WO2014082910A1

WO2014082910A1 - Method for producing polyisocyanates

Info

Publication number: WO2014082910A1
Application number: PCT/EP2013/074323
Authority: WO
Inventors: Torsten Mattke; Matthias KLÖTZER; Thomas Schulz; Michael ERBER
Original assignee: Basf Se
Priority date: 2012-11-28
Filing date: 2013-11-21
Publication date: 2014-06-05

Abstract

The invention relates to a method, preferably a multistage method, for continuously producing organic polyisocyanates, preferably diisocyanates, particularly preferably aromatic, aliphatic, or cycloaliphatic diisocyanates, by reacting the corresponding organic polyamines with carbon dioxide and secondary amines into low-molecular monomeric polyureas and cleaving same. The invention further relates to a corresponding production method in which the produced polyisocyanates and unusable residue are separated at specified reaction stages, and reusable auxiliary and intermediate products are recirculated to the initial stages.

Description

The invention relates to a process, preferably a multistage process for the continuous preparation of organic polyisocyanates, preferably of diisocyanates, particularly preferably of aromatic, aliphatic or cycloaliphatic diisocyanates, by reacting the corresponding organic polyamines with carbon dioxide and secondary amines in low molecular weight monomeric polyureas and their cleavage. A further subject of the invention is an associated preparation process in which the polyisocyanates prepared and unreactable residues are separated in certain reaction stages and reusable by-products and intermediates are recirculated to precursors.

The technical processes for the preparation of organic polyisocyanates, e.g. of aromatic, aliphatic or cycloaliphatic polyisocyanates are based on the phosgenation of the corresponding organic polyamines to form polycarbamoyl chlorides and their cleavage to the polyisocyanates and hydrogen chloride. Apart from the severe environmental, disposal and safety problems associated with the use of phosgene, these processes suffer from other significant disadvantages. Thus, the preparation of aliphatic or cycloaliphatic polyisocyanates succeeds only with fairly moderate space-time yields due to the greater basicity of the starting polyamines. Another disadvantage is the formation of undesirable by-products which, already present in traces, can lead to strong discoloration of the polyisocyanates. In hexamethylene diisocyanate 1, 6 (HDI) preparation, e.g. several by-products, of which the most important, 6-chlorohexyl isocyanate, also has the disadvantage that it can only be separated from the HDI with considerable distillative effort.

The problem with this procedure is in particular the high conversion of chlorine over phosgene and carbamoyl chloride in hydrogen chloride, the toxicity of the phosgene and the corrosivity of the reaction mixture, the lability of the solvents used in the rule and the formation of halogenated residues.

Although the cleavage of (cyclo) aliphatic and in particular aromatic mono- and di-urethanes into the corresponding isocyanates and alcohol has long been known and can be carried out both in the gas phase at high temperatures and in the liquid phase at comparatively low temperatures It is particularly the undesirable side reactions and especially the tendency of the reaction mixtures for the formation of occupancies, Verharzungen and blockages in reactors and reprocessing facilities that affect the efficiency of the processes sustainable.

In recent decades, therefore, many efforts have been made to eliminate these disadvantages of the process by a simpler and improved process. Thus, for the preparation of aliphatic and / or cycloaliphatic di- and / or polyurethanes according to EP 18588 A1 or also as in EP 28338 A2 primary aliphatic and / or cycloaliphatic di- and / or polyamines with O-alkylcarbamic acid esters in the presence of alcohols at temperatures Tures of 160 to 300 ° C reacted with and without catalyst. The resulting di- and / or polyurethanes can be converted into the corresponding isocyanates. The ammonia formed in the reaction of the amines can be separated off. Further publications are concerned with the partial substitution of urea and / or diamines by carbonyl-containing compounds (eg EP 27952 or EP 126299). The phosgene-free process is described in detail, for example, in EP 566925 A2.

A disadvantage of the latter method is the relatively long reaction time, which is given up to 50 hours.

WO 2007/082818 (= US 2010/274046) discloses a process which dispenses with the presence of alcohols and the formation of urethanes as an intermediate. However, there is still a need for improved yield processes.

A disadvantage of the previously described phosgene-free process is that can be prepared only undecomposed distillable isocyanates with these methods.

WO 98/54129 describes a process for the decomposition of diureas, which are each formed from secondary amines. These secondary amines are very specific amines in which the amino groups are substituted with a tertiary carbon atom, for example, tertiary butyl groups or 2,2-disubstituted piperidine groups.

The decomposition takes place purely thermally optionally in the presence of a carrier gas or an inert solvent. The disadvantage here is that in this type of reaction, the decomposition products secondary amine and isocyanate react quickly with each other, which is particularly due to the high reactivity of the secondary amines.

From the international patent application WO 2012/163894 (file reference

PCT / EP2012 / 059993, application date 29 May 2012) is a multi-step process for the continuous production of organic isocyanates by reacting the corresponding organic polyamines with urea and at least one secondary amine to the corresponding polyureas in at least one mixing device with downstream reactor and their cleavage known ,

A disadvantage of all the above methods is that they emanate from urea, so that ammonia is released, which must be consuming reused or disposed of.

The object of the present invention was to produce organic polyisocyanates with high selectivity in improved yields at low cost in a simple manner, bypassing urea as starting material.

This object could be achieved by a process for the preparation of polyisocyanates by preferably catalytic reaction of at least one polyamine with carbon dioxide and at least one secondary amine to the corresponding polyurea and subsequent cleavage of the resulting polyureas in the corresponding polyisocyanates.

The invention further relates to a multistage process for the continuous preparation of organic isocyanates by preferably catalytic reaction of the corresponding organic polyamines with carbon dioxide and at least one secondary amine to the corresponding polyureas in at least one downstream-stage mixing device and its cleavage, the following steps and in which a) at least one organic polyamine with carbon dioxide in the absence or preferably in the presence of at least one catalyst and at least one secondary amine optionally mixed together in the presence of at least one solvent, b) the mixture obtained from a) in at least one subsequent Reacting residence time reactor or several residence time reactors, c) separating unconverted carbon dioxide from the reaction mixture obtained from b) and optionally after an optional purification again in stage a) and / or b) recircles, d) from the effluent from b) excess secondary amine and further secondary components which boil more easily than the polyureas, f) the polyureas thermally or preferably acidly cleaves the polyureas in a continuous splitting device into the corresponding isocyanate and secondary amine at least one isocyanate-containing stream and at least one secondary amine-containing stream are obtained, g) purification of the obtained from the cleavage f) isocyanate-containing stream by

- gl) solvent is separated, as far as previously solvent was used, - g2a) in the case of distillable isocyanates, their purification by distillation or

g2b) in the case of non-distillable isocyanates, their optional purification by non-distillative means, and i) purification of the secondary amine-containing stream obtained from cleavage f) and its optional recycling.

The process according to the invention has a better yield than processes known in the art, in particular the process known from EP 566 925.

In purely formal terms, the method according to the invention can be schematically represented by the following equation: R- (NH ₂ ) _n + n CO ₂ + n HNR ¹ R ² -R (NCO) _n + n HNR ¹ R ² + n H ₂ O

For the preparation of the monomer usable in this invention as an intermediate poly- ureas R (NH-CO-NR ¹ R ²⁾ _n are suitable polyamines of the formula R (NH2) _n, an n-valent R, preferably three or divalent, most preferably bivalent organic radical, such as an optionally substituted, for example, substituted with an alkyl group substituted aromatic, a linear or branched chain aliphatic or optionally substituted cycloaliphatic radical. Examples of suitable aromatic polyamines which may be mentioned are 2,4- and 2,6-toluylenediamine, 4,4'-, 2,4'- and 2,2'-diaminodiphenylmethanes and the corresponding isomer mixtures.

It represents an embodiment of the present invention that aromatic amines can also be reacted with the process according to the invention to give the corresponding isocyanates, which are polyamine mixtures of the diphenylmethane series, as obtained in a conventional manner by polycondensation of formaldehyde with aniline can.

Suitable aliphatic or cycloaliphatic polyamines are, for example: butanediamine 1, 4, pentanediamine-1, 5, 2-ethylbutanediamine-1, 4, octanediamine-1, 8, decanediamine-1, 10, dodecanediamine-1, 12, cyclohexanediamine-1, 4, 2-methyl-, 4-methylcyclohexanediamine-1, 3, 1, 3- and 1, 4-diaminomethylcyclohexane and 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane , Preference is given to using 2-methylpentanediamine-1, 5, 2,2,4- or 2,4,4-trimethylhexanediamine 1, 6 and in particular 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, hexanediamine -1, 6 and 3-aminomethyl-3,5,5-trimethylcyclohexylamine.

Suitable secondary amines are, in principle, those secondary amines which are stable under the reaction conditions, i. Under the reaction conditions per hour to less than 5 mol%, preferably less than 3, more preferably less than 2 and most preferably less than 1 mol% based on the material decompose, especially those secondary amines having a molecular weight below 500 g / mol, which have no further functional groups and except the secondary amino function exclusively hydrocarbon radicals and ether groups, preferably only carry hydrocarbon radicals. Preference is given to selecting those secondary amines whose boiling points are sufficiently far from the boiling point of the polyisocyanate, preferably diisocyanate, obtained by the cleavage, so that the most quantitative possible separation of the cleavage products polyisocyanate, preferably diisocyanate, from the secondary amine by distillation is possible. Preferably, a boiling point difference between secondary amine and isocyanate of at least 20 ° C, more preferably of at least 30 ° C and most preferably at least 40 ° C.

The secondary amines are preferably those of the formula HNR ¹ R ² , where R ¹ and R ² independently of one another are 1 to 20, preferably 1 to 10 and particularly preferably 1 to 6 alkyl-containing alkyl, 3 to 12, preferably 5 to 12, particularly preferably 5 to 6 carbon atoms exhibiting cycloalkyl, 6 to 14, preferably 6 to 10, particularly preferably 6 to 8 carbon atoms having aryl, or an aralkyl radical, 6 to 14, preferably 6 to 8 carbon atoms in the aryl and 1 to 6, preferably 1 to 3 carbon atoms in the alkyl radical, or the radicals R ¹ and R ² together may form a five-to twelve-membered, preferably five- to six-membered ring, including the nitrogen atom The radicals may less preferably additionally have ether groups.

Examples of alkyl groups are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-hexyl, n-heptyl, 2-ethylhexyl, 2-propylheptyl, n-butyl Octyl, n-decyl, n-dodecyl, n-tetra- decyl, n-hexadecyl, n-octadecyl, n-eicosyl, preferably methyl, ethyl, iso-propyl, n-propyl, n-butyl, tert-butyl and n-hexyl, more preferably methyl, ethyl, iso-propyl and n-butyl.

Examples of cycloalkyl groups are cyclopentyl, cyclohexyl, cyclooctyl and cyclododecyl, preferably cyclopentyl and cyclohexyl.

Examples of aryl groups are phenyl, tolyl, xylyl and naphthyl, preferred are phenyl and tolyl, and particularly preferred is phenyl. Examples of aralkyl groups are benzyl, phenethyl and 2- or 3-phenylpropyl, preferred are benzyl and phenethyl, particularly preferred is benzyl.

Preferred secondary amines are dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, di-n-butylamine, dihexylamine, dioctylamine, ethylmethylamine, iso-propyl-methylamine, n-butylmethylamine, tert-butylmethylamine, iso-propylamine Ethylamine, n-butylethylamine, tert-butyl ethylamine, morpholine, piperidine and pyrrolidine, preferred are dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, di-n-butylamine, piperidine and pyrrolidine, particularly preferred are dimethylamine , Diethylamine, di-iso-propylamine, di-n-butylamine, very particularly preferred are dimethylamine and di-n-butylamine and especially di-n-butylamine.

Preferred cyclic secondary amines are pyrrolidine, piperidine and morpholine.

It can not be ruled out that sterically demanding primary amines can also react like the abovementioned secondary amines in the sense of the invention, for example tert-butylamine or iso-propylamine, but secondary amines are preferred in the context of the present invention.

Carbon dioxide can be used from any source, for example, in pure form or from combustion gases, optionally mixed with inert gases under the reaction conditions, such as oxygen or nitrogen, as well as minor amounts of water, methane, ethane, propane or carbon monoxide.

In a preferred embodiment, carbon dioxide is removed from crude natural gas or combustion gases by a gas scrubber in which carbon dioxide is absorbed by adsorption to a carbon dioxide gas Washing liquid and subsequent desorption is obtained therefrom. Also conceivable would be the use of carbon dioxide, which is still absorbed in a washing liquid. In a conceivable embodiment, such a washing liquid may also contain the secondary amine used in the process according to the invention, which is then fed into the reaction together with the carbon dioxide as a reactant.

The individual stages of the process are described below: a) mixing of the reaction components

To produce the polyureas in reaction step (a), the polyamines are reacted with carbon dioxide and at least one, preferably exactly one secondary amine in a molar ratio of polyamine, carbon dioxide and secondary amine of 1: 2 to 100: 5 to 40, preferably 1: 2 , 0 to 50: 6 to 10 at temperatures of 50 - 300 ° C and in particular at 130 - 220 ° C under a pressure of 0.1 to 300 bar, preferably 1 - 150 bar mixed together.

In a preferred embodiment, all three starting components polyamine, carbon dioxide and secondary amine are mixed together in step a).

However, it is also possible first to mix two of these three starting components together and then to mix the resulting mixture with the third starting component. Among the three such possible permutations, it is preferable to first mix polyamine and carbon dioxide and then mix the resultant mixture with the secondary amine.

However, it is a preferred possible embodiment, first vorzumischen secondary amine and carbon dioxide and to introduce into this mixture, the polyamine. In this case, carbon dioxide can be metered in gaseous, liquid or supercritical, preferably liquid or supercritical, into stage a).

The mixing in step (a) can be carried out in the presence of substituted ureas, expediently in an amount of 0.1 to 30 mol%, preferably 1 to 10 mol%, based on the polyamine, preferably diamine. In particular, mixtures of substituted ureas in the proportions mentioned are used. Substituted ureas used are preferably those whose substitution patterns correspond to those of the secondary amine used, ie the formal reaction products of carbon dioxide with one or two equivalents of secondary amine. This may, for example, be the discharge (di_) of stage d), see below.

The mixing in step (a) may optionally take place in the presence of at least one solvent. Preferred solvents are N-substituted lactams, Ν, Ν-disubstituted amides, ethers, hydrocarbons, halogenated hydrocarbons, ionic liquids and supercritical carbon dioxide. Examples of solvents are THF, dioxane and the dimethyl, ethyl or n-butyl ethers of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol or tripropylene glycol, N-methylpyrrolidone, N-ethylpyrrolidone, N-cyclohexylpyrrolidone, dimethylformamide, dimethylacetamide and supercritical carbon dioxide. It is a preferred embodiment to use carbon dioxide in a high excess and to adjust the reaction conditions so that supercritical carbon dioxide acts not only as a reactant but also as a solvent.

Examples of suitable hydrocarbons which are optionally substituted by halogen atoms include hexane, benzene, nitrobenzene, anisole, chlorobenzene, chlorotoluene, o-dichlorobenzene, trichlorobenzene, xylene, chloronaphthalene, decahydronaphthalene and toluene.

It is also possible to use ionic liquids as solvents in the reaction according to the invention. Conceivable ionic liquids are described, for example, in WO 2007/090755 A1, page 3, line 28 to page 26, line 32, which is hereby incorporated by reference into the present disclosure. Preferred ionic liquids are described there from page 25, line 6 to page 26, line 32.

Particularly preferred ionic liquids are those as described in

WO 201 1/061314 A1, page 17, line 35 to page 25, line 21, which is hereby incorporated by reference into the present disclosure.

Very particularly preferred ionic liquids are the halides, especially chlorides, hexafluorophosphates, tetrafluoroborates and in particular the hydroxides of 1, 2-dimethyl-3-propylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-butyl-2,3 dimethyl imidazolium, 1-benzyl-3-methylimidazolium, 3-ethyl-1-methylimidazolium, 1-propyl-3-methylimidazolium, 3-n-butyl-1-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-methyl-3 -octylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium, 1,3-diethylimidazolium, 1,3-diisopropylimidazolium, 1,3-di-n-butylimidazolium, 1,3-dihexylimidazolium, and 1 , 2,3,4,5-pentamethylimidazolium.

Conceivable, though less preferred, are ketones and esters.

As already stated, the mixing in stage (a) or else the reaction in stage b) can also be carried out in the presence of catalysts. These are expediently used in amounts of from 0.001 to 20% by weight, preferably from 0.001 to 1% by weight, in particular from 0.002 to 0.1% by weight, based on the weight of the polyamine.

Suitable catalysts are hydroxides, oxides, carbonates, bicarbonates, alkoxides, phenolates and carboxylates which contain one or more cations, preferably a cation of metal oxides. Group IA, IB, IIA, IIB, HIB, IVA, IVB, VA, VB, VIB, VIIB, VIIIB of the Periodic Table of the Elements, defined in Handbook of Chemistry and Physics 14th Edition, published by Chemical Rubber Publishing Co., 23 Superior Ave. NE, Cleveland, Ohio. Examples of cations are the following metals: lithium, sodium, potassium, cesium, magnesium, calcium, aluminum, gallium, tin, lead, bismuth, antimony, copper, silver, gold, zinc, mercury, cerium, titanium, vanadium, chromium, Molybdenum, manganese, iron and cobalt.

Particular preference is given to the hydroxides, oxides, carbonates and bicarbonates of the alkali metals and alkaline earth metals, very particularly preferably carbonates and bicarbonates of the alkali metals and alkaline earth metals, in particular carbonates and bicarbonates of the alkali metals.

Examples of typical catalysts are the following compounds: Preference is given to lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium oxide, sodium oxide, potassium oxide, cesium oxide, lithium hydrogencarbonate, sodium bicarbonate, potassium hydrogencarbonate, cesium hydrogen carbonate, lithium carbonate, sodium carbonate, potassium carbonate and cesium carbonate, lithium methoxide, lithium ethanolate, lithium propoxide , Lithium butanolate, sodium methoxide, potassium tert-butoxide, magnesium methoxide, calcium methoxide, copper (I) oxide, copper (II) oxide, copper (II) carbonate or copper (II) hydrogen carbonate. In particular, when using the metal salts mentioned as catalysts in the process according to the invention, the addition of traces of water may be advantageous, usually in the 0.1 to 100-fold, preferably in the 0.5 to 10-fold amount by weight based on the catalyst.

Further conceivable catalysts are tertiary organic amines, in particular trimethylamine, tributylamine, 2-dimethylaminoethanol, triethanolamine, dodecyldimethylamine, N, N-dimethylcyclohexylamine, N-methylpyrrolidine, N-methylmorpholine, 4-dimethylaminopyridine, 1,5-diazabicyclo [4.3 .0] non-5-ene, 1,8-diazabicyclo [5.4.0] undec-7-ene and 1,4-diazabicyclo [2.2.2] octane.

Also conceivable is the use of zeolites, in particular metal-doped zeolites, such as, for example, cesium-doped zeolites.

The mixing of the educt streams can optionally take place in a suitable special mixing device, which is characterized by short mixing times, in order then to achieve the substantial conversion in stage b) in at least one reactor.

During the mixing, a reaction of polyamine and carbon dioxide and optionally with secondary amine can take place, which as a rule is not problematic. b) Reaction of the mixture from a) The mixture leaving the mixing device is now fed to at least one one or more two-phase (gaseous / liquid) or preferably single-phase supercritical residence time reactors in which, in the case of a two-phase reaction, the gas phase with the liquid phase is conducted in DC. In the event that the residence time reactor in stage b) is sufficiently back-mixed, for example it is a stirred tank, it may be advantageous to combine stages a) and b) with one another, ie to carry out the mixing within stage b), for example in a stirred tank.

Optionally, in the residence time reactor, as stated above, at one or more points, for example at the beginning and in the middle of the reactor, further carbon dioxide and / or secondary amine or preferably polyamine can be post-dosed. The average residence time in the reactor is generally 10 minutes to 12 hours, preferably 60 minutes to 10 hours, particularly preferably 2 to 8 hours.

In order to keep the gas load for the subsequent stage low, the discharge from the reactor can be fed to a phase separator in a preferred embodiment and the liquid phase withdrawn from the phase separator can then be fed to the subsequent stage.

Such a phase separator is a container in which the phase separation between gas and liquid phase is achieved by the calming of the two-phase, emerging from the DC reactor flow.

The phase separator can be carried out isothermally or preferably heated to prevent the precipitation of poorly soluble by-products. The heating can be done for example via the jacket or via a circuit with an external heat exchanger. When using an external heat exchanger, normal insulation of the heat exchanger is sufficient. The temperature in the reactor or the reactor combination and in any phase separator is generally between 50 ° C and 300 ° C, preferably between 180 ° C and 220 ° C.

The pressure in stage b) is generally between 74 bar abs and 300 bar abs and preferably between 100 and 200 bar abs.

The residence time in step b) is selected so that the conversion, based on amino groups in the polyamine used to polyurea, after leaving the reactor at least 95%, preferably at least 98, more preferably at least 99 and most preferably at least 99.5% is.

Usually, the total residence time in stage a) and b) together is less than 12 hours, preferably less than 10 hours and more preferably less than 8 hours.

If the conversion, based on amino groups in the polyamine used to form urea groups, is not complete after leaving the reactor or the reactor combination and is, for example, less than 95%, then the discharge can be further reacted. For this purpose, the reaction mixture can be allowed to react to complete the conversion in another reactor, preferably until the conversion is 98% or more.

In one possible embodiment of the present invention, it is also possible to use stages a) and b) in a stirred kettle or a stirred tank cascade, preferably in one to four stirred kettles, more preferably one to three stirred kettles, more preferably two to three stirred kettles, and most preferably to carry out two stirred kettles. In this case, the first stirred tank at least partially functions as stage a) and the rest as stage b). Otherwise, the reaction conditions in such an embodiment are as described above. c) Carbon Dioxide Separation To separate the unconverted carbon dioxide from the reaction mixture obtained from stage b), it is expedient to use columns; the carbon dioxide is preferably removed by distillation or rectification. This achieves a good separation between the secondary amine and the carbon dioxide. Usually, the separation takes place in a pressure range of 0.01 to 20 bar, preferably 0.04 to 15 bar. The necessary temperatures depend on the secondary amine used or its mixture. For di-n-butylamine, for example, the temperature is 210 ° C, preferably 190 ° C.

The separated carbon dioxide may have a content of secondary amine of up to

70% by weight, preferably up to 10% by weight, particularly preferably up to 1% by weight, very particularly preferably up to 0.1% by weight. In this case, it may be conceivable to work up this secondary amine and carbon dioxide mixture for secondary amine recovery. In this case, however, it is preferable to recycle the mixture of carbon dioxide and secondary amine as such in stage a) and / or b). d) separation of the excess secondary amine

From the resulting reaction mixture, the remaining secondary amine, possibly unreacted carbon dioxide and optionally the solvent, as far as which was used, separated and preferably recycled to the reaction stage (a) and / or (b).

If solvent is used in the cleavage (step f), see below), complete removal of this solvent in this step d) is less preferred.

To separate the amine, the reaction mixture is advantageously depressurized from the pressure level of the reaction stage (b) to a pressure in the range from 1 to 2000 mbar, preferably from 10 to 900 mbar. This gives gaseous vapors (oil), which contain the predominant amount of secondary amine and 10 to 99 wt.%, Preferably 50 to 95 wt.% Solvent, and a liquid discharge, consisting essentially of the monomeric polyurea, preferably Diurea, and optionally contains high-boiling oligomers. The resulting vapors (di_) can optionally be separated in subsequent suitably distillative purification stages, preferably by rectification, and the product isolated here secondary amine and separated solvent, individually or as a mixture, preferably in the reaction stage (a) to form the monomeric polyureas ,

It is a preferred embodiment of the present invention, secondary amine and solvent, if used, not to separate, but as a mixture due.

For distillative removal of the secondary amine or its mixture, a so-called flash is often used. This apparatus may be a container or a combination of container and column, preferably a column, wherein in the head, the secondary amine or its mixture and in the bottom of the polyurea can be withdrawn. In addition to the secondary amine, other substances which boil more easily than the polyurea and which can be recycled, for example, to stage b), may be present in the top of the column in addition to the secondary amine. The separation takes place in a pressure range of 0.001 to 1 bar, preferably 0.02 to 0.8 bar. The distillation bottoms can generally still contain solvents, which can be carried out without disadvantages in the subsequent cleavage f), in particular if the cleavage f) is carried out acidically with phase separation.

If supercritical carbon dioxide was used as the solvent in the preceding stages and separated off from the reaction mixture, it may be useful at this point to take up the distillation bottoms for subsequent cleavage in a solvent.

Suitable solvents are preferably hydrocarbons which are optionally substituted by halogen atoms, such as hexane, benzene, nitrobenzene, anisole, chlorobenzene, chlorotoluene, o-dichlorobenzene, trichlorobenzene, diethyl isophthalate (DEIP), tetrahydrofuran (THF), dimethylformamide (DMF), Xylene, chloronaphthalene, decahydronaphthalene and toluene. The solvent used is particularly preferably dichlorobenzene. In a preferred embodiment, the same solvent as in steps a) and b) is used. f) polyurea cleavage

The reaction mixture containing polyureas obtained in the reaction step (b) is in a suitable device, preferably in a solvent or solvent mixture in the liquid phase in the presence of acids at temperatures of 20 to 250 ° C, preferably 100 to 200 ° C and under a pressure of 0.1 - 5 bar, preferably in the range of 0.3 - 2 bar continuously thermally or preferably acid split. Acids which may be used are organic or inorganic Bronsted acids, preferably those having a pKa of not more than 5, more preferably having a pKa of not more than 4, and most preferably having a pKa of not more than 3. Preference is given to inorganic Bronsted acids.

In a preferred embodiment, the acids are used anhydrous.

Preferred examples of such acids are sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and hydrobromic acid. Particularly preferred are sulfuric acid and hydrochloric acid, most preferably hydrochloric acid. In particular, gaseous hydrogen chloride is used.

To shift the reaction equilibrium from the polyurea to the isocyanate, the molar ratio of acid to urea group in the polyurea should be at least 2: 1, preferably at least 3: 1.

The conversions in the reaction device generally depend largely on the excess acid used and can be chosen largely freely. Conveniently, they are in a range of 10 to 100 wt.%, Preferably 80 to 99 wt.% Of the supplied amount of polyurea.

As acids for the chemical cleavage of the polyureas, the aforementioned, the urea formation catalyzing inorganic and organic compounds can be used.

The cleavage can be carried out in a stirred tank or a stirred tank cascade or a tube reactor with a Bodensteinzahl up to 5, preferably in a single stirred tank. The average residence time is up to one hour, preferably up to 40 minutes, more preferably up to 15 and most preferably up to 10 minutes. Alternatively, the reactor constructions known to those skilled in the art for gas-liquid reactions, such as bubble columns or reaction columns, can be used.

In a further preferred embodiment, preference may be given to using at least one, preferably exactly one gaseous acid, in particular hydrogen chloride as acid, cleavage in a mixing pump or a nozzle mixing device, for example coaxial mixing nozzles, Y or T mixers, or a vortex impinging jet Mixed configuration can be performed, which cause a rapid phase transition from the gas to the liquid phase.

The temperature in the cleavage in this case is generally from 100 to 200.degree. C., preferably from 120 to 190 and particularly preferably from 140 to 180.degree. In this embodiment, the

Reaction time is significantly less than 10 minutes, preferably up to 5 minutes, more preferably up to 3 minutes and most preferably up to 1 minute. The discharge from the cleavage reactor is then fed to at least one, preferably exactly one separation stage, in which an organic liquid phase containing polyisocyanates is separated from a second phase containing the secondary amine in the form of its ammonium salt with the acid residue.

The separation may be a solid-liquid separation, for example centrifugation or filtration, preferably a filtration of the solid salt phase. Optionally, the reaction mixture is cooled again to reduce the solubility prior to the solid-liquid separation.

However, any type of crystallization and phase separation can also be used in suitable apparatus known to the person skilled in the art, such as, for example, crystallizers. Alternatively, the reaction can be separated by extraction of an extractive extractive agent. g) isocyanate purification

The polyisocyanate obtained from stage f), preferably in the form of a solution in a solvent from the acidic cleavage from stage f), is purified in stage g). If a solvent was used in one of the previous reaction steps, this can be separated by distillation in a first purification step gl). The solvent thus separated can then preferably be conducted in stage a) and / or b) and / or f), if necessary there. Subsequently, in the case of distillable isocyanates, their purification by distillation can be carried out in a step g2a) as follows:

The crude isocyanate mixture is freed in a subsequent distillation of recombination products, by-products and any remaining traces of solvent. The by-products are preferably recycled to the reaction steps a) and b). A part can also be removed.

The distillation is advantageously carried out with the aid of one or more distillation columns, preferably by rectification at temperatures of 100 to 220 ° C, preferably 120 to 170 ° C and a pressure of 1 to 200 mbar, preferably 5 to 50 mbar, in low boilers (gi_) and a crude polyisocyanate mixture (givi) having a polyisocyanate content of 85 to

99% by weight, preferably from 95 to 99% by weight separated. The higher-boiling by-products (gH) obtained in the distillative separation and in particular the uncleaved and partially cleaved polyureas are passed into the cleavage (f) or preferably discharged.

The subscript "L" is used to denote low-boiling streams of the individual stages, with the index "H" high-boiling and "M" medium-boiling. The crude polyisocyanate mixture (givi), preferably obtained by rectification, can be further purified in a further distillation at a temperature of 100 to 180 ° C. and under a pressure of 1 to 50 mbar, the resulting pure polyisocyanate stream having a purity of at least 98% by weight. , in particular more than 99 wt.% Has.

However, according to other process variants, the bottoms fraction (gH) may also be recycled to the distillation column (d) for the separation of crude polyisocyanate and secondary amine or to reaction stage (a) and / or (b), the polyurea formation. It is also possible to divide the sump fraction into 2 or 3 product streams, these preferably being recycled in the polyurea formation (a) and the cleavage apparatus (f) and optionally in the distillation column (g).

If the isocyanate prepared is a non-distillable isocyanate, it can optionally be purified in a step g2b) by a non-distillative route, for example by extraction or washing with a solvent. i) recovery of the secondary amine

The product obtained from stage f) in the form of a salt of secondary amine and the acid used for the cleavage in a solvent can be liberated in a preferred embodiment for working up with a base, for example with hydroxides, oxides, carbonates or bicarbonates of alkali metal. or alkaline earth metals, preferably sodium hydroxide, sodium bicarbonate, sodium carbonate or milk of lime. The release is carried out at a temperature of 0 to 60 ° C, preferably 0 to 40 ° C at a residence time of 10 minutes to 3 hours, preferably 20 to 120 minutes and more preferably 30 to 90 minutes.

Obtained is a solution of the liberated secondary amine in the solvent, which is separated by solid-liquid phase separation, preferably by centrifugation or filtration, from the ammonium salt of the acid.

The released secondary amine is then preferably recycled to the reaction. Alternatively, it is possible to thermally separate the salt of secondary amine and the acid used for the cleavage in a solvent.

For this purpose, the salt, optionally in a solution, is heated above its decomposition temperature and the decomposition products are thermally separated. This can be done, for example, in a rectification column. But various combinations of thermal cleavage and subsequent separation by adsorption, absorption and partial condensation are possible.

With the multistage process according to the invention for the continuous production of organic polyisocyanates with recycling and removal of by-products Polyisocyanates, preferably diisocyanate can be prepared with high selectivity in very good yields.

The inventive method is particularly suitable for the preparation of aliphatic diisocyanates, such as 2-methylpentane-diisocyanate-1, 5, isomeric aliphatic diisocyanates having 6 carbon atoms in the alkylene radical and mixtures thereof and preferably hexamethylene diisocyanate-1, 6 and cycloaliphatic diisocyanates, in particular 3- isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate by an economical method. However, it is also conceivable to prepare 2,4- and 2,6-toluene diisocyanate and also polymeric diphenylmethane diisocyanate (pMDI).

The polyisocyanates prepared are particularly suitable for the production of urethane, isocyanurate, amide and / or urea group-containing plastics by the polyisocyanate polyaddition process. They are also used for the preparation of urethane, biuret and / or isocyanurate-modified polyisocyanate mixtures. Such polyisocyanate mixtures of aliphatic or cycloaliphatic diisocyanates are used in particular for the production of light-resistant polyurethane coatings and coatings.

The following examples are intended to illustrate the invention, but do not limit it to these examples.

Examples

1 . Preparation of aliphatic ureas based on n-hexylamine and pyrrolidone:

Reaction:

Execution:

In a pressure autoclave were catalytic amounts of cesium carbonate as well

138.6 mmol of n-hexylamine and pyrrolidine presented in three-fold excess. Subsequently, the autoclave was rinsed several times with CO2 and heated to 190 ° C under CO 2 atmosphere. After several hours of reaction time, a slightly brownish solid was obtained. For work-up, first 250 ml of water were added slowly to the crude product, after which the urea formed was extracted with about 100 ml of ethyl acetate. The organic phase was separated from the aqueous and evaporated to dryness. A colorless, crystalline solid with a yield of about 70% was obtained.

2. Preparation of Aromatic Ureas Based on Aniline and Pyrrolidone: Reaction Equation:

Procedure: In a pressure autoclave catalytic amounts of cesium carbonate and

138.6 mmol of aniline and pyrrolidine presented in three-fold excess. Subsequently, the autoclave was rinsed several times with CO2 and heated to 190 ° C under CO 2 atmosphere. After several hours of reaction, a brownish solid was obtained. For work-up, first 250 ml of water were added slowly to the crude product, after which the urea formed was extracted with about 100 ml of ethyl acetate. The organic phase was separated from the aqueous and shaken out against a dilute aqueous HCl solution. The organic phase was again separated and concentrated to dryness. A colorless, crystalline solid with a yield of about 30% was obtained.

Claims

claims

A process for the preparation of polyisocyanates by preferably catalytic reaction of at least one polyamine with carbon dioxide and at least one secondary amine to the corresponding polyurea and subsequent cleavage of the polyureas thus obtained in the corresponding polyisocyanates.

Process according to claim 1, characterized in that the polyamine is a diamine.

Method according to one of the preceding claims, characterized in that the polyamine is selected from the group butanediamine-1, 4, pentanediamine-1, 5, 2-ethylbutanediamine-1, 4, octanediamine-1, 8, decanediamine-1, 10, dodecanediamine-1, 12, cyclohexanediamine-1, 4, 2-methyl-, 4-methylcyclohexanediamine-1, 3, 1, 3- and 1, 4-diaminomethylcyclo- hexane, 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, hexanediamine-1, 6 and 3-amino-methyl-3,5,5-trimethylcyclohexylamine.

A method according to claim 1, characterized in that the polyamine is selected from the group consisting of 2,4- and 2,6-tolylene-diamine, 4,4'-, 2,4'- and 2,2'-diaminodiphenyl methane and their isomer mixtures and also polyamine mixtures of the diphenylmethane series, which are obtainable by polycondensation of formaldehyde with aniline.

Process according to any one of the preceding claims, characterized in that the secondary amine has the formula

HNR R ²

fulfilled, in which

R ¹ and R ² independently of one another may denote alkyl having from 1 to 20 carbon atoms, cycloalkyl having from 6 to 14 carbon atoms, aryl having from 6 to 14 carbon atoms, or an aralkyl radical having from 6 to 14 carbon atoms in the aryl and from 1 to 6 carbon atoms in the alkyl radical, or the radicals R ¹ and R ² together may form a five to twelve-membered ring, including the nitrogen atom, wherein the radicals may additionally have ether groups.

Method according to one of the preceding claims, characterized in that the secondary amine is selected from the group consisting of dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, di-n-butylamine, dihexylamine, dioctylamine, ethylmethylamine , Iso-propyl-methylamine, n-butylmethylamine, tert-butylmethylamine, iso-propyl-ethylamine, n-butylethylamine, tert-butylethylamine, morpholine, piperidine and pyrrolidine.

Process according to one of the preceding claims, characterized in that it is a multistage process for the continuous preparation of organic isocyanates by preferably catalytic conversion of the corresponding organic polyamines with carbon dioxide and at least one secondary amine to the corresponding Γ

WO 2014/082910 18 PCT / EP2013 / 074323

a) at least one organic polyamine with carbon dioxide in the absence or preferably in the presence of at least one catalyst and with at least one secondary amine optionally in the presence of at least one Solvent mixed together,

b) the mixture obtained from a) is reacted in at least one subsequent residence time reactor or multiple residence time c) unconverted carbon dioxide is separated from the reaction mixture obtained from b) and optionally returned to stage a) and / or b) after an optional purification, d) from the effluent from b) excess secondary amine and further secondary components which boil more easily than the polyureas, f) the polyureas thermally or preferably acidly cleaves the polyureas in a continuous splitting device into the corresponding isocyanate and secondary amine, at least one isocyanate-containing stream and g) purification of the obtained from the cleavage f) isocyanate-containing stream by

- gl) solvent is separated, as far as solvent was previously used,

g2a) in the case of distillable isocyanates, their purification by distillation or

Process according to Claim 7, characterized in that steps a) and b) are carried out in a common apparatus.

A method according to claim 7, characterized in that one mixes polyamine, carbon dioxide and secondary amine from 1: 2 to 100: 5 to 40, at temperatures of 50 - 300 ° C under a pressure of 0.1 to 300 bar and brings to reaction ,

0. The method according to any one of the preceding claims, characterized in that one carries out the reaction of polyamine with carbon dioxide and at least one secondary amine in the presence of at least one catalyst selected from the Group Γ

Consisting of hydroxides, oxides, carbonates, bicarbonates, alkoxides, phenates and carboxylates which contain one or more cations, preferably a cation of metals of group IA, IB, IIA, IIB, HIB, WO-A-201/02829 IVA, IVB, VA, VB, VIB, VIIB, VIIIB of the Periodic Table of the Elements.

1 1. A process according to claims 7 to 10, characterized in that step a) in the presence of at least one solvent selected from the group consisting of N-substituted lactams, Ν, Ν-disubstituted amides, ethers, hydrocarbons, halogenated hydrocarbons, ionic liquids and performs supercritical carbon dioxide.

12. The method according to claim 7 to 1 1, characterized in that one carries out step f) in the presence of an organic or inorganic Brönsted acid. 13. The method according to any one of claims 7 to 12, characterized in that one

Step f) in the presence of a solvent selected from the group consisting of hexane, benzene, nitrobenzene, anisole, chlorobenzene, chlorotoluene, o-dichlorobenzene, trichlorobenzene, diethyl isophthalate (DEIP), tetrahydrofuran (THF), dimethylformamide (DMF), Xy- lol, chloronaphthalene, decahydronaphthalene and toluene.

14. The method according to any one of claims 7 to 13, characterized in that one releases the secondary amine by a base in step i).

15. The method according to any one of claims 7 to 13, characterized in that one releases the secondary amine in step i) by a thermal separation of the salt formed with the acid.