JP2684095B2 - Method for producing diisocyanate compound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Field of Application >> The present invention provides a diisocyanate compound by distilling a mixture of a monoisocyanate compound and a diisocyanate compound from each other by distillation in the presence of a high-boiling solvent. This is for obtaining a good yield.

<< Background of Technology >> Isocyanate compounds are industrially useful compounds, and among them, diisocyanate compounds are particularly useful as raw materials for polyurethane.

The diisocyanate compound is industrially produced by the reaction of an amine compound and phosgene.

Although phosgene is a highly selective reactive substance, it is also a highly toxic substance and therefore requires careful handling.

The applicant has previously proposed a method for producing a diisocyanate compound that does not use phosgene (Japanese Patent Application No. 62-31618).
0).

 The outline of the above method is shown below.

As a first step, dimethyl carbonate and an amine compound are reacted using a basic substance such as sodium methylate as a catalyst to synthesize a urethane compound.

Then, as a second step, this urethane compound is added in the form of a methanol solution such as a metal simple substance such as manganese or molybdenum as a catalyst in a high boiling point solvent such as m-terphenyl or dibenzyltoluene, and then thermally decomposed. An isocyanate compound is obtained.

<< Problems to be Solved by the Invention >> The decomposition reaction of the urethane compound occurring in the preceding stage of the step of applying the method of the present invention is elimination of methanol from the urethane bond as described below.

 This proceeds in a sequential reaction.

Usually, a monoisocyanate compound, which is a by-product, is mixed in the diisocyanate compound that is the target product.

The amount of this mixture is the reaction temperature, the raw material urethane compound to be used in the reaction, the corresponding diisocyanate compound produced, the same monoisocyanate compound, the boiling point of the solvent used, the number of stages of the reactive distillation column used, the reflux ratio, the operation. Under practical conditions, the mixed amount of the monoisocyanate compound is on the order of several percent to several tens of percent, although it varies depending on the temperature, pressure and the like.

The diisocyanate compound, which is the target product, has the smallest molecular weight in the above mixture, and as a result, the boiling point is low.

Therefore, when the decomposition reaction is carried out in the reactive distillation column, the product diisocyanate compound is obtained from the top of the column.

As means for increasing the purity of the diisocyanate compound obtained from the reaction system, firstly, there are means such as increasing the reaction conversion rate and increasing the reaction temperature. However, this requires a solvent at a higher temperature and energy consumption. The cost also increases.

In order to remove the monoisocyanate compound from the above mixture to obtain a diisocyanate compound which is a more industrially effective component, a distillation method is generally used.

However, since the isocyanate compound is thermally unstable, if it is simply separated by distillation, polymerization will occur in the reboiler of the distillation column and the yield will deteriorate.

In addition, the polymer blocks the reboiler, making operation impossible.

Therefore, not only the production efficiency is poor, but also it is industrially unpractical.

Under these circumstances, a method for economically producing a diisocyanate compound with a higher yield than an isocyanate compound has been desired, and as a result of intensive investigations by the present inventors, the present invention has been completed.

<< Structure of the Invention >> That is, the present invention relates to "a urethane compound having two urethane bonds in a high-boiling solvent in the presence of at least one metal element selected from the group consisting of manganese, molybdenum, tungsten, and zinc, or in the presence of the metal compound catalyst. In the step of producing a corresponding diisocyanate compound by thermal decomposition under a reduced pressure of up to 700 Torr, the main component is a monoisocyanate compound and a diisocyanate compound corresponding to the urethane compound having two urethane bonds separated from the reaction crude liquid. When separating the mixed solution into a monoisocyanate compound and a corresponding diisocyanate compound, a high boiling point solvent having a boiling point higher than that of the corresponding diisocyanate compound is supplied to the bottom or any stage of the distillation column for separation. A method for producing a diisocyanate compound ".

Hereinafter, the situation when the method for producing a diisocyanate compound of the present invention is carried out will be described in detail with reference to FIG.

In FIG. 1, 1-1 is a distillation column, 2-2 is a condenser for capturing a diisocyanate compound, 3-3 is a reboiler, 4-4 is a tank for storing an isocyanate compound, 5-5 is a high boiling point solvent. Keeping tank, 6-6
And 7-7 are pumps for charging the isocyanate compound and the high boiling point solvent, respectively, and 8-8 is a pump for withdrawing from the reboiler. Arrows indicate the flow direction of the substance in each place.

 In addition, ~ indicates liquid flowing in various places.

For example, when synthesizing isophorone diisocyanate from isophorone diamine and dimethyl carbonate via isophorone dicarbamate, the main names of liquids flowing through each of the following are the liquid names and their approximate contents (% by weight) are as follows.

Isophorone diisocyanate: 95 to 99% (IPDI) Isophorone monoisocyanate: 1 to 5% (IPMI) High boiling point solvent: About 90% Others: About 10% Methanol only IPDI: 99.5 to 100% IPMI: 0 to 0.5% Methanol: Trace amount High boiling point solvent: 90 to 99% Others: 1 to 10% Mixed liquid containing a monoisocyanate compound and a diisocyanate compound as main components, that is, a liquid corresponding to a product liquid resulting from the second-stage thermal decomposition reaction, The mixed liquid of and is supplied to the distillation column 1-1.

The supply stage is arbitrarily determined by the amount of the monoisocyanate compound contained in the isocyanate compound. The high boiling point solvent is continuously supplied to the bottom of the column or to any stage of the distillation column.

The product is obtained by condensing the diisocyanate compound discharged as vapor from the distillation column in the condenser 2-2.

The monoisocyanate compound and the high boiling point solvent are continuously withdrawn from the bottom of each distillation column.

The withdrawn monoisocyanate compound and the high boiling point solvent are continuously supplied to a reactive distillation column for decomposing the urethane compound.

By doing so, the monoisocyanate compound and the diisocyanate compound can be efficiently recovered.

The operating temperature is determined by the physical properties of the isocyanate compound.

The high boiling point solvent used is required to be inert to the isocyanate compound, and can be used by selecting from an aliphatic compound, an aromatic compound, an alkyl compound, an ether compound and the like.

Even if it contains an inert group such as a halogen group, it does not interfere as a heat medium.

Further, it is preferable that the solvent is one that can be easily purified and separated from the diisocyanate compound which is the target product.

The solvent whose boiling point is different from that of the diisocyanate compound is
Purification and separation by distillation are possible and preferred.

A solvent having a boiling point lower than that of the diisocyanate compound distills out together with the diisocyanate compound, which is disadvantageous in terms of practically complicating the process. Therefore, a solvent having a higher boiling point than the diisocyanate compound is preferable. Further, a solvent having a boiling point higher than that of the diisocyanate compound by 10 ° C. or more is particularly preferable because it is easily separated by distillation from the diisocyanate compound.

Preferred solvents include O-terphenyl, m-terphenyl, P-terphenyl, mixed diphenylbenzene, partially hydrogenated triphenyl, dibenzylbenzene, biphenyl, phenyl ether, phenylcyclohexane,
Hexadecane, tetradecane, octadecane, eicosane, benzyl ether, tetramethyl ether, dibenzyltoluene and the like.

A suitable solvent should be selected according to the desired diisocyanate compound, but for example, m-terphenyl or dibenzyltoluene is particularly preferable in the case of producing isophorone diisocyanate.

The isocyanate compound and the solvent may be prepared in advance and supplied to the distillation column.

Further, the number of stages of the distillation column used is selected depending on the physical properties of the isocyanate compound and the solvent.

 This method is effective regardless of the number of stages.

Practically, it can be preferably carried out in a distillation column corresponding to 1 to 100 stages.

Towers with 100 or more plates are not practical because the equipment cost is high.

The mixing ratio of the high-boiling solvent and the diisocyanate compound used is arbitrarily selected from the range of 1/10 to 10/1, preferably 1/2 to 2/1.

If the mixing ratio of the high boiling point solvent is high, the equipment efficiency and thermal efficiency are poor, and if the mixing ratio is low, the effect is small.

<< Effects of the Invention >> The method of the present invention makes it possible to obtain a diisocyanate compound in good yield from a mixture containing a monoisocyanate compound and a diisocyanate compound as main components.

Hereinafter, the present invention will be described in more detail by showing Examples and Comparative Examples.

Comparative Example-1 Isophorone diisocyanate 96.8% (abbreviation: IPD) was measured using a 20-stage Aldershaw tower equipped with 80 ml of reboiler.
I) and isophorone monoisocyanate 3.2% (abbreviation: IPM)
The mixture of I) was continuously distilled.

200g of the mixture of isocyanate compounds at the 15th step from the bottom
When it was supplied at / Hr, the reboiler polymerized around 1 hour and distillation became impossible.

Example 1 As a solvent, 100 g of m-terphenyl was added at the third stage from the bottom.
The operation was performed in the same manner as Comparative Example-1 except that the supply was made at / Hr.

A continuous operation was carried out for 8 hours, but no polymer was observed. IPDI was distilled from the tower top at 190.7 g / Hr.

Further, the solvent containing isophorone monoisocyanate was removed from the bottom of the column so that the liquid surface of the reboiler was constant.

 The yield of IPDI at this time was 98.5%.

Example-2 The procedure of Example-1 was repeated except that partially hydrogenated triphenyl was used as the solvent instead of m-terphenyl,
The following results were obtained.

 The yield of IPDI at this time was 98.6%.

Example-3 The same results were obtained as in Example-1 except that dibenzyltoluene was used as the solvent instead of m-terphenyl, and the following results were obtained.

 The yield of IPDI at this time was 99.0%.

Example-4 The same results were obtained as in Example-1 except that dibenzyltoluene was used as the solvent instead of m-terphenyl, and the following results were obtained. The yield of IPDI at this time was 98.9%.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a situation in which distillation is continuously carried out. 1-1 is a distillation column, 2-2 is a condenser for capturing a diisocyanate compound, 3-3 is a reboiler, 4-4 is a tank for storing an isocyanate compound, 5-5 is a tank for storing a high boiling point solvent, 6 -6 and 7-7 are pumps for charging an isocyanate compound and a high boiling point solvent,
8-8 is a pump for extracting from the reboiler.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/30 B01J 23/30 X 23/34 23/34 X C07B 61/00 300 C07B 61/00 300

Claims (5)

(57) [Claims] 1. A urethane compound having two urethane bonds in a high boiling solvent in the presence of at least one metal selected from the group consisting of manganese, molybdenum, tungsten and zinc or in the presence of a catalyst for the metal compound under a reduced pressure of 1 to 700 Torr. Pyrolyzed,
In the step of producing the corresponding diisocyanate compound, a mixed solution containing a monoisocyanate compound corresponding to the urethane compound having two urethane bonds separated from the reaction crude liquid and a diisocyanate compound as main components is corresponded to the monoisocyanate compound. The method for producing a diisocyanate compound, characterized in that a high boiling point solvent having a boiling point higher than that of the corresponding diisocyanate compound is supplied to the bottom of the distillation column or any stage to separate the diisocyanate compound. 2. The high boiling point solvent is more than a diisocyanate compound.
The method for producing a diisocyanate compound according to claim 1, wherein the solvent has a high boiling point of 10 ° C or higher. 3. A high boiling point solvent is O-terphenyl, m-terphenyl, P-terphenyl, mixed diphenylbenzene, partially hydrogenated triphenyl, dibenzylbenzene, biphenyl, phenyl ether, phenylcyclohexane,
The method for producing a diisocyanate compound according to claim 1, wherein the diisocyanate compound is at least one selected from hexadecane, tetradecane, octadecane, eicosane, benzyl ether, and dibenzyltoluene. 4. The method for producing a diisocyanate compound according to claim 3, wherein the high boiling point solvent is at least one of m-terphenyl and dibenzyltoluene. 5. The method for producing a diisocyanate compound according to claim 1, wherein the catalyst is supplied as a mixed solution of the diisocyanate compound and alcohol.