JP2000086614A - Storage and transportation of carbamic esters - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which the deterioration of carbamic esters in a molten or a solution state is suppressed to stably store and transport the carbamic esters. SOLUTION: One or more kinds of stabilizers selected from thiazoles and thioureas are added to carbamic esters in a molten or a solution state.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for storing and transporting carbamic acid esters.

[0002]

BACKGROUND OF THE INVENTION Isocyanate, which is a raw material for polyurethane, is industrially produced from phosgene and the corresponding amine. However, there are problems with the toxicity of phosgene, the treatment of a large amount of by-produced hydrogen chloride, and the corrosion of equipment. Therefore, it is desired to develop an industrial production method of isocyanates that does not use phosgene. A method of thermally decomposing carbamic acid esters has been proposed as one of the methods for producing isocyanates that does not use phosgene and has a relatively high yield. As a flow reaction operation in this thermal decomposition, for example, Japanese Patent Application Laid-Open No. 7-25
In No. 8194, a raw material solution consisting of carbamic acid esters, an inert solvent, a catalyst and the like is supplied to a reaction tank to
It describes a method of thermally decomposing at a temperature of up to 350° C. and condensing the vapors of the isocyanates and alcohols produced outside the system.

As described above, carbamic acid esters are raw materials for a method for producing an isocyanate without using phosgene. Normally, carbamic acid esters are in a solid state at room temperature, and therefore when they are stored in a storage tank or from a storage tank. When continuously supplied to the reaction tank, they are handled in a molten or solution state. When the carbamic acid esters are heated in a molten state or in a solution and held in a storage tank or the like, a high boiling point by-product with an unknown structure is generated and deteriorates over time. Further, when the modified carbamic acid esters are supplied to the reaction tank to carry out the thermal decomposition reaction, not only the yield of isocyanates is lowered but also the production of high-boiling by-products increases, so that the polymerization products in the reaction tank and pipes Will be deposited or adhered, resulting in blockage or the like, which makes long-term operation difficult.

As a method for suppressing alteration of carbamic acid esters, for example, in JP-A-59-62561,
A method of adding an organic compound having a hydroxyl group to aromatic carbamic acid esters has been proposed. However, in this method, an alcohol having a boiling point lower than the melting point of carbamic acid esters is usually added, so that the inside of the storage tank is pressurized in the molten state, and a pressure resistant storage tank is required. In addition, a relatively large amount of carbamic acid ester needs to be added, and if it is directly used for thermal decomposition, the burden on the alcohol partial condensation system becomes large. Furthermore, a considerable amount of structurally unknown substances are produced, and the effect of suppressing alteration of carbamic acid esters is not sufficient.

Further, JP-A-10-7642 discloses a method of adding aromatic sulfonic acid, aromatic sulfonamide, sulfide and phosphite as a stabilizer. In this method, the storage tank is at normal pressure and the addition amount is relatively small, so it can be used as it is for thermal decomposition, but the structure unknown substance is formed, and the effect of suppressing alteration of carbamic acid esters is not sufficient. Not necessarily satisfied.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for suppressing deterioration of carbamic acid esters in a molten or solution state, and for stable storage and transportation.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on a method for suppressing alteration of carbamic acid esters in a molten or solution state, and as a result, added compounds of thiazoles or thioureas as stabilizers. By doing so, the inventors have found that alteration of the carbamic acid ester in the molten or solution state can be suppressed, and stable storage and transport can be achieved, and the present invention has been completed.

That is, the present invention provides a method for storing and transporting carbamic acid esters, which comprises adding one or more stabilizers selected from thiazoles or thioureas to carbamic acid esters in a molten or solution state. is there.

[0009]

[R ¹ and R ² are organic groups selected from saturated or unsaturated aliphatic groups, alicyclic groups, aromatic groups and aralkyl groups, and R ¹ and R ² may be the same or different from each other. good. n represents an integer of 1 to 4. ]

Specific examples of carbamic acid esters include 1,4-bis(methoxycarbonylamino)butane, 1,6-bis(methoxycarbonylamino)hexane and 1,8-bis(methoxycarbonylamino)octane. Aliphatic carbamic acid esters such as; 1,
3- or 1,4-bis(methoxycarbonylamino)cyclohexane, 1,3- or 1,4-bis(methoxycarbonylaminomethyl)cyclohexane, 3-methoxycarbonylaminomethyl-3,5,5-trimethyl-1
-Methoxycarbonylaminocyclohexane, bis(4
-Methoxycarbonylaminocyclohexyl)methane,
Alicyclic carbamate esters such as 1-methyl-2,4-bis(methoxycarbonylamino)cyclohexane; 1,3- or 1,4-bis(methoxycarbonylamino)benzene, 1-methyl-2,4- Bis(methoxycarbonylamino)benzene, 1-methyl-2,6-bis(methoxycarbonylamino)benzene, 2,4'-
Or an aromatic carbamate such as 4,4′-bis(methoxycarbonylamino)diphenylmethane, 4,4′-bis(methoxycarbonylamino)biphenyl, 1,5- or 2,6-bis(methoxycarbonylamino)naphthalene Kinds; 1,3- or 1,4-bis(methoxycarbonylaminomethyl)benzene, 1,5- or 2,6
Examples include aralkylcarbamic acid esters such as bis(methoxycarbonylaminomethyl)naphthalene and carbamic acid esters having an ethoxycarbonylamino substituent or a phenoxycarbonylamino substituent in place of the methoxycarbonylamino substituent of each compound.
These carbamic acid esters can be easily obtained by a generally known method, for example, a reaction between corresponding amines and carbonic acid esters.

The stabilizers used in the present invention include thiazoles such as 2-mercaptobenzothiazole and 2-mercaptobenzothiazole.
Examples include (4′-morpholinodithio)benzothiazole, and examples of thioureas include diethylthiourea, dibutylthiourea, ethylenethiourea, and dilaurylthiourea. One or a mixture of two or more of these compounds can also be used as a stabilizer. The stabilizer of the present invention is effective both as a stabilizer and in the case of thermally decomposing carbamic acid esters, and can be usually used as it is for the thermal decomposition reaction.

The stabilizer is added in an amount of 0.0001 to 10% by weight, preferably 0.001 to 1% by weight, based on the carbamic acid ester. If it is less than this, the effect of suppressing the alteration of the carbamic acid esters is not sufficient, and if it is too large, the production of isocyanates may be hindered in the thermal decomposition reaction.

The temperature of the carbamic acid ester storage tank is not particularly limited as long as it is equal to or higher than the melting or melting temperature, but in order to prevent alteration of the carbamic acid esters, a temperature as close as possible to the melting or melting temperature of the carbamic acid esters. Is preferred. The pressure of the carbamic acid ester storage tank is not particularly limited, but is usually atmospheric pressure.

In the present invention, a solvent is used for storage and transportation in a solution state, and the solvent needs to be inert to carbamic acid esters. Further, when the solution-state carbamic acid esters are supplied to the reaction tank to carry out the thermal decomposition reaction, it is also necessary that they are inert to isocyanates. Examples of the solvent satisfying such conditions include aliphatic, alicyclic and aromatic substituted or unsubstituted hydrocarbons, esters, ketones, ethers and the like. Specific examples include alkanes such as hexane, heptane, nonane, and decane; aromatic hydrocarbons such as benzene, toluene, xylene, biphenyl, naphthalene, benzyltoluene, pyrene, triphenylmethane, phenylnaphthalene, and benzylnaphthalene; phthalic acid Examples thereof include esters such as dibutyl, dioctyl phthalate and didodecyl phthalate; ketones such as methyl ethyl ketone and acetophenone; ethers such as anisole and diphenyl ether.

[0015]

EXAMPLES Next, the present invention will be described more specifically by way of Examples and Comparative Examples. However, the present invention is not limited to these examples. In the following Examples and Comparative Examples, the alteration rate (%) was calculated as [(initial carbamate weight-carbamate weight after thermal stability test)/
(Initial carbamate weight)]×100. In addition, in Examples after Example 2 and Comparative Examples after Comparative Example 3, the accelerated thermal stability test was conducted by raising the test temperature in order to compare the alteration of the carbamate in a short time.

Example 1 In a 50 ml glass container, 20 g of 1,3-bis(methoxycarbonylaminomethyl)benzene (hereinafter referred to as MXDU) was charged, and dibutylthiourea was added thereto.
A thermal stability test was conducted by adding 600 ppm to XDU, substituting the inside of the container with nitrogen, closing the cap, and placing the container in a dry oven heated to 150° C. and holding the same temperature for 144 hours. After 144 hours, the content in the container was subjected to composition analysis using a liquid chromatograph and the data was analyzed. As a result, the alteration rate of MXDU was 1.0%.

Comparative Example 1 A thermal stability test was conducted in the same manner as in Example 1 except that the stabilizer was not added. As a result of analyzing the data, the alteration rate of MXDU was 6.8%.

Comparative Example 2 In the same manner as in Example 1, paratoluene sulfonamide was used as a stabilizer. As a result of analyzing the data,
The alteration rate of MXDU was 2.5%.

Examples 2 to 4 In the same manner as in Example 1 except that the test temperature was 170° C. and the holding time was 48 hours, 2-mercaptobenzothiazole, diethylthiourea and ethylenethiourea were used as stabilizers. The accelerated thermal stability test was performed. The results are shown in Table 1.
Shown in.

Comparative Examples 3 to 4 In the same manner as in Example 2, an accelerated thermal stability test was conducted using no stabilizer and paratoluenesulfonamide. The results are shown in Table 1.

[0021]

[Table 1] Stabilizer type Degradation rate (%) of MXDU Example 2 2-mercaptobenzothiazole 26.9 Example 3 Diethylthiourea 26.2 Example 4 Ethylenethiourea 25.4 Comparative Example 3 None 32.8 Comparative Example 4 Paratoluenesulfonamide 29.5

Example 5 20 g of MXDU and 20 g of dibenzyltoluene as a solvent were charged in the same container as in Example 1, and dibutylthiourea as a stabilizer was added to the container at 600 pp with respect to MXDU.
m was added, the inside of the container was replaced with nitrogen, the container was capped, and the container was placed in a dry oven heated to 170° C. and held at the same temperature for 48 hours to perform an accelerated thermal stability test. As a result of analyzing the data, the alteration rate of MXDU was 24.4%.

Example 6 1,3-bis(methoxycarbonylaminomethyl)cyclohexane (hereinafter referred to as 1,3 as carbamate ester
-Referred to as BUC. ) Was used, and an accelerated thermal stability test was conducted under the same conditions as in Example 2. The results are shown in Table 2.

Comparative Examples 5 to 7 In the same manner as in Example 6, paratoluenesulfonic acid, dilauryl 3,3'-thiodipropionate and tris(2-ethylhexyl)phosphite were used as stabilizers. An accelerated thermal stability test was conducted. The results are shown in Table 2.

[0025]

[Table 2] Type of stabilizer Deterioration rate (%) of 1,3-BUC Example 6 Dibutylthiourea 15.1 Comparative example 5 Paratoluenesulfonic acid 21.1 Comparative example 6 Dilauryl 3,3' thiodipropionate 20 .5 Comparative Example 7 Tris(2-ethylhexyl)phosphite 22.7

[0026]

EFFECTS OF THE INVENTION According to the method of the present invention, alteration of carbamic acid esters in a molten or solution state is suppressed, and stable storage and transportation can be achieved. Further, since the stabilizer of the present invention suppresses alteration of carbamic acid esters,
The yield is improved and the side reaction products are reduced when the isocyanate is produced by the thermal decomposition reaction.

Claims (1)

[Claims] 1. A method for storing and transporting carbamic acid esters, which comprises adding one or more stabilizers selected from thiazoles and thioureas to carbamic acid esters in a molten or solution state.