DD296071A5 - PROCESS CONTROL OF ACID-CATALYZED ANILINE FORMALDEHYDE CONDENSATION - Google Patents

Abstract

The invention relates to a Prozeszsteuerung the acid-catalyzed aniline-formaldehyde condensation, which is used in the preparation of aromatic isocyanates. As a result of the viscosity of the reaction mixture being measured during and / or after the formaldehyde addition, and a correction of variable reaction parameters, such as reaction temperature and / or metering rate, being achieved if the viscosity falls below the predetermined limit, the acid-catalyzed aniline-formaldehyde condensation is controlled in such a way that to reduce the formation of interfering byproducts such as N-methyl compounds, quinazolines, and derivatives. {Process Control; acid-catalyzed aniline-formaldehyde condensation; Viskositaetsmessung; Influence on reaction parameters; Reaction temperature; metering rate}

Description

On the one hand, it causes considerable difficulties to carry out the UV spectroscopic measuring method in local and thus temporal proximity to the production process in the manufacturing process under operating conditions, and on the other hand, the occurrence of poor product quality is not prevented from the outset, it is only possible to correct subsequent syntheses

In the complicated Reaktionsabiauf the aniline-formaldehyde condensation can take as effective an effect on the Endproduktwalftat, the sooner after the mixing of the reactants, the existing reaction conditions are characterized

Object of the invention

The object of the invention is an easily realizable process control of the acid-catalyzed Anihn-formaldehyde condensation, which allows the production of polyisocyanates with improved quality parameters over the prior art

Explanation of the essence of the invention

To achieve the object, the invention has the object to control the Anihn-formaldehyde condensation process so that the formation of interfering by-products, such as N-methyl compounds, Chmazohnen and derivatives thereof, is reduced

Erfmdungsgemaß the object is achieved in that during and / or after the Formaldehyddosierung the viscosity of the reaction mixture is measured and falls below the predetermined limit value of the viscosity is a correction of variable reaction parameters The predetermined limit is erfmdungsgemaß 1.1 times the viscosity of the completely rearranged reaction mixture and / or a predetermined course of the viscosity over the Formahndosierung and / or related to the viscosity of the reclaimed amine Great Erfmdungsgemaß variable reaction parameters are the reaction temperature and / or the dosing of formalin The teaching of this invention, according to which - same boundary conditions, for example aniline Formaldehyde ratio, of course, assuming protonation - always polyamine mixtures with very low content of by-products can be obtained if gesor for the highest possible viscosity of the condensation mixture The expert had to assume the opposite, since a low viscosity is a prerequisite for the targeted good mixing optimal mixing is particularly important in the aniline-formaldehyde condensation of maximum importance to limit side reactions maximum Therefore, already in the Literature a variety of devices to ensure good mixing in this reaction, such as mixing lines and special nozzles, described addition to the important advantage of introducing a previously unused in this way quality criterion in the amine condensation, the application of this inventive method allows a process control with respect to the Prior art methods significantly reduced inertia

The invention can be applied in principle in the continuous process of aniline-formaldehyde condensation by the viscosity from the initial reaction zone, that is determined immediately after the mixing of the reactants Amhnhydrochlorid and Formahn Here, in particular the decisive advantage over the prior art, that The inventive method is therefore not bound to specific apparatus, it can be carried out both in discontinuous and continuously operating systems It is also not necessary, which molar ratios of the starting materials and which catalyst concentrations are applied The following examples illustrate the invention in more detail

Exemplary embodiments

In a reactor equipped with a stirrer, reflux cooler, cooling and metering devices and inert gas coating and Viskositatsmeßeinrichtung 1 8 parts by mole of aniline with 0.72 mole parts of hydrochloric acid (as 31.5% aqueous solution) are mixed together at 70 ° C in the course of one hour 1 mol part of formaldehyde (as a 37% waßnge solution) is added continuously, with an intensive mixing of the reactants is ensured then the reaction mixture is kept for three hours at 95 ° C and cooled to 70 ⁰ C, neutralized with excess sodium hydroxide solution, the organic phase separated with The mixture thus obtained is characterized by determination of core distribution, N-methyl content, dichlorine content and viscosity and the values obtained are recorded during the condensation and rearrangement of viscous viscous contrasted with the course of

In order to increase the viscosity of the condensation mixture during the Formahndosierung shortening the Formahndosierzeit was carried out for 30 minutes while maintaining all other parameters and the workup of the product according to Example 1 a

Starting with the formalin addition, the temperature of the reaction mixture is increased in the course of Formahndosierzeit of one hour from 30 ⁰ C to 70 ° C. The applied Ansatzverhaltnis and the work-up of the product corresponds to that of Example 1 a

Instead of the one-hour Formalindosierzeit applied in Examples 1 a and с the formalin is dosed at 70 ⁰ C in three doses with 25% of the total amount of formalin every 15 minutes, 25% of Gesamtalinalinmenge be dosed at the end of the reaction over a period of 15 minutes, so that the total metering time of one hour is maintained The applied approach ratio of the reactants and the work-up of the product corresponds to that of Example 1a

Instead of the constant reaction temperature m Example 1 d of 70 ⁰ C, the reaction temperatures of the reaction mixture of 30 ° C is increased continuously over one hour at 70 ⁰ C adhering to all other technological steps and parameters of Example 1 d at the beginning of Formalindosierung

Table 1 lists the analytical parameters determined, such as viscosity, N-methyl number, dichlorine content and core distribution, of Examples 1 a-e

Table 1 Example r | 25 ° C after Forma lindosierung (mPas) η 25 "C after repositioning (mPas) Amine (<St) N-methyl number (mmol / kg) Content is yours Core distribution (K) 2K 3K Core distribution (K) 4K 5-10K 9.4 5-10K 1a example 70 η 25 ⁰ C after Forma lindosierung (mPas) 60 t n25 ° C after storage (mPas) 200 n, 70 ° C amine (<St) 20 N methyl number (mmole / kg) 1,8 Dichin content 56.5 22.5 core distribution (K) 2K 3K 11.6 4K 10 10.5 9.5 9.5 1b с d e 90 1.2 95 1.27 95 1.22 105 1.23 75 75 78 85 235 160 210 185 18 14 12 10 1.6 1.5 1.3 0.85 55 23 54.5 23.5 56 23 56 23.5 12 11.5 11.5 11

The measurement of the viscosity of the reaction mixture carried out continuously during the execution of Examples 1 a, b, с is shown in FIG. 1 as a function of the formalin dosage.

In an apparatus analogous to Example 1 and the same Ansatzverhaltnis the starting materials was under specification of Example 1 с obtained the viscosity of the condensation mixture until the completion of Formalindosierung the condensation at 80 ⁰ C carried out at 50% of Gesamtalinalinmenge clearly emergent deviation from the viscosity curve of the default curve balanced by increasing the dosing speed of the formalin from 1.67% / min to 2.1% / min and brought in accordance with the default curve (Figure 1)

In the same way, the amine condensation is carried out according to Example 2a. However, the formalin dosage rate is kept constant at 1.67% / min. The viscosity progression is shown in FIG. 1. For Example 2, the following analytical parameters were determined

Table 2 Example r) 25 ° C after Forma lindosierung (mPas) η 25 "C after repositioning (mPas) η 70 ⁰ C amine (<St) N-methyl number (mmole / kg) Dichin content (%) Core distribution (K) 2K 3K (%) 22.5 23.5 4K 5-10k 2a с 95 1.17 60 1.15 81 52 90 95 12 25 1.1 2.0 56.5 54.5 11,6 11,5 9.4 10.5

From 31% hydrochloric acid and water-saturated aniline continuously a product flow of an aniline Anilinhydrochlondlosung aqueous produced continuously molar ratio of acid to aniline of 0.4 to 0.45 is present at a temperature of 40 ⁰ C, the Anilinhydrochlondlosung passes to a mixing device in the under turbulence a homogeneous mixing with a 37% aqueous and held at a temperature of 30 ⁰ C held Formaldehydlosung The volume flow of Anilinhydrochlondlosung and the Formaldehydlosung are in the ratio of 3.7 to 0.5 (molar ratio of aniline to formaldehyde 3.6 to 1) mixed After adiabatic reaching a reaction temperature of 70 ⁰ C is immediately cooled by means of a heat exchanger to 40 ⁰ C and turn in a mixer, the reaction mixture with the remaining formalin (37% aqueous solution, 30 ⁰ C, Gesamtmolverhaltnis aniline to formaldehyde 1.8zu 1) mixed under turbulence 60 seconds later a sample is taken and a viscosity of 70 mPas determined at 25 ⁰ C The exiting from the 2 reactor 65 ⁰ C hot reaction mixture is heated to 85 ⁰ C and maintained at a temperature of 85 ° C to 95 ⁰ C and a mean residence time of 120 minutes

After leaving the final reaction zone, the product is cooled to 70 ⁰ C, neutralized with excess sodium hydroxide solution, the organic phase separated, washed with water virtually free of chloride and then the excess aniline and dissolved water by gentle distillation The resulting MDA / polyamine mixture is characterized by Characteristics of analysis characterized

MDA 3 core 4 core 5-10 core (determined by GPC,

53,3 23,6 11,7 11,4 in% by weight)

1.7% by weight of dichromate (by UV measurement)

Methyl number 59 mmol / kg (by NMR)

290 mPas viscosity / 70 ⁰ C

This MDA / polyamine mixture is dissolved in monochlorobenzene and phosgenated. The diphenylmethane diisocyanate / polyisocyanate worked up after the distillation is characterized by the following analytical parameters: 0.39% by weight of hydrolyzable chlorine 170 mPasViscositat / 25 ° C

The procedure described in Comparative Example 3 a is applied with the modification that is cooled after the addition of 2 Formalin so that a final temperature of 50 ⁰ reached C. Sampling is again made 60 seconds after the mixing of Anihnhydrochlorid and formalin and a viscosity value of 105 mPas determined at 25 ° C. After the corresponding process steps, a methylenedianiline / polyamine mixture with the following analytical values is obtained

MDA 3 core 4 core 5-10 core

56.4 24.0 10.5 9.1

1.15% by weight of dichlorine. Methyl number 40 mmol / kg 290 mPas viscosity / 70 ° C.

After phosgenation and work-up, a diphenylmethane diisocyanate / polyisocyanate with the following characteristics is obtained

0.31% by weight of hydrolyzable chlorine 145 mPas viscosity / 25 ° C.

Claims (4)

1. Process control of the acid-catalyzed amine-formaldehyde condensation, characterized in that during and / or after the Formaldehyddosierung the viscosity of the reaction mixture is measured and falls below the predetermined limit value of the viscosity, a correction of variable reaction parameters. 2. Process control according to item 1, characterized in that the predetermined limit is 1.1 times the viscosity of the completely rearranged reaction mixture and / or a predetermined curve of the viscosity over the Formahndosierung and / or related to the viscosity of the worked-up amine size 3 process control according to item 1, characterized in that variable reaction parameters are the reaction temperature and / or the metering rate of formalin. For this 1 page drawing Field of application of the invention The invention relates to a process control of the acid catalyzed aniline formaldehyde condensation used in the preparation of aromatic isocyanates Characteristic of the known state of the art Isocyanates of the diphenylmethane series are generally obtained by phosgenation of methylene dianiline and its homologs. The preparation of this wet nurse takes place by condensation of formalin with a stoichiometric excess of aniline, in the presence of acidic catalysts and subsequent rearrangement. The acidic condensation of aniline and formaldehyde for large-scale production of isomers Methylenedianiline (MDA) and its higher oligomers, so-called polyamides, as important intermediates in the production of the corresponding isocyanates has long been known and described, for example, in DD-AP 89620, DD-AP 89723 or DE-OS 2134756 proceeded that first aniline with acidic catalyst, preferably hydrochloric acid, and then added formaldehyde is added, the reaction mixture reacts by rearrangement of the condensates in the desired methylene dianiline structure then has the generally strong salzsa The conditions in the initial phase of the anilm-formaldehyde reaction, such as temperature control, aniline-formaldehyde ratio and mixing of the components, already determine to a great extent the quality of the isocyanates used for the synthesis of polyurethanes It is important to control this reaction since the by-products formed by it after phosgenation are not isocyanate but persistent, hard or non-removable contaminants with certain amounts of fixed-bound MDA / polyarmnone, depending on the reaction parameters mentioned For example, these by-products interfere with the desired function of catalysts in polyurethane or polyisocyanurate synthesis and degrade the physical properties of the polyurethane product. As a feature of the poor quality of the product MDA / polyamine is given in the literature, for example in US Pat. No. 4,053,513, US Pat. No. 4,041,078 or DD-AP 125493, the N-methyl-MDI (MMM) or the content of N-methyl compounds. Characterization is carried out by gas chromatography or NMR spectroscopy on the neutral end product A process control regarding a Qualrtatsbestimmung the MDA / Polyamtns with respect to interfering by-products has been due to the acidic nature of the resulting reaction mixture, only after neutralization possible. That is, the necessary information in the technological process with a long time delay after the neutralization stage, respectively obtained after the subsequent distillation, ultimately with the analysis of the final product of MDA / polyamine production, if one does not remove samples prior to neutralization, but which can be analyzed according to the prior art only after appropriate processing The work-up in the laboratory becomes practical The isolation of the MDA / polyamines from the usually hydrochloric acid solution is carried out by neutralizing the product with aqueous alkali, and the aqueous phase is separated from the organic phase by analogy with the process steps which take place in the production process enn, the organic layer is washed several times with water and then generally the excess aniline including dissolved water is removed by gentle distillation. Only after this elaborate workup is the determination of the required characteristics by appropriate analytical methods, such as gas chromatography or NMR spectroscopy Nevertheless, the time expenditure is still too high and the reliability of the results due to possible sources of error of the method, mainly due to the workup is not satisfactory To shorten this time, has already been proposed in the unreacted acidic reaction product UV-spectroscopy the content of the by-product 3 To determine 4-dihydro-3-phenylquinazoline and to use this measured value as a quality criterion and control size Although an acceleration of process analysis and control has been achieved by this measure, significant disadvantages still remain. for re 9: о ;: ^l ~. 9 '