ² as the partial pressure of carbon monoxide.
400Kg/ ^cm2 , temperature 50~400℃, preferably 100~
The temperature is 300℃. When the temperature is lower than 50°C, the reaction rate is slow, and when the reaction temperature is higher than 400°C, side reactions such as decomposition and polymerization of carboxylic acid amide, carboxylic acid ester, and formamide are caused. The molar ratio of α-hydroxyisobutyric acid amide and methanol is 1:1 ~
The ratio is 1:30, preferably 1:3 to 1:20.

The catalyst used in this process is an amidine or a tertiary amine, and by using an amidine or a tertiary amine in combination with a metal carbonyl, a more favorable effect can be obtained than when using an amidine or a tertiary amine alone. .

Specifically, the amidine includes 1,3-diazabicyclo-[5,4,0]-undecene (DBU), 1,5-diazabicyclo-[4,3,
0]-noone (DBN), and the tertiary amines include N-methylpyrrolidine, N-ethylpyrrolidine, 4,4'-trimethylene, bis(N-methylpiperidine), N-methylpyrrolidine, N-ethyl Pyrrolidine, dipiperidinomethane, dipiperidinoethane, dipiperidinopropane, N,N'-dimethylpiperazine, N,N'-diethylpiperazine, trimethylamine, triethylamine, tripropylamine, tributylamine, tetramethylethylenediamine , tetramethyltetramethylenediamine, dimethylethylamine, triethylenediamine, N,N-dimethylcyclohexylamine, etc. are used.

In addition, metal carbonyls include chromium carbonyl Cr(CO) ₆ and molybdenum carbonyl Mo
(CO) ₆ , tungsten carbonyl W (CO) ₆ , manganese carbonyl Mn ₂ (CO) ₁₀ , rhenium carbonyl Re ₂ (CO) ₁₀ , iron carbonyl Fe (CO) ₅ , Fe ₂
(CO) ₉ , Fe ₃ (CO) ₁₂ , Ruthenium carbonyl Ru ₃
(CO) ₁₂ , Osmium carbonyl Os ₃ (CO) ₁₂ , Cobalt carbonyl Co ₂ (CO) ₈ , Rhodium carbonyl
Rh ₄ (CO) ₁₂ , Iridium carbonyl Ir ₄ (CO) ₁₂ ,
Nickel carbonyl Ni(CO) ₄ etc. are used.

In addition, in the present invention, instead of metal carbonyl, corresponding metal oxides, hydroxides, sulfates, nitrates, carbonates, formates, acetates, and oxalic acids that can form metal carbonyl under the reaction conditions are used. It is also possible to use salts, naphthenic acid or acetylacetone salts, chelate compounds of polyaminocarboxylic acids, halides, and the like.

The amount of catalyst used here is in the range of 0.001 to 1 mole per mole of carboxylic acid amide when amidine or tertiary amine is used.
It is not economically advisable to add more than necessary, and if the amount added is too small, a sufficient reaction rate cannot be obtained, so the preferable amount is 0.003 to 0.5 mol.

Further, the amount of metal carbonyl to be used can be selected in the range of 0.0001 to 0.5 mol, preferably in the range of 0.001 to 0.2 mol, per 1 mol of carboxylic acid amide. It is also effective to use a solvent during the reaction, and acetone, ethyl ether, methyl formate, dimethylformamide, etc. can be used as the solvent.

The reaction of the above α-hydroxyisobutyric acid amide with methanol and carbon monoxide is shown by the following formula.

Note that even if only isobutyric acid amide and methanol are reacted without using carbon monoxide,
As shown in No. 141216 and Japanese Patent Application Laid-open No. 144524, methyl α-hydroxyisobutyrate is produced by the following formula.

In formula (2), a completely different catalyst from the method of the present invention is used, and ammonia is produced as a by-product. Since this ammonia easily reacts with methyl α-hydroxyisobutyrate to form α-hydroxyisobutyric acid amide even without a catalyst, it is necessary to separate ammonia during the reaction.

On the other hand, in the method of the present invention, ammonia is not generated and formamide is produced according to the formula (1).
This formamide is stable even during the reaction and can be easily separated by distilling the reaction product liquid.

Methyl α-hydroxyisobutyrate is separated from formamide by vacuum distillation and then dehydrated to produce methyl methacrylate (MMA). Although sulfuric acid can be used as a dehydrating agent, it is not preferred because separation is disadvantageous. Dehydration can also be carried out using acetic anhydride, calcium oxide, etc.; however, in the liquid phase, the reaction is carried out in the presence of a catalyst while water or MMA is distilled off, whereas in the gas phase, the dehydration reaction is carried out by passing over a solid catalyst. The latter is particularly preferred.
A solid acid catalyst represented by silica alumina is generally used in a gas phase fixed bed reaction. Furthermore, the coexistence of steam or inert gas is also effective in suppressing the precipitation of carbon on the catalyst. In gas phase fixed bed, at normal pressure
A temperature of 200 to 500°C is appropriate.

Formamide separated from methyl α-hydroxyisobutyrate by distillation is dehydrated to form hydrocyanic acid.
This dehydration reaction is carried out by passing formamide over a solid catalyst at a high temperature of 200 to 800°C. It is a gas phase reaction, and either a fixed bed or a fluidized bed format may be used.

As the catalyst, an alumina-based catalyst, an iron-silica-based catalyst, a manganese-copper-based catalyst, etc. are suitably used. The yield of the reaction is good, and hydrocyanic acid and water are obtained almost quantitatively. Hydrocyanic acid is separated from water, sent to the acetone cyanohydrin synthesis process, and recycled.

According to the present invention, the raw material hydrocyanic acid can be recovered and recycled through formamide without producing ammonia as a by-product in the MMA manufacturing process, so it has extremely great industrial significance.

EXAMPLE The process of the present invention was carried out based on FIG. ACH851g/ that is supplied from the ACH process via line 1
hr, 580 g/hr of acetone from the recovery line 2, and 540 g/hr of water from the line 3 are mixed and supplied via line 4 to the hydration reactor 5 filled with a fixed bed manganese oxide catalyst 1. The reaction temperature was 60° C., and pressure was applied so that the reaction solution remained in a liquid phase. The 1970 g/hr of hydration reaction product extracted through line 6 contained 47.6 wt% α-hydroxyisobutyric acid amide, 29.5 wt% acetone, and water.
It contained 18.3wt%. This reaction product is supplied to a light boiling separation column 7, and acetone and water are recovered from the top of the column and recycled to the raw material system, and crude α-hydroxyisobutyric acid amide is extracted from the bottom of the column through a line 8. This bottom liquid contains 1600 g/hr of methanol from line 9 and unreacted α-hydroxyisobutyric acid amide from line 10.
980g/hr and catalyst Cr(CO) ₆ 40g/hr, N
- Methylpyrodine is fed into a perfusion type reactor 12 via line 11 with 80 g/hr and brought into contact with carbon monoxide fed from line 13 at a pressure of 200 Kg/cm ² G and a temperature of 180°C. CO is absorbed at a rate of 260 g/hr, yielding 3988 g/hr of esterification reaction product. This contains 25.9 wt% of methyl α-hydroxyisobutyrate, 9.3 wt% of formamide, 24.5 wt% of unreacted α-hydroxyisobutyric acid amide, and 32.9 wt% of methanol.

The reaction product liquid passes through a line 14 and is passed through a film evaporator 15 to separate the catalyst and a small amount of high boiling substances. A portion of this separated liquid is purged, but most of it is returned to the raw material system through line 10. On the other hand, the evaporated fraction is led to the methanol recovery column 17 via line 16, where unreacted methanol and by-product light-boiling fractions are separated and recovered from the top of the column and returned to the raw material system via lines 18 and 19. . The mixture of formamide, methyl α-hydroxyisobutyrate and unreacted α-hydroxyisobutyric acid amide recovered from the bottom of the column is represented by line 20.
through the α-hydroxyisobutyric acid amide separation column 21
α-Hydroxyisobutyric acid amide 980
g/hr is extracted from line 22 and recycled to the raw material system. On the other hand, the top distillate is sent to a formamide separation column 24 via a line 23, where methyl α-hydroxyisobutyrate is obtained from the top of the column and formamide is obtained from the bottom of the column. 1030 g/hr of the top distillate is sent via line 25 to a methyl α-hydroxyisobutyrate dehydration reactor 26, where it is dehydrated in the gas phase at 500°C over a fixed bed of silica-alumina catalyst. The dehydration reaction product (consisting of methyl methacrylate and water) passes through line 27, and water is separated in a decanter 28, and crude methyl methacrylate, 850 g/hr, is obtained as an upper layer through line 29.
Sent to refining process. Water is drawn off from the line 30. On the other hand, formamide obtained from the bottom of 24
360 g/hr is introduced through a line 31 to a formamide dehydration reactor 32, where a dehydration reaction is carried out in the gas phase at 550° C. in the presence of an iron oxide-alumina catalyst. The reaction product is fed to a hydrocyanic acid collection column 34 via line 33. 212 g/hr of HCN is recovered from the top of the column via line 35, and water is withdrawn from the bottom via line 3. 64 g/hr of fresh HCN is collected from line 37 and supplied to acetone cyanohydrin synthesis reactor 40 along with 593 g/hr of acetone from line 9 and catalyst (caustic soda) through line 38, and acetone cyanohydrin (ACH ) 851 g/hr are obtained which is recycled via line 41 as starting material.

[Brief explanation of drawings]

The drawings are process diagrams of the present invention.

Claims (1)

[Claims] 1 Acetone cyanohydrin obtained by reacting hydrocyanic acid and acetone is hydrated to produce α-hydroxyisobutyric acid amide, and this is reacted with carbon monoxide and methanol to produce methyl α-hydroxyisobutyrate and formamide. Separate methyl α-hydroxyisobutyrate and formamide, methyl α-hydroxyisobutyrate is dehydrated to form methyl methacrylate, formamide is dehydrated to form hydrocyanic acid,
This is a method for producing methyl methacrylate, which is characterized by reacting with acetone and recycling it.