JPS5848538B2 - Amine recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering organic amines corresponding to isocyanates from a distillation residue obtained as a by-product during the production of organic isocyanates.

In particular, the present invention relates to a method suitable for recovering organic amines from distillation residue having an incyanate content of 1% or less.

Organic incyanates are the main raw materials for polyurethanes and the like, and are usually obtained by phosgenating the corresponding amines.

Depending on the purpose, the phosgenation product may be used as a crude product, but if purification is required, distillation is performed, and at this time a large amount of distillation residue is produced as a by-product.

The chemical structure of this distillation residue is unknown, but absorptions thought to be based on urea bonds and carbodiimide bonds are observed in the infrared absorption spectrum, indicating that it is a polymer with multiple organic residues bonded by these functional groups. It is assumed that there will be.

Therefore, in order to recover amines from incyanate distillation residues, these functional groups may be hydrolyzed to convert them into amino groups.

U.S. Pat. No. 3,331,876 describes a method of hydrolyzing Incyanate distillation residue by adding 1 to 24% (by weight) of caustic soda.
Severe conditions of 0 to 350°C are required, and the internal pressure of the reactor reaches a maximum of 176 kg/ca.

When the urea bond or carbodiimide bond in the incyanate distillation residue undergoes hydrolysis to produce an amine,
At the same time, carbon dioxide is produced.

This carbon dioxide combines with caustic alkali to become carbonate, so if enough caustic alkali is introduced into the system to combine with the carbon dioxide produced, hydrolysis will continue after the caustic alkali is consumed. Therefore, in order to make the process industrially useful, it is presumed that it is necessary to increase the reaction rate by conducting the reaction at a high temperature.

That is, in the above-mentioned U.S. patent method, only a small amount of caustic soda is used as a catalyst for hydrolysis, so carbon dioxide generated as the hydrolysis reaction progresses is discharged outside the system at any time. It is surmised that this was consumed as carbonate, forcing L.Kioi to be heated to higher temperatures and pressures than necessary.

Furthermore, JP-A-50-142501 discloses that the solvent is at least one selected from water, alcohols, and amines, and the catalyst is selected from hydroxides, oxides, and amines of alkali metals or alkali metals. A method is described in which organic amines are recovered by heating at around 100 to 170° C. in the presence of at least one type of organic amine.

Inocyanate usually remains in the isocyanate distillation residue, and the remaining amount varies greatly depending on the method of distillation.

For example, when toluene diisocyanate is distilled using a conventional method, the distillation residue contains several tens of percent toluene diisocyanate, but the method described in JP-A-52-139043, that is, under vacuum, In the case where the distillation residue is continuously supplied to a heating tube located in the distillation tube and inocyanate is further flash-recovered, the content of toluene diisocyanate in the distillation residue is reduced to 1% or less.

The residue obtained by further recovering isocyanate from this ordinary distillation residue (hereinafter referred to as cracks residue).

If an amine is to be recovered from the amine, it must be carried out at a high temperature of at least 180°C or higher, otherwise it will not be decomposed, and in order to recover the amine at a high temperature of 180°C or higher, pressurized conditions are required.

The present inventors have conducted intensive studies on the industrially advantageous hydrolysis method of incyanate distillation residue under pressure and high temperature. As a result, we have discovered that calcium hydroxide is alkali-based in an amount sufficient to absorb the generated carbon dioxide. It was discovered that the presence of the amine as a catalyst and a carbon dioxide gas scavenger allows the reaction to proceed at a relatively low temperature and pressure, and that the amine can be recovered in high yield, thus achieving the first invention of the present invention. .

Next, by allowing calcium hydroxide and caustic alkali to coexist during hydrolysis and adjusting the total amount to be sufficient to absorb the generated carbon dioxide, even under milder conditions. It has been found that sufficient effects can be obtained, and the second invention of the present invention has been achieved.

According to the method of the present invention, isocyanate distillation residue can be hydrolyzed under relatively mild conditions, and amines can be recovered in high yield.

According to the method of the present invention, carbon dioxide generated by hydrolysis is absorbed, so that an increase in internal pressure due to carbon dioxide does not occur.

Therefore, there is no need to provide the reactor with extra pressure resistance, and equipment costs can be reduced.

British Patent No. 795,639 and the above-mentioned US patent specification propose a method of sequentially releasing carbon dioxide out of the system, but the method of the present invention does not require this and the process is simple.

Produced by hydrolysis of isocyanate distillation residue.
Since at least a portion of ymine is dissolved in the aqueous solution, it must be recovered by some method, but according to the method of the present invention, most of the inorganic substances are separated into the solid phase as calcium hydroxide and calcium carbonate. Because it is possible to
There is no fear that large amounts of inorganic substances will remain as residue in the pot even if the Σ-distillation is performed directly.

Incyanate distillation residues to be hydrolyzed in the method of the present invention include, for example, those having the general formula R-NGO (where R is, for example, phenyl, tolyl, xylyl, monochrome phenyl, cyclophenyl, α-naphthyl, β-naphthyl, carbon number 1 to Distillation residue of monoisocyanate represented by the general formula OCN-R'-NCO (representing an organic residue such as alkyl, cyclohexyl, etc. of 12); Phenylene, 2.4
- } IJ lene, 2, 6-tolylene, 1゜5-naphthylene, ■, 4-naphthylene, α, α'-xylylene, 4
・4'-biphenylene, 2,4'-biphenylene, diphenylmethane-4,4'-1, diphenylmethane-2,4
'-, cyphenylmethane-2, 27-, diphenyl ether-4, 4'-, other difunctional aromatic residues, polymethylene chains having 2 to 12 carbon atoms and other difunctional chain residues, 1・There are Ninomiya functional resin cyclic residues such as 4-cyclohexylene.

), toluene-2,4,6-triisocyanate, triphenylmethane-4,4',4'-triisocyanate and other triisocyanates, or these incyanates. There is a distillation residue of a mixture of

According to the method of the present invention, amines can be recovered in high yield not only from such ordinary distillation residues but also from residues after incyanate recovery.

As can be seen from this, there is no restriction on the distillation method applied to the isocyanate distillation residue referred to in the method of the present invention.

The caustic alkali used in the method of the present invention includes sodium hydroxide and potassium hydroxide, and both may be used in combination.

When the amount of carbon dioxide by-product is relatively small, even if an appropriate amount of caustic alkali is used as part of the calcium hydroxide, the yield and solid-liquid separation after the reaction will not be affected.

To carry out the process of the invention, incyanate distillation residue, calcium hydroxide and water are mixed, optionally adding caustic alkali as part of the calcium hydroxide;
It can be heated in a closed container.

The total amount of hydroxide required is determined by the amount of carbon dioxide generated during hydrolysis.

The amount of carbon dioxide generated during hydrolysis is in cyanor)
・It varies depending on the type and quality of the distillation residue, so it is preferable to perform preliminary hydrolysis and actually measure it.

The total amount of hydroxide used may be at least equivalent to this carbon dioxide.

The amount of carbon dioxide generated can also be calculated using the following equations 0) and (2)
It can be estimated from

■ ? However, CCO2) MAX is the maximum value of carbon dioxide generated [CO2], and is the minimum value of carbon dioxide generated, unit: m
ol/? (Incyanato Distillation Residue) The total amount of hydroxide used needs to be equal to or more than [CO2] MIN, but it is not necessary to use more than three times the equivalent to [CO2] MAX.

If the amount of hydroxide used is too small, the amine yield will be low.

Disadvantages such as increased internal pressure occur.

It is not preferable to use more hydroxide than necessary because it does not improve the yield of azeta and also requires post-treatment of a large amount of inorganic material.

The amount of water to be used should be determined taking into account the fluidity of the reactants, but it may be at least twice the weight of calcium hydroxide normally used.

There is no particular upper limit to the amount of water, but as long as it is necessary to separate it from the target amine, it should be kept to the maximum amount.

The reaction temperature is 14. The temperature may be between 0℃ and 280℃, but
For complete recovery from cracks residue, a temperature of 180°C to 260°C is required.

The reaction time is preferably 10 minutes to 20 hours.

The reaction can be carried out either batchwise or continuously.

It is also possible to use the reaction solution containing the alkali metal compound repeatedly; for example, after separating the solid content from the reaction solution, a part of the liquid part is continuously recycled to the reactor, or a batch method is used. In this case, methods such as reusing it as part of the reaction preparation solution can be implemented.

Additionally, the amine in aqueous solution may be recovered by extraction with a solvent before recycling or reuse.

The method for recovering the target amine from the hydrolysis reaction mixture varies depending on the type of amine, but conventional separation methods such as distillation and extraction can be used.

The amine can also be extracted with a convenient solvent for phosgenation,
After dehydration, it may be used as it is in the momme phosgenation step.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 The distillation residue by-produced during the production of 2,4- and 2,6-toluene diisocyanate (mixing ratio so: 20) was further distilled under vacuum to the remaining cracks distillation residue after recovering toluene diisocyanate ( Distillable incyanate content of 1% or less) 801, calcium hydroxide 81.
5S', (12 times the amount of calcium hydroxide when the estimated amount of generated carbon dioxide is calculated by (CO2) MAX in equation (1)) and 1631 water were charged into an electromagnetic stirring stainless steel autoclave. , and stirred at 220°C for 2 hours.

At this time, the internal pressure reached 22k9/crA. 60-70
After cooling to ℃ and discharging the contents, filtering out calcium carbonate by suction f-filtration and evaporating water from the p liquid, distillation was carried out under reduced pressure to obtain a fraction 34.2P with a boiling point of 133 to 7℃/5 mmHg.
I got it.

This fraction was solidified by cooling 1, and analysis using gas chromatography confirmed that it was toluene diamine with a purity of 98% (82% as a 2/4 component and 16% as a 2/6 component).

Example 2 The same distillation residue used in Example 1, 4.0? , 23 g of calcium hydroxide, and 217 g of water were placed in an autoclave and stirred at 260° C. for 2 hours.

At this time, the internal pressure is 4 1. It reached 5 kg/cyA.

The amount of toluenediamine recovered according to the method of Example 1 was 21.0 Da.

Example 3 To a mixture of 401 g of the same distillation residue used in Example 1, 25.8 g of calcium hydroxide, and 217 g of water, 5.41 g of caustic soda, 2.7 g, and 1. 35 g, and 0.689 g were added, and stirred at 220°C for 2 hours. Using the method of Example 1, the amounts of toluenediamine recovered were 20.5 g, 0.689 g,
19.3g, 18.61 and 1731.

Moreover, the yield of toluenediamine when caustic potash 7.62 is used instead of caustic soda is 20. It was Of.

☆☆Example
4 The same distillation residue 81' as used in Example 1, calcium hydroxide 5]. ．． 6? , sodium hydroxide 10.8? and 162.71 was stirred at 220°C for 2 hours.

After cooling to about 70°C and removing the calcium salt, the p-liquid contains 80 g of distillation residue and 51.6' of calcium hydroxide. was added and stirred again at 220°C for 2 hours.

After removing the solid content from the reaction solution and evaporating water from the p solution, toluenediamine 84. ．． OP was collected.

Example 5 80f of the same distillation residue used in Example 1, 51.1' of calcium hydroxide, 10.1' of sodium hydroxide, and 162.7 P of water were charged into an autoclave and stirred at 220°C for 2 hours. did.

The calcium salt was separated from the reaction mixture, and the solution was extracted eight times with 100 ml of O-dichlorobenzene at 60 to 70°C.

After evaporating the water from the 0-dichlorobenzene solution,
It was phosgenated by a conventional method.

From this reaction solution, 32.49 g of toluene diisocyanate was obtained by distillation.

Examples 6-8 Various incyanate distillation residues were hydrolyzed to obtain the respective corresponding amines.

The results are shown in Table 1.

Claims (1)

[Scope of Claims] 1. Calcium hydroxide in an amount sufficient to absorb the entire amount of carbon dioxide generated by hydrolysis as carbonate when hydrolyzing the organic incyanate compound distillation residue to recover the corresponding amino compound. A method for recovering a corresponding amino compound from a distillation residue of an organic incyanate compound, characterized in that the reaction is carried out under pressure at 180°C to 260°C in the presence of a reaction mixture. 2. When recovering the corresponding amino compound by hydrolyzing the organic isocyanate compound distillation residue, calcium hydroxide and caustic alkali are made to coexist, and the total amount of carbon dioxide generated by the hydrolysis is converted into carbonate. Presence of sufficient amount to absorb, under pressure, 180 ° C ~
A method for recovering a corresponding amino compound from an organic isocyanate compound distillation residue, the method being carried out at 260°C.