WO2006063749A1

WO2006063749A1 - Method for the production of polyisocyanates

Info

Publication number: WO2006063749A1
Application number: PCT/EP2005/013275
Authority: WO
Inventors: Carl Jokisch; Bernd Bruchmann; Andreas Wölfert; Oliver Bey; Alexander Bayer; Horst Binder; Eva Wagner
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-12-13
Filing date: 2005-12-10
Publication date: 2006-06-22
Also published as: WO2006063748A1; WO2006063746A1; WO2006063747A1; WO2006063745A1

Abstract

The invention relates to a method for producing polyisocyanates from diisocyanates and the use thereof.

Description

Process for the preparation of polyisocyanates

description

The present invention relates to a process for the preparation of polyisocyanates from diisocyanates and their use.

The preparation of isocyanurate polyisocyanates is known and widely used. For the preparation of such polyisocyanates containing isocyanurate groups, different reaction routes are known.

In general, discontinuous reaction routes are known in which isocyanate is heated to the desired reaction temperature and then catalyst is added. The reaction is then conducted and stopped until the desired target conversion is achieved.

The disadvantage of this is that the production must be carried out batchwise by the discontinuous reaction, so that the composition of the reaction mixture can change from batch to batch.

EP-A1 17998 describes the continuous carrying out of the trimerization of isocyanates in a reaction coil at residence times of 1 to 7 minutes for a conversion of 35-45%. Explicitly disclosed for carrying out the reaction is a coiled tubing of certain dimensions and a stirred premixer.

A disadvantage of this disclosed reaction regime is the formation of a relatively high proportion of higher, i. polynuclear isocyanurates, which can be seen from the NCO content obtained in the examples: e.g. in the examples of EP-A1 17998 in the case of 1,6-hexamethylene diisocyanate (HDI) as isocyanate an NCO content of only 20.9 to 21.4 is obtained, the NCO content for an ideal HDI isocyanurate being 25% by weight and for IPDI trimer is between 17.25 and 17.5, with the NCO content of an ideal trimer being 18.9% by weight. Such higher oligomers reduce the NCO content and undesirably increase the viscosity of the product.

DE-A1 102 32 573 describes a process for the preparation of isocyanurate groups containing polyisocyanates with aromatically bound isocyanate groups in a tubular reactor with turbulent flow at a Reynolds number of at least 2300 in one or more series-connected reactors (cell reactors) with a specific mixing power input of at least 0, 2 W / l is performed. A disadvantage of this method is that the method according to DE-A1 102 32 573 is disclosed only for aromatic isocyanates. An analogous feasibility for aliphatic or cycloaliphatic isocyanates is not readily expected for the skilled person, since the reactivity of aromatic isocyanates is usually greater by about a factor of 100 than that of (cyclo) aliphatic isocyanates.

The object of the present invention was to provide a continuous process for the preparation of polyisocyanates containing isocyanurate groups, with which the formation of higher oligomers can be largely suppressed.

The object has been achieved by a continuous process for the partial trimerization of (cyclo) aliphatic isocyanates in the presence of at least one catalyst which is carried out at least partly in at least two back-mixed reaction zones.

It is an advantage of the process according to the invention that the formation of higher oligomers can be reduced by a reaction procedure according to the invention.

Due to the continual reaction, a uniform product quality is produced.

In principle, aliphatic and / or cycloaliphatic isocyanates can be used for the process according to the invention, combined in this document as "(cyclo) aliphatic"^" isocyanates.

Aromatic isocyanates are those containing at least one aromatic ring system.

Cycloaliphatic isocyanates are those containing at least one cycloaliphatic ring system.

Aliphatic isocyanates are those which contain exclusively straight or branched chains, ie acyclic compounds.

The diisocyanates are preferably isocyanates having 4 to 20 C atoms. Examples of customary diisocyanates are aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (1,6-diisocyanatohexane), 1,5-diisocyanatohexane, 2-methyl-1,5-diisocyanatopentane, octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysine diisocyanate, tetramethylxylylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexane diisocyanate or tetramethylhexane diisocyanate, cycloaliphatic diisocyanates such as 1,4-, 1, 3- or 1,2-diisocyanatocyclohexane, 4,4'- or 2 , 4' Di (isocyanatocyclohexyl) methane, 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl) -cyclohexane (isophorone diisocyanate), 1, 3- or 1, 4-bis (isocyanatomethyl) cyclohexane or 2,4-, or 2,6-diisocyanato-1-methylcyclohexane.

There may also be mixtures of said diisocyanates.

The usable diisocyanates preferably have a content of isocyanate groups (calculated as NCO, molecular weight = 42) of 10 to 60% by weight, based on the di- and polyisocyanate (mixture), preferably 15 to 60% by weight and particularly preferably 20 to 55% by weight.

Preference is given to aliphatic or cycloaliphatic diisocyanates, more preferably the abovementioned aliphatic or cycloaliphatic diisocyanates, or mixtures thereof.

A preferred embodiment of the present invention is based on isocyanurates of 1,6-hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 2,2,4- or 2,4,4-trimethyl-1,6-hexamethylene diisocyanate manufacture.

2,2,4- and 2,4,4-trimethyl-1,6-hexamethylene diisocyanate fall production-related mostly as a mixture of isomers in the ratio of 1, 5: 1 to 1: 1, 5, preferably 1, 2: 1 - 1: 1 , 2, more preferably 1, 1: 1 - 1: 1, 1 and most preferably 1: 1 at.

Isophorone diisocyanate, for example, is also present as a mixture, namely the cis and trans isomers, usually in the ratio of about 60:40 to 80:20 (w / w), preferably in the ratio of about 70:30 to 75:25 and most preferably in the ratio of about 75:25.

Dicyclohexylmethane-4,4'-diisocyanate is also present as a mixture of the different cis and trans isomers.

The isocyanates which can be used according to the invention can be prepared by any desired process, for example by phosgenation of the corresponding diamines and thermal cleavage of the intermediately formed dicarbamic acid chlorides. Polyisocyanates prepared by phosgene-free processes are preferred starting compounds of the process according to the invention and do not contain any chlorine compounds as by-products and therefore have a fundamentally different by-product spectrum due to their production.

The preparation of the diisocyanates used for the process according to the invention is preferably carried out by phosgene-free process, preferably by thermal cleavage of the corresponding carbamates. This cleavage occurs at temperatures of 150 to 300 ⁰ C, usually using catalysts performed. The resulting in the cleavage diisocyanates and alcohols are removed, usually by distillation, from the reaction mixture and purified. Such methods are described, for example, in US-A-3 919 279 and EP-B-0 092 738.

Isocyanates originating from a phosgenation process often have a total chlorine content of 100-400 mg / kg, whereas the isocyanates preferably used in the process according to the invention, which are obtained from a phosgene-free process, have a total chlorine content of less than 80 mg / kg, preferably less than 60, more preferably less than 40, most preferably less than 20 and especially less than 10 mg / kg.

Of course, it is also possible to use mixtures of isocyanates prepared by the phosgene process and by phosgene-free processes, in particular in order to achieve a total chlorine content of less than 80 mg / kg.

The preparation of isocyanurates of isocyanates is known in principle.

Processes for the partial or complete trimerization of organic polyisocyanates for the preparation of isocyanurate group-containing polyisocyanates or cellular or compact isocyanurate groups containing polyurethanes are known and are described in numerous literature publications, such as. the Kunststoff-Handbuch, Polyurethane, volume 7, 2nd edition 1983 (page 81) edited by Dr. med. G. Oertel, Carl Hanser Verlag, Munich, Vienna, in Polyurethanes, Chemistry and Technology, Part 1, 1962, by J.H. Saunders and K.C. Frisch, (page 94), Advances in Urethane Science and Technology, Vol. 3, (Technomic Publishing Co., Inc. 1974, page 141) and Plastics and Rubber 23, pages 162ff and 177ff (1976), and patents.

In this case, the preferably aliphatic and / or cycloaliphatic diisocyanates are allowed to react in the presence of catalysts, if appropriate using solvents and / or auxiliaries, until the desired conversion is achieved. Thereafter, the reaction is stopped, for example, by deactivation of the catalyst and distilling off the excess monomeric diisocyanate. Depending on the type of catalyst used and the reaction temperature, polyisocyanates having different proportions of isocyanurate or uretdione groups are obtained.

The reaction of the isocyanate with the isocyanurate is optionally carried out with a solvent added in the presence of a catalyst.

Examples of suitable trimerization catalysts are alkali metal oxides, alkali metal hydroxides and strong organic bases, such as, for example, alkali metal alkoxides, phenolates, metal oxides salts of carboxylic acids, for example cobalt naphthoate, sodium benzoate, sodium acetate and potassium formate, tertiary amines, for example triethylamine, N, N-dimethylbenzylamine, triethylenediamine, tris-2,4,6- (dimethylaminomethyl) -phenol and tris-1, 3 , 5- (dimethylaminopropyl) -S-hexahydrotriazine, tertiary phosphines and tertiary ammonium compounds.

As catalysts it is also possible to use hydroxides or organic salts of weak acids with tetrasubstituted ammonium groups, hydroxides or organic salts of weak acids with hydroxyalkylammonium groups, alkali metal salts or tin, zinc or lead salts of alkylcarboxylic acids.

The nature of the trimerization catalyst plays no essential role in carrying out the process according to the invention.

The following catalysts may preferably be used for the process according to the invention:

Quaternary ammonium hydroxides, preferably N, N, N-trimethyl-N-benzylammonium hydroxide and N, N, N-trimethyl-N- (2-hydroxypropyl) -ammonium hydroxide, according to DE-A-38 06 276.

Hydroxyalkyl-substituted quaternary ammonium hydroxides according to EP-A-0 010 589 (US Pat. No. 4,324,879).

Organic metal salts of the formula (A) _n -RO-CO-O-M * ¹ according to US Pat. No. 3,817,939, in which A, a hydroxyl group or a hydrogen atom, n is a number from 1 to 3, R is a polyfunctional linear or branched, aliphatic or aromatic hydrocarbon radical and M is a cation of a strong base, for example an alkali metal cation or a quaternary ammonium cation, such as tetraalkylammonium.

Quaternary hydroxyalkylammonium compounds of the formula

as catalyst according to DE-A-26 31 733 (US-A-4 040 992). More preferred are quaternary ammonium carboxylates and / or hydroxylates of the general formula

R "

R - C - N - (X),

H,

OH

with Y = R ¹ COO- or OhT as catalyst, in which X independently of one another represent identical or different (cyclo) -aliphatic, araliphatic or heterocyclic hydrocarbon radicals, where two radicals X with the quaternary nitrogen contain a ring optionally containing one or more heteroatoms or three Radicals X can form a bicyclic ring via a common heteroatom with the quaternary nitrogen, R, R 'and R "independently of one another denote hydrogen or a radical from the group consisting of alkyl, cycloalkyl or aralkyl having 1-12 carbon atoms.

The ammonium ions may also be part of a mono- or poly-ring system, for example derived from piperazine, morpholine, piperidine, pyrrolidine or di-aza-bicyclo [2.2.2] octane. ^■

Particularly preferred are such trimerization catalysts as are known from the German patent application with the file reference 10 2004 012571.6, and from EP-A1 668 271, there especially from page 4, Z. 16 to page 6, Z. Al.

Very particular preference is given to N- (2-hydroxypropyl) -N, N, N-trimethylammonium 2-ethylhexanoate (DABCO TMR®) and N- (2-hydroxypropyl) -N, N, N-trimethylammonium 2-formate (DABCO TMR®-2) from Air Products.

For better handling, the catalyst may be dissolved or dispersed in a solvent. For this purpose, for example, alcohols, in particular diols, ketones, ethers and esters are suitable.

For example, the above-mentioned catalysts DABCO TMR® and DABCO TMR®-2 are preferably used as approximately 75% strength by weight solution in ethylene glycol.

The catalysts listed above are usually used in an amount of up to 2% by weight, based on the diisocyanate, preferably up to 1% by weight, more preferably up to 0.5, very preferably up to 0.25 and in particular up to to 0.1% by weight, optionally dissolved or dispersed in a solvent (mixture) as indicated above.

The catalyst is usually used in amounts of at least 10 ppm by weight, preferably at least 20, more preferably at least 30, very preferably at least 50 and in particular at least 70 ppm by weight, depending on the type of catalyst used.

The reaction of the isocyanate to the isocyanurate can optionally be carried out in the presence of a solvent.

The process according to the invention comprises in a typical embodiment the following reaction steps:

a) optionally pre-mixing of the reactants b) reaction of the reactants in at least two back-mixed reaction zones c) optionally after-reaction in at least one tubular reactor d) stopping the reaction e) distillation of the reaction mixture f) optionally mixing the reaction mixture with a solvent (mixture)

The stages are described in detail below:

a) optionally premixing the reactants

In stage a), the isocyanate- and catalyst-containing educt streams can be mixed with one another.

The catalysts listed above are usually used in an amount, based on the diisocyanate, as indicated above, optionally dissolved in a solvent (mixture), as indicated above.

The mixing of the educt streams, ie isocyanate and catalyst, optionally dissolved or dispersed in at least one solvent, can be carried out before being fed into the tubular reactor in a separate mixing device or in the tubular reactor or with a mixing device connected directly to the tubular reactor.

To produce the mixtures, an energy input into the mixing device of 0.2 W / l or more is generally sufficient, preferably 1 W / l, particularly preferably 2, very particularly preferably 10 W / l and in particular 100 W / l or more. The specified specific power input is to be understood here as a registered power per liter of mixing chamber volume of the mixing device. As mixer preferably a stirred tank, a static mixer or a pump is used. As a static mixer, all the usual static mixer (eg Sulzer SMX / SMV) or nozzle or orifice mixing devices, such as coaxial mixing, Y or T mixer can be used.

In a preferred embodiment, a mixing circuit is used. A mixing circuit is understood to mean a pumped-circulation system which contains at least one pump and optionally at least one heat exchanger and into which at least one of the components to be mixed, preferably the polyisocyanate, more preferably polyisocyanate and catalyst, is metered, preferably before a pump. The pumping circuit may also contain other static mixers and / or mixing elements.

When using a mixing circuit or a stirred tank as a mixing device, a component is injected at high speed. Usually, the velocities of the streams immediately before mixing are between 1 and 100 m / s, preferably between 2 and 80 m / s, more preferably between 5 and 50 m / s.

As mixing nozzles non-axisymmetric or preferably axially symmetrical mixing nozzles can be used. When using axially symmetrical mixing nozzles usually one of the educt streams is injected via a coaxial inlet pipe or more coaxially arranged inlet pipes in a mixing tube. The second reactant stream is introduced via the annular gap between the coaxial inlet tube and the mixing tube. The diameter ratio of the coaxial inlet tube to the mixing tube is usually 0.05 to 0.95, preferably 0.2 to 0.8. The catalyst-containing stream can be injected centrally via the internal coaxial introduction or through the annular gap. The catalyst is preferably introduced via the internal coaxial injection.

The length of the mixing tube is usually 2 to 20 times the mixing tube diameter, preferably 4 to 10 times the mixing tube diameter.

The pressure in the feed lines to the nozzle is higher than at the outlet of the mixing nozzle, but usually not higher than 110 bar abs, preferably not higher than 100 bar abs, more preferably not higher than 90 bar abs, most preferably not higher than 70 bar abs, in particular not higher than 50 bar abs and especially not higher than 20 bar abs.

Preferably, the mixing time in the mixing device is not more than one-tenth of the total average residence time, ie the mean time between starting and stopping the reaction, more preferably not more than one-twentieth, especially preferably not more than one thirtieth, and especially not more than one hundredth.

The mixing time in this mixing device is usually from 0.01 s to 120 s, preferably from 0.05 to 60 s, more preferably from 0.1 to 30 s, very particularly preferably from 0.5 to 15 s and in particular from 0, 7 to 5 s. The mixing time is understood to be the time which elapses from the start of the mixing operation until 97.5% of the fluid elements of the resulting mixture have a mixing fraction less, based on the value of the theoretical final value of the mixture fracture of the resulting mixture upon reaching the state of perfect mixing than 2.5% deviate from this final value of the mixture break (for the concept of mixture fracture, see, for example, J. Warnz, U. Maas, RW Dibble: Verbrennung, Springer Verlag, Berlin Heidelberg New York, 1997, 2nd edition, p. 134.)

The mixing in step a), at a temperature of 20 to 80 ⁰ C, forthcoming Trains t up to 60 ⁰ C take place.

If the mixing takes place at a temperature at which the reaction is already noticeably starting, the mixing time is preferably much less than the average residence time in the reactors until the reaction is stopped. Preferably, less than 5% of the isocyanate is reacted during the mixing of the reactants, more preferably less than 3%, very preferably less than 2%, in particular less than 1% and especially less than 0.5%.

In a preferred embodiment of the present invention, particularly when a mixture at higher temperature leads to an unfavorable result, the mixing takes place of the feed streams at a temperature below 50 ⁰ C, especially below preferably 45 and especially below preferably from 40 ⁰ C ₁ because experience shows that the reaction does not start noticeably at such temperatures and thus can only be started in a subsequent stage in which the reaction temperature is raised to a value above this critical temperature.

The discharge from the mixing device can be brought to the desired temperature there before being introduced into the step b) with the aid of, for example, a heat exchanger, preferably in order then to start the reaction.

In a preferred embodiment of the present invention, the step a) for premixing the reactants is present. This is especially the case when isophorone diisocyanate is reacted. If, on the other hand, 1, 6-hexamethylene diisocyanate is reacted or if the reaction product is a predominantly biuret-containing polyisocyanate, no premixing in a stage a) is generally required. In a particularly preferred embodiment, the isocyanate used in the partial trimerization is freshly distilled shortly before the partial trimerization. The period between distillation and mixing with the catalyst should not be more than 5 hours, preferably not more than 2 hours, more preferably not more than 1 hour, and most preferably not more than 30 minutes. In general, a simple distillation over, for example, a falling-film or thin-film evaporator is sufficient for this purpose.

This causes, inter alia, that the isocyanate used has a content of carbon dioxide (CO ₂ ) of less than 500 ppm, preferably less than 300, more preferably less than 200, most preferably less than 100 and in particular less than 50 ppm.

A further advantage of distilling the isocyanate before it is used is that, if appropriate, air is removed in the isocyanate. It is advantageous to carry out the reaction of the isocyanate in the absence of air, more precisely at a reduced oxygen content or even in the absence of air. The proportion of dissolved oxygen in the isocyanate is preferably <1000, preferably <200 ppm by weight.

b) reaction of the reactants in at least two backmixed reaction zones

In this context, back-mixed reaction zones are understood to mean that the number of bottoms of each reaction zone is less than 3, preferably less than 2 and particularly preferably 1.

If a pre-mixing has previously taken place in step a), the mixed stream can either be added directly to the first of the at least two back-mixed reaction zones or, if present, for example into a circulating stream (see below).

If, however, no premixing has occurred in step a), the educt streams into the first of the at least two back-mixed reaction zones can either be added directly to a strongly stirred zone or, if present, preferably into a circulating stream (see above), there particularly preferably right in front of a pump.

The step b) generally consists of two or more back-mixed reaction zones, for example 2 to 6, preferably 2 to 5, more preferably 3 to 5 and most preferably 4. More reaction zones are conceivable, but usually bring no significant advantage.

The average total residence time in all stirred containers together in stage b) can be up to 7 hours, preferably up to 90 minutes, more preferably up to 60 minutes, very particularly preferably up to 45 minutes and in particular up to 30 minutes. A longer residence time is possible but usually brings no benefits. The mean total residence time in stage b) is generally at least 2 minutes, preferably at least 5 minutes, particularly preferably at least 10 minutes, very particularly preferably at least 15 minutes in, and in particular at least 20 minutes.

The back-mixed reaction zones may be, for example, a series connection of several stirred tanks (stirred tank cascade) or at least one stirred tank, which is subdivided into a plurality of zones (cascaded stirred tank) by suitable partitioning of the reaction volume, for example by separating plates, or combinations thereof.

The volume specific power input per backmixed reaction zone should be not less than 0.1 W / L, preferably not less than 0.2 W / L, and more preferably not less than 0.5 W / L. In general, up to 10 W / l are sufficient, preferably up to 5, more preferably up to 3 and very particularly preferably up to 2 W / l. The specified specific power input is to be understood here as a registered power per liter reactor volume of the reactor.

The performance can be entered via all types of stirrers, such as propeller, swash plate, anchor, disc, turbine or bar stirrers. Disc and turbine stirrers are preferably used.

The stirred tank can be operated with or without baffle. Preferably, the operation is carried out with baffles. The operation is usually carried out with 1 to 10 Stromstö- rem, preferably with 2 to 4 baffles per segment.

In the case of a cascaded stirred tank, several stirrers may also be installed on the shaft. Preferably, a stirrer is used on the shaft per segment of the cascade. The diameter of the stirring elements is 0.1 to 0.9 times the Rührkesseldurchmessers, preferably 0.2 to 0.6 times the Rührkesseldurchmessers.

To carry out the method, in a preferred embodiment, a cascaded stirred reactor is provided which has a vertical tubular container in which a drive shaft is rotatably mounted parallel to the longitudinal axis, are fixed to the at least two disc stirrer with distance from each other and at between these Scheibenrührern the partition of the inner wall of the container are arranged, which have a central opening. It has been found that, depending on the reaction parameters, it is expedient to use 2 to 7 disk stirrers and 1 to 6 separating elements. The ratio of the opening of the separating elements to their total area results from the stirrer size. According to a development of the stirred reactor according to the invention, radially extending inwardly extending baffles may be disposed on the inner wall thereof parallel to its longitudinal axis. These may preferably be attached at a distance from the inner wall of the reactor. Advantageously, at least 4 are provided at the same angular distance from each other arranged Störleisten. The Stromstörleisten can take in their width while the 0.1-0.4 times the diameter of the container.

Furthermore, it may be useful to provide unstirred segments in the reactor (soothing zones). In a preferred embodiment of the invention may be located at the input and / or output, particularly preferably at the input and output such calming zones.

In a preferred embodiment, mixing and introduction of energy in the reaction zones can also be effected by at least one pumped circulation, which can optionally be tempered by at least one heat exchanger mounted in this pumping circulation.

The stirred tanks may be, for example, boilers with double-wall heating, welded-on full or half pipes, or internal heating coils. Alternatively, boilers with external heat exchanger and natural circulation, in which the circulation flow is accomplished without mechanical aids, or forced circulation (using a pump) are used.

Suitable circulation evaporators are known to the person skilled in the art and are described, for example, in R. Billet, Verdampfertechnik, HTB-Verlag, Bibliographisches Institut Mannheim, 1965, 53. Examples of circulation evaporators are tube bundle heat exchangers, plate heat exchangers, etc.

As pumps in the process according to the invention, preferably in all streams in which an isocyanate-containing stream is conveyed, positively-promoting pumps, for example gear, hose, screw, eccentric screw, spindle or piston pumps or centrifugal pumps are used.

Forced-conveying pumps are preferably used in the process according to the invention for conveying streams which have a viscosity of 250 mPas or more, particularly preferably 300 mPas or more, very particularly preferably 400 mPas or more and in particular 500 mPas or more. Centrifugal pumps are preferably used for conveying streams having a viscosity of up to 300 mPas, particularly preferably up to 250 mPas and very particularly preferably up to 200 mPas. Of course, several heat exchangers may be present in the circulation.

The back-mixed reaction zones are usually carried out heated. The heating can, for example, a jacket heating, welded full or half pipes, via internal pipes or plates and / or via a circuit with an external heat exchanger, for. B. tube or plate heat exchanger done. Preferably, a circuit with an external heat exchanger is used for the invention. The uniform mixing of the reaction solution is carried out in a known manner, e.g. by stirring, pumping, forced or natural circulation, preferably by forced or natural circulation. The heating can alternatively also be carried out by introducing gaseous, superheated solvent.

Optionally, catalyst and / or isocyanate, optionally in an inert solvent, can be added to stage b). This can then be done individually and independently of each other in each reaction zone.

In a preferred embodiment, when stage a) is absent, the catalyst and fresh isocyanate are mixed together in a pump circulation loop by contacting the two streams directly in front of a pump. This pumping circulation mixes the contents of the first reaction zone. Recycled isocyanate from step e) (see below) can be passed into the pumped circulation, directly into this first or second reaction zone.

A further embodiment of the invention consists in the construction of a mixing circuit, containing a pump for pumping the isocyanate, optionally provided with a pump reservoir and / or mixing device. The pump sucks the isocyanate-containing stream from the pump reservoir and conveys it to the mixing device. Before the stream enters the mixing device, the fresh isocyanate stream is added to the isocyanate-containing stream. To assist in mixing the fresh isocyanate stream into the isocyanate-containing recycle stream, a static mixer can be used.

The isocyanate-containing stream and the catalyst-containing stream are then mixed in the mixing device. The discharge from the mixing device is at least partially conveyed back into the pump template when executed as a mixing circuit. The remaining partial stream of the discharge is transferred to the reaction zone. The use of the pump template is not mandatory, it only facilitates the technically meaningful operation of the pump.

A preferred embodiment of the invention is the combination of a mixing circuit with the reaction zone. For this purpose, an isocyanate-containing stream is removed from the reaction zone via a pump and conveyed to the mixing device. In the mixed device, the catalyst-containing stream is mixed. The effluent from the mixer is returned to the reaction zone. The catalyst stream and the fresh isocyanate stream are either fed to the isocyanate-containing stream upstream of the mixing nozzle and / or introduced directly into the reaction zone. The fresh isocyanate stream is preferably premixed with the catalyst stream and this fresh isocyanate / catalyst mixture is added to the isocyanate stream before the mixing nozzle, more preferably in front of the pump.

The temperature in the mixing reactor system is in general between 40 ⁰ C and 110 ⁰ C, preferably between 50 ⁰ C and 110 ⁰ C, particularly preferably between 60 and 100 ⁰ C and most preferably between 60 and 90 ⁰ C.

The transfer of the reaction output from a reaction zone in the following can advantageously be done with level-controlled valves.

It is an advantage of the present invention that the individual reaction zones can be heated at different temperatures and operated with different residence times.

Thus, it may be useful, for example, to raise the reaction temperature along the reaction zones, so that, for example, the temperature in the second reaction zone to 5, preferably 10, more preferably 15 and very particularly preferably 20 ⁰ C higher than in the first reaction zone ,

In an optional third reaction zone, the temperature can be further increased by 5, preferably by 10, more preferably by 15 and most preferably by 20 ⁰ C.

It may also be useful to heat the last reaction zone to a temperature above 80, preferably 100, more preferably 120 ⁰ C to thermally deactivate the catalyst.

Furthermore, it may be useful to cool this third section to a temperature below 50, preferably 45, more preferably 40 ⁰ C to stop the reaction by cooling (see below under d)). In these cases step c) is omitted.

Furthermore, it may be useful to divide the first reaction zone in a mixing and / or preheating zone, the second in a reaction zone and the last in a catalyst deactivation or cooling zone. The temperature of the reaction zones is then expediently chosen so that the preheating, a temperature of about 40 - 6O ⁰ C, the reaction zone 70 - 12O ⁰ C, preferably 70-90 ⁰ C, and the waste Cooling zone 20 - 40 ⁰ C has. However, these temperature conditions are in each case adapted to the conditions required for the diisocyanate to be trimerized.

The residence times in the apparatus can be varied, for example, by overflow promotion the reaction volumes are reduced by displacer or reduced with active promotion the level of the reaction zone or be moved in the case of cascaded stirred tank overflow.

c) optionally afterreaction in at least one tubular reactor

In stage c), the discharge from stage b) can optionally be post-reacted in a tube reactor.

The liquid phase leaving the back-mixed reactor b) is then fed to a reactor system consisting of at least one tube reactor.

The tubular reactor should be largely free from back-mixing. This is achieved for example by the ratio of the diameter of the tubular reactor to its length or by internals, such as perforated plates, slot floors or static mixer. Preferably, the backmixing freedom is achieved by the ratio of length to diameter of the tubular reactor.

Suitable tubular reactors are all tubes whose length to diameter ratio is greater than 5, preferably greater than 6, particularly preferably greater than 10, very particularly preferably greater than 10 and in particular greater than 50.

The Bodenstein number of such a tubular reactor should be, for example, 3 or more, preferably at least 4, more preferably at least 5, even more preferably at least 8, especially at least 10 and especially at least 50.

In principle, the Bodensteinzahl is not limited to the top, in general, a Bodensteinzahl is sufficient up to 600, preferably up to 500, more preferably up to 300 and most preferably up to 200.

It is advantageous if a Reynolds number Re of at least 2300 in the tube reactor is achieved, preferably at least 2700, particularly preferably at least 4000, very particularly preferably at least 6000, in particular at least 8000 and especially at least 10000.

In addition, the power input in the tubular reactor should not be less than 0.2 W / l, preferably at least 0.3 W / l, more preferably at least 0.5 W / l, and most preferably not less than 1 W / l. As a rule, it is sufficient until at 100 W / l, preferably up to 50, particularly preferably up to 30, very particularly preferably up to 20 and in particular up to 10 W / l enter. The specified specific power input is to be understood here as a registered power per liter reactor volume of the reactor. The power input can be generated by the friction of the fluid with the reactor wall or by pressure loss-producing internals such as orifices, mixing elements, perforated or slotted plates.

The tubular reactor can have any orientation in space. Preferably, it is constructed as a vertical tube reactor, which is particularly preferably flowed through from bottom to top.

Additional mixing could, if desired, be achieved by mixing the reaction mixture in the tubular reactor with a gas or gas mixture which is inert under the reaction conditions, for example those having an oxygen content of less than 2, preferably less than 1, particularly preferably less than 0.5, vol %, preferred are nitrogen, argon, helium, nitrogen - noble gas mixtures, particularly preferred is nitrogen. In addition or alone, carbon dioxide (CO ₂ ) can also be used as the gas.

Such a gas phase is preferably conveyed in cocurrent to the liquid phase.

The tubular reactor can be carried out isothermally or tempered. A tempering can be done by a jacket heating, welded semi or Volirohre or through internal pipes or plates. The heating is preferably carried out by the jacket.

If desired, the tubular reactor can be subdivided into several sections with different temperatures, for example 2 to 4, preferably 2 to 3.

Thus, it may be useful, for example, to raise the reaction temperature along the tube reactor, so that, for example, the temperature in the second section is 5, preferably 10, more preferably 15 and most preferably 20 C higher than in the first reaction section.

In an optionally present third section, the temperature can be further increased by 5, preferably by 10, more preferably by 15 and most preferably by 20 ⁰ C.

It may also be useful to heat this third section to a temperature above 80, preferably 100, more preferably 120 ⁰ C in order to thermally deactivate the catalyst. Furthermore, it may be useful to cool this third section to a temperature below 50, preferably 45, more preferably 40 ⁰ C to stop the reaction by cooling (see below under d)).

Of course, the tubular reactor can also consist of several serially connected pipe sections.

In a preferred embodiment, the tube reactor is designed so that the Reynolds number Re of the reaction mixture in the course of the tubular reactor between Eiη- and output by at least 100 units, preferably by at least 500, more preferably by at least 1000 and most preferably by at least 2000 units sinks.

The tube reactor consists of a tube section, which can be constructed from a single tube or from an interconnection of several tubes. The tubes do not all have to have the same diameter, this can change over the reactor length in order to specifically react to the reaction conditions, such as a change in viscosity as the reaction progresses. The temperature control of the tubular reactor may e.g. be carried out so that the reactor is designed as a double tube heat exchanger.

To increase the production capacity, several tubular reactors can also be connected in parallel according to the invention.

Optionally, catalyst, isocyanate and / or solvent can be added to the tubular reactor at one or more points, for example at the beginning and in the middle of the tubular reactor.

The average residence time in the tubular reactor is generally at least 1 minute, preferably at least 2 minutes and more preferably at least 3 minutes.

The average residence time in the tubular reactor is generally up to 60 minutes, preferably up to 45 minutes and more preferably up to 30 minutes.

The temperature in the tubular reactor is generally between 40 ⁰ C and 150 ⁰ C, preferably between 45 ⁰ C and 130 ⁰ C and particularly preferably between 50 and 12O ⁰ C, wherein the temperature can be staggered, as stated above.

The pressure in stage c) is generally not more than 10 bar abs, preferably not more than 7 bar abs, more preferably not more than 5 bar abs, most preferably not more than 3 bar abs and in particular not more than 2 bar Section. The pressure in step c) should be at least 0.9 bar abs, preferably it is at least normal pressure, more preferably at least 1, 1 bar abs, most preferably at least 1, 2 bar abs and in particular 1, 5 bar abs.

The transfer of the reaction output from stage c) into the subsequent stage can advantageously take place via pressure-holding valves, wherein the pressure in stage c) should generally be at least 0.1 bar above the pressure prevailing in stage d). If this is not the case, transferring e.g. with the help of a pump or barometric. Particularly preferred level-controlled valves are used.

The inner walls of the tube reactor in stage c) are designed to be hydraulically smooth in a preferred embodiment of the invention:

d) stopping the reaction

After reaching the desired degree of conversion, the reaction can be stopped by deactivating the catalyst, for example by adding a deactivating agent, by thermal decomposition of the catalyst or by cooling.

The conversion can be chosen differently depending on the isocyanate used. Thus, advantageously, in the case of 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl) cyclohexane, the reaction can be stopped at a conversion of 20-30%, particularly preferably about 25%, whereas for 1,6-hexamethylene diisocyanate may be advantageous to stop the reaction at a conversion of 30 to 40%, preferably 30 to 35%.

The type of deactivation can be chosen differently depending on the isocyanate used. Thus, in the case of 1,6-hexamethylene diisocyanate, the reaction is preferably stopped thermally. In the reaction of 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl) cyclohexane, however, the reaction can be stopped thermally or by adding a deactivating agent.

Suitable deactivating agents are, for example, inorganic acids, e.g. Hydrogen chloride, phosphorous acid or phosphoric acid, carboxylic acid halides, e.g. Acetyl chloride or benzoyl chloride, sulfonic acids or esters, e.g. Methanesulfonic acid, p-toluenesulfonic acid, p-toluenesulfonic acid methyl or ethyl ester, m-chloroperbenzoic acid and preferably dialkyl phosphates such as e.g. Dibutyl phosphate and especially di-2-ethylhexyl phosphate.

The deactivating agents can be used in the reaction mixture, in equivalent or excess amounts, based on the amount of active trimerization catalyst, with the smallest effective amount being experimentally easily obtained. can be averaged, is preferred for economic reasons. For example, the deactivating agent in relation to the active trimerization catalyst is from 1 to 2.5: 1 mol / mol, preferably 1 to 2: 1, more preferably 1 to 1, 5: 1 and most preferably 1 to 1, 2: 1 mol / mol used. If the amount of active catalyst in the reaction mixture is not known, it is possible, based on the starting amount of catalyst used, to use 0.3-1.2 mol of deactivating agent per mole of catalyst used, preferably from 0.4 to 1.0 mol / mol. mol, more preferably 0.5 to 0.8 mol / mol.

The addition depends on the type of deactivating agent. Thus, hydrogen chloride is preferably passed through gaseous or preferably through the reaction mixture, liquid deactivating agents are usually added in bulk or as a solution in a solvent inert under the reaction conditions and solid deactivating agent in bulk or as a solution or suspension in a solvent inert under the conditions of reaction ,

The addition of the deactivating agent is usually carried out at the reaction temperature, but can also be carried out at a lower temperature.

A thermal deactivation can preferably take place when a trimerization catalyst having a 2-hydroalkylalkylammonium group is used. Such catalysts are thermolabile at temperatures above ^80.degree. C., preferably above 100.degree. C., more preferably above 120 and most preferably above 130, which can be exploited for their deactivation.

Such deactivation can be carried out, for example, in a section having the corresponding temperature in a back-mixed reaction zone b) or, if present, in the tubular reactor c) (see above), by a heat exchanger operating between stirred reactor b) or tubular reactor c) and distillation e) is switched and which is operated at the temperature in question, or in the distillation e) when operated at a corresponding wall temperature.

Of course, the reaction can also be stopped by cooling, for example by cooling to a temperature below 60 ⁰ C, preferably below 55, more preferably below 50, most preferably below 45 and in particular below 40 ° C.

Such cooling may be carried out, for example, in a section having the corresponding temperature of a back-mixed reaction zone b) or, if present, in the tubular reactor c) (see above) or by a heat exchanger operating between b) or tubular reactor c) and distillation e ) and is operated at the temperature in question. By a simple cooling of the catalyst remains, however, included in the reaction mixture and thus continues to be active so that the reaction is not det BEE in the strict sense, but to be resumed at any time by heating at a temperature above about 5O ⁰ C can.

It is therefore preferred according to the invention to stop the reaction by thermal deactivation of the catalyst or by a deactivating agent.

e) distillation

The reaction mixture containing isocyanurate-containing polyisocyanates prepared by the process according to the invention can finally be in a conventional manner, for example by thin film distillation, at a temperature of 100 to 180 ⁰ C, optionally in vacuo, optionally additionally with passing of inert stripping gas, optionally present Solvent or diluent and / or preferably be liberated from excess, unreacted diisocyanates, so that the isocyanurate polyisocyanates containing monomeric diisocyanates of, for example, under 1, 0 wt .-%, preferably below 0.5 wt. -%, more preferably less than 0.3, most preferably less than 0.2 and in particular not more than 0.1% by weight are available.

The apparatuses used for this purpose are flash, falling film, thin film and / or short path evaporators, to which optionally a short column can be placed.

The distillation is generally carried out at a pressure between 0.1 and 300 hPa, preferably below 200 hPa and more preferably below 100 hPa.

In a preferred embodiment, the distillation is carried out in several stages, for example in 2 to 5 stages, preferably 2 to 4 stages and particularly preferably 3 to 4 stages.

The pressure is advantageously lowered from stage to stage, for example starting at 300-500 hPa over 100 to 300 hPa to 10 to 100 hPa and then to 0.1 to 10 hPa.

The temperature in the individual distillation stages is in each case from 90 to 220 ⁰ C.

Advantageously, the first stage is carried out in a simple apparatus, for example a circulation, flash or candle evaporator and the subsequent stages in more complicated apparatus, for example in falling-film evaporators, thin-film evaporators, for example Sambay® or Luwa evaporators, or short-path evaporators It would be advantageous to adopt technical measures which because of the time the streams and thus their thermal load is reduced, for example, waiver of intermediate tank or storage tank, short pipe routes or smallest possible execution of the sump volumes.

The separated in step e) distillate of monomeric isocyanate is preferably recycled to the stage a) and used anew, supplemented by freshly fed isocyanate, in the reaction.

If necessary, this recycled distillate may be subjected to a color number-improving treatment such as filtration through a filter, activated carbon or alumina.

If necessary, the finished product can be treated before performing step f) to improve the color number, for example with a peroxide, as described in EP-A1 630 928.

The finished product can optionally be mixed in a step f) with a solvent.

Examples of such solvents are aromatic and / or (cyclo) aliphatic hydrocarbons and mixtures thereof, halogenated hydrocarbons, esters and ethers.

Preference is given to aromatic hydrocarbons, (cyclo) aliphatic hydrocarbons, alkanoic acid alkyl esters, alkoxylated alkanoic acid alkyl esters and mixtures thereof.

Particularly preferred are mono- or polyalkylated benzenes and naphthalenes, Alkansäurealkylester and alkoxylated Alkansäurealkylester and mixtures thereof.

As the aromatic hydrocarbon mixtures, preferred are those which comprise predominantly aromatic C ₇ - to C ₁₄ include hydrocarbons and may comprise a boiling range from 110 to 300 ⁰ C, particularly preferably toluene, o-, m- or p-xylene, trimethylbenzene isomers, tetramethylbenzene, Ethylbenzene, cumene, tetrahydronaphthalene and mixtures containing such.

Examples include Solvesso® brands from ExxonMobil Chemical, particularly Solvesso 100 (CAS No. 64742-95-6, predominantly _C9 and C ₁₀ aromatics, boiling range about 154 -. 178 ⁰ C), 150 (boiling range about 182-207 ⁰ C) and 200 (CAS No. 64742-94-5), as well as the Shellsol® brands of Shell. Hydrocarbon mixtures of paraffins, cycloparaffins and aromatics are also known under the names of crystal oil (for example, crystal oil 30, boiling range about 158-198 ⁰ C or crystal oil 60: CAS No. 64742-82-1), white spirit (for example, also CAS-No. 64742-82-1) or solvent naphtha (light: boiling range about 155-180 ⁰ C, heavy: boiling range about 225-300 ⁰ C ₁ ) commercially available. The aromatic content of such hydrocarbon mixtures is generally more than 90% by weight, preferably more than 95, more preferably more than 98, and very preferably more than 99% by weight. It may be useful to use hydrocarbon mixtures with a particularly reduced content of naphthalene.

It is an advantage of the present invention that with the inventive method, such solvents can be mixed with polyisocyanates having a density at 20 ⁰ C according to DIN 51757 of less than 1 g / cm ³ , preferably less than 0.95 and more preferably less than 0.9 g / cm ³ .

The content of aliphatic hydrocarbons is generally less than 5, preferably less than 2.5 and more preferably less than 1% by weight.

Halogenated hydrocarbons are, for example, chlorobenzene and dichlorobenzene or isomeric mixtures thereof.

Esters include, for example, n-butyl acetate, ethyl acetate, 1-methoxypropyl acetate-2 and 2-methoxyethyl acetate.

Ethers are, for example, THF, dioxane and the dimethyl, ethyl or n-butyl ethers of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol or tripropylene glycol.

Examples of (cyclo) aliphatic hydrocarbons include decalin, alkylated decalin and isomer mixtures of straight-chain or branched alkanes and / or cycloalkanes.

Preference is furthermore given to n-butyl acetate, ethyl acetate, 1-methoxypropyl acetate-2,2-methoxyethyl acetate, and mixtures thereof, in particular with the abovementioned aromatic hydrocarbon mixtures.

Such mixtures can be prepared in a volume ratio of 5: 1 to 1: 5, preferably in a volume ratio of 4: 1 to 1: 4, more preferably in a volume ratio of 3: 1 to 1: 3 and most preferably in a volume ratio of 2: 1 to 1 : 2nd

Preferred examples are butyl acetate / xylene, methoxypropyl acetate / xylene 1: 1, butyl acetate / solvent naphtha 100 1: 1, butyl acetate / Solvesso® 100 1: 2 and crystal oil 30 / Shellsol® A 3: 1. The content of the polyisocyanates in the solvent mixtures can generally be up to 98% by weight, based on the sum of polyisocyanate and solvent, preferably up to 95% by weight, more preferably up to 90% by weight, very preferably up to 86% by weight and in particular up to 80% by weight.

The content of the polyisocyanates in the solvent mixtures is generally 50% by weight or more, based on the sum of polyisocyanate and solvent, preferably 60% by weight or more, more preferably 63% by weight or more and most preferably 65% by weight or more.

The content of uretdione groups which can be achieved with the process according to the invention depends on the catalyst used and is generally less than 5% by weight, preferably less than 2.5, particularly preferably less than 1.5% by weight, very particularly preferably less than 1.0, and more preferably less than 0.5 wt%.

As a result of the reaction procedure according to the invention, the proportion of higher oligomers can be reduced so that the NCO content is closer to the ideal value of the pure trimer and the viscosity is lower compared to the prior art.

The available mixtures of polyisocyanates in solvents are usually used in the paint industry. The mixtures according to the invention can be used, for example, in coating compositions for 1-component or 2-component polyurethane coatings, for example for primers, fillers, pigmented topcoats and clearcoats in industrial, in particular aircraft or large-vehicle painting, automotive, in particular OEM - or car refinish, or paint finishes are used. Particularly suitable are the coating compositions for applications in which a particularly high application safety, outdoor weathering resistance, appearance, solvent and / or chemical resistance are required.

Ppm and percentages used in this specification, unless otherwise indicated, are by weight percent and ppm.

Claims

claims

1) Continuous process for the partial trimerization of (cyclo) aliphatic isocyanates in the presence of at least one catalyst, characterized in that the process is carried out at least partially in at least two backmixed reaction zones.

2) Method according to one of the preceding claims, characterized in that the isocyanate is selected from the group consisting of 1, 6-hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate,

2,2,4- and / or 2,4,4-trimethyl-1,6-hexamethylene diisocyanate.

3) Method according to one of the preceding claims, characterized in that the isocyanate has a total chlorine content of less than 80 mg / kg.

4) Method according to one of the preceding claims, characterized in that it comprises the following reaction steps:

a) optionally pre-mixing of the reactants b) reaction of the reactants in at least two back-mixed reaction zones c) optionally after-reaction in at least one tubular reactor d) stopping the reaction e) distillation of the reaction mixture f) optionally mixing the reaction mixture with a solvent (mixture).

5) Method according to one of the preceding claims, characterized in that the mixing of the catalyst with the isocyanate takes place with an energy input into the mixing device of 0.2 W / l.

6) Method according to one of the preceding claims, characterized in that the mixing device a) is selected from the group consisting of stirred tank, static mixers, pump, nozzle mixing devices, Blenden- mixing devices, Koaxialmischdüsen, Y and T-mixers.

7) Method according to one of the preceding claims, characterized in that mixing the educt streams in step a) at a temperature below 50 ⁰ C. 8) Method according to one of the preceding claims, characterized in that the pumps are at least partially positively promoting in the process.

9) Method according to one of the preceding claims, characterized in that the reaction is stopped by addition of a deactivating agent, by thermal decomposition of the catalyst or by cooling.

10) Process according to one of the preceding claims, characterized in that the separated in step e) distillate of monomeric isocyanate is recycled to the stage a).