WO2006063748A1

WO2006063748A1 - Method for the production of (cyclo)aliphatic polyisocyanates

Info

Publication number: WO2006063748A1
Application number: PCT/EP2005/013274
Authority: WO
Inventors: Carl Jokisch; Bernd Bruchmann; Andreas Wölfert; Oliver Bey; Alexander Bayer; Horst Binder
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-12-13
Filing date: 2005-12-10
Publication date: 2006-06-22
Also published as: WO2006063747A1; WO2006063746A1; WO2006063745A1; WO2006063749A1

Abstract

The invention relates to a method for producing polyisocyanates from (cyclo)aliphatic diisocyanates as well as the use thereof.

Description

Process for the preparation of (cyclo) aliphatic polyisocyanates

description

The present invention relates to a process for the preparation of polyisocyanates from (cyclo) aliphatic 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.

EP-A1 17998 describes carrying out 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 reactors connected in series 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 process for the preparation of isocyanurate-containing (cyclo) aliphatic polyisocyanates, with which the formation of higher oligomers can be largely suppressed. The object has been achieved by a process for the partial trimerization of (cyclo) aliphatic isocyanates in the presence of at least one catalyst which is carried out at least partially in at least one tubular reactor in which the flow in the tubular reactor at least partially, preferably in the entire tubular reactor, has a Reynolds Number Re of at least 2300 has at a power input of at least 0.2 W / l.

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.

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

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

Cycloaliphatic isocyanates are those which contain 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. 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 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 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 is carried out at temperatures of 150 to 300 ⁰ C, usually using catalysts. 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 I, 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 to the isocyanurate is optionally carried out with a solvent added in the presence of a catalyst.

Suitable trimerization catalysts include, for example, alkali oxides, alkali hydroxides and strong organic bases, e.g. Alkali metal alcoholates, phenates, metal salts of carboxylic acids, for example cobalt naphthenate, 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.

Further catalysts which may be used are 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-Ivf 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 one , 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).

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. 47th

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 can be dissolved 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 process according to the invention comprises in a typical embodiment the following reaction steps: a) Mixing of the reactants

b) optionally at least one back-mixed reaction zone

c) 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 individual reaction steps are described in more detail below:

a) Mixing of the reactants

In stage a), the isocyanate- and catalyst-containing educt streams are mixed together.

The catalysts listed above are usually added in an amount up to

2 wt .-%, based on the diisocyanate, used, preferably up to 1% by weight, more preferably up to 0.5, most preferably up to 0.25 and in particular up to 0.1% by weight, optionally dissolved in one 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 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 output 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.

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

It usually brings no advantage, the mixing time to choose extremely short, so that usually a two-thousandths of the total average residence time is sufficient, preferably one-thousandth, more preferably a five-hundredth and most preferably a two-hundredths.

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 the mixture break see, for example, J.Warnatz, U.Maas, RW Dibble: Verbrennungs, Springer Verlag, Berlin Heidelberg New York, 1997, 2nd edition, p. 134. )

The mixing in step a) can be carried out at a temperature of 20 to 80 ⁰ C, preferably up to 60 ⁰ C.

In a preferred embodiment of the present invention, the mixture of the educt streams is carried out at a temperature below 50 ⁰ C, since at such temperatures, the reaction is not noticeably starts according to experience and thus can be started only in a subsequent stage in which the reaction temperature to a value above - half of this critical temperature is increased.

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 usually a simple distillation over such as a case or thin film evaporator is sufficient.

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 dissolved in the isocyanate is thereby removed. 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.

The discharge from the mixing device can be brought to the desired temperature there before being introduced into the step b) or c) with the aid of a heat exchanger.

b) optionally at least one back-mixed reaction zone

The discharge from stage a) can be pre-reacted in one or more stirred tanks, for example 1 to 5, preferably 1 to 3, more preferably 1 to 2 and very particularly preferably a stirred tank, the average residence time being up to 7 hours up to 90 minutes, more preferably up to 60 minutes, most preferably up to 45 minutes and especially up to 30 minutes. A longer residence time is possible but usually brings no benefits.

The mean total residence time in the reaction stage is generally at least 2 minutes, preferably at least 5 minutes, more preferably at least 10 minutes, most preferably at least 15 minutes in, and in particular at least 20 minutes.

The volume-specific power input per stirred tank should be at least 0.1 watt / l, preferably at least 0.3, particularly preferably at least 0.5 watt / l. In general, up to 20 watts / l, preferably up to 6 watts / l and more preferably up to 2 watts / l is sufficient.

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.

In a preferred embodiment, the mixing and the energy input in the stirred tank but also by at least one Umpumpkreislauf done, the optionally can be tempered by at least one mounted in this Umpumpkreislauf heat exchanger.

The reactor may be, for example, a reactor with double wall heating and / or internal heating coils. Preferably, a reactor with external heat exchanger and natural or forced circulation (using a pump), particularly preferably forced circulation, in which the circulation flow is accomplished with mechanical aids, is 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.

Of course, several heat exchangers may be present in the circulation.

As back-mixed reaction zone, for example, a stirred tank, a stirred tank cascade of 2 to 4 stirred tanks, a two- to four-fold cascaded stirred tank, a loop reactor or an unstirred container can be used. Preferably, a stirred tank is used.

The backmixed reaction zone is usually carried out heated. The heating can, for example, a jacket heating, welded half or full tubes, via internal pipes or plates and / or via a circuit with an external heat exchanger, eg. B. tube or plate heat exchanger done. Alternatively, a circuit with an external heat exchanger may be 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.

If appropriate, it is also possible to add further amounts of catalyst or isocyanate, if appropriate in an inert solvent, to stage b).

Under backmixed reactor system is understood here that the Bodensteinzahl of the reactor system is less than 6, preferably less than 4, is.

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 the stage b) in the subsequent stage can be carried out advantageously via level-controlled valves. The conversion of isocyanate in stage b) is generally not more than 20%, preferably not more than 15%, more preferably not more than 10% and most preferably not more than 5%.

In stage c), the discharge from stage a) or stage b), if run through, is subsequently reacted.

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

The tube reactor according to the invention 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 bottoms or static mixers. 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 essential according to the invention that a Reynolds number Re of at least 2300 in the tube reactor is achieved, preferably at least 2700, more preferably at least 4000, very 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 to enter up to 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. The stated specific power input is to be understood here as a registered power per liter reactor volume of the reactor. The power input can be determined by the friction of the Fluids are produced with the reactor wall or by pressure loss producing internals such as orifices, mixing elements, perforated or slotted floors.

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.

The tubular reactor can consist of a pipe section which can be constructed from a single pipe or from an interconnection of several pipes. 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. carried out so that the reactor is designed as a double tube heat exchanger.

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, more preferably less than 0.5,% by volume. Preference is given to nitrogen, argon, helium, nitrogen-noble gas mixtures, nitrogen being particularly preferred.

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

The tubular reactor can be made adiabatic or tempered. A tempering can be done by a jacket heating, welded half or full tubes or by internal pipes or plates. The heating is preferably carried out by the jacket. According to the invention, a tempered design is preferred. The temperature is controlled by a heat transfer between the reaction medium and the tempered reactor wall. The reaction medium side heat transfer is characterized by a Nusselt number greater than 15, preferably greater than 40, more preferably greater than 80, and most preferably greater than 120.

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 to 5, preferably 10, more preferably 15 and very particularly preferably 20 ⁰ 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 this third section to a temperature above 80, preferably 100 , Particularly preferably 120 ⁰ C and most preferably 140 ⁰ C to heat to deactivate the catalyst thermally, or 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)).

Furthermore, it may be useful to divide the tubular reactor into a preheating zone, at least one reaction zone, optionally a deactivation zone and / or a cooling zone, as proposed, for example, in EP-A1 17998. The temperature of the reaction sections is then appropriately chosen so that the Preheating a temperature of about 40 - 60 ⁰ C, the reaction zone 70 - 120 ⁰ C, preferably 70 - 90 ⁰ C _1, the deactivation zone 120 to 180 ⁰ C, preferably 140 to 170 ⁰ C and the 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.

It is more favorable in terms of energy to dispense with a cooling zone and to direct the reaction output from the reaction zone or, if appropriate, from the deactivation zone directly into an evaporation.

Of course, the tubular reactor can also consist of several serially connected pieces of pipe, as long as the backmixing freedom is ensured.

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.

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 input and output by at least 100 units, preferably by at least 500, especially preferably decreases by at least 1000 and most preferably by at least 2000 units.

The temperature in the tube reactor is generally between 40 ⁰ C and 11O ⁰ C ₁ preferably between 50 ⁰ C and 110 ⁰ C, more preferably between 60 and 100 ⁰ C and most preferably between 60 and 90 ⁰ C, wherein the temperature are staggered can, 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 the stage c) in the subsequent stage can advantageously be done via level-controlled valves or directly, if necessary via a throttle.

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

It represents a further preferred embodiment of the present invention that the tubular reactor in c) is designed so that the disperse material and / or heat transfer perpendicular to the flow direction is significantly greater than in the axial direction. This is characterized for mass and / or heat transport by an axial Bodensteinzahl Bo of at least 3, preferably at least 5, more preferably at least 10, even more preferably at least 20, in particular at least 50 and especially at least 100.

For mass transport in the tubular reactor, Bo is defined as the product of axial empty tube velocity and tube length divided by the axial dispersion coefficient.

For heat transport in the tubular reactor, Bo is defined as the product of axial empty tube velocity, tube length, specific heat capacity and density divided by the axial thermal conductivity.

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.

In general, a conversion of 10 to 60% (based on the NCO content before the reaction) is desired. In the case of 1,6-hexamethylene diisocyanate, the conversion is preferably controlled to 20 to 50%, with isophorone diisocyanate preferably to 10 to 40%.

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, and the smallest effective amount, which can be easily determined experimentally, 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. 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 from 0.3 to 1.2 mol of deactivating agent per mole of catalyst used, preferably from 0.4 to 1.0 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 , 16

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 with a 2-hydroxyalkyl-ammonium group is used. Such catalysts are thermolabile at temperatures above 80 ^° C., preferably above 100 ^° C., more preferably above 120, and most preferably above 130, which can be exploited for their deactivation.

Such a deactivation can be carried out, for example, in a section with the corresponding temperature in the tubular reactor c) (see above), by a heat exchanger connected between tubular reactor c) and distillation e) and operated at the temperature concerned, or in US Pat Distillation e), if it is 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 ⁰ C.

Such cooling can be carried out, for example, in a section with the corresponding temperature in the tubular reactor c) (see above) or by a heat exchanger which is connected between tubular reactor c) and distillation e) and which is operated at the relevant temperature.

By a simple cooling, however, the catalyst remains in the reaction mixture and thus remains active, so that the reaction is not completed in the true sense, but at any time can be resumed when heated to a temperature above about 50 ⁰ C.

Thus, it is 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 in known manner, for example by thin film distillation, at a temperature of 100 to 180 ⁰ C, optionally in vacuo, optionally additionally with passing inert stripping gas, optionally existing solution or Diluents and / or are preferably freed from excess, unreacted (cyclo) aliphatic diisocyanates, so that the isocyanurate groups having Polyisocyanates having a content of monomeric diisocyanates of, for example, under 1, 0 wt .-%, preferably below 0.5 wt .-%, more preferably below 0.3, most preferably below 0.2 and in particular not more than 0.1 Gew% 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 particularly 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 recirculating, flash or candle evaporator and the subsequent stages in more complicated apparatuses, for example in falling-film evaporators, thin-film evaporators, for example Sambay® or Luwa evaporators, or short path evaporators. It is advantageous to take equipment measures by which the residence time of the streams and thus their thermal load is reduced, for example, waiving the intermediate container 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-enhancing 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, are particularly preferably toluene, o-, m- or p-xylose lol, trimethylbenzene, Tetramethylbenzene isomers, ethylbenzene, cumene, tetrahydronaphthalene and mixtures containing such.

Examples include the Solvesso® brands of ExxonMobil Chemical, especially Solvesso® 100 (CAS No. 64742-95-6, predominantly C ₉ and Cio-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 designations 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 particularly 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 also _. such solvents can be mixed with polyisocyanates having a density at 2O 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 ₁ 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 as a rule 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, most 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 that 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 in particular less than 0.5% by weight 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 and the viscosity is lower compared with 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 the field of industrial, in particular aircraft or large-vehicle painting, automotive, automotive, in particular OEM or Car refinish, or decorative paint can be 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. A process for the partial trimerization of (cyclo) aliphatic isocyanates in the presence of at least one catalyst which is at least partially carried out in at least one tubular reactor in which the flow in the tubular reactor at least partially has a Reynolds number Re of at least 2300 at a power input of at least 0.2 W / l.

2. The method according to any 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 2, 4,4-trimethyl-1,6-hexamethylene diisocyanate.

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

4. The method according to any one of the preceding claims, characterized in that it comprises the following reaction steps:

(a) mixing the reactants

(b) optionally at least one backmixed reaction zone

(c) 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. The method according to any one of the preceding claims, characterized in that one carries out the step a) with an energy input of at least 1 W / l.

6. The method according to any one of the preceding claims, characterized in that one carries out the step a) in a mixing device selected from the group consisting of stirred tank, static mixers, pump, nozzle mixing devices, Blendenmischeinrichtungen, Koaxialmischdüsen, Y and T mixers ,

7. The method according to any one of the preceding claims, characterized in that the tubular reactor in step c) has a Bodensteinzahl Bo of at least 20

8. The method according to any one of the preceding claims, characterized in that the Reynolds number Re of the reaction mixture in the course of the tubular reactor between input and output by at least 100 units decreases.

9. The method according to any one of the preceding claims, characterized in that the tubular reactor in step c) has a heat transfer, which is characterized by a Nusselt number greater than 15.

10. The method according to any one of the preceding claims, characterized in that one stops the reaction in step d) by addition of a deactivating, by thermal decomposition of the catalyst or by cooling.