JPH0649016A - Device and method continuously producing isocyanate compound - Google Patents

Abstract

PURPOSE:To continuously produce an isocyanate compound by thermally decomposing a carbamic ester at the boiling point of an inert solvent. CONSTITUTION:A device for production is equipped with means 22 and 23 which return an isocyanate compound as a main formed product from a distillation column 6 for removing a fraction consisting essentially of an alcohol compound and a recycling solvent to at least one zone except a column top zone of a column type reactor 4. In a method for production, the isocyanate compound and the solvent are returned from the distillation column 6 to at least one zone except the column top zone of the column type reactor 4. Since main reaction is promoted and reverse reaction and side reactions are suppressed, an isocyanate can be produced in high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for continuously producing isocyanate compounds, and more particularly to an apparatus and method for producing aromatic isocyanates by thermal decomposition reaction of aromatic carbamic acid esters.

[0002]

2. Description of the Related Art As a method for producing an isocyanate, which is a raw material for urethane and the like, many researches have recently been made on a production method which is an alternative to the phosgene method. Above all, various methods of thermally decomposing via a carbamate, then condensing this, have been proposed. This thermal decomposition reaction is an equilibrium reaction represented by the following formula (1), and a carbamate (urethane)
Is decomposed into isocyanate and alcohol, and one decomposition product, isocyanate, is recovered as the target product.

[0003]

[Chemical 1]

In the equilibrium reaction of the above formula (1), the other decomposition product of alcohol, which is formed together with the isocyanate, is rapidly removed out of the system to prevent the reverse reaction of urethane formation reaction, The reaction rate to the target product, isocyanate, can be made close to 100%. When this reversible thermal decomposition reaction is carried out in the liquid phase, the method of effectively extracting alcohol from the product to the outside of the system can be classified into the following two methods. That is, a method of introducing an inert gas and entraining it in an alcohol to guide it out of the system (for example, JP-A-51-29445 and JP-A-60-237058).
No. JP-A-2-250857) and a method of reacting at the boiling point of a solvent to evaporate alcohol together with the solvent out of the system (for example, JP-A-57-123159, JP-A-57-21356,
JP-B-61-13463, JP-A-63-150255, JP-A-1-2072
No. 61 publications, etc.).

Each of the methods described in the above-mentioned publications relating to the above-mentioned method of carrying out the thermal decomposition reaction at the boiling point of the solvent is such that the decomposition reaction is carried out rapidly by using a batch reactor to efficiently extract alcohol out of the system. is there. However, when the above-mentioned thermal decomposition reaction is continuously carried out industrially, the reactivity of the produced isocyanate is high, so that the isocyanates react with each other or the by-products with the intermediate product. However, the by-product (high-boiling substance) significantly deteriorates the quality of the product. Furthermore, since the solvent is distilled off by evaporation, the substrate concentration inside the reactor is increased, side reactions are promoted, and undesired reactions such as coking occur.

In order to deal with these problems, it is considered to use a device as shown in FIG. 2, for example, which is described in Japanese Patent Laid-Open No. 60-231640 (Japanese Patent Publication No. 3-5386). . That is, the carbamic acid ester and the solvent from the raw material container 1 are inserted into the packed tower type reactor 4 from the pipe 3 by the pump 2, and the thermal decomposition reaction is carried out in the reaction tower 4 at the boiling point of the solvent. Subsequently, a mixture of the reaction product of isocyanate, alcohol and solvent is introduced from the top of the reaction column 4 to the distillation column 6 via the pipe 5. In the distillation tower 6, the alcohol content is sent from the pipe 7 to the alcohol condensing tower 8 to remove the alcohol content from the reaction system. On the other hand, all of the isocyanate and the solvent are returned from the pipe 9 to the top of the reaction tower 4, or a part thereof is returned from the pipe 9 to the top of the reaction tower 4. The pressure inside the system is adjusted by the pressure gauge 11 and the pressure holding valve 12, and the reaction tower 4 and the alcohol condensing tower 8 are controlled.
Sampling tubes 13 and 14 are provided in the lower part of each.
In this way, the alcohol can be removed from the distillation column 6 provided at the upper part of the reactor 4 to the outside of the system, the solvent can be recycled into the system, and the increase of the substrate concentration inside the reaction column 4 can be prevented.

[0007]

However, even in the above method using the apparatus shown in FIG. 2, the evaporation amount of the solvent is cumulatively increased as it goes to the lower part of the reaction tower 4, and the amount of the solvent in the reaction system is increased. As it decreases, the concentration of product isocyanate and alcohol increases relatively. Therefore, in the lower part of the reaction tower 4, the reverse reaction and the side reaction between the product and the intermediate are promoted, and the undesirable reaction such as the generation of the by-product and coking is promoted, which lowers the isocyanate yield. It becomes a factor to cause. Furthermore, returning a large amount of the solvent to be recycled to one place such as the upper portion of the reaction tower 4 at once is not preferable because it may disturb the operation of the reaction tower 4 such as flooding.

The present inventor, as a result of extensive studies on a method for solving the above-mentioned problems, led the vapor distilled from the reaction column to a distillation column provided outside the reaction column, and removed the alcohol component from the top of the distillation column to the outside of the system. When the solvent (and isocyanate) distilled out from the bottom of the distillation tower is refluxed to the reaction tower, the recycled solvent is returned to one place (especially lower part) other than the top of the reaction tower, or the reaction tower By dividing and returning the recycled solvent (and isocyanate) to two or more arbitrary areas other than the top of the column, it is possible to accelerate the forward reaction and suppress the undesired reverse reaction and side reaction. It was found that the thermal decomposition reaction can proceed at a higher conversion rate and a higher selectivity. The present invention is based on these findings.

[0009]

SUMMARY OF THE INVENTION Therefore, the present invention provides
(1) a tower reactor capable of continuously performing a thermal decomposition reaction of a carbamic acid ester compound at the boiling point of an inert solvent, (2) a distillation tower connected to the tower reactor, (3)
Means capable of sending an isocyanate compound, an alcohol compound and a solvent from the tower reactor to the distillation column, and (4) a fraction containing an alcohol compound as a main component can be removed from the distillation column out of the system. And a means for continuously producing an isocyanate compound,
A means for returning at least a part of a fraction containing an isocyanate compound and a solvent as a main component from the distillation column to at least one region other than the top region of the column reactor, Of continuous manufacturing equipment. Furthermore, the present invention is a method for continuously producing an isocyanate compound by thermally decomposing a carbamic acid ester compound at a boiling point of an inert solvent using a tower reactor, an isocyanate compound from the tower reactor, An alcohol compound and a solvent are introduced into a distillation column that communicates with the tower reactor, a fraction containing an alcohol compound as a main component is removed from the distillation column to the outside of the system, and a fraction containing an isocyanate compound and a solvent as a main component is removed. It also relates to a continuous process for the production of isocyanate compounds, characterized in that at least one part is returned from the distillation column to at least one region other than the top region of the column reactor. The present invention preferably continuously produces an aromatic isocyanate compound (in particular, an aromatic polyisocyanate compound) by thermal decomposition of an aromatic carbamic acid ester compound (in particular, an aromatic polycarbamic acid ester compound). .

The present invention will be specifically described below with reference to FIG. The device shown in FIG. 1 is an example of a device that can be used when the present invention is implemented, and each element having the same reference numeral as in FIG. 2 is an element having the same or similar action. The device of the present invention shown in FIG. 1 is provided with an upper pipe 21, an intermediate pipe 22, and a lower pipe 23 in place of the pipe 9 in the conventional device shown in FIG. Intermediate valve 3
2 and has a lower valve 33. That is,
The thermal decomposition reaction of the carbamic acid ester compound is continuously carried out in the packed tower type reactor 4 at the boiling point of the solvent, and the isocyanate compound and the alcohol compound which are reaction products and the mixture of the solvent are discharged from the top of the reaction tower 4. Leading to the distillation column 6,
The total alcohol content is sent to the alcohol condensing tower 8 to remove the alcohol content from the reaction system, and the isocyanate compound and the solvent may either be returned to the reaction tower 4 or a part thereof may be returned to the reaction tower 4 and the rest may be drained. The point of taking out from the system 10 is the same as the method shown in FIG. But,
In the present invention, all or part of the isocyanate compound and the solvent is returned to at least one region other than the top region of the reaction column 4.

In the embodiment shown in FIG. 1, an upper pipe 21 for returning to the top region of the reaction tower 4 and two pipes 22 and 23 for returning to the middle and lower regions are provided. The upper pipe 21 for returning to the region may not be provided, and only one pipe or a plurality of pipes for returning to the region other than the tower top region may be provided. Further, it is possible to arrange a relatively large number of pipes in advance, provide valves in the middle of each of these pipes, and actually open or close each valve to increase or decrease the number of pipes or change the region for returning the recycled solvent. Further, the opening ratio of the valve can be adjusted to change the distribution ratio of returning to each region. The opening and closing of the valve and the adjustment of the degree of opening may be fixed for each operation or may be changed during the operation. The reaction rate can be improved by appropriately combining these valve adjustments with the adjustment of the reaction conditions (reaction temperature, concentration, etc.) in the reaction tower 4.

By adjusting the valve 16 provided in the drain 10, it is possible to return all of the isocyanate compound and the solvent to the reaction tower 4, or to return a part thereof to the reaction tower 4 and take the rest out of the system from the drain 10. it can. The amount returned to the reaction tower 4 is appropriately selected depending on the operating conditions in the reaction tower 4.
Further, the amount of distillate from the top of the distillation column 6 can be changed by adjusting the temperature condition of the distillation column 6.

Compared with the conventional method, the present invention is different from the conventional method only in the aspect of solvent recycling from the distillation column to the reaction column, and is otherwise substantially the same as the conventional method. Therefore, it is used in the present invention. Carbamic acid ester compound, inert solvent, reaction column, distillation column, reaction conditions, by-product removal method,
The method for obtaining the product may be the same as the conventional one. If desired, an inert gas such as nitrogen or helium, or vapor of a solvent used in the reaction may be introduced into the reactor as a carrier gas.

Although the present invention has been described with reference to the apparatus and method for producing an isocyanate compound by the continuous thermal decomposition reaction of a carbamic acid ester compound, the present invention is not limited to the specific thermal decomposition reaction of a starting compound. It is obvious that it can be generally applied to the reversible thermal decomposition reaction described below.

[0015]

[Chemical 2]

[0016]

EXAMPLES The present invention will be described in more detail below with reference to examples, but these do not limit the scope of the present invention. In the following examples, urethane conversion and isocyanate selectivity were determined as follows. First, the number of moles of urethane group and isocyanate group was calculated as follows. Here, the number of moles of methylene diphenyl dicarbamate, monoisocyanate carbamate and methylene diphenyl diisocyanate are [MDU] and [M
IC] and [MDI]. Number of moles of urethane group = 2 × [MDU] + [MIC] Number of moles of isocyanate group = [MIC] + 2 × [MD
I] Subsequently, the urethane conversion rate and the isocyanate selectivity were calculated according to the following definitions from the number of moles of the urethane group and the isocyanate group. Conversion rate of urethane group = [(charged urethane group-remaining urethane group) / charged urethane group] x 100 Isocyanate group selectivity = (generated isocyanate group /
Converted urethane group) x 100

Example 1 A test was conducted using a packed tower reactor shown in FIG. The reaction tower 4 was made of stainless steel having a diameter of 2.8 cm and a height of 1 m, and was filled with Helipack No. 2 (made by Tokyo Special Wire Mesh) inside. As the distillation column 6, a stainless steel cylinder having an inner diameter of 3 cm and a height of 15 cm is used, and a pipe 2 for returning the condensed solvent to the reaction column 4 is provided below the distillation column 6.
1, 22 and 23 are installed at the upper part of the reaction tower 4 and at positions of 30 cm and 60 cm respectively from the upper part, and valves 31, 32 and 33 are provided on each pipe, and opening and closing of the pipe and flow rate adjustment by these operations. I made it possible. The valves 31 and 33 were opened, the valve 32 was closed, and the reflux liquid was allowed to return to the top of the reaction column and two points 60 cm from the top of the column.

First, o-dichlorobenzene (hereinafter referred to as ODCB) as a solvent was supplied from the raw material container 1 to the reaction column 4 at a rate of 5 ml / min, and heated by an external heater (not shown) at about 200 W for reaction. Keep the temperature in the tower at about 280 ℃,
Further, the pressure inside the reaction tower was kept at about 6 kg / cm ² by the pressure holding valve 12, and the solvent was refluxed for about 30 minutes. At this time, by adjusting the openings of the valves 31 and 33, the liquid flow rate returning to the reaction tower 4 through the pipes 21 and 23 is about 15 respectively.
It was set to ml / min. The distillation column 6 installed on the upper part of the reaction column 4 was air-cooled at room temperature so that the amount of effluent from the upper part of the distillation column 6 was within 1 ml / min. After the temperature distribution in the reaction tower 4 becomes constant, the feed liquid from the raw material container 1 is
Methylene diphenylene dicarbamate (MDU) 3.7
The solution was switched to an ODCB solution containing wt%, and the solution was supplied to the reaction tower 4 at an amount of 5 ml / min to start the thermal decomposition reaction.

After 20 minutes from the start of the reaction, the reaction tower 4
After the temperature distribution inside was stabilized, a sample was taken from the sampling tube 13 provided in the lower part of the reaction tower 4, and the product was analyzed by liquid chromatography (GPC). As a result, urethane conversion is 100% and isocyanate selectivity is 9
It was 9.7%.

Example 2 The apparatus shown in FIG. 1 was used as in Example 1, except that the valve 3
1, 32, 33 are all opened, and the reflux liquid is the top of the reaction tower 4,
About 10 ml at each of 30 cm and 60 cm from the top of the tower
I tried to return evenly every minute. The distillation column 6 was air-cooled at room temperature, and the amount of effluent from the top of the distillation column 6 at this time was about 1 ml.
/ Min. Then, the same operation as in Example 1 is performed,
When a sample was taken and analyzed, the urethane conversion rate was 99.
It was 3% and the isocyanate selectivity was 99.6%.

Example 3 The apparatus shown in FIG. 1 was used as in Example 1, except that the valve 3 was used.
2 is completely closed and the opening degree of the valves 31 and 33 is adjusted,
The reflux liquid was made to return to the top of the reaction tower 4 and two points 60 cm from the top of the reaction tower 4 at different amounts of about 10 ml / min and about 20 ml / min, respectively. The distillation column 6 was air-cooled so that the amount of distillate from the top of the distillation column 6 was about 1 ml / min. Then, the same operation as in Example 1 was performed, and a sample was collected and analyzed, and it was found that the urethane conversion was 100% and the isocyanate selectivity was 99.2%.

Example 4 The apparatus shown in FIG. 1 was used as in Example 1, except that the valve 3
2 is completely closed and the opening degree of the valves 31 and 33 is adjusted,
The reflux liquid was made to return to the top of the reaction tower 4 and two points 60 cm from the top of the reaction tower at a rate of about 12 ml / min each. The distillation column 6 was kept warm with glass wool so that the amount of distillate from the top of the distillation column 6 would be 5 ml / min. Then, the same operation as in Example 1 was performed, and a sample was collected and analyzed. As a result, the urethane conversion was 100% and the isocyanate selectivity was 9%.
It was 9.0%.

Comparative Example 1 Using the apparatus shown in FIG. 1 used in Examples 1 to 4, the distillation column 6 was kept at room temperature, only the valve 31 was opened, and the valve 3 was used.
2, 33 were completely closed, and the reflux liquid was returned only to the top of the reaction column 4 (that is, the same operation as that by the apparatus shown in FIG. 2 was performed). At this time, the flow rate of the liquid refluxed was 30 ml / min.
Met. Further, the distillation column 6 was air-cooled, and the amount of effluent from the top of the distillation column 6 at this time was about 1 ml / min. Then, the same operation as in Example 1 was performed, and a sample was collected and analyzed, and it was found that the urethane conversion was 95.8% and the isocyanate selectivity was 99.0%.

[0024]

INDUSTRIAL APPLICABILITY In the present invention, the recycled solvent from the distillation column is introduced into a region other than the top column of the reaction column, that is, in the middle or lower stage.
Depending on the case, it is appropriately distributed and returned, so that the decrease in the amount of solvent in the lower part of the reaction column is eliminated, the positive reaction from the carbamic acid ester compound to the isocyanate compound is promoted, and the reverse reaction from the isocyanate compound etc. to the carbamic acid ester compound is Side reactions, such as between isocyanate compounds, can be suppressed, and the isocyanate compound can be produced in high yield.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a device of the present invention.

FIG. 2 is an explanatory view schematically showing a device according to a conventional method.

[Explanation of symbols]

 1 Raw Material Container 4 Reaction Tower 6 Distillation Tower 8 Alcohol Condenser 21, 22, 23 Pipe 31, 32, 33 Valve

Front Page Continuation (72) Inventor Masatsugu Mizuguchi Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Tube Co., Ltd. (72) Inventor Tetsuo Yatani Marunouchi 1-2-2 Nihon Steel Pipe Co., Ltd. Company (72) Inventor Hirotsugu Tsuchiya 1-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Katsunori Fujimura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (2)

[Claims] 1. A tower reactor capable of continuously carrying out a thermal decomposition reaction of a carbamic acid ester compound at a boiling point of an inert solvent, and (2) a distillation tower connected to the tower reactor. (3) Means capable of sending an isocyanate compound, an alcohol compound and a solvent from the tower reactor to the distillation tower, and (4) a fraction containing an alcohol compound as a main component from the distillation tower out of the system. In the continuous apparatus for producing an isocyanate compound having means capable of removing, at least a part of a fraction containing the isocyanate compound and a solvent as a main component from the distillation column except for the top region of the column reactor. A continuous manufacturing device as described above, characterized in that it comprises means capable of returning to at least one area. 2. A method for continuously producing an isocyanate compound by thermally decomposing a carbamic acid ester compound at the boiling point of an inert solvent using a tower reactor, wherein an isocyanate compound and an alcohol are produced from the tower reactor. The compound and the solvent are introduced into a distillation column that communicates with the column-type reactor, a fraction containing an alcohol compound as a main component is removed from the distillation column to the outside of the system, and at least a fraction containing an isocyanate compound and a solvent as a main component is removed. A continuous process for producing an isocyanate compound, characterized in that 1 part is returned from the distillation column to at least one region other than the top region of the column reactor.