JPS5835494B2 - Separation method of P-tolualdehyde - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for extracting p- from a mixture containing p-}raldehyde.
-} Raldehyde (hereinafter sometimes abbreviated as PTA)
Concerning how to separate.

More specifically, the present invention relates to a method for acetalizing and separating PTA contained in a mixture containing PTA.

P-}raldehyde (PTA) is itself useful as a soap fragrance agent, and is also industrially useful as a pharmaceutical intermediate or an intermediate for various industrial chemicals, but there is no known method for producing it at low cost. It has not been done.

Therefore, the present inventors investigated various methods of supplying PTA at a low cost, and found that PTA is used as an intermediate product during the production of dimethyl terephthalate, which has been industrially produced in large quantities as a raw material for polyester. We focused on the fact that some of these substances were contained, and conducted research on methods for separating and recovering them.

That is, terephthalic acid is produced in large quantities by oxidizing p-xylene in the liquid phase, but the oxidation reaction mixture contains various oxidation intermediates and impurities in addition to terephthalic acid. It is already known that p-}raldehyde (PTA) is one of the substances.

On the other hand, terephthalic acid is converted to dimethyl terephthalate by esterification with excess methanol, but after removing unreacted methanol from this esterification reaction mixture, a by-product fraction containing methyl benzoate as the main component is obtained. Furthermore, p-methylbenzyl ether, methyl benzoate,
A secondary by-product containing, for example, about 20 percent p-}rualdehyde and the like is recovered.

On the other hand, dimethyl terephthalate can also be obtained by esterifying terephthalic acid obtained by oxidizing p-xylene with methanol as described above, but by oxidizing a mixture of p-xylene and methyl p- p-
} Obtain an oxidized mixture mainly consisting of toluic acid and monomethyl terephthalate, and then esterify this with methanol to obtain an esterified mixture mainly consisting of methyl p-toluate and dimethyl terephthalate, from which dimethyl terephthalate is separated. It can also be obtained by the method of

This method is known as the so-called Pitten-Hercules method.

PTA is also contained in various distillation by-products generated in the Pitten-Hercules process, particularly in the distillation by-products generated when crude dimethyl terephthalate is purified by distillation.

Conventionally, as a method for separating aromatic aldehydes from a mixture containing aromatic aldehydes, a method is known in which, for example, sodium bisulfite is added to form a salt of aromatic aldehyde and sodium bisulfite. (See Japanese Patent Application Laid-open Nos. 50-71640 and 50-71641).

In this method, for example, as shown in the formula below, a mixture containing an aromatic aldehyde is brought into contact with an aqueous solution of sodium hydrogen sulfite, and the resulting adduct of the aromatic aldehyde and sodium hydrogen sulfite is decomposed with alkali or acid. This is a method to separate aromatic aldehydes.

(In each of the above formulas, R represents an aromatic group.) However, the above-mentioned alkali decomposition or acid decomposition methods are not preferred in terms of reaction operation because they use large amounts of dangerous vaporizing agents such as acids and alkalis.

Furthermore, it cannot be said to be an economically preferable method since all of the addition reaction components and the sodium bisulfite, acid or alkali used in the decomposition reaction are consumed.

Furthermore, SO2 produced during acid decomposition worsens the working environment.
Furthermore, a large amount of cost is required to dispose of the by-product Glauber's salt.

On the other hand, a method is also known in which hydrogen cyanide is used instead of sodium bisulfite and decomposed with an alkali, but this method cannot be said to be industrially advantageous either, like the above-mentioned known method.

The present inventors conducted research on a method for separating PTA from a mixture containing PTA using a method that does not have the disadvantages of the above-mentioned known methods, and as a result, they found that PTA can be easily separated by acetalizing it with alcohol. Heading This is what has led to the present invention.

Specifically, the present invention involves contacting a mixture containing p-)raldehyde (PTA) with an alcohol, acetalizing the p-)raldehyde (PTA) in the mixture, and then extracting p-)raldehyde from the acetalized mixture. p-)raldehyde (PTA) from said mixture, characterized in that the acetal of (PTA) is separated and then hydrolyzed to obtain p-)raldehyde (PTA).
This is a separation method for PTA).

According to the present invention, there is no disadvantage of the conventional method of using a large amount of a reagent such as sodium hydrogen sulfite in an equimolar amount to the aldehyde group, and there is no need to use large amounts of acids or alkalis. Since no SO2 is generated, PTA can be separated advantageously.

In addition, p-)raldehyde (PTA) forms acetals with alnur, especially lower alcohols with 2 or more carbon atoms, making it difficult to separate PTA by conventional distillation.
The difference in vapor pressure with methyl benzyl ether, methyl benzoate, methyl p-)ruylate and other mixtures becomes large, and PTA can be easily separated as acetal by a simple distillation operation under reduced pressure.

By hydrolyzing the separated acetal in the presence of a catalytic amount of acid, extremely high purity PTA can be easily obtained.

“PTA-containing mixture” targeted in the present invention
As long as it contains PTA, its origin, content, etc. are not particularly limited, but as mentioned above, various mixtures generated during the production of dimethyl terephthalate are particularly advantageous.

It is especially advantageous to use the distillation concentrate generated during the distillation purification of the crude dimethyl terephthalate obtained in the Pitten-Vercules process.

In the method of the present invention, methyl orthoformate, ethyl orthoformate,
Although it goes without saying that an acetalizing agent such as methyl orthoacetate and ethyl orthoacetate can be used, it is industrially more advantageous to carry out the acetalization directly using a general alcohol.

As such alcohols, aliphatic, alicyclic or aromatic monoalcohols having 1 to 20 carbon atoms are generally preferably used.

Among these, preferable alcohols have 1-carbon atoms.
20 aliphatic monoalcohols, particularly preferably 2 carbon atoms
-10 saturated and unsaturated aliphatic monoalcohols, especially saturated aliphatic monoalcohols having 2 to 10 carbon atoms, are preferred.

The amount of such alcohol is not particularly limited, but is generally 1 mol or more, preferably 2 mol or more, particularly preferably 2.5 mol or more per 1 mol of PTA contained in the mixture.

On the other hand, the upper limit of the alcohol used is not particularly limited, but generally 50
Within mol, particularly preferably within 20 mol, if desired 1
Even if the amount is less than 0 mol, the reaction can proceed sufficiently.

The acetalization reaction of the present invention is generally preferably carried out in the presence of a catalyst.

As such a catalyst, generally an acidic catalyst or a strong acid/weakly basic catalyst is used.

Such catalysts include perchloric acid, chloric acid, sulfuric acid, sulfurous acid,
Inorganic acids such as nitric acid, phosphoric acid, hydrochloric acid, multilayer phosphoric acid, hypophosphorous acid, and butyl phosphate, and their acid esters dimethanesulfonic acid, ethanesulfonic acid, furopanesulfonic acid, decanesulfonic acid, pengansulfone Lp -) Organic sulfonic acids represented by luenesulfonic acid, etc.; or organic carboxylic acids such as oxalic acid; strong acid weak basic salts such as dimethylamine p-toluenesulfonic acid ester ammonia sulfate; diethylamine p-toluenesulfonic acid ester; Ion exchange resins exhibiting acidity such as Amberlyst 15 and Amberlyte IR-120, solid acids such as alumina, silica, alumina, Amberlite, silica-magnesia, silica-zimania, and polyphosphoric acid can be used.

PTA1 in the starting mixture of these acids and strong acid weak basic salts
The amount used in terms of moles is generally 10-'-10 mol, preferably 10-5 to 1 mol, particularly preferably 5 x 10
~0.5 mole or less.

The acetalization can be carried out without removing water generated during the reaction, but it is generally preferable to carry out the reaction by removing water using an azeotrope or a dehydrating agent.

Advantageously, such an entrainer also serves as the reaction solvent.

Such substances include butane, pentane, hexane,
Aliphatic hydrocarbons such as heptane and octane, alicyclic hydrocarbons such as dichlorobutane, cyclopenkune, cyclohexane, and methylhexane; aromatics such as benzene, toluene, 0-xylene, m-xylene, p-xylene, mixed xylenes, ethylbenzene, punidocumene, etc. Group hydrocarbons: esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, methyl propionate, ethyl propionate, methyl butyrate, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, siftyl ether , ethers such as tetrahydrofuran:
Monochloromethane, dichloromethitane, chloroform,
Monochrome ethane, dichrome ethane, clohabenzene,
Examples include halogenated hydrocarbons such as chlorocyclohexane.

Among the above, hydrocarbon solvents and entrainers are particularly preferred.

When such solvents and entrainers are used, they are usually used in amounts of from 100 parts by weight to 1 part by weight of the starting mixture, with a range of 1 to 20 parts by weight being generally preferred.

Thus, acetalization can be advantageously carried out by using starting materials, solvents and catalysts in amounts within the ranges described above, and by dehydrating the reaction system.

In that case, it is preferable to set the reaction temperature and reaction time to appropriate conditions.

That is, a temperature of generally above room temperature, preferably above 30°C, particularly preferably above 40°C is used.

Although there is no particular upper limit to the reaction temperature, generally 400°C or less, usually 300°C or less, is preferably used from an industrial standpoint.

It may be advantageous if the reaction temperature in the method of the present invention is set to the azeotropic point of the azeotropic system with water as a solvent at normal pressure.

Furthermore, the reaction pressure can be normal pressure, reduced pressure, or increased pressure.

The reaction time varies depending on the temperature and pressure, but is generally 1 minute to 100 hours, preferably 5 minutes to 10 hours.

Acetals synthesized in the above manner can be produced at reduced pressure, normal pressure,
The acetal contained in the F solution can be separated by distillation under pressure, or after other substances are filtered out, the acetal contained in the F liquid can be separated by distillation or filtering.

The acetal separated by the method of the present invention is hydrolyzed with water in the absence or presence of an acid catalyst to regenerate p-tolualdehyde as in step 4).

(R: Hydrocarbon Residue) However, it is generally preferable to carry out the hydrolysis in the presence of an acid catalyst.

Such acid catalysts include chloric acid, peroxyacid, periodic acid,
Iodic acid, sulfuric acid, chloric acid, hydrogen chloride, hydrogen bromide, hydrochloric acid,
Inorganic acids such as nitric acid, phosphoric acid, soy phosphoric acid, hypophosphorous acid, butyl phosphate, and their acid esters: methanesulfonic acid, ethanesulfonic acid, furopanesulfonic acid, decanesulfonic acid, benzenesulfone i, p-toluene Organic sulfonic acids represented by sulfonic acid, etc.; or carboxylic acids such as carbonic acid, oxalic acid, phthalic acid, acetic acid, etc. are used.

By using such acid catalysts, the hydrolysis of acetal proceeds rapidly in a short period of time, and these acid catalysts are generally used in an amount of 10@4 mol or more, preferably 10@-3 mol or more, per 1 mol of acetal.

Particularly preferably, it is 102-[E-L or more.

There is no particular upper limit to the amount of the acid catalyst, but from an industrial standpoint it is 10 mol or less, particularly preferably 1 mol or less.

The amount of water used in the hydrolysis reaction is not particularly limited, but acetate is usually used.

Furthermore, the hydrolysis reaction is carried out at Oo to 400°C, preferably at 2
It can be carried out at a temperature range of 0°C to 300°C, particularly preferably 30°C to 250°C.

The reaction time varies depending on the reaction temperature, but is generally in the range of 1 second to 100 hours, preferably 10 seconds to 10 hours.

Note that the hydrolysis reaction can be carried out at normal pressure, increased pressure, or reduced pressure.

The reaction can be carried out in a non-oxidizing atmosphere such as helium, argon, neon nitrogen, etc. to obtain a higher purity PTA, but it can also be carried out in an atmosphere such as air.

The present invention will be described in detail below with reference to Examples.

In the examples, parts are parts by weight unless otherwise specified.

Example 1 (Acetalization) Terephthalic acid was oxidized to a large extent by oxidizing p-xylene and p-)ruyl, methyl acid with molecular oxygen or molecular oxygen-containing gas in the presence of a metal salt catalyst, and then esterifying with methanol. In the industrial production method, p-)raldehyde is produced as an aromatic aldehyde from a by-product mainly composed of methyl benzoate, which is inevitably produced as a by-product.
The secondary by-product (hereinafter abbreviated as raw material A) containing % by weight is replaced.

The composition of this product is shown in Table 1. 173 parts of raw material A containing
151 parts of n-propyl alcohol and 0.016 parts of p-)luenesulfonic acid were added to a 1,000 volume part glass Mitsuro flask, and after first purging with nitrogen, the internal temperature was 85-
At 87°C, while adding 250 cc of benzene over about 1 hour, 1 oooc of benzene is azeotroped by reflux.
I looked at c within an hour.

Thereafter, reflux and dehydration stirring was performed for 2 hours.

Thereafter, the reaction mixture was cooled, 3 parts of sodium carbonate was added, and vacuum distillation was carried out using a rectifier equipped with a Widmer rectifier to obtain dipropyl acetal of p-)raldehyde (82°C/ 1 mmHg) 34 parts were obtained.

This corresponds to conversion of 42% of the p-)raldehyde in raw material A and a selectivity of acetal of 87%.

Example 2 (Acetalization) In Example 1, n-propyl alcohol was replaced with
The reaction was carried out in the same manner as in Example 1 except that 186 parts of -butanol was used, and 66% of p-)raldehyde was converted, with a selectivity of 91% (mol) to acetal. Dibutyl acetal (111℃/2miHg
) 63 copies were changed.

Examples 3 to 10 (Hydrolysis reaction) The acetal obtained as in Examples 1 and 2 was charged in a ratio of 0.2 parts and water, and then treated with an acid catalyst and an acid catalyst in a nitrogen atmosphere.
When the acetal was hydrolyzed by changing the reaction temperature and reaction time, p-tolualdehyde was obtained with the results shown in Table 2.

Claims (1)

[Claims] 1. A mixture containing p-tolualdehyde is brought into contact with alcohol to acetalize p-)raldehyde in the mixture, and then the acetal of p-)raldehyde is separated from the acetalized mixture. , and then hydrolyzing the same to obtain p-)raldehyde. 2. A patented method for separating p-)raldehyde, characterized in that the acetal of p-)raldehyde is separated from the acetalization mixture by distillation.