HK1060561B - Process for the production of isocyanates in the gas phase - Google Patents

Description

Process for preparing gas-phase isocyanates

Technical Field

The invention relates to a method for producing isocyanates in the gas phase, which avoids fluctuations in temperature over time and asymmetries in the temperature distribution. This is achieved by flow-related measures, such as homogenization and centering of the educt flow, in order to improve the reaction characteristics in the tubular reactor. Thereby avoiding the formation of polymeric secondary products which lead to baked deposits in the reactor and a reduced reactor service life.

Background

EP-A0289840 describes a process for preparing (cyclo) aliphatic diisocyanates by phosgenation of the corresponding vaporous (cyclo) aliphatic diamines at 200-600 ℃. Phosgene is provided in stoichiometric excess. Superheated steam of vaporous (cyclo) aliphatic diamine or (cyclo) aliphatic diamine/inert gas mixture is passed continuously on the one hand and superheated steam of phosgene on the other hand into a cylindrical reaction chamber, where they mix together and cause the reaction. The exothermic phosgenation reaction proceeds while maintaining turbulence.

The gas-phase educts are continuously reacted in the tubular reactor. If the jet mixer principle is applied (Chemie-Ing. -Techn.44(1972), page 1055, FIG. 10), two educt streams A and B are supplied to the tubular reactor. The educt stream A is supplied via a central nozzle and the educt stream B via an annular space between the central nozzle and the tubular reactor wall. The flow rate of the educt stream a is higher than the flow rate of the educt stream B. This allows the reaction components in the tubular reactor to be thoroughly mixed and thus reacted. This method of carrying out the reaction has become industrially influential in the preparation of aromatic diisocyanates by phosgenation of aromatic diamines in the gas phase (e.g. EP-A0570799).

However, the known process exhibits temperature fluctuations of up to 50 ℃ during the reaction. Furthermore, an asymmetric temperature distribution of up to 100 ℃ can be detected in the circumferential direction of the cylindrical reaction chamber or the tubular reactor, for example, with thermocouples.

The result of the temperature fluctuations and the asymmetric temperature distribution is the formation of polymeric secondary products which lead to baked deposits and blockages in the reactor, thereby shortening the service life of the reactor.

Disclosure of Invention

It was therefore an object of the present invention to provide a process for preparing (cyclo) aliphatic and aromatic diisocyanates by phosgenation of the corresponding (cyclo) aliphatic and aromatic diamines in the gas phase at elevated temperature, which process avoids temperature fluctuations and asymmetries in the temperature distribution in the reaction zone to the greatest possible extent.

It has surprisingly been found that the homogenization of the educt stream B fed through the annular gap of the tubular reactor and the maximization of the feed of the two educt streams A and B to the center of the tubular reactor have a significant positive effect on the stability of the reaction zone and thus on the overall gas phase reaction. As a result of the reaction being carried out in a more stable manner, the observed temperature fluctuations are significantly reduced and the asymmetry of the temperature distribution is virtually completely eliminated. In this way, the drawbacks of the prior art processes can be significantly reduced by taking measures on the educt stream according to the invention, which is described in more detail below.

Brief Description of Drawings

The figure shows a tubular reactor suitable for carrying out the invention.

Detailed description of the invention

The invention provides a process for preparing diisocyanates and triisocyanates of the general formula (I)

R(NCO)_n (I)，

Wherein

R represents a (cyclo) aliphatic or aromatic hydrocarbon residue having up to 15 carbon atoms, preferably 4 to 13 carbon atoms, with the proviso that at least two carbon atoms are arranged between two NCO groups, and

n represents the number 2 or 3,

the method is achieved by phosgenating the corresponding diamines and/or triamines of the general formula (II) in the gas phase

R(NH₂)_n (II)，

Wherein

R represents a (cyclo) aliphatic or aromatic hydrocarbon residue having up to 15 carbon atoms, preferably 4 to 13 carbon atoms, with the proviso that at least two carbon atoms are arranged between two amino groups, and

n represents the number 2 or 3.

The phosgenation reaction is carried out in a tubular reactor comprising a central nozzle and an annular space between the central nozzle and the wall of the tubular reactor. The central nozzle is located in the center of the tubular reactor and at least two flow homogenizers are arranged in the annular space. The central nozzle is connected by a flexible connecting tube to the inlet of one of the educt streams and the inlet of the second educt stream is arranged in the annular space. The educt stream containing diamine and/or triamine is fed into the tubular reactor through a central nozzle. The educt stream containing phosgene is fed through the annular space into the tubular reactor and the flow velocity in the annular space is homogenized over the entire cross-section of the annular space by means of a flow homogenizer.

In an alternative embodiment of the process according to the invention, the diamine-and/or triamine-containing educt stream and the phosgene-containing educt stream are switched such that the diamine-and/or triamine-containing educt stream is fed through the annular space into the tubular reactor and the phosgene-containing educt stream is fed through the central nozzle into the tubular reactor.

According to the invention, it is preferred that the second flow homogenizer or the last homogenizer (if there are more than two homogenizers) is provided as a combined unit before the educt stream B enters the tubular reactor. The combined unit consists of a flow homogenizer and a flow balancer.

The task of the flow homogenizer is to homogenize the flow rate of the educt stream distributed into the annular space over the entire cross-section of the annular space. Known flow homogenizers are, in particular, perforated plates, screens, sintered metals, sintered elements or sintered beds. Perforated plates are preferably used.

The task of the flow balancer is to orient the flow axially, i.e. to avoid diagonal flows and eddies. Known flow balancers are, in particular, honeycomb structures and tube structures.

The hose and preferably the compensator (bellows made of e.g. stainless steel) are suitable for use as a flexible connection tube.

The process according to the invention provides that the local flow rate does not deviate more than + -10%, preferably + -2%, from the average flow rate of the educt stream distributed through the annular space over the entire cross-section.

In the process of the present invention, diisocyanates and/or triisocyanates are prepared from the corresponding diamines and/or triamines.

Diisocyanates are preferably prepared in the process of the present invention by phosgenation of the corresponding diamines.

In the process of the present invention, 1, 8-diisocyanato-4- (isocyanatomethyl) octane, Triisocyanatononane (TIN) are preferably prepared as triisocyanates represented by the general formula (I).

Typical examples of suitable aliphatic diamines are given, for example, in EP-A-0289840, and typical examples of suitable aliphatic triamines are given, for example, in EP-A-749958. These diamines are suitable for use by the process of the present invention for preparing the corresponding diisocyanates or triisocyanates.

Particularly preferred are Isophoronediamine (IPDA), Hexamethylenediamine (HAD) and bis (p-aminocyclohexyl) methane.

Typical examples of suitable aromatic diamines are the pure isomers or isomer mixtures of diaminobenzene, diaminotoluene, diaminodimethylbenzene, diaminonaphthalene and diaminodiphenylmethane. Preference is given to mixtures of 2, 4-/2, 6-toluenediamine isomers in isomer ratios of 80/20-65/35 or pure 2, 4-toluenediamine isomers.

The preferred triamines are 1, 8-diamino-4- (aminomethyl) octane and triaminononane.

The starting amine of the formula (II) is fed in the gas phase into the reactor and, before the process of the invention is carried out, is optionally evaporated and heated to preferably 200-600 ℃, more preferably 250-450 ℃ and optionallySuch as N₂Ne, He, Ar or diluted with a vapor of an inert solvent, and then fed into the reactor. Phosgene was fed into the tube reactor in stoichiometric excess and at a temperature of 200-600 ℃. If one or more aliphatic diamines are used, the molar excess of phosgene over amino groups is preferably from 25 to 250%, while if one or more aliphatic triamines are used, the excess is preferably from 50 to 350%. If aromatic diamines are used, the number of moles of phosgene in excess of amino groups is preferably 150-300%.

The invention is explained below by way of example with reference to the accompanying drawings. The educt stream a (diamine and/or triamine) flows through an inlet 1, a flexible connecting tube 2 and a central nozzle 3 into a tubular reactor 4. The inlet 1 for the educt stream a is rigidly connected to the cover 5 of the tubular reactor 4. The central nozzle 3 is movably connected to the inlet 1 for the educt stream a by means of a flexible connecting tube 2.

The central nozzle 3 is firmly positioned by a plurality of flow homogenizers 7, 8 and 9 and is located in the center of the axis of rotation 6 of the tubular reactor 4. For this purpose, at least two flow homogenizers 7 and 9, and optionally also flow homogenizer 8, are required. The flow homogenizers 7, 8 and 9 are fixed in the annular space 10 of the tubular reactor and extend over the entire flow cross section of the annular space.

The educt stream B (phosgene) flows into the annular space 10 of the tube reactor 4 via the inlet 11. The flow rate of the educt stream B is homogenized during passage through the flow homogenizers 7, 8 and 9, so that the homogenized fluid flows through the entire flow cross section of the annular space 10. The flow balancer 12 is arranged directly downstream of the last flow homogenizer 9 in the flow direction.

This also affects the axial positioning of the flow velocity of the educt flow B in the direction of the axis of rotation 6.

The invention is further illustrated but is not limited by the following examples in which all parts and percentages are by weight unless otherwise indicated.

Examples

The Hexamethylenediamine (HDA)/inert gas mixture is continuously fed to a tubular reactor of the type shown in the drawing as educt A and phosgene as educt B. Both educt streams were 300 ℃.

On the one hand, the tests were carried out according to the invention with a tubular reactor with two flow homogenizers 7 and 9, such as shown in the drawing. The flow homogenizer 8 and flow balancer 12 were not present in the tubular reactor 4 used for the tests of the present invention.

On the other hand, tests were carried out with a tubular reactor as comparative example, containing a packing instead of flow homogenizers 7 and 9, which easily ensures the homogenization and centring of the educt stream. The flexible connecting tube 2 is replaced by a rigid connection of the central nozzle 3 to the inlet 1 of the tubular reactor 4.

The temperature at the cylindrical outer wall of the tubular reactor was measured with thermocouples at three test plates located downstream of the central nozzle 3. Three thermocouples were in contact with the outer wall at each measurement plate and arranged at circumferential intervals of 120 degrees.

In the method performed as a comparative example, fluctuations in temperature over time of up to 50 ℃ occurred at the measurement point. Furthermore, there is an asymmetric temperature distribution in the circumferential direction of up to 100 ℃. With the process according to the invention, the temperature fluctuations with time are significantly reduced to about 10 ℃ while the temperature asymmetry is completely eliminated. The formation of polymeric secondary products deposited on the wall of the tubular reactor is thereby reduced, resulting in a significant increase in the reactor service life.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (9)

1. Process for producing diisocyanate and/or triisocyanate represented by general formula (I)

R(NCO)_n (I)，

Wherein

R represents an aliphatic, cycloaliphatic or aromatic hydrocarbon residue having from 2 to 15 carbon atoms, with the proviso that at least two carbon atoms are arranged between two NCO groups, and

n represents a number of 2 or 3,

the process comprises phosgenating the corresponding diamines and/or triamines of the general formula (II) in the vapor phase in a tubular reactor

R(NH₂)_n(II) wherein the tubular reactor further comprises

(a) A central nozzle located in the center of the tubular reactor, the nozzle being positioned by at least two flow homogenizers,

(b) at least two flow homogenizers, which homogenizers are arranged in the annular space,

(c) an annular space between the central nozzle and the tubular reactor wall,

(d) the wall of the tubular reactor is provided with a plurality of tubular holes,

(e) a flexible connection tube connecting the central nozzle and the first inlet,

(f) a first inlet for a first educt stream,

(g) a second inlet for a second educt stream arranged in the annular space,

the method is carried out in the following manner

(1) The first educt stream is fed to the tubular reactor through a central nozzle,

(2) the second educt flow is supplied to the tubular reactor through the annular space, and

(3) the flow velocity in the annular space is homogenized over the entire annular space cross section with a flow homogenizer.

2. The process of claim 1, wherein the first educt stream comprises a diamine and/or a triamine and the second educt stream comprises phosgene.

3. The process of claim 1, wherein the first educt stream comprises phosgene and the second educt stream comprises a diamine and/or a triamine.

4. The process of claim 1 wherein the diamine is phosgenated to produce a diisocyanate.

5. The process of claim 1 wherein the steam diamine is supplied to the tubular reactor through a central nozzle at 200-600 ℃ and phosgene is supplied to the tubular reactor through an annular space in stoichiometric excess at 200-600 ℃.

6. The process of claim 1 wherein isophorone diamine, hexamethylene diamine, or bis (p-aminocyclohexyl) methane is phosgenated.

7. The process of claim 1 wherein an isomeric mixture of 2, 4-/2, 6-toluenediamine or pure 2, 4-toluenediamine is phosgenated.

8. The process of claim 1 wherein triisocyanatononane is the product produced.

9. The process of claim 1, wherein R represents an aliphatic, cycloaliphatic or aromatic hydrocarbon residue having from 4 to 13 carbon atoms.