HK1081525B

HK1081525B - Process for the preparation of diisocyanates

Info

Publication number: HK1081525B
Application number: HK06101529.2A
Authority: HK
Inventors: Meyn Jürgen; Stutz Herbert
Original assignee: Bayer Materialscience Ag
Priority date: 2003-12-18
Filing date: 2006-02-03
Publication date: 2009-12-11

Description

Process for preparing diisocyanates

Cross reference to related patent applications

According to 35 u.s.c. § 119(a) - (d), the present patent application claims priority from german patent application 10359627.5 filed 12, 18/2003.

Background

1. Field of the invention

The invention relates to a method for producing diisocyanates and/or triisocyanates by phosgenating the corresponding diamines and/or triamines in the gas phase.

2. Background of the invention

The preparation of isocyanates by reaction of phosgene with amines in the gas phase has been known for a long time (cf. Siefken, Annalen)562,108, 1949). Gas phase reactions can be carried out by various routes. Nozzles, nozzles or mixing tubes are used to mix the raw materials. For the gas-phase phosgenation of diisocyanates, the use of nozzles has been described very generally, for example in EP-A1-0593334 with smooth nozzles and central feed lines. Typically, one of the materials is injected through a centrally located nozzle into a second material flowing at a low velocity through an annular gap around the nozzle tube. The fast flowing material sucks the slow flowing material to complete mixing. And determining the time or distance for completely mixing the raw materials according to the difference of the diameter of the nozzle and the flow rate of the materials. The chemical reaction is carried out while mixing. The reaction rate of the phosgenation of the amine in the gas phase is determined by the mixing of the starting materials. Since the isocyanate formed undergoes a secondary reaction with the amine, rapid mixing and excess phosgene are necessary to obtain the desired diisocyanate efficiently. Due to the back mixing process, the diisocyanate can react with unreacted diamine in the feed stream with solid precipitates. This causes fouling and plugging of the reactor in the mixing section.

It is also necessary to increase the reactor size, often with tubular reactors, to increase the mixing nozzle size, often with smooth nozzles. However, as the diameter of the smooth nozzle increases, the central nozzle reduces the mixing rate by requiring a greater range of diffusion, increases the risk of back-mixing, causes the formation of polymeric impurities and, therefore, causes the solids to agglomerate in the reactor.

In British patent specification 1165831, the reaction is carried out in a tubular reactor equipped with a mechanical stirrer. The reactor resembles a thin film evaporator with an internal agitator to mix the gases while rubbing against the heated walls of the tubular reactor to prevent the build-up of polymer material on the walls of the tube. However, the use of high speed stirrers while controlling the phosgene temperature around 300 ℃ requires a powerful safety measure to seal the reactor and to equip the stirrer with a highly corrosive medium.

It is therefore an object of the present invention to provide a process for preparing diisocyanates and/or triisocyanates in the gas phase, in which the starting diamines and phosgene can be mixed more rapidly and better in the reactor without internal transfer and polymer impurities and caking in the reactor can be avoided.

Detailed Description

The invention relates to a method for producing diisocyanates and triisocyanates of general formula (I),

R(NCO)_n (I)

wherein R represents a (cyclo) aliphatic or aromatic hydrocarbon group having up to 15 carbon atoms, with the proviso that at least 2 carbon atoms are arranged between 2 NCO groups, and n represents the number 2 or 3.

The process is carried out in a tubular reactor having a double-walled conduit extending centrally in the direction of the axis of rotation of the tubular reactor, a concentric annular gap being formed between the inner and outer walls of the double-walled conduit, and the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double-walled conduit to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double-walled conduit being from 1: 0.5 to 1: 4.

The method comprises the step of subjecting the corresponding diamine and/or triamine of the general formula (II) to gas phase phosgenation

R(NH₂)_n (II)

Wherein R represents a (cyclic) aliphatic or aromatic hydrocarbon radical having up to 15 carbon atoms, with the proviso that at least 2 carbon atoms are arranged between 2 amino groups and n represents the number 2 or 3,

the gas phase phosgenation is carried out by the following steps:

the diamine and/or triamine in vapor form and the phosgene are heated separately from one another to a temperature of from 200 ℃ to 600 ℃,

feeding the diamine and/or triamine in vapor form via concentric annular gaps to a tubular reactor at an average flow rate of from 20 to 150m/s, and

phosgene is fed into the tubular reactor over the remaining cross section of the tubular reactor at an average flow velocity of at least 1 m/s.

Brief description of the drawings

FIG. 1 is a schematic view of a tubular reactor suitable for use in the process of the present invention.

Detailed Description

Except in the examples and where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified by the term "about".

It has now been found that (cyclo) aliphatic or aromatic diisocyanates and/or triisocyanates can be prepared by the gas-phase phosgenation of the corresponding diamines and/or triamines if one of the starting materials is mixed at high speed through an annular gap located centrally in the other starting material stream, and the stated disadvantages of the prior art can be ruled out. Therefore, the diffusion distance at the time of mixing is small, and the diffusion time is very short. The reaction can be carried out with high selectivity to obtain the desired diisocyanate. The formation of polymeric impurities and agglomeration is also reduced.

R(NCO)_n (I)

wherein

R represents a (cyclo) aliphatic or aromatic hydrocarbon radical having up to 15, preferably 4 to 13, carbon atoms, with the proviso that at least 2 carbon atoms are arranged between 2 NCO groups, and

n represents the number 2 or 3,

the process comprises the gas-phase phosgenation of the corresponding diamines and/or triamines of the general formula (II)

R(NH₂)_n (II)

Wherein

R represents a (cyclic) aliphatic or aromatic hydrocarbon radical having up to 15, preferably 4 to 13, carbon atoms, with the proviso that at least 2 carbon atoms are arranged between 2 amino groups, and

n represents the number 2 or 3,

the gas phase phosgenation is carried out in a tubular reactor having a double-walled pipe extending centrally in the direction of the axis of rotation of the tubular reactor, a concentric annular gap being formed between the inner and outer walls of the double-walled pipe and the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double-walled pipe to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double-walled pipe being from 1: 0.5 to 1: 4, preferably from 1: 1 to 1: 3,

wherein the diamine and/or triamine in vapor form and the phosgene are heated separately from one another to a temperature of from 200 ℃ to 600 ℃,

and feeding the diamine and/or triamine in vapor form via the concentric annular gaps into the tubular reactor at an average flow velocity of from 20 to 150m/s, preferably from 40 to 100m/s, and feeding phosgene into the tubular reactor over the remaining cross section of the tubular reactor at an average flow velocity of at least 1m/s, preferably from 5 to 15 m/s.

The diamine in vapor form may also optionally be diluted with a vapor of an inert gas or an inert solvent prior to being fed to the reactor. Suitable inert gases are, for example, nitrogen and noble gases such as helium or argon. Preferably, nitrogen is used. Suitable solvents are, for example, chlorobenzene, o-dichlorobenzene, toluene, xylene, chlorotoluene, chloronaphthalene and decahydronaphthalene. Chlorobenzene is preferably used.

In the process of the present invention, the mixing of the two raw materials takes place at the annular interface of the diamine and phosgene raw material nozzles.

The starting materials for the process of the invention are diamines and/or triamines of the general formula (II)

R(NH₂)_n (II)

Wherein

n represents the number 2 or 3.

Typical examples of suitable aliphatic diamines are mentioned in EP-A1-0289840 at column 3, lines 19-26. Examples of suitable aliphatic triamines are also mentioned, as mentioned in EP-A-749958, column 3, lines 18-22 and lines 28-31. The following are particularly suitable: 1, 4-diaminobutane, 1, 3-diaminopentane, 1, 6-diaminohexane (HDA), 1, 11-diaminoundecane, 1, 4-diaminocyclohexane, 1-amino-3, 3, 5-trimethyl-5-aminomethylcyclohexane (isophoronediamine, IPDA), 2, 3-, 2, 4-and 2, 6-diamino-1-methylcyclohexane and mixtures thereof, 1, 3, 5-triisopropyl-2, 4-diaminocyclohexane, 2, 4-and 2, 6-diamino-1-isopropylcyclohexane or mixtures thereof and bis (p-aminocyclohexyl) methane.

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

Typical examples of suitable aromatic diamines are pure isomers or isomer mixtures of phenylenediamine, diaminotoluene, diaminodimethylbenzene, diaminonaphthalene and diaminodiphenylmethane; mixtures of 2, 4/2, 6-toluenediamine with isomer ratios of 80/20 and 65/35, or pure 2, 4-toluenediamine are preferred.

The triamine used is preferably 1, 8-diamino-4- (aminomethyl) octane or triaminononane.

Prior to carrying out the process of the present invention, the starting amine is vaporized and heated to 200-.

Before carrying out the process according to the invention, the phosgene used in the phosgenation reaction is likewise heated to a temperature of 200-600 ℃ and preferably 300-500 ℃.

To carry out the reaction according to the invention, a preheated stream containing diamine and/or triamine or a mixture of diamine and/or triamine and a preheated stream containing phosgene are fed continuously into the tubular reactor.

The tubular reactor is generally made of steel, glass, alloy or enameled steel and has a length sufficient to ensure complete reaction of the diamine with phosgene under the process conditions. The phosgene stream is generally fed in from one end of the reactor. The amine is mixed at high velocity into the phosgene stream via concentric annular gaps that are symmetrically radially disposed. Phosgene is also fed into the tubular reactor over a cross-section defined by the inner wall of the double walled conduit and a cross-section of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double walled conduit.

The mixing zone is preferably maintained at a temperature of from 200 ℃ to 600 ℃, preferably from 300 ℃ to 500 ℃, which temperature can be maintained by heating the tubular reactor if desired.

When carrying out the process according to the invention, the pressure in the feed pipe into the tubular reactor is preferably from 200 mbar to 4000 mbar and the pressure in the outlet from the tubular reactor is preferably from 150 mbar to 2000 mbar. To maintain a suitable pressure difference, the mean velocity of the phosgene stream is set to at least 1m/s, preferably from 2m/s to 60m/s, particularly preferably from 3 to 20m/s, very particularly preferably from 5 to 15m/s, at the inlet into the tubular reactor.

The amines are mixed via the concentric annular gaps at a speed of from 20 to 150m/s, preferably from 40 to 100 m/s. The mixing of the two gaseous starting materials diamine and phosgene takes place at the annular interface of the starting material nozzles.

Under these reaction conditions, turbulent conditions are generally predominant in the reaction space.

The invention is described below with reference to fig. 1.

Figure 1 is a tubular reactor 1 suitable for use in the process of the present invention. The tubular reactor 1 comprises a cylindrical wall 2 surrounding a reaction space 9 and a cover 3 sealing the cylindrical reaction space from the outside at one end of the cylindrical wall 2. The tubular reactor 1 is open on the opposite side to the lid 3. In the centre of the lid 3 is fitted a hole which is filled by a cylindrical tube part 4 protruding from both sides of the lid 3, i.e. which is rotationally symmetrical to the axis of rotation 8 of the cylindrical wall 2. On the side projecting into the reaction space 9, the tube member 4 opens through the connecting tube 5 into a double-walled pipe 6 fitted in the center of the reaction space 9, i.e., it is rotationally symmetrical to the axis of rotation 8 of the cylindrical wall 2. The tubular reactor 1 is equipped with a suction nozzle 7 on the cylindrical wall 2, at the level of the tubular element 4.

The stream A containing diamine and/or triamine flows through the tube part 4, the connecting tube 5 and the double-walled conduit 6 and is finally discharged from the double-walled conduit in the form of an annular jet. The stream B containing phosgene flows directly from the suction nozzle 7 into the space between the cylindrical wall 2 and the tube element 4, around the tube element 4, the connecting tube 5 and the double-walled conduit 6, approximately at the level of the tube element 4. The flow around the double-walled conduit 6 passes through both the cross-section of the interspace defined by the inner wall of the double-walled conduit and the cross-section of the interspace defined by the cylindrical wall 2 of the tubular reactor and the outer wall of the double-walled conduit. The flow paths of the materials a and B are shown in the figure by arrows in the form of flow lines. The stream A containing the diamine and/or triamine is discharged from the double-walled pipe 6 in the form of a free annular jet and is then mixed, usually under turbulent flow, with the stream B containing phosgene to form the corresponding di-and/or triisocyanate.

Examples

Example 1 (example according to the invention):

the isophoronediamine/inert gas mixture was used as feed stream A and phosgene as feed stream B continuously fed into the tubular reactor according to FIG. 1, including the downstream isocyanate condensation stage and downstream isocyanate work-up. The temperature of both feed streams was 300 ℃. The pressure in the tubular reactor was 1400 mbar slightly above atmospheric pressure.

The flow rate of component A in the double-walled conduit 6 was about 60m/s and the flow rate of component B before mixing was about 7 m/s. The ratio of the cross-sectional area of the tubular reactor 1 defined by the inner wall of the double walled conduit 6 to the cross-sectional area of the tubular reactor defined by the cylindrical wall 2 of the tubular reactor and the outer wall of the double walled conduit is 1: 1.

The flow rate of the reaction mixture at the outlet of the reactor was about 17 m/s.

After leaving the reactor, the reaction product isophorone diisocyanate (IPDI) is condensed, separated from excess phosgene and by-product hydrogen chloride, and then passed to a purification stage. The temperature on the cylindrical wall 2 of the tubular reactor 1 was measured by means of thermocouples at four temperature measurement points located in the downstream of the double-walled conduit 6. The maximum temperature is reached at a second temperature measurement point, which is located approximately twice the diameter of the cylindrical wall 2 in the downstream direction from the mixing point. The yield of IPDI, based on the IPDA used, was 98.8%.

Example 2 (comparative example)

Example 1 was repeated under the same conditions, except that a smooth nozzle was used instead of the double-walled pipe. The cross-sectional flow area of the isophorone diamine/inert gas mixture and phosgene at the nozzle outlet was equal to the cross-sectional flow area of the tubular reactor in example 1.

We have found that by using a conventional smooth nozzle at the mixing point with comparable component flow rates, the maximum temperature in the tubular reactor is only reached after a significant delay, i.e. only at about five times the diameter of the cylindrical wall 2 in the downstream direction from the mixing point. The yield of IPDI, based on the IPDA used, was 98.5%.

In addition, it has been found that the formation of polymeric by-products deposited on the walls of the tubular reactor is reduced due to better and faster mixing resulting from the use of a tubular reactor with a double walled conduit according to the present invention. This also extends the useful life of the tubular reactor.

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

1. A process for preparing diisocyanates and/or triisocyanates of the general formula (I),

R(NCO)_n (I)

wherein

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

n represents the number 2 or 3,

R(NH₂)_n (II)

Wherein

R represents an aliphatic or cycloaliphatic or aromatic hydrocarbon radical having up to 15 carbon atoms, with the proviso that at least 2 carbon atoms are arranged between 2 amino groups, and

n represents the number 2 or 3,

the gas phase phosgenation is carried out by the following steps:

providing a tubular reactor having a double walled conduit extending centrally in the direction of the axis of rotation of the tubular reactor, a concentric annular gap being formed between the inner and outer walls of the double walled conduit, and the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double walled conduit to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double walled conduit being from 1: 0.5 to 1: 4,

the diamine and/or triamine in vapor form is fed via concentric annular gaps to a tubular reactor at an average flow rate of from 20 to 150m/s,

phosgene is fed into the tubular reactor over the remaining cross section thereof at an average flow rate of 5-15 m/s.

2. The process according to claim 1, wherein the average flow rate of the diamine and/or triamine in vapor form is from 40 to 100 m/s.

3. The process according to claim 1, wherein isophoronediamine, hexamethylenediamine and bis (p-aminocyclohexyl) methane are used as diamines.

4. The process according to claim 1, wherein 1, 8-diamino-4- (aminomethyl) octane or triaminononane is used as triamine.

5. The process according to claim 1, wherein the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double-walled conduit to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double-walled conduit is from 1: 1 to 1: 3.

6. The process according to claim 2, wherein isophoronediamine, hexamethylenediamine and bis (p-aminocyclohexyl) methane are used as diamines.

7. The process according to claim 2, wherein 1, 8-diamino-4- (aminomethyl) octane or triaminononane is used as triamine.

8. The process according to claim 2, wherein the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double-walled conduit to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double-walled conduit is in the range from 1: 1 to 1: 3.

9. The process according to claim 3, wherein the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double-walled conduit to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double-walled conduit is in the range from 1: 1 to 1: 3.

10. The process according to claim 4, wherein the ratio of the cross-sectional area of the tubular reactor defined by the inner wall of the double-walled conduit to the cross-sectional area of the tubular reactor defined by the wall of the tubular reactor and the outer wall of the double-walled conduit is in the range from 1: 1 to 1: 3.

11. The method according to claim 1, wherein R has 4 to 13 carbon atoms.