DD295628A5 - METHOD FOR THE DISCONTINUOUS PREPARATION OF METHYLENDIANILIN / POLYAMINE MIXTURES - Google Patents

Abstract

The invention relates to a process for the batch production of methylenedianiline / polyamine mixtures, which is used in the preparation of aromatic isocyanates. Characterized in that 55% to 85% of the formaldehyde amount at the temperature 40C and 45% to 15% of the amount of formaldehyde in the temperature range 60C to 80C within at least 10 minutes to 30 minutes with the recirculated reaction mixture in the ratio 1 to 10 to 1 to 300 at the turbulence corresponding to the Reynolds number 10 000, in particular at the addition of the last part of the formaldehyde, is mixed or, soz 70% to 90% of the 37% formaldehyde aqueous amount within at least 10 minutes to 30 minutes and 30% to 10% The amount of formaldehyde, which is optionally diluted with water in the ratio of 1 to 1 to 1 to 5, is added to the reaction mixture in at least 10 minutes to 30 minutes is achieved by discontinuing methylene dianiline / polyamine mixtures batchwise by condensation of aniline and formaldehyde by an easily realizable process when using a relatively low aniline content, with a molar ratio of aniline to formaldehyde 2.2 to 1 and reduced formation of N-methyl compounds in the methylenedianiline / polyamine mixture {methylenedianiline / polyamine mixtures; discontinuous production; Condensation; Aniline; Formaldehyde; gradually adding formaldehyde; few by-products; isocyanate; polyurethane}

Description

-2- 295 628 Explanation of the essence of the invention

The invention is to achieve the objective of the object to control the acidic condensation process of aniline and formaldehyde by adhering to special technological conditions.

According to the invention the object is achieved in that 65% to 85% of the amount of formaldehyde at the temperature ≤ 40 ° C and Ί5% to 15% of the amount of formaldehyde in the temperature range 26C ⁰ C to s80 ° C within at least 10min to 30min with the circulated Reaction mixture in the ratio of 1 to 10 to 1 to 300 in the turbulence corresponding to the Reynolds number> 10000, especially when adding the last part of the formaldehyde, or that 70% to 90% of the 37% aqueous formaldehyde amount under adiabatic reaction conditions within of at least 10 minutes to 30 minutes and 30% to 10% of the amount of formaldehyde, optionally diluted with water in a ratio of 1: 1 to 1: 5, is added to the reaction mixture in at least 10 minutes to 30 minutes. *

With the addition of 55% to 85% of the total amount of formaldehyde at a temperature of 540 ⁰ C, the formation of by-products is very low and the reaction mixture is available as a clear homogeneous solution. It is surprising that the temperature increase to a CO ⁰ C to s 8O ⁰ C in the addition of the residual amount of formaldehyde is not only possible to maintain the homogeneity of the Ri Ationslösung, but also while maintaining a total formaldehyde dosage of at least 10min to 30 and To minimize the formation of side reactions in a quantitative ratio of formaldehyde to the circulated reaction mixture of 1 to 10 to 1 to 300.

In batch amine condensation, that is, a process in which a portion of one component is gradually added to the total of the other component, control of the final phase of formaldehyde addition plays a crucial role.

By the reaction according to the invention, that is by d> e reduction of the formaldehyde concentration per unit time in the last Zugabophase, the formation of N-methyl compounds and dichlorine, or their derivatives, is kept very low. In contrast to the methods of the prior art is minimized by the orführungsgemäße Reaktionsführuno both the formation of side reactions of formaldehyde, and at the same time a trouble-free technological control (including no Ablagerunyen of polymeric precondensates in the heat exchangers and mixing devices) of the process guaranteed.

After the usual complete rearrangement of present in the reaction mixture Aminobenzylanilin bonds / u primary amines at a temperature of 80 ° C to 100 ⁰ C and a residence time of 2 h to 4 h, the neutralization of the hydrochloric acid reaction mixture, washing and subsequent removal by distillation of Aniline and residual water to obtain an MDA / polyamine mixture with a very low content of N-methyl-MDA or higher-nuclear oligomers and dichlorine or its derivatives. The MDA / polyamine mixture thus produced can be readily phosgenated in an inert solvent and has a significantly improved quality with regard to the content of chlorine-containing compounds.

The process of the invention is applicable to all aniline-formaldehyde molar ratios of 1.4 to 4 to 1 and brings particular advantages at ratios of 1.6 to 2.2 to 1. The molar ratio of acid to aniline can be varied according to the desired isomer ratio between 0.3 and 0.9, wherein preferably hydrochloric acid is used as the acidic catalyst

 The advantages of the method according to the invention are that

minimizes the content of by-products in the MDA / polyamine mixture and thus substantially improves the isocyanate quality with respect to the content of chlorine-containing compounds,

- Deposits of polymeric intermediates are avoided, whereby the term of a large-scale plant is significantly increased due to the interference-free operation.

The invention will be explained in more detail below with exemplary embodiments.

Embodiment 1

In a reactor system consisting of reactor, external product cycle with heat exchanger and circulation pump, formalin storage vessel and mixer, 18.6 kg of aniline are submitted and after start-up of the circuit 9.3 kg of hydrochloric acid (31.5% strength) added steadily. By the circulation through the heat exchanger arranged outside, a temperature of 5O ⁰ C to 6O ⁰ C is maintained and after completion of the addition of hydrochloric acid, a temperature of 40 ⁰ C is set. The circulating cycle amount is adjusted by means of the circulation pump so that the amount ratio of the cycle product to the amount of formalin is 30 to 1. This is followed by the steady addition of 8.11 kg of formalin (3?% Strength, temperature = 3O ⁰ C) within 10 minutes by using nitrogen gas (0.9 MPa) in the circulatory product by means of a mixing device, so that turbulence at a Reynolds number of about 10000 is generated.

The temperature control during the formalin addition is designed so that 85% of of formalin (6,08kg) at 4O ⁰ C and after heating to 80 ° C, the remaining quantity is added at this temperature. After completion of the formalin addition, the reaction mixture is heated to 85 ° C to 95 ° C and held at this temperature for 120min. Then cooled to 7O ⁰ C, neutralized with umbarschüssiger sodium hydroxide solution, the organic phase separated, washed with water virtually free of chloride and then removed the excess aniline and dissolved water by gentle distillation.

The resulting MDA / polyamine mixture is characterized by the following analytical code:

MDA 3-core 4-core 5-10 core

64.5% 22.3% 8.1% 5.1% (determined by GPC, in% by weight)

MDA isomeric mixture including N-methyl-MDA

W 2 ^ 4 ^ N-methyl-MDA

0.2% 7.5% 92.1% 0.2% (determined by GC, reported in% by weight)

0.6% by weight of dichlorine (by UV measurement)

100mPasViskosität / 70 ° C

Implementation Bills 2

Analogously to Example 1, an aniline hydrochloride mixture is prepared from 16.74 kg aniline and 8.37 kg 31.5% hydrochloric acid, cooled to 30 ⁰ C and 4.46 kg 37% pure formalin (55% of the total) at this temperature within 15min continuously with a turbulence of Reynolds number about 10000 added. The amount of circulating product to formalin is 300 to 1. After heating to 6O ⁰ C, the remaining amount of formalin is also added in 15min. After the appropriate steps, an MDA / polyamine mixture with the following analytical values is obtained:

MDA 3-core 4-core 5-10-core 54.7% · 23.6% 11.7% 10.0% (determined by GPC, data in% by weight) MDA isomer distribution including N- 2,2 '2,4' 4,4 ' Methyl-MDA N-methyl-MDA

0.1% 4.7% 94.9% 0.3% (determined by GC, reported in% by weight)

0.8% by weight of dichlorine (by UV measurement)

230mPasViskosität / 70 ° C

Embodiment 3

In a equipped with mechanical stirrer, reflux condenser, thermometer and a line for the formaldehyde solution Reuktor 167.4g aniline and 83.4g 31.5% hydrochloric acid are mixed together and cooled to 40 ⁰ C. 56.8 g of a 37% strength aqueous formaldehyde solution (corresponding to 70% of the total amount of formaldehyde) are added dropwise to the reaction mixture by means of a metering pump within 10 minutes with vigorous stirring and the remainder of 24.3 g of formaldehyde solution is likewise added in 10 minutes (aniline to formaldehyde 1 molar ratio). 8 to 1). After completion of addition of formaldehyde, the reaction mixture is maintained at 95 ⁰ C for 3 h, cooled to 70 ° C, neutralized with excess sodium hydroxide solution, the organic phase separated, washed with water virtually free of chloride and then removed the excess aniline and dissolved water by gentle distillation. The resulting MDA / polyamine mixture is characterized by the following analytical parameters:

MDA 3-core 4-core 5-10-core 54.9% 23.3% 11.3 ° / 10.5% (by GPC, by weight) MDA isomer distribution including N-methyl 2,4 ', 4,4' N-methyl-MDA -MDA

4.52% 95.23% 0.25% (determined by GC, reported in% by weight)

0.95% by weight of dichlorine (by UV measurement)

250 mPas viscosity / 70 ° C

This MDA / polyamine mixture is dissolved in monochlorobenzene and phogenated. In the phosgenation, a bright chlorobenzene reaction solution is obtained which is free from deposits. After working up by distillation, the following analytical values are determined: 0.23% by weight of hydrolyzable chlorine 150 mPas viscosity / 25 ° C.

Embodiment 4

The procedure of Example 1 was repeated except that the addition of the formaldehyde solution was such that 90% (73 g) was added in 30 minutes and the remainder (8.1 g) was also added in 30 minutes. After the corresponding precursor stages, an MDA / polyamine mixture with the following characteristics is obtained:

MDA 3-core 4-core 5-10 core

55.6% 23.0% 11.3% 10.1% (by GPC, in% by weight)

MDA isomer distribution including N-methyl-MDA 2,4 ', 4,4'-N-methyl-MDA

4.74% 95.08% 0.18% (determined by GC, reported in% by weight)

0.89% by weight of dichlorine (by UV measurement)

220 mPas viscosity / 70 ° C

After phosgenation and work-up, the following characteristics are obtained in the analytical characterization:

0.2% by weight of hydrolyzable chlorine

125mPasViskosität / 25 ° C

Embodiment 5 In the same apparatus as in the embodiments 3 and 4 are 158.1 g of aniline with 78.8 g 31.5% strength, · hydrochloric acid

cooled, cooled to 4ö "C and 60.8 g of a 37% aqueous formaldehyde solution (corresponds to 75% of the total amount of

Formaldehyde) within 30 min. The remainder of the 20.3 g Formaldeh 'd solution is in a ratio of 1 to 3 with Was3er diluted and also in 30min zugegeuen the reaction mixture (molar ratio of aniline to formaldehyde 1.7 to 1). The

resulting product is analogous to the exemplary embodiments 1 and 2 b 'continues and characterized by the following analysis:

MDA 3-core 4-core 5-10 core

49.0% 24.2% 12.2% 14.6% (determined by GPC, in% by weight)

MDA isomer distribution including N-methyl-MDA 2,4 ', 4,4'-N-methyl-MDA

4.12% 95.30% 0.58% (by GC, in% by weight)

1.0% by weight of dichlorine (by UV measurement)

380mPasViskosität / 70 ° C

The analytical examination of the MDI / polyisocyanate mixture gives: 0.31 wt .-% hydrolyzable chlorine 200 mPas viscosity / 25 ^<1 C.

Claims (1)

Process for the batchwise preparation of methylenedianiline / polyamine mixtures by condensation of aniline and formaldehyde in an acidic medium, characterized in that 55% to 85% of the formaldehyde amount at the temperature <4O ⁰ C and 45% to 15% of Formaldohydmenge in the temperature range from 60 ° C to ^ 8O ⁰ C within at least 10min to 30min with the recycled reaction mixture in the ratio of 1 to 10 to 1 to 300 in the turbulence corresponding to the Reynolds number> 10000, especially in the addition of the last part of the formaldehyde, in a reactor with external Heat exchanger is mixed or that 70% to 90% of the 37% aqueous formaldehyde under adiabatic reaction conditions within at least 10min to 30min and 30% to 10% of the amount of formaldehyde, which is optionally diluted with water in the ratio 1 to 1 to 1 to 5 , is added to the reaction mixture in customary reactors in at least 10 minutes to 30 minutes. Field of application of the invention The invention relates to a process for the batch production of methylenedianiline / polyamine mixtures, which is used in the preparation of aromatic isocyanates. Characteristic of the known state of the art The acidic condensation of aniline and formaldehyde for the large-scale production of isomers of methylenedianiline (MDA) and their higher oligomers, so-called polyamines, as important intermediates in the production of the corresponding isocyanates, has long been known and, for example, in DD-AP 89620, DD AP 89723, DE-OS 2134756 or DE-OS 2302381 described. In general, the procedure is such that aniline is initially mixed with acidic catalyst, preferably hydrochloric acid, and then formaldehyde is added. The reacted after several hours, generally strong hydrochloric acid reaction mixture is worked up alkaline to obtain the reaction product and washed several times with water and unreacted aniline and dissolved water removed by distillation. From the MDA / polyamine mixture, a polyphenylmethane diisocyanate (MDD / polyisocyanate mixture which is worked up in a known manner by phosgenation in an inert solvent, for example monochlorobenzene, is obtained.) In the preparation of MDA / polyimine mixtures by acid condensation, the initial reaction stage is particularly critical The initial reaction is understood to be the actual condensation reaction, that is to say the primary reaction taking place with dehydration of formaldehyde and the nitrogen-bonded hydrogen and the conversion to aminobenzylaniline bonds and mixing of the components already determine significantly the quality of the MDA / polyamine mixture and thus the quality of the correlating MDI / polyisocyanates.So, the extent of the occurrence of undesired side reactions depends on these reaction parameters n, resulting in, for example, secondary and tertiary amines in the form of monomeric N-methyl-MDA or higher-nuclear oligomers and 3,4-dihydro-3-phenyl-quinazoline (dichlorine) or derivatives thereof. It is important to control these reactions since, for example, the by-products they form after phosgenation do not give isocyanate but consistent, hard or non-removable contaminants with certain amounts of fixed chlorine. For example, these by-products interfere with the desired function of catalysts in polyurethane synthesis and degrade the physical properties of the polyurethane product. The initial phase of the acidic MDA / polyamine condensation is in principle dominated when the temperature is kept <40 ° C and a local excess of formaldehyde is avoided by sufficient mixing. However, compliance with these conditions is problematic even with discontinuous processes in the technically relevant aniline-formaldehyde molar ratios, especially because at the favorable for product quality temperatures physically inhomogeneous stages are passed, the technological problems, especially blockages due to deposition of polymeric precondensates in the heat exchangers, bring with it. Various process developments are known, which accordingly seek to improve the initial reaction phase in MDA / polyamine production. Thus, for example, there is a variant described in DE-OS 2134756 in a special addition process of formaldehyde to the aniline-hydrochloric acid mixture. The main part of the amount of formaldehyde (60% to 80%) is slowly added se that the temperature gradually rises to about 6O ⁰ C and then the rest is allowed to shrink virtually instantaneously. During this rapid addition, the temperature rises to about 100 ⁰ C. Although this procedure, deposits in the heat exchangers are avoided, but the content of by-products is relatively high due to the high reaction end temperature. Object of the invention The aim of the invention is, by an easily implementable method, discontinuous methylenedianiline / polyamine mixtures by condensation of aniline and photmaldehyde using a relatively low aniline content, at a molar ratio of aniline to formaldehyde 2.2 pounds to 1 and reduced formation of N-methyl compounds in methylenedianiline / Polyamine mixture, to strain.