DD285593A5 - PROCESS FOR CLEANING ORGANIC ISOCYANATES - Google Patents

Abstract

The invention relates to a process for the purification of organic isocyanates, such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenylene polyisocyanate of chlorine-containing compounds. The achieved thereby high degree of purification of the organic isocyanates has a fundamental effect on the production of polyurethane systems with improved product and processing properties. In this case, organic isocyanate in the presence of 0.001 to 1 parts by mass in% Saeureamiden with at least one NH group at a temperature of 473 to 513 K subjected to a thermal treatment. The hydrogen chloride is then removed by stripping with inert gas {organic isocyanates; diisocyanate; Polymethylene polyphenylene polyisocyanate; chlorine-containing impurities; Cleaning; Stripping with inert gas; thermal treatment; Sour amides as additions}

Description

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.

Characteristic of the known state of the art

Organic isocyanates prepared by phosgenating amines typically contain a number of chlorine-containing compounds that are undesirable. Particularly 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. Some of these compounds are found to be relatively stable under the conditions of preparation and remain in the isocyanates even after distillation. 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, patent applications DE 1138040, DE 1286025, NL 6411863, US 3264336 and DE 2210607 describe treatments with metals, metal oxides and metal salts. These ancestors 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 Destillationsi residues. Similar limitations are found in the use of other additives such as imidazole (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 3274225) can prevent the formation of sediments, but only insignificantly affects 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 1384065, US4118286).

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 prior art processes have a number of principal disadvantages, which mainly affect the effectiveness, the technological expenses, the accessibility of the recommended additives in the necessary qualities associated with a high cost and the usability of the distillation residues.

Object of the invention

The invention is based on the objective, according to an economical purification process from crude isocyanates with reduced expenditure of time and energy, in particular to minimize the amount of chlorine-containing compounds as far as possible.

Explanation of the essence of the invention

The invention is to achieve the objective of the object to achieve the fullest possible effective removal of 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, this object is achieved in that chlorine-containing organic isocyanates are thermally treated in the presence of cyclic or open-chain amides having at least one NH group at a temperature of 473 to 513K and then at these temperatures the volatile chlorine-containing compounds formed by passing an inert gas and / or of a high boiling solvent.

Surprisingly, acid amides also react with acyl ureas despite the preferred reaction with NCO groups

contained Ν, Ν-Oijubstituted carbamoyl chlorides with elimination of hydrogen chloride. This can be a significant

Part of the chlorine-containing impurities contained in isocyanates are removed. Suitable acid amides are derived from organic or inorganic acids or represent, for example, heterocyclic Compounds which have an acid amide group. Examples of suitable acid amides are: acetamide, benzamide, Sul / amide, toluenesulfonic acid amide, pyrrolidone, ε-caprolactam ur.d analogous compounds. The amount of acid amides necessary for the removal of chlorine-containing compounds is between 0.001 and 1 part by weight

in%, preferably between 0.01 and 0.2 parts by weight in%. The use depends on the content of chlorine-containing

Impurities in the isocyanates. As a rule, one chooses the small amount necessary to reduce the yield To avoid side reactions. To increase the effectiveness of the method according to the invention, it is often advantageous if a catalytic amount of

0.01 to 0.2 parts by mass in% hydrogen chloride is present, which can be removed after the treatment together with the volatile chlorine compounds formed.

The inventive treatment of chlorine-containing isocyanates is carried out at a temperature of 473 bs 513K. Under certain circumstances, it may be favorable to proceed according to a specific temperature program. The treatment time is

generally between 7 and 10 hours according to 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 about 0.3 to a thermal treatment at 498K

3 hours. The catalytic decomposition of chlorine compounds can be determined by the determination of acidity and hydrolyzable

Chlorine can be traced. It is possible to decompose specific chlorine compounds, for example, by NMR spectroscopy

determine.

Compared with most of the prior art processes, the process of the invention offers the advantage that the

formed easily volatile chlorine compounds after thermal treatment by stripping with a simple

Inert gas can be removed at a temperature of 473 to 513K, while the conditions used in the treated Isocyanates may remain. From the reaction mixture may then optionally high purity diisocyanates, for example

4,4'-diphenylmethane diisocyanate, are distilled off, whereby a use of the distillation residue can be carried out. For carrying out the HCL-catalyzed cleavage of chlorine compounds, all types of reactors of the prior art are suitable

Technology in which temperatures of 473 to 513 K are reached. If the cleavage reactions and the subsequent stripping

the low-boiling chlorine compounds are to be realized in an apparatus, for example, fumigated stirred tank,

Bubble bed columns or sprinkler columns are used. When separating the two process stages are for the Cleavage reactions also flow reactors, such as tubular heat exchangers, jacketed pipes and other usable. After 6,. 'Spending residence time in these reactors, the expulsion of the cleavage products takes place in a downstream Apparatus. After cleaning, the isocyanate is either processed by distillation or on depending on the type and intended use Temperatures of about 293 to 333K cooled to prevent sedimentation. The isocyanates treated according to the invention are used for the preparation of diisocyanates and optionally after Distillation and mixing processes used as high-quality isocyanate components for polyurethane systems. Especially

suitable is the process for aromatic isocyanates, such as Mothylendiphenyldiisocyanat, polymethylene polyphenylene polyisocyanate and toluene diisocyanates. The invention will be explained in more detail by means of subsequent embodiments.

Exemplary embodiment 1

300 g of polymethylene polyphenylene polyisocyanate with 70 parts by mass in% diphenylmethane diisocyanate, containing 0.364 parts by mass in% hydrolyzable chlorine and 0.070 parts by mass in% acidity are treated at 498K for a total of 30min, of which 15min while passing nitrogen, with 0.3g ε-caprolactam. After cooling, the polyisocyanate obtained has the following data:

0.213% by mass of hydrolyzable chlorine 0.019 Mussenantoil in% Acidity

Without addition, the corresponding values are 0.298 and 0.017% by mass. Embodiment 2

250 g of 4,4'-diphenylmethane diisocyanate, containing 0.077 parts by weight of% hydrolyzable chlorine and 0.37 parts by weight in% acidity, are mixed with 0.10 g of acetamide and heated to 498K for a total of 180 minutes, of which 60 minutes while passing nitrogen through. You get a product with the following data:

0.0060 parts by weight in% hydrolyzable chlorine 0.0015 parts by weight in% acidity

By vacuum distillation, high purity 4,4'-diphenylmethane diisocyanate can be obtained (0.0012 parts by weight in% hydrolyzable chlorine).

Claims (2)

1. A process for the purification of organic isocyanates of chlorine-containing compounds by thermal treatment and stripping at a temperature of 473 to 513 K, characterized in that organic isocyanate in the presence of 0.001 to 1 mass% of acid amides having at least one NH group exposed to the thermal treatment and then the stripping is done by known methods. 2. A process for the purification of organic isocyanates according to claim 1, characterized in that the thermal treatment with acid amides 0.01 to 0.2 parts by mass in% is provided with at least one NH group.