JPH04253951A - Thermal decomposition of carbamic acid ester - Google Patents

Abstract

PURPOSE:To operate a reactor with an extremely small amount of polymer attached to the reactor in high yield and in high selectivity stably for a long period of time in manufacturing an isocyanate by thermally decomposing a carbamic acid ester. CONSTITUTION:In a method for decomposing a carbamic ester, (a) a reaction part for thermally decomposing mainly the carbamic acid ester and (b) an evaporation part for mainly vaporizing at least one component of an isocyanate and an organic hydroxyl compound mainly formed by the thermal decomposition, from a liquid phase are provided. When the carbamic acid ester is decomposed while circulating a liquid phase component between the reaction part and the evaporation part, the decomposition is carried out while separating a solid content floating in the liquid phase component.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for continuously producing isocyanates by thermal decomposition of carbamate esters.

0002

[Prior Art] It has been known for a long time that isocyanates and hydroxyl compounds can be obtained by thermal decomposition of carbamate esters (for example, H. Schiff, B.
er. , 3, 635 (1870); A. W. Hoffm
ann, Ber. , 3, 653 (1870)), the basic reaction of which is illustrated by the following equation. R(NHCO
OR')n → R(NCO)n + n R'OH or (R'NHCOO)nR → n R'NCO + R
(OH)n (where R is an n-valent organic residue, R' is a monovalent organic residue, and n is an integer of 1 or more.) The thermal decomposition reaction represented by the above general formula is reversible. The equilibrium is biased towards the carbamate ester on the left side on the low temperature side,
At high temperatures, isocyanates and hydroxyl compounds are favored.

[0003] As described above, the thermal decomposition reaction of carbamate esters requires severe reaction conditions, such as being carried out at high temperatures, and various irreversible side reactions occur simultaneously. As a side reaction, the above-mentioned H. Schiff's literature and E. Dyer and G. C. W
right research (J. Am. Chem. Soc., 8
1, 2138 (1959)), for example, the production of substituted ureas, biurets, carbodiimides, isocyanurates, etc. These side reactions not only cause a decrease in the yield and selectivity of the target isocyanate, but also cause the production of high molecular weight products, especially in the production of polyisocyanate.
In some cases, the precipitation of solids may cause problems such as blockage of the reactor, making long-term operation difficult.

Most of the undesirable side reactions occur on the high temperature side.
In addition, as the reaction time increases and the time that the produced isocyanate is in contact with each component of the reaction mixture increases, it tends to increase. Various methods have been proposed for suppressing the formation of undesirable by-products during thermal decomposition of carbamate esters and obtaining good isocyanate yields.

One of the methods is to reduce the thermal load by using a catalyst, for example, as disclosed in US Pat. No. 271,359.
No. 1, No. 2692275, No. 2727020,
JP-A-54-88201 describes a method for producing isocyanates by thermally decomposing carbamate esters in the presence of a basic catalyst. however,
It has been reported that when these basic catalysts are used, the amount of solid by-products produced increases and the yield of isocyanate does not become very high (FW. Abbate et al.
t. al. , J. Appl. Pol. Sci. ,16,
1213 (1972)), which cannot be said to be favorable.

[0006] Many thermal decomposition methods using various metal compounds as catalysts have also been proposed. Japanese Patent Publication No. 51-19
In Publication No. 721, heavy metal compounds are disclosed in JP-A-52-196.
No. 24 and JP-A-56-166160, Ib, IIb, IIIa, IVa, IVb, Vb, V
Group III metal compounds include zinc chloride, a Lewis acid, in JP-A-56-79657 and JP-A-57-21356, and aluminum and iron in U.S. Pat. Nos. 4,290,968 and 4,369,141, respectively. Acetylacetonate is disclosed in JP-A-58-12835.
Publication No. 4 states that compounds of thallium, tin, antimony, and zirconium each act effectively as a homogeneous thermal decomposition catalyst. In addition, as a solid catalyst,
JP-A-56-65856, JP-A-56-6585
No. 7 and JP-A-56-65858 describe the use of surface-rich metallic zinc, aluminum, titanium, iron, chromium, cobalt and nickel. Further, in JP-A No. 57-158747, various metal oxides and sulfides are disclosed.
Japanese Patent No. 158746 proposes a method using carbides and nitrides of various metals as solid catalysts. However, for example, Hiratsuka, Yokoyama, Polymer Processing, Vol. 34, 502
(1985) and Iwata, "Polyurethane Resin Handbook" (published by Nikkan Kogyosha, 1987), pages 90-98, many metals and metal compounds exhibit catalytic activity in the thermal decomposition reaction of carbamate esters. It is well known that it also exhibits catalytic effects on side reactions such as allophanatization, buret formation, and trimerization, and the formation of undesirable byproducts in the thermal decomposition of carbamate esters can be suppressed simply by using a catalyst. However, there are limits to obtaining a good isocyanate yield.

Another method proposed is thermal decomposition in an inert solvent. For example, JP-A-51-137
No. 45, JP-A No. 19721-1972 and JP-A No. 5
No. 1-29445 discloses a thermal decomposition method using an inert solvent such as a hydrocarbon, ether, ester, or ketone. Although a catalyst and a carrier agent are used in addition to an inert solvent, a sufficient overhead yield cannot be obtained, and it cannot be said to be industrially satisfactory.

The reason why it is difficult to obtain a good industrially practicable isocyanate yield despite the use of the above-mentioned catalysts and solvents is thought to be due to the following problems. Since thermal decomposition of carbamate ester is an equilibrium reaction, in order to complete the reaction, it is necessary to extract the produced isocyanate and/or hydroxyl compound into the gas phase and shift the equilibrium toward the production side. However, in the above-mentioned prior art, thermal decomposition is carried out using a stirred tank reactor, which makes it impossible to efficiently extract the produced isocyanate and hydroxyl compounds into the gas phase, resulting in unnecessary reaction. This takes time and causes side reactions to proceed unnecessarily, making it difficult to obtain isocyanate in high yield. for example,
Even if a catalyst is used to increase the rate of the thermal decomposition reaction, the extraction of the product into the gas phase becomes worse due to the liquid depth effect, and the reaction becomes difficult to proceed due to equilibrium, resulting in insufficient yield.
The reaction time becomes long, and the active NCO groups cause various side reactions, reducing the improvement effect of the catalyst.

[0009] In other words, in order to thermally decompose carbamate esters and obtain isocyanates in high yields, a reaction format is adopted in which the product is efficiently extracted into the gas phase and the reaction is completed as quickly as possible. There must be. From this point of view, Japanese Patent Application Laid-Open No. 50-117745 discloses that a powdered carbamate ester is fed together with a large amount of inert gas into a reactor filled with a filler and heated to 350 to 550°C. A technique has been disclosed in which the material is thermally decomposed while melting and flowing down on the surface of the material, the generated gas component is entrained in the inert gas, and the gas component is extracted from the decomposition zone within a short period of time. However, using a large amount of inert gas is extremely disadvantageous from an industrial perspective, and heating and cooling such a large amount of gas within a short period of time is accompanied by technical difficulties.

Furthermore, in Japanese Patent Publication No. 2-11581, a high-speed stirrer equipped with a movable metal blade is used in a continuous thermal decomposition method of a polyfunctional N-monosubstituted carbamic acid ester, that is, polyurethane, which does not use an inert organic solvent. A technique characterized by using a thin film evaporator equipped with the following has been disclosed. However, this method also has a low yield of isocyanate, requires extremely expensive equipment such as a thin film evaporator equipped with a high-speed stirrer with a movable metal blade, and has a low yield per surface area per hour. When used on an industrial scale, it is difficult to say that it is satisfactory when considering implementation on an industrial scale, such as the equipment becoming larger.

[0011] The present inventors have conducted intensive studies to establish a method for industrially producing isocyanates continuously with high yields without the various problems seen in the above-mentioned prior art. This was proposed in Japanese Patent Application No. 2-131219. That is, (a) a reaction part that mainly thermally decomposes carbamate esters into corresponding isocyanates and organic hydroxyl compounds in a liquid phase, and (b) mainly isocyanates and organic hydroxyl compounds produced by thermal decomposition of carbamate esters. This is a method for thermally decomposing carbamate esters, comprising an evaporation section that vaporizes at least one component from the liquid phase, and the liquid phase component is circulated between the reaction section and the evaporation section. According to this method, when a carbamate ester with very few impurities is thermally decomposed, the desired isocyanate can be obtained with high yield and high selectivity, and it can be carried out with almost no polymer adhesion during long-term operation.

On the other hand, as a method for producing aromatic esters of carbamic acid so far, there has been a method of reductive synthesis from nitro compounds, nitroso compounds, azo compounds, azoxy compounds, etc. and carbon monoxide (for example, JP-A-54-1999 4156
01 Publication, etc.), or a method of oxidative synthesis from a primary amine, carbon monoxide, and an oxidizing agent (for example, JP-A No. 55
-120551, etc.), a method of synthesis from diphenyl carbonate and an amine (J.Pol.Sci.
Polymer Chem. ED, 17,835 (1
979)), a method of synthesis from a primary amine, urea, and a hydroxy compound (for example, JP-A-55-1456
55, Japanese Unexamined Patent Publication No. 2-759), etc. have been known for a long time. In either method, it is difficult to obtain the carbamate ester in almost 100% yield, and the reaction crude product usually contains a urea bond (-NHCONH
-), urea terminal (-NHCONH2), amine terminal
High-boiling by-products having active hydrogens capable of bonding with -NCO groups such as (-NH2) coexist. If the carbamate ester is thermally decomposed in the presence of a large amount of these by-products, the produced polyisocyanate will combine with the by-products, resulting in not only a decrease in yield but also the generation and adhesion of polymeric substances. Therefore, even if the method proposed in Japanese Patent Application No. 2-131219 is used, polymer adhesion is unavoidable when thermally decomposing carbamate esters containing these high-boiling by-products, which makes long-term stable operation difficult. It is hard to say that it is satisfactory.

[0013]

[Problems to be Solved by the Invention] Therefore, the present inventors have conducted extensive studies in order to establish a method for producing isocyanate stably for a long period of time with high yield without the various problems seen in the prior art. As a result, the present invention was completed.

[0014]

[Means for Solving the Problems] That is, the present invention provides (a)
(b) at least one component of the isocyanate and organic hydroxyl compound mainly produced by thermal decomposition of the carbamate ester; A method in which the carbamate ester is decomposed while the liquid phase component is circulated between the reaction section and the evaporation section, and the solid content floating in the liquid phase component is separated. This is a method for thermally decomposing carbamate esters.

The carbamic acid ester used as a raw material in the present invention may be an N-monosubstituted carbamic acid ester in which the boiling points of the isocyanate and the hydroxyl compound produced by decomposition differ by 5°C or more under the reaction conditions. It can be anything like that. Such carbamate esters have the general formula R(NHCOOR')n or (R'NHCOO)
It is a compound represented by nR (where n represents an integer of 4 or less).

[0016] Here, R is n-valent (n is an integer from 1 to 4)
represents an organic group selected from a saturated or unsaturated aliphatic group, an alicyclic group, an aromatic group, an aralkyl group, R' is a monovalent saturated or unsaturated aliphatic group, and an alicyclic group, Represents an organic group selected from aromatic groups and aralkyl groups. Furthermore, these organic groups may contain other substituents that do not react with the isocyanate group, such as halogen atoms, nitro groups, cyano groups, acyl groups, acyloxy groups, and carbamoyl groups, or may contain other substituents that do not react with the isocyanate group itself. May contain. It may also contain divalent functional groups that do not react with isocyanate groups, such as ether groups, thioether groups, carbonyl groups, carboxyl groups, and sulfone groups.

[0017] As such a carbamate ester,
For example, methyl carbanilate, ethyl carbanilate,
Propyl carbanilate, butyl carbanilate, cyclohexyl carbanilate, phenyl carbanilate,
Carbanilates represented by the formula: Ph-NHCOOR'(R' is as described above, Ph represents a phenyl group); methyl ester, ethyl ester, phenyl ester, etc. of o-, m- or p-tolylcarbamic acid tolylcarbamic acid esters; phenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, diphenyl ester of o-, m- or p-phenylenedicarbamic acid; 2,4- or 2,6-tolylenedicarbamic acid dimethyl ester, diethyl ester,
Tolylene dicarbamic acid diesters such as diphenyl ester; 2,2'-, 2,4'-, 2,6'- or 4
, dimethyl ester, diethyl ester, dibutyl ester of 4'-methylenebisphenylenedicarbamic acid,
Methylenebisphenylenedicarbamic acid diesters such as diphenyl ester; polymeric aromatic carbamic acid esters represented by chemical formula 1

[0018]

[Chemical formula 1]

R'OCONH-Ph-X-Ph-NHC
OOR'(R' is as described above, X represents a simple bond or a divalent group selected from -O-, -S-, -SO2-, -CO-, and Ph represents a phenyl group. esters of aromatic carbamic acids represented by ); Naphthylcarbamic acid esters such as dimethyl ester, diethyl ester, dibutyl ester, and diphenyl ester of naphthylcarbamic acid; 1,4-, 1,5-, 1,6- ,
or naphthylenecarbamate esters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 2,6-naphthylenecarbamate; ethylene biscarbanilate, propylene biscarbanilate, glyceryl triscarbanilate, pentaerythryl tetrakis Polyhydric alcohols such as carbanilates,
Methyl ester, ethyl ester, polypyl ester, butyl ester, phenyl of alkylcarbamic acids such as methylcarbamate, ethylcarbamate, propylcarbamate, butylcarbamate, amylcarbamate, hexylcarbamate, octylcarbamate, octadecylcarbamate, etc. Alkyl carbamate esters such as esters; alicyclic carbamate esters such as methyl ester, ethyl ester, and phenyl ester such as cyclopentylcarbamate and cyclohexylcarbamate; ethylene dicarbamate, trimethylene dicarbamate, and tetramethylene dicarbamate Carbamic acid, pentamethylene dicarbamate, hexamethylene dicarbamate, 2,
Alkylene dicarbamic acid esters such as methyl ester, ethyl ester, phenyl ester such as 2,4- or 2,4,4-trimethyldicarbamic acid; methylcyclohexane-2,4- or 2,6-dicarbamic acid;
Alicyclic dicarbamic acid diesters such as dimethyl ester, diethyl ester, diphenyl ester such as methyl 3-carbamate-3,5,5-trimethylcyclohexylcarbamic acid; dimethyl ester, diethyl ester, diphenyl ester of xylylene dicarbamic acid, etc. aralkyl dicarbamic acid diesters; o-, m-
or p-chlorophenylcarbamic acid, 2,5-,3
, 4- or 3,5-dichlorophenylcarbamic acid, and halogenated phenylcarbamic acid esters such as methyl ester, ethyl ester, and phenyl ester. These carbamate esters may be a single type or a mixture of two or more types.

In the present invention, the reaction section which mainly thermally decomposes carbamate ester into the corresponding isocyanate and organic hydroxyl compound in the liquid phase may be a flow operation type reactor normally used in the chemical industry. For example, “Chemical Engineering Handbook, Revised 4th Edition” edited by the Chemical Engineering Society, 1470
A tank-type, tube-type or tower-type reactor as shown in 1475 pages (published by Maruzen, 1978) is used. In addition, the evaporation section that vaporizes at least one component of isocyanate and organic hydroxyl compound mainly produced by thermal decomposition of carbamate ester from the liquid phase may be a flow operation type evaporation device normally used in the chemical industry. For example, “Chemical Engineering Handbook Revised 4” edited by the Chemical Engineering Society
An evaporator with a heating tube inside, as shown in "Edition", pp. 402-406 (published by Maruzen, 1978), a flash evaporator, or in some cases, a packed tower is used to spread the liquid phase over the surface of the packing material. A method of evaporating adiabatically while flowing down can also be used.

[0021] For the circulation of the liquid phase between the reaction section and the evaporation section, either a natural circulation system or a forced circulation system can be adopted depending on the type of apparatus. The liquid phase component referred to here mainly consists of the reaction solvent described later, unreacted carbamate ester (including intermediates in the case of polyfunctional) reaction by-products, and in some cases, the product isocyanate, Also included are organic hydroxyl compounds. Although the amount of the liquid phase to be circulated varies depending on the type of apparatus, it is usually at least twice the amount of the liquid phase present in the reaction section and the evaporation section, preferably at least five times the amount per hour.

[0022] In addition, the method used in the present invention to separate and remove solids floating in the liquid phase component includes various separation methods commonly used in the chemical industry, such as filtration, compression, sedimentation, and centrifugation. The operation is applied. For example, "Chemical Engineering Handbook, Revised 4th Edition," edited by the Chemical Engineering Society, 1131-12.
Examples include the apparatus and method shown on pages 03 and 1049 to 1129 (published by Maruzen, 1978). More specifically, methods such as filtration using a filter and centrifugation using a liquid cyclone can be exemplified.

[0023] According to detailed studies by the inventors, it has been found that the smaller the particle size of the suspended solids to be separated, the more the amount of the suspended solids adhering to the reactor can be reduced. Although the reason is not certain, it is assumed as follows. That is, the polymer generated during the reaction is dissolved in the solvent while the molecular weight is low, but after a certain molecular weight, it precipitates and becomes a fine solid substance. Fine solid particles aggregate or fuse together,
It is thought that adhesion to the reactor surface occurs when the particles reach a certain size.

The setting of this particle size varies depending on the experimental conditions and the type of carbamate ester handled, but it is preferably 50
It is 0μ or less. . If it is larger than this, the effect of reducing adhesion to the reactor will be reduced. In the method of the present invention, the solid content may be separated anywhere as long as the liquid phase component is present, and several suitable methods can be exemplified. For example, there is a method in which a liquid phase component is circulated between a reaction section and an evaporation section. In this case, for example, when forced circulation is performed using a pump, it may be on the suction side or the delivery side of the pump. Further, for example, the reaction section or the evaporation section itself may have a built-in device capable of performing the above-described separation operation. Alternatively, when thermal decomposition is carried out by connecting several reactors in series, it may be carried out at the time of transferring the liquid phase component between the reactors. Furthermore, various methods can be applied, such as a method in which a part of the liquid phase component in the reactor is extracted, subjected to a separation operation, and then returned to the reactor.

The reaction temperature may be any temperature as long as the raw material carbamate ester is decomposed, but it is usually maintained at an appropriate temperature within the range of 140 to 380°C. The temperature is more preferably in the range of 160 to 350°C, and even more preferably in the range of 180 to 330°C. A temperature as high as possible is desirable in order to increase the decomposition rate, but a low temperature is desirable in order to suppress side reactions, so an appropriate temperature should be adopted depending on each carbamate ester. Furthermore, the temperatures of the reaction section and the evaporation section do not need to be the same; for example, if the evaporation section is operated under adiabatic conditions, the temperature of the evaporation section will naturally be lower than that of the reaction section;
In the case of an evaporator having a heating tube, it is also possible to arbitrarily set the temperature of the evaporator within the above temperature range.

The reaction pressure must be such that at least one of the decomposition products, isocyanate or hydroxyl compound, is vaporized at the reaction temperature. Furthermore, when a solvent is used, it is necessary to select a pressure that is below the boiling point of the solvent. If these conditions are met, under reduced pressure, e.g. 1 mmHg, or under increased pressure, e.g. 40 k
It is carried out under a wide range of pressures up to g/cm2.

Decomposition catalysts well known to those skilled in the art may be used in the process of the invention. Examples of such catalysts include:
JP-A-51-19721, JP-A-52-1962
Publication No. 4, JP-A-56-166160, JP-A-5
No. 6-79657, JP-A-57-21356, U.S. Pat. No. 4,290,968, No. 43691
Homogeneous thermal decomposition catalysts are disclosed in JP-A No. 41 and JP-A-128354-1983, and solid catalysts are disclosed in JP-A-58-128354.
6-65856, JP 56-65857, JP 56-65858, JP 57-15
Examples include those described in Japanese Patent Application Laid-open No. 8747 and Japanese Patent Application Laid-Open No. 57-158746.

When carrying out the present invention, the reaction time varies depending on the reaction conditions and whether or not a catalyst is used, but the average residence time in the reaction section is usually 1 to 240 minutes, preferably 3 minutes.
~150 minutes, average residence time in the evaporator section 1~240
minutes, preferably 3 to 150 minutes. The average residence time ratio in the reaction section and the evaporation section is not particularly limited, but is usually in the range of 1:30 to 30:1. If the ratio of the reaction section is smaller than this range, the evaporation section equipment will become larger; conversely, if the ratio is larger than this range,
The produced isocyanate and hydroxyl compound are insufficiently extracted into the gas phase, leading to a decrease in the yield of isocyanate.

Furthermore, a plurality of combinations of reaction sections and evaporation sections as used in the present invention can be sequentially combined. In the present invention, it is more preferable to use a solvent. The solvent need only be substantially inert under thermal decomposition conditions, and it is necessary to select a solvent whose boiling point is higher than the boiling point of at least one of the isocyanate and the hydroxyl compound to be produced. Such solvents include aliphatic, cycloaliphatic or aromatic unsubstituted or substituted hydrocarbons or mixtures thereof, as well as certain oxygen compounds such as ethers, ketones, and esters, phosphoric esters. Examples include phosphorus-containing compounds such as , phosphorous acid esters, and sulfur-containing compounds such as thioethers, sulfoxides, and sulfones. Preferred solvents include hexane, heptane, octane, nonane, decane, n-hexadecane,
Alkanes such as n-octadecane, eicosane, squalane, and alkenes equivalent to these; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, diisopropylbenzene, dibutylbenzene, naphthalene, lower alkyl-substituted naphthalene, dodecylbenzene, etc. and alkyl-substituted aromatic hydrocarbons; aromatic hydrocarbons substituted with nitro or halogen groups such as chlorobenzene, dichlorobenzene, bromobenzene, dibromobenzene, chlornaphthalene, bromo-naphthalene, nitrobenzene, nitronaphthalene; diphenyl,
Polycyclic hydrocarbon compounds such as substituted diphenyl, diphenylmethane, terphenyl, anthracene, phenanthrene, various isomers of dibenzyltoluene, and triphenylmethane; alicyclic hydrocarbons such as cyclohexane and ethylcyclohexane; ketones such as methyl ethyl ketone and acetophenone esters such as dibutyl phthalate, butyl benzyl phthalate, dioctyl phthalate; phosphorus-containing esters such as tributyl phosphate, tricresyl phosphate, tributyl phosphite, triphenyl phosphite; ethers and esters such as diphenyl ether, diphenyl sulfide; dimethyl sulfoxide,
Examples include sulfoxides such as diphenylsulfoxide; sulfones such as dimethylsulfone, diethylsulfone, diphenylsulfone, and sulfolane; and silicone oil.

If such a solvent is used in too large a quantity, it will deteriorate the space-time yield of isocyanate and lead to an increase in the size of the reaction apparatus. It is preferably used within a range of 10 times or less. The solvent may be introduced into the reaction system either as a mixture with the carbamate ester or separately.

The carbamate ester and solvent may be introduced into the reaction system through the reaction section, evaporation section, or liquid phase circulation line. Furthermore, a carrier agent can also be used for the purpose of more quickly expelling low-boiling components produced by thermal decomposition. Such carrier agents include nitrogen, argon, helium, carbon dioxide, inert gases such as methane, ethane, propane, pentane, hexane, heptane,
Examples include lower hydrocarbons such as benzene, halogenated hydrocarbons such as dichloromethane, chloroform, and carbon tetrachloride, and ethers such as tetrahydrofuran and dioxane.

It is also possible to use a reaction stabilizer as disclosed in, for example, JP-A-1-125359 and JP-A-2-11581. If the isocyanate produced by decomposition in the process of the invention is obtained as a gas phase component, it may be possible to combine it with other gas phase components (e.g. the hydroxyl compound produced and optionally part of the reaction solvent) as known to those skilled in the art. It is separated by a different method. Examples include a method in which a gas phase component is introduced into a distillation column and separated, a method in which a partial condenser is used for partial condensation separation, and the like. On the other hand, if the desired isocyanate has a high boiling point and can be obtained as a liquid phase component, it is separated from other liquid phase components (for example, reaction solvent) by a method such as evaporation.

[0033]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples. The present invention is not limited to these examples. In addition, in the following examples, Ph represents a phenyl group.

[0034]

[Example 1] As shown in Figure 1, as a reaction part, 50
Single tube type reaction part (■) with a volume of 0 cc and an inner diameter of 1
It has a wet wall falling film type evaporator (■, evaporation area approximately 0.24 m2) with a jacket of 9.4 mm and height 4.0 M, a pump (■) used for circulation of the liquid phase, and a condenser (■). A pyrolysis device equipped with a metal mesh filter (■) with 60 μ holes between the reaction zone and the evaporation zone was used, the temperature of the liquid phase in the reaction zone was set to 220°C, the pressure was 7 mmHg, and the pump ■
While circulating the liquid phase at a rate of 40 l/hr and continuously filtering the liquid phase components, Ph-OOCN was introduced from the inlet of the reactor.
29% by weight of hexamethylene diphenyl urethane represented by H(CH2)6NHCOO-Ph, Ph-OOCNH
(CH2)6NHCONH(CH2)6NHCOO-P
1% by weight of impurities whose main component is a urea compound represented by h
A mixture consisting of 70% by weight of butylbenzyl phthalate was preheated to 120° C. and fed at a rate of 500 gr/hr. The gas components are all condensed at approximately 40°C in the condenser ■, and from the bottom of the evaporation section, butylbenzyl phthalate, unreacted hexamethylene diphenyl urethane, reaction intermediates hexamethylene monoisocyanate monophenyl urethane, and hexamethylene A liquid containing diisocyanate etc. was obtained overflowing. The reaction was continued for 100 hours, during which time the yield of hexamethylene diisocyanate, the target product, obtained in the condenser ① was 94 mol % based on the fed hexamethylene diphenyl urethane, and the selectivity was 97 mol %. Met. After 100 hours had elapsed, the reactor was disassembled and the amount of polymer adhering to the reaction and evaporation parts was measured and found to be 0.5 gr.

[0035]

[Comparative Example 1] The same procedure as in Example 1 was carried out except that the metal mesh filter (■) was not used. The yield of the desired product, hexamethylene diisocyanate, was 94 mol% based on the fed hexamethylene diphenyl urethane, and the selectivity was 96 mol%. After 100 hours had elapsed, the reactor was disassembled and the amount of polymer attached to the reaction and evaporation parts was measured and found to be 4.5 g.
It was r.

[0036]

[Example 2] 3-phenoxycarbonylaminomethyl-3,5,5-trimethyl-1-phenoxycarbonylaminocyclohexane represented by the following chemical formula 2 as a raw material
(Hereinafter, abbreviated as Ph-OOCNH-Ri-NHCOO-Ph, Ri indicates the hydrocarbon group part of urethane) 29% by weight, Ph-OOCNH-Ri-NHCONH-Ri-
1% by weight of impurities whose main component is a urea compound with the structure NHCOO-Ph, 70% by weight of butylbenzyl phthalate
Using a mixture consisting of
The operation was carried out in the same manner as in Example 1 except that the temperature was changed to .degree. The yield of diisocyanate OCN-Ri-NCO is based on the fed urethane Ph-OOCNH-Ri-NHCOO-
It is 92 mol% with respect to Ph, and the selectivity is 96 m
It was ol%. After 100 hours had elapsed, the reactor was disassembled and the amount of polymer adhering to the reaction and evaporation parts was measured and found to be 0.6 gr.

[0037]

[Case 2]

[0038]

[Comparative Example 2] The same procedure as in Example 2 was carried out except that the metal mesh filter (■) was not used. The yield of hexamethylene diisocyanate, the target product, was 9% based on the fed hexamethylene diphenyl urethane.
The selectivity was 96 mol%. After 100 hours had elapsed, the reactor was disassembled and the amount of polymer adhering to the reaction and evaporation sections was measured and found to be 7.2 gr.

[0039]

[Example 3] 2,4- represented by the following chemical formula 3 as a raw material
(phenoxyaminocarbonyl)toluene (hereinafter referred to as Ph
-OOCNH-φ-NHCOO-Ph, φ indicates the hydrocarbon group portion of urethane) 29% by weight, Ph-OO
A mixture consisting of 1% by weight of impurities mainly composed of a urea compound having the structure CNH-φ-NHCONH-φ-NHCOO-Ph and 70% by weight of butylbenzyl phthalate was used, and the temperature of the liquid phase in the reaction part was set at 210°C. The operation was performed in the same manner as in Example 1 except for this. The yield of diisocyanate OCN-φ-NCO is based on the feed urethane P.
h-OOCNH-φ-NHCOO- For Ph 9
3 mol%, and the selectivity was 95 mol%. After 100 hours had elapsed, the reactor was disassembled and the amount of polymer adhering to the reaction and evaporation parts was measured and found to be 0.6 gr.

[0040]

[Chemical formula 3]

[0041]

[Effects of the Invention] As is clear from the comparison of Examples and Comparative Examples, the method of the present invention provides the desired isocyanate in higher yield and higher selectivity than the methods known as prior art.
Furthermore, polymer adhesion during long-term operation is extremely small.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the steps of Examples 1 to 3.

[Explanation of symbols]

■Reaction part ■Evaporation part ■Pump ■Condenser ■Filter ■Raw material input port ■Side overflow outlet

Claims (1)

[Claims] Claim 1: (a) a reaction part that thermally decomposes mainly carbamate esters into corresponding isocyanates and organic hydroxyl compounds in a liquid phase, and (b) isocyanates and In a method for decomposing carbamate esters, the method includes an evaporation section that vaporizes at least one component of the organic hydroxyl compound from the liquid phase, and decomposes the carbamate ester while circulating the liquid phase component between the reaction section and the evaporation section. A method for thermally decomposing carbamate esters, characterized in that the process is carried out while separating the solid content.