JP2003267925A - Method for continuously producing carboxylic acid ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously producing a 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 a carboxylic acid ester by performing a reaction of an unsaturated aldehyde with an alcohol in the presence of oxygen by using at least 2 reactors in series is characterized by measuring the pH value of the reaction solution by installing a pH meter at least at the outlet port of the final reactor, and automatically controlling the reaction by changing the feeding rate of a basic compound to the reactor based on the difference between the pH value and the objective value in accordance with a program inputted in advance. <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 and an alcohol with a catalyst in the presence of oxygen to stabilize a high aldehyde conversion rate and a high carboxylic acid ester selectivity. And then provide a way to maintain.

[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. 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.
1-220367 exemplifies a catalyst using ruthenium and lead. The catalysts shown in these disclosures are all
A solid catalyst supported on a carrier such as calcium carbonate, silica, or alumina. The reaction is carried out by dispersing these solid catalysts in a solution of an alcohol and an unsaturated aldehyde (hereinafter, abbreviated as catalyst slurry in some cases) oxygen. In general, the present inventors have conducted an experiment of producing methyl methacrylate from methacrolein and methanol using a bubble column reactor continuously for a long period of time. One of the features of this reaction is that methacrylic acid is produced in the reaction, and the reaction liquid is biased to the acidic side to inhibit the reaction. By adding caustic soda to the reaction system to render it neutral and harmless, and adjusting the pH to 7 which is the most preferable, a high aldehyde conversion rate and a high carboxylic acid ester selectivity can be realized.

However, the present reaction is an extremely slow reaction, and the reaction time varies from 1 hour to a maximum of 20 depending on the conditions.
This is a time-consuming reaction, and once the amount of basic substance added is changed, it takes days until the results are obtained (as a common knowledge of a stirred tank reactor, a time of 3 to 4 times the residence time is required). Therefore, it was a reaction that was difficult to control, because almost all the liquid in the reactor was replaced. Moreover, in actual plant operation, it is often expected that the reaction conditions will change significantly due to, for example, reaction start-up, shutdown, and production volume adjustments. The method of controlling the slow reaction is extremely important in practice and has been strongly demanded.

[0005]

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.

[0006]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the slow response to the condition change. In the present reaction, the pH value of the reaction solution is preferably 6 to 9, but both in the basic region above and in the acidic region below, both the aldehyde conversion rate and the carboxylic acid ester selectivity decrease, which is preferable. I knew it wasn't. Since the pH value of the reaction solution has an optimum point in the vicinity of neutrality and the reaction results decrease before and after that, and in the present reaction, the response to changes in the reaction conditions is slow, the present inventors In carrying out the continuous reaction, in particular, when the reaction time was long, as described below, it was extremely difficult to encounter the situation where the conditions could not be determined for a long period of time.

1. Based on the expected reaction results, the conversion amount of the basic substance was determined by setting the target pH = 7. 2. It took 1-2 days for the reaction to start and stabilize. 3. So when I checked the pH, it was 6, so I added more basic substances. 4. After 2 days, the pH returned to 7, but the shaking did not stop, and eventually it stopped at pH 8 4 days later. 5. The amount of basic substance is 1. And 3. In the case of. 6. After 2 days, the pH had reached about 7. 7. The reaction temperature was raised to investigate the effect of reaction temperature. 8. 1. ~ 6. The above procedure was repeated, and it took about one week again to stabilize. If it is carried out in one reaction tank, it may be possible to control manually (human) even if it takes an extremely long time. Since the reactors are used in series, their control is extremely difficult, and it is unavoidable that manual control is almost impossible.

Therefore, the inventors of the present invention p at the exit of the second tank.
An H meter is installed and the pH is continuously or regularly measured every hour.
By measuring the pH value and controlling it using a program such as a proportional band control method based on the measured value, promptly focus the pH to a predetermined value and establish a method to maintain it, and link it to the present invention. I was able to. 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 using at least two reactors in series, a pH meter is provided at least at the outlet of the final reactor to carry out the reaction. P of solution
A carboxylic acid characterized by measuring the H value and automatically controlling the rate of supply of the basic compound to the reactor based on the difference between the pH value and the target value by changing it according to a program incorporated in advance. The present invention relates to a continuous method for producing an ester. 2. The method for continuously producing a carboxylic acid ester according to the above 1, wherein the catalyst contains palladium and / or ruthenium and X (X represents at least one selected from lead, bismuth, mercury and thallium). 3. The present invention relates to the continuous production method of a carboxylic acid ester according to 1 or 2, wherein the aldehyde is acrolein or methacrolein and the alcohol is methanol.

[0009]

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 amount ratio of aldehyde and 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 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 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 reaction can be carried out without a solvent, but a solvent inert to the reaction components, such as hexane, decane,
It can be carried out using benzene, dioxane or 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. Palladium compounds and ruthenium compounds used for catalyst preparation include organic acid salts such as formate salts and acetate salts, inorganic acid salts such as sulfates, hydrochlorides and nitrates, ammine complexes, benzonitrile complexes, acetylacetonate complexes. , An organic metal complex such as a carbonyl complex, an oxide, a hydroxide, or the like, but the palladium compound is preferably palladium chloride, palladium acetate, or the like, and the ruthenium compound is preferably ruthenium chloride or the like.

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 present invention relates to a method of adding this basic compound. Table 1 shows the relationships among the reaction solution pH, the aldehyde conversion rate (mol%), and the carboxylic acid ester selectivity (mol%). The reaction conditions were carried out in a one-tank reaction according to the reference production example described later. It is understood that both the aldehyde conversion rate and the carboxylic acid ester selectivity have the maximum values at around pH = 7.

[0020]

[Table 1]

In the present invention, a program in which the above relationships are mathematically expressed is incorporated into a computer in advance, and the amount of the basic compound added to the reactor is automatically controlled using the measured pH value to obtain a desired target. It can approach pH. Various known methods can be adopted as the control program, and proportional band control, proportional band differential control, proportional band integral control, equilibrium value prediction method, etc. are exemplified. So-called PID control, which is frequently used for process control, is also one of the preferable control methods.

The pH meter used in the present invention may be any commercially available pH meter. Since the measurement is performed in an organic solvent system, glass electrode pH
Preferred examples include meters and the like. The pH meter is installed at least at the final reactor outlet. It is preferably installed at the outlet of each reactor, but it is not always necessary to install it at all reactors. For example, only at the outlet of the final reactor is the pH
It is also possible to adjust to a predetermined pH value by installing a meter and automatically controlling the addition amount of the basic substance in the final reactor or the reactor further upstream thereof depending on the pH.

The automatic control according to the present invention not only controls the pH value of the reaction solution in the steady state, but also promptly in the case of from the startup to the steady state, from the steady state to the next condition, and from the steady state to the shutdown. Target pH
It can also be used for control to approach the value. 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 and cannot be uniquely determined because it depends on the set conditions, but it is usually 1 to 20 hours. Hereinafter, embodiments of the present invention will be specifically described with reference to examples.

(Reference Production Example) As a carrier, 150 g of a catalyst prepared 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 size 50 μm) was prepared. A stainless steel external circulation type bubble column reactor with a phase part of 1.2 liters and a catalyst separator was charged, and 34 wt% of methacrolein / methanol was 0.54 liters / h, NaOH.
/ Methanol at 0.06 liter / h, temperature 8
The reaction was carried out while supplying air at 0 ° C. and a pressure of 5.03 kg / cm ² . The reaction was carried out using a 3-tank series reactor.

Lead acetate was dissolved in methacrolein / methanol so as to have a lead concentration of 20 ppm in the raw material 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 ) 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 . Further, the outlet gas of the two-stage reactor is ventilated into the three-stage reactor so that the oxygen concentration at the outlet of the reactor of the three-stage reactor is 1.2.
Add the deficient air so that the reaction rate becomes 4.2.
The reaction was carried out at kg / cm ² . The pH of the reaction solution is 7.1.
Was set as the target value, and the solution feeding amounts of the NaOH / methanol solution and the methanol solution were adjusted to adjust the concentrations so that the total solution feeding amount was obtained.

The reaction results were determined as follows. (1) Aldehyde conversion rate (mol%), carboxylic acid ester selectivity (mol%) The reaction liquid and the reactor outlet gas were analyzed by an ordinary gas chromatogram method using a Shimadzu GC-8A type chemical product. An inspection association G-100 column (eluting in the order of boiling points) was attached, the temperature of the thermostat was programmed, and the hydrogen flame detector (FID) was used. (2) Analysis of high-boiling products So-called high-boiling components such as high-boiling compounds and low-polymerization compounds have compounds having a boiling point higher than that of the carboxylic acid by gas chromatography, and the carboxylic acid is eluted from the FID detection peak. The peak areas of the components that elute after the retention time are summed up and divided by the area of the carboxylic acid ester.

[0027]

Example 1 A pH meter was provided at the outlet of each reactor,
Measurement was performed once, and the concentration of NaOH was controlled using the proportional band control method. The reaction was carried out for 200 hours, and the reaction solution for 200 hours was stored in a tank, and this solution was analyzed to obtain the reaction result. Table 2 shows the conversion of methacrolein, the selectivity of methyl methacrylate, the proportion of high boiling substances, and the maximum fluctuation range of the pH value during the reaction for 200 hours.

[0028]

[Table 2]

[0029]

Example 2 The reaction was carried out in the same manner as in Example 1 except that a pH meter was provided only at the outlet of the final reactor.

[0030]

[Comparative Example 1] A pH meter was not installed at the outlet of the final reactor, and the pH of the reaction solution was measured by carrying out sequential sampling at this location at intervals of four times the residence time as a guide, and the pH value was kept at the target value. Therefore, the NaOH supply concentration was adjusted according to the proportional band control method. Others were the same as in Example 1.

[0031]

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.

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Claims (3)

[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 using at least two reactors in series, wherein at least a pH value is present at a final reactor outlet. A meter is provided to measure the pH value of the reaction solution, and based on the difference between the pH value and the target value, the supply rate of the basic compound to the reactor is changed according to a pre-installed program and automatically controlled. A method for continuously producing a carboxylic acid ester, comprising: 2. The continuous carboxylic acid ester according to claim 1, wherein the catalyst comprises palladium and / or ruthenium and X (X represents at least one selected from lead, bismuth, mercury and thallium). Manufacturing method. 3. The continuous process for producing a carboxylic acid ester according to claim 1, wherein the aldehyde is acrolein or methacrolein and the alcohol is methanol.