JPH03264551A - Recovery of methyl methacrylate - Google Patents

Abstract

PURPOSE:To efficiently recover the objective compound from the bottom residue mentioned below using simple operations by bringing the bottom residue obtained in purification process of an esterification product into contact with a zeolite catalyst in gas phase in production of the subject compound using acetone cyanhydrin method. CONSTITUTION:In production of methyl methacrylate by reacting acetone cyanhydrin with sulfuric acid and methanol, the bottom residue obtained in purification of crude methyl methacrylate produced in esterification process is brought into contact with a zeolite catalyst preferably having 2-20 SiO2/Al2O3 molar ratio and -5.6-+4.8 pKa acid strength in gas phase after distillation of the bottom residue or without distillation, thus efficiently recovering the objective compound from a high boiling composition mainly composed of methyl 2-hydroxyisobutyrate and methyl 3-methoxyisobutyrate in the above-mentioned bottom residue in a high yield in a short time and stably for long hours without requirement of a large quantity of catalyst or solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for recovering methyl methacrylate from the bottom liquid of an esterified product in a method for producing methyl methacrylate using the acetone cyanohydrin method.

(Prior art) When methyl methacrylate is synthesized by the acetone cyanohydrin method, methyl methacrylate, 2
The main components are high-boiling substances such as methyl -hydroxyisobutyrate, methyl 2-methoxyisobutyrate, methyl 3-methoxyisobutyrate, and methacrylic acid, and small amounts of polymers, polymerization inhibitors, etc. are included.

A method for recovering active ingredients such as methyl methacrylate and methacrylic acid from these high-boiling substances is steam distillation in the presence of sulfuric acid (Japanese Patent Publication No. 4635726).
, a method of dehydrating methyl 2-hydroxyisobutyrate with sulfuric acid (JP-A-60-184047), a method of converting a high-boiling substance into methyl methacrylate or methacrylic acid with an aqueous sulfuric acid solution containing acidic ammonium sulfate (JP-A-52-12)
127), and methyl 2-hydroxyisobutyrate,
A method of dehydrating or demethanolizing methyl 3-methoxyisobutyrate using an alkali metal methoxide (JP-A-63188-648, JP-A-66-188-650, JP-A-63-188-649, JP-A-63-
190855), etc. are known.

(Problem to be Solved by the Invention) However, in the method of distillation in the presence of sulfuric acid, the coexisting methyl 2-hydroxyisobutyrate and methyl 3-methoxyisobutyrate also azeotrope with water, so methyl 2-hydroxyisobutyrate is added to the purification system. and methyl 3-methoxyisobutyrate accumulate, and a separate operation is required to extract them, resulting in operational complexity. Furthermore, when sulfuric acid is used, methyl 2-hydroxyisobutyrate is generally easily decomposed, resulting in low yields of methyl methacrylate and methacrylic acid, and furthermore, there are disadvantages such as difficulty in removing decomposition products.
In order to solve these problems and increase the yield, there are problems in that a large amount of sulfuric acid is required as well as complicated operations to strictly control the reaction temperature, contact time, sulfuric acid molar ratio, etc.

3 when using a sulfuric acid aqueous solution containing acidic ammonium sulfate
-Since the conversion rate of methyl methoxyisoacetate is lower than that of methyl 2-hydroxyisobutyrate, there is a problem that it accumulates in the system.

In addition, when alkali metal methoxide is used, there are problems in that the water contained in the system or the water generated by the reaction tends to deactivate the catalyst, making it difficult to regenerate the catalyst.
There was a problem in that alkali hydroxide (metal), which was a deactivated catalyst, precipitated in the system and promoted the production of methacrylic acid. Furthermore, if the reaction is carried out continuously, the residence time is relatively long and the reaction is in the liquid phase, so there is a risk of polymerization.
It is difficult to avoid adding a polymerization inhibitor, which has the disadvantage that the inhibitor tends to accumulate.

Therefore, the present invention solves the above-mentioned problems, and in a method for producing methyl methacrylate by the acetone cyanohydrin method, it is possible to easily produce methyl methacrylate from methyl 2-hydroxyisobutyrate and methyl 3-methoxyisoacetate in the still boiling matter of the esterification product. The purpose is to efficiently recover methyl methacrylate through operations.

(Means for Solving the Problems) As a result of careful consideration of the dehydration reaction of methyl 2-hydroxyisobutyrate and the demethanolation reaction of methyl 3-methoxyisobutyrate, the present inventors found that the dehydration reaction proceeds under an acid catalyst. In contrast, the demethanolation reaction proceeds under acid and base catalysts, and was found to be an irreversible reaction under acid catalysts, but an equilibrium reaction under base catalysts. Based on this new fact, we conducted intensive research on various catalysts and reaction systems, and found that methyl methacrylate can be produced with high selectivity and yield by carrying out dehydration and demethanolation reactions using zeolite in a gas phase catalytic reaction. It was discovered that the catalyst can be recovered and that the catalyst can be easily regenerated, leading to the completion of the present invention.

That is, the object of the present invention is to produce methyl methacrylate by reacting acetone cyanohydrin with sulfuric acid and methanol. This can be achieved by performing a distillation operation and then performing a contact reaction with a zeolite catalyst in the gas phase to recover methyl methacrylate.

The present invention will be explained in detail below.

Generally, methyl methacrylate is produced using acetone cyanohydrin by mixing acetone cyanohydrin with sulfuric acid or fuming sulfuric acid, reacting at high temperature to form methacrylic acid amide sulfate, and then esterifying this reaction product with water and methanol. , to obtain crude methyl methacrylate.

Crude methyl methacrylate contains methyl ether, methyl formate, acetone, methyl acetate, methanol, water, etc. as low boiling point impurities, and methyl 2-hydroxyisoacetate, methyl 3-methoxyisobutyrate, methacrylic acid, etc. as high boiling point impurities. They are separated by distillation to obtain purified methyl methacrylate.

The bottom liquid obtained in this purification process contains high-boiling substances such as methyl methacrylate, methyl 2-hydroxyisobutyrate, methyl 3-methoxyisobutyrate, and methacrylic acid as main components, as well as small amounts of polymers and polymerization inhibitors. Contains. The proportions of these high-boiling substances in the bottom liquid are, for example, 10 to 40% by weight of methyl methacrylate, 10 to 35% by weight of methyl 2-hydroxyisobutyrate, 1 to 5% by weight of methyl 2-methoxyisobutyrate, and 3-methoxyisobutyric acid. Mention may be made of 2 to 15% by weight of methyl.

In the present invention, this can residual liquid may be used as it is,
Alternatively, methyl methacrylate and methacrylic acid may be removed by distillation or other means to obtain a liquid containing methyl 2-hydroxyisoacetate and methyl 3-methoxyisobutyrate as main components, but the latter is preferred.

The zeolite used in the present invention refers to one having a specific crystal structure among crystalline aluminosilicates, and the A type (Sing/^t; t 2o 3 = 1.8-1.9
), X type (Si(h/A 1 go+ = 2 to 4.5
), Y type (SiO□/Al 203 = 4 to 6), offretite type (SiOz/8i 2 to 3 = 5.6 to 10)
, mordenite type (SiOz/Al zO+ = 1
0-20), and ZSM-11 (SiO□/8I!,
In terms of catalyst performance, it is desirable that the molar ratio of 5iOz/A 1□03 is in the range of 2 to 20, particularly in the range of 2.2 to 6. desirable. In this way, SiO□/l□03 molar pressure is 2~
Although it is not clear why a range of 20 is desirable, the acid strength effective for the gas phase catalytic reaction of the present invention (introduction of acid sites and basic sites) depends on the type of exchange element, conditions for exchange, etc.
It is thought that this is because the granting of

Various elements can be selected as the exchange elements of the zeolite used in the present invention for the purpose of adjusting the activity of the catalyst, the acid strength, and the pore diameter.

The acid strength of the zeolite catalyst used in the present invention is in the pKa range of -5.6 to +4.8, preferably in the range of more than -5.6 to +3.3, particularly preferably in the range of -3, It ranges from over 0 to +3.3.

The range of these acid strengths can be easily determined by using indicators such as benzalacetophenone, benzeneazodiphenylamine, and dicinnamalacetone.

Setting the zeolite catalyst to the above acid strength range is a preferred embodiment of the present invention, and although the reason for this is not clear, it is thought that it is probably related to the steric distribution of acid sites and base sites. It will be done. The advantage of using this kind of zeolite is that it has a strong acid strength (like when using conventional sulfuric acid (approximately 100%)).
It is necessary to strictly control the contact time and molar ratio of sulfuric acid (pKa = 11.0), otherwise methyl 2-hydroxyisobutyrate will decompose and disappear. By using the zeolite catalyst, the contact time can be easily selected within an appropriate range, so decomposition and disappearance of methyl 2-hydroxyisobutyrate can be reduced, and the operation can be simplified.

Such zeolites can be easily prepared by combining commonly used ion exchange methods and calcination conditions. For example, after immersing general zeolite (commercially available or synthesized in the sodium form) in an aqueous solution containing exchanged cations adjusted to pn 3.5 to 12, the temperature of this aqueous solution is set between room temperature and 100°C. 30 minutes to 2
After ion exchange at least once in 4 hours and removing attached water,
It can be obtained by firing at 200 to 500°C. Moreover, zeolite substituted with hydrogen can also be prepared by calcining zeolite exchanged with ammonium ions at 250 to 350°C.

Since reactions using zeolite catalysts are generally diffusion-controlled, it is desirable to increase the pore diameter in order to reduce diffusion resistance.
High valence elements and high valence elements with small ionic radius are introduced. However, since elements that increase the pore size tend to increase the acid strength of the catalyst, it is necessary to select the exchange element appropriately. Such exchange elements are preferably hydrogen, alkali metals, alkaline earth metals, and rare earth metals, with hydrogen, sodium, potassium, magnesium, calcium, and the like being particularly preferably used. These exchange elements can be introduced singly or in combination of two or more.

The present invention mainly dehydrates methyl 2-hydroxyisobutyrate in the bottom liquid by contacting it with the zeolite catalyst in the gas phase either as it is or after performing a distillation operation, thereby dehydrating methyl 2-hydroxyisobutyrate and This is done by demethanolizing methyl butyrate and recovering it as methyl methacrylate. The reaction temperature ranges from 180 to 450°C,
The temperature is preferably in the range of 220 to 350°C, and the reaction pressure is not particularly limited, but is usually carried out under normal pressure to slightly increased pressure. It is desirable that the high-boiling gas such as bottom liquid introduced during the reaction be diluted with a gas such as air, nitrogen, argon, helium, etc., but it may be introduced into the catalyst as it is without dilution.

An advantage obtained by carrying out the dehydration and demethanolization reaction of the present invention by gas phase contact reaction using a zeolite catalyst is that when conventional sulfuric acid or an aqueous sulfuric acid solution containing acidic ammonium sulfate is used, the reaction temperature cannot be raised. Compared to the difficulty, it is possible to adjust the reaction temperature to a desired suitable range according to the progress of the reaction, and it is easy to operate.

Furthermore, the recovery method of the present invention is characterized in that it can cope with considerable fluctuations in the concentrations of methyl 2-hydroxyisoacetate and methyl 3-methoxyisobutyrate, which is a great advantage when carried out industrially.

Furthermore, the catalytic activity of the zeolite catalyst of the present invention can be almost completely recovered by calcining it while circulating air at a temperature that does not destroy the crystal structure of the zeolite, preferably at a temperature that does not exceed 700°C. So it can be easily played and used.

(Effects of the Invention) As described above, the present invention uses the liquid obtained as a boiling product in the can when purifying crude methyl methacrylate from the esterification step in the acetone cyanohydrin method, either as it is or after performing a distillation operation. , 1 2 This method uses zeolite as a catalyst when recovering methyl methacrylate by simultaneously dehydrating and demethanolizing methyl 2-hydroxyisobutyrate and methyl 3-methoxyisobutyrate in the high-boiling substances in the gas phase, large amount of catalyst,
A method for recovering methyl methacrylate efficiently in a short time and stably over a long period of time, as there is no need to use a solvent, the contact time is easy to control, and the reaction temperature can be arbitrarily selected within an appropriate range. can be provided advantageously.

This method is also useful because it can improve the yield.

(Example) The present invention will be specifically described below using Examples.

However, the present invention is not limited thereto.

The conversion rate, selectivity, and yield were calculated using the following formula.

2-MH4B conversion rate Conversion rate - distillation 2-MH4B/introduction 2
-MHiB) X 100310O3-conversion rate-(1-
Distillate 3-MM1B/Introduction 3-MMlB)
B-distillate 2M) 1iB)/118+(introduction 3-M old B-
Distillate 3-M cylinder B)/132)
B-distillate 2MHiB)/118+(introduction 3-MMlB-
Distillate 3-MMlB)/132)
X100M static yield = ((distilled MAA-introduced MAA)/8
6)/(Introduction 2-M old B/118+Introduction 3-MM1B/
132) X 100 where 2-M old B, 3-MM
1B and MMMAA each represent methyl 2-hydroxyisoacetate, methyl 3-methoxyisobutyrate, methyl methacrylate, and methacrylic acid (the same applies hereinafter).

Example 1.2 Commercially available (manufactured by Tosoh ■) 4-8 mesh Na-χ type zeolite catalyst (SiO□/AlzO: += 2.37
, acid strength -3.0≦+1.5) was filled into a 23 mm inner diameter quartz tube fixed in an electric furnace, and the catalyst layer was maintained at the reaction temperature shown in Table 1 under normal pressure. Next 2-
Mixture gas of methyl hydroxyisobutyrate and methyl 3-methoxyisobutyrate 3 4 (50150 wt/wt) 0.35 g/m
in is passed through the catalyst layer together with nitrogen at 1.2j2/min. After stabilizing for 1 hour from the start of passage, sampling was performed for 10 minutes. The obtained fraction was quantified by gas chromatography. The results are shown in Table 1.

Further, using the same catalyst, the reactivity over time was measured after 1.4.10 hours when the reaction was carried out at a reaction temperature of 270°C, and the results are shown in Table 2.

Example 3 A commercially available (manufactured by Tosoh) 4-8 mesh Na-Y type zeolite catalyst (SiOz/8 I!, He03 = 5.60) was added to a 1N aqueous potassium chloride solution (pH 5.2) at 80°C. After repeating the ion-exchange operation for 3 hours in the zeolite 10 times, the water adhering to the zeolite was removed under reduced pressure, dried at 110°C for 2 hours, and further calcined at 200°C for 2 hours to prepare the zeolite catalyst (acid strength +1.5 ≦+3.3) was prepared. 80 mj2 of the zeolite catalyst thus obtained was filled into a 23 mm inner diameter quartz tube fixed in an electric furnace as in Example 1, and the catalyst layer was maintained at the reaction temperature shown in Table 3 under normal pressure. Next, the raw material was passed through and sampled under the same conditions as in Example 1, and the obtained fraction was quantified. The results are shown in Table 3.

Examples 4 to 14 The activity and selectivity of the various catalysts shown in Table 1 were investigated in the same manner as in Example 1 at a reaction temperature of 270°C or 330°C. The results obtained are shown in Table 4.

Examples 15 to 17 Na-X type which gave good results among Examples 4 to 14,
Recovery of methyl methacrylate was attempted by changing the concentration ratio of methyl 2-hydroxyisobutyrate and methyl 3-methoxyisobutyrate for H-Na-Y type and K-Na-Y type. The results obtained are shown in Table 5.

Example 18 The reaction in Example 11 was further continued, and Ni-Na-Y type zeolite, whose reactivity was halved, was air-calcined at 600-650°C for 3 hours (SV, 300 h-', linear velocity -27 cm/m).
1n) and reproduced. Example 1 was repeated using this regenerated catalyst.
The reaction was carried out in the same manner as in 1, and after 1 hour 5 6 from the start of passage of the raw material gas, it was sampled and quantified. On the other hand, the reaction was continued until the reactivity was reduced by half. Furthermore, the above regeneration reaction operation studied under the same conditions as in Example 1 at a reaction temperature of 330°C was repeated to test the effect of catalyst regeneration on catalyst activity, and the results are shown in Table 6.

Example 19 In a method for producing methyl methacrylate by reacting acetone cyanohydrin with sulfuric acid and methanol, 25% by weight of methyl methacrylate, 2-hydroxyisomer, obtained during purification of crude methyl methacrylate from the esterification step The can residual liquid consisting of 20% by weight of methyl butyrate, 8% by weight of methyl 3-methoxyisobutyrate, 40% by weight of methacrylic acid, and 7% by weight of other substances such as polymers and polymerization inhibitors, and the H-Na- of Example 9. The reaction was carried out in the same manner as in Example 1 except that a Y-type zeolite catalyst was used at a reaction temperature of 280°C, and the fraction was quantified. The results obtained are shown in Table 7.

Example 20 40% by weight of methyl methacrylate was obtained by removing a portion of the polymer, inhibitor and methacrylic acid from the bottom liquid of the can by distillation.
Methyl 2-hydroxyisoacetate 33% by weight, methyl 3-methoxyisobutyrate 12% by weight, methacrylic acid 15% by weight
The reaction was carried out in the same manner as in Example 20, except that a high boiling material having the composition was used, and the fraction was quantified.

The results obtained are shown in Table 7.

Table 1 160 0.0 220 3.4 270 9B, 0 360 100.0 4], 5 93.2 500 100.0 o, o, o,.

O,434,6 87,379,5 100,031,2 90,90,4 100,00,0 7 B Table 2 1 93.0 43.3 79.5 5.4 92.4 40.6 84.5 5.3 Table 3 9.0 46.1 95.0 99.6 0.4 10.1 69.6 98.8 32.8 69.8 86.0 52.6 23.5 18.7 4.1 1.6 ■ 1 0 Table 6 71.3 94.8 70.2 95.1 72.0 95.3 86.1 85.8 86.0 Table 7 9 0 92.1 96.9 63.5 76.5

Claims (1)

[Claims] 1. In a method for producing methyl methacrylate by reacting acetone cyanohydrin with sulfuric acid and methanol, the bottom liquid obtained when refining crude methyl methacrylate from the esterification step is used as it is or A method for recovering methyl methacrylate, which comprises carrying out a catalytic reaction with a zeolite catalyst in the gas phase after a distillation operation. 2. The recovery method according to claim 1, which uses a zeolite catalyst having a SiO_2/Al_2O_3 molar ratio in the range of 2 to 20. 3. The recovery method according to claim 1, which uses a zeolite catalyst having an acid strength in the range of -5.6 to +4.8 in pKa value.