JPS632951A - Production of methyl methacrylate - Google Patents

Abstract

PURPOSE:To obtain the titled substance inexpensively and simply, by reacting propionic acid with methylal in a gaseous phase by the use of a calcined solid phosphate catalyst and bringing a formed mixture to a silica catalyst containing an alkali metal of group I of the periodic table immediately. CONSTITUTION:Propionic acid is reacted with methylal in a gaseous phase by the use of a solid phosphate catalyst calcined at high temperature of 500-1,000 deg.C and a formed gas containing formaldehyde, methanol and methyl propionate is immediately brought into contact with an alkali metal of Group I of the periodic table to give the titled substance. The solid phosphate catalyst, for example, is prepared by a method wherein a solution obtained by diluting 85% phosphoric acid sold on the market in water is sprayed upon a carrier (e.g. silica gel of alumina) and preferably previously calcining the carrier at <=300 deg.C before high-temperature calcination is carried out. The catalyst of the second stage is preferably that obtained by supporting an alkali metallic compound on a porous amorphous silica.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides methyl methacrylate (industrial application field), which is industrially useful as a raw material for methacrylic resin, from propionic acid and methylal.
The present invention relates to a method for producing MMA (hereinafter referred to as MMA).

(Prior art) Industrial methods for producing MMA include a method for producing MMA from hydrocyanic acid and acetone via acetone cyanohydrin;
Alternatively, there is a method of producing MMA through air oxidation of isobutylene or t-butanol to methacrolein and methacrylic acid.

As another production method, a method for producing methacrylic acid and MMA using an aldol condensation reaction of propionic acid or propionic acid ester and formaldehyde has been proposed.

For example, IJSP3247248. USP3840
587. In JP-A-61-15737, a solid base catalyst having an alkali metal supported on silica gel was used.

CH, CH2C0OH+ CH20→CH.

CH2=C-C0OH+ H2O(1)CH,CH2
C00CH3+ CH20→CH.

Methacrylic acid or MMA is obtained from propionic acid or methyl propionate by the reaction CH2=C-COOCH3+ H2O (2).

(Problems to be Solved by the Invention) The acetone cyanohydrin method has the problem of generating a large amount of by-product ammonium sulfate, and the method of air oxidation via methacrolein and methacrylic acid has a low yield.

Separation from by-products is difficult. In addition, both methods have concerns about the supply of raw materials.

There are two routes for producing MMA using the aldol condensation reaction: formula (1) and formula (2); route (1) is preferable because propionic acid is easily available industrially; Requires methacrylic acid esterification step. Further, in formula (2), esterification must be performed in advance. That is, both types require an esterification step.

Furthermore, in both equations (1) and (2), since water is produced as a by-product in the aldol condensation reaction, unreacted formaldehyde is recovered as an aqueous solution. Further, the raw material itself of formaldehyde is industrially available as a 37-55% aqueous solution.

As a monomer, formaldehyde is a gas.

Because it is highly polymerizable, it must be kept at high temperatures.

Further, in an aqueous solution, formaldehyde monomer cannot be easily removed from the aqueous solution because it associates with water to form methylene glycol.

Furthermore, it is not preferable to subject the aqueous solution to the reaction because the presence of a large amount of water accelerates the deactivation of the catalyst and also causes hydrolysis of methyl propionate and MMA.

A practical method is to use formal.

The method using formal, ie, methylal in most cases, does not have the above-mentioned drawbacks because methylal is easily synthesized from a normal aqueous formaldehyde solution and methanol and can be separated from water. For example, 1IsP 411858B
, ll5P 4447641 and GB2001647
Now let's react as shown below.

CH,C)(2C00CH,+CH2(OCR,)
2H3 →CH,=C-C00CH,+2C1(30H(3)C
Ha CH2C0OH+ CH2(OCH3)2
CH.

→CH2=C-COOCH3+ H3O+ CH30
H(4) In formula (3), water produced by aldol condensation is used for decomposition of methylal, so no water is produced.

Therefore, there is an advantage that hydrolysis of methyl propionate and MMA is suppressed, but it is necessary to esterify the raw material methyl propionate in advance. - direction.

Formula (4) has the advantage that MMA is directly generated from propionic acid, and the amount of by-product methanol is also half that of formula (3).

However, in order to proceed with the reactions of formulas (3) and (4) above, a catalyst with acid sites for decomposing methylal is required, and when propionic acid is used as a raw material, esterification activity and aldol condensation activity are required. A catalyst that possesses three functions is required.

For this reason, the aforementioned USP 4118588 uses a phosphate alumina catalyst, 115P 4447641 uses a synthetic zeolite catalyst, and GB2001647 uses a phosphate-supported alumina catalyst. However, it is difficult to obtain good selectivity to methacrylic acid and MMA using such acidic catalysts, and it is generally necessary to use propionic acid or methyl propionate in a large excess of methyl propionate relative to the stoichiometric amount. Therefore, the single-stream yield is also insufficient. Furthermore, if carbon is deposited on the catalyst, the reaction activity decreases, so it has not been possible to implement it industrially.

(Means for Solving the Problems) The present inventor discovered that MMA could be easily obtained by dividing the reaction of formula (4) into the following two steps and proceeding sequentially, and arrived at the present invention. .

CH3CH2C0OH+ CH2(OCHa)*→
CHa CH2COOCH3+CH2O+CH,OH(
5) CH3CH2COOCH, + CH20CH.

→CH,=CCOOCH3+ H2O (6) Then, unreacted formaldehyde, methanol, and produced water synthesize methylal using the following formula, which is separated from water.

CH2O+ 2CH,OH →CH2(OCRll)2 + 820 (
7) In the present invention, different catalysts are used in formulas (5) and (6). That is, in formula (5), a solid phosphoric acid catalyst is used as the acidic catalyst for decomposing methylal and esterifying propionic acid, and a high selectivity can be obtained.

The reaction product gas of formula (5) is then directly supplied to the second-stage reactor to carry out the reaction of formula (6). The catalyst for this aldol condensation reaction is preferably a basic catalyst, and a silica catalyst supporting an alkali metal is used.

That is, 1 the present invention uses propionic acid and methylal in an amount of 500 to
The reaction is carried out in the gas phase using a solid phosphoric acid catalyst calcined at 1100°C, and the resulting gas containing formaldehyde, methanol and methyl propionate is immediately brought into contact with a silica catalyst containing an alkali metal of Group 1 of the periodic table. This is a characteristic method for producing MMA.

The solid phosphoric acid catalyst suitable for the decomposition of methylal and the esterification reaction of propionic acid is phosphoric acid such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, or polyphosphoric acid (triphosphoric acid, tetraphosphoric acid), or phosphoric acid such as ammonium phosphate, lysium phosphate, etc. This is a catalyst in which phosphate is supported on a carrier and fired.

Supports used for solid phosphoric acid catalysts include silica gel,
Examples include alumina, zirconia, titania, thoria, and composite oxide 1 synthetic zeolites such as silica alumina, silica titania, and silica zirconia, as well as natural diatomaceous earth, acid clay, and zeolites. These carriers can be used alone or in combination of two or more.

As a method for supporting phosphoric acid on a carrier, for example, commercially available 85
% phosphoric acid diluted in water onto a heated carrier, or by immersing the carrier in an aqueous phosphoric acid solution or an aqueous phosphate solution and then drying and baking, or by kneading and molding a powdered carrier and phosphoric acid or phosphate. Common methods include drying and firing things.

The amount of phosphoric acid or phosphate salt supported on the carrier varies depending on the type of carrier and cannot be generally specified.

In terms of P2O5, it is practically appropriate to use 1 to 50 parts by weight, preferably 2 to 30 parts by weight, based on 100 parts by weight of the carrier.

The catalyst has a particle size of at least 60 mesh, and industrially it is preferably formed into a size of about 1 to 5 mm in diameter x 2 to 10 mm.

It is preferable that the catalyst supporting phosphoric acid is dried or pre-calcined at a temperature of 300°C or lower before being subjected to a high-temperature firing treatment of 500°C or higher.

The high-temperature firing process is performed in a Matsufuru furnace, rotary kiln, hot blast furnace, etc., and the firing atmosphere is preferably a gas inert to the catalyst, such as air or nitrogen.

The high temperature firing process is carried out at 500-1100°C. 50
If the firing temperature is lower than 0°C, dimethyl ether will be produced as a significant by-product, and formaldehyde will be more likely to decompose. Furthermore, if the temperature exceeds 1100°C, the activity of the catalyst will be significantly reduced. The firing time varies depending on the amount of P2O supported, the firing temperature, and the type of carrier, but it is usually 0.5 to 50 hours.

The catalyst used for carrying out the aldol condensation reaction of formula (6) is one in which an alkali metal compound of Group 1 of the periodic table is supported on a silica compound.

The silica compound of the carrier may be either crystalline or amorphous, but a porous amorphous compound with a large surface area is preferred.

The catalyst is prepared by impregnating commercially available silica gel with an aqueous alkali salt solution and drying and calcining it.

A method in which an aqueous alkali salt solution is passed through a packed bed of silica gel to cause the silica gel to adsorb and ion-exchange the alkali metal, and then dry and sinter, or an aqueous alkali salt solution is added to colloidal silica to form a gel, which is then dried and sintered. There are several methods to do this, but the method is not limited to these.

The silica gel carrier usually contains alumina, sodium, etc. depending on the manufacturing method, but in order to improve the physical properties of the carrier, substances such as alumina, zirconia, boric acid, etc. that do not deteriorate the catalyst performance can be added.

Alkali metal compounds, hydroxides and Na01
l, KOII, Rb0II, Cs011. NazCOa, Na1lCOa, as carbonates and bicarbonates;
K2CO3, KIICO3, R1)2cOs, Rb
1lCO3, [:52COa, Cs1lCL, as nitrate NaN0a, KNOa, RhN0i, Cs
N0. , Na25O as sulfate and bisulfate, , Na
1lSQ,.

K2SO4, KIISO4, Rb*SO4, Rh1l,
so4. C82SO4, C3llSO4, as halides Nap, NaCL, NaBr, Nal
, KF, KCL, Kl.

RbP, RbCL, Rbl, CsP, C5CL
, Csl, phosphate and hydrogen phosphate as Na*P0
4. Na, 1IPo4. Na1lzP[ln, R
b, PO4, Rb1lPOn, Rb1lzPOn,
There are C83PO4, C8211PO4, Cs112P04, etc. As the alkali metal, those with large atomic weights are more suitable, and Rh and Cs are preferable, but N is preferable because the price is low.
a, K are also used.

The amount of the alkali metal compound supported is 1 to 30 parts, preferably 0.5 to 2 parts of 01O per 100 parts (parts by weight) of the carrier.
It is 0 copies.

The charging methods for both catalysts include (1) a two-stage reactor in which the solid phosphoric acid catalyst and the alkali silica catalyst are separate reactors;
There are two types: 2) a multi-stage reactor in which both catalyst layers are arranged alternately in a single reactor, and (3) a mixed bed reactor in which both catalyst layers are arranged in a mixed manner. (1) has the advantage that both catalysts can be operated at different temperatures, and (2) and (3) can be operated thermally advantageously because the endothermic reaction and exothermic reaction cancel each other out. In the case of the mixed bed (3), in addition to a fixed bed, a fluidized bed or a moving bed can also be used.

Next, the reaction conditions will be described.

On a solid phosphoric acid catalyst that performs decomposition and esterification.

Reaction temperature 150-400°C, preferably 200-400°C
Operated in the °C range. When the temperature is lower than 150°C, the reaction does not proceed sufficiently, and when the temperature is higher than 400°C, the decomposition of formaldehyde and the formation of dimethyl ether become significant, which is not preferable. On alkali-silica catalysts carrying out aldol condensation, one reactor temperature is 250-450°C, preferably 3
Operate in the range of 00-400°C.

The reaction pressure is not particularly limited and can be selected from reduced pressure to increased pressure within a range that keeps one reaction system in the gas phase, but normal pressure is generally preferred.

The molar ratio of raw material propionic acid to methylal is 17
A ratio of 2 to 4/1 is suitable. When the molar ratio is less than 172, recovery of unreacted formaldehyde becomes difficult.

If the molar ratio is 471 or more, the amount of circulating unreacted propionic acid and methyl propionate increases, which is not preferable. In the actual process, the recycled methyl propionate is used again in the reaction. Methyl propionate may be supplied to the decomposition and esterification steps together with newly supplied propionic acid and methylal, or may be combined with the gas generated from the decomposition and esterification steps and supplied to the aldol condensation step.

The contact time with the catalyst is defined by the feed rate of raw material per unit weight of catalyst (WIISV). 0.05 to 50 g/g catalyst/hr for the solid phosphoric acid catalyst in the first stage, preferably 0.2 to 20 g/g, hr, and an alkali catalyst in the second stage.
For silica catalysts, it is 0.1 to 50 g/g, hr, preferably 0.3 to 20 g/g, hr. During long-term operation, coke is deposited on both the first and second stage catalysts, so it is desirable to periodically burn and remove the coke.

(Effects) According to the present invention, the three functions of methylal decomposition, esterification, and aldol condensation required of the catalyst described above are shared between two types of catalysts, and the optimal catalyst for each reaction is selected. Can be done. Moreover, the reaction is divided into two stages,
Since there is no process inserted in the middle and there is a direct connection, there is virtually no difference from a single-stage reaction.

List the advantages of this process compared to conventional methods.

(1) Cheap propionic acid and methylal can be used as raw materials.

(2) Since esterification occurs simultaneously, a separate esterification step is not necessary.

(3) Since the reaction is carried out in two stages and the optimum catalyst can be used, the reaction results and catalyst life are excellent.

(4) Since it is not necessary to use a large excess of propionic acid relative to methylal, the MMA concentration in one reaction product is high and the separation cost is low.

As described above, according to the present invention, the conventional problems are greatly improved, and the industrial significance thereof is great.

(Example) The effects of the present invention will be shown below through Examples.

Of course, it is not limited to these. The definitions of abbreviations and terms used in each example are as follows.

PA: Propionic acid MA: Methacrylic acid FA: Formaldehyde MPΔ: Methyl propionate MA L: Methyral FA skeleton conversion rate - MMΔ selectivity (PA base) - MA selectivity (PΔ base) = MMA + MA selectivity - Selection to MM8 rate ten MA selection rate MMA
Selectivity (FA based) - Example 1 As a solid phosphoric acid catalyst for methylal decomposition and esterification, 10 to 32 mesh of commercially available N-631 manufactured by JGC Chemical was used.
After crushing into pieces and immersing them in a 15% ammonium phosphate aqueous solution overnight, water is distilled off using a rotary evaporator and impregnated. This was dried in an oven at 100°C for 16 hours, and then burned at 1000°C in an air atmosphere for 6 hours. The P2O content at this time was 10%. 20 g of this catalyst was packed into the upper part of a reaction tube made of Pyrex glass and having an inner diameter of 15 mm and a length of 60 cm.

Further, as a catalyst for the aldol condensation reaction, a 15% Cs01 solution was immersed in silica gel In-57 manufactured by Fuji Davison, and then water was distilled off using a tarry evaporator. After drying this at 110℃ for 16 hours, it was heated to 500℃ in a Matsufuru furnace.
A product was prepared by firing for hr. At this time, the Cs supported concentration was 4.3%. This catalyst was placed at the bottom of the reaction tube for 10 minutes.
filled with g.

The upper and lower parts of the reaction tube were controlled by separate heaters, and the temperature was maintained at 290 to 300°C in the upper decomposition esterification layer and 350 to 360°C in the lower aldol condensation reaction layer.

The raw material is a mixture of propionic acid and methylal in a molar ratio of 1:1, and the mixture is pumped from the top of the reaction tube at 30 g/hr using a plunger pump.
It was supplied by The top of the reaction tube is a packed bed of glass spheres with a diameter of 1 to 2 mm, and the raw material is evaporated, preheated, and decomposed by a heater from the outside.

Enters the esterification catalyst layer. The gas generated from this was further led to the aldol condensation catalyst bed through a packed bed of glass bulbs. The reaction product gas from the lower part of the reaction tube was cooled and collected to obtain a reaction product liquid, which was analyzed by gas chromatography to determine the reaction results.

Therefore, the reaction result is of the first order.

PΔ conversion rate: 96.1% PA
Skeleton conversion rate; 32.9 MMA selectivity (PA base); 82. IMA selection rate (PA base)
;8.6 MMA+MΔ selectivity (PΔ base); 90.7 formaldehyde conversion rate; 41. OMMA selection rate (
FA base); 71. IMA selectivity (FA base); 7.4 MMA + MA selectivity (FA base); 7 g, 5 Examples 2 to 5 Experiments were conducted using the same reactor and catalyst as in Example 1, but changing the raw material composition 1 reaction conditions. I did it.

The experimental results are shown in Table 1.

Examples 6 to 9 Various methylal decomposition, esterification catalysts and aldol catalysts were selected, charged in the same manner as in Example 1, and reacted through raw materials with a PA/MAL molar ratio of -1.0. Table 2 shows the reaction results. show.

Claims (1)

[Claims] Propionic acid and methylal are reacted in the gas phase using a solid phosphoric acid catalyst calcined at 500 to 1100°C, and the resulting gas containing formaldehyde, methanol, and methyl propionate is immediately converted to a gas containing an alkali metal of Group 1 of the periodic table. A method for producing methyl methacrylate, which comprises bringing it into contact with a silica catalyst.