DE1037444B - Process for the production of organic isocyanates - Google Patents

Description

The present invention relates to a process for producing organic isocyanates by reaction of phosgene with amines.

In the production of organic isocyanate, an amine is reacted with phosgene, whereby the form organic isocyanate and, as a by-product, hydrogen chloride. Usually there is an excess used by phosgene, so that the gas produced as a by-product is a mixture of hydrogen chloride ■ and phosgene represents. There are already various methods for carrying out this process in the literature described. In general, the process is, and has been, carried out in batches It was suggested early on that the reaction should take place in an autoclave under the pressure of the gases Release the gases after the reaction has ended and the isocyanate solution is distilled is to be carried out in an organic solvent. In a newer method it is suggested that that the gases can be vented in the course of the reaction, but still in that Autoclave relatively high pressures are maintained. In this latter procedure, allegedly reduced the reaction time, although according to the description of the process the reaction extended over a period of 45 minutes to 2 hours.

The present invention relates to a continuous process for the production of organic isocyanates, with which one. an inert solvent in a pressurized, swirled in Introduces the reaction zone located in the river, feeds phosgene continuously under pressure into the solvent and the solution of the phosgene in the solvent continuously the organic amine, which in the isocyanate to be converted is added to the reaction solution in a low pressure standing zone transferred, whereby the hydrogen chloride and the excess phosgene escape as gases, and then the isocyanate is recovered from the remaining organic solvent by distillation. Optionally, the solution of the isocyanate in the organic solvent can be returned to the Reaction zone are recycled, with fresh solvent and further phosgene at the same time and amine to be reacted are fed. When the desired concentration of isocyanate and organic Solvent is reached, part of the solution is continuously removed throughout the system fresh solvent is added.

In the drawing, a device is shown schematically in which the method according to the invention can be carried out. The container can be provided with a jacket, whereby the solution process
for the production of organic isocyanates

Applicant:

E. I. du Pont de Nemours and Company, Wilmington, Del. (V. St. A.)

Representative: Dipl.-Ing. E. Prinz, patent attorney,
Munich-Pasing, Bodenseestr. 3 a

Claimed priority:
V. St. v. America March 15, 1954

Theodore Richard Beck, Cupertino, Calif. (V. St. Α.), Has been named as the inventor

Means is kept at the desired reaction temperature, or the container can only be a Be the evaporation tank into which the reaction solution is blown. The one to come about The heat required for the reaction can be added to the phosgene solution after the amine solution has been introduced are supplied in the solvent. Anything with the hydrogen chloride and the excess Phosgene entrained solvent can be returned to the container or together with fresh Solvent can be introduced on the low pressure side of the pump. If that Process is carried out without recycling the solution of the isocyanate in the solvent, the isocyanate and the solvent can be taken directly from the container into a suitable distillation device be transferred. In this embodiment, fresh solvent is on the low pressure side of the pump supplied.

The organic solvent is introduced on the suction side of a pump 1 and through a Line 2 is pumped upwards, with phosgene being injected through a valve 3 into the solvent.

809 599/570

The solution of the phosgene in the solvent, which rises upwards, becomes the solution of the reaction With the phosgene certain amine is injected through a valve 4 into the reaction zone 5, where a thorough mixing and reaction takes place. The temperature of the reaction mass is by a Maintain heater 6 and the desired pressure in the reaction zone 5 through the throttle valve 7, the works against the pressure of pump 1. The solvent solution of the isocyanate is in the under a lower pressure than prevails in the reaction zone, standing collecting container 8 is sprayed. This is where the volatile components escape, namely the hydrogen chloride and excess gaseous Phosgene, through a line 9 into a condenser 10 and leave the system through a valve 11. The Condensed solvent can be in the collecting tank 8 through a line 12 or on a other path 13 can be returned through a feed line 14 for solvent. As follows is explained in more detail, all or part of the isocyanate solution after reaching the desired Concentration at 15 can be withdrawn or returned through a line 16 to the circuit. Further fresh solvent can be supplied from a storage container through line 14.

It was found that when the described reaction was carried out, there was essentially no reaction of the amine with the isocyanate takes place even if the isocyanate solution is recycled. The amine appears to preferentially react with the phosgene to form the isocyanate. If the Isocyanate content of the product in the cycle rises significantly above 15%, a certain amount may seem Reaction of the isocyanate with the amine to reduce the yield of the desired isocyanate enter. In this case, the recycle stream can be diluted by adding fresh solvent will. That passed over from the stream with the phosgene and hydrogen chloride dissolved in it Solvent can be returned to the system immediately without further purification.

One of the advantages of the process according to the invention is that, as a result of the increased solubility of phosgene in the solvent, less solvent to a certain amount of amine and phosgene needs to be passed through the line in which the reaction takes place. L ^T nder the conditions of the invention is carried out of the hydrogen chloride from the solvent solution of the isocyanate at a substantially lower pressure than that at which the reaction is expelled, thus its removal is facilitated. Since the phosgene is added under pressure, the ratio of phosgene to hydrogen chloride can be kept higher, which greatly promotes the direct formation of the isocyanate without intermediate formation of the amine hydrochloride, and it is assumed that this is the reason for the improved yields achieved.

The isocyanate is returned to the system by distilling off the solvent can be won. The isocyanate can then optionally be distilled again. Both distillations are expediently carried out under reduced pressure.

Pressures of 0.35 to 1.4 kg / cm ² have proven to be suitable for carrying out the process according to the invention, although higher pressures, even up to 14 kg / cm ² , can also be used if necessary. A centrifugal pump or a positive displacement pump can be used.

It is essential that the phosgene is introduced into the solvent stream in such a way that it is introduced prior to introduction the amine solution is dispersed therein or completely dissolved. The molar ratio of phosgene to the amine should be such that the phosgene is in at least a 25% stoichiometric excess is located, d. i.e., one should at least 1.25 moles

ίο Use phosgene per NH ₂ group. Typically a much larger excess of phosgene will be used and the preferred range is between about 70 and 110 percent excess phosgene. As a rule, an excess greater than 110% need not be used.

The temperature at which the reaction is carried out should be above the decomposition temperature of the carbamyl chloride formed as an intermediate product in the reaction of phosgene with the amine lie. This temperature is between 90 and 180 ° C, depending on the type of amine used. Higher temperatures can be used but are not required. The escape of the Hydrogen chloride on entry of the reaction stream into the kept under a lower pressure The container enables its easy removal from solution at these temperatures.

The concentration of the organic amine in the solvent should be between about 5 and 30%.

With smaller amounts, the required amount of solvent is unnecessarily large, and when working at The yield can be significantly higher due to the formation of tarry by-products be reduced.

The solvents used according to the invention are preferably the chlorinated, aromatic ones Hydrocarbon solvents in which the phosgene under the pressures used is relatively soluble. The solvent expediently has a lower boiling point than that Isocyanate to be produced so that the isocyanate remains dissolved in the solution, but easily from it by distillation of the solvent can be obtained. Monochlorobenzene, o-dichlorobenzene, p-dichlorobenzene, the trichlorobenzenes, the corresponding toluenes and xylenes, chloroethylbenzene, monochlorodiphenyl and stund /? - Naphthyl chloride are typical examples of the solvents to be used. Because of its special Boiling point, o-dichlorobenzene is a preferred solvent. However, it can be any other inert organic solvents in which the phosgene and the amine are among those used coming pressures are relatively soluble, can be used.

The process of the invention is very general to the production of isocyanates, which too otherwise can be obtained by reaction of amines with phosgene, applicable. It can be so either the mono-, di- or polyisocyanates prepared from the corresponding mono-, di- and polyamines will. The process is particularly suitable for the reaction of aromatic amines with phosgene, e.g. B. from Aniline, toluidine, benzidine, naphthylamines, 2,4-tolylenediamine, 2,6-tolylenediamine, phenylenediamines, 4,4'-diaminodiphenylmethane, 1,5-naphthylenediamine, 1-amino-3- (4-aminophenyl) propane, anisidine. the chloranilines etc.

The following examples are intended to illustrate the invention. The yields given are based on the Based on the weight of the amine used.

example 1 Example 2

The equipment used is the same as in the drawing. o-Dichlorobenzene is used as a solvent and m-tolylenediamine is used to make 2,4-tolylenediisocyanate used. At the beginning of the process there are 55 parts of o-dichlorobenzene in the container. This is pumped through the pipeline in which the reaction takes place, first phosgene and then an 8% (weight percent) solution of m-tolylenediamine in o-dichlorobenzene to be introduced. The solution is then passed through a valve, which is designed to achieve the desired Pressure is set, returned to the collecting tank.

In this device, the collecting container consists of a 37.85 l capacity, provided with a jacket enamelled kettle. The heating mantle is heated by a system that works with hot oil. The heated pump is a stainless steel centrifugal pump. The phosgene inlet consists of one 1.27 cm pipe, which is in the form of a T-piece into the pipe in which the reaction takes place and the working cycle is going on is inserted. The line in which the reaction takes place and the Substances are circulated consists of a stainless steel tube with a diameter of 2.54 cm. The linear distance from the phosgene inlet to the inlet for the diamine solution is approximately 122 cm. The inlet for the diamine solution consists of a T-tube with a diameter of 2.54 cm, the bends at right angles into the line. A one-inch valve, which extends 20.3 cm in the direction of flow, serves as a pressure release seen, located away from the site of introduction of the diamine solution. The reaction conditions are given below:

Initial loading of the
Collection container with o-dichlorobenzene

m-Tolylenediamine in the feed solution

Temperature of the m-tolylenediamine feed solution ...

Feed speed of
m-tolylenediamine

Feed speed of
Phosgene

orbital speed caused by the pump

linear speed in the
Reaction zone

Temperature in the reaction zone

Temperature in the collecting tank

Pressure in the collecting tank

Pressure in the reaction line

applied phosgene excess
compared to the theoretically required amount

Test duration

Yield of 2,4-tolylene diisocyanate

lot

25 kg 8Vo HO ⁰ C 1.43 kg / h 4.54 kg / hour 30.3 l / min.

92 cm / sec.

165 ⁰ C

165 ⁰ C

Atmospheric pressure

0.56 kg / cm ²

96%

3 hours

90

If the m-tolylenediamine is replaced by an equimolar amount of 4,4'-diaminodiphenylmethane, obtained one in the same yield diphenylmethane-4,4'-diisocyanate.

Benzidine gives 4,4'-diphenylene diisocyanate in the same way in a corresponding yield.

The procedure of Example 2 is carried out in the same facility and by the same procedure as in Example 1 carried out.

Quantity Initial loading of the collecting tank with o-dichlorobenzene 25 kg

m-Tolylenediamine in the feed solution 16%

Speed of addition of

m-tolylenediamine 2.13 kg / hour.

Temperature of the m-tolylene

diamine feed solution ... HO ⁰ C feed rate of

Phosgene 7.26 kg / hour

Circulation speed caused by the pump 30.3 l / min.

linear speed in the

Reaction zone 92 cm / sec.

applied phosgene excess compared to the theoretically required Amount 110%

Temperature in the reaction zone 165 ° C. Temperature in the collecting tank 165 ° C

Pressure in the collecting tank atmospheric pressure

Pressure in the reaction line 0.56 kg / cm ²

Duration of experiment 4 hours

Yield of 2,4-tolylene diiso-

cyanate 86.5%

This example illustrates the use of a higher concentration of m-tolylenediamine in o-dichlorobenzene and increased phosgene supply.

Example 3

In this example the apparatus and procedure of Example 1 are used. The reaction temperature is lower, and the feed rate of the solution of m-tolylenediamine in o-Dichlorobenzene and phosgene are also lower.

Quantity Initial loading of the collecting tank with o-dichlorobenzene 25 kg

m-Tolylenediamine in the

shipping solution 8%

Speed of addition of

m-tolylenediamine 1.29 kg / hour

M-tolylenediamine feed solution temperature ... HO ⁰ C feed rate of

Phosgene 4.31 kg / hour

Circulation speed caused by the pump 30.3 1 / min.

linear speed in the

Reaction zone 92 cm / sec.

applied phosgene excess compared to the theoretically required Amount 106%

Temperature in the reaction zone 140 ° C. Temperature in the collecting tank 140 ° C

Pressure in the collecting tank atmospheric pressure

Pressure in the reaction line 0.56 kg / cm ²

Duration of experiment 4 hours

Yield of 2,4-tolylene diisocyanate 92%

40

45

60

65

If the same process is carried out at a temperature of the reaction zone and in the collecting vessel of 110 ^° C., a 90.5% yield is achieved.

If in the above process the m-tolylenediamine is replaced by benzidine and a 12% solution of the same in o-dichlorobenzene is used at a phosgene feed rate of 5.45 kg / hour, ie a 100% excess of phosgene, and the temperature in both the Reaction zone and in the collecting vessel is 175 ° C. at a pressure of 0.7 kg / cm ² in the reaction zone, a high yield of 4,4'-diphenylene diisocyanate is achieved.

Example 4

In place of the m-tolylenediamine of Example 3, 4,4'-diamino-diphenylmethane is used under the following conditions converted into the corresponding isocyanate:

lot
Initial loading of the

Collecting container with o-dichlorobenzene 25 kg

Concentration of 4,4'-diaminodiphenylmethane in the o-di-

chlorobenzene feed solution 12%
Feed speed of

Amine 1.36 kg / hour

Temperature of the amine

Feed solution 110 ° C

Feed speed of

Phosgene 2.77 kg / hour

applied phosgene excess

compared to the theoretically

required amount 100%

Circulation speed caused by the pump 75.7 l / min.

linear speed in the

Reaction zone 229 cm / sec.

Temperature in the reaction zone 175 ° C
Temperature in the collecting container 175 ° C
Pressure in the reaction zone ... 0.07 kg / cm ²

Pressure in the collecting tank atmospheric pressure

Test duration 5 hours

Yield of diphenylmethane

4,4'-diisocyanate 95%

The throttle valve is not used in this attempt.

Example 5

In this example, the equipment used in the first four examples is modified to replace the 37.85 liter kettle with a 122 cm long glass cylinder 10.16 cm in diameter. In this way, the total amount of liquid that can be contained in the system is reduced to about 11.36 liters. A tubular steel heat exchanger used for heating is placed in the reaction line between the inlet for the amine solution and the throttle valve. The heat exchanger has a heating surface of ^{0.4645 m 2.}

The linear distance from the amine feed to the throttle valve is now about 183 cm. In the The line in which the cycle takes place is an inlet between the collecting container 8 and the pump 1 provided through which additional solvent can be introduced.

This method differs from the previous examples in that an additional Amount of o-dichlorobenzene between the collecting tank 8 and the pump 1 in the circulating solution is initiated in order to reduce the concentration of the recycled 2,4-tolylene diisocyanate.

The amount added in this example is sufficient to lower the diisocyanate concentration to 10%, which corresponds to the concentration achieved when an 8% strength m-tolylenediamine solution is fed in. This dilution allows a 16% m-tolylenediamine feed solution to be used, without the yield suffering as a result of the formation of tarry products. The conditions are that following:

lot

Concentration of m-tolylenediamine in the feed solution 16%

Feed speed of the

Diamines 1.36 kg / hour

Temperature of the diamine

Feed solution 110 ⁰ C

Feed speed of

Phosgene 4.54 kg / hour

Phosgene excess compared to the theoretically required

Amount 100%

Return speed

through the pump 30.3 l / min.

Feed rate of o-dichlorobenzene into the circuit 10 kg / hour.

Temperature in the reaction zone 155 ° C. Pressure in the reaction zone .... 0.49 kg / cm ²

Pressure in the collecting tank atmospheric pressure

Duration of experiment 3 hours

Yield of 2,4-tolylene diisocyanate, based on the diamine used 93%

Example 6

The modified setup of Example 5 is repeated with a further change in the section in which the amine distribution takes place is used. Instead of the amine solution through a T-tube into a one-inch Introduce pipe, giving a linear velocity of 91.5 cm / sec. at a pump throughput of 30.3 l / min, the amine solution is introduced through a nozzle which is soft at an angle of 45 ° is inserted into a pipe that has an inner diameter of 0.95 cm. One achieves such a linear flow rate of 610 cm / sec. with a pump throughput of 30.3 l / min. This significantly increases the Reynolds number of the swirled river at this point.

The experimental conditions are as follows:

lot

Concentration of m-tolylenediamine in the feed solution (o-dichlorobenzene) 16%

Feed speed of the

Diamines 1.5 kg / hour

Temperature of the diamine

Feed solution 110 ° C

Feed speed of

Phosgene 4.54 kg / hour

Claims (1)

9 10 Quantity of shaped form to be introduced in liquid form, Phosgene excess compared to that because it is antheoretical when observed through an in line required brought sight glass completely soluble in the solution amount 85% medium under the applied pressures Return speed appears to be 5. through the pump 30.3 l / min. The advantage of the method according to the invention Feed rate of Hegt is that for any given product o-Dichlorobenzene in the circulatory speed is a much smaller facility run 10 kg / h is required and that it, as can be seen from some of the Temperature in the reaction zone 155 ⁰ C io examples results, is not necessary, a large, Pressure in the reaction zone 0.49 kg / cm ² to use jacketed vessel, Pressure in the collecting tank Atmospheric pressure _where simple heat exchangers are provided. There& Test duration 3 hours The procedure also has the advantage that the Continuously arises yield of 2,4-Tolylendiiso- isocyanate, wherein the Reaktionscyanat, based on the switch 15 it _ze of the amine with the phosgene in the solvent diamine Compound 95% solution, only a fraction of seconds. Following the same procedure as in this example is described, but using a Pump, which has a recirculation speed of 20 1. Process for the production of organic iso- of a 3.785 l / min, and at a pressure in cyanate from organic amines and phosgene, there- the reaction zone of 2.8 kg / cm ² at a Tempe characterized in that a solution of the temperature of 110 ⁰ C without addition of further o-di- amine in an inert organic solvent chlorobenzene and using liquid in a solution of phosgene in an inert Phosgene was obtained essentially the same as organic solvent under excess pressure and yield of 2,4-tolylene diisocyanate. initiates under conditions which are a turbulent ü. . , - flow yield, taking the temperature ^eis P ^ie always above the one for whom the The Setup and Procedure of Example 6 Carbamyl chloride of the particular amine used are used, with the exception that no 30 is decomposed and that after the reaction o-dichlorobenzene is fed to the circulating stream, the solution is immediately relaxed and the chlorine since the concentration of the hydrogen in o-dichlorobenzene and the excess phosgene from the led m-tolylenediamine is only 8%. Removed when the isocyanate formed is dissolved, this attempt is a lower working temperature. 2. Method according to claim 1, characterized in that rature applied. 35 shows that the temperature is between 90 and Quantity holds 180 ° C. Concentration of the m-tolylene 3. The method according to claim 1 and 2, characterized diamins in the feed characterized in that one has a molar ratio of solution 8% phosgene per - NH ₂ group of the amine of min- Addition rate of 40 at least 1.25: 1 complies. Diamine 1.5 kg / hour 4. The method according to claim 1 to 3, characterized Temperature of the diamine characterized in that the solution of the formed Feed solution 110 ⁰ C th isocyanate with continuous addition of Feed rate of phosgene and further amounts of the solution of the Phosgene 4.9 kg / hour 45 amine in the inert solvent in the cycle recycle rate .. 30.3 l / min. run back until the desired iso temperature in the reaction zone 90 ° C cyanate concentration in the solvent is reached Pressure in the reaction zone .... 0.42 kg / cm ² , whereupon part of the solvent is continuously Test duration 3 hours solution of the isocyanate in the solvent from the Yield of 2,4-tolylenediiso- 50 system removed, while a constant- cyanate 95.5% keeping the volume in the system sufficient Adds amount of solvent. As indicated in the preceding examples, 5. The method according to claims 1 to 4, characterized in that the amine solution is usually precharacterized by heating m-tolylenediamine as the amine in order to obtain a complete solution of the amine to 55 or 4.4 ^/ -Diaminodiphenylmethane is used. ensure before putting it in the solvent solution of phosgene is introduced. As in Example 6, Older Patents Considered: is shown, the phosgene can also as in gas German patents 949 227, 949 228, 958 558. 1 sheet of drawings © 809 599/570 8.58