Process for preparing a polyisocyanate mixture comprising methylene diphenyl diisocyanate (MDI)

Abstract

The present invention relates to a process for preparing a polyisocyanate composition comprising at least one polyisocyanates of the diphenylmethane series comprising providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2); preparing a mixture (M3) from mixture (M1) and mixture (M2); and conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition; wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %. The present invention furthermore is directed to the isocyanate composition obtained or obtainable according to said process and the use thereof for the preparation of polyurethanes or polyisocyanurates.

Description

[0001] Process for preparing a polyisocyanate mixture comprising methylene diphenyl diisocyanate (MDI)

[0002] The present invention relates to a process for preparing a polyisocyanate composition comprising at least one polyisocyanates of the diphenylmethane series comprising providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) comprising di- and polyamines of the diphenylmethane series with a 2- ring content (2RC-2); preparing a mixture (M3) from mixture (M1) and mixture (M2); and conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition; wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %. The present invention furthermore is directed to the isocyanate composition obtained or obtainable according to said process and the use thereof for the preparation of polyurethanes or polyisocyanurates.

[0003] Aromatic isocyanates are important raw materials for the production of polyurethane materials. In this connection the diisocyanates and polyisocyanates of the diphenylmethane series (MDI) play the greatest role, quantitatively.

[0004] Polyisocyanates of the diphenylmethane series are understood to denote isocyanates and isocyanate mixtures of the following type: x = 2 to n where n denotes a natural number >2.

[0005] Similarly, polyamines of the diphenylmethane series are understood to denote compounds and compound mixtures of the following type: x = 2 to n where n denotes a natural number >2. In the context of the present invention isomers of methylenedianiline having only 2 aromatic rings are 4,4'-MDA, 2,4'-MDA and 2,2'-MDA. It is known that diisocyanates and polyisocyanates of the diphenylmethane series (MDI) are produced by phosgena- tion of the corresponding diamines and polyamines of the diphenylmethane series (MDA). The diamines and polyamines of the diphenylmethane series (MDA) are themselves produced on a large scale by condensation of aniline and formaldehyde. MDA may also be obtained in recycling processes such as the remonomerization of polyurethanes The corresponding diisocyanates, 2,2'-MDI, 2,4-MDI and 4,4'-MDI, which are described in the specialist circles as 2- ring (also monomer-MDI in the context of the present invention) compounds of MDI (i.e. diisocyanates of the diphenylmethane series), are obtained by phosgenation of diamines of the diphenylmethane series. During the condensation of aniline and formaldehyde, the 2-ring (also monomer-MDA) MDA (methylenediphenyldiamine), however, also continues to react further with formaldehyde and aniline to form higher-nuclear (i.e. poly-nuclear or poly-ring) MDA types, which after the phosgenation constitute the polynuclear content in the polymeric MDI (i.e. polyisocyanates of the diphenylmethane series).

[0006] Accordingly, the crude product of the phosgenation also contains the corresponding isocyanates, namely not only dinuclear but also oligomers of MDI. Normally, the polyisocyanate mixture comprising MDI is separated by thermal separation processes (distillation, condensation or combinations thereof) into different fractions, which are then further processed in various applications. Such post-treatments are time and energy consuming. Further, mixtures of oligomers of methylene diphenyl diisocyanate (PMDI), which are depleted in the dinuclear content, are usually only used in foam applications. Therefore, there is a need to develop a process for producing polyisocyanate mixture comprising methylene diphenyl diisocyanate (MDI) according to the needs, while taking into account the sustainability of such processes.

[0007] Also the chemical recycling of MDI-based polyurethanes, such as for example the hydrolytic, mostly catalytic, decomposition of MDI-based polyurethanes yields an MDA which is rich in higher oligomers. If this recycled MDA is phos- genated, then a product mixture is obtained which no longer meets market requirements, but can only serve the applications from which the recycled material was obtained. For many applications, the 2-ring content has to be adjusted by the addition of the respective components. Furthermore, phosgenation of MDA mixtures which are rich in higher oligomers often causes problems in the reactor due to fouling.

[0008] Accordingly, it was an object of the present invention to provide an improved process for producing polyisocyanate mixture comprising methylene diphenyl diisocyanate (MDI).

[0009] According to the present invention, this object has been solved by a process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0010] (i) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);

[0011] (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0012] (iii) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %.

[0013] Surprisingly, it has been found that by using different polyamine mixture sources it is possible to adapt the production of MDI to the market needs. Further, it has been shown that even polyamine mixtures obtained from recycling processes can be used for preparing polyisocyante for any applications.

[0014] According to the present invention, the ratio of polyamine composition (PA1) and (PA2) may be vary in broad ranges and is for example in the range of from 100:1 to 1 : 100, preferably 50:1 to 1 :50, more preferable 20: 1 to 1 :20, in particular in the range o from 10: 1 to 1 :10.

[0015] It has been found that the 2-ring content can be adjusted by adjusting the ratio of mixtures (M 1 ) and (M2) and also by adjusting the 2-ring content in the respective mixtures.

[0016] According to one embodiment, the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 %, preferably in the range of from 50 to 80 %, in particular in the range of from 55 to 74 %.

[0017] According to a further embodiment, the present invention relates to a process as disclosed above, wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4).

[0018] Mixtures comprising di- and polyamines of the diphenylmethane series with a varying 2-ring content can be obtained by known processes and by adjusting the conditions of the preparation process. According to a further embodiment, the present invention relates to a process as disclosed above, wherein polyamine composition (PA1) and (PA2) are compositions obtained in different processes, preferably in different plants.

[0019] The production of MDI mixed products that contain the various MDI isomers, by a specific synthesis of the MDA containing the corresponding MDA isomer, is known and described in the literature. EP-B1 158059 discloses the production of a particularly high 2-ring content in an MDA mixture containing ca. 80% 4,4'-MDA and ca. 10% 2,4'-MDA with a 2- ring content of ca. 90%. On the other hand, the yield of 2,4'-MDA can be purposefully increased, as is disclosed in EP-B1 3303 with an MDA which contains 88 wt. % of 2-nuclear MDA with 19 wt. % of 2,2'-MD A, 36 wt. % of 2,4'- MDA and 45 wt. % of 4,4'-MDA. In particular, the production of monomer-rich MDA types containing a large content of 2,4'-MDA generally leads to a large amount of 2,2'-MDA as by-product. On account of its lack of reactivity, the 2,2'- MDI formed from the resulting 2,2'-MDA is, however, undesirable in large concentrations in many applications.

[0020] Further, processes using an acid catalyst such as HOI are also known in the art. For example, HOI can be added after the production of aminal as in US2016068474 A1. Alternatively, HOI can be added to aniline before formaldehyde or together with formaldehyde as disclosed in EP 2145874 A1 , EP 2000459 A1 , DE10141620 and DE19804915, The production of high polymer content MDA with 2-ring contents of from 46% to 65% is described in, for example, DE-A1 2750975 and DE-A1 2517301.

[0021] The essential parameters by means of which the proportion of 2,4'-MDA can be adjusted in the condensation of aniline and formaldehyde are known. As a rule, the content of 2-ring MDA is adjusted by the excess of aniline in the condensation. The proportion of 2,4'-MDA present in the 2-ring MDA can be increased by a low degree of protonation during the condensation, or in other words, by a low molar ratio of HCI: aniline such as, for example, <0.2: 1 , or by a high reaction temperature, as described in DE-A1 3407494.

[0022] Depending on the method of preparation, the 2-ring content of mixtures (M1) and (M2) may vary. Mixtures obtained by remonomerization may for example comprise monomer MDA in a range of from 20 to 50%, mixtures obtained by homogeneously catalyzed condensation of formaldehyde and aniline may for example comprise monomer MDA in a range of from 45 to 75% and mixtures obtained by heterogeneously catalyzed condensation of formaldehyde and aniline may for example comprise monomer MDA in a range of from 80 to 98%.

[0023] Suitable processes for the preparation of mixtures (M1) and (M2) are in particular the condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate or the remonomization of MDI-based polyurethanes.

[0024] According to a further embodiment, the present invention relates to a process as disclosed above, wherein polyamine composition (PA1) and (PA2) are compositions obtained by one or more of the following processes :

[0025] (a) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a homogeneous acidic catalyst;

[0026] (b) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a heterogeneous acidic catalyst;

[0027] (c) condensation of aniline and formaldehyde in presence of an acidic catalyst and subsequent rearrangement;

[0028] (d) remonomization of MDI-based polyurethanes.

[0029] In the context of the present invention, remonomerization of MDI-based polyurethanes is understood to mean processes resulting in the respective amines. Suitable remonomerization processes are in principle known and include for example hydrogenation, amonolysis and in particular hydrolytic cleavage of the MDI-based polyurethanes such as hydrolysis, hydroaminolysis, hydroamonolysis or hydroglycolysis.

[0030] In particular the choice of catalyst and reaction conditions influence the 2-ring content of the composition obtained by the reaction of aniline and formaldehyde in the presence of a catalyst to form diamines and polyamines of the diphenylmethane series which contain 2-ring methylenediphenyldiamine. According to the present invention, mixture (M3) is obtained from mixtures (M1) and (M2). According to step (iii) of the process according to the present invention, mixture (M3) is reacted to obtain mixture (M4) comprising a polyisocyanate composition (PI). Preferably, step (iii) comprises a phosgenation of mixture (M3) but also phosgene free conversion to obtain mixture (M4) is possible in the context of the present invention.

[0031] Suitable processes for the conversion according to step (iii), in particular phosgene free conversion and also phosgenation, are in principle known. Suitable processes are for example liquid phosgenation, gasphase phosgenation or gas-liquid phosgenation or a phosgenation via salt. Suitable conditions for the phosgenation are in principle also known to the person skilled in the art and are for example disclosed in Ullmann's Encyclopedia of Industrial Chemistry, 7thed. Vol. 20, 2012, p. 63-82, WO 99 / 54289 A, WO 2004 / 056756 A (liquid phosgenation); Ullmann's Encyclopedia of Industrial Chemistry, 4thed. Vol. 13, 2012, p. 353, DE 25870847 A, EP 1532107 A, EP 0570799 A EP 0289840 A (gasphase phosgenation); or EP 2044009 A1 , WO 2013 / 060836 A, WO 2013 / 079517 A (gas-liquid phosgenation). An example of gas-liquid phosgenation process is disclosed in WO 2022 / 106716, examples of gas phase phosgenation processes are disclosed in EP 1761483 B1, EP 2079684 B1 , EP 2188247 B1 , EP 2408738 B1 and EP 2539314 B1 and examples of phosgene-free conversion are disclosed in WO2018 / 185168 and EP 3 250 622 B1.

[0032] Preferably, the phosgenation comprises admixing a solvent to the amine component and mixing, more preferably at a temperature in the range of from 50 to 180 °C, more preferably in the range of from 70 to 140 °C, more preferably in the range of from 80 to 120 °C, obtaining a polyamine mixture; and bringing the polyamine mixture in contact with phosgene in a suitable apparatus, such as for example a reaction mixing nozzle and realize final conversion to polyisocyanates in one or more reactors for example stirred tank vessels, or reaction columns obtaining a mixture comprising one or more polyisocyanates.

[0033] The process according to the present invention might also comprise further separation and purification steps, in particular steps for further adjustment of the 2-ring content of the composition. The process might for example comprise one or more distillation or crystallization steps to separate the polyisocyanates obtained. Suitable apparatuses and conditions for distillation and crystallization are in principle known to the person skilled in the art. Preferably, distillation at a reduced pressure may be used for the separation of the polyisocyanates obtained.

[0034] According to a further embodiment, the present invention is also directed to the process as disclosed above, wherein the process further comprises step (iv)

[0035] (iv) distillation of mixture (M4) comprising the isocyanate component. Distillation may be carried out according to the present invention to remove impurities and side products but also to separate different isocyanate products, such as for example monomer MDI and oligomer MDI or different MDI isomers but also separate different isocyanate products, such as for example different monomeric products or a oligomeric product (PMDI) with different content of monomers..

[0036] The present invention is also directed to the isocyanate composition obtained or obtainable according to the process as disclosed above. Furthermore, the present invention is directed to the use of the isocyanate composition according to the present invention or the isocyanate composition obtained or obtainable according to the process according to the present invention for the preparation of polyurethanes or polyisocyanurates.

[0037] The produced polyurethane material can be used in any suitable polyurethane application.

[0038] According to a further aspect, the present invention also relates to the isocyanate composition obtained or obtainable according to the process as disclosed above. Typically, the isocyanate composition (PI) has a viscosity measured at 25 °C in the range of from 20 to 200 mPas, preferably 15 to 150 mPas.

[0039] According to a further aspect, the present invention also relates to the use of the isocyanate composition according to the present invention or an isocyanate composition obtained or obtainable according to the process as disclosed above for the preparation of polyurethanes or polyisocyanurates.

[0040] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 3", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1, 2 and 3". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0041] 1 . Process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0042] (i) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);

[0043] (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0044] (iii) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %.

[0045] 2. The process according to embodiment 1 , wherein the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 %.

[0046] 3. Process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0047] (I) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);

[0048] (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0049] (ill) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %; and wherein the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 %.

[0050] 4. The process according to any one of embodiments 1 to 3, wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4), wherein preferably the 2- ring content of mixture (M4) is adjusted in the range of from 40 to 90 %.

[0051] 5. Process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0052] (I) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);

[0053] (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0054] (ill) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %; and wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4), wherein preferably the 2-ring content of mixture (M4) is adjusted in the range of from 40 to 90 %. 6. Process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0055] (I) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);

[0056] (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0057] (ill) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %; wherein the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 % and wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4), wherein preferably the 2-ring content of mixture (M4) is adjusted in the range of from 40 to 90 %.

[0058] 7. The process according to any one of embodiments 1 to 6, wherein polyamine composition (PA1) and (PA2) are compositions obtained in different processes, preferably in different plants.

[0059] 8. The process according to any one of embodiments 1 to 7, wherein polyamine composition (PA1) and (PA2) are compositions obtained by one or more of the following processes :

[0060] (a) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a homogeneous acidic catalyst;

[0061] (b) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a heterogeneous acidic catalyst;

[0062] (c) condensation of aniline and formaldehyde in presence of an acidic catalyst and subsequent rearrangement;

[0063] (d) remonomization of MDI-based polyurethanes.

[0064] 9. Isocyanate composition obtained or obtainable according to the process according to any one of embodiments 1 to 8.

[0065] 10. Isocyanate composition obtained or obtainable according to a process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0066] (I) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2); (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0067] (iii) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %. The isocyanate according to embodiment 10, wherein the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 %. The isocyanate according to embodiment 10 or 11, wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4), wherein preferably the 2-ring content of mixture (M4) is adjusted in the range of from 40 to 90 %. The isocyanate according to any one of embodiments 10 to 12, wherein polyamine composition (PA1) and (PA2) are compositions obtained in different processes, preferably in different plants. The isocyanate according to any one of embodiments 10 to 13, wherein polyamine composition (PA1) and (PA2) are compositions obtained by one or more of the following processes :

[0068] (a) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a homogeneous acidic catalyst;

[0069] (b) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a heterogeneous acidic catalyst;

[0070] (c) condensation of aniline and formaldehyde in presence of an acidic catalyst and subsequent rearrangement;

[0071] (d) remonomization of MDI-based polyurethanes. Use of the isocyanate composition according to any one of embodiments 9 to 14 or an isocyanate composition obtained or obtainable according to the process of any one of embodiments 1 to 8 for the preparation of polyurethanes or polyisocyanurates. Use of the isocyanate composition obtained or obtainable according to a process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising

[0072] (I) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);

[0073] (ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);

[0074] (iii) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %.

[0075] 17. The use according to embodiment 16, wherein the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 %.

[0076] 18. The use according to embodiment 16 or 17, wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4), wherein preferably the 2-ring content of mixture (M4) is adjusted in the range of from 40 to 90 %.

[0077] 19. The use according to any one of embodiments 16 to 18, wherein polyamine composition (PA1) and (PA2) are compositions obtained in different processes, preferably in different plants.

[0078] 20. The use according to any one of embodiments 16 to 19, wherein polyamine composition (PA1) and (PA2) are compositions obtained by one or more of the following processes :

[0079] (a) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a homogeneous acidic catalyst;

[0080] (b) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a heterogeneous acidic catalyst;

[0081] (c) condensation of aniline and formaldehyde in presence of an acidic catalyst and subsequent rearrangement;

[0082] (d) remonomization of MDI-based polyurethanes.

[0083] It is explicitly noted that the above set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0084] The present invention is further illustrated by the following examples.

[0085] Examples

[0086] 1. Example 1 : ( Comparative)

[0087] About 10 1 of PMDA was produced by condensation of aniline with formaldehyde (50wt% aqueous solution) via homogeneous catalysis with hydrochloric acid (30wt% aqueous solution) according to the process described in DE19804915. The molar ratio of aniline to formaldehyde was 2.3:1 and the molar ratio of acid to aniline was 0.15:1. This leads to a PMDA with about 62.1 wt% monomeric MDA ( 0,3 wt% 2,2'-MDA, 6,85 wt% 2,4'-MDA and 54,96 wt% 4,4’-MDA).

[0088] The PMDA was phosgenated to get finally about 12,51 crude MDI containing 55,6 wt% monomeric MDI ( 0,2 wt% 2,2'-MDI, 6,5 wt% 2,4'-MDI and 48,9 wt% 4,4'-MDI). The crude MDI was separated by destillative workup to get 8,751 of a PMDI product containing 29.2 wt% monomeric MDI, about 3.2 1 of a 4,4'-MD I product and about 1,1 1 of a product with 50 / 50-mixture of 2,4'- and 4,4'-MDI. The products were used in different applications and the distribution of the products fit the market demand.

[0089] 2. Example 2 (according to invention)

[0090] From a hydrolytic cleavage of PIR foam about 1 .51 of a MDA product was obtained containing about 35,7 % of monomeric MDA (3,8 wt% 2,4'-MDA and 31 .9 wt% 4,4'-MDA). The low monomer content does not fit the market demand of MDI products as described in example 1. Therefor according to the invention this MDA was admixed with 8.51 MDA from a process described in example 1. However, the aniline to formaldehyde ratio was increased to 2.6 and the acid to aniline ratio to 0.18. This MDA had a monomer content of about 68.3 % (0.4 wt% 2,2'-MDA, 7.8 wt% 2,4'-MDA and 60.1 wt% 4,4'-MDA). The difference in the monomer content of both streams is about 32.6 wt%. The mixture of both streams of about 10 1 had a monomer content of 62.4 wt% ( 0,3 wt% 2,2'-MD A, 6,8 wt% 2,4'-MDA and 55.3 wt% 4,4'-MDA) that is very similar to the MDA from example 1 . Accordingly the product after phosgenation as well as the amount of the 3 products was comparable and fit the market demand.

[0091] 3. Example 3 (according to invention)

[0092] MDA is produced in a two-step process. In the first step aniline and formaldehyde are condensed followed by a phase-separation into aniline / aminal rich phase and an aqueous phase. The aniline / aminal phase was converted in a heterogeneous catalysis to get after aniline removal about 1,81 of MDA with a monomer content of 92.6 wt% (1 .3% 2,2'-MD A, 7.1 wt% 2,4'-MDA and 85.5 wt% 4,4’-MDA). The content of monomeric MDA is too high to fit the market split of products.

[0093] Therefore according to the invention the stream is admixed with MDA obtained from process described in example 1. However, the aniline to formaldehyde ratio was reduced to 2.1 and the acid to aniline ratio to 0.08 to get a MDA 55.6 wt% monomeric MDA ( 0.4wt% 2,2'-MD A, 6.6 wt% 2,4'-MDA and 48.6 wt% of 4,4’-MDA). A portion of 8.2 1 of this product was mixed with the 1 .2 1 produced by heterogeneous catalysis. The difference in monomer content of both streams is 37 wt%. The mixture of both streams contains 62,2 wt% monomeric MDA (0.5% 2,2'-MDA, 6.7 wt% 2,4'-MDA and 55.2 wt% 4,4'-MDA) that is very similar to the composition mentioned in example 1 . Hence the phosgenated and the product mix is comparable.

[0094] Literature cited

[0095] US2016068474 A1

[0096] EP 2145874 A1

[0097] EP 2000459 A1

[0098] DE10141620

[0099] DE19804915

[0100] DE-A1 2750975

[0101] DE-A1 2517301

[0102] DE-A1 3407494

[0103] Ullmann's Encyclopedia of Industrial Chemistry, 7thed. Vol. 20, 2012, p. 63-82

[0104] WO 99 / 54289 A

[0105] WO 2004 / 056756 A

[0106] Ullmann's Encyclopedia of Industrial Chemistry, 4thed. Vol. 13, 2012, p. 353

[0107] DE 25 870847 A

[0108] EP 1532107 A

[0109] EP 0570799 A

[0110] EP 0289840 A

[0111] EP 2044009 A1

[0112] WO 2013 / 060836 A

[0113] WO 2013 / 079517 A

[0114] WO 2022 / 106716

[0115] EP 1761483 B1

[0116] EP 2079684 B1

[0117] EP 2188247 B1

[0118] EP 2408738 B1

[0119] EP 2539314 B1

[0120] WO2018 / 185168

[0121] EP 3 250 622 B1

Claims

Claims1 . Process for preparing a polyisocyanate composition (PI) comprising at least one polyisocyanate of the diphenylmethane series comprising(I) providing a mixture (M1) comprising a polyamine composition (PA1) comprising di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-1) and a mixture (M2) comprising a polyamine composition (PA2) di- and polyamines of the diphenylmethane series with a 2-ring content (2RC-2);(ii) preparing a mixture (M3) from mixture (M1) and mixture (M2);(ill) conversion of mixture (M3) to obtain mixture (M4) comprising a polyisocyanate composition (PI); wherein the difference in the 2-ring content (2RC-1) of polyamine composition (PA1) and the 2-ring content (2RC-2) of polyamine composition (PA2) is more than 10 %.

2. The process according to claim 1 , wherein the 2-ring content of polyisocyanate composition (PI) is in the range of from 40 to 90 %.

3. The process according to claim 1 or 2, wherein the ratio of polyamine composition (PA1) and (PA2) in mixture (M3) is adjusted to adjust the 2-ring content in mixture (M4), wherein preferably the 2-ring content of mixture (M4) is adjusted in the range of from 40 to 90 %.

4. The process according to any one of claims 1 to 3, wherein polyamine composition (PA1) and (PA2) are compositions obtained in different processes, preferably in different plants.

5. The process according to any one of claims 1 to 4, wherein polyamine composition (PA1) and (PA2) are compositions obtained by one or more of the following processes :(a) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a homogeneous acidic catalyst;(b) condensation of aniline and formaldehyde solutions and subsequent rearrangement of the condensate using a heterogeneous acidic catalyst;(c) condensation of aniline and formaldehyde in presence of an acidic catalyst and subsequent rearrangement;(d) remonomization of MDI-based polyurethanes.

6. Isocyanate composition obtained or obtainable according to the process according to any one of claims 1 to 5.

7. Use of the isocyanate composition according to claim 6 or an isocyanate composition obtained or obtainable according to the process of any one of claims 1 to 5 for the preparation of polyurethanes or polyisocyanurates.

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