JPH10168007A - Production of high-purity benzyl alcohol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of economically producing high-purity benzyl alcohol. SOLUTION: Benzyl acetate is fed from the upper part of a reaction distillation tower and methanol is fed from the lower part of the reaction distillation tower and benzyl acetate is countercurrently subjected to contact reaction with methanol in the presence of a basic catalyst to afford a tower top fraction consisting essentially of methyl acetate and methanol and a tower bottom solution consisting essentially of methanol and benzyl alcohol and the tower bottom solution of the reaction distillation tower is fed to a methanol separation tower and distilled to separate the solution into a tower top fraction consisting essentially of methanol and the tower bottom solution consisting essentially of benzyl alcohol and the tower top fraction of the methanol separation tower is circulated to the reaction distillation tower and the tower bottom solution of the methanol separation tower is fed to an alcohol purification tower and distilled to provide the objective benzyl alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing benzyl alcohol.

[0002] Benzyl alcohol obtained by transesterification of benzyl acetate with methanol is a very important compound as a solvent having excellent solubility, being non-toxic and thus being an intermediate for pharmaceutical additives, agricultural chemicals and pharmaceuticals.

[0003]

2. Description of the Related Art As a method for producing benzyl alcohol,
The following methods are known and are industrially manufactured by the methods 1) and 3).

1) A method of hydrolyzing benzyl chloride using caustic soda.

2) A method of hydrolyzing benzyl acetate in the presence of a catalyst.

3) A method of reducing benzaldehyde with hydrogen in the presence of a catalyst.

The above 1) and 2) are all methods for producing benzyl alcohol by hydrolysis. Among them, in the method 1), caustic soda undergoes a stoichiometric reaction, so that an equivalent amount or more of benzyl chloride is required, and after the reaction, a large amount of a saline solution containing organic substances is by-produced. Also, the method 3) is not economically advantageous because it uses relatively expensive benzaldehyde as a raw material.

On the other hand, the method of 2) for producing benzyl alcohol by hydrolyzing benzyl acetate is a process without drainage because acetic acid by-produced in the reaction is reused, and is economical and environmentally friendly. is there.

This method is described in J. Chem. Soc.
No. No. 5,1952,1607 discloses a method for producing benzyl alcohol by hydrolysis with water / benzyl acetate (volume ratio) 25 at 20 to 30 ° C. in the presence of Amberlite IR-100, a sulfonic acid type cation exchange resin. Has already been reported. However, this method has low catalytic activity and uses a remarkably large amount of water, so that the raw material concentration is low, and it is not practical as an industrial method considering the energy for removing unreacted water from the product liquid. Further, there is no specific description of a method for separating and purifying benzyl alcohol.

Although not a method for producing benzyl alcohol, a method for obtaining a corresponding alcohol from an ester by a transesterification reaction is known. For example, JP
JP-A-61109 and JP-A-55-59122 describe a method for producing butanediol from butanediol or an acetate of butenediol.
However, when these methods are applied to the present invention as they are, solids are precipitated in the reactive distillation column, causing a flooding phenomenon, so that there is a problem that the operation cannot be continued or the reaction does not proceed as expected.

As described above, when considering the actual industrialization of the benzyl alcohol production method, a production method including a detailed separation / purification step has not been studied. It is not satisfactory as a manufacturing method.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for economically producing high-purity benzyl alcohol.

[0013]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, benzyl acetate was transesterified with methanol in the presence of a basic catalyst, followed by separation. -It has been found that high-purity benzyl alcohol can be economically produced by rationally combining the fractions of each step in consideration of the purification process, and completed the present invention.

That is, the present invention provides a method for producing benzyl alcohol by subjecting benzyl acetate to transesterification with methanol in the presence of a basic catalyst, wherein benzyl acetate is supplied from the top of the reactive distillation column and methanol is supplied to the reactive distillation column. Supplied from the lower part, in the presence of a basic catalyst, benzyl acetate and methanol are brought into contact countercurrently to react with each other, and a top fraction mainly composed of methyl acetate and methanol, and a main fraction mainly composed of methanol and benzyl alcohol A bottom liquid is obtained, and the bottom liquid of the reactive distillation column is supplied to a methanol separation column and distilled, and separated into a top fraction mainly composed of methanol and a bottom liquid mainly composed of benzyl alcohol. The top fraction of the separation tower is circulated to the reactive distillation tower, and the bottom liquid of the methanol separation tower is supplied to the alcohol purification tower and distilled to obtain benzyl alcohol. A method for producing high-purity benzyl alcohol, wherein.

Hereinafter, the present invention will be described in detail.

In the method of the present invention, benzyl acetate is supplied to the upper portion of the reactive distillation column, and methanol is supplied to the lower portion of the reactive distillation column, and benzyl acetate and methanol are supplied in countercurrent in the presence of a basic catalyst. The benzyl alcohol is produced by contact and transesterification.

In this case, impurities in the raw material may cause a reduction in the reaction rate or a blocking problem. For example, when sodium methylate is used as a basic catalyst, the reaction of the following formula occurs when an acidic substance such as benzoic acid or acetic acid as a raw material or water is present in benzyl acetate or methanol as a raw material,
Produces sodium benzoate and sodium acetate.

[0018]

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[0019]

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[0020]

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[0021]

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These soda salts hardly dissolve in benzyl acetate as a raw material or methyl acetate as a by-product of the transesterification reaction, and precipitate, deposit and scale near the benzyl acetate feed stage where these concentrations are high. May cause flooding trouble. In addition, since a catalyst (sodium methylate) is involved in these reactions, the catalysts themselves are deactivated (consumed) and inhibit the reactions.
In addition, when sodium hydroxide is used as a catalyst, a similar reaction occurs when sodium methylate is used.

Therefore, it is preferable to use benzyl acetate or methanol as a raw material having a low concentration of an acidic substance such as benzoic acid or acetic acid and a low concentration of water. The concentration of these impurities contained in the raw material is not particularly limited because it varies depending on the molar ratio of methanol to benzyl acetate, the catalyst concentration or the concentration of each impurity, but for example, the concentration of benzoic acid contained in benzyl acetate is , Usually 0.0
It is at most 5% by weight, preferably at most 0.03% by weight, more preferably at most 0.02% by weight. The acetic acid concentration in benzyl acetate is usually 0.1% by weight or less, preferably 0.0% by weight.
It is at most 5% by weight, more preferably at most 0.03% by weight. The water concentration in benzyl acetate is usually 0.05% by weight
Or less, preferably 0.03% by weight or less, more preferably 0.02% by weight or less. The concentration of water contained in methanol is usually 0.2% by weight or less, preferably 0.1% by weight or less, more preferably 0.05% by weight or less.

In a preferred embodiment of the present invention, benzyl acetate as a raw material is obtained by an oxyacetoxylation reaction described later. The raw material methanol is
Methanol that is by-produced in the transesterification reaction is hydrolyzed, and methanol that is distilled and recovered in a methanol recovery tower, and methanol that is distilled and recovered by supplying the bottom liquid of the reactive distillation tower to a methanol separation tower is used. Therefore, the amount of newly supplied methanol is small because of only the loss of distillation.

In the present invention, examples of the basic catalyst include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide, and alcoholates such as sodium alcoholate and potassium alcoholate. Since these are solids, they are generally dissolved in alcohol and supplied.

The alcohol used in the transesterification reaction is not limited to methanol. However, methanol is not preferred because of the solubility of the catalyst and the distillative separation of water and the alcohol after hydrolysis of the acetic acid ester by-produced in the transesterification reaction. Is most suitable. Therefore, methanol is the most suitable alcohol for dissolving the catalyst. It is also effective to dissolve the target product in benzyl alcohol for use.

The amount of the catalyst used depends on the type of the catalyst and cannot be determined unconditionally. The higher the reaction rate, the more advantageous in terms of the reaction. However, since it is related to the above-mentioned problem of salt precipitation, it is necessary to determine the salt in consideration of the problem. For example, when sodium hydroxide is used, 0.01 to 1% by weight, preferably 0.02% by weight based on benzyl acetate as a raw material.
~ 0.2% by weight is suitable. When sodium methylate is used, a value obtained by multiplying the amount used in the case of sodium hydroxide by the molecular weight ratio (54/40) is appropriate.

The type of the reactive distillation column may be a commonly used type, and may be a packed column type distillation column or a tray type distillation column, and is not particularly limited.

The position for supplying the catalyst to the reactive distillation column is preferably the same as or higher than the benzyl acetate supply position (supply stage) (upper stage).

The form of the reactive distillation column is a distillation section in which a portion from the methanol supply position to the benzyl acetate supply position is a reaction portion, and a concentration portion is provided above the benzyl acetate supply position and a discharge portion is provided below the methanol supply position. It is preferable to provide a separation part. The role of the concentrating unit is to not distill benzyl acetate as a raw material or benzyl alcohol as a product.
On the other hand, the role of the emission part is to prevent the generated methyl acetate from dropping to the bottom of the tower. The boiling points of benzyl acetate and benzyl alcohol are sufficiently higher than those of the distillate components methyl acetate and methanol, so that separation is easy. Therefore, a large number of stages of these distillation separation sections are not required. The size of the reaction section is determined in consideration of the residence time of benzyl acetate as a raw material and the number of theoretical plates in distillation. The required residence time is not particularly limited because it depends on the gas-liquid contact efficiency in the column, the catalyst concentration, the molar ratio of benzyl acetate to methanol in the reaction section, and the reaction temperature. Long stay time and large number of theoretical plates do not hinder the reaction, but economical considerations should be taken into account. Therefore, the stay time is 1 minute to 6 minutes.
0 minutes, the theoretical plate number of the entire reactive distillation column is 3 to 50
Steps are appropriate.

Although benzyl alcohol is a substance having relatively high thermal stability, it is preferable to avoid exposure to high temperatures in the presence of a catalyst or a sodium salt as much as possible, and to keep the bottom temperature below the standard boiling point of benzyl alcohol. Therefore, it is preferable to discharge a part of methanol from the bottom of the column.

The operating pressure of the reactive distillation column is not particularly limited, but it is most reasonable and economical to operate at normal pressure in consideration of the vapor pressure of methyl acetate and methanol which are the main components at the top of the column. The temperature of each part in the column is determined by determining the operating pressure, the supply molar ratio of benzyl acetate and methanol, the catalyst concentration, the bottom temperature or composition, the number of stages of each part and the reflux ratio.

The supply molar ratio of methanol to benzyl acetate as a raw material may be greater than equimolar, but if it is too large, the amount of methanol sent to the hydrolysis step together with the produced methyl acetate increases, and the energy consumption increases due to an increase in the amount of methanol circulation. Increase. Therefore, the supply molar ratio of methanol to benzyl acetate as a raw material is usually 1.1 to 1.1.
10, preferably 1.5 to 5.

In the present invention, a mixture containing benzyl alcohol and methanol as main components obtained from the bottom of the reactive distillation column is supplied to a methanol separation column and distilled, and a top fraction mainly containing methanol is subjected to reactive distillation. Circulated to the tower. At this time, when the water content in the methanol is large, it is preferable to carry out the distillation separation so that the water content remains on the benzyl alcohol side at the bottom of the column.

The type of the methanol separation column may be a commonly used type.

The operating pressure of the methanol separation column is not particularly limited, but it is preferable to operate under reduced pressure so as to be treated at a temperature not higher than the standard boiling point of benzyl alcohol as described above.

Since the specific volatility of benzyl alcohol and methanol is very large, separation of both is possible with a low number of stages and a low reflux ratio. From this, methanol is distilled without being constrained by the water concentration in the distilled methanol, and the methanol containing water is passed through a drying tower filled with a water adsorbent such as silica gel, zeolite, or activated carbon before being circulated through the reactive distillation column. It is also effective to recycle through a reactive distillation column after passing through a dehydration treatment.

The bottom liquid of the methanol separation column containing benzyl alcohol as a main component is supplied to an alcohol purification column,
Low boiling impurities such as methanol, water and benzaldehyde are removed from the top of the column, and high-purity benzyl alcohol is taken out from the middle of the column. At this time, before supplying the bottom liquid of the methanol separation tower to the alcohol purification tower, the liquid is supplied to the solid substance separator and concentrated, and solid substances such as sodium benzoate, sodium acetate and catalyst dissolved in the liquid are precipitated. Separation is preferred.
The evaporate from the solids separator containing benzyl alcohol as a main component is supplied to an alcohol purification column, and low boiling impurities such as methanol, water, and benzaldehyde are removed from the top of the column. And the bottoms are recycled to the solids separator.

The pressure in the solids separator and the alcohol purification column is preferably operated under reduced pressure in consideration of the thermal stability of benzyl alcohol. The type of the solid separator is not particularly limited, and examples thereof include an evaporator having a solid scraper therein, for example, a thin-film evaporator.

The alcohol purification column can be divided into two columns, that is, an impurity separation column and an alcohol purification column. In this case, impurities such as methanol, water, and benzaldehyde are taken out from the top of the impurity separation tower and discarded, the bottom liquid is supplied to an alcohol purification tower, benzyl alcohol as a product is taken out from the top, and the bottom liquid is a solid substance. Circulated to the separator.

The mixture containing methyl acetate and methanol as main components taken out from the top of the reactive distillation column is supplied to an intermediate portion of the extractive distillation column, and water is supplied from above to perform distillation. Take out the mixture mainly composed of water,
It is preferable to supply the distillate and water from the acetic acid recovery tower together with the water to a hydrolysis reactor for hydrolysis treatment. At this time, the bottom liquid of the extractive distillation column mainly composed of water and methanol is supplied to a methanol recovery column and distilled, and the top distillate mainly composed of methanol is circulated to the reactive distillation column, and The water recovered from is recycled to the extractive distillation column.

The reaction mixture exiting the hydrolysis reactor is supplied to a methyl acetate recovery column for distillation, and a mixture mainly composed of unreacted methyl acetate and methanol obtained from the top is circulated to an extractive distillation column. . A mixture mainly composed of water and acetic acid obtained from the bottom of the methyl acetate recovery tower is supplied to the acetic acid recovery tower for distillation, and a distillate mainly composed of water or an aqueous acetic acid solution obtained from the top is hydrolyzed. Circulate to the reactor.

The type of the extractive distillation tower, the methanol recovery tower, the methyl acetate recovery tower and the acetic acid recovery tower may be the type of a general distillation tower.

The amount of water supplied to the extractive distillation column is usually 0.05 to 5, preferably 0 to 5 by weight, relative to the amount of the mixture containing methyl acetate and methanol as main components supplied from the reactive distillation column. .1 to 1. If the amount of water is too small, the methanol concentration in the distillate will increase, and the methyl acetate concentration in the bottom liquid will increase. If the amount of water is too large, energy consumption increases and it is not economical.

The water content in the methanol recovered from the top of the methanol recovery tower is preferably as small as possible, usually 0.2% by weight or less, preferably 0.1% by weight or less, more preferably 0.05% by weight. % Or less. The methanol concentration in the bottom liquid of the methanol recovery column containing water as a main component is not particularly limited, but it is preferable that the amount of water to be supplied to the extractive distillation column is not increased, and that the methanol concentration is low in order to reduce the amount of circulating methanol. .

The amount of water to be supplied to the hydrolysis reactor depends on the amounts of methyl acetate and methanol supplied from the extractive distillation column and the hydrolysis rate. Preferably it is 1-5. Examples of the catalyst for the hydrolysis reaction include liquid acids such as sulfuric acid, phosphoric acid, and alkylsulfonic acid, and solid acids such as acidic cation exchange resins, silica, silica alumina, and acid clay. The acid cation exchange resin is easy to use and suitable because of the equipment material.

The type of the hydrolysis reactor may be any of a stirring type, a fixed bed type, and a tower type. When an acidic cation exchange resin is used as a catalyst, the fixed bed type without damaging the catalyst is preferred. .

Further, as a preferable method, a reactive distillation system in which the acidic cation exchange resin is molded into a shape having a small pressure loss, or a reaction distillation and a reaction are carried out in a single column by incorporating the resin into a vessel and incorporating the same in a distillation column is adopted. This is advantageous because a methyl acetate recovery tower is not required. The size of the device depends on the required contact time. The contact time for a normal fixed bed type is usually 0.03
10 to 10 hours, preferably 0.1 to 5 hours. The reaction temperature is set at 50 from the reaction rate and the heat resistance of the acidic cation exchange resin.
~ 120 ° C is preferred. The operating pressure of the reactor is not particularly limited, but usually 1 to 5 atm in absolute pressure is appropriate.

In the methyl acetate recovery column, separation is easy due to a large boiling point difference between a distillate mainly composed of a mixture of methyl acetate and methanol and a bottom liquid mainly composed of acetic acid and water. May be selected based on economics. According to the present invention, the distillate from the acetic acid recovery tower is recycled to the hydrolysis reactor. However, considering the economics of the process, there is no problem if a certain amount of acetic acid is contained therein.

In the method of the present invention, the method for producing benzyl acetate used as a raw material is not particularly limited. For example, it can be produced by oxyacetoxylation of toluene, acetic acid and oxygen.

At this time, toluene and acetic acid used as raw materials may be those produced by any production method. For example, toluene can be used that is separated from a petroleum fraction, one that is separated from a cracked oil obtained by decomposing a petroleum fraction, and acetic acid is produced by oxidizing acetaldehyde. Any of those produced by oxidizing hydrocarbons and those synthesized from methanol and carbon monoxide can be used.

In the above method, in order to obtain benzyl acetate by oxyacetoxylation of toluene, acetic acid and oxygen, an oxyacetoxylation reactor is charged with a catalyst having oxyacetoxylation ability and used.

As the catalyst having an oxyacetoxylation ability, a catalyst capable of obtaining a desired oxyacetoxylation reaction result can be used without any particular limitation, and a catalyst mainly composed of palladium having oxyacetoxylation activity can be used. It is mentioned as a suitable thing.

Specifically, for example, a catalyst system comprising a catalyst in which palladium is supported on alumina and an alkali metal acetate (Japanese Patent Publication No. Sho 42-13081); Catalysts in which one selected is combined with palladium (JP-A-52-151135, JP-A-52-151135)
No. 151136), a catalyst system comprising a catalyst comprising one component selected from bismuth, cobalt and iron supported on silica, palladium and potassium acetate (Japanese Patent Publication No. 50-28)
No. 947), a catalyst comprising silica and palladium, bismuth and chromium supported thereon and an alkali metal acetate (Japanese Patent Publication No. 52-16101), a catalyst and reaction system comprising palladium and bismuth or lead supported on silica A catalyst system comprising both a bismuth compound and a lead compound soluble in water (JP-A-63-174950), comprising palladium and bismuth, palladium / bismuth = 2.5 to 3.
A catalyst in which an alloy having a ratio of 5 (atomic ratio) is supported on silica may be used. Among these, a catalyst in which an alloy composed of palladium and bismuth and having a palladium / bismuth ratio of 2.5 to 3.5 (atomic ratio) supported on silica is particularly preferable in consideration of the catalyst activity and the catalyst life. Consisting of palladium and bismuth, palladium / bismuth = 2.5 to
An alloy having a ratio of 3.5 (atomic ratio) is shown in Table 1 when 2θ is 30 to 80 °.

[0055]

[Table 1]

The characteristic X-ray diffraction pattern shown in FIG.

In the above method, the reaction may be carried out by dissolving a bismuth soluble compound in toluene and / or acetic acid in order to suppress the deterioration of the catalyst.

In this case, the amount of the bismuth soluble compound dissolved in toluene and / or acetic acid is determined by the following formula (5)

[0059]

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It is preferable to be within the range.

The catalyst comprises the above-mentioned palladium and bismuth, and palladium / bismuth = 2.5 to 3.5.
When a catalyst in which an alloy having an atomic ratio (atomic ratio) is supported on silica is used, the catalyst is stable in the present reaction system, so it is not necessary to coexist a bismuth-soluble substance in particular. It is enough within the range. If the range is significantly exceeded, a bismuth compound may precipitate in the step of purifying the product benzyl acetate, which may cause blockage.

Examples of the soluble compound of bismuth include, but are not limited to, bismuth nitrate, bismuth oxide,
Bismuth oxyacetate, bismuth hydroxide, bismuth chloride,
Examples include bismuth oxychloride, basic bismuth carbonate, bismuth acetate, bismuth oxalate, and trimethylbismuth.

The above-mentioned catalyst having oxyacetoxylation ability is used by filling it in a reactor. The amount of the catalyst to be used cannot be specified uniformly because it varies depending on the reaction method. However, in consideration of economy, in the case of a fixed bed, the unit catalyst volume and the total supply amount of toluene and acetic acid per unit time (LHSV) are used. , 0.1 to 50 h ^-1 , more preferably a catalyst amount of 0.1 to 30 h ^-1 ,
In the case of a suspension bed, the concentration of the catalyst is preferably in the range of 0.1 to 30% by weight based on the raw material.

In the above method, from the industrial viewpoint, in order to secure the activity and selectivity of the catalyst and to maintain the life of the catalyst, the oxygen partial pressure of the gas phase in the reactor is reduced to 0.1%. ~
It is preferable to control it within the range of ² kg / cm ² . 0.
If it is less than 1 kg / cm 2, industrially sufficient activity cannot be obtained, and if it exceeds ² kg / cm ² , the elution of palladium increases, and the activity may decrease significantly. Also,
The supply amount of oxygen is 0.5 to 1 liter of the catalyst volume.
4.5 mol / h is preferred.

The above oxyacetoxylation reaction is usually carried out under heating and under pressure. The reaction temperature is usually 80
-230 ° C, preferably 120-200 ° C.
If it is higher than this, only the progress of the side reaction increases, and if it is lower, the reaction speed is disadvantageous. The pressure may be set so long as the catalyst surface is maintained in a liquid phase at the reaction temperature.
１００100 kg / cm ² G, preferably 4-50 kg / c
m ² G is chosen. In the method of the present invention, the desired reaction sufficiently proceeds within this range, so that a higher pressure than this is unnecessary.

In the above method, oxygen is used as an oxidizing agent. Oxygen may be diluted with an inert gas such as nitrogen or may be air. The optimum supply amount of oxygen varies depending on the reaction temperature, the amount of catalyst, and the like, but it is sufficient that the gas composition after passing through the catalyst is less than the explosion range. Unit catalyst amount, oxygen supply amount per unit time (GHS
V) is preferably 5000 h ^-1 or less at 0 ° C. and 1 atm.

The reaction time varies depending on the method of setting the reaction temperature, pressure, amount of catalyst and the like or the reaction method, so that it is difficult to determine the range in a straightforward manner.
In a semi-batch system, usually 0.5 hours or more is required, and preferably 1 to 10 hours. In the case of a continuous reaction using a suspension bed or a fixed bed flow reaction, the residence time may usually be 0.03 to 10 hours.

The type of the oxyacetoxylation reactor is not particularly limited, and may be, for example, a single-tube or multi-tube reactor. In addition, this reaction is an oxidation reaction and is a reaction accompanied by heat generation. It is possible to adopt a raw material split supply format or the like.

The effluent from the oxyacetoxylation reactor is supplied to a gas-liquid separator, which is a gas-liquid separator.

As the gas-liquid separation device, in addition to an independent gas-liquid separator, a gas-liquid separation operation can be performed depending on the method of removing the effluent at the outlet of the oxyacetoxylation reactor. It can be considered as an integrated gas-liquid separation device and operation, and such a form may be used.

The liquid phase from the gas-liquid separator is a mixture containing toluene, acetic acid and benzyl acetate as main components, which are supplied to a raw material recovery column. Distillation is performed in the raw material recovery column, and a mixed solution mainly composed of unreacted raw materials, toluene and acetic acid, is collected as a fraction from the top of the column, and benzyl acetate, which is the target product, is mainly collected from the bottom of the column. The resulting mixture is obtained. The top fraction mainly containing toluene and acetic acid recovered in the raw material recovery tower is circulated to the oxyacetoxylation reactor.

The bottom liquid mainly composed of benzyl acetate recovered in the raw material recovery tower is supplied to the low-boiling substance removal tower as it is or by adjusting the temperature and pressure. In the low-boiling matter removal column, distillation is performed to separate into a top solution mainly containing benzaldehyde and a bottom solution mainly containing benzyl acetate. The distillation conditions of the low-boiling substance removal column are not particularly limited as long as components having a lower boiling point than benzyl acetate such as benzaldehyde can be removed from the top of the column.

The bottom liquid containing benzyl acetate as a main component recovered in the low-boiling substance removing column is supplied to the high-boiling substance removing column as it is or by adjusting the temperature and pressure. Distillation is performed in the high-boiling substance removal column, and high-purity benzyl acetate is obtained from the top of the column. In addition, components having a higher boiling point than benzyl acetate, such as benzoic acid and benzyl benzoate, are removed from the bottom of the high-boiling substance removal tower. The distillation conditions of the high-boiling substance removal column are not particularly limited, and arbitrary distillation conditions are selected according to the purity of the product benzyl acetate. In order to produce benzyl acetate of higher quality, benzyl acetate can be distilled and purified using another distillation column.

By employing such a process, high-purity benzyl acetate and high-purity benzyl alcohol can be efficiently and continuously produced.

[0075]

Embodiments of the present invention will now be described with reference to the drawings. Various embodiments of the present invention are conceivable, and are not limited to the example of the embodiment shown in the drawings.

FIG. 1 shows an example of the transesterification reaction process of the present invention.

Benzyl acetate is supplied to the upper portion of the reactive distillation column 1, and methanol is supplied from the lower portion of the reactive distillation column 1, and the transesterification reaction is carried out by countercurrent contact in the presence of a basic catalyst.

Most of the raw material methanol is covered by methanol recovered from the top of the methanol separation tower 2 in the subsequent step and methanol recovered from the top of the methanol recovery tower 6 in the hydrolysis step of methyl acetate. A small amount of loss is supplied as new make-up. At this time, it is preferable to control the water concentration in methanol as described above.

The basic catalyst is supplied at the same position or higher than the supply position of the starting material benzyl acetate. It is preferable to provide several enrichment sections above the benzyl acetate supply stage so that the starting benzyl acetate does not distill from the top of the column. This is advantageous because the number of concentrating units and the reflux ratio are reduced by the amount of the reaction contribution.

Benzyl alcohol, which is the target substance produced by the transesterification reaction, is taken out from the bottom of the reactive distillation column 1 together with a part of excess methanol and supplied to the methanol separation column 2, where methanol is separated by distillation from the top and reactive distillation is performed. Circulated to tower 1. At this time, when water coexists, it is preferable to control the distillation conditions so that the water concentration in the circulated methanol does not exceed a predetermined concentration.

The bottom liquid of the methanol separation tower 2 is supplied to a solid separator 3 and concentrated to separate solids. As an example of the solid matter separator 3, a scraping type thin film evaporator or the like is effective.

Evaporation vapor of the solid separator 3 is a mixture containing benzyl alcohol as a main component, and does not contain solid components unless mixed with droplets. The evaporated vapor is supplied to the alcohol purification column 4 and low-boiling impurities are distilled off from the top of the column.
High-purity benzyl alcohol is taken out of the middle stage of the alcohol purification tower 4. The bottom liquid of the alcohol purification tower 4 is circulated to the solid separator 3. Needless to say, it is also possible to divide the alcohol purification column 4 into two columns: a distillation column for separating low-boiling impurities and a product column for removing the product from the top.

A mixture mainly composed of methyl acetate and excess methanol obtained from the top of the reactive distillation column 1 is supplied to the central portion of the extractive distillation column 5 in the hydrolysis step of methyl acetate. From the upper part of the extractive distillation column 5, the bottom liquid of the methanol recovery column 6 mainly composed of water is supplied, and extractive distillation of methanol with water is performed. The mixture mainly composed of water and methanol taken out from the bottom of the extractive distillation column 5,
The mixture containing water as a main component, which is supplied to the methanol recovery column 6 and distilled and obtained from the bottom of the column, is circulated to the upper portion of the extractive distillation column 5. The distillate mainly composed of methanol recovered from the top of the methanol recovery column 6 is supplied to the lower part of the reactive distillation column 1 together with the methanol circulated from the methanol separation column 2 and, if necessary, the makeup methanol. .

On the other hand, the top liquid of the extractive distillation column 5 containing methyl acetate and water as the main components is combined with water or the top solution of the acetic acid recovery column 9 containing water and acetic acid as the main components and water for make-up. It is supplied to the decomposition reactor 7 to perform a hydrolysis reaction of methyl acetate. The effluent from the hydrolysis reactor 7 is supplied to the methyl acetate recovery column 8 and distilled, and a mixture containing unreacted methyl acetate and methanol as main components is taken out from the top of the column, and circulated to the extractive distillation column 5. It is supplied to the extractive distillation column 5 together with the top liquid of the reactive distillation column 1. The bottom liquid of the methyl acetate recovery tower 8 is supplied to the acetic acid recovery tower 9.

FIG. 2 shows an example of a process for producing benzyl acetate.

In FIG. 2, toluene and acetic acid and air supplied as raw materials, and a circulation mainly composed of toluene and acetic acid circulated from the raw material recovery tower 12 and the water removal tower 16 are supplied to the oxyacetoxylation reactor 10. Liquid phase, static settling tank 17
The upper phase portion mainly containing toluene, the circulating gas phase portion mainly containing oxygen and nitrogen circulated at least partially from the condenser 15, and the acetic acid in the acetic acid recovery tower 9 (see FIG. 1) as the main component. Bottom liquid is supplied.

The method of supplying the raw material is not particularly limited, but the reaction is performed in a liquid phase, so that the surface of the catalyst only needs to be covered with the raw material liquid. The flow direction of the gas and liquid may be a downward flow or an upward flow. In addition, the raw material liquid and / or air
It may be divided and supplied to the oxyacetoxylation reactor 10.

The effluent of the oxyacetoxylation reactor 10 that has become a gas-liquid mixed phase flow is supplied to a gas-liquid separator 11.

The gas phase removed from the gas-liquid separator 11 is supplied to a condenser 15 which is a condenser, and is supplied with toluene,
It is separated into a liquid phase mainly composed of acetic acid, water and benzyl acetate, and a gas phase mainly composed of oxygen and nitrogen.

At least a part of the liquid phase separated by the condenser 15 is mixed with the liquid phase from the gas-liquid separator 11 and supplied to the raw material recovery tower 12, and the remaining liquid phase is separated from the water removal tower. 16. At least a part of the gas phase separated by the condenser 15 is circulated to the oxyacetoxylation reactor 10, and the remaining gas phase is purged out of the system. The amount of circulation of the gas phase part which is at least partially circulated to the oxyacetoxylation reactor 10 is preferably such that the oxygen concentration in the whole gas phase part when mixed with the air supplied to the oxyacetoxylation reactor 10 is desired. Is controlled so that the density becomes

Most of the liquid phase from the condenser 15 supplied to the water removal tower 16 is mainly composed of toluene, acetic acid and water, and is distilled in the water removal tower 16. From the top, toluene and water are obtained as main fractions. The overhead fraction mainly composed of toluene and water is subjected to liquid-liquid two-phase separation in a static settling tank 17, and the upper phase mainly composed of toluene is circulated as it is to the oxyacetoxylation reactor 10, and the main phase is mainly composed of water. The lower phase is removed. Also, acetic acid is obtained from the bottom of the water removal tower 16 and is circulated to the oxyacetoxylation reactor 10 as it is.

The liquid phase from the gas-liquid separator 11 is
It is mixed with at least a part of the liquid phase part separated in 5 and supplied to the raw material recovery tower 12. Non-condensable gas components such as oxygen and nitrogen are dissolved in a liquid mixture of the liquid phase from the gas-liquid separator 11 and at least a part of the liquid phase separated by the condenser 15, and the raw material is recovered. It is preferable to remove dissolved non-condensable gas components by a known apparatus and operation such as a flash evaporator and a vacuum deaerator before supplying to the tower 12. If this method is employed, the size of the raw material recovery tower 12 can be reduced, and a special device such as a condensing device attached to the raw material recovery tower 12 for suppressing loss of the effective components released outside the system simultaneously with the non-condensable gas components. No special equipment and operation are required.

The top fraction of the raw material recovery tower 12 is toluene,
It is mainly composed of acetic acid and circulated to the oxyacetoxylation reactor 10 as it is.

The circulating liquid phase mainly composed of unreacted raw materials, toluene and acetic acid, circulated through the oxyacetoxylation reactor 10 contains a small amount of water. When the concentration of water is increased, the activity and selectivity of the catalyst may be adversely affected. In this case, the starting toluene and acetic acid supplied to the oxyacetoxylation reactor 10 and the recycled toluene and acetic acid are used. The gas-liquid separation condition of the gas-liquid separator 11, the condensation condition of the condenser 15, and the raw material recovery so that the concentration of water in the whole liquid mixture with the circulating liquid phase portion containing as a main component is 5% by weight or less. Tower 12
Alternatively, it is preferable to control the distillation conditions of the water removal tower 16.

[0095]

As described above, according to the method of the present invention,
By transesterifying benzyl acetate as a raw material with methanol, high-purity benzyl alcohol can be economically produced under a stable operation.

[0096]

Next, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples. In the following text, weight%
%, Benzyl alcohol as BzOH, and benzyl acetate as BzOAc.

Embodiment 1 An embodiment will be described with reference to FIG.

427 g / h of 99.7% pure BzOAc
(Benzaldehyde: 0.03%, BzOH: 0.24
%, Acetic acid: 0.01%, benzoic acid: 0.01%, moisture:
0.01%) in the reactive distillation column 1 (30 stages, reaction section 2).
(5 stages) were continuously fed to the top of the column. Methanol recovered from the tops of the methanol separation tower 2 and the methanol recovery tower 6,
And a total of 242 g / h of make-up methanol (containing 0.16% of methyl acetate and 0.01% of water) were supplied to the fifth stage of the reactive distillation column 1. From the top of the column, a methanol solution containing 2% sodium methylate as a catalyst 1
3.8 g / h were fed. The bottom temperature was operated at 96.0 ° C.

As a result, 349 g of the reaction mixture /
h (composition BzOH: 86.8%, methanol: 13.
1%). In addition, in the gas chromatogram of this reaction mixture, the peak of the raw material BzOAc was about a trace.

The reaction mixture was supplied to the methanol separation column 2 for distillation, and 44 g / h of the distilled methanol was circulated to the reaction distillation column 1. The bottom liquid of the methanol separation tower 2 is stored in a receiver, and 5.0 kg of the bottom liquid is charged to a rotary thin film evaporation type solid separator 3, and the pressure is gradually changed to 350 to 100 Torr, and the liquid is evaporated and concentrated. 4.8% BzOH 4.9
kg.

On the other hand, the distillate 33
4 g / h (composition: methyl acetate: 62.5%, methanol: 35.7%, BzOAc: 0.9%, BzOH:
0.9%). This distillate is mixed with the distillate of the methyl acetate recovery column 8 and supplied to the middle stage of the extraction distillation column 5,
Extraction distillation was performed by supplying 177 g / h of water from the top of the tower. The bottom liquid of the extractive distillation is supplied to the methanol recovery column 6 for distillation, and the distillate at the top of the column is 205 g / h (composition methanol: 9
(9.8%, methyl acetate: 0.2%) was recycled to the reactive distillation column 1.

The distillate 6 obtained from the top of the extractive distillation column 5
35 g / h (composition: methyl acetate: 95.5%, methanol: 2.0%, water: 2.5%) is 454 g / h (composition water: 69.6%) of the top distillate of the acetic acid recovery tower 9 , Acetic acid: 3
0.0%) and 109 g / h of water, and placed in a hydrolysis reactor 7 (fixed glass bed having an inner diameter of 4 cm and a height of 80 cm) on a commercially available acidic cation exchange resin Amberlite IR-120.
B (manufactured by Organo Co., Ltd.) in H-form was charged to 1000 ml, and hydrolyzed at 40 ° C.

The reaction mixture from the hydrolysis reactor 7 is supplied to a methyl acetate recovery column 8 for distillation, and a distillate 55
7 g / h (composition: methyl acetate: 71.5%, methanol: 18.5%, water: 10%) circulated to the extractive distillation column 5, and the bottom liquid was supplied to the acetic acid recovery column 9 for distillation. The top distillate of the acetic acid recovery tower 9 was circulated to the hydrolysis reactor 7, and 188 g / h of a 90% aqueous acetic acid solution was recovered from the bottom of the tower.

[Brief description of the drawings]

FIG. 1 is a process diagram specifically showing an example of a transesterification reaction process in a method for producing benzyl alcohol of the present invention.

FIG. 2 is a process chart specifically showing an example of a method for producing benzyl acetate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reactive distillation tower 2 methanol separation tower 3 solids separator 4 alcohol purification tower 5 extractive distillation tower 6 methanol recovery tower 7 hydrolysis reactor 8 methyl acetate recovery tower 9 acetic acid recovery tower 10 oxyacetoxylation reactor 11 gas-liquid separation Container 12 Raw material recovery tower 13 Low boiler removal tower 14 High boiler removal tower 15 Condenser 16 Water removal tower 17 Stabilization tank

Claims (8)

[Claims] 1. A method for producing benzyl alcohol by transesterifying benzyl acetate with methanol in the presence of a basic catalyst, wherein benzyl acetate is supplied from the upper part of the reactive distillation column and methanol is supplied from the lower part of the reactive distillation column. Then, in the presence of a basic catalyst, benzyl acetate and methanol are brought into countercurrent contact reaction with each other, and a top fraction mainly composed of methyl acetate and methanol and a bottom liquid mainly composed of methanol and benzyl alcohol And the bottom liquid of the reactive distillation column is fed to a methanol separation column and distilled, and separated into a top fraction mainly composed of methanol and a bottom liquid mainly composed of benzyl alcohol. Circulating the overhead fraction to the reactive distillation column, supplying the bottom liquid of the methanol separation column to the alcohol purification column and distilling to obtain benzyl alcohol; Degree of benzyl alcohol production. 2. The method according to claim 1, wherein the bottom liquid of the methanol separation column is supplied to a solid separator to remove solids, and then supplied to an alcohol purification column. Method for producing pure benzyl alcohol. 3. The method according to claim 1, wherein the top fraction of the reactive distillation column is supplied to an extractive distillation column for distillation, and then a bottom liquid mainly composed of water and methanol. Is supplied to a methanol recovery tower for distillation, a top fraction mainly composed of methanol is circulated to a reactive distillation column, and a bottom liquid mainly composed of water is circulated to an extraction distillation column. A method for producing high-purity benzyl alcohol. 4. The production method according to claim 3, wherein a top fraction of an extractive distillation column containing water and methyl acetate as main components is supplied to a hydrolysis reactor, and water is added in the presence of an acidic catalyst. After hydrolysis, the product liquid is supplied to a methyl acetate recovery tower for distillation, the top fraction mainly composed of methyl acetate and methanol is circulated to an extraction distillation tower, and the bottom liquid is distilled in an acetic acid recovery tower. And then circulating a top fraction containing water as a main component through a hydrolysis reactor. 5. A benzyl acetate is produced by supplying toluene, acetic acid and oxygen to an oxyacetoxylation reactor packed with a catalyst capable of oxyacetoxylation and reacting the same to produce benzyl acetate. A process for producing high-purity benzyl alcohol, which comprises producing benzyl alcohol by the production method described in any of (1) to (4). 6. The process for producing benzyl acetate according to claim 5, wherein toluene, acetic acid and oxygen are supplied to an oxyacetoxylation reactor and reacted to obtain a reactor effluent. It is supplied to a separator, separated into a gas phase mainly composed of oxygen and nitrogen, and a liquid phase mainly composed of toluene, acetic acid and benzyl acetate, and the liquid phase removed from the gas-liquid separator is used as a raw material. It is fed to the recovery tower and distilled, and separated into a top fraction mainly composed of toluene and acetic acid and a bottom liquid mainly composed of benzyl acetate, and the top fraction of the raw material recovery tower is oxyacetoxylated. Circulated in the reactor, the bottom liquid of the raw material recovery tower was supplied to the low-boiling substance removal tower and distilled to separate into a top liquid mainly composed of benzaldehyde and a bottom liquid mainly composed of benzyl acetate. , The bottom liquid of the low-boiling substance removal tower is fed to the high-boiling substance removing tower and distilled, A process for producing high-purity benzyl alcohol, characterized by obtaining more benzyl acetate. 7. The method according to claim 6, wherein a gas phase portion taken out of the gas-liquid separator is supplied to a condenser, and a liquid phase portion containing toluene, acetic acid, water and benzyl acetate as main components and oxygen And at least part of the liquid phase is supplied to the raw material recovery column, and at least part of the gas phase is circulated to the oxyacetoxylation reactor. Method for producing high-purity benzyl alcohol. 8. The method according to claim 7, wherein the liquid phase portion taken out of the condenser is supplied to a water removal tower and distilled.
A method for producing high-purity benzyl alcohol, comprising removing most of the water and circulating it in an oxyacetoxylation reactor.