Method for making methylene dianiline and polymethylene polyanilines using SAPO-18 molecular sieve

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 SAPO-18 molecular sieve. Further rearrangement may be performed in the presence of a homogeneous catalyst to convert the remaining aminobenzyl aniline isomers and any residual aminal to methylene dianiline and polymethylene polyanilines.

Description

86348METHOD FOR MAKING METHYLENE DIANILINE AND POLYMETHYLENE POLYANILINES USING SAPO-18 MOLECULAR SIEVECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and all advantages of U.S. Provisional Patent Application No. 63 / 731,000 filed on 12 December 2024, the content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present invention relates to a method for making polyanilines, in particular methylene dianiline mixtures.

[0003] Methylene dianiline (MDA) and polymethylene polyanilines are made in large volumes globally, mainly for use in making polyisocyanates for manufacturing polyurethanes.

[0004] 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: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). HCI is by far the most common acid catalyst. 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-formaledhyde condensation products that have at least 3 rings. Mixtures of MDI isomers and polymethylene polyphenylene polyisocyanates made by phosgenating pMDA are referred to herein as “pMDI” or “polymeric MDI”.

[0005] The use of HCI or other strong mineral acids has certain drawbacks. The acids are highly corrosive to many metals, so the manufacturing equipment needs to be made of special and highly expensive corrosion-resistant metals. The acid must be neutralized using strong bases. The neutralization step requires large amounts of water and the salts produced present a86348 significant disposal problem. In addition, when the catalyst is HCI, the MDA fraction of pMDA tends to contain the o,p’- and o,o’-isomers within somewhat narrow ranges: 5 to 12% by weight of o,p’-MDA and 0.25 to 2% by weight, of o,o’-MDA. The isomer ratio of the MDA is unaffected by subsequent phosgenation to produce a 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 that is phosgenated, i.e., as little as about 5% and as much as about 15% by weight. Sometimes, higher or lower amounts of 2,4’- and 2,2’-MDI isomers are sometimes wanted. Products having higher or lower amounts of 2,4’- and 2,2’-MDI isomers are usually produced by distilling the MDI to separate it into the various MDI and pMDI products. Distillation on an industrial scale is both capital-intensive and energy-intensive and therefore adds considerable expense. There is also the problem of “balancing” the output of the manufacturing facility to match output to the demand for the various products.

[0006] It has been proposed to replace HCI or other mineral acids with a heterogeneous catalyst. 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. Other heterogeneous catalysts such as cation exchange resins have been found to favor greater 4, 4’-isomer production. 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 pMDA under increasing temperature conditions using attapulgite clay or diatomaceous earth as the catalyst.

[0007] Similarly, WO 2021 / 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. Continuing the reaction another 19 hours does not increase conversion. Certain metal-modified zeolite catalysts are shown to reduce 2,4’- and 2,2’-isomer production, at the cost of lower conversions of aniline to product.

[0008] US 2011 / 0021741 describes a process in which aminal is rearranged to pMDA 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 a cation exchange resin in the acid form.

[0009] Indian Patent No. 200290B describes condensing aniline and formaldehyde using certain molecular sieves. Among these are silica-alumina-phosphates known as SAPO-5 and SAPO-10, which are said to have large to medium-sized pores. This patent reports yields to MDA of 88% and 70.6% for SAPO-5 and SAPO-10, respectively. However very harsh reaction conditions are required, including temperatures as high as 140°C and 160°C, reaction times of over 6 hours and catalyst concentrations are approximately 20% by weight. The product has somewhat higherconcentrations of o,p’- and o,o’-MDA isomers than are normally produced using HCI catalysis; this is likely due to the very high reaction temperatures and long residence times.BRIEF SUMMARY

[0010] Disclosed in one aspect is a method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprising: a) forming a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve; b) heating the reaction mixture at a temperature of 50 to 250°C to convert at least a portion of 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, polymethylene polyanilines and optionally residual aminal in aniline; and c) separating the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline from the SAPO-18 molecular sieve.

[0011] Surprisingly, the SAPO-18 molecular sieve exhibits good catalytic activity even when the aminal rearrangement reaction of step b) is performed at moderate temperatures such as 50 to 120°C or 60 to 100°C. As demonstrated in the following comparative runs and in Indian Patent No. 200290B, other SAPO catalysts either exhibit poor activity or else only produce high conversions of the aminal when the rearrangement reaction is performed under stringent reaction conditions.

[0012] When step b) is performed at the lower reaction temperatures, PABA and p,p’-MDA production is favored. At those lower reaction temperatures, “ortho-species”, i.e., OABA, o,p’- MDA and o,o’-MDA, tend to be produced in lower proportions than is typically seen when HCI is the catalyst. Ortho-species are typically produced in the range of 2 to 6 mole-percent. Thus, the process of the invention is particularly suitable for producing raw materials for the production of MDI mixtures having especially high 4,4’-isomer contents.

[0013] The aminal rearrangement reaction of step b) typically will not go to 100% conversion. Therefore, the product obtained from step b) is a solution that contains aminobenzyl anilines (ortho- and / or para-isomers) and typically residual aminal in addition to MDA and polymethylene polyanilines. It is desirable to obtain complete or nearly complete conversions of the aminal. This can be done in the presence of a homogeneous catalyst such as HCI. Thus, a specific method of the invention further includes a step d) of heating the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline obtained in step c) to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogeneous catalyst to convert residual aminal and the aminobenzyl anilines to additional methylene dianiline isomers and additional polymethylene polyanilines. This specific method hasan important advantage in that it can be integrated into anindustrial-scale production facility that uses a homogeneous catalyst to produce pMDA. A solution of aminobenzyl aniline, MDA and polymethylene polyanilines isomers in aniline produced according to step b) of the foregoing method can be fed as a side-stream into such an industrial-scale process and conversion of the remaining aminal (if any) and aminobenzyl anilines to MDA and polymethylene polyanilines completed within the conventional process in the presence of a homogeneous catalyst.

[0014] Thus, in a second aspect, the invention is a method for producing a mixture of methylene dianiline and polymethylene polyanilines, comprising:A) forming a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve;B) heating a reaction mixture from step A) to a temperature of 50 to 250°C to convert 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, polymethylene polyanilines and optionally residual aminal in aniline;C) separating the first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline from the SAPO-18 molecular sieve,D) separately producing a second solution of aminobenzyl anilines, methylene dinaniline isomers, polymethylene polyanilines and optionally residual aminal in aniline by partially rearranging aminal in the presence of a homogenous catalyst;E) combining the first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline;F) heating the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous catalyst to convert residual aminal and the aminobenzyl anilines in the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline to additional methylene dianiline isomers and additional polymethylene polyanilines and thenG) after step F), separating the methylene dianiline isomers and polymethylene polyanilines formed in steps B), D) and F) from the aniline to recover the mixture of methylene dianiline isomers and polymethylene polyaniline.BRIEF DESCRIPTION OF THE DRAWING

[0015] The invention is described in greater detail below with reference to the accompanying figures, in which Figure 1 schematically illustrates an embodiment of the second aspect of the invention.DETAILED DESCRIPTION

[0016] Disclosed in one aspect is a method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprising: a) forming a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve; b) heating the reaction mixture at a temperature of 50 to 250°C to convert at least a portion of 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, polymethylene polyanilines and optionally residual aminal in aniline; and c) separating the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline from the SAPO-18 molecular sieve.

[0017] Surprisingly, the SAPO-18 molecular sieve exhibits good catalytic activity even when the aminal rearrangement reaction of step b) is performed at moderate temperatures such as 50 to 120°C or 60 to 100°C. As demonstrated in the following comparative runs and in Indian Patent No. 200290B, other SAPO catalysts either exhibit poor activity or else only produce high conversions of the aminal when the rearrangement reaction is performed under stringent reaction conditions.

[0018] When step b) is performed at the lower reaction temperatures, PABA and p,p’-MDA production is favored. At those lower reaction temperatures, “ortho-species”, i.e., OABA, o,p’- MDA and o,o’-MDA, tend to be produced in lower proportions than is typically seen when HCI is the catalyst. Ortho-species are typically produced in the range of 2 to 6 mole-percent. Thus, the process of the invention is particularly suitable for producing raw materials for the production of MDI mixtures having especially high 4,4’-isomer contents.

[0019] The aminal rearrangement reaction of step b) typically will not go to 100% conversion. Therefore, the product obtained from step b) is a solution that contains aminobenzyl anilines (ortho- and / or para-isomers) and typically residual aminal in addition to MDA and polymethylene polyanilines. It is desirable to obtain complete or nearly complete conversions of the aminal. This can be done in the presence of a homogeneous catalyst such as HCI. Thus, a specific method of the invention further includes a step d) of heating the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline obtained in step c) to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogeneous catalyst to convert residual aminal and the aminobenzyl anilines to additional methylene dianiline isomers and additional polymethylene polyanilines. This specific method has an important advantage in that it can be integrated into anindustrial-scale production facility that uses a homogeneous catalyst to produce pMDA. A solution of aminobenzyl aniline, MDA andpolymethylene polyanilines isomers in aniline produced according to step b) of the foregoing method can be fed as a side-stream into such an industrial-scale process and conversion of the remaining aminal (if any) and aminobenzyl anilines to MDA and polymethylene polyanilines completed within the conventional process in the presence of a homogeneous catalyst.

[0020] Thus, in a second aspect, the invention is a method for producing a mixture of methylene dianiline and polymethylene polyanilines, comprising:A) forming a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve;B) heating a reaction mixture from step A) to a temperature of 50 to 250°C to convert 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, polymethylene polyanilines and optionally residual aminal in aniline;C) separating the first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline from the SAPO-18 molecular sieve,D) separately producing a second solution of aminobenzyl anilines, methylene dinaniline isomers, polymethylene polyanilines and optionally residual aminal in aniline by partially rearranging aminal in the presence of a homogenous catalyst;E) combining the first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline;F) heating the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous catalyst to convert residual aminal and the aminobenzyl anilines in the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline to additional methylene dianiline isomers and additional polymethylene polyanilines and thenG) after step F), separating the methylene dianiline isomers and polymethylene polyanilines formed in steps B), D) and F) from the aniline to recover the mixture of methylene dianiline isomers and polymethylene polyaniline.

[0021] In step a) of the first aspect of the invention, a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve is formed. This can be done by producing the aminal in aniline solution separately and combining it with the molecular sieve. Alternatively, the reaction mixture can be formed by producing the aminal in the presence of the molecular sieve.

[0022] A 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, alternatively 0 to 50°C. The mole ratio of aniline to formaldehyde may be, for example 2:1 to 20:1, alternatively 3:1 to 20:1,alternatively 3:1 to 15:1, alternatively 4:1 to 10:1 or 4:1 to 6:1. Although this reaction can be performed in the presence of the SAPO-18 molecular sieve, the reaction is typically performed in the absence of the SAPO-18 molecular sieve or any catalyst for the rearrangement of aminal to aminobenzyl anilines, 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.

[0023] Water is produced as a by-product of the aminal-forming reaction. Water, including this reaction product and water added with the formaldehyde, may be 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 forms a separate phase which can be separated from the liquid organic phase by separation techniques such as decantation. Some water remains in the organic phase. This can be partially or 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 2.0% or 0.5 to 2.0% by weight water.

[0024] 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.

[0025] In step b) of the first aspect of the invention, the aminal in aniline solution is heated to a temperature of 50 to 250°C in the presence of the SAPO-18 molecular sieve. In particular embodiments, the temperature is 50 to 120°C or 60 to 100°C. An advantage of this invention is that good conversions of aminal to aminobenzyl aniline isomers and MDA isomers are obtained under these mild temperature conditions. These lower temperatures also tend to disfavor the production of ortho-species, leading to an MDA product (upon complete rearrangement of the aminal and aminobenzyl aniline) that contains very high proportion of the p,p’-isomer and low proportions of the o,p’- and o,o’-isomers. Ortho-species may comprise, for example 1 to 10 mole- %, 1 to 5 mole-% or 2 to 4 mole-% of the produce obtained in step b). Higher proportions of orthospecies can be obtained by using higher reaction temperatures in step b).

[0026] Adequate pressures are maintained during step b) to keep the aniline, residual aminal (if any), aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines from volatilizing.

[0027] The SAPO-18 molecular sieve is a silica-alumina-phosphate having an AEI framework topology. Its composition corresponds to about 35-45 weight percent AI2O3, 45-50 weight percentP2O5 and 10-15 weight percent SiO2, with up to 0.5% of trace impurities. The SAPO-18 molecular sieve can be prepared according to methods such as described by Chen et al. in Catalyst Leters vol. 28, pp. 241-248 (1994). SAPO-18 molecular sieves are also commercially available from sources such as Zeolyst International (Kansas City, Kansas, US).

[0028] The SAPO-18 molecular sieve 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 specific amount may be at least one part or at least 2 parts and up to 10 parts on the same basis. It is typically calcined or otherwise dried to remove residual water and other volatiles before use.

[0029] During step b), at least 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 MDA isomers (i.e., the p,p’-, o,p’- and o,p’- isomers). Some polymethylene polyanilines may be formed during this step.

[0030] Step b) may be performed for a time long enough to rearrange at least 30%, alternatively at least 40% or at least 50% of the aminal to aminobenzyl anilines, methylene dianiline isomers and polymethylene polyanilines. Longer reaction times favor more rearrangement of the aminobenzyl anilines to MDA and polymethylene polyanilines. However, complete rearrangement of the aminobenzyl anilines is generally not feasible under the conditions of step b) under any reasonable reaction time. The rearrangement reaction in step b) may be performed for a period of, for example, 0.5 to 10 hours. A typical reaction time in step a) is at least 2 hours, at least 3 hours or at least 4 hours and up 8 hours or up to 6 hours.

[0031] The product of step b) is a solution of aminobenzyl anilines, various methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal 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, residual aminal (if any) and aniline.

[0032] Steps a) and / or b) may be conducted batch-wise or continuously, as convenient.

[0033] In step c) of the first aspect of the invention, the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline obtained in step b) is separated from the SAPO-18 molecular sieve. This can be performed using any convenient solid-liquid separation method such as decantation, filtering, centrifugation or the like. 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.

[0034] The thus-recovered solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline can be further processed in various ways. The methylene dianiline and polymethylene polyanilines can be separated fromthe aniline, OABA, PABA and any residual aminal, 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. OABA, PABA and any residual aminal may be recycled into steps a) and / or b) for further rearrangement. Aniline may be recycled into steps a) or b), or into an upstream step of condensing aniline and formaldehyde.

[0035] In certain aspects, however, the solution obtained from step c) is subjected to further rearrangement reactions in the presence of a homogeneous catalyst, i.e., step d) as mentioned above. In such a step d), the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline obtained from step c) is heated to a temperature of 50 to 150°C in the presence of a catalytic amount of the homogeneous catalyst. Under these conditions, residual aminal and the aminobenzyl anilines that remain after step b) rearrange to form additional methylene dianiline isomers and / or polymethylene polyanilines. The heating in step d) therefore may be continued until substantially all (at least 90 weight-%, at least 95 weight-% or at least 99 weight-%) of the residual aminal and aminobenzyl amines remaining after step b) are converted to methylene dianiline isomers and / or 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 typical 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.

[0036] The homogenous catalyst is a liquid and / or soluble in the reaction mixture under the conditions employed in step d). Mineral acids are suitable, as are Lewis acids that are liquids or soluble in the reaction mixture. Protonic homogeneous catalysts are typical; mineral acids, especially HCI, are most common utilized. HCI 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 dianiline isomers or polymethylene polyanilines under the conditions employed in step d). A suitable amount of homogenous catalyst is, for example, 0.05 to 1 part per 100 parts by weight of the solution obtained in step c).

[0037] The product of step d) 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 b) and d) of the process. Small residual amounts of aminobenzyl anilines may remain. Residual aminal is present, if at all, in very small amounts. 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, based on the total weight of residual aminobenzyl anilines (if any), methylene dianiline isomers, polymethylene polyanilines and aniline.86348

[0038] In embodiments in which step d) is performed, the methylene dianiline isomers and polymethylene polyanilines (including those formed in each of steps b) and d) are then separated from the aniline (step e). 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 obtained after step e) of the process is a mixture of methylene dianiline isomers and polymethylene polyanilines.

[0039] Steps A), B) and C) of the second aspect of the invention are as described above with regard to steps a), b) and c), respectively, of the first aspect, to produce a first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline.

[0040] In step D) of the second aspect of the invention, a second solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline is produced by rearranging aminal (the “second solution”) 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 in a separate step, in the absence of the homogeneous catalyst or other aminal rearrangement catalyst, prior to performing rearrangement step D), in the manner described above; alternatively the second solution can be produced 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 obtained from step C).

[0041] In certain embodiments, step D) 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 are conveniently as described above; the homogeneous catalyst and amounts thereof are conveniently as described above with regard to step d) above. In such embodiments, the aniline, formaldehyde and homogeneous catalyst may be 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.

[0042] Although some aminal may be present in the second solution produced in step D), 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 plus polymethylene polyanilines produced 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.

[0043] “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, -IQ-86348 polymethylene polyanilines and optionally residual aminal in the second solution produced in step D).

[0044] In step E) of the second aspect of the invention, the first and second solutions obtained from steps C) and D), respectively, 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 D) will be different (either higher or lower) than the proportion of ortho species in the first solution obtained from step C). 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 E). The proportion of ortho species in the first solution from step C) is in some embodiments greater than the proportion of ortho species in the second solution produced in step D). Alternatively, the proportion of ortho species in the first solution from step C) is less than or equal to than the proportion of ortho species in the second solution produced in step D). Similarly, the proportion of polymethylene polyanilines in the first solution from step C) may be greater than, less than or the same as the proportion of polymethylene polyanilines in the second solution produced in step D).

[0045] Ortho species, therefore, may constitute as little as about 2% and as much as 75% of the total weight of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in the combined first and second solutions formed in step E). The mole ratio of aminobenzyl anilines to methylene dianiline isomers plus polymethylene polyanilines in the combined first and second solutions formed in step E) 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.

[0046] In step F) of the second aspect of the invention, the combined first and second solutions are then heated to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous catalyst to convert residual aminal and any remaining aminobenzyl anilines to additional methylene dianiline isomers and / or additional polymethylene polyanilines. Reaction conditions and catalyst as generally described with regard to optional step d) of the first aspect of the invention are entirely suitable. The heating may be continued until substantially all (at least 90 weight-%, at least 95 weight-% or at least 99 weight-%) of the residual aminal and aminobenzyl amines remaining in the combined first and second solutions are converted to methylene dianiline isomers and / or 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.

[0047] It is unnecessary to remove residual homogeneous catalyst from the second solution produced in step D) before combining it in step E with the first solution, although it is within the scope of the invention to do so. That residual catalyst can form all or part of the homogeneous86348 catalyst used in step F). 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 E), and / or can be added to the combined solutions formed in step E). Any such additional homogeneous catalyst may be the same catalyst used in step D) and is most typically a protonic catalyst such as a mineral acid, e.g. HCL

[0048] In step G) of the second aspect, the methylene dianiline isomers and polymethylene polyanilines formed in steps B), D) and F) are separated from the aniline to recover a mixture of methylene dianiline isomers and polymethylene polyanilines. Separation methods as described above are suitable. The product so obtained contains methylene dianiline isomers as well as some proportion of polymethylene polyanilines. The o,p’-MDA isomer may constitute, for example, at least 1%, at least 2%, at least 3%, at least 4% or at least 5% of the total weight of methylene dianiline isomers, and as much as 75%, as much as 50%, as much as 25%, as much as 20% or as much as 15% thereof. The o,o’-isomer typically constitutes at most 3% of the weight of the methylene dianiline isomers, alternatively at most 2% or at most 1.5% thereof. The p,p’- isomer may constitute up to 99%, up to 98%, up to 97%, up to 95%, up to 90%, up to 87%, up to 80%, up to 60%, up to 50%, up to 40% or up to 30% of the total weight methylene dianiline isomers.

[0049] Figure 1 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 the SAPO-18 molecular sieve under reaction conditions as described above to produce a first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline (Step B). The first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal is withdrawn from reactor 12 via line 14.

[0050] In the embodiment shown, the SAPO-18 molecular sieve remains within reactor 12 (being a fixed bed catalyst, for example), and the first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal are separated from the homogeneous catalyst (Step C) upon being removed from reactor 12. Alternatively, the SAPO-18 molecular sieve can be removed from reactor 12 with the first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal and separated therefrom in additional apparatus (not shown) before being combined with the second solution produced in step D).

[0051] Aniline is fed into reactor 3 via line 1 . Homogeneous catalyst (identified as HCI in Figure 1) is introduced into line 1 via line 2 and is fed into reactor 3 together with the aniline.86348Formaldehyde 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 (Step D). 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 is withdrawn from reactor 3 via line 5. In the embodiment shown, the homogeneous catalyst introduced into reactor 3 remains with the second solution withdrawn via line 5.

[0052] The first and second solutions obtained from steps C) and D) are combined (Step E). 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 of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal 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 can be withdrawn separately from reactor 3 and / or line 5, and combined with the first solution obtained from step C).

[0053] Figure 1 includes the optional feature of adding homogeneous catalyst (again indicated as being HCI) to the first solution, 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 into line 5 via line 14, and / or within reactor 17, as may be convenient.

[0054] Reactor 17 is maintained under reaction conditions to convert any residual aminal and 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 F). This solution is transferred via line 18 to second separator 19, where the methylene dianiline isomers and polymethylene polyanilines are separated from aniline (step G). Aniline is withdrawn via line 20 and may be recycled into line 1 and / or line 6 (typically after removing impurities). The methylene dianiline isomers and polymethylene polyanilines are withdrawn from second separator 19 via line 21.

[0055] In large-scale industrial pMDA production facilities that use a homogeneous catalyst, it is common to divide the aminal-forming and / or rearrangement reactions into two or more separate vessels. For example, aniline, formaldehyde 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, polymethylene polyanilines and optionally residual aminal (J.e., the rearrangement of aminobenzyl anilines to methylene dianiline isomers86348 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 polyanilines. An important advantage of this invention is that it is easily and inexpensively incorporated into such a facility. In essence, the first solution obtained from step C) 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, polymethylene polyanilines and optionally residual aminal is produced using the homogeneous catalyst) and upstream of the last reactor (prior to complete conversion of any residual aminal and 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 can be introduced at an appropriate point along the length of the tubular reactor.

[0056] 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.

[0057] 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.Examples 1-3 and Comparative Runs A -D

[0058] Production of aminal solution: 5 moles of aniline are cooled to 5°C in a reactor under a nitrogen atmosphere. 1 mole of formaldehyde (provided as a 37% solution in water and methanol) is fed into the aniline over three hours with stirring 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 over 5 hours 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 resulting aminal solution contains 1.6% water by weight by Karl-Fischer titration.

[0059] General aminal rearrangement procedure: 0.15 g of catalyst (as described below) is added to a 20 mL scintillation vial equipped with a stir bar. 4 g of the aminal in aniline solution produced above are added. The vial is padded with nitrogen and sealed. The vial and its contents are heated at 80°C with stirring for 4 hours and then cooled and filtered to remove the catalyst. The liquid phase is evaluated by gas chromatography for aniline, PABA, OABA, p,p’-MDA, o,p’- MDA and o,o’-MDA. The relative areas under the peak corresponding to each of these species are as indicated in Table 1. The % conversion of aminal to PABA, OABA, p,p’-MDA, o,p’-MDA and o,o’-MDA combined is estimated from the peak areas. Any unreacted aminal decomposes to produce aniline under the conditions of the gas chromatography; the area of aniline peak includes aniline regenerated in this way.86348

[0060] For Comparative Sample A, the catalyst is a SAPO-34 catalyst obtained from China Catalyst Holding Co., Ltd. (product ID CCG04Z05), which is calcined under air at 550°C for 2 hours. X-ray fluorescence indicates the composition of the calcined catalyst corresponds to about 42.4% AI2O3, 51.0% P2O5 and 5.4% SiO2, with trace amounts of impurities. This catalyst has CHA topology.

[0061] For Comparative Sample B, the catalyst is a second sample of SAPO-34 catalyst obtained from China Catalyst Holding Co., Ltd. (product ID CCG04Z06), which is calcined under air at 550°C for 2 hours. X-ray fluorescence indicates the composition of the calcined catalyst corresponds to about 43.4% AI2O3, 51.5% P2O5 and 5.1% SiO2, with trace amounts of impurities. This catalyst has CHA topology.

[0062] For Comparative Sample C, the catalyst is a SAPO-34 catalyst obtained from Zeolyst (product ID ZD07005), which is calcined under air at 550°C for 2 hours. X-ray fluorescence indicates the composition of the calcined catalyst corresponds to about 42.4% AI2O3, 48.2% P2O5 and 9.3% SiO2, with trace amounts of impurities. This catalyst has CHA topology.

[0063] For Comparative Sample D, the catalyst is a SAPO-35 catalyst obtained from Zeolyst (product ID ZD17003), which is calcined under air at 550°C for 2 hours. X-ray fluorescence indicates the composition of the calcined catalyst corresponds to about 43.9% AI2O3, 44.8% P2O5 and 11.2% SiO2, with trace amounts of impurities. This catalyst has LEV topology.

[0064] For Example 1 , the catalyst is a SAPO-18 catalyst obtained from Zeolyst (product ID ZD19018), which is calcined under air at 550°C for 2 hours. X-ray fluorescence indicates the composition of the calcined catalyst corresponds to about 40.3% AI2O3, 47.6% P2O5 and 12.0% SiO2, with trace amounts of impurities. This catalyst has AEI topology.Table 186348‘Comparative.

[0065] As the data in Table 1 show, the SAPO-34 and SAPO-35 catalysts only provide very low conversions of aminal to ABA and MDA. The SAPO-18 catalyst produces a conversion of almost 55% under these reaction conditions. All the SAPO-catalysts are highly selective for the paraspecies (PABA and p,p’-MDA) under these reaction conditions.

Claims

86348WHAT IS CLAIMED IS1. A method for producing a mixture of methylene dianiline isomers and polymethylene polyanilines, comprising: a) forming a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve; b) heating the reaction mixture at a temperature of 50 to 250°C to convert at least a portion of 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, polymethylene polyanilines and optionally residual aminal in aniline; and c) separating the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline from the SAPO-18 molecular sieve.

2. The method of claim 1 wherein the temperature in step b) is 50 to 120°C.

3. The method of claim 1 wherein the temperature in step b) is 60 to 100°C.

4. The method of any preceding claim wherein the reaction mixture formed in step a) contains 1 to 10 parts of the SAPO-18 molecular sieve per 100 parts by weight of aminal in aniline solution.

5. The method of any preceding claim wherein step a) includes a step of condensing aniline and formaldehyde in the presence of the SAPO-18 molecular sieve.

6. The method of any of claims 1-4 further comprising, prior to step a), a step of i) reacting an excess of aniline with formaldehyde in the absence of catalyst at a temperature of 0 to 100°C to produce the solution of aminal in aniline and then ii) 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.

7. The method of preceding claim, further comprising the steps of: d) heating the solution of the aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline obtained in step c) to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogeneous catalyst to convert residual aminal and the aminobenzyl anilines to additional methylene dianiline isomers86348 and additional polymethylene polyanilines and form a solution of the methylene dianiline isomers and polymethylene polyanilines formed in in steps b) and d) in aniline; and e) separating the methylene dianiline isomers and polymethylene polyanilines formed in steps b) and d) from the aniline to recover a mixture of methylene dianiline isomers and polymethylene polyaniline.

8. A method for producing a mixture of methylene dianiline and polymethylene polyanilines, comprising:A) forming a reaction mixture comprising a solution of aminal in aniline and a SAPO-18 molecular sieve;B) heating a reaction mixture from step A) to a temperature of 50 to 250°C to convert 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, polymethylene polyanilines and optionally residual aminal in aniline;C) separating the first solution of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline from the SAPO-18 molecular sieve,D) separately producing a second solution of aminobenzyl anilines, methylene dinaniline isomers, polymethylene polyanilines and optionally residual aminal in aniline by partially rearranging aminal in the presence of a homogenous catalyst;E) combining the first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline;F) heating the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally residual aminal in aniline to a temperature of 50 to 150°C in the presence of a catalytic amount of a homogenous catalyst to convert residual aminal and the aminobenzyl anilines in the combined first and second solutions of aminobenzyl anilines, methylene dianiline isomers, polymethylene polyanilines and optionally aminal in aniline to additional methylene dianiline isomers and additional polymethylene polyanilines and thenG) after step F), separating the methylene dianiline isomers and polymethylene polyanilines formed in steps B), D) and F) from the aniline to recover the mixture of methylene dianiline isomers and polymethylene polyanilines.

9. The method of claim 8 wherein the temperature in step B) is 50 to 120°C.

10. The method of claim 8 wherein the temperature in step C) is 60 to 100°C.11 . The method of any of claims 8-10 wherein the reaction mixture formed in step A) contains 1 to 10 parts of the SAPO-18 molecular sieve per 100 parts by weight of aminal in aniline solution.

12. The method of any of claims 8-11 wherein step A) is performed by condensing aniline and formaldehyde in the presence of the SAPO-18 molecular sieve.

13. The method of any of claims 8-11 wherein step A) is performed by i) reacting an excess of aniline with formaldehyde in the absence of catalyst at a temperature of 0 to 100°C to produce the solution of aminal in aniline and then ii) 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.

14. The method of any of claims 8-13 wherein the homogeneous catalyst is protonic.

15. The method of claim 14 wherein the homogeneous catalyst is HCI.

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