Method for making polymethylene polyanilines using lewis acid-modified clay catalysts

Abstract

Mixtures of methylene dianiline isomers and polymethylene polyanilines are made with controllable methylene dianiline isomer ratios. Aniline and formaldehyde are reacted to produce N,N'-diphenylmethylene diamine (aminal), which is then partially rearranged to a mixture of aminobenzyl aniline isomers and methylene dianiline isomers in the presence of a Lewis acid-modified clay catalyst. Further rearrangement is performed in the presence of a homogeneous catalyst to convert the remaining aminobenzyl aniline isomers to methylene dianiline and polymethylene polyanilines.

Description

METHOD FOR MAKING POLYMETHYLENE POLYANILINES USING LEWIS ACID-MODIFIED CLAY CATALYSTSThe present invention relates to a method for making polyanilines, in particular methylene dianiline mixtures that contain controllable amounts of the o,p'- isomers.Methylene dianiline (MDA) polyaminopolyphenyl methanes are made in large volumes globally, mainly for use in making polyisocyanates for manufacturing polyurethanes.MDA is almost always made in industrial quantities by reacting aniline with formaldehyde in the presence of a mineral acid such as HCl. Aniline and formaldehyde react to form N,N'-diphenylmethylene diamine (“aminal”), which has the structure:Aminal engages in an acid-catalyzed rearrangement reaction to form a mixture of para-aminobenzyl aniline (PABA) and ortho-aminobenzyl aniline (OABA), which have the structures:(PABA) and (OABA)Further acid-catalyzed rearrangement of PABA produces p,p'-MDA (4,4'-MDA) and o,p'-MDA (2,4'-MDA), whereas further acid-catalyzed rearrangement of OABA produces o,p'-MDA and o,o'-MDA (2,2'-MDA). Some polymethylene polyanilines that have three, four, five or even more rings form along with the MDA isomers. The product stream that is obtained, therefore, is a mixture of MDA isomers and polymethylene polyanilines, which mixture for convenience here is referred to as "pMDA". As used herein, “polymethylene polyanilines" refers specifically to aniline-formaldehyde condensation products that have at least 3 rings, and thus does not include any methylene dianiline isomer.The MDA fraction of the product tends to contain 5 to 12% by weight of o,p'-MDA and a much smaller and usually insignificant amount, in the range of 0.25 to 2% by weight, of o,o'-MDA. The isomer ratio of MDA is unaffected by subsequent phosgenation to produce diphenylmethane diisocyanate (MDI), so the MDI so produced will have the same ratio of 4,4'-, 2,4'- and 2, 2'- isomers as the MDA, i.e., as little as about 5% and as much as about 15% by weight of 2,4'- and 2,2'-MDI isomers combined.There are reasons a higher proportion of the 2,4'-isomer is sometimes wanted in the MDI product. 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 reduces the melting temperature of MDI, again affording process advantages in some cases.2,4'-MDI can be separated from 4,4'-MDI by distillation. This method is used industrially to make MDI products enriched in the 2,4'- isomer such as, for example, 50 / 50 mixture of 4,4'- and 2,4'- MDI. In addition to the product enriched in the 2,4'-isomer, a separate product stream enriched in the 4,4'- isomer is produced. The latter product stream may or may not be wanted in the quantities that are produced, and / or may have lower value. For example, distilling 100 parts of an MDI isomer mixture containing 15% of the 2,4'-isomer produces 30 parts of a product containing a 50 / 50 mixture of the 2,4'-and 4,4'-isomers and more than twice that amount, 70 parts, of pure (or nearly pure) 4,4'-MDI.Less material would need to be distilled, or the distillation step could be eliminated altogether, if more of the o,p'-isomer was made in the MDA manufacturing step. The 2,4'-isomer content of the MDI made by phosgenating that MDI would be correspondingly higher. For example, if the o,p'- isomer content of MDA were increased from 15% to 30%, the phosgenation product would also contain 30% of the o,p'-isomer. The amount of material that would need to be distilled to produce 30 parts of a 50 / 50 mixture of o,p'- and p,p'-MDI would be reduced from 100 parts to only 60 parts, and the amount of pure MDI produced in the distillation would be reduced from 70 to 30 parts.To this end, various methods have been proposed to produce MDA products enriched in the o,p'-isomer. In particular, certain heterogeneous catalysts have been shown to favor greater o,p'-isomer production. US, 4,071,588 describes condensing aniline with formaldehyde using activated acid clays and synthetic silica-alumina and silica-magnesium catalysts. The proportion of the o,p'-isomer produced using these catalysts increases with increasing reaction temperature. Unfortunately, low conversions of aniline to product are obtained, and very large amounts of polymethylene polyanilines are obtained.The first step of forming aminal from aniline and formaldehyde does not require either catalyst or significantly elevated temperatures. Accordingly, it has been proposed to separate aminal formation from the subsequent rearrangement reactions. US 4,039,581 describes reacting aniline with formaldehyde at room temperature in the absence of catalyst to produce amimal. The aminal is recovered and residual water removed before being converted to MDA isomers and polymethylene polyanilines under increasing temperature conditions using attapulgite clay or diatomaceous earth as the catalyst. About 85 to 90% of the product is MDA and at most 21.2% of the MDA is the o,p'-isomer.Similarly, WO 201 / 116419 describes, in a comparative example, condensing aniline with formaldehyde in the presence of a silica-alumina catalyst (MCM-22, from China Catalyst Group). About 85% of the aniline is converted to product in 5 hours, but a very high reaction temperature (150°C) is needed. The product after 5 hours reaction contains 15% by weight polymethylene polyanilines and about 85% MDA. 35% of the MDA is the o,p'- isomer, and 4.2% of the MDA is the o,o'-isomer. Continuing the reaction another 19 hours does not increase conversion, nor does it meaningfully affect isomer ratios of the MDA component of the product. However, slightly more polymethylene polyanilines are obtained. Certain metal-modified zeolite catalysts are shown to reduce o,p'- and o,o'-isomer production, at the cost of lower conversions of aniline to product.In a similar vein, US 2011 / 0021741 describes a process in which aminal is rearranged to methylene dianline and polymethylene polyanilines by heating it in the presence of a silica-alumina catalyst, followed by further conversion at moderate temperatures (60-120°C) in the presence of an ion exchange resin in the acid form. Long reaction times are needed, and only 9-12% of the methylene dianiline fraction of the product is the 2,4'-isomer.This invention is in one aspect a method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprisinga) heating a solution of aminal in aniline to a temperature of 50 to 250°C in the presence of a Lewis acid-modified clay catalyst to convert the aminal in the solution of aminal in aniline to a mixture of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines and produce a solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline;b) separating the solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline from the Lewis acid-modified clay catalyst, thenc) heating the solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogeneous protonic catalyst to convert the aminobenzyl anilines to additional methylene dianiline isomers and polymethylene polyanilines and form a solution of the methylene dianiline isomers and polymethylene polyanilines formed in in steps a) and c) in aniline; andd) separating the methylene dianiline isomers and polymethylene polyanilines formed in steps a) and c) from the aniline to recover the mixture of methylene dianiline isomers and polymethylene polyanilines.The method of the invention produces a that contains methylene dianiline (MDA) isomers polymethylene polyanilines. The MDA isomers are enriched in the o,p'-isomer, compared to the case in which the product is made conventionally by reacting formaldehyde and aniline in the presence of HCl. The Lewis acid-modified clay catalyst has been found to favor the production of OABA more strongly than an unmodified clay catalyst, which upon complete rearrangement leads to the production of greater amounts of o,p'-MDA. In addition, complete conversion of the aminobenzyl anilines to methylene dianiline isomers and polymethylene polyanilines is obtained in commercially reasonable reaction time.Another important advantage of the invention is that it can be integrated into conventional, industrial-scale production facilities to produce mixtures of methylene dianiline isomers and polymethylene polyanilines that have controlled and tunable amounts of the o,p'-MDA isomer. A solution of aminobenzyl aniline, methylene dianiline isomers and polymethylene polyanilines in aniline produced according to step a) of the foregoing method can be fed as a side-stream into the conventional process and conversion of the aminobenzyl anilines to methylene dianiline isomers and polymethylene polyanilines completed within the conventional process in the presence of a homogeneous catalyst.Therefore, in a second aspect, the invention is also a method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprising:A) heating a solution of aminal in aniline to a temperature of 50 to 250°C in the presence of a Lewis acid-modified clay catalyst to convert the aminal in the solution of aminal in aniline into a first mixture of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines and form a first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline;B) separating the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline from the Lewis acid-modified clay catalyst;C) separately producing a second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline by partially rearranging aminal in the presence of a homogenous catalyst;D) combining the first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline;E) heating the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous catalyst to convert the aminobenzyl anilines in the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline to additional methylene dianiline isomers and polymethylene polyanilines and thenF) separating the methylene dianiline isomers and polymethylene polyanilines formed in steps A), C) and E) from the aniline to recover the mixture of methylene dianiline isomers and polymethylene polyanilines.By manipulating the ratios of the first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline combined in step D), the o,p'-MDA content of the final product can be adjusted to predetermined values. This can eliminate or reduce the need to distill the product or a polyisocyanate product made therefrom to enrich the content of the o,p'-isomer.The starting solution of aminal (N,N'-diphenylmethylene diamine) can be produced by reacting an excess of aniline with formaldehyde at a temperature of 0 to 100°C, preferably 0 to 50°C. The mole ratio of aniline to formaldehyde may be, for example, 2:1 to 20:1 3:1 to 20:1 and is preferably 3:1 to 20:1, 3:1 to 15:1, 4:1 to 10:1 or 4:1 to 6:1. This reaction can be and preferably is performed in the absence of a homogeneous catalyst, a Lewis acid-modified catalyst as described more fully below, or other catalyst for the rearrangement of aminal to aminobenzyl amilines methylene dianiline isomers and / or polymethylene polyphenylenes. The formaldehyde can be provided in any convenient form such as formalin or as an aqueous solution. An aqueous solution may contain 30 to 37% formaldehyde by weight and may also be stabilized with methanol or other stabilizer that does not react with aniline under the conditions of the aminal-forming reaction. In the absence of catalyst, formaldehyde reacts with aniline to produce aminal. Further rearrangement to aminobenzyl anilines is negligible under the aminal-forming reaction conditions. The aminal so produced is dissolved in the excess aniline.Water is produced as a by-product of the reaction. Water, including this reaction by-product and water added with the formaldehyde, preferably is removed from the aminal solution until the water content of the solution of aminal in aniline is reduced to no greater 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. Some water remains in the organic phase, this can be partially or entirely removed by addition of a solid desiccant, followed by separating the desiccant with sorbed water from the aminal solution. In some embodiments, the aminal in aniline solution used in step a) of the process contains 0 to 6%, 0 to 5%, 0.25 to 5%, 0.25 to 1.5% or 0.5 to 1.5% by weight water.The aminal in aniline solution may contain, for example, at least 14%, at least 27% or at least 42% by weight, and up to 76% or up to 61% by weight aminal, based on the combined weight of aminal and aniline.In step a), the aminal in aniline solution is heated to a temperature of 50 to 250°C in the presence of a Lewis acid-modified clay catalyst. During this step, a portion of the aminal rearranges to form aminobenzyl aniline isomers, i.e., the para-isomer PABA and the ortho-isomer (OABA). A portion but not all of the aminobenzyl anilines further rearrange to produce methylene dianiline isomers (i.e., the p,p'-, o,p'- and o,o'- isomers). Some polymethylene polyanilines form during this step.The Lewis acid-modified clay catalyst comprises a clay having ion exchange capacity, which is treated with a Lewis acid, in particular a metal- or semi-metal-containing Lewis acid. Examples of suitable clays include attapulgite clay and montmorillonite clay. The metal or semi-metal may 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 may be a compound of the form MmXn, where M is a metal or semi-metal including any of just listed, 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 the Lewis acids may include waters of hydration.The clay is conveniently modified by forming a slurry of the clay in water or other liquid dispersant and adding the Lewis acid as a solid. This is conveniently done at a temperature of 0 to 40°C, although higher or lower temperatures below the boiling temperature of the water or other dispersant can be use. Conveniently, 0.5 to 50 parts by weight, preferably 1 to 10 parts by weight, of the Lewis acid are provided per 100 parts by weight of the clay (ignoring the weight of waters of hydration). The slurry of clay and Lewis acid can be stirred for a period of a few minutes to a few hours. The thus-modified clay is then dewatered, dried and if necessary ground to produce a powder.The Lewis acid-modified clay catalyst is used in a catalytically effective amount. A suitable amount may be, for example 0.1 to 20 parts by weight per 100 parts by weight aminal in aniline solution. A more preferred amount may be at least one part or at least 2 parts and up to 10 parts on the same basis.Step a) is performed for a time period long enough to rearrange at least 90%, preferably at least 95% or at least 99% of the aminal to aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines. All of the aminal may be so converted. Longer reaction times favor more rearrangement of the aminobenzyl anilines to methylene dianiline isomers and polymethylene polyanilines. However, complete rearrangement of the aminobenzyl anilines is generally not feasible under the conditions of step a) under any reasonable reaction time. The rearrangement reaction in step a) may be performed for a period of, for example, 0.5 to 10 hours. A preferred reaction time in step a) is at least 2 hours, at least hours or at least 4 hours and up 8 hours or up to 6 hours. The mole ratio of aminobenzyl anilines to methylene dianiline isomers plus polymethylene polyanilines produced in step a) 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.Higher temperatures during step a) favor greater production of “ortho” species, i.e., OABA, o,p'-MDA and 0,0'-MDA, as well as greater production of polymethylene polyanilines. Thus, the temperature at which step a) is performed may be selected to produce greater or lesser amounts of ortho species. Ortho species 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 combined weight of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines, and as much as 75% thereof. In particular embodiments, ortho species constitute 15 to 50% or 20 to 50% of the combined weight of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines.In some embodiments, the temperature during step a) may be 40 to 80°C. In other embodiments, the temperature may be 80 to 150°C or 150 to 250°C.Adequate pressures are maintained to keep the aniline, aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines from volatilizing.The product of step a) is a solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline. The solution may contain, for example, at least 10%, at least 25% or at least 40% by weight, and up to 80% or up to 65% by weight aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines combined, based on the total weight of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and aniline.The solution of the aminobenzyl anilines, methylene dianiline isomers and the polymethylene polyanilines in aniline is separated from the Lewis acid-modified clay catalyst. Any solid-liquid separation techniques are suitable, including filtration, centrifugation or decantation. In a continuous process using a fixed-bed catalyst, separation can be achieved by removing the solution from the reaction vessel containing the fixed bed catalyst.In step c) of the method of the first aspect, the solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline obtained from step b) is heated to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogeneous catalyst. Under these conditions, the aminobenzyl anilines that remain after step b) rearrange to form additional methylene dianiline isomers and polymethylene polyanilines. The heating in step c) therefore preferably is continued until substantially all (at least 90 weight-%, at least 95 weight-% or at least 99 weight-%) of the aminobenzyl amines remaining after step b) are converted to methylene dianiline isomers and polymethylene polyanilines. The time of reaction may be, for example, at least 0.5 hour, at least 1 hour, at least 2 hours, at least 3 hours or at least 4 hours, and, for example, up to 20 hours, up to 10 hours, up to 8 hours or up to 6 hours. A preferred temperature is 50 to 100°C, especially 70 to 90°C. Adequate pressures are maintained to keep the liquid components of the reaction mixture from volatilizing.The homogenous catalyst is a liquid and / or soluble in the reaction mixture under the conditions employed in step c). Mineral acids are suitable, as are Lewis acids that are liquids or soluble in the reaction mixture. Protonic homogeneous catalysts are preferred; mineral acids, especially HCl, are most preferred. HCl and other mineral acids may be provided in the form of a solution in water or other solvent that does not react with aniline, aminobenzyl anilines, methylene dianilines and polymethylene polyanilines under the conditions employed in step c). A suitable amount of homogenous protic catalyst is, for example, 0.05 to 1 part per 100 parts by weight of the solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline.The product of step c) is a solution of methylene dianiline isomers and polymethylene polyanilines in aniline. The methylene dianiline isomers and polymethylene polyanilines include those formed in both steps a) and c) of the process. Small residual amounts of aminobenzyl anilines may remain. The solution may contain, for example, at least 10%, at least 25% or at least 40% by weight, and up to 80% or up to 65% by weight, methylene dianiline isomers and polymethylene polyanilines combined, based on the total weight of residual aminobenzyl anilines (if any), methylene dianiline isomers, polymethylene polyanilines and aniline.The methylene dianiline isomers and polymethylene polyanilines (including those formed in each of steps a) and c)) are then separated from the aniline to recover a product mixture of methylene dianiline isomers and polymethylene polyanilines. This is conveniently done using methods such as distillation under reduced pressure, solvent crystallization, melt crystallization, solvent extraction, wiped film evaporation and the like, or some combination of any two or more of these methods.The product contains methylene dianiline isomers as well as some proportion of 3-ring and higher polymethylene polyanilines. 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 methylene dianiline isomers, and as much as 75% thereof. In particular embodiments, 15 to 50% or 20 to 50% of the methylene dianiline is the o,p'-isomer. The o,o'-isomer typically constitutes at most 4% of the weight of the methylene dianiline isomer, preferably at most 3% or at most 2.5% thereof. 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 total weight of methylene dianiline isomers.Steps A) and B) of the second aspect of the invention are as described above with regard to steps a) and b) of the first aspect, to produce a first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline.As before, the mole ratio of aminobenzyl anilines to methylene dianiline isomers plus polymethylene polyanilines in the first solution of aminobenzyl anilines and polymethylene polyanilines 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. Ortho species 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 combined weight of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in the first solution, and as much as 75% thereof. In particular embodiments, ortho species constitute 15 to 50% or 20 to 50% of the combined weight of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in the first solution.In step C) of the second aspect, a second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline is produced by rearranging aminal in the presence of a homogeneous catalyst as described above with regard to step c) of the first aspect of the invention. The aminal may be made separately in the manner described before and isolated; alternatively the second solution can be made by reacting an excess of aniline with formaldehyde in the presence of the homogenous catalyst. This second solution is produced separately from the first solution produced in steps A) and B).In certain embodiments, step C) is performed by combining formaldehyde and an excess of aniline in the presence of a homogenous catalyst and subjecting the resulting combination to reaction conditions sufficient to convert a portion of the starting materials to aminobenzyl anilines methylene dianiline isomers and polymethylene polyanilines. The mole ratio of aniline and formaldehyde is conveniently as described above with regard to step a); the homogeneous catalyst and amounts thereof are conveniently as described above with regard to step c). In such embodiments, the aniline, formaldehyde and homogeneous catalyst are combined and subjected to reaction conditions, under which aniline and formaldehyde react to produce aminal and at least some of the aminal rearranges to produce the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines.Although some aminal may be present in the second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines produced in step C), the second solution may contain no amimal or only residual quantities (such as 1% by weight or less) of aminal. The mole ratio of aminobenzyl anilines to methylene dianiline isomers and polymethylene polyanilines combined 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."Ortho" species as described above may constitute, for example, 5 to 15%, especially 8 to 15% of the total weight of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in the second solution produced in step C).In step D) of the second aspect of the invention, the first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline are combined. The first and second solutions can be combined in any ratio. Typically, the proportion of ortho species in the second solution produced in step C) will be lower than the proportion of ortho species in the first solution obtained from step B). In such typical case, the combined first and second solutions will have a proportion of ortho species intermediate to those of the first and second solutions by themselves. Therefore, the content of ortho species can be adjusted freely within a wide range of values through the selection of the ratios of the first and second solutions combined in step D). Further control of the content of ortho species can be achieved by adjusting the content of ortho species produced in the first solution by, for example, manipulation of temperature, reaction time and / or choice of catalyst as described above.Ortho species, therefore, may constitute at least 10%, at least 15%, at least 20%, at least 25% or at least 30% of the total weight of the aminobenzyl anilines and polymethylene polyanilines in the combined first and second solutions formed in step D), and as much as 75%, as much as 50% or as much as 40% thereof. The mole ratio of aminobenzyl anilines to polymethylene polyanilines in the combined first and second solutions formed in step D) 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.In step E) of the second aspect of the invention, the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline are then heated to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous catalyst to convert remaining aminobenzyl anilines to additional methylene dianiline isomers and polymethylene polyanilines. Reaction conditions and catalyst as generally described with regard to step c) of the first aspect of the invention are entirely suitable. The heating preferably is continued until substantially all (at least 90 weight-%, at least 95 weight-% or at least 99 weight-%) of the aminobenzyl amines remaining in the combined first and second solutions are converted to methylene dianiline isomers and polymethylene polyanilines. The time of reaction may be, for example, at least 0.5 hour, at least 1 hour, at least 2 hours, at least 3 hours or at least 4 hours, and, for example, up to 20 hours, up to 10 hours, up to 8 hours or up to 6 hours.It is unnecessary to remove residual catalyst from the second solution of aminobenzyl anilines and polymethylene polyanilines before combining it with the first solution in step D, although it is within the scope of the invention to do so. That residual catalyst can form all or part of the homogeneous catalyst used in step E). Additional homogenous catalyst can be added if necessary or beneficial; this can be added to either or both the first and second solutions before combining them in step D), and / or can be added to the combined solutions formed in step D). Any such additional homogeneous protic catalyst preferably is the same catalyst used in step C) and is most preferably a protonic catalyst such as a mineral acid, most preferably HCl.In step F) of the second aspect, the methylene dianiline isomers and polymethylene polyanilines formed in steps A), C) and E) are separated from the aniline to recover the product. Separation methods as described in regard to step d) of the first aspect are suitable. The product so obtained contains methylene dianiline isomers as well as some proportion of polymethylene polyanilines. 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 methylene dianiline isomers, and as much as 75% thereof. In particular embodiments, 15 to 50% or 20 to 50% of the methylene dianiline is the o,p'-isomer. The o,o'-isomer typically constitutes at most 4% of the weight of the methylene dianiline isomer, preferably at most 3% or at most 2.5% thereof. 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 total weight of methylene dianiline isomers.The Figure schematically illustrates an embodiment of the second aspect of the invention. Aniline and formaldehyde are introduced into reaction vessel 8 via lines 6 and 7, respectively, where they react to form a solution of aminal in excess aniline. The aminal solution is transferred to separation vessel 10 via line 9. Water is removed from the aminal solution in separation vessel 10. The partially or entirely dewatered aminal solution is transferred via line 11 to reactor 12, where the aminal solution is contacted with heterogenous catalyst under reaction conditions as described above to produce a first solution of aminobenzyl anilines and polymethylene polyanilines (Step A). The first solution of aminobenzyl anilines and polymethylene polyanilines is withdrawn from reactor 12 via line 14.In the embodiment shown, heterogeneous catalyst remains within reactor 12 (being a fixed bed catalyst, for example), and the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyamine are separated from the heterogeneous catalyst (Step B) upon being removed from reactor 12. Alternatively, the heterogeneous catalyst can be removed from reactor 12 with the first solution of and separated therefrom in additional apparatus (not shown) before being combined with the second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline obtained from Step C).Aniline is fed into reactor 3 via line 1. Homogeneous catalyst (identified as HCl in the Figure) is introduced into line 1 via line 2 and is fed into reactor 3 together with the aniline. Formaldehyde is separately introduced into reactor 3 via line 4. Reactor 3 is maintained under reaction conditions, the residence time of the reactants within reactor 3 being selected so that the formaldehyde and a portion of the aniline react to form aminal, which rearranges in reactor 3 to produce a second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline (Step C). As before, the aminal in alternative embodiments can be produced separately and then combined with the homogenous catalyst to effect the partial rearrangement. This second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline is withdrawn from reactor 3 via line 5. In the embodiment shown, the homogeneous protic catalyst introduced into reactor 3 remains in the second solution withdrawn via line 5.The first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline are combined (Step D). In the embodiment shown, this is done 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 can be fed separately into reactor 17. Alternatively, a separate mixing apparatus may be present upstream of reactor 17, in which the first and second solutions are combined. Such a separate mixing apparatus may be or include one or more in-line mixing devices, such as one or more static mixers incorporated into line 5. In yet another variation of the process, a portion of the second solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in anilne can be withdrawn separately from reactor 3 and / or line 5, and combined with the first solution.The Figure includes the optional feature of adding homogeneous catalyst (again indicated as being HCl) to the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline, prior to mixing the first and second solutions. This addition of additional catalyst may be omitted or may instead or in addition be done within line 5, upstream or downstream of the point of introduction of the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines into line 5 via line 14, and / or within reactor 17, as may be convenient.Reactor 17 is maintained under reaction conditions to convert the aminobenzyl anilines in the combined first and second solutions to methylene dianiline isomers and polymethylene polyanilines, to produce a solution of methylene dianiline isomers and polymethylene polyanilines in aniline (step E). This solution is transferred via line 18 to second separator 19, where the methylene dianiline isomers and polymethylene polyanilines are separated from aniline (step F). Aniline is withdrawn via line 20 and is preferably recycled into line 1 and / or line 6 (preferably after removing impurities). The methylene dianiline isomers and polymethylene polyanilines are withdrawn from second separator 19 via line 21.In large-scale industrial polymethylene polyaniline facilities, it is common to divide the aminal-forming and / or rearrangement reactions into two or more separate vessels. For example, aniline, formaldedhyde and homogenous catalyst can be combined and partially reacted in a first reaction vessel to produce an intermediate solution that contains aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines (i.e., the rearrangement of aminobenzyl anilines to methylene dianiline isomers and polymethylene polyanilines is not completed). The rearrangement reaction is then continued in one or more downstream vessels to produce the final solution of methylene dianiline isomers and polymethylene polyaniline. An important advantage of this invention is that it is easily and inexpensively incorporated into such a facility. In essence, the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline produced in step B) can be introduced into such a facility as a side-stream at any convenient point downstream of the first reactor (after a mixture of aminobenzyl amines, methylene dianiline isomers and polymethylene polyanilines in aniline is produced using the homogeneous catalyst) and upstream of the last reactor (prior to complete conversion of aminobenzyl amines to methylene dianiline isomers and polymethylene polyamines). In cases in which the reaction in the presence of the homogenous catalyst is performed continuously, as in a tubular reactor, the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline can be introduced at an appropriate point along the length of the tubular reactor.The PMDA product is useful for making polyisocyanates by reaction with phosgene. The polyisocyanate are useful raw materials for making polyurethanes, polyisocyanurates, polyureas and similar polymers.The following examples are provided to illustrate the invention but are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.Preparation of modified clay catalysts25 parts of a montmorillonite clay (K10, from Sigma-Aldrich) are dispersed in 150 parts of deionized water. 1.316 parts of a Lewis acid as indicated in Table 1 are added as a dry powder and stirred in for one hour at room temperature; for Example 5, the weight of waters of hydration is ignored. Water is then removed under vacuum at 90°C, followed by further drying overnight at 60°C. The resulting solid is then ground to a fine powder.Table 1Catalyst DesignationLewis acidANone1FeCl22TaCl33MnCl24ZnCl25YbCl3 6H2O6AlCl3Examples 1-6 and Comparative Sample AProduction of aminal solution: 465.5 g of aniline are cooled to 5°C in a reactor under a nitrogen atmosphere. 500 g of a 37% formaldehyde solution in water (stabilized with 10-15% methanol) are fed into the aniline with stirring over 3 hours while maintaining the temperature below 10°C. The resulting reaction mixture is heated to 20°C. Stirring is discontinued and the reaction is permitted to settle under nitrogen to allow the aqueous and organic phases to separate. The bottom aminal in aniline phase is drained, mixed with anhydrous sodium sulfate to remove residual water and filtered. The aminal solution contains 1.6% water.Aminal rearrangement: 4 parts of the aminal in aniline solution produced as above are added to a 20 mL scintillation vial equipped with a stir bar. 0.2 part of a catalyst as indicated in Table 2 is added. The vial is padded with nitrogen, sealed and heated with stirring for 4 hours at 80°C. The resulting reaction mixture is cooled to 45°C. A sample is removed, filtered to remove catalyst particles and diluted with anhydrous acetonitrile that contains 1% nitroanisole as an internal standard. The diluted sample is analyzed by gas chromatography for OABA, PABA, and MDA isomers. Selectivity to ortho isomers, calculated as (ortho-ABA + o,p'-MDA) ÷ (ortho-ABA + para-ABA + o,p'-MDA + 0,0'-MDA + p,p'-MDA), is calculated, with results as indicated in Table 2. % Conversion is determined and is as reported in Table 2. A 37% HCl solution is added to the remaining liquid phase and the resulting reaction mixture is heated at 90°C for 5 hours, at which time all OABA and PABA has been converted to polymethylene polyanilines. MDA portion of the polyamines in each of Examples 1 to 6 is enriched in 2,4'-isomers, compared to Example A, commensurate with the increase in ortho species indicated in Table 2.Table 2DesignationCatalyst% Ortho Species% ConversionA*A (unmodified clay)18.669.71FeCl2-modified K10 clay29.063.22TaCl3-modified K10 clay25.164.53MnCl2-modified K10 clay21.763.44ZnCl2-modified K10 clay19.971.55YbCl3 6H2O-modified clay28.264.06AlCl3-modified clay25.663.6

Claims

WHAT IS CLAIMED IS:

1. A method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprising:a) heating a solution of aminal in aniline to a temperature of 50 to 250°C in the presence of a Lewis acid-modified clay catalyst to convert the aminal in the solution of aminal in aniline to a mixture of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines and produce a solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines isomers in aniline;b) separating the solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline from the Lewis acid-modified clay catalyst, thenc) heating the solution of the aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogeneous catalyst to convert the aminobenzyl anilines to additional methylene dianiline isomers and polymethylene polyanilines and form a solution of the methylene dianiline isomers and polymethylene polyanilines formed in steps a) and c) in aniline; andd) separating the methylene dianiline isomers polymethylene polyanilines formed in steps a) and c) from the aniline to recover the product mixture of methylene dianiline isomers and polymethylene polyanilines.

2. The method of claim 1 wherein the solution of aminal in aniline is made in a process comprising i) reacting an excess of aniline with formaldehyde in the absence of catalyst at a temperature of 0 to 100°C to produce a solution of aminal in aniline and then b) removing water from the solution of aminal in aniline to reduce the water content of the solution of aminal in aniline to no greater than 6% by weight.

3. The method of claim 1 or 2 wherein the Lewis acid is one or more of AlCl3, FeCl2, TaCl2, MnCl2, ZnCl2 and YbCl3.

4. The method of any preceding claim wherein the clay is a montmorillonite.

5. The method of any preceding claim 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 of any preceding claim wherein ortho species constitute 15 to 75% of the combined weight of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in the solution of the aminobenzyl aniline, methylene dianiline isomers and polymethylene polyanilines isomers in aniline obtained from step b).

7. The method of claim 6 wherein the mixture of methylene dianiline isomers and polymethylene polyaniline obtained in step d) contains 15% to 75% by weight 2,4'-MDA isomer, based on of the total weight of all methylene dianiline isomers.

8. The method of any preceding claim wherein step a) is performed at a temperature of 40 to 80°C.

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

10. A method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprising:A) heating a solution of aminal in aniline to a temperature of 50 to 250°C in the presence of a Lewis acid-modified clay catalyst to convert the aminal in the solution of aminal in aniline into a first mixture of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines and form a first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline;B) separating the first solution of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline from the Lewis acid-modified clay catalyst,C) separately producing a second solution of amionobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline by partially rearranging aminal in the presence of a homogenous catalyst;D) combining the first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline;E) heating the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous protonic catalyst to convert the aminobenzyl anilines in the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in aniline to additional methylene dianiline isomers and polymethylene polyanilines and thenF) separating the methylene dianiline isomers and polymethylene polyanilines formed in steps A), C) and E) from the aniline to recover the mixture of methylene dianiline isomers and polymethylene polyanilines.

11. The method of claim 10 wherein the solution of aminal in aniline is made in a process comprising i) reacting an excess of aniline with formaldehyde in the absence of catalyst at a temperature of 0 to 100°C to produce a solution of aminal in aniline and then b) removing water from the solution of aminal in aniline to reduce the water content of the solution of aminal in aniline to no greater than 6% by weight.

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

13. The method of any of claims 10-12 wherein the clay is a montmorillonite.

14. The method of any of lcaims 10-13 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 of claims 10-14 wherein ortho species constitute 15 to 75% of the combined weight of aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines in the solution of the aminobenzyl aniline, methylene dianiline isomers and polymethylene polyanilines isomers in aniline obtained from step B).

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

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

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

19. The method of any of claims 10-17 wherein the homogeneous catalyst is protonic.

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

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