JP2003267928A - Method for continuously producing carboxylic acid ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously producing an unsaturated carboxylic acid ester stably for a long period by performing reaction of an unsaturated aldehyde with an alcohol in the presence of oxygen in a high unsaturated aldehyde conversion rate and a high unsaturated carboxylic acid ester selectivity. <P>SOLUTION: This method for continuously producing the unsaturated carboxylic acid ester stably for a long period by performing the reaction of the unsaturated aldehyde with the alcohol in the presence of oxygen is characterized by controlling an oxygen partial pressure distribution in the reactor within a range of 4-1/4 fold of an average oxygen partial pressure. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for continuously producing a carboxylic acid ester by reacting an aldehyde with an alcohol in the presence of oxygen, which is not desirable due to a decrease in aldehyde conversion rate or a reaction between alcohols. Provided is a continuous production method of a carboxylic acid ester which simultaneously achieves a high aldehyde conversion rate and a high desired carboxylic acid ester selectivity without causing a significant by-product of the carboxylic acid ester.

[0002]

2. Description of the Related Art As a method for producing industrially useful methyl methacrylate or methyl acrylate, methacrolein or acrolein is directly reacted with methanol.
An oxidative esterification method for producing methyl methacrylate or methyl acrylate has been proposed. In this production method, methacrolein or acrolein is reacted with molecular oxygen in methanol. An example using a catalyst containing palladium and lead, bismuth, thallium, and mercury is disclosed in JP-B-57-35856-35861. And again
An example of using an intermetallic compound of palladium and these metals as a catalyst is disclosed in JP-B-62-7902.

A catalyst using palladium and bismuth is disclosed in JP-A-9-216850 and others.
1-220367 exemplifies a catalyst using ruthenium and lead. The reaction using these catalysts is alcohol,
The slurry liquid phase of the aldehyde and the catalyst is carried out by a method of blowing a gas containing oxygen, and it is common to use air or a gas obtained by diluting air with nitrogen or the like. The reaction for synthesizing methyl methacrylate from was carried out by blowing air diluted with nitrogen into the catalyst slurry using a bubble column reactor.

The oxygen supplied to the reaction is dissolved and diffused from the bubbles in the reaction slurry. Therefore, in order to efficiently dissolve and supply the oxygen, for example, in a bubble column reactor, the gas linear velocity in the reactor is set to Measures such as making it smaller, that is, making the residence time of bubbles in the reactor longer and generating fine bubbles, are taken. However, it has been found that when the gas linear velocity is set too low, methyl formate produced as a by-product in the reaction between methanol increases and the methacrolein conversion rate decreases.

On the contrary, when the linear velocity of gas is increased, extra diluting nitrogen is required, and as the outlet gas amount increases, it is necessary to cool the organic substances that are vaporized together and return them to the reactor. There is also a risk that the catalyst slurry will not flow or the flow of the catalyst slurry will become too violent, resulting in deterioration of the catalyst into powder. Therefore, it is difficult to increase the gas linear velocity unnecessarily when considering the cost and long-term operation. Therefore, there has been a demand for solving the problem of what linear gas velocity is acceptable.

[0006]

The present invention has been made in view of the above problems, and provides a method for stably maintaining a high aldehyde conversion rate and a high carboxylic acid ester selectivity. Is.

[0007]

Therefore, the present inventors have
When the behavior of oxygen in the reactor was examined in detail,
By homogenizing the oxygen partial pressure distribution in the reactor within a certain range, it is possible to reduce the above-mentioned inconvenient by-products such as methyl formate, and also to secure a high aldehyde conversion rate and a high desired carboxylic acid ester selectivity. Was found, and the beginning of the present invention was obtained. The strategy of increasing the gas linear velocity is one of the measures to make the oxygen partial pressure distribution uniform, and in addition, blowing a high partial pressure of oxygen and stirring the inside of the reactor at the same time,
The inventors have found that the same excellent reaction results can be obtained by taking measures such as dispersing and blowing a small amount of gas in some places, and have completed the present invention.

That is, the present invention is: In a method for continuously producing a carboxylic acid ester by reacting an aldehyde and an alcohol with a catalyst in the presence of oxygen, the oxygen partial pressure distribution in the reactor is set to a range of 4 to 1/4 times the average oxygen partial pressure. The present invention relates to a continuous production method of a carboxylic acid ester characterized by controlling. 2. The reaction produces oxygen partial pressures at the reactor inlet and the reactor outlet,
The present invention relates to the continuous production method of a carboxylic acid ester according to the above 1, which is operated in a range of 4 to 1/4 times the average oxygen partial pressure.

3. The reaction relates to the continuous production method of a carboxylic acid ester according to the above 1, wherein a part of the reactor outlet gas is recycled to the reactor. 4. 4. The carboxylic acid according to any one of 1 to 3 above, wherein the catalyst is a catalyst containing palladium and / or ruthenium and X (X represents at least one metal selected from lead, bismuth, mercury and thallium). It relates to a continuous production method of an ester. 5. The present invention relates to the continuous production method of a carboxylic acid ester according to the above 4, wherein the aldehyde is acrolein or methacrolein and the alcohol is methanol.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
Examples of the aldehyde used in the present invention include:
Aliphatic saturated aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, and glyoxal; unsaturated aliphatic aldehydes such as acrolein, methacrolein, and crotonaldehyde; aromatic aldehydes such as benzaldehyde, tolylaldehyde, benzylaldehyde, and phthalaldehyde;
And derivatives of these aldehydes.
These aldehydes can be used alone or as a mixture of two or more kinds.

Particularly, acrolein and methacrolein are preferably used. Examples of the alcohol used in the present invention include aliphatic saturated alcohols such as methanol, ethanol, isopropanol and octanol;
Diols such as ethylene glycol and butanediol;
Aliphatic unsaturated alcohols such as allyl alcohol and methallyl alcohol; aromatic alcohols such as benzyl alcohol. Particularly, lower alcohols such as methyl alcohol and ethyl alcohol are preferred because of quick reaction. These alcohols can be used alone or as a mixture of two or more kinds.

There is no particular limitation on the ratio of aldehyde to alcohol used in the reaction of the present invention.
It can be carried out in a wide range such as 10 to 1/1000 in terms of the molar ratio of alcohol, but it is generally preferable that the amount of aldehyde is small, and it is preferable to set it in the range of 1/2 to 1/50. The oxygen used in the present invention may be in the form of molecular oxygen, that is, oxygen gas itself or a mixed gas obtained by diluting oxygen gas with a reaction-inert diluent such as nitrogen or carbon dioxide, and air is used. You can also The amount of oxygen present in the reaction system is sufficient if it is at least the stoichiometric amount necessary for the reaction, preferably at least 1.2 times the stoichiometric amount.

The total pressure of the reaction can be carried out in any wide pressure range from reduced pressure to increased pressure, but usually 1 to 20 k.
It is carried out at a pressure of g / cm ² . The oxygen concentration was measured at room temperature after the sampled gas was once sufficiently cooled with a condenser or the like to condense organic vapor. The oxygen concentration meter may be of any type, and a commercially available diffusion electrode type oxygen concentration meter is preferably exemplified.

The partial pressure of oxygen supplied to the reaction system was a value obtained by multiplying the total pressure by the oxygen concentration according to the above measuring method. The oxygen partial pressure on the outlet side of the reactor is preferably controlled to be 0.8 kg / cm ² or less, more preferably 0.4 kg / cm ² or less, and further preferably 0.2 kg / cm ^2.
It is not more than cm ² . On the other hand, it is advisable to set the total pressure so that the oxygen concentration of the reactor outflow gas does not exceed the explosion range (8%). The reaction of the present invention can be carried out by any conventionally known method such as a gas phase reaction, a liquid phase reaction and a perfusion reaction. For example, when it is carried out in the liquid phase, it may be carried out in any reactor type such as a bubble column reactor, a draft tube type reactor and a stirred tank reactor. The reactor type may be any conventionally known type such as a fixed bed type, a fluidized bed type, and a stirring tank type.

The teaching of the present invention is the preferred range of oxygen partial pressure distribution in the reactor and its control method. The oxygen partial pressure in the reactor is within a range of 4 times at the maximum and 1/4 times at the minimum with respect to the average oxygen partial pressure expressed by the geometric mean of the oxygen partial pressures at the inlet and the outlet of the reactor. It is indispensable that the content is within the range, and the narrower the range, the better. When the oxygen partial pressure distribution is wider than the range of 4 times to 1/4 times, the decomposition of the aldehyde becomes remarkable at the place where the oxygen partial pressure is high, and the desired carboxylic acid ester selectivity is deteriorated or the reaction between alcohols is caused. It is inconvenient because undesired by-product of carboxylic acid ester becomes remarkable, and in a place where oxygen partial pressure is low, the aldehyde conversion rate is lowered, which is inconvenient.

Since the oxygen partial pressure distribution varies depending on the type of reactor used, the case of a typical reactor will be exemplified below.
At the same time, the average oxygen partial pressure is also defined. When the present reaction is carried out in a bubble column reactor, the oxygen partial pressure decreases monotonically from the reactor inlet (bottom) toward the reactor outlet (top). Therefore, the average oxygen partial pressure is the geometric mean of the oxygen partial pressures at the reactor inlet and the reactor outlet. The draft tube reactor is also a reactor exhibiting an oxygen partial pressure distribution similar to that of a bubble column reactor. When the present reaction is carried out in a stirred tank reactor, the oxygen partial pressure is made uniform by stirring at the moment when the gas containing oxygen is blown, so the average oxygen partial pressure is actually the oxygen partial pressure at the reactor outlet. Is equal to Various methods can be used to control the oxygen partial pressure, some of which are listed below.

1. In a bubble column reactor, etc., oxygen required for the reaction is diluted with a large amount of nitrogen and then blown in to shorten the gas residence time and suppress the decrease in partial pressure due to the consumption of oxygen in the reaction. 2. In place of a large amount of nitrogen, the reactor outlet gas having a reduced oxygen concentration is partially recycled and used. The method described. 3. A method of homogenizing the oxygen partial pressure distribution by blowing diluted air or air containing oxygen necessary for the reaction in a stirred tank reactor and stirring the inside of the reactor. 4. Even in a bubble column reactor, the oxygen required for the reaction is divided into several parts and blown in at several points to suppress fluctuations in the oxygen partial pressure in the reactor.

Either method is an industrially feasible measure and is a preferred embodiment. The reaction can be carried out without a solvent, but can be carried out using a solvent inert to the reaction components, for example, hexane, decane, benzene, dioxane and the like. It is essential that the catalyst used in the present invention contains palladium and / or ruthenium and X (X is at least one metal selected from lead, bismuth, mercury and thallium). Palladium and / or ruthenium and X may form an alloy or an intermetallic compound.

Fe, Te, Ni, and
Cr, Co, Cd, In, Ta, Cu, Zn, Zr, H
f, W, Mn, Ag, Re, Sb, Sn, Rh, Ru,
Ir, Pt, Au, Ti, Al, B, Si, Ge, S
e, Ta, etc. may be included. These different elements are usually
It may be contained in an amount not exceeding 5% by weight, preferably 1% by weight. Further, those containing at least one member selected from alkali metal compounds and alkaline earth metal compounds are advantageous in that the reaction activity becomes high. The alkali metal and alkaline earth metal are usually selected in the range of 0.01 to 30% by weight, preferably 0.01 to 5% by weight.

A small amount of these different elements, alkali metals, alkaline earth metal compounds, etc. may penetrate into the crystal lattice or may be substituted with a part of the crystal lattice metal. Also,
The alkali metal and / or alkaline earth metal compound may be added to a solution containing a palladium compound, a ruthenium compound, or a compound of X at the time of catalyst preparation and may be adsorbed or attached to a carrier, or a carrier carrying these in advance may be used. It can also be utilized to prepare the catalyst. It is also possible to add it to the reaction system under the reaction conditions.

These catalyst constituents may be supported alone or on a carrier such as silica, alumina, silica-alumina, titanium, carbonate, hydroxide, activated carbon or zirconia. The amount of the palladium- and / or ruthenium-supported catalyst supported in the present invention is not particularly limited, but is usually 0.1 to 20% by weight, preferably 1 to 10% by weight, and the amount of alkali metal compound or alkaline earth metal compound When used, the supported amount is usually 0.01 to 30% by weight, preferably 0.01 to 15% by weight.

The catalyst of the present invention can be prepared by a known preparation method. A typical catalyst preparation method will be described. For example, a carrier is added to an aqueous solution containing a soluble lead compound and a soluble palladium salt such as palladium chloride, and the mixture is warmed and impregnated with palladium and lead. Then, it is reduced with formalin, formic acid, hydrazine or hydrogen gas. In this example, lead may be loaded before loading palladium, or palladium and lead may be loaded simultaneously.

The palladium compound and ruthenium compound used for preparing the catalyst include organic acid salts such as formate salts and acetate salts, inorganic acid salts such as sulfates, hydrochlorides and nitrates, ammine complexes, benzonitrile complexes and acetyl. It is appropriately selected from organic metal complexes such as an acetonate complex and a carbonyl complex, oxides, hydroxides and the like. Palladium compounds such as palladium chloride and palladium acetate are preferred, and ruthenium compounds such as ruthenium chloride are preferred.

As the compound of X, inorganic salts such as nitrates and acetates, and organic metal complexes such as phosphine complexes can be used, and nitrates and acetates are preferable. The alkali metal compound and alkaline earth metal compound are also selected from organic acid salts, inorganic acid salts, hydroxides and the like. The amount of the catalyst used can be widely changed depending on the type of reaction raw material, the composition and preparation method of the catalyst, the reaction conditions, the reaction format, etc.
Although not particularly limited, when the catalyst is reacted in the slurry state, it is preferable to use 0.04 to 0.5 kg in 1 liter of the reaction liquid.

In the reaction of the present invention, the pH of the reaction system is adjusted to 6 to 6 by adding an alkali metal or alkaline earth metal compound (eg, oxide, hydroxide, carbonate, carboxylate) to the reaction system. It is preferable to hold at 9. Particularly, setting the pH to 6 or higher has the effect of preventing the dissolution of the X component in the catalyst. These alkali metal or alkaline earth metal compounds can be used alone or in combination of two or more. The reaction of the present invention can be carried out at a high temperature of 100 ° C or higher, but is preferably 30 to 100 ° C, more preferably 60 to 90 ° C.

The reaction time is not particularly limited,
It is usually 1 to 20 hours, although it cannot be determined uniquely because it depends on the set conditions. Hereinafter, embodiments of the present invention will be specifically described with reference to examples. As a carrier, silica gel manufactured by Fuji Silysia Ltd.
150 g of catalyst in which 5% by weight of palladium, 5% by weight of lead and 4% by weight of magnesium are supported on an average particle size of 50 μm)
Was charged into a stainless steel external circulation bubble column reactor having a liquid phase part of 1.2 liter and equipped with a catalyst separator and a condenser, and 34 wt% of methacrolein / methanol was added to 0.5
4 liter / h, NaOH / methanol at 0.06 liter / h, temperature 80 ° C, pressure 5.03 kg / c
The reaction was carried out while supplying air at m ² . PH of reaction solution
Was performed by adjusting the concentration of the NaOH / methanol solution so that it became 7.1.

Lead acetate was dissolved in methacrolein / methanol so as to have a lead concentration of 20 ppm in the feedstock solution and continuously supplied. On the other hand, air was supplied to the reactor while adjusting the amount of air so that the oxygen concentration at the reactor outlet was 4 mol% (oxygen partial pressure 0.20 kg / cm ² ), and the reaction was continued for about 200 hours. For analysis of the reaction liquid and the reactor outlet gas, a conventional gas chromatogram method was used, in which a Shimadzu GC-8A machine was equipped with a G-100 column manufactured by the Chemicals Inspection Association (which elutes in the order of boiling points), and a thermostatic chamber was used. Was programmed and the temperature was raised using a hydrogen flame detector (FID).

[0028]

Example 1 The reaction was performed by adjusting the amounts of nitrogen and air so that the oxygen concentration at the reactor outlet was 4 mol% (oxygen partial pressure 0.20 kg / cm ² ). In the steady state, the reactor inlet oxygen concentration was 6% (oxygen partial pressure 0.30 kg / cm ² ) and the average oxygen partial pressure was 0.24 kg / cm ² (oxygen concentration 5%). Methacrolein (Macr) conversion (mol%), methyl methacrylate (MMA) selectivity (mol%), propylene (C3 =) selectivity (mol%), methyl formate (MF) production ratio (mol to mol-MMA) ) Are summarized in Table 1 together with the results of the following examples and comparative examples.

[0029]

[Table 1]

[0030]

Example 2 To a 60 ml stainless steel autoclave equipped with an electromagnetic induction stirrer, 7.5 g of the catalyst used in Example 1 and 30 ml of methanol having a methacrolein concentration of 34 wt% as a raw material were added, and methanol having a methacrolein concentration of 34 wt% was added. 27 cc / h and NaOH / methanol solution 3 cc / h continuously, temperature 80 ° C., pressure 5 kg / h
cm ² , rotation speed 1000 rpm (stirring tip speed: 1.
2m / s) and pH 7 with a NaOH / methanol solution at an outlet oxygen concentration of 5% (oxygen partial pressure of 0.25 kg /
Air and nitrogen were supplied so as to have a pressure of ² cm ^2, and a continuous reaction was performed for about 200 hours.

[0031]

Comparative Example 1 The reaction shown in Example 1 was carried out for about 200 hours by re-adjusting the amounts of air and nitrogen so that the average oxygen partial pressure became 0.24 kg / cm ² (oxygen concentration 5%). went.
The inlet gas was undiluted air (oxygen concentration 21%, oxygen partial pressure 1.05 kg / cm ² ), and the outlet oxygen concentration was 1% (oxygen partial pressure 0.05 kg / cm ² ).

[0032]

Example 3 In the reaction of Comparative Example 1, the outlet gas after condensing organic substances and water by passing through a condenser set at 0 ° C. and −20 ° C. in this order was partially recycled to obtain an average oxygen partial pressure. 0.
The reaction was carried out for about 200 hours by adjusting the amounts of air, nitrogen and recycle gas so that the concentration was 24 kg / cm ² (oxygen concentration 5%). The oxygen concentration at the reactor outlet was 4 mol% (oxygen partial pressure 0.20 kg / cm ² ), and the reactor inlet oxygen concentration was 6 mol% (oxygen partial pressure 0.30 kg / cm ² ).

[0033]

Example 4 In the reaction of Comparative Example 1, it was considered that the bubble column reactor was divided into four stages in the vertical direction, and piping was provided so that gas could be blown into each stage from below. A gas having an oxygen concentration of 6% was blown into each stage to carry out the reaction for about 200 hours. The oxygen concentration at the reactor outlet was 5 mol% (oxygen partial pressure 0.24 kg / cm ² ). The average oxygen partial pressure in each stage could not be measured because it was in the warm high-pressure reactor.

[0034]

Industrial Applicability According to the method for producing a carboxylic acid ester of the present invention, it is possible to continuously produce a carboxylic acid ester stably with a high aldehyde conversion rate and a high carboxylic acid ester selectivity over a long period of time. Highly useful.

Continued front page    F-term (reference) 4H006 AA02 AC48 BA07 BA09 BA11                       BA13 BA23 BA25 BA55 BC10                       BC11 BC18 BC30 BC32 BC34                       BD20 BD33 BD52 BE30 KA06                       KC14                 4H039 CA66 CC30 CD30

Claims (5)

[Claims] 1. A method for continuously producing a carboxylic acid ester by reacting an aldehyde and an alcohol with a catalyst in the presence of oxygen, wherein the oxygen partial pressure distribution in the reactor is 4 to 1/1 / the average oxygen partial pressure. A continuous process for producing a carboxylic acid ester, which is characterized by controlling the range to 4 times. 2. The carbonization according to claim 1, wherein the reaction is carried out in such a manner that the oxygen partial pressure at the reactor inlet and the reactor outlet is in the range of 4 to 1/4 times the average oxygen partial pressure. Continuous production method of acid ester. 3. The continuous process for producing a carboxylic acid ester according to claim 1, wherein the reaction recycles a part of the reactor outlet gas to the reactor. 4. The catalyst comprising palladium and / or ruthenium and X (X represents at least one metal selected from lead, bismuth, mercury and thallium), and the catalyst is characterized in that: 4. A method for continuously producing a carboxylic acid ester according to any one of 3 to 3. 5. The continuous process for producing a carboxylic acid ester according to claim 4, wherein the aldehyde is acrolein or methacrolein and the alcohol is methanol.