JPS58185540A - Production method of unsaturated carboxylic acid ester - Google Patents

Abstract

PURPOSE:In reacting methacrolein with methanol and molecular oxygen in the presence of a catalyst, to obtain the titled substance economically in high yield without causing by-products, by connecting two or more continuous reactors of the perfect blending type in series, whose pH is kept at 6-9. CONSTITUTION:Two or more perfect blending type reactors such as agitated reactor, or gas introduction liquid-jet column type reactor, are connected in series, methacrolein or acrolein is reacted with methanol and molecular oxygen in the presence of a catalyst containing palladium with keeping the pH of reaction solutions of the reactors 1, 2, and 3 at 6-9, to give the desired substance. In the reaction, a molecular oxygen containing gas to be fed the reactors is especially effectively made to flow into the following reactors and discharged from the final stage reactor to the outside of the system in the same way as the reaction solutions. In order to maintain the pH of the reaction solutions of each stage, a carboxylate of an alkali metal or alkaline earth metal as a metal solution, etc. is added to them.

Description

Detailed Description of the Invention The present invention is a method for suppressing the production of by-products when producing methyl methacrylate or methyl acrylate by reacting methacrolein or acrolein with methanol and molecular oxygen in the presence of a catalyst containing Pd. This paper relates to improvements in efficient continuous manufacturing methods.

A new route for producing methacrolein or acrolein all at once using methanol and molecular oxygen (i.e., a process that can be called an oxidative esterification reaction) has recently been in the spotlight as a method for producing industrially useful methyl methacrylate or methyl acrylate. I have been bathed in This method has shorter steps and higher yield than the two-step method of converting aldehyde, which has traditionally been removed, to acid and then to ester.
This is of great significance as a new method for producing industrially useful polymer raw materials.

To carry out such a process, which is carried out by reacting methacrolein or acrolein with molecular oxygen in excess methanol, the presence of a catalyst containing Pd is essential. The reaction is carried out at a temperature of 10°C or less, preferably 30°C or less.
The process proceeds at a sufficient rate even at a low temperature of θ°C, and the selectivity to the methyl ester based on methacrolein or acrolein exceeds θ, but at the same time, methyl formate has a lifetime. This was one drawback. It is estimated that methyl formate is produced by Pd contained in the catalyst and methanol present in the large wrinkles according to the reaction formula shown in equation (1).

2 CHsOH+ Ox −→HCOOCHs+ 2
Hz O (1) The present inventors have found that when attempting to carry out this reaction continuously, if a portion of the reactor is uneven in pH, it will have an unfavorable effect on the sustainability of the catalyst activity. found out. In tubular reactors, it is difficult to maintain sufficient gas-liquid dispersion, especially when implemented on an industrial scale. Furthermore, since the reaction is accompanied by a large amount of heat and requires mass transfer between gas and liquid, it is industrially advantageous to use a complete mixing type reactor and to carry out continuous operation.

However, in this case, in addition to the drawback that the production of methyl formate is significantly increased, it has been found that a single conversion cannot be achieved in a reaction with a methacrolein or acrolein concentration. Further, studies by the present inventors have revealed that the method has the disadvantage that a large amount of basic substance must be used to maintain the pH.

In view of the current situation, the present inventors realized the importance of continuously producing methyl methacrylate or methyl acrylate in a completely mixed reactor, and aimed to produce methyl formate as much as possible. After conducting intensive studies on a method to continuously carry out the highly selective reaction of the methyl ester while suppressing the reaction, we found that it is possible to suppress side reactions by connecting one or more complete mixing reactors in series and allowing the reaction to occur under special conditions. heading,
We have arrived at the present invention.

That is, the present invention provides methacrolein or acrolein with P
In a method for continuously producing methyl methacrylate or methyl acrylate by reacting it with methanol and molecular oxygen in the presence of a catalyst containing d, λ or more complete mixing reactors are connected in series, and each Is the pn of the reaction solution in the reactor 6~? The present invention relates to a method characterized in that the reaction is carried out while maintaining the following conditions.

Furthermore, the molecular oxygen-containing gas supplied to the first stage reactor and the subsequent reactor is passed through a complete mixing reactor connected in series in the same direction as the reaction liquid moves, and flows out of the system from the I & final reactor. It is effective to do so.

In the method of the present invention, the key point is to conduct the reaction by connecting one or more complete mixing type continuous reactors maintained at pH 7:6 to 6 in series, thereby preventing the production of methyl formate for any reason. Although it is not sufficient to conduct a rigorous analysis of whether the more effectively suppressed.

The complete mixing type reactor is multi-staged, and the pu of the reaction liquid is 6 to 6.
It is thought that the regular formation of methyl formate was significantly suppressed by maintaining the temperature at a constant temperature, and this phenomenon is always observed in this reaction if the catalyst contains Pd, regardless of the types of other metals in the system. The present inventors found out.

It is especially effective to flow the molecular oxygen-containing gas supplied to each reactor into the subsequent reactor and then flow it out of the system from the final reactor, as in the reaction method described in Section 2. The meaning of this is that it significantly suppresses the production of methyl formate.

After the molecular oxygen-containing gas supplied to each reactor is subjected to a reaction, a portion or the entire amount is allowed to flow into an adjacent reactor without allowing the entire amount to flow out of the system.

By using it again in the reaction, the amount of gas used can be reduced, which is economical. In this case, the unconsumed oxygen-containing reaction gas moves through the series reactors in the same direction as the reaction liquid (cocurrent flow type) or in the opposite direction (countercurrent type).
is possible. However, the unconsumed oxygen-containing reaction gas obtained by introducing a molecular oxygen-containing gas, such as air, into the final stage reactor flows in the opposite direction to the flow of the reaction liquid, and finally flows out of the first stage reactor. The present inventors have found that in the case of a counter-current type, methyl formate is produced significantly more than in a co-current type. Therefore, in order to carry out the reaction continuously using a multistage complete mixing reactor, a molecular oxygen-containing gas,
For example, a parallel flow type in which unconsumed oxygen-containing reaction gas obtained by introducing air into the @/stage reactor and subsequent reactor is flowed in the same direction as the flow of the reaction liquid, and then flows out of the system from the 1M final stage reactor. This fact was completely unexpected.

The method of flowing molecular oxygen-containing gas in parallel flow will be explained in more detail with reference to the drawings. The reaction solution flows through, for example, three stirred tank reactors /, :, j connected in series, and the inside of each reactor is maintained in a completely mixed state by a stirrer. (Meta)acrolein and methanol are fed from y to the reactor/! After passing through the reactors λ and 3, it is transferred to the reactors λ and 3, and taken out as a reaction solution containing methyl (meth)acrylate via 7.

If necessary! ,9. It is also possible to additionally supply methacrolein from /θ and use it for the reaction. It is preferable to collect the unreacted (meth)acrolein of 7 and apply it to this by cycling.

A basic substance for pH adjustment is supplied to reactors 7.2 and 3 through the /2 and /3 channels. Molecular oxygen-containing gas, such as air, is supplied from /4t to the reactor /, and the reaction gas containing unconsumed oxygen is supplied to the reactors λ and 31' through 15 and /B, and finally exits the system from 20. It will be leaked. Part or all of the reaction gas flowing out of each stage reactor is supplied to the succeeding reactor.

The remainder flows out of the system through 2/, 2λ, and 3.

It is more advantageous and preferable to feed the entire amount to the subsequent reactor in terms of suppressing the production of methyl formate. If necessary, add molecular oxygen to 77, /J', /? Replenish more.

Although air is preferably used for this, each plate effluent reactant gas, e.g.

-3 can also be recycled and used.

According to the final method, when the methyl ester is continuously produced in a complete mixing reactor, the production of methyl formate and other brain organisms 1, such as β-methoxy form of raw material aldehyde, dimethyl acetal, etc., is suppressed, and methanol and raw material It has become clear that in addition to significantly reducing the loss of aldehyde, there are significant advantages particularly in terms of reaction speed. On the other hand, if the process is carried out in a single stage of a complete mixing type reactor, and if highly concentrated methanol or acrolein is to be reacted and a high conversion rate is aimed at, the degree per reactor will be extremely low. It has become clear that if this is done, a high conversion rate can be achieved without reducing the reaction rate, and a smaller reactor can be used. Furthermore, it has also been discovered that in such a case, the number of methanol recycling stations is significantly reduced, and the cost required for the methanol recovery process can be significantly reduced.

It has been unexpectedly discovered that another advantage of this process is that the use of basic substances fed to each stage of the reactor for pH maintenance can be significantly reduced.

This has great economic significance.

To carry out the process, a stirred tank reactor or a liquid column gas-injected base reactor is used as the complete mixing reactor. In either case, it is important to maintain a complete mixing state in the reactor in order to suppress side reactions. In the seed reactor, the reaction solution and catalyst are vigorously stirred with a stirrer to uniformly suspend the catalyst, and a molecular oxygen-containing gas is introduced into this through appropriate blowing, and the stirrer breaks up the air bubbles finely. The reaction is carried out by ensuring sufficient contact between the liquids. On the other hand, in a liquid column gas-blown reactor, the catalyst is uniformly suspended in the reactor by the upward movement of bubbles blown from the bottom of the column through a gas distribution plate. In order to prevent coalescence of bubbles and obtain a good fluidization state, it is preferable to set the gas blowing strength to /~-)/θden- based on the empty column. Gas dispersion function 1 to redisperse air bubbles
It is also effective to use a packing with a number. In order to achieve sufficient mixing in each of the columns, it is preferable to install a liquid circulation tank in the west column or outside the 5 columns, through which the reaction liquid and catalyst are circulated to improve complete mixing in the column. It is effective for If there is a west tower within the tower, it doesn't matter if either the ascending tower or the west tower becomes the downcomer.

In the present invention, λ or more of the above-mentioned complete mixing type reactors are connected in series to carry out the reaction in a continuous manner. After the reaction liquid is extracted so that the liquid level is constant and the catalyst is separated by a liquid-solid separator, only the reaction liquid is sent to the succeeding reactor.The separated catalyst is transferred to the reactor along with a part of the reaction liquid. Return to. There is no particular limitation on the number of reactors, but 1.2
It is advantageous from the viewpoint of reaction performance and economy to select from the range of .

The molecular oxygen used as the oxidizing agent is pure oxygen gas or its diluted form with an inert gas such as nitrogen, preferably air. It is sufficient that the oxygen supplied to each stage is at least 7.2 times the stoichiometric amount necessary for the reaction, preferably at least 7.2 times the stoichiometric amount, and is 1 mole or 0.2 mole per mole of methacrolein or acrolein. The amount is 3 moles or more, and the upper limit is selected within a range in which the oxygen concentration of the outflow gas from each stage does not exceed the explosive range (♂capacity).

To maintain the pH of the reaction solution in each stage at 6 to 9, more preferably 7 to 1, one or more of alkali metal and alkaline earth metal carboxylates, carbonates, bicarbonates, and hydroxides can be used. Select two or more types (meta).

It is supplied to each stage as a Nord bath solution or a standing water solution. The alkali metals are selected from Li, Na, Ni, etc., and the alkaline earth metals are selected from Mg, Cm, Sr, Ba, etc. As the carboxylic acid, saturated fatty acids such as formic acid, acetic acid, and propionic acid, or aromatic carboxylic acids such as benzoic acid can be used, but lower fatty acids are generally preferred. Further, the carboxylic acid salt may contain C containing water of crystallization.

The reaction temperature in the present invention can be carried out at a high temperature of 100°C or higher, but preferably 30°C or higher. θ°C.

The reaction temperature for each stage is selected within this temperature range.

It is not necessary that the temperature be the same.

A wide range of reaction pressures can be used, from reduced pressure to increased pressure.
It is usually carried out at a pressure of / - θV-.

Although the reaction pressure of each stage can be selected from this pressure range, the reaction pressure of the first stage is usually set higher than the reaction pressure of the second stage. There is an operational advantage in that a compressor is not required when feeding the reaction gas to a subsequent reactor.

The reaction time (residence time: i.e., the flow rate of the liquid Wkl retentate in the reactor) is not particularly limited and cannot be unambiguously determined as it varies depending on the set conditions, but it is usually 1θ minute as the total reaction time. ~It's time.

Methacrolein or acrolein used in the present invention is industrially generally prepared by oxidizing isobutylene and/or t-butanol or propylene, but it may be obtained by any other method. As methanol, it is preferred to use substantially dianhydrous methanol, especially pure methanol. As raw materials to be supplied to the @/stage reactor, methacrolein or acrolein and methanol may be supplied separately or as a mixture in advance.

The concentration of methacrolein or acrolein in methanol is more than / blood grave! θ electricity amount, preferably j~3! Heavy 1
I am an overseas student. The reaction liquid in the @/stage reactor is sequentially sent to subsequent reactors connected in series and subjected to reaction, but methacrolein or acrolein may be supplied to the subsequent reactors as necessary.

In this case, it is operationally advantageous to recover unreacted methacrolein or acrolein from the final stage reactor and use it as recycled methacrolein or acrolein. A solvent is not particularly necessary for this reaction system.

An inert charge medium such as a saturated hydrocarbon may also be present.

The catalyst used in the present invention is palladium alone or in combination with other foreign elements such as lead, mercury, thallium, bismuth, tellurium, nickel, chromium, copper, cadmium, indium, tantalum, and copper.

Bent lead, zirconium, hafnium, tungsten.

It may contain iron, silver, rhenium, antimony, tin, metal, ruthenium, iridium, platinum, gold, titanium, aluminum, boron, silicon, and the like. It may further contain an alkali metal compound or an alkaline earth metal compound. Preferably, < is a catalyst containing palladium and at least one element selected from lead, mercury, thallium, or bismuth, and if necessary, at least one member selected from an alkali metal compound or an alkaline earth metal compound. is preferable. These catalyst components may be silica or alumina alone.

It may be supported on a carrier such as titanium, carbonate, hydroxide, or activated carbon. The amount of these catalysts to be used is not particularly limited, but it is preferable to use them in the reaction solution lt in the order of θ, θg to θ,j.

In the present invention, since the catalyst is used in a liquid phase suspension state, it is sufficient that it is in the form of a powder finer than a 3θ mesh.
A particle size of 00 to 330 mesh is preferred.

The present invention will be described in detail below. Example 中忤 indicates a person who has been given a gift, unless otherwise specified.

Example -/ Inner +Vj: y-owam, internal volume/, two 2 t stainless steel branched stirred reactors were connected in series to carry out the reaction.

The reactor is equipped with a reflux condenser, a liquid feeder, a liquid outlet El, and a gas inlet, and is stirred by an electromagnetic rotary stirrer. Heating is provided by the jacket.

Each reactor was charged with 0.3 kg of a catalyst consisting of γ-alumina (Mizusawa Kagaku Neobead) supported with palladium 2.3'4-lead s, o s, and magnesium θ-aluminum.
2.3 'lk methacrolein/methanol θ, ♂6L
/br, NaOH/ NaOH solution θ, θ6 t/
br, and the air is supplied at a temperature of ♂θU and a pressure of 3 Lg/cjG. The reaction was conducted while venting through a stainless steel sintered plate at a rate of NL/hr. After the catalyst suspension reaction solution is liquid-solid separated and the catalyst is returned to the reactor, only one reaction solution is subsequently transferred to a Cm two-stage reactor with NmOH/MeOH solution O.
Introduced with 1θj t/br, temperature lθ℃, co, I
Vent the effluent gas from the 7th stage reactor into the 2nd stage reactor at a pressure of K/dO.

The reaction was performed by adding air/, jNt/ah to the history. i) H of the reaction solution is 7. in both @/stage and @2 stage reactor. θ～7
The amount of NaOH was controlled to keep it at ,j.

When the reaction solution was analyzed, the conversion of methacrolein was 4t, 71G, and the yield of methyl methacrylate was 71.
2%<IA selectivity tt, t arrogant), #acid/chirka θ,
3 moles of θtaco/mol of MMA were produced.

Comparative Example-/The reaction was carried out in a stirred tank reactor/stage similar to Example-/. As raw materials 22.3% methacrolein/methanol 0.27 L/at, NaOH/MeO) 10.03
When the reaction was carried out in the same manner as in Example 7 except that air was used at 20 Nt/-h as the supplied gas, the methacrolein conversion rate was 74. j 1 , methyl methacrylate yield A@,/s (selectivity/1./s), methyl formate was produced at θ, 317 mol 1 mol MM.

Comparative Example - pH of the reaction solution in each stage was set to 9.0-2. The reaction was carried out in the same manner as in Example-/, except that j was changed. Methacrolein conversion rate: 9/3, Methyl methacrylate yield: 411.9
．． After 3 hours (selectivity 7t/long), 1 mol of male MMA of methyl formate was produced at θ, 3.

Comparative Example-3 The reaction was carried out in the same manner as in Example-/, except that the pH of the reaction solution in each stage was set to s, s-t, and o. Methacrolein conversion book 6/, θ, methyl methacrylate yield 4t93*
(selection *//, sound).

Example-1 Inner diameter θ■, internal volume 2. The reaction was carried out by connecting two JT stainless steel liquid column gas injection type reactors (inside the towers, !metsch gold plates were installed horizontally at I!'' intervals) in series.The reactors were refluxing. condenser.

It is equipped with a liquid feeder, a liquid outlet, and one circulation pipe outside the tower, and heating is performed by a jacket.

Alumina (product name: Sumitomo Activated Aluminum T) was charged with a catalyst supporting palladium, IG, bismuthco, lithinmuco, and 0- to each reactor at a rate of 0.3 hours. Sorry, methacrolein/methanol &amp;
/ j/hr, NaOH amount CHsOl (liquid θ,
/l/hr, the catalyst is suspended by passing air through a stainless steel sintered plate at a ratio of jN/Alk at a temperature of lθ°C and a pressure of jKe'ajG. The reaction was carried out while circulating. After the catalyst suspension reaction liquid was separated into liquid and solid and the catalyst was returned to the reactor, only the reaction liquid was successively introduced into the second stage reactor together with the NaOH/MeOH liquid θ, /L/br, and the temperature was maintained at /θ. °C, 2. ♂K
The effluent gas of the II/stage reactor was vented to the second stage reactor under a pressure of v'cd G, and the reaction was carried out by adding 3 NA/- of air. The pH of the reaction solution is II! / stage and second stage reaction solution are both 7. θ~7. ! The amount of NaOH was controlled to maintain the same amount. Analysis of the first stage reaction solution revealed that the methacrolein conversion rate lθ was 3, and the yield of methyl methacrylate was 7.
/, ¥ reference (selectivity r?, 9), methyl formate is θ, θ
r/1 mole/mol of MMA was produced.

Example-3 Palladium 2. !
-, thallium 2. ! Using a catalyst supporting Calcilamco, 33.3% metaglolein/methanol as the raw material, air 7 Nt/w-1 as the gas supplied per stage, 3 Nt/m of nitrogen, and 2 Nt/m of air as the fM2 additional gas.
, nitrogen ￥ Nt/h and the pH of the reaction solution in each stage to 7. ,
When the reaction was carried out in the same manner as in Example 2 except that j-f and θ were changed, the methacrolein conversion rate was 76, and the methyl methacrylate yield was 7.2-(M refraction rate r7.J excellent). , 0.076 mol/mol MMA of methyl formate was produced.

Example-y As raw material/2. The reaction was carried out in the same manner as in Example -/, except that male sac acrolein and methanol were used.

The conversion rate of acrolein was / j, r *, the yield of methyl acrylate was 4!7 J-, j% (selectivity / 7. θ), and the methyl formate produced θ, // j7/7-l MMA. .

[Brief explanation of the drawing]

The drawings are schematic diagrams illustrating the invention in detail. 8, 2.3...Reactor, y-...Methacrolein/methanol supply 0.7...Reaction liquid outflow [], /8/to-
/3...L basic substance supply port, /L...Molecular oxygen is supplied 1°/7. /l /9...additional oxygen supply 1],
θ... Reactive gas outlet patent applicant Asahi Kasei Corporation

Claims (2)

[Claims] (1) In the method of producing methyl methacrylate or methyl acrylate by reacting methacrolein or acrolein with methanol and molecular oxygen in the presence of a catalyst containing palladium, two to seven complete mixing reactors are used. A method for continuously producing methyl methacrylate or methyl acrylate, which comprises connecting the reactors in series and carrying out the reaction while maintaining the pH of the reaction solution in each reactor at g to 9. (2) A molecular oxygen-containing gas is caused to flow in the same direction as the movement of the reaction liquid through two or more complete mixing reactors arranged in series. Claim 1: A method for continuous production of konkisen, in which it is discharged from the final reactor to the outside of the system.