JPH01203354A - Method for recovering anilines - Google Patents

Abstract

PURPOSE:To recover anilines useful as a synthetic raw material for polyamides, polyurethanes, etc., and synthetic intermediate therefor, etc., by thermally decomposing a condensate of aniline with formaldehyde in the presence of a catalyst. CONSTITUTION:Aniline is condensed with formaldehyde in the presence of an acidic catalyst to provide a condensate, which is then subjected to thermal decomposition reaction in the presence of a catalyst consisting of an aluminum alkoxide compound and/or aluminum phenoxide compound at 150-500 deg.C temperature under 0.001kg/cm<2>-2atm. pressure for 0.1-10hr to afford anilines. The catalyst is used in an amount so as to provide 0.001-0.05 value expressed in terms of number of mol of aluminum constituting the catalyst/number of mol of nitrogen atoms in the raw material condensate. The thermal decomposition reaction can be carried out in the absence of a solvent; however, an aromatic hydroxy compound or alcohols are preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for recovering anilines from a condensate of aniline and formaldehyde.

Methylene dianiline, which is obtained by condensing aniline and formaldehyde in the presence of an acidic catalyst, is used in the synthesis of polyamides and polyurethanes. In particular, 4,4°-methylene dianiline is useful as a synthetic intermediate for 4,4°-methylene diphenyl isocyanate (generally referred to as high-purity MDI), which is useful as a raw material for polyurethane.

However, when this condensation reaction between aniline and formaldehyde is carried out, not only methylene dianiline is produced, but also polymethylene polyphenylamine (PMPPA), which is a polymeric condensate of aniline and formaldehyde, is produced as a by-product. This polymer condensate cannot be used as a raw material for high-purity MDI, and in addition to the 4.4° isomer, methylene dianiline also contains the 2,4° isomer and the 2,2° isomer.
There are various isomers such as 2,4° isomer and 2,2° isomer, which are less useful.

Therefore, if it is possible to effectively recover anilines by decomposing the above-mentioned polymeric clamps and condensates such as less useful isomers, the recovered aniline can be reused in the condensation reaction of methylene dianiline. This is very industrially advantageous.

By the way, conventional methods for recovering aniline from a condensate of aniline and formaldehyde include treating this condensate with mineral acids such as sulfuric acid and hydrochloric acid, or with mineral acids such as AjO and °5iO.
A method of thermal decomposition using an oxide catalyst consisting of 7 is known (Frank J, Weiqert, Ind.
Eng, Chan, Prdod, Res, Dev, Vo
118, No, 3. Among the thermal decomposition products produced by thermal decomposition of the condensate of aniline and formaldehyde, aniline is the most useful. Needless to say, it is necessary to have a high production rate (selectivity) of aniline in the decomposition product.

However, when the condensate of aniline and formaldehyde is thermally decomposed using a mineral acid or oxide catalyst as described above, the production rate (selectivity) of aniline decreases as the decomposition rate of the condensate increases. This results in a tendency to decrease.

Therefore, the method described in the above-mentioned document is an advantageous method for efficiently recovering anilines from the condensate of aniline and formaldehyde, and also for recovering industrially useful aniline with a high selectivity. It cannot be said that it is.

The present invention aims to solve the problems associated with the prior art as described above, and is capable of effectively recovering anilines, especially aniline, from a condensate of aniline and formaldehyde. The purpose is to provide a method.

The method for recovering anilines according to the present invention is characterized by thermally decomposing a condensate of aniline and formaldehyde in the presence of a catalyst consisting of an aluminum alkoxide compound and/or an aluminum phenoxide compound.

According to the method for recovering anilines according to the present invention, anilines can be recovered from the condensate of aniline and formaldehyde at a high recovery rate by thermally decomposing the condensate of aniline and formaldehyde using a specific aluminum compound. Can be done.

In particular, according to the method for recovering anilines according to the present invention, aniline can be recovered with high selectivity from a condensate of aniline and formaldehyde.

The method for recovering anilines according to the present invention will be explained in detail below.

The condensate of aniline and formaldehyde used in the present invention can be obtained by condensing aniline and formaldehyde in the presence of an acidic catalyst. The condensate obtained by this reaction mainly contains a compound represented by the following formula [I]... [I] In the above formula [I], the compound where n is O is methylene dianiline. Further, in polymethylene polyphenylamine, n is 1 or more, and polymethylene polyphenylamine in which n is 1 is contained in a relatively large amount.

In the present invention, a condensate containing the above-mentioned methylene dianiline and polymethylene polyphenylamine is usually used after necessary components have been separated from the condensate. Furthermore, in the present invention, it is also possible to separate polymethylene polyphenylamine from the above condensate and use the separated polymethylene polyphenylamine.

In the method for recovering anilines of the present invention, the above condensate is thermally decomposed in the presence of an aluminum alkoxide compound and/or an aluminum phenoxide compound.

Here, as the aluminum alkoxide compound and the aluminum phenoxide compound, a compound in which 1 to 3 alkoxide groups or phenoxyto groups are bonded to an aluminum atom can be used, but in particular in the present invention, this compound is formed by the following formula [II] Preferably, it is an aluminum compound represented by:

AJ (0-B)3 ... [II] However, in the above formula []I], B represents an aliphatic residue or an aromatic residue, where the aliphatic residue is linear or branched. an aliphatic residue or an alicyclic hydrocarbon residue, and these residues may further have an aromatic substituent; This aromatic ring may have an aliphatic substituent.

Specific examples of aluminum phenoxides represented by the above formula [I] include phenol, cresols,
Mention may be made of compounds obtained by the reaction of metal aluminum with aromatic hydroxy compounds such as alkylphenols (e.g. isopropylphenol and t-butylphenol), halogenated phenols (e.g. chlorophenol and bromophenol) and nitrophenols. can.

Examples of the aluminum alkoxides represented by the above formula [n] include compounds obtained by reacting a primary to tertiary alcohol having about 1 to 10 carbon atoms with metal aluminum.

Examples of aluminum alkoxides that can be used in the present invention include compounds obtained by reacting a secondary or tertiary alcohol with metallic aluminum, such as aluminum isopropoxide, aluminum isobutoxide, aluminum t-butoxide, etc. be able to.

These aluminum phenoxides and aluminum alkoxides such as the aluminum compound represented by the above formula [n] can be used alone or in combination.

In the present invention, the catalyst is preferably a catalyst containing aluminum phenoxides as a main component, and among aluminum phenoxides, aluminum phenoxide is particularly preferred.

In the present invention, as a catalyst, the aluminum compound represented by the above formula [11rl can be used as it is, but in some cases, aluminum compounds such as those dispersed in alcohols or aromatic hydroxy compounds used in synthesizing the above aluminum compounds etc. may be used as catalysts. The amount of aluminum alkoxide compounds and aluminum phenoxide compounds to be used, which are catalysts that can be used by dissolving them, is usually calculated by the number of moles of aluminum constituting the catalyst divided by the number of moles of nitrogen atoms in the raw material condensate. ,o,oooi~0.1
and preferably within the range of 0
．． It is set within the range of 001 to 0.05.

The reaction of thermally decomposing the condensate of alinine and formaldehyde in the presence of a catalyst as described above can be carried out without using a reaction solvent, but aromatic hydroxy compounds such as phenol, ethylene glycol, etc. can be used as the reaction solvent. This can be carried out using alcohols such as, ethers such as tetragram, amines such as trimethylamine, hydrocarbons such as benzene, and the like.

Particularly in the present invention, it is preferable to use the aromatic hydroxy compound or alcohol used in preparing the catalyst as a reaction solvent. In this case, the reaction solvent may be introduced into the reaction system together with the catalyst, or A solvent may be introduced into the reaction system in a state used to dissolve or disperse the condensate of aniline and formaldehyde.

When using a reaction solvent, the concentration of the condensate is 10 to 90
It is preferable to adjust the amount of the reaction solvent used so that it falls within the range of weight %.

The thermal decomposition temperature in the present invention is usually 150 to 500°C
It is particularly preferable to carry out this thermal decomposition reaction at a temperature within the range of 200 to 400°C.

The reaction time varies depending on the amount of condensate used, but is usually 0.1 to 10 hours, preferably 0.2 to 3 hours.
It's time.

The pressure in the present invention is 0.001 kg/- to 2 atm,
Preferably it is 0.01 kg/- to 1 atm.

Since the reaction of thermally decomposing the condensate of aniline and formaldehyde according to the present invention is an equilibrium reaction, the decomposition reaction can be carried out while removing decomposition products such as aniline generated by the thermal decomposition reaction from the reaction system. , the thermal decomposition reaction can be carried out without reducing the thermal decomposition reaction rate of the condensate. By reducing the pressure of the reaction system at this time, decomposition products can be efficiently removed from the reaction system.

The reaction apparatus used when carrying out the reaction according to the present invention is preferably one equipped with a distillation column for separating decomposition products and decomposition intermediates, and if the reaction mode is liquid phase, it is a continuous type. Alternatively, any batch method may be used.

In this way, the condensate of aniline and formaldehyde is efficiently decomposed, and anilines are recovered in high yield. Therefore, useful reaction raw materials can be economically recovered from the condensate of aniline and formaldehyde, which is a by-product with low utility value.

That is, the aniline thus obtained can be used repeatedly for reaction with formaldehyde. In addition, toluidine and xylidine other than aniline are also available.
It can be effectively used as a raw material for the synthesis of other organic compounds.

According to the method for recovering anilines according to the present invention, a specific aluminum compound is used to thermally decompose a condensate of aniline and formaldehyde. Aniline can be recovered with a high recovery rate.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these Examples.

Missing soil ■ Prepare a phenol solution (catalyst solution) of aluminum triphenoxide by heating 20 g of euphenol and 0.5+r of metal aluminum at 160°C for 303 minutes in a nitrogen atmosphere.

0.62 g of this catalyst solution and methylene dianiline 2, Or
(Number of moles of nitrogen in the compound: 20 mmol) is mixed in a flask equipped with a distillation device, and this reaction system (, Q
The pressure was reduced to nnHg and heated using an oil bath at 250°C.

As the reaction progressed, aniline was distilled out together with phenol.

When the reaction was carried out for 30 minutes and the distillate was analyzed, it was confirmed that aniline was produced in an amount of 50% based on the methylene dianiline used [based on the number of moles of nitrogen (hereinafter the same)].

In Example 1, instead of the catalyst solution: a sulfuric acid 0.3
The thermal decomposition reaction was carried out in the same manner except that K was used.

The yield of aniline was 35% based on the methylene dianiline used.

In Example 1, the amount of catalyst solution was 0.50 r, and instead of methylene dianiline, aniline and formaldehyde were reacted in the presence of an HCJ catalyst. amine) to 1.9z (
A thermal decomposition reaction was carried out in the same manner as in Example 1, except that the number of moles of nitrogen in the compound was 18 mmol).

When the above polymethylene polyphenylamine was analyzed by Gel Per chromatography analysis (detection means: 254 nll ultraviolet absorption spectrophotometer), the area percentage of the component in Gel Per chromatography analysis was determined by the formula [
26% of compounds where n=o, 48% of compounds where n=1, 18% of compounds where n=2 and n=3 in [I]
It contained 9% of the compound.

The yield of aniline was 14 mol % based on the number of moles of nitrogen in the polymethylene polyphenylamine used.

Claims (2)

[Claims] (1) A method for recovering anilines, which comprises thermally decomposing a condensate of aniline and formaldehyde in the presence of a catalyst consisting of an aluminum alkoxide compound and/or an aluminum phenoxide compound. (2) The method for recovering anilines according to claim 1, characterized in that the condensate of aniline and formaldehyde is thermally decomposed while at least a part of the anilines produced is removed from the reaction system. .