JPH035386B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for continuously producing isocyanates by thermal decomposition of carbamate esters. It has long been known that isocyanates and hydroxyl compounds can be obtained by thermal decomposition of carbamate esters (for example, H. Schiff,
Ber.der dtsch.chem.Ges., Volume 3, Page 649, 1870
Year; AWHofmann, Ber.der dtsch.chem.Ges.,
(Vol. 3, p. 653, 1870), and its basic reaction is illustrated by the following formula. R(NHCOOR') _o →R(NCO) _o +n・R′OH or (R′NHCOO) _o R→n・R′NCO+R(OH) _o (However, R is n-valent organic residue, R′ is (monovalent organic residue, n represents an integer of 1 or more) In this thermal decomposition reaction, various side reactions occur because the reaction conditions are generally severe, and the yield and selectivity of the target isocyanate are affected. lower. These side reactions include, for example, decarboxylation of the raw material carbamate ester (generation of primary amine and olefin or secondary amino); reaction of the produced isocyanate with the raw material carbamate ester ( (Formation of allophanate); Reaction between the generated isocyanate and by-produced amine (Formation of urea compound); Decarboxylation reaction of the generated isocyanate (Formation of carbodiimide); Cyclization or polymerization reaction of the generated isocyanate (Formation of isocyanate) nurate or polymer formation). In addition, the thermal decomposition reaction represented by the above general formula is reversible, and the equilibrium is biased toward the carbamate ester on the left side at low temperatures, but upon heating, it shifts to the right side, and the equilibrium is shifted to the isocyanate of the carbamate ester. Thermal decomposition to hydroxyl compounds occurs. In this case, the thermal decomposition temperature varies depending on the type of carbamate ester and reaction conditions. Therefore, in order to efficiently produce isocyanates by this method, it is necessary to selectively carry out the main reaction represented by the above general formula and to prevent undesirable side reactions and reverse reactions such as those mentioned above. Special pyrolysis methods and/or
Alternatively, pyrolysis equipment becomes important. Most of the undesirable side reactions tend to increase as the reaction temperature is generally higher and the reaction time is longer, increasing the amount of time that the formed isocyanate is in contact with the components of the reaction mixture. Furthermore, when attempting to produce isocyanate at a high concentration, side reactions are likely to occur. However, lowering the reaction temperature to slow the reaction rate or attempting to produce isocyanate at a low concentration poses problems in industrial implementation. In particular, tolylene diisocyanate, diphenylmethane diisocyanate, and polymethylene, polyphenyl isocyanate, hexamethylene diisocyanate, 1-isocyanate-3,3,5, which are used in large quantities as polyurethane raw materials.
If diisocyanates and polyisocyanates such as -trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate) are to be produced industrially by thermal decomposition reaction of the corresponding carbamate ester, the above-mentioned It is important to suppress side reactions such as these as much as possible, and to allow the decomposition reaction to occur substantially completely. This is because, if the decomposition reaction is incomplete, unreacted carbamate esters and/or various reaction intermediates having both isocyanate groups and carbamate groups coexist in the reaction mixture. This is because separating the desired polyfunctional isocyanate is accompanied by great difficulty or is virtually impossible. In polymethylene polyphenyl polyisocyanate produced by thermal decomposition of polymethylene polyphenyl carbamic acid polyester, if the undecomposed carbamate group is 10 mol% or less based on the total isocyanate groups, it is considered a special polyurethane. JP-A-Sho revealed that it can be used as a raw material for foam.
54-156919 (U.S. Pat. No. 4,381,405), it is natural that isocyanate products containing undecomposed carbamate groups are generally not preferred. The thermal decomposition methods for carbamate esters that have been proposed so far can be roughly divided into reactions carried out in the gas phase at high temperatures and reactions carried out in the liquid phase at relatively low temperatures. In addition, two methods have been proposed for the liquid phase reaction method: one method is to conduct the carbamate ester in a molten state without a solvent or in the presence of a small amount of solvent, and the other is to conduct the reaction in a solution in the presence of a relatively large amount of pyrolysis solvent. . The present invention is directed to a method of carrying out pyrolysis using relatively large amounts of pyrolysis solvent. Various solution methods have also been proposed in which the decomposition reaction is carried out in the liquid phase using a thermal decomposition solvent. The main one concerns catalysts to increase reaction rates. US Patent No. 2713591 (German Patent No.
No. 1016699), US Pat. No. 2,692,275 (German Patent No. 1022222) and US Pat. No. 2,727,020 describe The production of aliphatic isocyanates by thermal decomposition of aliphatic carbamate esters in which carbamate groups are bonded to aliphatic secondary carbons and aliphatic tertiary carbons in the presence of a catalyst has been described, and JP-A-54 -88201 describes the production of tolylene diisocyanate by thermal decomposition of tolylene dicarbamic acid diethyl ester in the presence of a basic catalyst such as an alkaline earth metal and an alkaline earth metal oxide. . On the other hand, it has been reported that when a basic catalyst is used, the amount of insoluble solid by-products produced increases and the yield of isocyanate is not so high (F.
W. Abbate et al., J. Appl. Pol. Sci., Volume 16, No. 1213
Page, 1972), and basic catalysts are not preferred. Many thermal decomposition methods have also been proposed in which a metal compound uniformly dissolved in a reaction solution is used as a catalyst. Japanese Patent Application Publication No. 1972-19721 (U.S. Patent No. 3919279)
In JP-A-52-19624 (U.S. Pat. No. 4,081,472) and JP-A-56-
Publication No. 166160 lists B, B, and B of the periodic table of elements.
A, A, B, B and group metal compounds are disclosed in JP-A-56-79657 (U.S. Patent No. 4307029).
Zinc chloride, which is a Lewis acid, is used in JP-A-57-21356 and aluminum acetylacetonate and iron acetylacetonate are used in U.S. Pat. −128354 (British Patent No. 2113673), thallium, tin, antimony,
There is a description that zirconium compounds act effectively as homogeneous thermal decomposition catalysts in the reaction solution. However, problems arise when separating decomposition products from reaction solutions containing these metal compounds. If the decomposition products, isocyanates and hydroxyl compounds, have relatively low boiling points and are each separated as overhead components by distillation, these metal compounds can be separated together with high-boiling by-products as bottom components. Although this method can be said to be preferable since it is less likely to be contained in the product, it becomes difficult to separate and recover the catalyst from the resinous high-boiling by-products. If either the isocyanate or the hydroxyl compound, which is a decomposition product, has a high boiling point and cannot be separated from the reaction mixture by distillation or the like, it becomes even more difficult to separate the catalyst.
Particularly when the target isocyanate is the bottom component, as in the case of producing crude MDI consisting of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanate, it is not possible to separate these metal compounds. This is virtually impossible, and these metal compounds will be included in the product, degrading the physical properties of the product. It can be seen that using a metal compound as a homogeneous catalyst in this way is not a common method and has various drawbacks. Attempts have also been made to increase the reaction rate and suppress the formation of polymeric by-products by including certain organic compounds in the reaction solution as catalysts or stabilizers for the produced isocyanate. . JP-A-54-39002 describes a method of thermal decomposition in the coexistence of active hydrogen compounds such as benzyl p-hydroxybenzoate and diethyl benzoylmalonate, but the space-time yield (STY) is low. In addition, since these active element compounds must necessarily be high-boiling compounds, they have the same drawbacks as homogeneous catalysts, and therefore are not considered to have much industrial value. Unexamined Japanese Patent Publication 1987-
Publication No. 159752 (European Publication Patent No. 61013) describes a method of thermal decomposition in the coexistence of active chlorine-containing compounds such as hydrogen chloride and organic acid chlorides. In addition to causing equipment corrosion, these chlorines are incorporated into the produced isocyanate, increasing the acidity of the product, increasing the total chlorine content, and forming hydrolyzable chlorine compounds. Therefore, it is undesirable. Therefore, if a catalyst is used, it is most preferable to use a solid catalyst that does not dissolve in the reaction solution under the reaction conditions. As solid catalysts, JP-A-56-65856 (US Pat. No. 4349484), JP-A-56-65857 (US Pat. No. 4330479) and JP-A-56-65858 are used.
(U.S. Pat. No. 4,290,970), surface-rich metallic zinc, aluminum, titanium,
The use of iron, chromium, cobalt and nickel is described. The present inventors also discovered various effective solid catalysts, and in JP-A-57-158747,
In JP-A-57-158748, elements of the copper group, zinc group, aluminum group, carbon group other than carbon, and titanium group are defined as elements of the carbon group other than carbon, titanium group, and vanadium group. , carbides and nitrides of elements of the chromium group, published in Japanese Patent Application Laid-open No. 1983-
No. 158746 has already proposed boron carbide, boron nitride, etc., and JP-A-57-159751 has already proposed rare earth elements, bismuth, antimony, etc. Attempts have also been made to increase the reaction rate and suppress the production of high-boiling byproducts by using special thermal decomposition catalysts. JP-A-56-166160
In the publication, aromatic nitrile is
No. 109755 (US Pat. No. 4,294,774) proposes N,N-dialkylanilines, but in all cases the space-time yield (STY) is not satisfactory for industrial implementation. A method of thermal decomposition in an inert catalyst without using a catalyst has also been proposed. JP-A-50-30832 (US Patent No. 3962302), JP-A-51-13745 (US Pat. No. 3919278) and JP-A-51-29445
Publication No. 3,919,280 (US Pat. No. 3,919,280) describes a decomposition method using an inert catalyst with a high boiling point.
In both cases, not only are compounds such as phenyl isocyanate and tolylene diisocyanate that can be separated as an overhead component by distillation from a high-boiling solvent solution, but the reaction method is also limited. Perhaps because it is not suitable, the space-time yield (STY) is low, which poses a problem for industrial implementation. Tokukai Akira
In Publication No. 54-88222, a high boiling point solvent is used.
Tolylene dicarbamic acid diester is continuously supplied to a reaction tank maintained at a temperature of 255 to 280°C under reduced pressure of 100 mmHg or less, and the average residence time is 10 minutes or less. Although it is stated that tolylene diisocyanate can be obtained, this method is not only limited to the production of isocyanate that can be separated as an overhead component by distillation, but also requires maintaining a reduced pressure state. Therefore, operating costs are expected to increase. Most of the methods proposed so far for thermal decomposition of carbamate esters using a decomposition solvent use a distillation column or a tank reactor equipped with a reflux condenser at the top. Most of the reaction methods are batch-type, and there are few specific descriptions of reaction methods for continuous production. In the method using a distillation column or a tank reactor equipped with a condenser at the top, isocyanate and hydroxyl compounds, which are decomposition products, both have relatively low boiling points, and while they are produced by decomposition, each component is released into gas. It is often used in cases where it forms a phase and is separated as a component at the top of a distillation column. for example,
Japanese Patent Application Laid-open No. 50-30832 (US Patent No. 3962302),
JP-A-51-13745 (US Patent No. 3919278),
Japanese Patent Application Publication No. 1972-19721 (US Patent No. 3919279),
Japanese Patent Publication No. 51-29445 (US Patent No. 3919280),
Japanese Patent Application Publication No. 1962-19624 (US Patent No. 4081472),
JP-A-54-39002, JP-A-54-88201, JP-A-54-88222 and JP-A-54-
Publication No. 122225 (US Patent No. 4195031) etc.
Both are methods for producing isocyanate and hydroxyl compounds that can be separated by distillation, such as phenyl isocyanate, methyl isocyanate, tolylene diisocyanate, methanol, ethanol, butanol, hexanol, and phenol, respectively, and both components are separated by distillation. is obtained as the top component of the distillation column. However, in this reaction method in which isocyanate and hydroxyl compounds are vaporized together and each is separately condensed and recovered, it is inevitable that some of these compounds will recombine to form carbamate esters. I can't escape it. Diphenylmethanedicarbamic acid diester and polymethylene polyphenylcarbamic acid polyester are thermally decomposed using a tank-type reactor equipped with a reflux condenser at the top, and the volatile hydroxyl compound is extracted from the top of the condenser and reacted. The reaction method for obtaining a non-evaporable crude MDI solution in a tank is also disclosed in JP-A-56-79657 (US Patent No. 4307029), JP-A-56-166160, JP-A-57-21356,
JP-A-57-159752 (European Publication Patent No.
61013) and JP-A-58-128354 (British Patent No. 2113673),
In either case, the reaction is a batch type reaction, requiring a reaction time of 1 hour to several hours, and the space-time yield (STY) is low for industrial implementation. Continuously produce crude MDI using a similar reactor consisting of multistage vessels
Only the above-mentioned Japanese Unexamined Patent Application Publication No. 159752/1983 (European Publication Patent No. 61013) specifically describes the method for producing . However, this method also has the problem of low space-time yield (STY) of crude MDI. A method for continuously producing aromatic monoisocyanates, diisocyanates, and polyisocyanates from aromatic carbamate esters using a tubular reactor filled with a solid metal catalyst was also disclosed in JP-A-56 -65856 publication (US Patent No. 4349484),
Japanese Patent Application Publication No. 56-65857 (US Patent No. 4330479)
and JP-A-56-65858 (U.S. Patent No.
No. 4290970). This method, unlike other prior art methods, appears to be an effective method for the continuous production of isocyanates;
It seems to be particularly effective when producing non-evaporable crude MDI. However, in such a reaction method using only a tubular reactor, due to the short residence time, compounds having undecomposed carbamate groups remain, especially when producing non-distillable isocyanates. This was a problem because it was virtually impossible to separate these undecomposed carbamate group-containing compounds from the target isocyanate. In order to prevent this undecomposed carbamate group-containing compound from remaining, the reaction temperature must be raised. Raising the reaction temperature is undesirable because it increases the production of polymeric substances due to side reactions of the produced isocyanate. A further problem when carrying out a decomposition reaction using only such a tubular reaction tube is that such polymeric by-products gradually accumulate in the lower part of the reaction tube. It has been found that once such deposits occur, further side reactions occur on the material, which in turn causes the solids to grow larger, eventually leading to blockage of the reactor. This showed that continuous production over a long period of time was difficult. In order to suppress the formation of polymeric by-products, it is possible to reduce the concentration of the raw material carbamate ester in the solvent, but the space-time yield (S.
TY) is unfavorable from the point of view. Therefore, the present inventors have made extensive studies to establish a method that can continuously produce high-yield, high-quality isocyanates industrially without the various problems seen in the prior art. As a result, the present invention was completed. That is, the present invention provides a method for producing an isocyanate and a hydroxyl compound by thermally decomposing a carbamate, comprising: (a) 1 to 50% by weight of a carbamate and substantially inert under the thermal decomposition reaction conditions; and (b) decomposes the carbamate ester, and The decomposition products, which have a lower boiling point than the thermal decomposition solvent, are continuously introduced into the first reactor, which is a vertical tubular reactor maintained at a temperature (T ₁ °C) and pressure sufficient to vaporize them, and the reaction begins. Average residence time inside the pipe is 0.5~
While flowing down for 150 minutes, a first stage decomposition reaction is carried out to decompose most of the carbamate ester, but not to completely decompose it,
A reaction mixture containing a high-boiling decomposition product and a compound having an undecomposed carbamate ester group is taken out from the bottom of the reaction tube, and the reaction mixture is treated by (c) decomposing the carbamate ester, and (T ₁ − 50) into a second reactor consisting of a tank-type reactor maintained at a temperature in the range of ℃ to (T ₁ + 50) ℃, and the average residence time in the reactor is 0.5 to 150.
The second decomposition reaction is carried out to almost completely decompose the undecomposed carbamate ester group-containing compound in the reaction mixture in such a manner that the compound having an undecomposed carbamate group is decomposed into isocyanate and hydroxyl compound. (d) decomposition products having a lower boiling point than the pyrolysis solvent, or low-boiling decomposition products and pyrolysis solvent vapor, in gaseous form from the first reactor or both the first and second reactors; (e) recovering the isocyanate and the hydroxyl compound separately by continuously withdrawing the decomposition product having a higher boiling point than the pyrolysis solvent from the second reactor along with the pyrolysis solvent; An object of the present invention is to provide a continuous method for producing isocyanate consisting of: In this way, a mixture of a solvent and a carbamate ester having a certain composition and relationship is assembled into a first reactor consisting of a vertical tube reactor and a second reactor consisting of a tank reactor. By using a method in which the decomposition reaction is carried out in two stages in a combined thermal decomposition reactor, low-boiling decomposition products are taken out in gaseous form, and high-boiling decomposition products are taken out from a second reactor together with the thermal decomposition solvent, It has become clear that high-quality isocyanates can be produced continuously and stably with high space-time yields without the presence of compounds containing undecomposed carbamate groups and without producing polymeric by-products. It has also been found that the process of the invention is particularly effective for producing high-boiling isocyanates and non-evaporable isocyanates, in which case high-quality isocyanate solutions can be produced at high concentrations. Such a thing is not suggested at all in the various prior art documents mentioned above, nor can it be easily inferred from these documents. The carbamate used as a raw material in the present invention may be an N-monosubstituted carbamic acid ester in which the isocyanate and hydroxyl compound produced by decomposition have different boiling points under the reaction conditions. It may be something. Such a carbamate ester is a reaction represented by the general formula R(NHCOOR') _o or (R'NHCOO) _o R. Here, R represents an organic group selected from an n-valent (n is an integer of 1 to 4) saturated or unsaturated aliphatic group, alicyclic group, aromatic group, and aralkyl group,
R' represents an organic group selected from monovalent saturated or unsaturated aliphatic groups, alicyclic groups, aromatic groups, and aralkyl groups. Further, these organic groups may contain other substituents that do not react with the isocyanate group, such as a halogen atom, a nitro group, a cyano group, an alkyl group, an alkoxy group, an acyl group, an acyloxy group, a carbamoyl group, etc. , may contain the isocyanate group itself. 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. As such carbamate esters,
For example, methyl carbanilate, ethyl carbanilate, propyl carbanilate, butyl carbanilate, cyclohexyl carbanilate, phenyl carbanilate, etc.

Carbanilate represented by [Formula] (R' is as above); methyl ester of o- or m- or p-tolylcarbamic acid;
Tolylcarbamate esters such as ethyl ester and phenyl ester; o- or m- or p
- phenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, diphenyl ester of phenylenedicarbamic acid; 2,4
- or tolylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 2,6-tolylene dicarbamic acid; 2,2'- or 2,4' or 4,4'-methylene bis Methylenebisphenylenedicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of phenylenedicarbamic acid; Formula R' is as described above, m is an integer of 1 to 5); esters of polymeric aromatic carbamic acids; (R' is as described above, and X represents a simple single bond or a divalent group selected from -O-, -S-, -SO ₂ -, -CO-). Naphthylcarbamate esters such as methyl ester, ethyl ester, butyl ester, phenyl ester of 1- or 2-naphthylcarbamate; 1,4- or 1,5-
or naphthylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester of 1,6- or 2,6-naphthylene dicarbamic acid; ester biscarbanilate, propylene biscarbanilate, glyceryl tricarbanilate; carbanilates of polyhydric alcohols such as carbanilate, pentaerythryl tetrakis carbanilate; methylcarbamate, ethylcarbamate, propylcarbamate, butylcarbamate, amylcarbamate,
hexylcarbamate, octylcarbamate,
Alkyl carbamate esters such as methyl ester, ethyl ester, propyl ester, butyl ester, phenyl ester of alkyl carbamate such as octadecyl carbamate; methyl ester, ethyl ester, phenyl ester such as cyclopentyl carbamate, cyclohexyl carbamate, etc. Alicyclic carbamate esters such as;
Ethylenedicarbamic acid, trimethylenedicarbamic acid, tetramethylenedicarbamic acid, pentamethylenedicarbamic acid, hexamethylenedicarbamic acid, 2,2,4- or 2,4,4-trimethylhexamethylenedicarbamic acid, etc. Alkylene dicarbamic acid diesters such as dimethyl ester, diethyl ester, dibutyl ester, diphenyl ester; methylcyclohexane
Dimethyl ester, diethyl ester, diphenyl ester of 2,4- or 2,6-dicarbamic acid, methyl 3-carbamate-3,5,5-trimethylcyclohexylcarbamate, 4,4'-methylenebiscyclohexylcarbamate, etc. Alicyclic dicarbamic acid diesters such as; aralkyl dicarbamic acid diesters such as dimethyl ester, diethyl ester, diphenyl ester of xylylene dicarbamic acid; o- or m- or p-chlorophenylcarbamic acid, 2,5 - or methyl ester, ethyl ester, such as 1,4- or 3,5-dichlorophenylcarbamic acid,
Examples include halogenated phenylcarbamate esters such as phenyl ester. These carbamate esters may be a single type or a mixture of two or more types. Particularly preferred carbamic acid esters are those which allow the preparation of polyfunctional isocyanates such as diisocyanates and/or polyisocyanates, for example dialkyl esters of 2,4- and/or 2,6-tolylene dicarbamic acid or Diaryl esters; dialkyl esters or diaryl esters of 2,2'- and/or 2,4'- and/or 4,4'-methylenebisphenylenedicarbamic acid, and diphenylmethanedicarbamic acid diesters thereof; Mixtures with polymethylene polyphenylcarbamic acid polyesters, which are higher homologues; hexamethylene-1,6-dicarbamic acid dialkyl esters or diaryl esters, dicarbamic acid dialkyl esters of isophorone diisocyanate and alcohol or phenols; Diaryl esters; dicarbamic acid dial or diaryl esters of 4,4'-dicyclohexylmethane diisocyanate and alcohol or phenols; 1,8-diisocyanate-4-isocyanatomethyl-octane and alcohol or phenols tricarbamate trialkyl or triaryl esters. The thermal decomposition solvent used in the present invention may be any solvent as long as it is substantially inert under the reaction conditions, but its boiling point is between the respective boiling points of the isocyanate and hydroxyl compound produced. It is necessary to choose something. Such solvents include aliphatic, cycloaliphatic or aromatic substituted or unsubstituted hydrocarbons or mixtures thereof, and also certain oxygenated compounds such as ethers, ketones and esters or thioethers, Also included are certain sulfur compounds such as sulfoxides and sulfones. Preferred solvents include hexane, heptane,
Octane, nonane, decane, n-hexadecane,
Alkanes such as n-octadecane, eicosane, squalane, and alkenes corresponding to these;
Aromatic hydrocarbons and alkyl-substituted aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, diisopropylbenzene, dibutylbenzene, naphthalene, lower alkyl-substituted naphthalene, dodecylbenzene; chlorobenzene, dichlorobenzene, bromobenzene, Aromatic compounds substituted with nitro groups and halogens such as dibromobenzene, chlornaphthalene, bromnaphthalene, nitrobenzene, nitronaphthalene; diphenyl, substituted diphenyl, diphenylmethane, terphenyl, anthracene, phenanthrene, various isomers of dibenzyltoluene , polycyclic hydrocarbon compounds such as triphenylmethane; alicyclic hydrocarbons such as cyclohexane and ethylcyclohexane; ketones such as methyl ethyl ketone and acetophenone; esters such as dibutyl phthalate, dihexyl phthalate, and dioctyl phthalate; diphenyl Ethers and thioethers such as ether and diphenyl sulfide; sulfoxides such as dimethyl sulfoxide and diphenyl sulfoxide; sulfones such as dimethyl sulfone, diethyl sulfone, diphenyl sulfone, and sulfolane; and silicone oil. The composition of such a thermal decomposition solvent and the raw material carbamate ester should be adjusted so that the carbamate ester content is 1 to 50% by weight, preferably 3 to 40%, and more preferably 3 to 40%. 5～30
%. When the carbamate ester is less than 1% by weight, the isocyanate space-time yield (STY)
is low, which is disadvantageous for industrial implementation, and if it exceeds 50% by weight, side reactions occur during thermal decomposition, which is a problem. The raw material mixture consisting of the thermal decomposition solvent and the carbamate ester is introduced from the upper part of the tubular first reactor, but it is also preferable that it is preheated to a temperature below the reaction temperature prior to introduction. Further, this raw material mixture is preferably introduced into the reactor in a solution or molten state, but of course may be introduced in a suspended state. The tubular reactor used as the first reactor in the present invention has an internal temperature of 140 to 380 during the thermal decomposition reaction.
If it can be maintained at a suitable temperature between ℃,
It can be made of any material. In addition, the cross section may have any shape, but usually,
A circular shape is preferred. In addition, its length depends on the type and concentration of carbamate to be decomposed,
Decomposition reaction temperature and pressure, presence or absence of filler and type of filler, presence or absence of tray and type of tray,
Although it varies depending on other reaction conditions, the length is preferably 50 cm to 15 m, more preferably 1 m to 7 m.
In addition, if the cross section is circular, the diameter is 1 cm ~
3 m, preferably 2 cm to 50 cm. In a preferred embodiment, the vertical tubular reactor is filled with a solid filler, a solid catalyst, or both. Examples of solid fillers include those commonly used in distillation columns and absorption columns, such as Raschig rings, Lessing rings, spiral rings, ball rings, interlock saddles, Stetsman packing, and McMahon packing. , Dickson packing, helix packing, coil packing, beehive packing, etc. are preferred, but of course any shape may be used. Although the material may be porcelain, metal, or any other material, a filler made of a material with high thermal conductivity is particularly preferred. These filled solid substances not only have the effect of increasing the surface area and residence time of the flowing liquid components, but also
It serves as a good medium to impart heat of decomposition reaction to the liquid components. Furthermore, when a solid catalyst is charged, unlike a homogeneous catalyst, there is no need to perform a separation operation from a reaction liquid, which is advantageous in terms of industrial implementation. These thermal decomposition catalysts are effective in lowering the decomposition temperature and increasing the reaction rate, and those with particularly good thermal conductivity are more convenient for supplying the heat of the thermal decomposition reaction. However, using a solid catalyst is not necessarily an essential requirement of the present invention. As such a thermal decomposition catalyst, JP-A-57-
Publication No. 158746, Japanese Patent Publication No. 57-158747, Publication No. 158747, Japanese Patent Publication No. 158746
It is described in Japanese Patent Application Laid-open No. 57-158748 and Japanese Patent Application Laid-open No. 159751/1983. For example, rare earth elements, antimony, bismuth, and their oxides, sulfides, and salts; elemental boron and boron compounds; metals from the copper, zinc, aluminum, carbon, and titanium groups of the periodic table; oxides and sulfides of metals; carbides and nitrides of elements of the carbon group other than carbon in the periodic table, titanium group, vanadium group, chromium group, etc. are preferably used. In a further preferred embodiment, a packed tubular reactor equipped with a liquid distributor and/or a liquid redistributor is used as the first reactor. This liquid distributor is installed above the filler layer to uniformly distribute the liquid in the filler layer, and may have any shape. Examples include ring-type distributors, flood-type distributors, funnel-type distributors, and orifice-type distributors, which are used in ordinary packed columns. The liquid redistributor prevents liquid components from drifting while flowing down in the packed bed, and not only helps in uniform distribution of the liquid, but also has the effect of narrowing the residence time distribution width of the reaction liquid. have. By narrowing the residence time distribution width of such a reaction solution, it is possible to prevent undecomposed carbamate esters from remaining and to suppress the production of polymeric by-products due to side reactions of the produced isocyanate. This made it possible to obtain high-quality isocyanate. Preferably, such a liquid redistributor is provided for each appropriate filling height of the filling material. The liquid redistributor may be of any material and shape. In another preferred embodiment, this tubular reactor is equipped with a tray inside. This tray refers to a stage used in a conventional plate distillation apparatus, and includes, for example, a bubble bell tray, a uni-flux tray, a perforated plate tray, a perforated tray, and the like. Such a tray has the same effect as a liquid redistributor installed in a packed reaction tube, and is useful for narrowing the residence time distribution width of the reaction liquid. Furthermore, in another preferred embodiment, the first reactor is a tubular reactor with a tray installed therein and filled with a solid filler or a solid catalyst or both. be. The temperature of the first reactor may be any temperature as long as it decomposes the raw material carbamate ester, but it is usually maintained at an appropriate temperature (T ₁ °C) within the range of 140 to 380 °C. Ru. Although it depends on the type of carbamate ester used, a more preferable temperature range is 160 to 350°C, and an even more preferable temperature range is 160 to 350°C.
The temperature ranges from 180 to 330°C. In order to increase the decomposition reaction rate, it is desirable to use a high temperature as much as possible, but in order to suppress side reactions, a low temperature is desirable, so an appropriate relationship should be adopted depending on each carbamate ester. Further, the temperature distribution in the reaction tube may be uniform from the top to the bottom, or it may be possible to provide an appropriate temperature gradient, which is a preferable method depending on the case. The pressure in the first reactor is preferably adjusted such that the reaction temperature is below the boiling point of the thermal decomposition solvent, and the low boiling point of either isocyanate or hydroxyl compound, which is a decomposition product. The pressure must be such that the components vaporize at the reaction temperature. Therefore, if these conditions are met, it may be carried out under a wide range of pressures, from reduced pressure, for example 1 mmHg, to elevated pressure, for example 40 Kg/cm ² . A raw material mixture consisting of a carbamic acid ester and a thermal decomposition catalyst continuously introduced from the upper part of the first tubular reactor is decomposed into isocyanate and hydroxyl compounds as it flows down inside the reaction tube, and the low boiling point components of these are decomposed into isocyanate and hydroxyl compounds. is vaporized and continuously taken out in gaseous form from the top of the reaction tube. In this case, it is of course possible to take it out together with a part of the solvent vapor. Most of the carbamate ester is decomposed into isocyanate and hydroxyl compounds inside this first reactor, but some carbamate ester remains undecomposed. Particularly in the case of polycarbamic acid polyester, isocyanate compounds having partially undecomposed carbamate groups, which are decomposition reaction intermediates, tend to remain. In order to completely decompose these undecomposed carbamate esters and/or isocyanate compounds having undecomposed carbamate groups in the tubular first reactor, it is necessary to raise the reaction temperature to a higher temperature,
It is necessary to increase the residence time. However, when the reaction conditions are made more severe in this way, side reactions occur and the production of polymeric by-products is unavoidable. This tendency is particularly pronounced when producing polyfunctional isocyanates such as diisocyanates and polyisocyanates, and polymeric by-products may accumulate at the bottom of the reaction tube, eventually clogging the reaction tube. There was found. These facts are
This shows that it is difficult to continuously produce high-quality isocyanate using only a tubular reactor. Therefore, in the method of the present invention, most of the carbamate esters are decomposed in the tubular first reactor, but some remaining carbamate esters and/or undecomposed carbamates are not completely decomposed. The compound having a high boiling point and the solvent is continuously taken out in liquid form from the bottom of the reaction tube, and then introduced into a second reactor consisting of a tank reactor, where it is completely decomposed. This is one of its major characteristics. The upper and lower parts of the reaction tube here refer to the portions up to about 1/3 from the upper end of the tube of the first reactor, respectively;
and the portion up to approximately 1/3 from the lower end of the tube. The temperature of the second reactor varies depending on the degree of decomposition in the first reactor, the type of carbamate ester, etc., but it is usually the temperature at which the carbamate ester is decomposed, and the temperature of the first reactor ( It should be kept within the range of _{(T 1 -50} )°C to (T ₁ +50)°C. More preferably (T ₁ −20) °C ~
(T ₁ +30)°C. The low-boiling decomposition products produced in the second reactor are continuously removed from the reactor in gaseous form. In this case, it is of course possible to take it out together with a part of the solvent vapor. In a preferred embodiment, the gaseous components removed from the second reactor are introduced into the first reactor from the lower part of the reaction tube. In this case, the gas component preferably contains thermal decomposition solvent vapor in addition to low-boiling decomposition products. Further, one second reactor is usually sufficient, but if necessary, it can be made into a multi-stage reactor with two or more reactors. The gaseous low-boiling decomposition products produced in this way can be recovered in liquid form as is, for example by introducing it into a cooler, if it does not contain solvent vapors, or can be recovered in liquid form, for example by introducing it into a cooler. In this case, the solvent is either separated from the solvent and recovered by introducing it into a condenser kept at an appropriate temperature, or it is recovered together with the solvent. In addition, high-boiling decomposition products are
The high-boiling decomposition product is continuously taken out from the second reactor together with the pyrolysis solvent and is continuously obtained by separating the pyrolysis solvent, for example by distillation. If the high-boiling decomposition product is an isocyanate and the pyrolysis solvent is separated by distillation, it is carried out at as low a temperature as possible, preferably at a temperature below 150°C. In another preferred method of the present invention, the low boiling point product and solvent vapor are continuously extracted from the upper part of the first reactor or the upper parts of each of the first reactor and the second reactor. by introducing the gaseous component consisting of , most or all of the gaseous product is separated into a liquid component containing the pyrolysis solvent as a main component, and part or all of the liquid component is transferred into a first reactor, or a first reactor and a second reactor. The method of returning each of the above is adopted. This method was found to be particularly effective in suppressing side reactions. In a more preferred embodiment of this scheme,
A gaseous component consisting of a low boiling point product and solvent vapor extracted from the upper part of the second reactor is introduced into the first reaction tube from the lower part of the reaction tube. It is also a preferred method to introduce a carrier agent from the lower part of the first reactor and/or the second reactor in order to quickly withdraw the low-boiling products produced in the first reactor and the second reactor from the reactor. be. The gaseous components, including carrier agent and low-boiling products, and optionally solvent vapor, withdrawn from the reactor and/or partial condenser are separated into their respective components by a method such as partial condensation. , the carrier medium is recycled and reused. Preferably, the carrier agent is introduced into the reactor preheated. In a preferred embodiment, the carrier agent is introduced into the liquid at the bottom of the second reactor and is introduced into the lower part of the first reactor together with the low boiling products produced and the solvent vapor. Such a carrier agent needs to be substantially inert and in a gaseous state under the pyrolysis reaction conditions. Such carrier agents include nitrogen,
Inert gases or hydrocarbon gases such as argon, helium, carbon dioxide, methane, ethane, and propane are used. Low-boiling organic solvents that have similar effects include halogenated hydrocarbons such as dichloromethane, chloroform, and carbon tetrachloride, lower hydrocarbons such as pentane, hexane, heptane, and benzene, and tetrahydrofuran and dioxane. Ethers can also be used. These carrier agents can be used alone or in combination of two or more. When carrying out the present invention, the reaction time is usually between 0.5 and 150 times the average residence time in the first reactor.
minutes, preferably 1 to 60 minutes, and the average residence time in the second reactor is set to be 0.5 to 150 minutes, preferably 1 to 90 minutes. The process of the invention comprises pyrolyzing carbamate esters to give hydroxyl compounds as low boiling products and isocyanates as high boiling products.
It is particularly suitable for the continuous production of high quality isocyanates in high yields. Furthermore, the method of the present invention is particularly advantageous for the thermal use of dicarbamic acid diesters and/or polycarbamic acid polyesters, which yield polyfunctional isocyanates such as diisocyanates and/or polyisocyanates, among such carbamic esters. This is the method. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. In addition, the reaction product can be analyzed by gas chromatography,
Analyzes were performed using high performance liquid chromatography, mass spectrometry, etc. Example 1 A mixture consisting of 15% by weight of diethyl diphenylmethanedicarbamate and 85% by weight of orthodichlorobenzene was first preheated to 160°C in the raw material preheating device 1 using a thermal decomposition reactor as shown in Fig. 1. is,
It was sent to the upper part of the tubular first reactor 2 and was continuously introduced at a flow rate of 600 g/hr. The tubular first reactor 2 has an inner diameter of 5 cm, and a distributor is installed at the top to uniformly distribute the raw material mixture introduced.
The interior is filled with a stainless steel Raschitz ring. In addition, a liquid redistributor is provided every 15 cm of the packed bed. Dry nitrogen gas preheated to 250° C. is continuously introduced at 200 N/hr into the liquid in the second reactor 3, which is a tank-type reactor. Pipe-type first reactor 2 and tank-type second reactor 3
The temperature of both is maintained at 250℃, and the pressure is 8
Kg/cm ³ is maintained. The average residence time of the reaction solution is 20 minutes in the first tubular reactor 2 and 15 minutes in the second tank reactor. The ethanol and orthodichlorobenzene vapors coming out of the tank-type second reactor 3 are
From the bottom of the reaction tube together with nitrogen gas as a carrier,
It is introduced into the tubular first reactor 2. The gaseous components from the upper part of the tubular first reactor 2 are passed through the partial condenser 4 maintained at 130°C, thereby converting them into a liquid component consisting mostly of ortho-dichlorobenzene and a small amount of ortho-dichlorobenzene. It is separated into gaseous components consisting of ethanol vapor containing benzene vapor and nitrogen gas. The liquid component separated by the partial condenser 4 is returned as it is from the upper part of the tubular first reactor 2, and the gas component is led to the cooler, where it is converted into a liquid component consisting of ethanol containing a small amount of ortho-dichlorobenzene. and nitrogen gas. Further, from the lower part of the tank-type second reactor 3, an orthodichlorobenzene solution containing diphenylmethane diisocyanate is continuously extracted. After the reaction reached a steady state, analysis of the orthodichlorobenzene solution revealed that undecomposed diethyl diphenylmethanedicarbamate and the reaction intermediate ethyl diphenylmethane monoisocyanate monocarbamate were not present. It was found that diphenylmethane diisocyanate was produced with a selectivity of over 98%. This decomposition reaction was carried out continuously for 200 hours, but no polymeric by-products were observed to adhere to the interior of the reactor, and diphenylmethane diisocyanate could be stably produced with the same composition. Comparative Example 1 A raw material mixture having the same composition as in Example 1 was continuously introduced from the top of a pyrolysis apparatus consisting only of the same tubular reactor as that used in Example 1, which was maintained at 250°C. The thermal decomposition reaction of diethyl diphenylmethanedicarbamate was carried out by the following method. Nitrogen gas preheated to 250°C was introduced from the bottom of the reaction tube, and gas components were continuously extracted from the top of the reaction tube. Approximately 1 hour after the reaction started, it reached a steady state, and the orthodichlorobenzene solution obtained from the bottom of the reaction tube was analyzed, and the reaction rate of diethyl diphenylmethanedicarbamate was 95%. However, the selectivity of diphenylmethane diisocyanate is 80%, and the selectivity of the reaction intermediate diphenylmethane monoisocyanate monocarbamate ethyl is
At 12%, polymeric by-products were formed with a selectivity of 3%. However, after 5 hours, the reaction rate of diethyl diphenylmethanedicarbamate was 98
%, but the selectivity for diphenylmethane diisocyanate was 67%, and the selectivity for diphenylmethane monoisocyanate monoethyl carbamate was 18%. The amount of polymeric byproducts had increased considerably, and the mass balance was becoming unbalanced, suggesting that the polymeric byproducts had adhered to the inside of the reactor. The reaction continued for another 5 hours, but as the mass balance no longer matched, the reaction was stopped and the inside of the reaction tube was examined.
A significant amount of polymeric material was observed on the support plate, liquid redistributor, and inner walls. In addition, a similar thermal decomposition reaction was carried out at a reaction temperature of 280°C to prevent undecomposed substances from remaining.
Two hours after the start of the reaction, polymeric by-products increased,
After 5 hours, the filler support plate at the bottom of the reaction tube was clogged by deposition of polymeric by-products. Example 2 A raw material mixture consisting of 20% by weight of a carbamate ester mixture consisting of 95% by mole of diethyl diphenylmethane dicarbamate, 5% by mole of triethyl dimethylenetriphenyltricarbamate, and 80% by weight of orthodichlorobenzene was prepared in Example 2. Thermal decomposition was carried out continuously using a reactor similar to 1. The temperature of the first tubular reactor is maintained at 265℃, and the temperature of the second tank-type reactor is maintained at 255℃, the pressure in the system is 10Kg/ ^cm2 , and the nitrogen gas for conveyance is
℃ and was continuously introduced at 300N/hr. Other conditions were almost the same as in Example 1. After reaching a steady state, analysis of the orthodichlorobenzene solution obtained from the second tank reactor revealed that the reaction rate of carbamate ester was 100%, and that diphenylmethane diisocyanate and dimethylenetriphenyl triphenol were Isocyanate is
It was found that they were produced with a selectivity of 98% or more and 97% or more, respectively. This decomposition reaction was carried out for 300 hours.
Although it was carried out continuously, no polymeric by-products were observed to adhere to the inside of the reactor, and the isocyanate mixture consisting of diphenylmethane diisocyanate and dimethylenetriphenyl triisocyanate was stably produced with the same composition. was able to manufacture. Example 3 Mixture 17 consisting of 65% by weight of dimethyl diphenylmethane dicarbamate and 35% by weight of polymethyl polymethylene polyphenylcarbamate having 3 or more nuclear bodies
A raw material mixture consisting of 83% by weight of orthodichlorobenzene was continuously thermally decomposed using the same reactor as in Example 1. The reaction was carried out in the same manner as in Example 1, except that the temperatures of the tube-type first reactor and tank-type second reactor were maintained at 260°C. After reaching a steady state, 500 ml of the orthodichlorobenzene solution drawn out from the bottom of the tank-type second reactor was
Orthodichlorobenzene was distilled off by vacuum distillation at a temperature below .degree. Crude MDI consisting of a dark brown liquid was obtained. Its NCO content is 31.5
It was %. Example 4 A raw material mixture consisting of 16% by weight of diethyl 2,4-tolylene dicarbamate and 84% by weight of chlorobenzene was used, the reaction pressure was kept at 15 Kg/cm ² , and the temperature of the partial condenser was kept at 110°C. The decomposition reaction was carried out using the same apparatus and method as in Example 1. After the steady state was reached, the chlorobenzene solution obtained from the bottom of the second tank reactor was analyzed and found to be 2,4
-The reaction rate of diethyl tolylene dicarbamate is
It was found that at 100%, 2,4-tolylene diisocyanate was produced with a selectivity of 98% or more.
This decomposition reaction was carried out continuously for 200 hours.
No polymeric by-products were observed to adhere to the interior of the reactor, and 2,4-tolylene diisocyanate could be stably produced with the same composition. Example 5 Hexamethylene-1,6- preheated to 180°C
A raw material mixture consisting of 22% by weight of diethyl dicarbamate and 78% by weight of orthodichlorobenzene was
It was continuously introduced at a flow rate of 400 g/hr from the upper part of the tubular first reactor of the pyrolysis reactor as shown in the figure. The first tubular reactor was made of a stainless steel tube with an inner diameter of 5 cm, and perforated plate trays were installed inside at 5 cm intervals. Dry nitrogen gas preheated to 280° C. is continuously introduced at 200 N/hr into the liquid in the second reactor, which is a tank-type reactor.
The temperature of both the tube-type first reactor and the tank-type second reactor is maintained at 280°C, and the pressure is maintained at 13Kg/cm ³ . The average residence time of the reaction solution was 12 minutes in the first tube reactor and 20 minutes in the second tank reactor. Other conditions were set almost the same as in Example 1, and ethanol vapor containing a small amount of orthodichlorobenzene was continuously extracted from the upper part of the partial condensate together with nitrogen. An orthodichlorobenzene solution containing hexamethylene-1,6-diisocyanate is continuously drawn out from the bottom of the vessel. After the reaction reached a steady state, analysis of the orthodichlorobenzene solution revealed undecomposed diethyl hexamethylene-1,6-dicarbamate and the reaction intermediate hexamethylene-1,-isocyanate-6-carbamine. Ethyl acid is not present, 98
It was found that hexamethylene diisocyanate was produced with a selectivity of more than %. This decomposition reaction was carried out continuously for 150 hours, but no polymeric by-products were observed to adhere to the inside of the reactor, and hexamethylene diisocyanate could be stably produced with the same composition. Example 6 A mixture consisting of 10% by weight of di-n-propyl diphenylmethanedicarbamate and 90% by weight of diphenyl ether was preheated to 160° C., and was heated to 160° C. in a tubular first reactor 2 and a tank as shown in FIG. It is continuously introduced from the upper part of the tubular first reactor 2 of the pyrolysis reactor equipped with the second reactor 3 at a flow rate of 500 g/hr. The tubular first reactor 2 has an inner diameter of 2.5 cm and is filled with surface-rich silicon carbide granules and stainless steel Dickson packing. Dry nitrogen gas preheated to 260° C. is continuously introduced into the liquid in the tank-type second reactor 3 at a rate of 200 N/hr. The first tubular reactor 2 was kept at 250°C, the second tank reactor 3 was kept at 260°C, and the pressure was normal pressure. The average residence time of the reaction solution was 25 minutes in the first tube reactor and 10 minutes in the second tank reactor. The vapors of n-propanol and diphenyl ether coming out of the second tank reactor are introduced into the first tubular reactor from the lower part of the reaction tube together with nitrogen gas as a carrier. The gas component exiting from the upper part of the tubular first reactor was led to a cooler and was continuously separated into a liquid component consisting of n-propanol containing a small amount of diphenyl ether and nitrogen gas. Further, a diphenyl ether solution containing diphenylmethane diisocyanate is continuously extracted from the lower part of the tank-type second reactor. After the reaction reached a steady state, the diphenyl ether solution was analyzed and the decomposition rate of di-n-propyl diphenylmethanedicarbamate was 100%, and the selectivity of diphenylmethane diisocyanate was over 98%. It was generating. Example 7 Continuous thermal decomposition in the same manner as in Example 5 using a raw material mixture consisting of 12% by weight of 1,8-diethoxycarbamoyl-4-ethoxycarbamoylmethyl-octane and 88% by weight of orthodichlorobenzene. As a result of the reaction, 1,8 as a liquid component
An orthodichlorobenzene solution containing -diisocyanate-4-isocyanatomethyl-octane was obtained continuously and stably. By distilling off orthodichlorobenzene under reduced pressure at a temperature below 100°C, 1,8-diisocyanato-4-isocyanatomethyl-octane was obtained with a selectivity of over 97%.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a thermal decomposition reactor used in the method of the present invention, and FIG. 2 is an explanatory diagram showing another example. 1... Raw material preheating device, 2... Tubular first reactor,
3... Tank-type second reactor, 4... Partial condenser.

Claims (1)

[Scope of Claims] 1. A method for producing isocyanates and hydroxyl compounds by thermally decomposing a carbamate, comprising: (a) 1 to 50% by weight of a carbamate and substantially inert under thermal decomposition reaction conditions; (b) A mixture consisting of 99 to 50% by weight of a thermal decomposition solvent whose boiling point is between the respective boiling points of isocyanate and hydroxyl compound produced by thermal decomposition. , and the decomposition product having a lower boiling point than the pyrolysis solvent is continuously introduced into a first reactor consisting of a vertical tubular reactor maintained at a temperature (Ti° C.) and pressure sufficient to vaporize the decomposition product, and the decomposition product has a lower boiling point than the pyrolysis solvent. Average residence time inside the reaction tube is 0.5~
A first-stage decomposition reaction is carried out to decompose most of the carbamate ester but not to completely decompose it while flowing down for 150 minutes, and high boiling point decomposition products and undecomposed carbamate ester The reaction mixture containing the group-containing compound is taken out from the bottom of the reaction tube, and the reaction mixture is (c) decomposed of the carbamate ester and heated to a temperature in the range of (T ₁ -50)°C to (T ₁ +50)°C. It is introduced into a second reactor consisting of a tank reactor maintained at a certain temperature, and the average residence time in the reactor is 0.5 to 150.
The second decomposition reaction is carried out to almost completely decompose the undecomposed carbamate ester group-containing compound in the reaction mixture in such a manner that the compound having an undecomposed carbamate group is decomposed into isocyanate and hydroxyl compound. (d) decomposition products having a boiling point lower than that of the pyrolysis solvent, or low-boiling decomposition products and pyrolysis solvent vapor, continuously in gaseous form from the first reactor or both the first and second reactors; (e) The isocyanate and the hydroxyl compound are separately recovered by continuously removing the decomposition product having a higher boiling point than the pyrolysis solvent from the second reactor together with the pyrolysis solvent. Continuous production method of isocyanate. 2. Low-boiling decomposition products together with pyrolysis solvent vapor,
Continuously withdrawn in gaseous form from the first reactor or both the first and second reactors, this gaseous component is then subjected to condensation of a portion or most or all of the pyrolysis solvent vapor, but the gaseous decomposition By introducing most or all of the products into a partial condenser maintained at a temperature that does not condense, a gaseous component mainly composed of low-boiling decomposition products and a liquid component mainly composed of the pyrolysis solvent are separated. The method according to claim 1, wherein a part or all of the liquid component is returned to the first reactor or both the first reactor and the second reactor. 3. The method according to claim 1 or 2, wherein a tubular reactor filled with a solid filler, a solid catalyst, or both is used as the first reactor. 4. The method according to claim 1 or 2, wherein a tubular reactor having a tray installed inside is used as the first reactor. 5. Claim 1 or 2 uses a tubular reactor as the first reactor, which is equipped with a tray and filled with a solid filler, a solid catalyst, or both. the method of. 6. The method according to any one of claims 1 to 5, wherein the gaseous component coming out of the second reactor is introduced from the lower part of the first reactor. 7 Claims in which a carrier agent that is substantially inert and in a gaseous state under pyrolysis reaction conditions is introduced from the lower part of the first reactor and/or the second reactor, and the gaseous component is carried out from the upper part of the reactor. Paragraphs 1 to 6
The method described in any of the paragraphs. 8. The method according to claim 6 or 7, wherein the carrier agent is introduced into the liquid from the bottom of the second reactor. 9. Claims 1, 2, 7, and 8, wherein the carbamate is a carbamate that provides a hydroxyl compound as a low-boiling product and an isocyanate as a high-boiling product.
The method described in any of the paragraphs. 10. Any one of claims 1, 2, and 9, wherein the carbamate is a dicarbamate and/or polycarbamate polyester for producing diisocyanate and/or polyisocyanate. The method described in.