Process for the continuous production of mono- or polyisocyanates

] In order to achieve the best economy in the continuous preparation of organic monoisocyanates and polyisocyanates by reacting the monoamines or polyamines corresponding to the phosgene imonoisocyanates or polyisocyanates dissolved in an organic solvent, the phosgene solution and the reagent are combined. of amine, optionally dissolved in a nozzle (1), subjecting the current of one of the reactants to a narrowing (3) and feeding the other reactant to that narrowing (3) through various lateral holes (5) below; the form of partial currents.

The present invention relates to a process for the continuous preparation of organic monoisocyanates or polyisocyanates by Reaction of the monoamines or polyamines corresponding to the phosgene monoisocyanates or polyisocyanates dissolved in an organic solvent at elevated temperatures.

The preparation of reaction mixtures of this type is known from organic amine solutions and organic phosgene solutions in moving part mixers, such as in a circulation pump mixer (DE-AS .....). ..

153 268 or US Patent 3,947,484). Due to the toxicity of phosgene, preparation methods especially in cylindrical mixing chambers such as these present the danger of fungi. Since solid substances are also produced in the reaction, it is often not possible to avoid the formation of incrusI || tations.

(For these reasons, the development of processes in which mixing is performed without moving parts has already been investigated. According to the publication of German Patent Application DE-OS, the two components of the reaction are allowed to collide. against each other in a cylindrical mixing chamber in the form of fan spray streams In this process, an initial pressure is unnecessary and obstructions may occur because of the dead corners of the mixing chamber.

Finally, a process is known (US Pat.². No. 3,226,410) wherein the amine solution is sprayed through holes drilled laterally in a tube toward the phosgene solution passing through the tube. With the reduced reagent concentrations required to obtain acceptable yields, the amount of isocyanates produced in proportion to the corresponding solvent amount is also low. The high energy consumption required for solvent recovery becomes inconvenient. It is not always possible to avoid accumulation of solids in the chamber walls.

In known processes, one must also work with a strong dilution of the reagents. This fact and the periods of pa! Cleaning costs due to frequent clogging lead to a negative balance in the economics of known processes.

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There is therefore a need to provide a new process for the continuous preparation of organic monoisocyanates and polyisocyanates in which the amount of the auxiliary solvent can be markedly reduced and the difficulties related to scale formation can be avoided. solid substances and the resulting clogging. In addition, the new process must dispense with moving parts in order to avoid the above mentioned problem of process safety (toxicity).

| This goal has been achieved through the present process!

invention for the preparation of the reaction mixture by assembly | of the amine reagent optionally dissolved with the phosgene solution) in a special nozzle described below.

I '[' detail.

The subject of the present invention is a process for the continuous preparation of organic monoisocyanates and polyisocyanates by reacting the monoamines or polyamines corresponding to the phosgene monoisocyanates or polyisocyanates dissolved in an organic solvent at elevated temperatures followed by processing of the resulting reaction mixture by distillation. , characterized in that, for the preparation of the original mixture, contact the amine reagent if necessary | dissolved in an inert solvent and the phosgene solution in a nozzle (1), one of the reagents being directed to that nozzle; (1) through a narrowing and the other component being fed into that narrowing (3) into the stream of the first component in the form of several partial currents through a corresponding number of side holes (5) laterally proximal to the narrowing perimeter (3).

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li Surprisingly it was found that in this process it is possible | work at lower pressure losses and higher concentrations, a high

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- product with shorter residence times in the reaction chamber connected to the mixing device and in particular avoiding fouling on the walls and clogging. The nozzle used is also referred to as the annular nozzle with holes. Strangulation of the solution stream may be carried out discontinuously or continuously. Preferably, the narrowing

I is effected by a sudden decrease in the diameter of the conduit. Since, in order to obtain an optimum mixture, only a pressure loss of about 2 bar is generally required, it is generally possible to keep the inlet pressures of the solution streams low. | use the pumps normally used so far. However, pressure losses can also be used to good effect (they are higher if the drawback of employing a higher inlet pressure is acceptable.

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Organic amines used as starting materials are (aliphatic, cycloaliphatic, aliphatic-aromatic or aromatic amines and diamines and / or polyamines such as aniline, halogen substituted phenylamines such as 4-chlorophenylamine, 1,6- diaminohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,4-diaminotoluene, technical mixtures thereof (with 2,6-diaminotoluene generally containing a maximum of 35%, jiem Weight, of 2,6-diaminotoluene relative to the total weight of the diphenylmejitane series polyamine mixture / mixtures, such as can be obtained by the known (aniline condensation / formaldehyde reactions themselves. In addition, they may employ good results are for example the (amines mentioned in U.S. Pat.². 3,321,283, column 4, lines 19-61.

Phosgene-treated amines according to the process of the present invention may be used as such, that is, without inert solvent. However, the amine reagent may also be introduced as a solution in an inert solvent, i.e.

Any concentration can then be used. A high amine concentration allows, on the one hand, a savings of | energy in solvent recovery and may, on the other hand, result in lower yield losses. These advantages and disadvantages must be assessed together.

Frequently, the amines are used in a concentration of 5 to 50% by weight, preferably 5 to 40% and especially in the form of a 50% solution.

Preferably from 10 to 25% inert solvent. Preferred solvents are hydrocarbons) I

Chlorinated aromatics, such as chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, trichlorobenzene, the corresponding chlorotoluenes and chloroxylenes, chloroethylbenzene, monochlorodiphenyl chloride, naphthyl chloride and P-naphthyl chloride, dialkyl benzoate, phthalate, diethyl diisophthalate,

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Jtoluene and xylols. Solvents may be used singly or in mixtures. Other suitable solvents are mentioned, for example, in US Pat. 3 321 283, | column 4 line 66 to column 5 line 2. j

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In accordance with the process of the present invention, it will generally be used in the form of solutions by weight, preferably 40 to 70% and especially: preferably 40 to 65% in Inert solvents, using for phosgene of preferably the same solvent used for the amine.

Phosgene solutions may also contain the recirculating end product (monoisoclanate or polyisocyanate). If the phosgene solution contains the final product, it should in any case, if there is a greater excess of phosgene in order to considerably prevent the formation of urea (reaction of the primary amines in the case of phosgene may be 10 to 85% ry with isocyanate). This means that in the use of phosgene solutions containing monoisocyclate or polyisocyanate, there must be a minimum molar excess of phosgene equal to 2.5 fold over the isocyanate groups in the soil.

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The equivalent ratio of phosgene to amine is generally at least 1.5: 1, in particular up to 20: 1, preferably 1.5: 1 to 7: 1 and especially. from 2: 1 to 5: 1.

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For the preparation of the reaction mixture according to the process of the present invention by using the mixing device of the present invention, the following may be performed:

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The temperature of the phosgene solution should be below the boiling temperature of the solution, which means that cooled phosgene solutions are generally used. The temperature of the amine reactant generally depends on the physical properties of the amine, that is, the melting point of the amine or the crystallization point of the amine solution used and may be varied within broad limits.

Preferably the larger volume solution is passed through the nozzle narrowing (3) and may, in case of use; If the flow rate is approximately equal, either reagent is the center stream or the side stream. Observing these conditions allows for perfect mixing and thus an optimal reaction course.

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According to a preferred embodiment of the present invention a strait current velocity of 1 to 10 m / s is established. It is possible, however, to establish higher current speeds at narrowing, for example up to 50 m / s, when the inconvenience of using the high inlet pressures in the pumps hitherto required is admitted. Conversely, it is of course possible under conditions of preferred current velocity of 1 to 10 m / s to advantageously maintain a reduced inlet pressure. The current velocity in the narrowing zone should generally be from 2 to twice, preferably from 2 to 10 times, the current velocity upstream of the narrowing zone.

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In general, the length L is chosen at least 1 time, preferably at least about 2 times the diameter of the nip D.

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This improvement allows for especially intense mixing and the current stabilizes satisfactorily.

It is especially advantageous to select for the length L from the axially introduced stream narrowing zone [to the confluence with the parcel currents of the second reagent a value of 0.5 to 2 times the diameter D of the narrowing.

According to a further improvement of the novel process of the present invention, the product stream from the two reactant streams is subjected to a constant, constant choke whose length corresponds at least to the distance at which the amine reaction can be considered as 'essentially terminated. 0 length L? θⁱⁿ gs ^ al at most 2 times the diameter D. L? Higher pressure losses result in higher pressure losses without any advantage.

The above measures ensure that no scale forms on the nozzle.

/ It is possible to obtain an especially high efficiency by maintaining a ratio of loads between the inlet flow i | , jaxialâ ^ and the lateral inlet flow rate A₌ ^ A 'V ^ A £ L · VL ^VTHE² —---- = 0.01 to 3.0,

VL² Preferably between 0.01 and 1.0 and especially preferably

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I is between 0,05 θ 0,7, where means the density (kg / m ^), v /^ç means the volume flow rate (m ^ / s) and ί¹ i, i! γ / means the flow velocity (m / s) where in each case »the index A is used for the axial input currents and the index S for the input currents.^f side.

The high efficiencies achieved in this way guarantee low energy consumption at the same time.

In accordance with another embodiment of the present invention, ¹ the cross section of the chain after narrowing is alarming! gada.

Ί ^!In this way, turbulence and regenerated currents can be avoided. Enlargement is found to end at a maximum corresponding to the diameter of the outlet tube. By avoiding retrogressive currents, no clogging is ensured.

The number of holes i for the introduction of the tidal currents is selected, according to another process variant, from 2 µm, preferably from 6 µm, to a value according to the formula especially.

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preference

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- This way of proceeding also influences fa!

the mixing and consequently the reaction as well as the elimination of scale formation.

Preferably, all holes are in the same plane perpendicular to the axis of narrowing, although possible modifications of this orientation are possible. In this way, the reaction can only be started at this level, thus preventing the reaction product from

I ^! react again with the second reagent. The yield is therefore higher and the danger of scale formation is reduced, improving the process economy.

Since the phosgene solution generally represents the largest volume, this is the solution which, according to the defined embodiments, is generally directed through narrowing.

b The figures are intended to elucidate in more detail the mixing device according to the present invention.

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Figure 1 shows the nozzle in longitudinal section; Figure 2 is a section along line AB of Fig. 1 and Figure 3 the transition between the inlet pipe and the narrowing.

I,) the meaning of the reference numbers is as follows:

ii (l) is the nozzle according to the present invention;

1 (2) is the inlet pipe for the main current;

(3) is the sudden narrowing of the main stream;

(4) is the part that forms the narrowing with the holes: integrated;

(5) are the side holes;

ji ji (6) is the side current feed;

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(7) is the chamber surrounding the narrowing (3) and from which the holes (5) depart;

(8) is the gradual widening at the nozzle outlet;

(9) is the outlet tube;

(10) is the level surface at the inlet tube outlet (2);

(11) are the edges at the beginning of the narrowing (3);

D is the inner diameter of the nip;

, ': d is the diameter of the side holes;

II is the total length of the narrowing;

' , ;

Ι »! is the distance from the beginning of the narrowing to the plane | of side holes |

I and he l | l_? is the distance from the plane of the lateral holes to the beginning of the gradual widening.

I For the preparation of the reaction mixture using the dis | Positive mixing according to the present invention it is possible to proceed, for example, as follows:

ί ¹ The main stream is fed into a nozzle 1 through a feed tube 2 which abruptly undergoes a narrowing at the edges 11 in the plane of the level 10 surface. The level 10 surface preferably forms an angle of 90 +/45 ° with the direction of the current which, as can be easily seen, corresponds to the angle of the starting edges of the narrow. Narrow 3 is integrated in one piece 4. 0 I- | Figure 3 shows along its entire length L1 the constant diameter D and the distance Lp which corresponds, for example, to 1.5 times the diameter D of the Nip 3.^sFor example, six holes 5 are normally distributed regularly at the perimeter. The holes 5 facing each other are offset from each other around the diameter of such that the partial streams flowing from these holes are directed towards each other. The second reagent is introduced through the inlet tube 6 into a chamber 7 surrounding the nip p3 from which the holes 5. depart.₂^of The narrowing beyond the holes 5 corresponds, for example, to the diameter D of the narrowing 3 and, therefore, to the approximate region in which the free amine reaction is essentially completed.

I: After narrowing 3, nozzle 1 shows a gradual widening 8 whose angle with the axis is for example 20 °. To this flare 8 is connected a diameter outlet tube 9. equal to the inlet tube. II

Reaction mixtures prepared by using the mixing device according to the present invention may be reacted following their preparation in standard reactors, such as stirred reactors or phosgenization towers to obtain the desired product, that is, monoisocyanate or polyisocyanate. The chemical reaction which produces the desired product is generally carried out at a temperature between 20 and 180 ° C.

[An especially preferred embodiment of the process of the present invention is to pass the reaction mixture prepared by using the mixing device according to the present invention from below through a reaction column containing perforated plates. such that the interior space of the column is divided into at least 10 chambers, preferably 20 to 50 chambers, separated from each other by the horizontal perforated plates. Basically it is possible, although not considered to be preferable, i: the use of several columns with connected perforated bottoms [in series containing in total at least 10 chambers, preferably 20 to 50 chambers.

An even larger number of chambers is not convenient because on the one hand, below each perforated plate, a gas cushion is formed which loses room for reaction between the solid and liquid reactants of the reaction mixture and, on the other hand, Further improvement of the time spectrum of stay is minimal.

The perforations of the perforated plates generally have a maximum diameter of 20 mm, preferably from 2 to 11 and the number of preferably chosen holes mm, the dependently being

It is of the section so as to avoid as much as possible a return of the reaction mixture from one chamber to the previous one flowing downwards.

The rising reaction mixture in the column consists of || a mixture of liquid components (solutions of raw materials and isocyanates formed), gaseous components (phosgene and hydrogen chloride formed) and (at least at the beginning^! reaction) solid components (carbamoyl chlorides

I, and amine hydrochlorides suspended in the solvent). The conditions^!Optimal reaction conditions occur when the velocity of the _;of the rising gas phase in the perforated plate perforations is between 2 to 20 m / s, preferably between 3.5 and 10 m / s, and the velocity of the rising liquid phase in the perforated plate perforations is between 0.05 to 0.4 m / s, preferably between 0.1 and 0.2 m / s.

The temperature of the reaction mixture at the exit of the mixing device is generally in the case of preferred procedures using perforated plate columns between 40 ° C; and 100 ° C, while the temperature at the top of the reaction column is below 150 ° C, preferably between 70 and 130 ° C, | especially preferably between 90 and 125 ° C. These temperatures are generally achieved by proper heating of the reaction columns. In order to minimize the amount of phosgenation required, it is advantageous to provide the necessary energy

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It would be necessary to reach the desired working temperature at the bottom of the phosgenization tower or just before the reactor inlet. This prevents a portion of the reactor volume from being ineffective due to the low temperature and consequent lower gross reaction rate.

The size of the reaction bed as well as the construction of the bottoms and the quantities of the reaction mixture introduced at the lower end into the column are otherwise chosen such that the average residence time of the reaction mixture in the columns of reaction is at most 120 minutes, preferably at most 60 minutes.

[The pressure at the top of the reaction column is generally between 1.2 and 3 bar (abs.), Preferably between 1.5 and 2.5 bar (abs.). It is possible, however, to work at higher or lower pressures.

Ί

The reaction mixture containing liquid and gaseous components exiting the upper end of the column is primarily

First, it is released from the gaseous components (excess phosgene and hydrogen chloride) by proceeding in a manner known per se and then distilled off. When using a normal stirred reactor as mentioned above, to carry out the phosgenization reaction, of course, the chemical reaction is followed by distillation of the reaction mixture. Prior to this distillation separation, however, a portion of the reaction mixture which is in solution with fresh phosgene solution may be enriched and recirculated.

I formulate this mixture for the beginning of the process.

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In the following examples all percentages data refer to percentages by weight. In all examples cylindrical nozzles were used in which the

1, ¹⁴ (3) are realized by abrupt reduction of the conduit (2), making the level plane (10) an angle β of 90 ° with the direction of the current.

Example 1

In a cylindrical nozzle with holes in the side surface 1 'with a diameter D of 14 mm and a length L of the narrowing zone of 28 mm (1 = 18 mm) and 10 holes of 2,1 mm diameter at the perimeter of the A solution consisting of 550 kg / hr of 3-chloro-4-methylphenylamine and 650 kg / hr of monochlorobenzene (MCB) with 3240 kg / hr of a 50% phosgene solution in MCB was passed. the amine solution being introduced attracts through 10 holes in the side surface. The velocity of η, current of the phosgene solution in the narrowing was 4.9 æ!

µm / s of amine solution in 9.2 m / s side holes

The charge ratio of the two solutions was E = 0.75. Then the reaction mixture was reacted on a set I; 3 go 3 reactors in series, each reactor having a volume of 6 m!^!at temperatures of 80, 110 and 140 ° C respectively and finally; The final mixture was distilled.

Yield: 98.0%.

Example 2

In a cylindrical nozzle with a diameter D of 19 mm, a length L of the narrowing zone of 38 mm (L ^ = 28,5 mm) and 12 holes of 2,6 mm diameter at the perimeter of the narrowing was passed through. 450 kg / h hexamethylenediamine i (HDA) solution and 4050 kg / h o-dichlorobenzene (ODB) with 9000 kg / h of a 30% phosgene solution in ODB, the amine solution being introduced through 12 side holes. The current velocity of the phosgene solution in the narrow was 6.5 m) see of the amine solution in the side holes of

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“16.4 m / s. The charge ratio of the two solutions was E1 / E3 = 0.32. Then, the reaction mixture was reacted on a reaction column with a capacity of 17 m 2, containing 45 plates perforated at temperatures up to about 150 ° C, and finally, the final mixture was distilled.

Yield: 96%.

il i:

1 'Example 3

A cylindrical nozzle with a diameter D of 10 mm. a 20 mm narrowing of the narrowing zone (Lp = 15 mm) and 4 1.5 mm diameter holes in the perimeter of the narrowing), a 120 kg / h solution of trimethylhexamethylene diamine (TIIBA) was passed and 145 kg / h of monochlorobenzene (MCB) with 2835 kg / h of a 50% phosgene solution in MCB, the amine solution being introduced through the 4 lateral holes.

The flow velocity of the phosgene solution in the narrowing was 5.7 m / s and the amine solution in the side holes 11.6 m / s. The charge ratio of the two solutions) was E1 / E2 = 1.92. The reaction mixture was then reacted in a series of 3 reactors in series, each reactor having a volume of 6 m 2 at temperatures of 80, 110 and 140 ° C. respectively and finally the final mixture was distilled off.

Yield: 94

Example 4

In a cylindrical nozzle with a diameter D of 20 mm, a length L 36 mm of the narrowing area of ​​20 mm (L ^ = 26 mm) and 12 holes of 2.6 mm diameter at the perimeter of the narrowing were passed through. 450 kg / h solution of 2.44oluenediamine (TBA) and 2350 kg / h of o-dichlorobenzene (OBB) with 7300 kg / h of a 50% phosgene solution in OBB, where ii

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amine solution introduced through the 12 side holes. The velocity of the phosgene solution stream on demand was 4.8 m / s and the amine solution in the side holes 10.3 m / s. The charge ratio of the two solutions was E1 / E2 = 0.55. Then, the reaction mixture was reacted on a reaction column with a capacity of m 2 containing 23 plates drilled at temperatures up to about 100 ° C and finally the final mixture was distilled. dog.

Yield: 96.7%.

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Example 5 In a cylindrical nozzle having a diameter D of 20 mm, a length L of the narrowing zone of 36 mm (L = 26 mm) and 12 'holes of 2.2 mm diameter at the perimeter of the narrowing, a 550 kg / h solution of a mixture of 65% 2,4-toluylenediamine (2,4-TDA) and 35% 2,6-toluylenedia: mine (2,6-TDA) and 2500 kg / h of -dichlorobenzene (ODB) with 6160 kg / h of a 58% phosgene solution in ODB, the amine solution being introduced through the 12 lateral holes. The flow rate of the phosgene solution in the narrowing was 4.0 m / s and the amine solution in the 12 holes: lateral 15.7 m / s. The charge ratio of the two solutions was E1 / E2 = 0.13. The reaction mixture was then reacted on a 7 m @ 2 reaction column containing 23 plates drilled at temperatures up to about 100 ° C and finally the final mixture was distilled off. Yield: 97%.

Example 6 i

a cylindrical nozzle with a diameter D of 23 mm, a narrowing zone length L of 40,2 mm (L ^ = 30,2 mm) and

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3.7 mm diameter holes at the perimeter of the narrowing, a 1000 kg / h solution of a diphenylmethane series polyamine mixture (MDA, two-core fraction 65%, viscosity 55 cP at 80 ° C) ° C) and 4000 kg / hr, o-dichlorobenzene (ODB) with 7140 kg / hr of a 45 F phosgene solution in ODB, the amine solution being introduced through the 12 lateral holes. The flow rate of the phosgene solution in the narrowing was 3.5 m / s and the amine solution in the 12 side holes 9.2 m / s. The proportion of the quantities of the two solutions was = 0.20. The reaction mixture was reacted on two serially linked reaction columns each containing 23 perforated plates with a capacity of 7 and 3.5 respectively at temperatures of 0 ° C. up to 85 ° C in the first column and up to 155 ° C in the second. After distilling off the solvent the viscosity of the resulting solvent free crude was 45 mPa.s. at 25 ° C. Yield: 100%. i

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