Process for the preparation of polymethylene polyphenylamine using a lewis acid modified clay catalyst

Abstract

A mixture of methylenedianiline isomers and polymethylenepolyaniline is produced at a controlled ratio of methylenedianiline isomers. Aniline and formaldehyde are reacted to produce N,N'-diphenylmethylene diamine (aldolamine), which is then partially rearranged in the presence of a Lewis acid-modified clay catalyst into a mixture of aminobenzylaniline isomers and methylenedianiline isomers. Further rearrangement is performed in the presence of a homogeneous catalyst to convert remaining aminobenzylaniline isomers to methylenedianiline and polymethylenepolyaniline.

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), a polyamino-polyphenylmethane, has a huge global production volume and is 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). Some polymethylene polyanilines having three, four, five, or even more rings are formed together with MDA isomers. Therefore, the resulting product stream is a mixture of MDA isomers and polymethylene polyaniline, which, for convenience, will be referred to herein as "pMDA". As used herein, "polymethylene polyaniline" specifically refers to an aniline-formaldehyde condensation product having at least three rings, and therefore excludes any methylene diphenylamine isomers.

[0007] The MDA fraction of the product tends to contain 5% to 12% by weight of o,p'-MDA and much smaller, usually insignificant amounts of o,o'-MDA in the range of 0.25% to 2% by weight. The isomer ratio of the MDA is not affected by subsequent phosgenation to produce diphenylmethane diisocyanate (MDI), so the MDI thus produced will have the same ratio of 4,4'-isomers, 2,4'-isomers, and 2,2'-isomers as the MDA, i.e., a combination of 2,4'-MDI and 2,2'-MDI isomers ranging from about 5% to about 15% by weight.

[0008] There are sometimes reasons why a higher proportion of the 2,4'-isomer is required in MDI products. 2,4'-MDI is less reactive than the 4,4'-isomer, which can be advantageous in some polyurethane processes. Increasing the proportion of the 2,4'-isomer also lowers the melt temperature of MDI, providing a process advantage in certain situations.

[0009] 2,4'-MDI can be separated from 4,4'-MDI by distillation. This method is used industrially to prepare MDI products rich in the 2,4'-isomer, such as, for example, a 50 / 50 mixture of 4,4'-MDI and 2,4'-MDI. In addition to the product rich in the 2,4'-isomer, a separate product stream rich in the 4,4'-isomer is also produced. The latter product stream may be desirable or undesirable in terms of the amount produced, and / or may have a lower value. For example, distilling 100 parts of an MDI isomer mixture containing 15% of the 2,4'-isomer yields 30 parts of a 50 / 50 mixture containing both the 2,4'-isomer and the 4,4'-isomer, and more than twice that amount, i.e., 70 parts, of pure (or nearly pure) 4,4'-MDI.

[0010] If more o,p'-isomers are prepared in the MDA manufacturing process, less material needs to be distilled, or the distillation step can be eliminated entirely. The 2,4'-isomer content of MDI prepared by phosgenation of MDI will correspondingly be higher. For example, if the o,p'-isomer content of MDA increases from 15% to 30%, the phosgenation product will also contain 30% o,p'-isomers. The amount of material requiring distillation to produce a 50 / 50 mixture of 30 parts o,p'-MDI and p,p'-MDI will be reduced from 100 parts to only 60 parts, and the amount of pure MDI produced in the distillation will be reduced from 70 parts to 30 parts.

[0011] To this end, various methods have been proposed to produce MDA products rich in o,p'-isomers. In particular, certain heterogeneous catalysts have been shown to promote 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 polymethylene polyaniline are obtained.

[0012] 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 acetals are recovered and residual water is removed, then converted to MDA isomers and polymethylene polyaniline under elevated temperature conditions using palygorskite clay or diatomaceous earth as catalysts. Approximately 85% to 90% of the product is MDA, and at most 21.2% of the MDA is the o,p'-isomer.

[0013] Similarly, WO 201 / 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, slightly more 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.

[0014] Similarly, US 2011 / 0021741 describes a process in which an acetal amine is rearranged into methylene diphenylamine and polymethylene polyaniline 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 ion exchange resin in acidic form. This process requires a long reaction time, and only 9%–12% of the methylene diphenylamine fraction of the product is the 2,4'-isomer.

[0015] In one aspect, the present invention is a method for producing a mixture of methylene diphenylamine isomers and polymethylene polyaniline, the method comprising:

[0016] a) In the presence of a Lewis acid-modified clay 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 mixture of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline, and to produce a solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline;

[0017] b) Separate the solutions of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline with a Lewis acid-modified clay catalyst, and then...

[0018] c) In the presence of a catalytic amount of a homogeneous proton 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 polymethylene polyaniline, forming a solution of the methylene diphenylamine isomer and polymethylene polyaniline formed in steps a) and c) in aniline; and

[0019] 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.

[0020] The method of this invention produces a mixture containing a methylene diphenylamine (MDA) isomer and polymethylene polyaniline. Compared to cases where the product is conventionally prepared by reacting formaldehyde and aniline in the presence of HCl, the MDA isomer is rich in the o,p'-isomer. Lewis acid-modified clay catalysts have been found to significantly promote OABA production compared to unmodified clay catalysts, which leads to a greater amount of o,p'-MDA production upon complete rearrangement. Furthermore, complete conversion of aminobenzylaniline to the methylene diphenylamine isomer and polymethylene polyaniline is achieved within commercially reasonable reaction times.

[0021] Another important advantage of this invention is that it can be integrated into conventional industrial-scale production facilities to produce mixtures of methylene diphenylamine isomers and polymethylene polyaniline, which have controlled and adjustable amounts of o,p'-MDA isomers. The solution of aminobenzylaniline, methylene diphenylamine isomers, and 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 aminobenzylaniline to methylene diphenylamine isomers and polymethylene polyaniline can be completed within the conventional process in the presence of a homogeneous catalyst.

[0022] 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:

[0023] A) In the presence of a Lewis acid-modified clay 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 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;

[0024] B) Separate the first solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline with a Lewis acid-modified clay catalyst;

[0025] 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.

[0026] D) Combining a first solution and a second solution of aminobenzylaniline, methylene diphenylamine isomer and polymethylene polyaniline in aniline;

[0027] E) In the presence of a catalytic amount of homogeneous catalyst, a first 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 polymethylene polyaniline, then...

[0028] 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.

[0029] By manipulating the ratio of the first and second solutions of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline combined in step D) in aniline, the o,p'-MDA content of the final product can be adjusted to a predetermined value. This eliminates or reduces the need to enrich the o,p'-isomer content in the distillation product or the polyisocyanate product prepared therefrom.

[0030] 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, 3:1 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 can be carried out in the absence of a homogeneous catalyst, a Lewis acid-modified catalyst as described more fully below, or other catalysts for rearranging the acetalamine to aminobenzylaniline, methylenediphenylamine isomers, 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 acetal. Further rearrangement to aminobenzylaniline is negligible under the reaction conditions that form the acetal. The resulting acetal is then dissolved in an excess of aniline.

[0031] Water is produced as a byproduct of the reaction. Preferably, water (including the reaction byproduct 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 tends to form a separate phase; this can be separated from the liquid organic phase by separation techniques such as decantation. A portion of the water remains in the organic phase, which 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 method 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.

[0032] 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.

[0033] 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 Lewis acid-modified clay 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). A portion, but not all, of the aminobenzylaniline further rearranges to produce methylene diphenylamine isomers (i.e., the p,p'-isomer, the o,p'-isomer, and the o,o'-isomer). Some polymethylene polyaniline is formed during this step.

[0034] Lewis acid-modified clay catalysts include clays with ion exchange capacity treated with Lewis acids, particularly those containing metals or half-metals. Examples of suitable clays include palygorskite clay and montmorillonite clay. The metal or half-metal can be, for example, B, Al, Si, Ti, V, Mn, Fe, Co, Zn, Ga, Ge, Zr, Nb, Tc, Ru, Rh, Ag, Cd, In, Sn, Sb, Hf, Ta, Re, Os, Ir, Pb, or Bi. The Lewis acid can be of formula M... m X n The compound, wherein M is a metal or half-metal including any of the above-listed substances; X is a halogen, preferably fluorine or chlorine, and most preferably chlorine; and n is the valence of M. Specific examples of Lewis acids include AlCl3, FeCl2, TaCl2, MnCl2, ZnCl2, and YbCl3. Any of these Lewis acids may contain hydrated water.

[0035] Clay is conveniently modified by forming a slurry of clay in water or other liquid dispersant and adding a Lewis acid in solid form. This is conveniently carried out at temperatures from 0°C to 40°C, but higher or lower temperatures below the boiling point of water or other dispersant can be used. Conveniently, 0.5 to 50 parts by weight, preferably 1 to 10 parts by weight, of Lewis acid are provided per 100 parts by weight of clay (ignoring the weight of hydration water). The slurry of clay and Lewis acid can be stirred for several minutes to several hours. The thus modified clay is then dehydrated, dried, and, if necessary, ground to produce powder.

[0036] Lewis acid-modified clay catalysts are used in catalytically effective amounts. Suitable amounts 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, more preferred amounts may be at least one part or at least two parts and at most ten parts.

[0037] Step a) is 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 converted in this way.

[0038] The longer the reaction time, the more aminobenzylaniline rearranges to the methylene diphenylamine isomer 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. The preferred reaction time in step a) is 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.

[0039] The higher the temperature during step a), the more "ortho" substances, namely OABA, o,p'-MDA, and o,o'-MDA, are produced, and the more polymethylene polyaniline is produced. Therefore, the temperature at which step a) is performed can be selected to produce larger or smaller amounts of the ortho substances. The ortho substances 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 a specific embodiment, the ortho substances constitute 15% to 50% or 20% to 50% of the combined weight of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline.

[0040] In some embodiments, the temperature during step a) can be from 40°C to 80°C. In other embodiments, the temperature can be from 80°C to 150°C or from 150°C to 250°C.

[0041] Maintain sufficient pressure to prevent the volatilization of aniline, aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline.

[0042] The product of step a) is a solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline. Based on the total weight of aminobenzylaniline, 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 a combination of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline.

[0043] Solutions of aminobenzylaniline, methylene diphenylamine isomers, and polymethylene polyaniline in aniline are separated from a Lewis acid-modified clay 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.

[0044] In step c) of the method of the first aspect, the solution of aminobenzylaniline, 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 isomer and 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 isomer and 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, especially 70°C to 90°C. Sufficient pressure is maintained to prevent the evaporation of the liquid components of the reaction mixture.

[0045] The homogeneous catalyst is liquid and / or soluble in the reaction mixture under the conditions used in step c). 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, and polymethylene polyaniline under the conditions used in step c). A suitable amount of homogeneous proton catalyst is, for example, 0.05 to 1 part per 100 parts by weight of a solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline.

[0046] 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 the method. A small amount of residual aminobenzylaniline may remain. Based on the total weight of the residual aminobenzylaniline (if present), the 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 a combination of methylene diphenylamine isomer and polymethylene polyaniline.

[0047] 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 product mixture of methylene diphenylamine isomers and polymethylene polyaniline. 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.

[0048] The product contains a methylene diphenylamine isomer and a certain proportion of 3-cyclic and higher polymethylene polyaniline. The o,p'-isomer may 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 total weight of the methylene diphenylamine isomer, and up to 75% thereof. In a specific embodiment, 15% to 50% or 20% to 50% of the methylene diphenylamine is the o,p'-isomer. 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%. 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 isomer.

[0049] 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, methylene diphenylamine isomer and polymethylene polyaniline in aniline.

[0050] As previously described, in the first solution of aminobenzylaniline and polymethylene polyaniline, the molar ratio of aminobenzylaniline 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. The ortho-substance 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 in the first solution, and up to 75% thereof. In a specific embodiment, the ortho-substance constitutes 15% to 50% or 20% to 50% of the combined weight of aminobenzylaniline, the methylene diphenylamine isomer, and polymethylene polyaniline in the first solution.

[0051] 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 isolated separately as described above; alternatively, the second solution can be prepared 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).

[0052] 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 a homogeneous catalyst are 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.

[0053] Although a portion of the acetalamine may be present in the second solution of aminobenzylaniline, the methylene diphenylamine 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 combined methylene diphenylamine isomer and polymethylene polyaniline 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.

[0054] 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).

[0055] 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 solution and the second solution can be combined in any ratio. Typically, the proportion of the ortho-substance in the second solution produced in step C) will be 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 solution and the second solution will be between the proportions of the ortho-substance in the first solution and the second solution themselves. Therefore, by selecting the ratio of the first solution and the second solution combined in step D), the content of the ortho-substance can be freely adjusted within a wide range of values. 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 produced in the first solution.

[0056] Therefore, the ortho-substance can constitute at least 10%, at least 15%, at least 20%, at least 25%, or at least 30% of the total weight of aminobenzylaniline and polymethylene polyaniline in the first and second solutions of the combination formed in step D), and constitute up to 75%, up to 50%, or up to 40% thereof. The molar ratio of aminobenzylaniline to 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.

[0057] In step E) of the second aspect of the invention, the first and second solutions of the combined aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline 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 the additional methylene diphenylamine isomer and 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 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.

[0058] Before combining the second solution of aminobenzylaniline 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 proton 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.

[0059] 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 the product. The separation method described with respect to step d) of the first aspect is suitable. The product thus obtained contains the methylene diphenylamine isomer and a certain proportion of polymethylene polyaniline. The o,p-isomer may constitute, for example, at least 10%, at least 15%, at least 20%, at least 25%, or at least 30% of the total weight of the methylene diphenylamine isomer, and up to 75% thereof. In a specific embodiment, 15% to 50% or 20% to 50% of the methylene diphenylamine is the o,p'-isomer. 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%. The p,p'-isomer may constitute up to 85%, up to 80%, up to 75%, up to 70%, up to 65%, up to 60%, or up to 50% of the total weight of the methylene diphenylamine isomer.

[0060] Appendix picture An embodiment of the second aspect of the invention is illustrated schematically. Aniline and formaldehyde are introduced into 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 separation vessel 10 via line 9. Water is removed from the acetalamine solution in separation vessel 10. The partially or completely dehydrated acetalamine solution is transferred to 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 and polymethylene polyaniline (step A). ​​The first solution of aminobenzylaniline and polymethylene polyaniline is removed from reactor 12 via line 14.

[0061] In the illustrated embodiment, the heterogeneous catalyst remains within reactor 12 (e.g., a fixed-bed catalyst), and the first solution of aminobenzylaniline, methylene diphenylamine 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, methylene diphenylamine isomer, and polymethylene polyaniline in aniline, and separated from the first solution in a separate apparatus (not shown) before being combined with the second solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline obtained from step C).

[0062] Aniline is fed into reactor 3 via pipeline 1. Homogeneous catalyst (in the presence of...) pictureThe aniline (represented as HCl) is introduced into the reactor 3 via line 2 and fed together with aniline. Formaldehyde is introduced into the reactor 3 separately via line 4. The reactor 3 is maintained under reaction conditions, and the residence time of the reactants in the reactor 3 is selected such that a portion of the aniline reacts with formaldehyde to form an acetal, which rearranges in the reactor 3 to produce a second solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline in aniline (step C). As previously mentioned, in an alternative embodiment, the acetal can be prepared separately and then combined with a homogeneous catalyst for partial rearrangement. This second solution of aminobenzylaniline, a methylene diphenylamine isomer, and polymethylene polyaniline in aniline is removed from the reactor 3 via line 5. In the illustrated embodiment, the homogeneous proton catalyst introduced into the reactor 3 remains in the second solution removed via line 5.

[0063] 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 into reactor 17 separately. 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 method, a portion of the second solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline may be separately removed from reactor 3 and / or line 5 and combined with the first solution.

[0064] Appendix picture An optional feature includes adding a homogeneous catalyst (again denoted as HCl) to the first solution of aminobenzylaniline, methylene diphenylamine isomer, and polymethylene polyaniline in aniline 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 is introduced into line 5 via line 14, and / or within reactor 17, as conveniently possible.

[0065] Reactor 17 is maintained under reaction conditions to convert aminobenzylaniline in the combined first and second solutions into methylene diphenylamine isomers and 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.

[0066] In large-scale industrial polymethylene polyaniline (PMPA) facilities, acetal formation and / or rearrangement reactions are typically separated into two or more individual 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 PMPA (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 PMPA. 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 in aniline produced in step 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 in aniline is produced using a homogeneous catalyst) and upstream of the last reactor (before aminobenzylaniline is completely converted to methylene diphenylamine isomer and polymethylene polyaniline). 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 in aniline can be introduced at an appropriate location along the length of the tubular reactor.

[0067] 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.

[0068] 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.

[0069] Preparation of modified clay catalysts

[0070] 25 parts of montmorillonite clay (K10, from Sigma-Aldrich) were dispersed in 150 parts of deionized water. 1.316 parts of Lewis acid as indicated in Table 1 were added as a dry powder and stirred at room temperature for one hour; for Example 5, the weight of hydrated water was ignored. The water was then removed under vacuum at 90°C, followed by further drying at 60°C overnight. The resulting solid was then ground into a fine powder.

[0071] Table 1

[0072] Catalyst name Lewis acid A none 1 <![CDATA[FeCl2]]> 2 <![CDATA[TaCl3]]> 3 <![CDATA[MnCl2]]> 4 <![CDATA[ZnCl2]]> 5 <![CDATA[YbCl3·6H2O]]> 6 <![CDATA[AlCl3]]>

[0073] Examples 1 to 6 and Comparative Sample A

[0074] Preparation of acetal amine solution 465.5 g of aniline was cooled to 5 °C in a reactor under a nitrogen atmosphere. 500 g of a 37% formaldehyde aqueous solution (stabilized with 10%-15% methanol) was fed into the aniline over 3 hours with stirring, while maintaining the temperature below 10 °C. The resulting reaction mixture was heated to 20 °C. Stirring was stopped, and the reaction was allowed to settle under nitrogen to separate the aqueous and organic phases. The bottom acetal amine in the aniline phase was removed, mixed with anhydrous sodium sulfate to remove residual water, and filtered. The acetal amine solution contained 1.6% water.

[0075] Acetal rearrangement 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 the catalyst as indicated in Table 2. Fill the vial with nitrogen, seal, and heat at 80°C for 4 hours with stirring. Cool the resulting reaction mixture to 45°C. Remove the sample, filter to remove catalyst particles, and dilute with anhydrous acetonitrile containing 1% nitroanisole as an internal standard. Analyze the OABA, PABA, and MDA isomers of the diluted sample by gas chromatography. Calculate the selectivity for the ortho isomer as (ortho-ABA + o,p'-MDA) ÷ (ortho-ABA + para-ABA + o,p'-MDA + o,o'-MDA + p,p'-MDA), and the results are indicated in Table 2. Determine the conversion percentage (%) and report it in Table 2. A 37% HCl solution was added to the remaining liquid phase, and the resulting reaction mixture was heated at 90°C for 5 hours, at which point all OABA and PABA had been converted into polymethylene polyaniline. Compared to Example A, the MDA moiety of the polyamine in each of Examples 1 to 6 was enriched with the 2,4'-isomer, commensurate with the increase in ortho-substances indicated in Table 2.

[0076] Table 2

[0077] name catalyst ortho-substances% Conversion rate % <![CDATA[A * ]]> A (Unmodified clay) 18.6 69.7 1 <![CDATA[K10 clay modified by FeCl2]]> 29.0 63.2 2 <![CDATA[TaCl3 modified K10 clay]]> 25.1 64.5 3 <![CDATA[K10 clay modified by MnCl2]]> 21.7 63.4 4 <![CDATA[K10 clay modified by ZnCl2]]> 19.9 71.5 5 <![CDATA[YbCl3·6H2O modified clay]]> 28.2 64.0 6 <![CDATA[AlCl3 modified clay]]> 25.6 63.6

Claims

1. A method for producing a mixture of methylene diphenylamine isomer and polymethylene polyaniline, the method comprising: a) In the presence of a Lewis acid-modified clay 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 Lewis acid-modified clay catalyst, and then... c) In the presence of a 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 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, the polymethylene polyaniline, and the aniline formed in steps a) and c) to recover the product 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 by 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 b) 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 Lewis acid is one or more of AlCl3, FeCl2, TaCl2, MnCl2, ZnCl2 and YbCl3.

4. The method according to any one of the preceding claims, wherein the clay is montmorillonite.

5. The method according to any one of the preceding claims, wherein the clay catalyst is modified with 1 to 10 parts by weight of the Lewis acid per 100 parts by weight of the clay.

6. The method according to any one 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 aniline 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 2,4'-MDA isomers based on the total weight of all methylene diphenylamine isomers.

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

9. The method according to any one of claims 1 to 7, wherein step a) is performed at a temperature of 80°C to 150°C.

10. A method for producing a mixture of methylene diphenylamine isomer and polymethylene polyaniline, the method comprising: A) In the presence of a Lewis acid-modified clay 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 Lewis acid-modified clay 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 a homogeneous proton catalyst, the first and second solutions 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 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.

11. The method of claim 10, wherein the solution of acetalamine in aniline is prepared by 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 b) 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.

12. The method according to claim 10 or 11, wherein the Lewis acid is one or more of AlCl3, FeCl2, TaCl2, MnCl2, ZnCl2 and YbCl3.

13. The method according to any one of claims 10 to 12, wherein the clay is montmorillonite.

14. The method according to any one of claims 10 to 13, wherein the clay catalyst is modified with 1 to 10 parts by weight of the Lewis acid per 100 parts by weight of the clay.

15. The method according to claims 10 to 14, 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 aniline obtained from step B), the aminobenzylaniline obtained from step B), the methylene diphenylamine isomer and the polymethylene polyaniline isomer.

16. The method of claim 15, wherein the mixture of methylene diphenylamine isomers and polymethylene polyaniline obtained in step F) contains 15% to 75% by weight of 2,4'-MDA isomers based on the total weight of all methylene diphenylamine isomers.

17. The method according to any one of claims 10 to 16, wherein step A) is performed at a temperature of 40°C to 80°C.

18. The method according to any one of claims 10 to 16, wherein step a) is performed at a temperature of 80°C to 150°C.

19. The method according to any one of claims 10 to 17, wherein the homogeneous catalyst is a proton homogeneous catalyst.

20. The method of claim 19, wherein the homogeneous catalyst is HCl.

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