JPH07119190B2 - Method for producing isocyanates - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a carbamic acid ester or a thiocarbamate ester (hereinafter collectively referred to as carbamic acid esters) in the gas phase in the presence of a catalyst to undergo thermal decomposition in an isocyanate or thioisocyanate. (Hereinafter, these are collectively referred to as isocyanates) in a high yield. Isocyanates are highly reactive and useful compounds widely used as raw materials for urethanes, pharmaceuticals, agricultural chemicals and the like.

[0002]

BACKGROUND OF THE INVENTION Isocyanates are industrially produced by reacting amines with phosgene, but this method uses highly toxic phosgene and produces a large amount of hydrogen chloride that corrodes equipment. Since it has serious problems such as the above, a method for producing isocyanates without using phosgene is strongly desired.

As one of them, a number of methods by thermal decomposition of carbamic acid esters have been proposed. They are a method carried out in a liquid phase in the presence of a catalyst and a method carried out in a high temperature gas phase in the presence of a catalyst. It is roughly divided into.

As an example of the liquid phase reaction, a method using a basic catalyst such as an alkaline earth metal and its inorganic compound (JP-A-54-88201), a heavy metal catalyst or a heavy metal compound catalyst in an inert solvent is used. Method (JP-A-51-197)
21), Ib, IIb, IIIa, IVa, IVb in an inert solvent,
Method using at least one metal compound catalyst selected from the group consisting of Vb and VIII (JP-A-56-16616)
0), a method of using zinc chloride as a catalyst (JP-A-57-21).
356), a method of using a compound of Tl, Sn, Sb, and Zr as a catalyst (JP-A-58-128354), and a simple substance of Mn, Mo, W, or Zn in a high-boiling solvent or a metal compound under reduced pressure. A method (JP-A-2-134355) and the like are disclosed. However, all of these methods use a catalyst that is homogeneously dissolved in the reaction solution, which requires a large amount of energy to separate the catalyst from the decomposition products and also allows the incorporation of catalyst components into the products. In addition, the catalyst is difficult to recover and reuse, and must be disposed of as waste.

As an effective method for solving these problems, a method using a solid catalyst insoluble in the reaction solution under the reaction conditions has been proposed. For example, a method in which surface-rich metal zinc, aluminum, titanium, iron, chromium, cobalt, and nickel are used as catalysts (JP-A-56-65857), copper group, zinc group, aluminum group, carbon group other than carbon, and A method of using a titanium group simple substance, an oxide or a sulfide as a catalyst (JP-A-57-158747), and a method of using a carbon group other than carbon, a titanium group, a vanadium group, a chromium group of carbides and nitrides as a catalyst. (JP-A-57-158748),
Method using a boron-containing catalyst (JP-A-57-15874)
8) etc. are disclosed. However, since these methods have low catalyst activity and use a relatively large amount of solvent, the productivity of the isocyanate is low for industrial implementation, and further, the cost for separating and recovering the solvent is high. It costs.

On the other hand, as an example of the gas phase reaction, a method of carrying out a gas phase thermal decomposition reaction at 400 ° C. to 600 ° C. in the presence of a Lewis acid catalyst (JP-A-46-17773) is disclosed. The method has the drawbacks that a large amount of polymer is by-produced, the catalyst is thermally decomposed to have a short life, the reactor is corroded, and the yield of the target product is low. Further, the method is carried out under reduced pressure in the vapor phase in the presence of a heat-resistant gas-permeable filler composed of steel, brass, copper, zinc, aluminum, titanium, chromium, cobalt, nickel, carbon, and quartz (JP-A-59). -2053
52 and JP-A-59-205353), this method has a low yield of the desired product and a pressure of 41
Since it is carried out at a high temperature of 0 ° C., the equipment cost is high.

As described above, there is an example in which a solid acid or a solid base is used as a catalyst for a gas phase thermal decomposition reaction of carbamic acid esters into isocyanates.
All of them have low yields and a large amount of by-products of polymers or urea compounds, and industrially usable gas phase reaction catalysts have not yet been obtained.

[0008]

DISCLOSURE OF THE INVENTION In the present invention, when a carbamic acid ester is pyrolyzed to produce an isocyanate, a low yield of the objective isocyanate as described above, separation and recovery of a catalyst and a solvent are obtained. To solve problems such as difficulty in production, increase in cost, and by-product of polymer, and easy separation of product and catalyst, high space-time yield, high selectivity and stable isocyanate for a long time. It provides a method of obtaining a class.

[0009]

Means for Solving the Problems The inventors of the present invention have earnestly studied a method of thermally decomposing carbamic acid esters to produce isocyanates, and as a result, have found that an oxide sintered body is used as a catalyst for a gas phase thermal decomposition reaction. As a result, it was found that the objective isocyanates can be obtained in high yield and stably for a long time, and the present invention has been completed. The carbamic acid ester used in the present invention is a compound having a -NHCOO- group or a -NHCOS- group, and is a halogen which is inactive to a saturated or unsaturated aliphatic group, aromatic group, or isocyanate group. Group, nitro group, cyano group,
It may have a substituent such as an alkoxy group or an acyl group, but it must have a vapor pressure capable of being substantially used for a gas phase reaction under normal pressure or reduced pressure.

Examples of such carbamic acid esters include, for example, methyl carbamic acid, ethyl carbamic acid, propyl carbamic acid, butyl carbamic acid, pentyl carbamic acid, hexyl carbamic acid, methyl ester, ethyl ester, propyl ester and butyl ester. Alkylcarbamic acid esters such as ester, hydroxyethyl ester and phenyl ester; cyclopentylcarbamic acid, cyclohexylcarbamic acid and other alicyclic carbamine such as methyl ester, ethyl ester, propyl ester, butyl ester, hydroxyethyl ester and phenyl ester Acid esters, ethylenedicarbamic acid, propylenedicarbamic acid, butylenedicarbamic acid, pentamethylenedicarbamic acid, hexamethylenedicarbamine Etc., dimethyl ester, diethyl ester, dipropyl ester, dibutyl ester, dihydroxy ethyl ester, alkylene carbamic acid diesters such as diphenyl ester, 1,4
Alicyclic dicarbamic acid diesters such as cyclohexyldicarbamic acid and isophoronedicarbamic acid such as dimethyl ester, diethyl ester, dipropyl ester, dibutyl ester, dihydroxyethyl ester and diphenyl ester, phenylcarbamic acid and tolylcarbamic acid Aromatic carbamic acid esters such as methyl ester, ethyl ester, propyl ester, butyl ester, hydroxyethyl ester, phenyl ester, phenylenedicarbamic acid, 2,4- or 2,
Dimethyl ester such as 6-tolylene dicarbamic acid,
Examples thereof include aromatic dicarbamic acid diesters such as diethyl ester, dipropyl ester, dibutyl ester, dihydroxyethyl ester, diphenyl ester, and thiolcarbamic acid esters thereof, but the present invention is not limited thereto.

The catalyst according to the present invention is an oxide sintered body. In general, oxide particles are bonded to each other by heating at a high temperature to form larger particles. This phenomenon is called sintering. In the sintering, volume shrinkage occurs due to a decrease in voids between particles as a physical change, and strength and amount of acid-base points of an oxide decrease as a chemical change. Therefore, the oxide-sintered body is considered to be inactive as a catalyst because the acid-base strength is weak, the amount of acid sites and base sites is small, and the specific surface area is a few m ² or less. Use is a substance that has never been neglected. Therefore, there is no case where the carbamic acid ester was used for the gas-phase thermal decomposition reaction of the isocyanate to the isocyanate.

Among oxide sintered bodies, in the periodic table
Oxide sintered body of at least one element selected from the group Ib to group VIII transition metal elements, lanthanoid group elements and actinoid group elements or alkali metal elements and / or alkaline earth metal elements The oxide sintered body containing is excellent in performance. Examples of these elements are Cu, Zn, Cd, Sc, Y, Ti,
Zr, Nb, Ta, Mo, W, Mn, Fe, Ni, L
Examples thereof include a, Ce, Pr, Nd and Th, but the catalyst according to the present invention is not limited thereto.

These are used in the form of either a single oxide or a complex oxide. In the present invention, oxide sinters also include sintered bodies of various oxo acid salts (titanate, niobate, molybdate, tungstate, etc.).

The method for preparing the catalyst is not particularly limited, and any commonly used method can be applied. Raw materials for the catalyst are oxides, oxide sols, hydroxides, halides,
Salts (carbonate, sulfate, nitrate, organic acid salt, ammonium salt, etc.), oxo acid salts (titanate, niobate, molybdate, tungstate, etc.) and metals are used.

As an example of the method for preparing the catalyst of the present invention, various catalyst raw materials are dissolved or suspended in water, heated and concentrated under stirring, molded and dried and sintered to obtain a catalyst, or various catalyst raw materials are submerged in water. After dissolving or suspending and adjusting the pH to make hydroxide, filtration, washing with water, molding, drying,
A method in which a catalyst is obtained through sintering, and further, a method in which oxides or hydroxides of various elements are mixed as powders with an appropriate molding aid (for example, water, alcohol, etc.), molded, dried, and sintered. Etc. The sintering temperature depends on the constituent elements of the oxide and is usually 800 ° C to 2000 ° C.

In carrying out the present invention, the reactor may be either a fixed bed flow type or a fluidized bed type. The reaction can be carried out at normal pressure or under reduced pressure using an inert gas such as nitrogen, helium or argon as a diluent, or under reduced pressure without using an inert gas for dilution. The depressurization reaction varies depending on the kind of the raw material carbamate, and is usually 1 mmHg to 5 mm.
It is in the range of 00 mmHg. The space velocity is 500 / hr to 20000 / hr, preferably 1000 / hr to 10000 / hr when a diluent is used, and 10 / hr to 1000 / hr when a reduced pressure reaction without a diluent is used.
It is preferably 50 / hr to 500 / hr. The reaction temperature is usually 250 ° C. to 450 ° C., though it depends on the kind of raw material.

[0017]

The details of the cause of the high performance of the catalyst according to the present invention are unknown, but in the gas phase thermal decomposition reaction of carbamic acid esters carried out at a relatively high temperature, the catalytic active site (acid site and base It is considered that if the strength of point is too strong, the decomposition reaction into other than the desired isocyanates and the polymerization of the raw material or the produced isocyanates are likely to occur.
The catalyst according to the present invention is an oxide sintered at a very high temperature, its active site strength is weak and nearly neutral, and its specific surface area is very small, less than a few m ^2. With respect to the thermal decomposition reaction, weak acid points and basic points act in cooperation to exert sufficient activity, and there are no unnecessary high-strength active points, and since the specific surface area is small, The desorption of the product from the catalyst becomes rapid,
It is considered that such high performance is exhibited.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

The conversion of carbamate, the selectivity of isocyanate, and the single-flow yield of isocyanate in the examples are defined as follows.

Carbamate conversion rate (mol%) =
(Mole number of reacted carbamic acid ester) / (Mole number of supplied carbamic acid ester) × 100 Selectivity of isocyanate (mol%) = (Mole number of produced isocyanate) / (Mole of reacted carbamic acid ester) Number) × 100 Single-flow yield of isocyanate (mol%) = (mol number of produced isocyanate) / (mol number of fed carbamate) × 100 Example 1. Water (5 g) was added to zinc oxide (16.3 g) and calcium hydroxide (0.74 g) and kneaded, followed by drying in air (120 ° C, 6 hours), firing (1000 ° C, 2 hours), sintering After (1400 ° C., 2 hours), a catalyst having a composition of Zn ₂₀ Ca ₁ at an atomic ratio excluding oxygen was obtained.

5 m of this catalyst crushed to 9-16 mesh
1 was filled in a stainless steel reaction tube having an inner diameter of 10 mm, and 37
After dipping in a molten salt bath at 0 ° C., a raw material gas containing 10% by volume of methyl ethylcarbamate and 90% by volume of nitrogen was passed through the reaction tube at a space velocity of 2000 / hr (STP) to carry out a reaction. The reaction products are collected separately by infrared absorption spectrum,
It was identified by nuclear magnetic resonance spectrum, weight spectrum, etc., and was collected in dioxane and quantified by gas chromatography. Table 1 shows the reaction conditions, and Table 2 shows the reaction results.

Example 2. Yttrium oxide (22.6
g) and magnesium hydroxide (1.2 g) in water (10 g)
After adding and kneading, drying in air (120 ° C, 6 hours), firing (1000 ° C, 2 hours), sintering (1400
After 2 hours), a catalyst having a composition of Y ₁₀ Mg _{1 in} terms of atomic ratio excluding oxygen was obtained.

Using 5 ml of the catalyst crushed to 9 to 16 mesh, the thermal decomposition reaction of ethyl carbamic acid phenyl ester was carried out under the reaction conditions shown in Table 1 in the same manner as in Example 1, and the results shown in Table 2 were obtained.

Example 3. Titanium oxide (26.6g),
A solution of potassium hydroxide (0.85g) in water (15g) was added and kneaded, then dried in air (120 ° C, 6 hours), baked (1000 ° C, 2 hours), sintered (1400 ° C, 2 hours). Thus, a catalyst having a composition of Ti ₂₀ K ₁ in terms of atomic ratio excluding oxygen was obtained.

The thermal decomposition reaction of carbamic acid methyl ester of isocyanatoethyl methacrylate was carried out in the same manner as in Example 1 under the reaction conditions shown in Table 1 using 5 ml of the catalyst crushed to 9 to 16 mesh, and the results shown in Table 2 were obtained. Got

Example 4. Zirconium oxide (18.6
g), calcium hydroxide (0.74 g) and basic zirconia sol (containing 30% by weight of ZrO ₂ ) (20
g) was added and kneaded, then dried in air (120 ° C., 6 hours) and sintered (1400 ° C., 2 hours) to obtain a catalyst having a composition of Zr ₂₀ Ca ₁ in terms of atomic ratio excluding oxygen.

The thermal decomposition reaction of carbamic acid hydroxyethyl ester of isocyanatomethacrylate was carried out in the same manner as in Example 1 under the reaction conditions shown in Table 1 using 5 ml of the catalyst crushed to 9 to 16 mesh, and the results shown in Table 2 were obtained. Got

Example 5. Zirconium oxide (25g) in basic zirconia sol (containing 30% by weight of ZrO ₂ )
(7 g) was added and kneaded, and then dried in air (120 ° C,
After 6 hours) and sintering (1400 ° C., 2 hours), a catalyst was obtained.

Using 5 ml of a catalyst crushed to 9 to 16 mesh, the thermal decomposition reaction of cyclohexylcarbamic acid ethyl ester was carried out under the reaction conditions shown in Table 1 in the same manner as in Example 1 to obtain the results shown in Table 2.

Example 6. To niobium oxide (26.6g),
After adding a solution of sodium hydroxide (0.40 g) in water (10 g) and kneading, drying in air (120 ° C., 6 hours),
Firing (1000 ° C., 2 hours) and sintering (1400 ° C., 2 hours) gave a catalyst having a composition of Nb ₂₀ Na ₁ in terms of atomic ratio excluding oxygen.

2.5 m of catalyst crushed to 9-16 mesh
The thermal decomposition reaction of cyclohexylcarbamic acid hydroxyethyl ester was carried out in the same manner as in Example 1 under the reaction conditions shown in Table 1 to obtain the results shown in Table 2.

Example 7. Tungsten oxide (23.2
g) and barium hydroxide (octahydrate) (1.6 g) were mixed with water (10 g) and dried in air (120 g).
℃, 6 hours), firing (1000 ℃, 2 hours), sintering (1
200 ° C, 2 hours), and then the atomic ratio excluding oxygen is W ₂₀ Ba.
A catalyst having a composition of ₁ was obtained.

The thermal decomposition reaction of phenylcarbamic acid methyl ester was carried out in the same manner as in Example 1 under the reaction conditions shown in Table 1 using 5 ml of the catalyst crushed to 9 to 16 meshes.
The results shown in are obtained.

Example 8. Iron nitrate (9 hydrate) (20.2
g) and cesium nitrate (0.49 g) were dissolved in water (100 g), and aqueous ammonia was added to adjust the pH to 8. Then, it is concentrated to dryness in a 90 ° C water bath and dried in air (1
20 ℃, 6 hours), high temperature drying (230 ℃, 12 hours),
After sintering (1000 ° C., 2 hours), a catalyst having a composition of Fe ₂₀ Cs _{1 in} terms of atomic ratio excluding oxygen was obtained.

Using 5 ml of a catalyst crushed to 9 to 16 mesh, hexamethylenedicarbamic acid dimethyl ester having a concentration of 100% by volume was supplied under the conditions of a reaction pressure of 10 mmHg, a reaction temperature of 350 ° C. and a space velocity of 200 / hr (STP). Then, a thermal decomposition reaction was performed. The reaction product was collected by cooling, dissolved in dioxane, and quantified by gas chromatography. Table 1 shows the reaction conditions, and Table 2 shows the reaction results.

Example 9. Water (20 g) was added to lanthanum oxide (32.6 g) and strontium hydroxide (octahydrate) (5.3 g), and the mixture was kneaded and then dried in air (120
℃, 6 hours), firing (1000 ℃, 2 hours), sintering (1
400 ° C., 2 hours), and La ₁₀ S in atomic ratio excluding oxygen
A catalyst having a composition of r ₁ was obtained.

The thermal decomposition reaction of isophorone dicarbamic acid dimethyl ester was carried out in the same manner as in Example 8 under the reaction conditions shown in Table 1 using 5 ml of the catalyst crushed to 9 to 16 mesh, and the results shown in Table 2 were obtained.

Example 10. Titanium oxide (26.6g)
To the above, a solution of sodium hydroxide (1.33 g) in water (10 g) was added and kneaded, followed by drying in air (120 ° C., 6 hours), firing (1000 ° C., 2 hours), and sintering (1400
(° C., 2 hours) to obtain a catalyst having a composition of Ti ₁₀ Na ₁ in terms of atomic ratio excluding oxygen.

Using 5 ml of a catalyst crushed to 9 to 16 mesh, a thermal decomposition reaction of 2,4-toluylenedicarbamic acid dimethyl ester was carried out under the reaction conditions shown in Table 1 in the same manner as in Example 8 and shown in Table 2. I got the result.

[0040]

[Table 1]

[0041]

[Table 2]

Comparative Example 1. The calcination temperature of the catalyst of Example 6 was set to 5
Catalyst preparation and reaction were performed in exactly the same manner as in Example 6 except that the temperature was set to 00 ° C. and the sintering was not performed. As a result, the conversion rate of cyclohexylcarbamic acid ethyl ester was 96.
Although it was as high as mol%, there were many solid substances (urea compounds) as by-products, and the selectivity and yield of the target cyclohexyl isocyanate were remarkably low at 30 mol% and 29 mol%, respectively. In this reaction, continuous reaction was impossible due to clogging of the side tube of the reaction tube with solid matter.

[0043]

INDUSTRIAL APPLICABILITY When the catalyst according to the present invention is used in the gas phase thermal decomposition reaction of carbamic acid esters to isocyanates, the isocyanates are continuously produced in a high space-time yield with high selectivity. it can. Moreover, since this continuous reaction does not accompany by-products of the polymer, it can be continued stably for a long time. Furthermore,
Since the carbamic acid ester is converted into the isocyanate only by passing through the catalyst layer, there is no need to separate and recover the catalyst, and no catalyst-containing waste liquid is generated.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/06 X 23/10 X 23/20 X 23/30 X 23/78 X C07B 61/00 300 C07C 263/04

Claims (3)

[Claims] 1. A method for producing isocyanates, which comprises thermally decomposing carbamic acid esters in a gas phase using an oxide sintered body as a catalyst. 2. The catalyst is a group Ib to VIII of the periodic table.
The method according to claim 1, which is an oxide sintered body of at least one element selected from the group consisting of transition metal elements, lanthanoid group elements, and actinoid group elements. 3. The oxide sintered body, wherein the catalyst contains an alkali metal element and / or an alkaline earth metal element.
Alternatively, the method according to claim 2.