DD288599A5 - CLEANING PROCESS OF ORGANIC ISOCYANATES FROM CHLORINE-CONTAINING COMPOUNDS - Google Patents

Abstract

The invention relates to a purification process of organic isocyanates, such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenylene polyisocyanate of chlorine-containing compounds. The achieved thereby high degree of purity of the organic isocyanates has a fundamental effect on the production of polyurethane systems with improved product and processing properties. Here, organic isocyanate in the presence of 0.1 to 5 parts by mass in percent carbodiimides at a temperature of 453 to 513 K subjected to a thermal treatment. The hydrogen chloride formed is then removed by stripping with inert gas {organic isocyanates; diisocyanate; Polymethylene polyphenylene polyisocyanate; chlorine-containing impurities; Cleaning; Stripping with inert gas; thermal treatment; Carbodiimides as additives}

Description

Characteristic of the known state of the art

Organic isocyanates prepared by phosgenating amines generally contain a number of chlorine-containing compounds that are undesirable. Especially in the phosgenation products of aniline-formaldehyde condensates, a high content of these products is known. The chemical nature of these products is very different and is determined analytically by determining the content of hydrolyzable chlorine. Part of these connections are shown below; the production conditions as relatively stable and remains even after distillation in the isocyanates. These compounds adversely affect the stability, color retention and other properties of the crude isocyanates and the pure isocyanates prepared therefrom.

There has therefore been no lack of attempts to find ways to remove the chlorine-containing compounds. For example, the patent specifications DE 1138040, DE 1286 025, NL 6411863, US 3264336 and DE 2210607 describe treatments with metals, metal oxides and motor salts. These processes lead to a number of technological difficulties relating to the separation of the metals or metal compounds from the isocyanates or the limited usability of metal-containing isocyanates and metal-containing distillation residues. Similar restrictions can be found when using other additives such as Imidazo! (GB 1347647), sulfuric acid and its esters (GB 1459691) and toluenesulfonic acids and their esters (GB 1458747).

From the patent DE 1240849 it is known to eliminate the content of hydrolyzable chlorine by a Chloridhydrolyse performed in a certain way. In DE 2316028 formic acid and formamides are recommended for the same purpose, but only tested for their usefulness in tolylene diisocyanate.

Furthermore, it has been found that short-term thermal treatments (FR 1411934, GB 1015977, US 3 274225) can prevent the formation of sediments, but only insignificantly acts on other impurities. The effectiveness of the temperature treatments can be improved when stripping simultaneously with inert gas and / or inert solvents (US 3219678, BE 659740, GB 1080717, US 3156950, GB 1362708, US 3857871, GB 1114690, DD 118105, GB 138406b, US 4118286) ,

In this case, the content of easily cleavable chlorine compounds is preferably reduced, which are detected analytically as acidity.

It is also known to purify isocyanates by means of special distillation techniques (DE 2631168) or crystallization processes (DE 1950101, DE 2322574, DE 1938384 and DE 2532722).

It is clear that the processes of the prior art have a number of principal drawbacks, which relate above all the efficiency, the technological expenses, the accessibility of the recommended additives in the necessary qualities at a high cost and the usability of the distillation residues.

Object of the invention

The invention is based on the objective to minimize the content of chlorine-containing compounds as far as possible after an economical purification process from crude isocyanates with reudziertem time and energy expenditure.

t Presentation of the essence of the invention

The invention is to achieve the objective of the task, the fullest possible effective elimination of

To achieve hydrolyzable chlorine compounds in order to ensure a high degree of purity of the isocyanates by significantly improving the characteristics of acidity and hydrolyzable chlorine.

According to the invention the object is achieved in that chlorine-containing organic isocyanates in Gegenv.art of carbodiimides

be heated to a temperature of 453 to 513K and then at these temperatures, the hydrogen chloride through

Passage of an inert gas and / or a high-boiling inert solvent is removed. Although the process of the invention can be used for the treatment of any isocyanates, preferred However, the field of application is isocyanates, which may contain thermally poorly degradable secondary carbamoyl chlorides,

such as diphenylmethane diisocyanate and its mixtures with homologous polyisocyanates.

Suitable carbodiimides or carbodiimidabspaltende substances are low molecular weight carbodiimides of aliphatic and aromatic monoisocyanates ^ low molecular weight adducts of carbodiimides with isocyanates (uretonimines), dimeric carbodiimides, salts of carbodiimides, carbodiimidhaltige reaction products of diisocyanates, Uretonlminpolyisocyanate and analogous products. Of particular importance is a solution of tris-4- (isocyanatobenzyl) -phenyl-uretonimine (uretonimine polyisocyanate) prepared by carbodilution of 4,4'-diphenylmethane in excess of 4,4'-diphenylmethane diisocyanate. The content is about 16 to 20 mass%. In addition, 1 to 2 parts by mass in% dimeric Carbodiimidpolyisocyanat and about 1 mass fraction in% contain other polyisocyanates.

The amount of additives according to the invention necessary for the removal of chlorine-containing compounds can be chosen differently. In general, from 0.1 to 5% by mass are used. Smaller amounts are chosen if a distillative workup e.g. to produce high-purity diisocyanates. In polymethylene polyphenylene polyisocyanates, higher amounts are also possible because increased levels of uretonimine polyisocyanates are often desired for adjusting certain processing properties.

The treatment according to the invention of chlorine-containing isocyanates is carried out at a temperature of 453 to 513K. Under certain circumstances, it may be favorable to proceed according to a specific temperature program. The treatment time is generally between 7 to 10 hours by conventional methods. Compared to the prior art, the inventive method allows a significant reduction in the reaction time. The treatment time is reduced to 0.2 to 6 hours. It is at a thermal treatment at 498 K about 0.3 to 3 hours. Catalytic degradation of chlorine compounds can be monitored by determining acidity and hydrolyzable chlorine. It is possible to determine the degradation of special chlorine compounds, for example by NMR spectroscopy.

The effect of the invention was surprising, since it could not be assumed that chlorine-containing compounds react with carbodiimides to form volatile products. From the literature it was previously only known to form aliphatically substituted carbodiimides with acid chlorides, aryl-chloroformamidines (Chem. Ber. 99.3155 [1966]). In contrast, arise under the conditions of the invention, for. B. from N, N-disubstituted carbamoyl chlorides and carbodiimides, heterocyclic compounds with amidine structures and hydrogen chloride. Carbodiimides are therefore suitable for the removal of chlorine-containing impurities from isocyanates.

Compared with the use of metal halides, the inventive method has the advantage that the hydrogen chloride formed can be easily removed by stripping after the thermal treatment with an inert gas at a temperature of 453 to 513 K. High-purity diisocyanates, for example 4,4'-diphenylmethane diisocyanate, can then optionally be distilled off from the reaction mixture, it also being possible to use the distillation residue.

For carrying out the degradation of chlorine compounds according to the invention, all reactor types of the prior art are suitable, in which temperatures of 453 to 513 K are reached. If the cleavage reactions and the subsequent stripping off of the low-boiling chlorine compounds in an apparatus are to be realized, it is possible to use, for example, bogaste stirred tanks, bubble bed columns or sprinkling columns. When the two process stages are separated, flow reactors, such as shell-and-tube heat exchangers, double-walled tubes and others can also be used for the cleavage reactions. After a sufficient residence time in these reactors, the removal of d6r cleavage products takes place in a downstream apparatus. After purification, the isocyanate is either processed by distillation or cooled to temperatures of about 293 to 333 K, depending on the type and intended use, in order to prevent sedimentation.

The isocyanates treated according to the invention are used for the preparation of diisocyanates and optionally after distillation and mixing processes as high-quality isocyanate components for polyurethane systems. Particularly suitable is the process for aromatic isocyanates, methylene diphenyl diisocyanate, polymethylene polyphenylene polyisocyanate and toluene diisocyanates. The invention will be explained in more detail by means of subsequent embodiments.

Embodiment 1

a) 300 g of 4,4'-diphenylmethane diisocyanate, containing 0.077 parts by weight of% hydrolyzable chlorine and 0.037 parts by mass in% acidity, are heated to 498K with 6 g of carbodiimidized diphenylmethane diisocyanate (Systanat ML) for 2 hours. Nitrogen is introduced for the last 0.5 hours.

b) For comparison, an analogous experiment without addition is made. The following product values are obtained:

a) hydrolyzable chlorine: 0.0183 parts by weight in% acidity: 0.0032 parts by weight in%

b) hydrolyzable chlorine: 0.0233 parts by mass in% acidity: 0.0019 parts by mass in%

Embodiment 2

270 g polymethylene polyphenylene polyisocyanate containing 70 parts by mass in% diisocyanates, 0.375 parts by mass in% hydrolyzable chlorine, 0.105 mass parts in% acidity, are mixed with 30g carbodiimidized diphenylmethane diisocyanate (Systanat ML) and heated to 498 K while passing nitrogen through. After cooling, a product is obtained with the following analytical values:

hydrolyzable chlorine: 0,227 parts by weight in% acidity: 0,019 parts by weight in%

NCO: 29.68 parts by weight in%.

-3- 288 Embodiment 3

250 g polymethylene polyphenylene polylsocyanate of Example 2 are heated with each of 0.6 parts by mass in% of the additives indicated in Table 1 for 30 min at 498K while passing nitrogen through. After treatment, the values given in Table 1 are determined.

Table 1

additive • Di-2-tolylcarbodiimide hydrolyzable chlorine acidity dicyclohexylcarbodiimide Mass shares in% Mass shares in% Triphenyluretonimin 0,216 0,020 Diphenyl-chlorformamidinium- 0.195 0,013 chloride 0.209 0.016 dimeric diphenylcarbodiimide 0.232 0,021 without 0.240 0.019 0.308 0.031

Claims (1)

Cleaning process of organic isocyanates of chlorine-containing compounds by thermal treatment and stripping at a temperature of 453 to 513K, characterized in that organic isocyanate in the presence of 0.1 to 5 parts by mass in% carbodiimides is subjected to the thermal treatment and then stripping by known methods , Field of application of the invention The invention relates to a purification process of organic isocyanates, such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenylene polyisocyanate of chlorine-containing compounds. The achieved thereby high degree of purity of the organic isocyanates has a fundamental effect on the production of polyurethane systems with improved product and processing properties.