JP2003277323A - Method for continuously producing carboxylic ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously producing carboxylic ester by reacting an aldehyde with an alcohol in the presence of oxygen and a catalyst, wherein a high aldehyde conversion and a high carboxylic ester selectivity are realized and the carboxylic ester is stably and continuously produced for a long term. <P>SOLUTION: This method for continuously producing carboxylic ester comprises using two or more reactors in series and reacting the aldehyde with the alcohol in the presence of the oxygen and the catalyst, wherein the method is characterized by using at least one catalyst separator before the final reactor and at least one other catalyst separator at the outlet of the final reactor. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a carboxylic acid ester by reacting an aldehyde with an alcohol in the presence of oxygen, and more specifically, to a high aldehyde conversion rate and a high carboxylic acid ester selectivity. The present invention relates to a method for realizing a continuous and stable production of a carboxylic acid ester over a long period of time.

[0002]

2. Description of the Related Art An industrially useful method for producing methyl methacrylate or methyl acrylate is an oxidative esterification method for directly producing methyl methacrylate or methyl acrylate by reacting methacrolein or acrolein with methanol. Proposed. In this production method, methacrolein or acrolein is reacted with molecular oxygen in methanol, and an example using a catalyst containing palladium and lead, bismuth, thallium, and mercury is disclosed in JP-B-57-35856-35861. Further, Japanese Patent Publication No. 62-7902 discloses an example in which an intermetallic compound of palladium and these metals is used as a catalyst.

A catalyst using palladium and bismuth is disclosed in JP-A-9-216850 and others.
In JP-A-1-220367, a catalyst using ruthenium and lead is exemplified. The catalysts shown in these disclosed examples are all solid catalysts supported on a carrier such as calcium carbonate, silica, or alumina, and the reaction is carried out by dispersing these solid catalysts in a solution of alcohol and aldehyde (hereinafter, It may be abbreviated as "catalyst slurry.") It is performed by blowing a gas containing oxygen.

Since the reactions shown in these disclosed examples generally have a slow reaction rate, when directed to a commercial process, they are carried out in a series multi-stage system using a plurality of reactors aiming at a high raw material aldehyde conversion. It is also common knowledge in chemical engineering that by-products can be generally reduced by adopting this method, and the present inventors have also conducted continuous reaction experiments aiming at practical application,
Two or three reactors are arranged in series and initially,
The reaction was carried out with an inexpensive and simple device in which a catalyst separation device was used only at the outlet of the final reactor.

That is, as shown in FIG. 1, the catalyst slurry is moved from one reactor to the next reactor through a pipe, the catalyst and the reaction solution are separated at the outlet of the final reactor, and the catalyst is the first reaction. It was returned to the reactor and carried out (see FIG. 1, description of gas containing oxygen and reactor outlet gas was omitted).

However, in the above reaction method, the aldehyde conversion rate did not increase as expected, and the carboxylic acid ester selectivity also deteriorated. Further, also in the catalyst separation, the sedimentation property of the catalyst is remarkably poor in the sedimentation separation, clogging is likely to occur in the filter separation, and worse, the catalytic activity is not stable, and the aldehyde conversion rate and the carboxylic acid ester selectivity are also low. Both of them declined over time, and there was no prospect of establishing a practical process.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a method for producing a carboxylic acid ester by reacting an aldehyde with an alcohol using a catalyst in the presence of oxygen, and has a high reaction rate, good selectivity and long-term use. It is an object of the present invention to provide a method for continuously and continuously producing a carboxylic acid ester.

[0008]

As a result of the inventors' earnest efforts to develop a reactor for the purpose of solving the above-mentioned problems, as a result, in the series multistage reactor, particularly in the final reactor, the liquidity of the reaction solution is It was found that the concentration of the compound which is extremely viscous and inhibits the reaction such as water and carboxylic acid becomes remarkably high.

In the above-mentioned process of FIG. 1 before the present invention, the compound inhibiting these reactions circulates in all stages of the multistage series reactor as the catalyst circulates, so that the reaction rate of aldehyde decreases. It was also found that the carboxylic acid ester selectivity was significantly deteriorated.

From these findings, by providing a catalyst separation device in front of and at the outlet of the final reactor, a reaction liquid having poor liquidity and a high concentration of a reaction inhibitor can be retained in the final reactor, which is high. Not only was the aldehyde conversion rate and high carboxylic acid ester selectivity obtained, but stable reaction results could be maintained over a long period of time, leading to the completion of the present invention.

That is, the present invention has a configuration as described below. (1) In a method for continuously producing a carboxylic acid ester by reacting an aldehyde and an alcohol in the presence of oxygen and a catalyst using at least two reactors in series, a process before and after a final reactor. A continuous process for producing a carboxylic acid ester, characterized in that at least one catalyst separation device is provided at each outlet of the reactor.

(2) The method for continuously producing a carboxylic acid ester according to (1) above, wherein the catalyst and / or the solution containing the catalyst separated by the catalyst separation device is returned to the reactor.

(3) 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), and the above ( The continuous production method of the carboxylic acid ester according to 1) or (2).

(4) The continuous process for producing a carboxylic acid ester according to any one of (1) to (3) above, wherein the aldehyde is acrolein or methacrolein and the alcohol is methanol.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the aldehyde used in the present invention include formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde,
Aliphatic saturated aldehydes such as glyoxal; aliphatic unsaturated 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. Also,
Acrolein and methacrolein are particularly 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. And aromatic alcohols such as benzyl alcohol. Particularly, lower alcohols such as methyl alcohol and ethyl alcohol are preferable 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 amount ratio of aldehyde and alcohol used in the reaction of the present invention.
Although it can be carried out in a wide range such as 10/1 to 1/1000 in terms of the molar ratio of alcohol, it is generally preferred that the amount of aldehyde is small, preferably 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 diluent inert to the reaction, such as nitrogen and carbon dioxide gas, and air. Can also be used. 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 catalyst separation device used in the present invention may be any known solid-liquid separation device such as a sedimentation separation type, a filter filtration type, and a centrifugal separation type, and is not particularly limited, but a sedimentation separation type and a filter are used. A filtration method is preferable, and a method in which both are combined in this order is more preferable.

The catalyst separation device may be installed inside or outside the reactor. The catalyst separation device is a reactor in which at least two or more reactors are connected in series and in multiple stages (hereinafter, in some cases, n-type reactors are connected in series to carry out n-stage reactions, and final reactors are n-stage reactors). It may be abbreviated as a stage reactor, etc.), and it is indispensable to provide it in front of the final reactor and at the outlet, and in the reactors before the n-1 stage reactor, the catalyst is provided at the outlet of any reactor. A separation device may be provided. A catalyst separator may be provided at the outlet of each stage reactor.

The catalyst separated by the catalyst separator installed in front of the final reactor may be returned to any reactor up to the n-1 stage reactor, or may be returned to the n-1 stage reactor as it is. Is also preferable. An example of the arrangement of the devices in the case of a three-step reaction is illustrated in FIG.

The total pressure of the reaction can be carried out in any wide pressure range from reduced pressure to increased pressure, but is usually 1 to 20 k.
It is carried out at a pressure of g / cm ² . The partial pressure of oxygen supplied to the reaction system is such that the oxygen partial pressure on the outlet side of the reactor is 0.8 kg / cm.
^It is preferable to control it to be ² or less, and more preferably 0.4 kg / cm ² or less. 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 gas phase reaction, liquid phase reaction and 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 reaction can be carried out without solvent, but a solvent inert to the reaction components, such as hexane, decane,
It can be carried out using benzene, dioxane or the like.

The catalyst used in the present invention is palladium and / or
Alternatively, it is essential to contain 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, Se
Etc. may be included. These different elements can be contained in the range of usually 5% by weight, preferably 1% by weight. Further, those containing at least one selected from alkali metal compounds and alkaline earth metal compounds have the advantage 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.

These different elements, alkali metal compounds,
A small amount of the alkaline earth metal compound may penetrate into the crystal lattice or may be substituted with a part of the crystal lattice metal. Further, the alkali metal compound and / or the alkaline earth metal compound may be added to the solution containing the palladium compound, the ruthenium compound, or the compound of X at the time of catalyst preparation and adsorbed or attached to the carrier, or these may be loaded in advance. The catalyst can be prepared by utilizing the above-mentioned carrier. 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 supported amount of the palladium and / or ruthenium supported catalyst 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 added is 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 and acetate, 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 varied widely depending on the type of reaction raw material, the composition and preparation method of the catalyst, the reaction conditions, the reaction format, etc., but it is not particularly limited, but the catalyst is reacted in a slurry state. In some cases, 0.
It is preferable to use 04 to 0.5 kg.

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, etc.) 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 compounds 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, preferably 30 to 100 ° C., more preferably 60 to 90 ° C. The reaction time is not particularly limited and cannot be uniquely determined because it depends on the set conditions, but it is usually 1 to 20 hours.

[0035]

The embodiments of the present invention will be specifically described below with reference to examples. The measuring methods used in the examples of the present invention are as follows.

(1) Measurement of Aldehyde Conversion Rate and Carboxylic Acid Ester Selectivity The reaction solution and the outlet gas of the reactor were analyzed by a normal gas chromatogram method using a Shimadzu GC-8A machine manufactured by the Chemicals Inspection Association. A G-100 column (eluting in the order of the boiling points) was attached, the temperature of the thermostatic chamber was programmed, and a hydrogen flame detector (FID) was used. .

(2) Analysis of high-boiling products Analysis of so-called high-boiling components such as high-boiling compounds and low-polymerization compounds is carried out by gas chromatograph method. Also, the peak areas of the components eluting at the back were summed and expressed as a ratio divided by the area of the carboxylic acid ester.

(3) Analysis of carboxylic acid Since carboxylic acid is recovered as a salt, it was converted back to carboxylic acid with formic acid and analyzed by gas chromatography.

[0039]

Example 1 A reactor and a catalyst separation device were assembled in the arrangement shown in FIG. The catalyst separator has an average diameter of 1
A pressure resistant sintering filter made of stainless steel having a diameter of 0 μm, a diameter of 3 cm and a length of 15 cm was used. As a carrier, 150 g of a catalyst obtained by supporting 5% by weight of palladium, 5% by weight of lead and 4% by weight of magnesium on silica gel manufactured by Fuji Silysia Chemical Ltd. (Carrieract 10 <trade name>, average particle diameter 50 μm) was used in the liquid phase part 1. A 2 liter stainless steel external circulation bubble column reactor was charged, and 34 wt% of methacrolein / methanol was 0.54 liter / h and NaOH / methanol was 0.0.
Supply at 6 liters / h, temperature 80 ℃, pressure 5.03k
The reaction was carried out while supplying air at g / cm ² . The NaOH concentration was adjusted so that the pH of the reaction solution was 7.1, and lead acetate was dissolved in methacrolein / methanol and continuously supplied so that the lead concentration in the feed material solution was 20 ppm.

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% (oxygen partial pressure 0.20 kg / cm ² ) in the one-stage reactor. The outlet gas of the first-stage reactor was ventilated to the second-stage reactor, and the insufficient air was added so that the oxygen concentration at the outlet of the reactor of the second-stage reactor was 2.2%, and the reaction pressure was 4.6 kg / cm. ^The reaction was carried out at ² . Furthermore, the outlet gas of the two-stage reactor was ventilated to the three-stage reactor, and the air shortage was added so that the oxygen concentration at the outlet of the reactor of the three-stage reactor was 1.2%, and the reaction pressure was 4.2 kg. / C
The reaction was carried out at m ² . The analysis results at the outlet of the three-stage reactor are
Table 1 shows the results over time. From the results shown in the table, it can be seen that both the conversion of methacrolein and the selectivity of methyl methacrylate are maintained at high values over a long period of time in this example.

[0041]

[Table 1]

[0042]

Comparative Example 1 A reaction was carried out in the same manner as in Example 1 except that the reactor was arranged as shown in FIG. The results are shown in Table 2 over time. At the reaction time of 510 hours, it became difficult to continue the reaction due to clogging of the filter at the outlet of the three-stage reactor, so the reaction was stopped and the solid substance clogged in the filter was analyzed. As a result, sodium was detected and infrared absorption derived from carbonyl was also observed, so it was assumed that sodium salts such as sodium methacrylate and sodium carbonate, and polymers such as methacrolein, methyl methacrylate, and methacrylic acid were formed. .

[0043]

[Table 2]

[0044]

According to the method for producing a carboxylic acid ester of the present invention, a high aldehyde conversion rate and a high carboxylic acid ester selectivity can be realized, and a carboxylic acid ester can be continuously produced stably over a long period of time. There is high industrial utility.

[Brief description of drawings]

FIG. 1 is a flow sheet diagram of an apparatus for carrying out a conventional method for continuously producing a carboxylic acid ester.

FIG. 2 is a flow sheet diagram of an apparatus for carrying out the continuous method for producing a carboxylic acid ester of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toru Watanabe             1-3-1 Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa               Asahi Kasei Corporation F-term (reference) 4H006 AA02 AC48 BA06 BA07 BA09                       BA11 BA23 BA25 BA55 BA60                       BD35 BD36 BD52 BD84 BE30                       KA35 KE00                 4H039 CA66 CC30 CD10 CD20 CL25

Claims (4)

[Claims] 1. A method for continuously producing a carboxylic acid ester by reacting an aldehyde with an alcohol in the presence of oxygen and a catalyst using at least two reactors in series, which is used before a final reactor and A continuous process for producing a carboxylic acid ester, characterized in that at least one catalyst separation device is provided at each outlet of the final reactor. 2. The method for continuously producing a carboxylic acid ester according to claim 1, wherein the catalyst and / or the solution containing the catalyst separated by the catalyst separation device is returned to the reactor. 3. 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: Or the continuous method for producing a carboxylic acid ester according to 2. 4. The continuous method for producing a carboxylic acid ester according to claim 1, wherein the aldehyde is acrolein or methacrolein and the alcohol is methanol.