Process for the preparation of methylenedianiline and polymethylenepolyphenylamine

Abstract

A mixture of methylene diphenylamine isomers and polymethylene polyaniline is prepared with a controllable ratio of methylene diphenylamine isomers. Aniline and formaldehyde are reacted to produce N,N'-diphenylmethylenediamine (acetalamine), which is then partially rearranged in the presence of a heterogeneous catalyst to a mixture of aminobenzylaniline and methylene diphenylamine isomers. Further rearrangement is performed in the presence of a homogeneous catalyst to convert the remaining aminobenzylaniline isomers to methylene diphenylamine and polymethylene polyaniline.

Description

[0001] This invention relates to a method for preparing polyaniline, particularly a mixture of methylene diphenylamine containing a controllable amount of the o,p'-isomer.

[0002] Methylene diphenylamine (MDA) and polymethylene polyaniline are produced in huge quantities globally and are mainly used to prepare polyisocyanates for the manufacture of polyurethanes.

[0003] MDA is almost always prepared on an industrial scale by reacting aniline with formaldehyde in the presence of an inorganic acid such as HCl. Aniline and formaldehyde react to form N,N'-diphenylmethylenediamine (“acetalamine”), which has the following structure:

[0004] Acetalamines participate in acid-catalyzed rearrangement reactions to form a mixture of p-aminobenzylaniline (PABA) and o-aminobenzylaniline (OABA), which have the following structures:

[0005] (PABA) and (OABA).

[0006] Further acid-catalyzed rearrangement of PABA yields p,p'-MDA (4,4'-MDA) and o,p'-MDA (2,4'-MDA), while further acid-catalyzed rearrangement of OABA yields o,p'-MDA and o,o'-MDA (2,2'-MDA). HCl is by far the most common acid catalyst. Some polymethylene polyanilines having three, four, five, or even more rings are formed together with MDA isomers. As used herein, "polymethylene polyaniline" specifically refers to an aniline-formaldehyde condensation product having at least three rings. Therefore, the resulting product stream is a mixture of MDA isomers and polymethylene polyaniline, which, for convenience, will be referred to herein as "pMDA".

[0007] When the catalyst is HCl, the MDA fraction of pMDA tends to contain 5 wt% to 12 wt% o,p'-MDA and much smaller, typically insignificant, o,o'-MDA in the range of 0.25 wt% to 2 wt%. The isomer ratio is not affected by subsequent phosgenation to produce diphenylmethane diisocyanate (MDI), so the resulting MDI will have the same ratio of 4,4'-isomers, 2,4'-isomers, and 2,2'-isomers as the phosgenated MDA, i.e., a combination of 2,4'-MDI and 2,2'-MDI isomers ranging from about 5 wt% to about 15 wt%. Similarly, the proportion of tricyclic and higher-ring structures in pMDA does not change during phosgenation, so the molar proportion of polymethylene polyphenylene polyisocyanate (i.e., substances having phenyl isocyanate groups linked by 3 or more methylene groups) in the phosgenation product will be the same as the proportion of polymethylene polyaniline in the phosgenated pMDA. Therefore, the direct product obtained by phosgenating pMDA feed contains 4,4'-, 2,4'-, and 2,2'- isomers of MDI and polymethylene polyphenylene polyisocyanate. The mixture of MDI isomers and polymethylene polyphenylene polyisocyanate is referred to herein as "pMDI" or "polymeric MDI".

[0008] Industrial-scale MDI plants produce a range of products with varying ratios of MDI isomers and contents of polymethylene polyphenylene polyisocyanate. For example, the main products include: “pure MDI,” typically consisting of 96-100 wt% 4,4'-MDI and 0-4 wt% 2,4'- and / or 2,2'- isomers, and 0.5 wt% or less polymethylene polyphenylene polyisocyanate; 2,4'-isomer-rich MDI products, such as 65 / 35 and 50 / 50 mixtures of 4,4'- and 2,4'- isomers (each containing 2% or less of the 2,2'- isomer); and pMDI products containing varying proportions of polymethylene polyphenylene polyisocyanate, thus exhibiting different isocyanate functional groups. These products differ in certain physical properties (such as melt temperature and viscosity), reactivity, and the amount of branching and / or crosslinking density produced when converted to polyurethane. These different properties allow various MDI and pMDI products to be used in a range of processes to produce a wide variety of polyurethanes.

[0009] Different MDI and pMDI products are not produced by phosgenating different MDA and pMDA feed streams. Instead, the pMDA feed stream is fed into a phosgenation process, and the resulting phosgenated material is then distilled to separate it into various MDI and pMDI products. Industrial-scale distillation is capital- and energy-intensive, thus adding considerable costs. There is also the problem of “balancing” the output of the manufacturing facility to match the output with the demand for various products. For example, distilling phosgenated material to produce “pure MDI” produces a stream rich in polymethylene polyphenylene polyisocyanate. Similarly, distilling a 65 / 35 or 50 / 50 mixture of 4,4'-MDI and 2,4'-MDI also produces a stream rich in the 4,4'-isomer. At any given time, there may not be sufficient demand for all these co-produced products, and the various products may have different economic values.

[0010] These problems can be improved or even eliminated if dedicated MDA and / or pMDA feedstocks can be used as feedstocks for phosgenation. If MDA or pMDA with isomer ratios closer to those required in MDI or pMDI products, and a molar proportion of 3-ring and higher-ring compounds, is available as feedstock, subsequent distillation of the phosgenation material can be reduced, if not eliminated. Different MDI and pMDI products can be generated directly by modifying the MDA or pMDA feedstock, rather than forming a generic mixture of phosgenation products that need to be distilled into individual products.

[0011] Unfortunately, HCl-catalyzed pMDA manufacturing processes are not well-suited for producing a range of MDA and pMDA products. The MDA isomer ratios can be slightly altered before the process becomes uneconomical. In HCl-catalyzed processes, the proportion of polymethylene polyaniline can be slightly varied by changing the aniline-to-formaldehyde ratio, but the ability to repeat this variation is limited by economic factors. Therefore, it is not feasible on an industrial scale to provide dedicated MDA or pMDA feedstocks for phosgenation closely associated with a variety of MDI and pMDI products.

[0012] Various methods have been proposed to produce pMDA products with different MDA isomer ratios and different molar proportions of polymethylene aniline. Certain heterogeneous catalysts have shown a preference for the production of more o,p'-isomers. US 4,071,588 describes the condensation of aniline with formaldehyde using acid-activated clay and synthetic silica-alumina and silica-magnesium catalysts. The proportion of o,p'-isomers produced using these catalysts increases with increasing reaction temperature. Unfortunately, the conversion of aniline to the product is low, and extremely large quantities of 3-cyclic and higher-cyclic polymethylene polyaniline are obtained. Other heterogeneous catalysts, such as cation exchange resins, have been found to favor the production of more p,p'-isomers.

[0013] The first step in the formation of acetals from aniline and formaldehyde does not require a catalyst or significantly elevated temperatures. Therefore, it has been proposed to separate acetal formation from subsequent rearrangement reactions. US 4,039,581 describes the reaction of aniline with formaldehyde at room temperature in the absence of a catalyst to produce acetals. The acetal is recovered and residual water is removed, then converted to pMDA under elevated temperature conditions using palygorskite clay or diatomaceous earth as a catalyst. Approximately 85% to 90% by weight of the product is MDA, and up to 21.2% of the MDA is the o,p'-isomer.

[0014] Similarly, WO 2021 / 116419 describes the condensation of aniline with formaldehyde in the comparative example in the presence of a silica-alumina catalyst (MCM-22, from China Catalyst Group). Approximately 85% of aniline was converted to the product within 5 hours, but this required a very high reaction temperature (150°C). The product after 5 hours of reaction contained 15% by weight of polymethylene polyaniline and approximately 85% MDA. 35% of the MDA was the o,p'-isomer, and 4.2% was the o,o'-isomer. Continuing the reaction for another 19 hours did not increase the conversion rate or significantly affect the isomer ratio of the MDA component in the product. However, a slightly higher amount of polymethylene polyaniline was obtained. Some metal-modified zeolite catalysts have shown reduced formation of both o,p'- and o,o'-isomers, but at the cost of decreased conversion of aniline to the product.

[0015] Similarly, US 2011 / 0021741 describes a process in which an acetal amine is rearranged to pMDA by heating it in the presence of a silica-alumina catalyst and then further converting it at a moderate temperature (60°C–120°C) in the presence of an acidic cation exchange resin. This requires a long reaction time, and only 9%–12% of the MDA fraction of the product is the o,p'-isomer.

[0016] In one aspect, the present invention is a method for producing a mixture of methylene diphenylamine isomers and polymethylene polyaniline, the method comprising:

[0017] a) In the presence of a heterogeneous catalyst, a solution of acetalamine in aniline is heated to a temperature of 50°C to 250°C to convert the acetalamine in the solution of acetalamine in aniline into a mixture of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline, and to produce a solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline isomer in aniline;

[0018] b) Separate the solutions of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline from the heterogeneous catalyst, and then...

[0019] c) In the presence of a catalytic amount of homogeneous catalyst, a solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline in aniline is heated to a temperature of 50°C to 150°C to convert aminobenzylaniline into another methylene diphenylamine isomer and another polymethylene polyaniline, forming a solution of the methylene diphenylamine isomer and polymethylene polyaniline in aniline formed in steps a) and c); and

[0020] d) Separate the methylene diphenylamine isomer and polymethylene polyaniline formed in steps a) and c) from aniline to recover the mixture of methylene diphenylamine isomer and polymethylene polyaniline.

[0021] The method of this invention produces pMDA products containing methylene diphenylamine (MDA) isomers and polymethylene polyaniline. The composition of the pMDA can be readily tuned to produce a dedicated pMDA feedstock for phosgenation to produce MDI and pMDI products. This tuning can be achieved in part by manipulating the reaction parameters in step a). For example, the selection of a specific heterogeneous catalyst allows for more or less production of the o,p'-isomer, and to a lesser extent, the o,o'-isomer. The molar proportion of polymethylene polyphenylene polyisocyanate can be increased or decreased by selecting the heterogeneous catalyst and / or the operating temperature in step a).

[0022] The MDA isomer ratio and the molar ratio of polymethylene polyphenylene polyisocyanate change only slightly during step c), i.e., further rearrangement catalyzed by homogeneous acid. Therefore, this process allows for adjustment of the pMDA composition due to the choice of catalyst and / or operating conditions used in step a), while providing substantially complete conversion of aniline to pMDA within commercially reasonable reaction times.

[0023] Another important advantage of this invention is that it can be integrated into conventional industrial-scale production facilities to produce pMDA of various MDA isomers and / or molar amounts of polymethylene polyaniline with controlled and adjustable quantities. The aminobenzylaniline, MDA isomers, and the solution of polymethylene polyaniline in aniline produced according to step a) of the aforementioned method can be fed as a sidestream into a conventional process, and the conversion of the remaining aminobenzylaniline to MDA to polymethylene polyaniline can be completed within the conventional process in the presence of a homogeneous catalyst.

[0024] Therefore, in a second aspect, the present invention is also a method for producing a mixture of methylene diphenylamine isomer and polymethylene polyaniline, the method comprising:

[0025] A) In the presence of a heterogeneous catalyst, a solution of acetal amine in aniline is heated to a temperature of 50°C to 250°C to convert the acetal amine in the solution of acetal amine in aniline into a first mixture of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline, and to form a first solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline;

[0026] B) Separate the first solution of aminobenzylaniline, methylene diphenylamine and polymethylene polyaniline in aniline from the heterogeneous catalyst;

[0027] C) By partially rearranging acetal amines in the presence of a homogeneous catalyst, a second solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline is produced separately.

[0028] D) Combining the first solution and the second solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline;

[0029] E) In the presence of a catalytic amount of homogeneous catalyst, a first solution and a second solution of the combined aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline are heated to a temperature of 50°C to 150°C to convert the aminobenzylaniline in the first and second solutions of the combined aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline into another methylene diphenylamine isomer and another polymethylene polyaniline, then...

[0030] F) Separate the methylene diphenylamine isomer and polymethylene polyaniline formed in steps A), C) and E) from aniline to recover the mixture of methylene diphenylamine isomer and polymethylene polyaniline.

[0031] By manipulating the ratio of the first and second solutions of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline combined in step D), the ratio of methylene diphenylamine isomer and the molar ratio of polymethylene polyaniline in the final pMDA product can be adjusted to predetermined values. These ratios can be adjusted to approximate or even match the corresponding ratios required in the phosgenation products prepared from pMDA, thereby reducing or eliminating the need to distill the phosgenation products into different product grades.

[0032] A starting solution of acetalamine (N,N'-diphenylmethylenediamine) can be produced by reacting excess aniline with formaldehyde at a temperature of 0°C to 100°C, preferably 0°C to 50°C. The molar ratio of aniline to formaldehyde can be, for example, 2:1 to 20:1, and preferably 3:1 to 20:1, 3:1 to 15:1, 4:1 to 10:1, or 4:1 to 6:1. The reaction can and preferably is carried out in the absence of a homogeneous catalyst, a heterogeneous catalyst as described more fully below, or other catalysts for rearranging the acetalamine to aminobenzylaniline and / or polymethylene polyphenylene. Formaldehyde can be provided in any convenient form, such as formalin or an aqueous solution. The aqueous solution may contain 30% to 37% by weight of formaldehyde and may also be stabilized with methanol or other stabilizers that do not react with aniline under the conditions of the acetalamine formation reaction. In the absence of a catalyst, formaldehyde reacts with aniline to produce an acetalamine. In the presence of a catalyst, the further rearrangement to aminobenzylaniline under the reaction conditions for the formation of acetals is negligible. The resulting acetal is dissolved in an excess of aniline.

[0033] Water is produced as a byproduct of the reaction. Preferably, water (including the reaction product and water added with formaldehyde) is removed from the acetalamine solution until the water content of the acetalamine solution in aniline is reduced to no more than 6% by weight. Most of the water forms a separate phase, which can be separated from the liquid organic phase by separation techniques such as decantation. Some water remains in the organic phase. This can be partially or completely removed by adding a solid desiccant, followed by separating the water-adsorbed desiccant from the acetalamine solution. In some embodiments, the acetalamine solution in aniline used in step a) of this process contains 0% to 6% by weight, 0% to 5% by weight, 0.25% to 5% by weight, 0.25% to 1.5% by weight, or 0.5% to 1.5% by weight of water.

[0034] Based on the combined weight of acetalamine and aniline, the aniline solution of acetalamine may contain, for example, at least 14% by weight, at least 27% by weight, or at least 42% by weight and at most 76% by weight or at most 61% by weight of acetalamine.

[0035] In step a), the aniline solution of the acetal amine is heated to a temperature of 50°C to 250°C in the presence of a heterogeneous catalyst. During this step, a portion of the acetal amine rearranges to form aminobenzylaniline isomers, namely the para-isomer (PABA) and the ortho-isomer (OABA). Some, but not all, of the aminobenzylaniline further rearranges to produce MDA isomers (i.e., the p,p'-isomer, the o,p'-isomer, and the o,o'-isomer). Some polymethylene polyaniline is formed during this step.

[0036] Step a) is preferably carried out for a sufficiently long time to allow at least 90%, preferably at least 95%, or at least 99%, of the acetalamines to rearrange into aminobenzylaniline, methylene diphenylamine isomers, and polymethylene polyaniline. All acetalamines can be thus converted.

[0037] Longer reaction times favor greater rearrangement of aminobenzylaniline into MDA and polymethylene polyaniline. However, complete rearrangement of aminobenzylaniline is generally not feasible under the conditions of step a) at any reasonable reaction time. The rearrangement reaction in step a) can proceed for, for example, from 0.5 hours to 10 hours. Preferred reaction times in step a) are at least 2 hours, at least 1 hour, or at least 4 hours and at most 8 hours or at most 6 hours. The molar ratio of the aminobenzylaniline produced in step a) to the methylene diphenylamine isomer plus polymethylene polyaniline can be, for example, 1:10 to 100:1, 1:5 to 100:1, 1:5 to 10:1, or 1:2 to 10:1.

[0038] Heterogeneous catalysts are solids that do not melt, dissolve, or degrade under the conditions of step a). Examples of suitable heterogeneous catalysts include various silica-alumina and silica-magnesium oxide materials, which can be synthetic (such as zeolites) or natural (such as various clays and diatomaceous earths), including acidic silica-alumina and acidic silica-magnesium zeolites, palygorskite clay, montmorillonite clay, or diatomaceous earth. These catalysts typically have ion-exchange capabilities and can be protons, i.e., at least partially in the form of hydrogen. Other heterogeneous catalysts include metal and half-metal oxides, such as Al2O3, MgO, Al2O3-MgO mixed oxides, SiO2-Al2O3 mixed oxides, SiO2-MgO mixed oxides, and B2O3·H3BO3; magnesium and / or aluminum silicates; BaN3, MoB2, AlSi3, WSi2, WS2, W2B3, Mo3Al, Ag2WO4, activated carbon, and fluorinated graphite. Some such catalysts have been found to more strongly promote the formation of "ortho" substances (i.e., OABA, o,p'-MDA, and o,p'-MDA). In particular, silica-alumina zeolite catalysts with Si / Al ratios of 10 to 40, especially 10 to 20, have been found to promote the formation of more ortho substances. An example of the last type of catalyst is H-MCM-22, which is available from companies such as Zhongshunai Group Co., Ltd.

[0039] Other suitable catalysts include sulfonated polymers, such as sulfonated polyfluoroolefins (including Nafion). ®Polymers), and ion exchange resins, including both gel-type and (preferably) microporous ion exchange resins. Such ion exchange resins are characterized by having a cross-linked organic polymer backbone or scaffold with ionic groups, preferably anionic groups, attached thereto, which bind to counterions. The polymer backbone or scaffold can be, for example, a styrene / divinylbenzene copolymer or a cross-linked aliphatic acrylate polymer. The preferred counterion for the anionic groups is hydrogen, but other countercations may be present. Examples of suitable cation exchange resins include those made by DuPont with Amber ® This product line sells cation exchange resins under various trade names. Cation exchange resins in the hydrogen form tend to favor reducing the yield of ortho-substances.

[0040] Therefore, the selection of the heterogeneous catalyst in step a) becomes a working parameter that allows for the adjustment of the MDA isomer ratio of the pMDA product. Choosing a catalyst that favors the formation of more ortho-isomers (such as silica-alumina and silica-magnesium oxide heterogeneous catalysts) ultimately results in pMDA rich in o,p'-isomers and less o,o'-isomers (compared to products prepared using HCl catalysis). Conversely, choosing a heterogeneous catalyst that discourages the formation of ortho-isomers, such as cation exchange resins (especially in hydrogen form), ultimately results in pMDA rich in p,p'-MDA isomers.

[0041] Catalysts can be immobilized on a suitable support.

[0042] The catalyst is used in a catalytically effective amount. A suitable amount may be, for example, 0.1 to 20 parts by weight of aniline solution per 100 parts by weight of acetalamine. On the same basis, a more preferred amount may be at least one part or at least two parts and at most ten parts.

[0043] Higher temperatures during step a) tend to favor the production of more "ortho" compounds (i.e., OABA, o,p'-MDA, and o,o'-MDA) and more polymethylene polyaniline. Therefore, the temperature for step a) can be selected to produce larger or smaller amounts of ortho compounds. Temperature and catalyst can be selected together to further promote or inhibit the formation of ortho compounds, and conversely, to favor or discourage the production of polymethylene polyaniline.

[0044] In some embodiments, the temperature during step a) can be 40°C to 80°C, which is beneficial for reducing the yield of the ortho-substance and polymethylene polyaniline. In other embodiments, the temperature can be 80°C to 150°C or 150°C to 250°C, with the yield of the ortho-substance and polymethylene polyaniline increasing as the temperature increases.

[0045] Maintain sufficient pressure to prevent the volatilization of aniline, acetal, aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline.

[0046] Therefore, in some embodiments, a catalyst and / or a combination of catalyst and temperature are selected in step a) to promote the formation of the ortho-substance. In this case, the ortho-substance in the product formed in step a) may constitute at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 50% by weight of, and up to 75% thereof, of, for example, a combination of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline. In a specific embodiment, the ortho-substance constitutes 15% to 50% or 20% to 50% by weight of the combination of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline formed in step a).

[0047] In an alternative embodiment, in step a), a catalyst and / or a combination of catalyst and temperature is selected to be unfavorable to the formation of the ortho-substance. In this case, the ortho-substance in the product formed in step a) may constitute, for example, up to 15%, up to 12%, up to 10%, up to 8%, up to 6%, up to 4%, or up to 3% by weight of a combination of aminobenzylaniline, MDA isomer, and polymethylene polyaniline. In a specific embodiment, the ortho-substance constitutes 2% to 15%, 2% to 10%, or 2% to 6% by weight of the combination of aminobenzylaniline, MDA isomer, and polymethylene polyaniline formed in step a).

[0048] The aniline:formaldehyde ratio in step a) can also affect the molar ratio of the polymethylene polyaniline formed in step a), with a higher aniline:formaldehyde ratio favoring the production of more polymethylene polyaniline.

[0049] The product of step a) is a solution of aminobenzylaniline, various methylene diphenylamine isomers, and polymethylene polyaniline in aniline. Based on the total weight of aminobenzylaniline, methylene diphenylamine isomers, polymethylene polyaniline, and aniline, the solution may contain, for example, at least 10% by weight, at least 25% by weight, or at least 40% by weight and at most 80% by weight, or at most 65% by weight of a combination of aminobenzylaniline, methylene diphenylamine isomers, and polymethylene polyaniline.

[0050] In step b), the solution of aminobenzylaniline, MDA, and polymethylene polyaniline formed in step a) in aniline is separated from the heterogeneous catalyst. Any solid-liquid separation technique is suitable, including filtration, centrifugation, or decantation. In continuous processes using fixed-bed catalysts, separation can be achieved by removing the solution from the reaction vessel containing the fixed-bed catalyst.

[0051] Steps a) and / or b) can be performed in batches or consecutively, depending on the circumstances.

[0052] In step c) of the method of the first aspect, a solution of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline obtained in step b) in aniline is heated to a temperature of 50°C to 150°C in the presence of a catalytic amount of homogeneous catalyst. Under these conditions, the aminobenzylaniline remaining after step b) rearranges to form additional methylene diphenylamine isomers and / or polymethylene polyaniline. Therefore, heating in step c) is preferably continued until substantially all (at least 90% by weight, at least 95% by weight, or at least 99% by weight) of the aminobenzylaniline remaining after step b) is converted to the methylene diphenylamine isomers and / or polymethylene polyaniline. The reaction time can be, for example, at least 0.5 hours, at least 1 hour, at least 2 hours, at least 3 hours, or at least 4 hours, and for example, at most 20 hours, at most 10 hours, at most 8 hours, or at most 6 hours. The preferred temperature is 50°C to 100°C, particularly 70°C to 90°C. Sufficient pressure is maintained to prevent the evaporation of the liquid components of the reaction mixture.

[0053] The homogeneous catalyst used in step c) is liquid and / or soluble in the reaction mixture. Inorganic acids are suitable, as are liquid or Lewis acids soluble in the reaction mixture. Proton-based homogeneous catalysts are preferred; inorganic acids, especially HCl, are most preferred. HCl and other inorganic acids may be provided in the form of solutions in water or other solvents that do not react with aniline, aminobenzylaniline, methylene diphenylamine isomers, or polymethylene polyaniline under the conditions used in step c). A suitable amount of homogeneous catalyst is, for example, 0.05 mol to 1 mol per 100 parts by weight of a solution of aminobenzylaniline, MDA isomers, and polymethylene polyaniline in aniline.

[0054] The product of step c) is a solution of methylene diphenylamine isomer and polymethylene polyaniline in aniline. The methylene diphenylamine isomer and polymethylene polyaniline include those formed in steps a) and c) of this process. Small amounts of residual aminobenzylaniline and / or acetalamine may remain. Based on the total weight of the residual aminobenzylaniline and / or acetalamine (if any), methylene diphenylamine isomer, polymethylene polyaniline, and aniline, the solution may contain, for example, at least 10% by weight, at least 25% by weight, or at least 40% by weight and at most 80% by weight, or at most 65% by weight of methylene diphenylamine isomer and polymethylene polyaniline.

[0055] The methylene diphenylamine isomers and polymethylene polyaniline (including those formed in each of steps a) and c) are then separated from aniline to recover the pMDA product. This can be conveniently accomplished using methods such as vacuum distillation, solvent crystallization, melt crystallization, solvent extraction, scraped-film evaporation, or any combination of two or more of these methods.

[0056] The product obtained after step d) of this process is a mixture of methylene diphenylamine isomers and polymethylene polyaniline. Surprisingly, the ratio of o,p'-MDA isomers to o,o'-MDA isomers in the product obtained after step d) is closely related to the ratio of the ortho-substance formed in step a). The further rearrangement reaction occurring in step c) has only a small effect on the ratio of methylene diphenylamine isomers and the molar ratio of polymethylene polyaniline.

[0057] In some embodiments where step a) is carried out under conditions favorable to the formation of ortho-substances, the product obtained after step d) may contain, for example, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 50% of the o,p'-MDA isomer, and up to 75% thereof, based on the total weight of all methylene diphenylamine isomers. In specific embodiments, 15% to 50% or 20% to 50% of the methylene diphenylamine is the o,p'-isomer. In such embodiments, the o,o'-isomer typically constitutes at most 4% of the weight of the methylene diphenylamine isomers, preferably at most 3% or at most 2.5%. In such embodiments, the p,p'-isomer may constitute at most 85%, at most 80%, at most 75%, at most 70%, at most 65%, at most 60%, or at most 50% of the total weight of the methylene diphenylamine isomers.

[0058] In an alternative embodiment where step a) is carried out under conditions unfavorable to the formation of ortho-substances, the product obtained after step d) may contain, for example, up to 15%, up to 12%, up to 10%, up to 8%, up to 6%, up to 4%, or up to 2% of the o,p'-MDA isomer, based on the total weight of all methylene diphenylamine isomers. In such embodiments, the o,o'-isomer typically constitutes up to 1% or up to 0.5% of the weight of the methylene diphenylamine isomers, and the p,p'-isomer may constitute at least 84%, at least 87%, at least 89%, at least 91%, at least 93%, at least 95%, or at least 97% of the total weight of the methylene diphenylamine isomers.

[0059] Polymethylene polyaniline can constitute as little as 1% and as much as 95% of the total mass of the mixture of methylene diphenylamine isomer and polymethylene polyaniline obtained in step d).

[0060] Steps A) and B) of the second aspect of the invention are as described above with respect to steps a) and b) of the first aspect, to produce a first solution of aminobenzylaniline, MDA isomer and polymethylene polyaniline in aniline.

[0061] As previously described, in the first solution of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline, the molar ratio of aminobenzylaniline to the methylene diphenylamine isomer plus polymethylene polyaniline can be, for example, 1:2 to 100:1 or 1:2 to 10:1. In embodiments where the conditions for promoting the formation of the ortho-substance are selected in step A), the ortho-substance in the product formed in step A) can constitute, for example, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, or at least 50% of the combined weight of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline, and up to 75% thereof. In specific embodiments, the ortho-substance constitutes 15% to 50% or 20% to 50% of the combined weight of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline formed in step A).

[0062] In an embodiment where conditions unfavorable to the formation of the ortho-substance are selected in step A), the ortho-substance in the product formed in step A) may constitute, for example, up to 15%, up to 12%, up to 10%, up to 8%, up to 6%, up to 4%, or up to [amount] by weight of a combination of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline. In a specific embodiment, the ortho-substance constitutes 2% to 15%, 2% to 10%, or 2% to 6% by weight of the combination of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline formed in step A).

[0063] In step C) of the second aspect, a second solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline is produced by rearranging the acetal amine in the presence of a homogeneous catalyst, as described above with respect to step c) of the first aspect of the invention. The acetal amine can be prepared and separated separately as described above; alternatively, the second solution can be produced by reacting excess aniline with formaldehyde in the presence of a homogeneous catalyst. This second solution is produced separately from the first solution produced in steps A) and B).

[0064] In some embodiments, step C) is carried out by combining formaldehyde and an excess of aniline in the presence of a homogeneous catalyst, and subjecting the resulting combination to reaction conditions sufficient to convert a portion of the starting material into aminobenzylaniline, methylene diphenylamine isomers, and polymethylene polyaniline. The molar ratio of aniline to formaldehyde is conveniently as described above with respect to step a); the homogeneous catalyst and its amount are conveniently as described above with respect to step c). In such embodiments, aniline, formaldehyde, and the homogeneous catalyst are preferably combined and subjected to reaction conditions under which aniline and formaldehyde react to produce an acetal, and at least a portion of the acetal rearranges to produce aminobenzylaniline, methylene diphenylamine isomers, and polymethylene polyaniline.

[0065] Although a portion of the acetalamine may be present in the second solution of aminobenzylaniline, the MDA isomer, and polymethylene polyaniline produced in step C), the second solution may be free of acetalamine or contain only residual amounts (such as 1% by weight or less) of acetalamine. The molar ratio of aminobenzylaniline to the MDA isomer plus polymethylene polyaniline produced in step C) may be, for example, 1:10 to 100:1, 1:5 to 100:1, 1:5 to 10:1, or 1:2 to 10:1.

[0066] The "ortho" substance as described above may constitute 5% to 15% by weight, particularly 8% to 15%, of the total weight of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in the second solution produced in step C).

[0067] In step D) of the second aspect of the invention, a first solution and a second solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline in aniline are combined. The first and second solutions can be combined in any proportion. Typically, the proportion of the ortho-substance in the second solution produced in step C) will be different from (higher or lower than) the proportion of the ortho-substance in the first solution obtained from step B). In this typical case, the proportion of the ortho-substance in the combined first and second solutions will be between the proportions of the ortho-substances in the first and second solutions themselves. Therefore, by selecting the proportion of the first and second solutions combined in step D), the content of the ortho-substance can be freely adjusted within a wide range of values. In some embodiments, the proportion of the ortho-substance in the first solution from step B) is greater than the proportion of the ortho-substance in the second solution produced in step C). Alternatively, the proportion of the ortho-substance in the first solution from step B) is less than or equal to the proportion of the ortho-substance in the second solution produced in step C). Similarly, the proportion of polymethylene polyaniline in the first solution from step B) can be greater than, less than, or equal to the proportion of polymethylene polyaniline in the second solution produced in step C).

[0068] Further control of the content of the ortho-substance can be achieved, for example, by manipulating the temperature, reaction time and / or catalyst selection as described above, by adjusting the content of the ortho-substance generated in the first solution.

[0069] Therefore, the ortho-substance can constitute less than about 2% and more than 75% of the total weight of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in the first and second solutions of the combination formed in step D). The molar ratio of aminobenzylaniline to methylene diphenylamine isomer plus polymethylene polyaniline in the first and second solutions of the combination formed in step D) can be, for example, 1:10 to 100:1, 1:5 to 100:1, 1:5 to 10:1, or 1:2 to 10:1.

[0070] In step E) of the second aspect of the invention, the combined aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in a first and second solution in aniline are then heated to a temperature of 50°C to 150°C in the presence of a catalytic amount of homogeneous catalyst to convert the remaining aminobenzylaniline into another methylene diphenylamine isomer and / or another polymethylene polyaniline. The reaction conditions and catalyst generally described with respect to step c) of the first aspect of the invention are perfectly suitable. Preferably, heating continues until substantially all (at least 90% by weight, at least 95% by weight, or at least 99% by weight) of the remaining aminobenzylaniline in the combined first and second solutions is converted into the methylene diphenylamine isomer and / or polymethylene polyaniline. The reaction time can be, for example, at least 0.5 hours, at least 1 hour, at least 2 hours, at least 3 hours, or at least 4 hours, and for example, at most 20 hours, at most 10 hours, at most 8 hours, or at most 6 hours.

[0071] Before combining the second solution of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline with the first solution in step D), it is not necessary to remove the residual catalyst from the second solution, although doing so is within the scope of the invention. This residual catalyst may form all or part of the homogeneous catalyst used in step E). If necessary or advantageous, additional homogeneous catalyst may be added; this additional homogeneous catalyst may be added to either or both of them before combining the first and second solutions in step D), and / or may be added to the combined solution formed in step D). Any such additional homogeneous catalyst is preferably the same as the catalyst used in step C), and most preferably a proton catalyst, such as an inorganic acid, most preferably HCl.

[0072] In step F) of the second aspect, the methylene diphenylamine isomer and polymethylene polyaniline formed in steps A), C), and E) are separated from aniline to recover a mixture of methylene diphenylamine isomer and polymethylene polyaniline (“pMDA”). The separation method described with respect to step d) of the first aspect is suitable. The product thus obtained contains methylene diphenylamine isomer and a certain proportion of polymethylene polyaniline. The o,p'-isomer may constitute, for example, at least 2%, at least 14%, at least 6%, at least 8%, or at least 10% of the total weight of the methylene diphenylamine isomer, and up to 75%, up to 60%, up to 50%, or up to 40% thereof. The o,o'-isomer typically constitutes at most 4% of the weight of the methylene diphenylamine isomer, preferably at most 3% or at most 2.5% thereof. The p,p'-isomer may constitute up to 97%, up to 95%, up to 93%, up to 91%, up to 89%, up to 87%, up to 80%, up to 60%, up to 50%, up to 40%, or up to 30% of the total weight of the methylene diphenylamine isomer.

[0073] The accompanying drawings schematically illustrate an embodiment of the second aspect of the invention. Aniline and formaldehyde are introduced into a reaction vessel 8 via lines 6 and 7, respectively, where they react to form a solution of acetalamine in excess aniline. The acetalamine solution is transferred to a separation vessel 10 via line 9. Water is removed from the acetalamine solution in the separation vessel 10. The partially or completely dehydrated acetalamine solution is transferred to a reactor 12 via line 11, where it is contacted with a heterogeneous catalyst under the reaction conditions described above to produce a first solution of aminobenzylaniline, MDA isomer, and polymethylene polyaniline (step A). ​​The first solution of aminobenzylaniline, MDA isomer, and polymethylene polyaniline is removed from the reactor 12 via line 14.

[0074] In the illustrated embodiment, the heterogeneous catalyst remains within reactor 12 (e.g., a fixed-bed catalyst), and the first solution of aminobenzylaniline, MDA isomer, and polymethylene polyamine is separated from the heterogeneous catalyst upon removal from reactor 12 (step B). Alternatively, the heterogeneous catalyst may be removed from reactor 12 together with the first solution of aminobenzylaniline, MDA isomer, and polymethylene polyamine, and separated from the first solution in a separate apparatus (not shown) before being combined with a second solution of aminobenzylaniline, MDA isomer, and polymethylene polyaniline in aniline.

[0075] Aniline is fed into reactor 3 via line 1. A homogeneous catalyst (shown as HCl in the figures) is introduced into line 1 via line 2 and fed into reactor 3 along with aniline. Formaldehyde is introduced separately into reactor 3 via line 4. Reactor 3 is maintained under reaction conditions, and the residence time of the reactants in reactor 3 is selected such that a portion of the aniline reacts with formaldehyde to form an acetal, which rearranges in reactor 3 to produce a second solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline (step C). As previously described, in an alternative embodiment, the acetal can be produced separately and then combined with the homogeneous catalyst for partial rearrangement. This second solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline is removed from reactor 3 via line 5. In the illustrated embodiment, the homogeneous catalyst introduced into reactor 3 is retained together with the second solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline removed via line 5.

[0076] A first solution and a second solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline are combined (step D). In the illustrated embodiment, this is accomplished by feeding the first solution directly into line 5 and feeding the combined first and second solutions into reactor 17. Alternatively, the first and second solutions may be fed separately into reactor 17. Alternatively, a separate mixing device may be present upstream of reactor 17, in which the first and second solutions are combined. Such a separate mixing device may be or include one or more online mixing devices, such as one or more static mixers incorporated into line 5. In another variation of the process, a portion of the second solution may be separately withdrawn from reactor 3 and / or line 5 and combined with the first solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline.

[0077] The accompanying drawings include the optional feature of adding a homogeneous catalyst (again, HCl) to the first solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline prior to mixing the first and second solutions. This addition of additional catalyst may be omitted, or may alternatively or additionally be carried out upstream or downstream of the location where the first solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline isomer is introduced into line 5 via line 14, and / or within reactor 17, as conveniently possible.

[0078] Reactor 17 is maintained under reaction conditions to convert aminobenzylaniline in the combined first and second solutions into methylene diphenylamine isomers and / or polymethylene polyaniline, to produce a solution of methylene diphenylamine isomers and polymethylene polyaniline in aniline (step E). This solution is transferred via line 18 to a second separator 19, in which the methylene diphenylamine isomers and polymethylene polyaniline are separated from aniline (step F). Aniline is removed via line 20 and preferably recycled to lines 1 and / or 6 (preferably after impurity removal). The methylene diphenylamine isomers and polymethylene polyaniline are removed from the second separator 19 via line 21.

[0079] In large-scale industrial pMDA production facilities using homogeneous catalysts, acetal formation and / or rearrangement reactions are typically split into two or more separate vessels. For example, aniline, formaldehyde, and a homogeneous catalyst can be combined and partially reacted in a first reaction vessel to produce an intermediate solution containing aminobenzylaniline, a methylenediphenylamine isomer, and polymethylene polyaniline (i.e., the rearrangement of aminobenzylaniline to the methylenediphenylamine isomer and the incomplete polymethylene polyaniline). The rearrangement reaction is then continued in one or more downstream vessels to produce a final solution of the methylenediphenylamine isomer and polymethylene polyaniline. A significant advantage of this invention is its ease and inexpensive incorporation into such facilities. Essentially, the first solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline produced in steps A) and B) can be introduced as a side stream into such a facility at any convenient location downstream of the first reactor (after the mixture of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline isomer is produced using a homogeneous catalyst) and upstream of the last reactor (before aminobenzylaniline isomer isomer and polymethylene polyaniline are completely converted). In the case of a continuous reaction in the presence of a homogeneous catalyst, such as in a tubular reactor, the first solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline can be introduced at an appropriate location along the length of the tubular reactor.

[0080] pMDA products can be used to prepare polyisocyanates by reacting with phosgene. Polyisocyanates are raw materials that can be used to prepare polyurethanes, polyisocyanurates, polyureas, and similar polymers.

[0081] The following examples are provided to illustrate the invention, but are not intended to limit the scope of the invention. Unless otherwise specified, all parts and percentages are by weight.

[0082] Examples 1-3 and Comparative Example AD

[0083] Preparation of acetal amine solution 5 moles of aniline were cooled to below 10°C in a reactor under a nitrogen atmosphere. 1 mole of formaldehyde (provided as a 37% solution in water and methanol) was fed into the aniline with stirring, while maintaining the temperature below 10°C. The resulting reaction mixture was stirred for 5 hours and gradually heated to 20°C. Stirring was stopped, and the reaction was allowed to settle overnight under nitrogen to separate the aqueous and organic phases. The bottom acetal amine in the aniline phase was removed, mixed with 200 g of anhydrous sodium sulfate to remove residual water, and filtered.

[0084] Comparative Example AAdd 6 parts of the aniline solution of the acetalamine produced above to a 20 mL scintillation vial equipped with a stir bar. Add 2.2 parts of 37% HCl solution in portions. Fill the vial with nitrogen, seal, and heat at 80°C for 4 hours with stirring, then heat at 90°C for another 5 hours. Cool the resulting reaction mixture to 4°C, neutralize with NaOH aqueous solution, and extract with 2-methyltetrahydrofuran. Gas chromatography analysis of the 2-methyltetrahydrofuran solution showed that the acetalamine was completely converted to the MDA isomer and polymethylene polyaniline. Gel permeation chromatography (GPC) determined that the MDA isomer constituted 77% by weight of the combined weight of the MDA isomer and polymethylene polyaniline. MDA consisted of 87% p,p'-isomer, 12.4% o,p'-isomer, and 0.6% o,o'-isomer.

[0085] Comparative example BD Add 4 parts of the aniline solution of the acetal amine produced above to a 20 mL scintillation vial equipped with a stir bar. Add 0.2 parts of a silica-alumina catalyst (H-MCM-22, obtained from China Catalyst Group Co., Ltd.) with a Si / Al ratio of approximately 14. Fill the vial with nitrogen and seal it.

[0086] For Comparative Example B, the vial and its contents were heated at 80°C with stirring for 4 hours, and then cooled, neutralized, and extracted with 2-methyltetrahydrofuran as described in Comparative Example A. Gas chromatography showed that a significant amount of aminobenzylaniline remained. The selectivity for the ortho-isomer was 32%, calculated as (ortho-ABA + o,p'-MDA + o,o'-MDA) ÷ (ortho-ABA + para-ABA + o,p'-MDA + o,o'-MDA + p,p'-MDA).

[0087] For Comparative Example C, the vial and its contents were heated at 120°C with stirring for 4 hours, and then cooled, neutralized, and extracted with 2-methyltetrahydrofuran as described in Comparative Example A. Gas chromatography showed that despite the high reaction temperature, a significant amount of aminobenzylaniline remained. The selectivity for the ortho-isomer was 40%, confirming that the higher reaction temperature favored the formation of more o,p'-isomers.

[0088] For Comparative Example D, the vial and its contents were heated at 80°C with stirring for 38 hours, and then cooled, neutralized, and extracted with 2-methyltetrahydrofuran as described in Comparative Example A. Gas chromatography showed that despite the very long reaction time, a significant amount of aminobenzylaniline remained. The selectivity for the ortho-isomer was 35%, confirming that the higher reaction temperature favored the formation of more o,p'-isomers.

[0089] For Example 1, 3 parts of the aniline solution of the acetal amine produced above were added to a 20 mL scintillation vial equipped with a stir bar. 0.15 parts of a silica-alumina catalyst (H-MCM-22, obtained from China Catalyst Group Co., Ltd.) with a Si / Al ratio of approximately 14 were added. The vial was filled with nitrogen and sealed. The vial and its contents were heated at 80°C and stirred for 4 hours, then cooled. A liquid phase having a composition substantially as described in Comparative Example B was filtered from the solid catalyst. 1.1 parts of a 37% HCl solution were added to the liquid phase, and the resulting reaction mixture was heated at 90°C for 5 hours. The product mixture was then neutralized and extracted with 2-methyltetrahydrofuran as described in Comparative Example A. Gas chromatography showed that the starting acetal amine was completely converted to the MDA isomer and polymethylene polyaniline. GPC determination showed that the MDA isomer constituted 85% of the combined weight of the MDA isomer and polymethylene polyaniline. The MDA consisted of 70% p,p'-isomer, 27.6% o,p'-isomer, and 2.4% o,o'-isomer. The combined amount of o,p'-isomer and p,p'-isomer (30%) correlated well with the 32% ortho-isomer produced in Comparative Example B, indicating that the ortho-isomer content remained almost unchanged during the HCl-catalyzed phase of the reaction.

[0090] Example 2 was conducted in the same manner as Example 1, except that the temperature during the HCl catalytic phase of the reaction was 80°C. Again, complete conversion to MDA isomers and polymethylene polyaniline was observed. MDA constituted 85% of the combined weight of the MDA isomers and polymethylene polyaniline. MDA comprised 71% p,p'-isomer, 26.6% o,p'-isomer, and 2.4% o,o'-isomer. Again, the combined amount of o,p'-isomers and o,o'-isomers (29%) correlated well with the 32% ortho-isomer produced in Comparative Example B, indicating that the ortho-isomer content remained almost unchanged during the HCl catalytic phase of the reaction.

[0091] Example 3 was conducted in the same manner as Example 1, except that montmorillonite clay (K10, from Aldrich) was used instead of the H-MCM catalyst. Complete conversion to MDA isomers and polymethylene polyaniline was again observed. MDA constituted 81% of the combined weight of the MDA isomers and polymethylene polyaniline. MDA comprised 82% p,p'-isomer, 17.3% o,p'-isomer, and 0.7% o,o'-isomer. The K10 catalyst promoted more o,p'-isomer formation than the HCl catalyst itself, but less than observed with the H-MCM-22 catalyst, while also forming a slightly larger amount of polymethylene polyaniline.

Claims

1. A method for producing a mixture of methylene diphenylamine isomer and polymethylene polyaniline, the method comprising: a) In the presence of a heterogeneous catalyst, a solution of acetalamine in aniline is heated to a temperature of 50°C to 250°C to convert the acetalamine in the solution of acetalamine in aniline into a mixture of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline, and to produce a solution of said aminobenzylaniline, said methylene diphenylamine isomer and said polymethylene polyaniline isomer in aniline; b) Separate the solution of the aminobenzylaniline, the methylene diphenylamine isomer, and the polymethylene polyaniline in aniline from the heterogeneous catalyst; then c) In the presence of a catalytic amount of homogeneous catalyst, the solution of aminobenzylaniline, the methylene diphenylamine isomer, and the polymethylene polyaniline in aniline is heated to a temperature of 50°C to 150°C to convert the aminobenzylaniline into another methylene diphenylamine isomer and another polymethylene polyaniline, and to form the solution of the methylene diphenylamine isomer and the polymethylene polyaniline in aniline formed in steps a) and c). as well as d) Separate the methylene diphenylamine isomer and the polymethylene polyaniline formed in steps a) and c) from the aniline to recover the mixture of the methylene diphenylamine isomer and the polymethylene polyaniline.

2. The method of claim 1, wherein the solution of acetalamine in aniline is prepared in a process comprising the steps of: i) reacting excess aniline with formaldehyde at a temperature of 0°C to 100°C in the absence of a catalyst to produce a solution of acetalamine in aniline, and then ii) removing water from the solution of acetalamine in aniline to reduce the water content of the solution of acetalamine in aniline to no more than 6% by weight.

3. The method according to claim 1 or 2, wherein the heterogeneous catalyst is a silica-alumina and / or silica-magnesium oxide material.

4. The method according to claim 3, wherein the heterogeneous catalyst is one or more of acidic silica-alumina zeolite, acidic silica-magnesium zeolite, palygorskite clay, montmorillonite clay, or diatomaceous earth.

5. The method according to claim 1 or 2, wherein the heterogeneous catalyst is a cation exchange resin in the form of hydrogen.

6. The method according to any of the preceding claims, wherein the ortho-substance constitutes 15% to 75% by weight of the combination of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in the solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline obtained from step b).

7. The method of claim 6, wherein the mixture of methylene diphenylamine isomers and polymethylene polyaniline obtained in step d) contains 15% to 75% by weight of o,p'-MDA isomers based on the total weight of all methylene diphenylamine isomers.

8. The method according to any one of claims 1 to 5, wherein the ortho-substance constitutes 2% to 10% by weight of the combination of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in the solution of aniline formed in step b).

9. The method of claim 8, wherein the mixture of methylene diphenylamine isomers and polymethylene polyaniline obtained in step d) contains up to 8% by weight of the o,p'-MDA isomer, based on the total weight of all methylene diphenylamine isomers.

10. The method according to any of the preceding claims, wherein step a) is performed at a temperature of 40°C to 80°C.

11. The method according to any one of claims 1 to 9, wherein step a) is carried out at a temperature of 80°C to 150°C.

12. The method according to any one of claims 1 to 9, wherein step a) is carried out at a temperature of 150°C to 250°C.

13. A method for producing a mixture of methylene diphenylamine and polymethylene polyaniline, the method comprising: A) In the presence of a heterogeneous catalyst, a solution of acetal amine in aniline is heated to a temperature of 50°C to 250°C to convert the acetal amine in the solution of acetal amine in aniline into a first mixture of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline, and to form a first solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline; B) Separate the first solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline from the heterogeneous catalyst; C) By partially rearranging acetal amines in the presence of a homogeneous catalyst, a second solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline is produced separately. D) Combining the first solution and the second solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline; E) In the presence of a catalytic amount of homogeneous catalyst, heat the first and second solutions of the combined aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline to a temperature of 50°C to 150°C to convert the aminobenzylaniline in the first and second solutions of the combined aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline into another methylene diphenylamine isomer and another polymethylene polyaniline, then... F) Separate the methylene diphenylamine isomer and the polymethylene polyaniline formed in steps A), C), and E) from the aniline to recover the mixture of the methylene diphenylamine isomer and the polymethylene polyaniline.

14. The method according to claim 13, wherein the heterogeneous catalyst is a silica-alumina and / or silica-magnesium oxide material.

15. The method according to claim 14, wherein the heterogeneous catalyst is one or more of acidic silica-alumina zeolite, acidic silica-magnesium zeolite, palygorskite clay, montmorillonite clay, or diatomaceous earth.

16. The method according to claim 13 or 14, wherein the heterogeneous catalyst is a cation exchange resin in the form of hydrogen.

17. The method according to any of the preceding claims, wherein the ortho-substance constitutes 15% to 50% by weight of the combination of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in the solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline obtained from step B).

18. The method of claim 18, wherein the mixture of methylene diphenylamine isomers and polymethylene polyaniline obtained in step F) contains 15% to 75% by weight of o,p'-MDA isomers based on the total weight of all methylene diphenylamine isomers.

19. The method according to any one of claims 13 to 17, wherein the ortho-substance constitutes 2% to 10% by weight of the combination of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in the first solution of aniline obtained in step B).

20. The method of claim 20, wherein the mixture of methylene diphenylamine isomers and polymethylene polyaniline obtained in step F) contains up to 8% by weight of the o,p'-MDA isomer, based on the total weight of all methylene diphenylamine isomers.

21. The method according to any one of claims 13 to 21, wherein step A) is performed at a temperature of 40°C to 80°C.

22. The method according to any one of claims 13 to 21, wherein step A) is performed at a temperature of 80°C to 150°C or 150°C to 250°C.

23. The method according to any one of claims 13 to 21, wherein step A) is performed at a temperature of 150°C to 250°C.

24. The method according to any one of claims 13 to 24, wherein the homogeneous catalyst is proton.

25. The method of claim 25, wherein the homogeneous catalyst is HCl.

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