Process for preparing an aromatic polyamine mixture

Abstract

A process for preparing an aromatic polyamine mixture including 4,4′-methylenedi(phenylamine) and higher homologues of MDA is provided. The process includes steps of (i) reaction of aniline with formaldehyde by means of an acid catalyst to form a crude product mixture (I), (ii) neutralization of the crude product mixture (I) and removal of the salts formed; (iii) isolation of aniline; (iv) distillation of the resulting crude product mixture so as to separate off (iv-1) a mixture (II) of MDA isomers (II-1) containing from 8 to 20% by weight of 4,4′-methylenedi(phenylamine) and not more than 0.3% by weight of secondary components (II-2) and (iv-2) a low boiler mixture of at least 55% by weight of secondary components (II-2) and MDA isomers (II-1); and (v) recirculation of the mixture (II).

Claims

1. A process for preparing an aromatic polyamine mixture comprising 4,4′-methylenedi(phenylamine) and higher homologues of methylenedi(phenylamine), the process comprising (i) reacting aniline with formaldehyde in the presence of an acid catalyst to form a crude product mixture (I) in a plant which comprises a mixing zone (a), a condensation zone (b), a rearrangement zone (c) and optionally an after-reaction zone (d); (ii) neutralizing the crude product mixture (I) obtained in (i) and removing salts thus formed, to obtain a crude product mixture (II); (iii) separating aniline from the crude product mixture (II) obtained in (ii), to obtain separated aniline and a crude product mixture (III), and optionally recirculating the separated aniline to the mixing zone (a); then (iv) distilling the crude product mixture (III) obtained in (iii) wherein the distilling comprises (iv-1) isolating a mixture (II) consisting of methylenedi(phenylamine) isomers (II-1) and secondary components (II-2) which are different therefrom, where, based on (II-1), a proportion of 4,4′-methylenedi(phenylamine) is from 8 to 20% by weight and, based on (II), a proportion of secondary components (II-2) is not more than 0.3% by weight, and (iv-2) isolating a low boiler mixture which consists of secondary components (II-2) and methylenedi(phenylamine) isomers (II-1) and in which a proportion of the secondary components (II-2) is at least 55% by weight; and (v) recirculating the mixture (II) to one of the zones (a) to (d), wherein the aromatic polyamine mixture has a content of 4,4′-methylenedi(phenylamine) and higher homologues of methylenedi(phenylamine) of greater than 85% by weight.

2. The process according to claim 1, wherein, in the distilling (iv), the isolating (iv-2) is carried out simultaneously with the isolating (iv-1) in a column having a dividing wall or a side stream offtake.

3. The process according to claim 1, wherein, in the distilling (iv), the isolating (iv 2) is effected from an overhead stream from a first distillation column, a bottom stream obtained is fed to a further successive distillation column and the mixture (II) is separated off from the overhead stream from the further distillation column.

4. The process according to claim 1, wherein a dividing wall or side stream column which has from 2 to 15 theoretical plates in an upper region between a side stream and an overhead stream and from 10 to 20 theoretical plates in a lower region between a bottom stream and the side stream is used for the distilling (iv).

5. The process according to claim 1, wherein the distilling (iv) is carried out in a first distillation column having from 2 to 15 theoretical plates for the isolating (iv-2) and a further distillation column having from 10 to 20 theoretical plates for the isolating (iv-1).

6. The process according to claim 1, wherein the distilling (iv) is carried out at a pressure at a top of a distillation column of from 1 to 10 mbar and a temperature of from 120 to 210° C. for separating off the low boiler mixture and a side stream pressure of from 1 to 10 mbar and a temperature of from 170 to 230° C. for separating off the mixture (II).

7. The process according to claim 5, wherein, in the first distillation column, the distilling (iv) is carried out at a pressure at a top of the first distillation column of from 1 to 10 mbar and at a temperature of from 120 to 210° C., and in the further distillation column, the distilling (iv) is carried out at a pressure at a top of the further distillation column of from 1 to 10 mbar and at a temperature of from 170 to 230° C.

8. The process according to claim 1, wherein the low boiler mixture is discharged from the process.

9. The process according to claim 1, wherein the mixture (II) is recirculated to the mixing zone (a).

10. The process according to claim 1, wherein the aromatic polyamine mixture is separated as a bottom stream from a column in the distilling (iv).

Description

(1) FIG. 1 illustrates a preferred embodiment of the process of the invention.

(2) In the FIGURE, the reference numerals have the following meanings: 1 Mixing zone (a) 2 Condensation zone (b) 3 Rearrangement zone (c) 4 After-reaction zone (d) 5 Work-up zone (e) 6 Distillation column(s) 7 Introduction of aniline in admixture with catalyst 8 Introduction of formaldehyde 9 Discharge of 4,4′-MDA and higher homologues of MDA 10 Recirculation of the mixture (II) composed of 2,2′-MDA, 2,4′-MDA and 4,4′-MDA 11 Isolation of low boilers 12 Discharge of water and salts 13 Recirculation of aniline

(3) According to FIG. 1, the mixture (II) comprising 2,2′-MDA, 2,4′-MDA and 4,4′-MDA which has been separated off is recirculated 10 and mixed with aniline 7, to which an acid catalyst has been added, and formaldehyde 8 in a mixing zone (a) 1. A mixing chamber of a reaction mixing pump or a nozzle, which are located upstream of the condensation zone (b) 2, are preferably used here so that complete mixing occurs very rapidly. Rapid mixing decreases undesired parallel reactions.

(4) A tube reactor or stirred reactor here represents, for example, a reaction zone which comprises a condensation zone (b) 2, a rearrangement zone (c) 3 and an after-reaction zone (d) 4. Aniline 7 or aniline hydrochloride is usually initially charged and a formalin solution 8 is fed in. The introduction can be effected directly into the reaction vessel or via a suitable mixing unit. In general, a suitable temperature profile is subsequently applied. After the condensation and rearrangement reactions, the reactor is emptied and the crude product is subsequently worked up. In a work-up zone (e) 5, the neutralization of the crude product and the discharge of water and salts 12 and also the isolation of aniline are carried out. The aniline which has been separated off is recirculated 13 to the mixing zone (a) 1. The crude product is then fed to a distillation in a distillation column 6. Here, the low boilers 11 are separated off. The mixture (II) composed of 2,2′-MDA, 2,4′-MDA and 4,4′-MDA which has been separated off is recirculated 10 to the mixing zone (a) 1 and the product composed of 4,4′-MDA and higher homologues of MDA is discharged 9.

(5) The present invention is illustrated by the following examples.

EXAMPLES

(6) Example 1 which is not according to the invention:

(7) Recirculation of a 2,2′-/2,4′- and 4,4′-MDA isomer mixture, obtained by isolation by means of a distillation column having 40 theoretical plates, into the mixing zone (a) of an MDA plant as per FIG. 1 without prior isolation of a low boiler stream comprising secondary components formed

(8) 625 g of aniline (purity >99%) and 19 g of a recycle stream as per tab. 2 were placed in a stirred vessel and 131 g of a 32% strength hydrochloric acid were added thereto. 213 g/h of a 35.5% strength formalin solution were continuously mixed in at 60° C. over a period of 1 hour by means of a mixing pump. The mixing pump is located in the pumped circuit of the mixing vessel. The pump circulation was 25 l/h. After one hour, the introduction of formalin was stopped and the reaction mixture was heated to 90° C. and circulated by pumping for another 1.5 hours. The pump circulation was subsequently stopped and the reaction mixture was heated to 120° C. and dispersed further for 2 hours.

(9) The fully reacted reaction mixture was cooled to 80° C. and then neutralized with aqueous sodium hydroxide solution (25% by weight). After the aqueous phase has been separated off, the organic phase is washed with water and the aniline is subsequently distilled off on a rotary evaporator at 1 mbar and an oil bath temperature of 100° C.

(10) Table 1 shows the product composition after the work-up zone (e):

(11) TABLE-US-00001 TABLE 1 2,2-MDA % by weight 0.6 2,4-MDA % by weight 9.4 4,4-MDA % by weight 59.1 3-ring MDA % by weight 20.3 4-ring MDA % by weight 5.6 N-Methyl-MDA % by weight 0.120

(12) The proportion of secondary components having a boiling point equal to or greater than that of aniline and less than that of 2,2″-MDA in the product mixture as per tab. 1 was about 500 ppm.

(13) To separate off the 2,2′-/2,4′- and 4,4′-MDA recycle stream, the product mixture as per tab. 1 was fed at plate 20 into a distillation column having 40 theoretical plates. At a pressure at the top of 10 mbar and a temperature at the top of 224° C., a recycle stream having the following composition was obtained at the top of the column at a reflux ratio of 9 g/g:

(14) TABLE-US-00002 TABLE 2 2,4′-MDA 73.5% 2,2′-MDA 11.5% 4,4′-MDA 13.9% Sum of secondary components 1.1%

(15) The composition of this recycle stream corresponds to the composition of the recycle stream which was introduced into the mixing zone (a) at the beginning of the experiment.

(16) The product mixture obtained at the bottom of the column has the following product composition:

(17) TABLE-US-00003 TABLE 3 2,2-MDA % by weight 0.07 2,4-MDA % by weight 6.5 4,4-MDA % by weight 61.2 3-ring MDA % by weight 21.3 pMDA % by weight 10.8 N-Methyl-MDA % by weight 0.125

(18) Example 1 according to the invention:

(19) Recirculation of a 2,2′-/2,4′- and 4,4′-MDA isomer mixture, obtained by isolation by means of a first distillation column and a second distillation column having 8 and 15, respectively, theoretical plates, into the mixing zone (a) of an MDA plant as per FIG. 1 with prior isolation of a low boiler stream comprising secondary components formed and discharge of the low boiler stream from the process

(20) 720 g of aniline (purity>99%) and 19 g of a recycle stream as per tab. 5 were placed in a stirred vessel and 154 g of a 32% strength hydrochloric acid were added thereto. 253 g/h of a 35.5% strength formalin solution were continuously mixed in at 60° C. over 1 hour by means of a mixing pump. The mixing pump is located in the pumped circuit of the mixing vessel. The pumped circulation was 25 l/h. After 1 hour, the introduction of formalin was stopped and the reaction mixture was heated to 90° C. and circulated by pumping for another 1.5 hours. The pumped circulation was subsequently stopped and the reaction mixture was heated to 120° C. and dispersed further for 2 hours.

(21) The fully reacted reaction mixture was cooled to 80° C. and then neutralized with aqueous sodium hydroxide solution (25% by weight). After the aqueous phase has been separated off, the organic phase is washed with water and the aniline is subsequently distilled off in a rotary evaporator at 1 mbar and an oil bath temperature of 100° C.

(22) Table 4 shows the product composition after the work-up zone (e):

(23) TABLE-US-00004 TABLE 4 2,2-MDA % by weight 0.4 2,4-MDA % by weight 8.8 4,4-MDA % by weight 59.5 3-ring MDA % by weight 21.4 4-ring MDA % by weight 6.6 N-Methyl-MDA % by weight 0.096

(24) The proportion of secondary components having a boiling point equal to or greater than that of aniline and less than that of 2,2′-MDA in the product mixture as per tab. 4 was about 500 ppm.

(25) To separate off the 2,2′-/2,4′- and 4,4′-MDA recycle stream, the product mixture as per tab. 4 was fed at plate 5 into a first distillation column having 8 theoretical plates. At a pressure at the top of 2 mbar and a temperature at the top of 152° C., a low boiler stream having a content of secondary components of 86% was obtained at a reflux ratio of 150 g/g and discharged from the process.

(26) The product stream obtained at the bottom of the first column is fed at plate 10 into a second distillation column having 15 theoretical plates. At a pressure at the top of 5 mbar and a temperature at the top of 207° C., a recycle stream having the following composition is obtained at the top of the column at a reflux ratio of 26 g/g:

(27) TABLE-US-00005 TABLE 5 2,4′-MDA 75.5% 2,2′-MDA 11.8% 4,4′-MDA 12.6% Sum of secondary components 0.1%

(28) The composition of this recycle stream corresponds to the composition of the recycle stream which was introduced into the mixing zone (a) at the beginning of the experiment.

(29) The product mixture obtained at the bottom of the second column has the following product composition:

(30) TABLE-US-00006 TABLE 6 2,2-MDA % by weight <0.01 2,4-MDA % by weight 6.3 4,4-MDA % by weight 61.2 3-Kern-MDA % by weight 22.2 p-MDA % by weight 10.2 N-Methyl-MDA % by weight 0.100

(31) The content of N-methyl-MDA could be reduced from 0.125% to 0.100%. This corresponds to a decrease in the undesirable secondary components of 20%.

(32) Example 2 according to the invention:

(33) Recirculation of a 2,2′-/2,4′- and 4,4′-MDA isomer mixture, obtained by isolation by means of a first distillation column and a second distillation column having 10 and 15, respectively, theoretical plates, into the mixing zone (a) of an MDA plant as per FIG. 1 with prior isolation of a low boiler stream comprising secondary components formed and recirculation of the low boiler stream into the product stream from the second distillation column 690 g of aniline (purity>99%) and 19 g of a recycle stream as per tab. 8 were placed in a stirred vessel and 144 g of a 32% strength hydrochloric acid were added thereto. 235 g/h of a 35.5% strength formalin solution were continuously mixed in at 60° C. over a period of 1 hour by means of a mixing pump. The mixing pump is located in the pump circuit of the mixing vessel. The pumped circulation was 25 l/h. After 1 hour, introduction of the formalin solution was stopped and the reaction mixture was heated to 90° C. and circulated by pumping for another 1.5 hours. The pumped circulation was subsequently stopped and the reaction mixture was heated to 120° C. and dispersed further for 2 hours.

(34) The fully reacted reaction mixture was cooled to 80° C. and then neutralized with aqueous sodium hydroxide solution (25% by weight). After the aqueous phase has been separated off, the organic phase is washed with water and the aniline is subsequently distilled off on a rotary evaporator at 1 mbar and an oil bath temperature of 100° C.

(35) Table 7 shows the product composition after the work-up zone (e):

(36) TABLE-US-00007 TABLE 7 2,2-MDA % by weight 0.5 2,4-MDA % by weight 9.0 4,4-MDA % by weight 58.8 3-ring MDA % by weight 21.2 4-ring MDA % by weight 6.5 N-Methyl-MDA % by weight 0.086

(37) The proportion of secondary components having a boiling point equal to or greater than that of aniline and less than that of 2,2″-MDA in the product mixture as per tab. 7 was about 500 ppm.

(38) To separate off the recycle stream, the product mixture as per tab. 7 was fed at plate 4 into a first distillation column having 10 theoretical plates. At a pressure at the top of 2 mbar and a temperature at the top of 150° C., a low boiler stream having a content of secondary components of 82% was obtained at a reflux ratio of 500 g/g.

(39) The product stream obtained at the bottom of the first column is fed at plate 10 into a second distillation column having 15 theoretical plates. At a pressure at the top of 4 mbar and a temperature at the top of 202° C., a recycle stream having the following composition is obtained at the top of the column at a reflux ratio of 22 g/g:

(40) TABLE-US-00008 TABLE 8 2,4′-MDA 75.0% 2,2′-MDA 12.4% 4,4′-MDA 12.6% Sum of secondary components <0.01%

(41) The composition of this recycle stream corresponds to the composition of the recycle stream which was introduced into the mixing zone (a) at the beginning of the experiment.

(42) The product mixture obtained at the bottom of the second column was mixed with the overhead stream from the first column (low boiler stream). The resulting final product mixture has the following product composition:

(43) TABLE-US-00009 TABLE 9 2,2-MDA % by weight 0.02 2,4-MDA % by weight 6.3 4,4-MDA % by weight 60.6 3-ring MDA % by weight 22.0 p-MDA % by weight 10.9 N-Methyl-MDA % by weight 0.09

(44) The content of N-methyl-MDA could be reduced from 0.125% to 0.09%. This corresponds to a decrease in the undesirable secondary components of 28%.