Process for the preparation of di- and polyamines from the diphenylmethane series

Abstract

The present invention provides a process for preparing di- and polyamines from the diphenylmethane series by converting aniline and formaldehyde in the absence of an acid catalyst to give aminal and water, removing the aqueous phase and further processing the organic aminal phase to give the di- and polyamines of the diphenylmethane series, in which use of a coalescence aid in the phase separation of the process product obtained in aminal reaction reduces the proportion of water and hence also of water-soluble impurities in the organic phase containing the aminal. The di- and polyamines of the diphenylmethane series obtained by acid-catalyzed rearrangement and workup after further processing of the aminal phase are outstanding suitably for preparation of the corresponding isocyanates.

Claims

1. A process for the preparation of di- and polyamines of the diphenylmethane series, comprising: a) converting aniline and formaldehyde in the absence of an acidic catalyst to a reaction mixture comprising aminal and water, where the formaldehyde to be used comprises at most 2.0% by mass of methanol; b) removing water at least in part from the reaction mixture obtained in step a), giving an organic phase comprising the aminal; c) converting the organic aminal-comprising phase obtained in step b), in the presence of an acidic catalyst, to a reaction mixture comprising di- and polyamines of the diphenylmethane series; and d) neutralizing the reaction mixture comprising di- and polyamines of the diphenylmethane series obtained in step c) and then subjecting the reaction mixture to a work-up comprising washing and distillation; wherein in step a) at least one auxiliary reagent from at least one of the groups (i) to (v) or at least one auxiliary reagent from exclusively group (vi) is added in the mass fractions stated in each case, the mass fractions referring to the total mass of all of the feed substances used in step a) including the mass of the auxiliary reagents added: (i) 0.05% by mass to 3.0% by mass of aliphatic alcohols having 1 to 6 carbon atoms, (ii) 0.0001% by mass to 3.0% by mass of alkali metal halides, (iii) 0.0001% by mass to 0.030% by mass of alkali metal hydroxides, (iv) 0.0001% by mass to 1.0% by mass of carboxylic acids having 1 to 4 carbon atoms, (v) 0.0001% by mass to 1.0% by mass of salts of carboxylic acids having 1 to 4 carbon atoms, (vi) 0.1% by mass to 3.0% by mass of cycloaliphatic alcohols having 5 to 7 carbon atoms, where the mass fraction of the auxiliary reagent of group (vi) is selected such that this is greater than 0.5% by mass, based on the total mass of the aniline used in step a) and of the auxiliary reagent of group (vi).

2. The process of claim 1, in which the auxiliary reagent of group (i) is selected from the group consisting of methanol and a methanol-containing process stream, the auxiliary reagent of group (ii) is selected from the group consisting of sodium chloride, potassium chloride and aqueous process streams of these salts, the auxiliary reagent of group (iii) is selected from the group consisting of sodium hydroxide and potassium hydroxide, the auxiliary reagent of group (iv) is formic acid, the auxiliary reagent of group (v) is selected from the group consisting of sodium formate and potassium formate, the auxiliary reagent of group (vi) is cyclohexanol.

3. The process of claim 1, in which only auxiliary reagents of groups (i), (ii), (iii) and (vi) are used and in which the auxiliary reagent of group (i) is selected from the group consisting of methanol and a methanol-containing process stream, the auxiliary reagent of group (ii) is selected from the group consisting of sodium chloride and a sodium chloride-containing aqueous process stream, the auxiliary reagent of group (iii) is an aqueous sodium hydroxide solution, the auxiliary reagent of group (vi) is cyclohexanol.

4. The process of claim 1, in which only auxiliary reagents of the groups (i), (ii) and (iii) are used, and in which the auxiliary reagent of group (i) is selected from the group consisting of methanol and a methanol-containing process stream, the auxiliary reagent of group (ii) is selected from the group consisting of sodium chloride and a sodium chloride-containing aqueous process stream, the auxiliary reagent of group (iii) is an aqueous sodium hydroxide solution.

5. The process of claim 1, comprising introducing the at least one auxiliary reagent separately from the starting materials aniline and formaldehyde′ to the conversion of step a) or adding the at least one auxiliary reagent to at least one of the starting materials aniline and formaldehyde of step a) before they are mixed or adding the at least one auxiliary reagent after mixing aniline and formaldehyde.

6. A process for the preparation of di- and polyisocyanates of the diphenylmethane series comprising phosgenation of di- and polyamines of the diphenylmethane series prepared by the process of claim 1.

7. The process of claim 1, in which only auxiliary reagents of groups (ii), (iii) and (vi) are used.

Description

DETAILED DESCRIPTION

(1) Embodiments of the invention are described in more detail below. Different embodiments can be combined with one another as desired provided the opposite does not clearly arise for the person skilled in the art from the context.

(2) The condensation of aniline and formaldehyde in step a) can be carried out by a process according to the prior art apart from the requirement according to the invention of the addition of an auxiliary reagent (see in this respect the paragraph which follows). Here, preferably aniline and aqueous formaldehyde solution are condensed at a molar ratio of aniline to CH2O of 1.7:1 to 20:1, preferably 1.7:1 to 5.0:1 at a temperature of 20° C. to 100° C., preferably from 30° C. to 95° C., particularly preferably from 40° C. to 90° C., to give aminal and water. The conversion usually takes place at atmospheric pressure. Suitable aniline grades are described e.g. in EP 1 257 522 B1, EP 2 103 595 A1 and EP 1 813 598 B1. Preference is given to using technical grades of formalin (aqueous solution of formaldehyde) with 30% by mass to 50% by mass of formaldehyde in water. However, formaldehyde solutions with lower or higher concentrations or else the use of gaseous formaldehyde are also conceivable.

(3) According to the invention, in step a) at least one auxiliary reagent is added as defined above. The auxiliary reagents can be added in a continuous, semicontinuous or batch process everywhere between inlet of the aminal reactor (i.e. the reactor in which step a) is carried out) to the inlet of the phase separation apparatus of step b). They can also be mixed beforehand with the feed streams aniline and/or formaldehyde. Moreover, it is possible to also firstly allow aniline and formaldehyde to react and only then to add the auxiliary reagent.

(4) Particularly preferred auxiliary reagents are: methanol and a methanol-containing process stream; sodium chloride, potassium chloride and aqueous process streams of these salts; sodium hydroxide and potassium hydroxide; formic acid; sodium formate and potassium formate; cyclohexanol.

(5) (In this connection, a “process stream” is understood as meaning a stream such as is produced as a result of the process at another point in the MDA production plant or in another production plant.) It is also possible to use mixtures of two or more of these auxiliary reagents provided it is ensured that cyclohexanol is not used in such mixtures: If solutions of auxiliary reagents are used (e.g. process streams or aqueous solutions of salt-like auxiliary reagents), then the respective concentration data which is to be observed according to the invention refers to the mass of the dissolved auxiliary reagent and not to the mass of the solution.

(6) Very particularly preferably, methanol, a methanol-containing process stream, sodium chloride, a sodium chloride-containing aqueous process stream, an aqueous sodium hydroxide solution (sodium lye) or a combination of these auxiliary reagents or (exclusively) cyclohexanol is used. Extraordinarily very particular preference is given to the use of methanol, a methanol-containing process stream, a sodium chloride-containing process stream, an aqueous sodium hydroxide solution or a combination of these auxiliary reagents. Even more preferred is the use of methanol, a methanol-containing process stream, a sodium chloride-containing process stream or a combination of these auxiliary reagents.

(7) If a combination of auxiliary reagents of different groups is used, then such a combination comprises according to the invention only the above-defined groups (i) to (v). This is because it has surprisingly been observed that combinations of (vi) cycloaliphatic alcohols with 5 to 7 carbon atoms, in particular cyclohexanol, with one or more of the other auxiliary reagents listed above from groups (i) to (v) lead to longer phase separation times than when dispensing with the addition of auxiliary reagents.

(8) Based on the total mass of the feed materials of the aminal reaction (step a)), 0.05% by mass to 3.0% by mass, preferably 0.1% by mass to 1.5% by mass, of aliphatic alcohols having 1 to 6 carbon atoms and/or 0.0001% by mass to 3.0% by mass, preferably 0.01% by mass to 1.5% by mass, of alkali metal halides and/or 0.0001% by mass to 0.030% by mass, preferably 0.001% by mass to 0.015% by mass, of alkali metal hydroxides and/or 0.0001% by mass to 1.0% by mass, preferably 0.001% by mass to 0.50% by mass, of carboxylic acids having 1 to 4 carbon atoms or the salts of carboxylic acids having 1 to 4 carbon atoms or 0.1% by mass to 3.0% by mass, preferably 0.2% by mass to 1.5% by mass, of cycloaliphatic alcohols having 5 to 7 carbon atoms are added as auxiliary reagent. In the case of the cycloaliphatic alcohols having 5 to 7 carbon atoms, the restriction whereby the mass fraction of such an auxiliary reagent must be selected such that it is greater than 0.5% by mass, based on the total mass of the aniline used in step a) and the auxiliary reagent, must additionally be taken into account.

(9) In the MDA process, preference is given to using inherently occurring chemical auxiliary reagents so as not to unnecessarily contaminate the process with foreign substances.

(10) This procedure is also therefore not obvious to the person skilled in the art because the technical-grade formalin available on the market, which is usually used in the preparation of MDA, already comprises, depending on the preparation process, methanol in the order of magnitude from 1% by mass to 2% by mass, based on the total mass of the formalin. The person skilled in the art is in no way encouraged by the prior art to admix such formalin of technical grade with additional methanol (or one of the other specified auxiliary reagents).

(11) In step b) the phase separation of organic aminal phase and aqueous phase takes place at a temperature of 20° C. to 100° C., preferably from 30° C. to 95° C., particularly preferably from 40° C. to 90° C., preferably at ambient pressure. As a result of the addition according to the invention of an auxiliary reagent, the organic fraction in the aqueous phase separated after the aminal reaction (step a)) (so-called “aminal water”) is minimized (clarification of the residual cloudiness) and thus the phase separation is facilitated.

(12) The rearrangement of the aminal in step c) takes place in the presence of an acidic catalyst, usually a strong mineral acid such as hydrochloric acid. Preference is given to the use of mineral acid in a molar ratio mineral acid:aniline of 0.001:1 to 0.9:1, preferably 0.05:1 to 0.5:1. It is naturally also possible to use solid, acidic catalysts as described in the literature. In this connection, formaldehyde can be added to a mixture of aniline and acidic catalyst and the reaction solution can be fully reacted by stepwise heating. Alternatively, aniline and formaldehyde can also firstly prereact and then be admixed, with or without prior water removal, with the acidic catalyst or a mixture of further aniline and acidic catalyst, after which the reaction solution is fully reacted by stepwise heating. This reaction can be carried out continuously or discontinuously with one of the numerous processes described in the literature (e.g. in EP 1 616 890 A1 or EP 1 270 544 A1).

(13) In step d) the reaction mixture comprising the di- and polyamines of the diphenylmethane series is firstly neutralized optionally with the addition of water and/or aniline (step d.1)). The neutralization preferably takes place at a temperature of 90° C. to 100° C. without the addition of further substances. However, it can also take place at a different temperature level in order to increase the rate of e.g. the degradation of troublesome byproducts. Suitable bases are preferably the hydroxides of the alkali metal and alkaline earth metal elements. Preference is given to using sodium hydroxide solution. The base used for the neutralization is preferably used in an amount of more than 100%, particularly preferably 105% to 120%, of the amount required stoichiometrically for the neutralization of the acidic catalyst used (see EP 1 652 835 A1). The two-phase mixture obtained in this way is then separated into an organic phase comprising di- and polyamines of the diphenylmethane series and an aqueous phase. This can be assisted by the addition of aniline and/or water. If the phase separation is assisted by adding aniline and/or water, then their addition preferably already takes place with intensive mixing in the neutralization. In this connection, the mixing can take place in mixing sections with static mixers, in stirred tanks or stirred-tank cascades or else in a combination of mixing sections and stirred tanks. The neutralized reaction mixture, optionally diluted by adding aniline and/or water, is then preferably fed to an apparatus which, on account of its configuration and/or internals, is particularly suitable for separation into an organic phase comprising MDA and an aqueous phase, preferably phase separation or extraction devices corresponding to the prior art, as are described for example in Mass-Transfer Operations, 3rd Edition, 1980, McGraw-Hill Book Co, p. 477 to 541, or Ullmann's Encyclopedia of Industrial Chemistry (Vol. 21, Liquid-Liquid Extraction, E. Miller et al., pages 272-274, 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, DOI: 10.1002/14356007.b03_06.pub2) or in Kirk-Othmer Encyclopedia of Chemical Technology (see “http://onlinelibrary.wiley.com/book/10.1002/0471238961”, Published Online: Jun. 15, 2007, pages 22-23) (mixer-settler cascade or settling container). The residence times and residence time distributions in the phase separation apparatuses of the neutralization and washing can be improved by technical internals in order to bring about improved separation effects.

(14) The organic phase obtained in this way is then subjected to a washing (step d.2)). The washing liquid used is preferably water. The wash water is then separated by means of phase separation. In this way, the salt content of the organic phase is reduced. A suitable preferred process is described for example in DE-A-2549890, in particular on page 3. The phase separation can be improved by adding a small amount of sodium hydroxide solution to the wash water in step d.2). The amount of sodium hydroxide solution can be readily determined by a person skilled in the art. The organic phase obtained in step d.2) preferably has a composition, based on the total mass of this organic phase, of 5.0% by mass to 15% by mass of water and, depending on use ratios of aniline and formaldehyde, 5.0% by mass to 90% by mass, preferably 5.0% by mass to 40% by mass, of aniline and 5.0% by mass to 90% by mass, preferably 50% by mass to 90% by mass, of di- and polyamines of the diphenylmethane series. After emerging from the phase separation in step d.2), the organic phase comprising di- and polyamines of the diphenylmethane series usually has a temperature of 80° C. to 150° C.

(15) Then, water and aniline are separated off by distillation, as known in the prior art, from the resulting neutralized and washed organic phase comprising di- and polyamines of the diphenylmethane series (step d.3)). This takes place preferably as described in EP 1 813 597 B1, in particular in paragraphs [0014] to [0043].

(16) The thus obtained di- and polyamines of the diphenylmethane series can be converted by the known methods with phosgene to the corresponding di- and polyisocyanates of the diphenylmethane series. In this connection, the phosgenation can be carried out by one of the processes known from the prior art (e.g. DE-A-844 896 or DE-A-198 17 691).

(17) If an auxiliary reagent is added in the aminal reaction (step a)) in order to assist the removal of organic substances (essentially aminal) from the aminal water which is then to be performed, i.e. if the organic substance content in the aminal water is reduced and the thus obtained organic substances are further processed according to the invention in steps c) and d), then the following advantages arise inter alia: 1) The preparation costs of the process are improved because the losses of feed materials and intermediates via the aqueous phase are minimized. 2) The reduced loading of the aqueous phase with organic substances leads to a lower treatment cost in the waste water processing (energy costs are saved because less steam is required for stripping off organic substances from the MDA waste water). 3) The use of overdimensioned phase separation apparatuses which permit a phase separation of the aminal reaction mixture over a very long residence time can be dispensed with. 4) Reduction in impurities and deposits in the reaction apparatuses and in the stripping of the waste water. 5) More efficient use of the acidic catalyst in the rearrangement reaction of the aminal.

EXAMPLES

(18) Content data in % are percentages by mass based on the total mass of the particular substance.

Example 1 (Comparison)

(19) A multi-neck round-bottomed flask was charged with 279 g of pure aniline and, at 80° C. with stirring, 134 g of a 32% strength aqueous technical-grade formaldehyde solution, which had a methanol content of 1.2% by mass, were added dropwise over the course of 20 min. When the addition of formaldehyde was complete, the mixture was after-stirred for a further 5 min and a phase separation was performed at 80° C. 89 seconds after switching off the stirrer the onset of phase separation became evident from the appearance of a foam-like consistency; after 160 seconds, the separation of the organic and aqueous phase was complete (see also table 1).

Example 2 (According to the Invention)

(20) A multi-neck round-bottomed flask was charged with 279 g of pure aniline and, at 80° C. with stirring, 134 g of a 32% strength aqueous technical-grade formaldehyde solution, which had a starting methanol content of 1.2% by mass and to which, prior to use as starting material, an additional 1.0% by mass of methanol, based on the total mass of the aqueous formaldehyde used, had been admixed as auxiliary, were added dropwise over the course of 20 min. After completion of the addition of formaldehyde, the mixture was after-stirred for a further 5 min and a phase separation was performed at 80° C. 20 seconds after switching off the stirrer, the onset of phase separation became evident from the appearance of a foam-like consistency; after 36 seconds, the separation of the organic and aqueous phase was complete (see also table 1).

Examples 3-8 and 10-12 (According to the Invention), Example 9 (Comparison)

(21) A multi-neck round-bottomed flask was charged with 279 g of pure aniline and, at 80° C. with stirring, 134 g of a 32% strength aqueous technical-grade formaldehyde solution, which had a starting methanol content of 1.2% by mass and to which, prior to use as starting material, additional auxiliary reagents had been admixed, were added dropwise over the course of 20 min. Following completion of the addition of formaldehyde, the mixture was after-stirred for a further 5 min and after switching off the stirrer at 80° C. a phase separation was performed. Table 1 summarizes the auxiliaries and the observed separation times of the phase separation.

(22) TABLE-US-00001 TABLE 1 Fraction of added Complete auxiliary reagent Foam separation in % by mass, based forma- of the Auxiliary on the total mass of tion in phases in Example reagent the reaction mixture seconds seconds 1 (comparison) Without — 89 160 2 (according to Methanol 0.32 .sup.[a] 20 36 the invention) 3 (according to NaCl 0.0032 21 55 the invention) 4 (according to NaCl 0.032  21 42 the invention) 5 (according to NaCl 0.16  21 43 the invention) 6 (according to NaCl 0.32  24 54 the invention) 7 (according to NaOH 0.0016 22 43 the invention) 8 (according to NaOH 0.0065 20 47 the invention) 9 (comparison) NaOH 0.032  120 210 10 (according to Formic 0.0016 21 35 the invention) acid 11 (according to Formic 0.0065 21 50 the invention) acid 12 (according to Formic 0.032  22 38 the invention) acid .sup.[a] Only the deliberately added fraction of methanol is given, without the methanol already present in technical-grade formaldehyde.

(23) The table shows that the presence of auxiliary reagents in the concentrations according to the invention in the aminal reaction (step a)) improves the subsequent phase separation (step b)). Surprisingly, this is also applicable for methanol, which is indeed already present in amounts of 1 to 2% by mass in the aqueous technical-grade formaldehyde solution. Example 9 with the auxiliary reagent NaOH shows that the auxiliary reagents only have a positive effect within a certain concentration range.

Examples 13-17 (Comparison)

(24) A multi-neck round-bottomed flask was charged with 279 g of pure aniline, to which cycloaliphatic amines were admixed with stirring. Then, at 80° C. and with stirring, 134 g of a 32% strength aqueous technical-grade formaldehyde solution, which had a methanol content of 1.2% by mass, were added dropwise over the course of 20 min. After the addition of formaldehyde was complete, the mixture was after-stirred for a further 5 min and, after switching off the stirrer at 80° C., a phase separation was performed. Table 2 summarizes the additives and the observed separation times of the phase separation.

Examples 18-21 (According to the Invention)

(25) A multi-neck round-bottomed flask was charged with 279 g of pure aniline, to which different amounts of cyclohexanol were admixed with stirring. Then, at 80° C. and with stirring, 134 g of a 32% strength aqueous technical-grade formaldehyde solution, which had a methanol content of 1.2% by mass, were added dropwise over the course of 20 min. After the addition of formaldehyde was complete, the mixture was after-stirred for a further 5 min and, after switching off the stirrer at 80° C., a phase separation was performed. The results can likewise be found in table 2.

(26) TABLE-US-00002 TABLE 2 Fraction of added Complete auxiliary reagent Foam separation in % by mass, based forma- of the Auxiliary on the total mass of tion in phases in Example reagent the reaction mixture seconds seconds 1 (comparison) Without — 89 160  13 (comparison) Cyclo- 0.0068 110 No hexyl- complete amine separation 14 (comparison) Cyclo- 0.068 330 No hexyl- complete amine separation 15 (comparison) Cyclo- 0.135 600 No hexyl- complete amine separation 16 (comparison) Dicyclo- 0.068 No No hexyl- phase phase amine sepa- separation ration 17 (comparison) Dicyclo- 2 1800 No hexyl- complete amine separation 18 (according to Cyclo- 0.0068 19 49 the invention) hexanol 19 (according to Cyclo- 0.068 17 54 the invention) hexanol 20 (according to Cyclo- 0.68 19 47 the invention) hexanol 21 (according to Cyclo- 2 20 58 the invention) hexanol

(27) The table shows that the presence of cycloaliphatic amines in the aminal reaction interferes with the subsequent phase separation. Surprisingly, the addition of cyclohexanol within a wide concentration range significantly improves the phase separation.

Example 22 (Comparison, Auxiliary Mixture with Cyclohexanol)

(28) A multi-neck round-bottomed flask was charged with 279 g of pure aniline, to which 2.8 g of cyclohexanol were admixed with stirring. Then, at 80° C. and with stirring, 134 g of a 32% strength aqueous technical-grade formaldehyde solution, which had a methanol content of 1.2% by mass and to which additionally 0.7 g of NaCl, 0.07 g of NaOH and 1.3 g of methanol had been added, were added dropwise over the course of 20 min. When the addition of formaldehyde was complete, the mixture was after-stirred for a further 5 min and, after switching off the stirrer at 80° C., a phase separation was performed. The result of this experiment can be found in table 3.

(29) TABLE-US-00003 TABLE 3 Fraction of added Complete auxiliary reagent Foam separation in % by mass, based forma- of the Auxiliary on the total mass of tion in phases in Example 22 reagents the reaction mixture seconds seconds Auxiliary Methanol 0.32 150 210 mixture with NaCl 0.16 cyclohexanol NaOH 0.016 Cyclo- 0.68 hexanol

Example 23 (Comparison, Operational Test in a Production Plant)

(30) In a continuous reaction process (step a)), 24.4 t/h of feed aniline (comprising 90% by mass of aniline) and 6.1 t/h of 50% strength formaldehyde solution, which comprised 1.0% by mass of methanol, were mixed and converted continuously to the aminal at 95° C. in a stirred reaction vessel. The subsequent phase separation (step b)) in a phase separation apparatus proved difficult since the phase separation layer was difficult to see on account of clouding in the aqueous phase and the appearance of a mulm layer. On account of an emerging emulsion, the plant had to be shut down and the phase separation container had to be emptied before restarting the aminal reaction.

Example 24 (According to the Invention, Operational Test in a Production Plant)

(31) In a continuous reaction process (step a)), 24.4 t/h of feed aniline (comprising 90% by mass of aniline) and 6.1 t/h of 50% strength formaldehyde solution, which comprised 1.0% by mass of methanol, were mixed and converted continuously to the aminal at 95° C. in a stirred reaction vessel. Additionally, in a continuous procedure, 200 l/h of a salt-containing aqueous process stream which comprised 8% by mass of NaCl and 0.5% by mass of NaOH and had a conductivity of 145 mS were added to the reactor. The reaction mixture leaving the reaction vessel was admixed continuously with 60 l/h of a methanol-containing process stream (45% by mass of methanol in water) and passed to a phase separation apparatus (step b)). The phase separation took place without problems since a highly visible phase separation layer was formed. The process could be performed stably over a long production phase.

(32) Following phase separation to remove the aqueous phase, the organic phase was admixed with 31% strength aqueous hydrochloric acid (degree of protonation 10%, i.e. 0.1 mol of HCl was added per mole of amino groups) and reacted at 50° C. to 150° C. in a reactor cascade (step c)). Following complete reaction, the resulting reaction mixture was admixed with 32% strength sodium hydroxide solution in the molar ratio of 1.1:1 sodium hydroxide solution to HCl and reacted in a neutralization stirred container (step d.1)). The temperature was 115° C. The absolute pressure was 1.4 bar. The neutralized base mixture was then separated in a neutralization separator into an aqueous, lower phase, which was passed to a waste water collecting container, and into an organic phase. The organic, upper phase was passed to the washing (step d.2)). In a stirred washing container, the alkaline MDA was washed with condensate. After separating off the wash water in a wash water separator, the crude MDA obtained in this way was freed from water and aniline in step d.3)) by distillation, with 17 t/h of MDA being obtained as bottom product.