DD288598A5 - PROCESS FOR CLEANING ORGANIC ISOCYANATES FROM CHLORINE-CONTAINING COMPOUNDS - Google Patents

Abstract

The invention relates to a process for purifying organic isocyanates of chlorine-containing compounds, 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. In this case, organic isocyanate in the presence of 0.001 to 1 parts by mass in% tetrasubstituted urea at a temperature of 473 to 513 K subjected to a thermal treatment. The resulting volatile chlorine compounds are then removed by stripping with inert gas. {Organic isocyanates; diisocyanate; Polymethylene polyphenylene polyisocyanate; chlorine-containing compounds; Cleaning; Stripping with inert gas; thermal treatment with tetrasubstituted ureas}

Description

Field of application of the invention

The invention relates to a process for purifying organic isocyanates, such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanate, of hydrolyzable chlorine compounds. The isocyanates purified by the process according to the invention have improved properties during storage and in the production of polyurethane plastics.

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. Especially in the phosgenation products of aniline-formaldehyde condensates, a high content of these products is observed. 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. It adversely affects the stability, color retention and other properties of the crude isocyanates.

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 1286025, NL 6411863, US 3264336, DE 2210607 describe treatments with metals, metal oxides and metal salts. These processes lead to a number of technological difficulties which relate to the separation of the metals or metal compounds from the isocyanates or the limited usability of metal-containing isocyanates or metal-containing distillation residues.

Similar limitations are found in the use of other additives such as imidazole (GB 1347647), sulfuric acid and its esters (GB 1459691) and arylsulfonic acids and their esters (GB 14b8747).

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

Furthermore, it has been found that while short-term thermal treatments suppress the formation of sediment, they only insignificantly reduce the content of chlorine-containing compounds. In general, however, only the content of easily cleavable chlorine compounds is reduced, which is analytically detected as acidity (see FR 1411934, GB 1015977, US 3274225). The effectiveness of the temperature treatments can be improved by stripping simultaneously with inert gas (US 3219678, BE 659740, GB 1080717, US 3156950, GB 1362708, US 3857871, GB 1114690, DD 118105, GB 1384065, 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 prior art processes have a number of principal disadvantages, particularly the efficacy, the technological expenses, the availability of the recommended additives in the necessary qualities 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 time and energy expenditure, in particular to minimize the content of chlorine-containing compounds to a large extent.

Explanation of the essence of the invention

The aim of the invention is to achieve the goal of achieving the most complete possible effective removal of hydrolyzable chlorine compounds, in order to ensure a high degree of purity of the isocyanates by significantly improving the acidity and hydrolyzable chlorine parameters.

According to the invention, this object is achieved in that chlorine-containing organic isocyanates with tetraalkylureas of the general structures I and II are heated at temperatures of 473-513K optionally with passage of an inert gas and / or in the presence of high-boiling solvent.

«B

As tetraalkylureas are any substances with alkyl, cycloalkyl, aryl or other groups to use. Preferred are Alkyl chains with a small chain length, such as. Methyl or ethyl. Also suitable are heterocyclic ureas of the formula II

(R = H, alkyl, n = 2-4).

It can be assumed that tetrasubstituted ureas react with chlorine-containing compounds in isocyanates,

producing low boiling chlorine-containing reaction products and other compounds.

The process of the invention can be used for the treatment of any isocyanates. Preferred field of application

however, are isocyanates which may contain thermally poorly degradable secondary carbamoyl chlorides, such as

Diphenylmethandiisocyanate and its mixtures with homologous polyisocyanates. The amount of tetrasubstituted ureas necessary for the removal of chlorine-containing compounds is between 0.001

to 1 parts by mass in percent, preferably between 0.02 and 0.4 parts by mass in percent. It usually chooses the smallest amount necessary to avoid loss of isocyanates or strong viscosity changes. The smallest necessary

Amount results from the molar ratios of difficult hydrolysisrbaren chlorine compounds to the inventive

tetrasubstituted ureas, which should be between 10 and 1.

The inventive method is not affected by the presence of hydrogen chloride, but in his Effectiveness increased. It is therefore advisable to remove the contained or formed hydrogen chloride by Stripping with inert gas to begin after a certain treatment time. The treatment according to the invention of chlorine-containing isocyanates is carried out at a temperature of 473 to 513 K. Under certain circumstances, it may be favorable to proceed according to a specific temperature program. The treatment time is

according to conventional methods e.g. for the purification of diphenylmethane diisocyanate at 7 to 10 hours. Compared to the

State of the art egg lauht the inventive method a significant reduction in the reaction time, for. B. 2 to 6 hours

for the above diisocyanate.

The catalytic degradation of chlorine compounds can be traced by the determination of acidity and hydrolyzable chlorine

become. It is also possible to follow the degradation of special chlorine compounds by spectroscopic methods (NMR, GC-MS).

The effect of tetrasubstituted ureas according to the invention was surprising insofar as it is known that

React tetrasubstituted ureas with isocyanates to guanidines and other products.

All types of prior art reactors are suitable for carrying out the process according to the invention, in which Temperatures of 473 to 513K can be achieved. If the treatment and the subsequent removal of the low-boiling Chlorine compounds are to be realized in an apparatus, Beispei! Batchable 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 shell and tube heat exchangers, jacketed tubes and others are usable. After appropriate Residence time in these reactors is the expulsion of the cleavage products in a downstream apparatus. After Depending on the type and intended use, the isocyanate is either distilled or purified to temperatures of

about 293 to 333K cooled to achieve a sedimentation stability.

The isocyanates according to the invention are used for the preparation of diisocyanates and, if appropriate, for distillation and Mixed processes used as a high-quality isocyanate component for polyurethane systems. The inventive method offers in particular the possibility of producing high purity

4,4'-diphenylmethane diisocyanate, which can be distilled off after treatment from the reaction mixture. A use of the distillation residue is possible. Other possibilities of application are in the cleaning of

Polymethylene-polyphenylene-polyisocyanaten.Toluylendiisocyanat and other technical isocyanates. The invention will be explained in more detail by means of subsequent embodiments. Aflsfohrungsbeisplel 1

250g of diphenylmethane diisocyanate containing 0.077 weight percent hydrolyzable chlorine and an acidity of 0.037 weight percent are treated at 498K for 2 hours with 0.2 grams tetramethylurea. Subsequently, in the course of 1 hour at 498 K, the volatile chlorine compounds are removed by passing nitrogen through. There remains a product with 0.0076 parts by mass in percent hydrolyzable chlorine and 0.0010 parts by mass in percent acidity.

Embodiment 2

250 g of polymethylene polyphenylene-pclyisocyanate with about 70 parts by mass in percent diphenylmethane diisocyanate, containing 0.375 parts by mass of hydrolyzable chlorine and 0.105 parts by mass in percent acidity, are treated with 0.25 g of tetramethylurea at 498K while passing nitrogen through for 30 min. After cooling, a polyisocyanate is obtained with the following data: 0.151 parts by weight of hydrolyzable chlorine, 0.009 parts by weight in percent acidity, η = 180 m Pa.s (2O ⁰ C).

Embodiment 3 The procedure is as in Example 2, but used

a) 0.25 g of N, N'-dimethyl-N, N'-diphenylurea

b) 0.25 g of N, N'-dibutyl-imidazolidone-2. It will get:

hydrolyzable chlorine: a) 0.248 parts by mass in percent b) 0.137 parts by mass In percent Acidity: a) 0.011 parts by mass in percent b) 0.012 parts by mass in percent

Claims (2)

1. A process for the purification of organic isocyanates of chlorine-containing compounds by thermal treatment and stripping with inert gas at a temperature of 473 to 513K, characterized in that organic isocyanate in the presence of 0.001 to 1 parts by mass in% of tetrasubstituted ureas subjected to a thermal treatment and then the Stripping by known methods takes place. 2. A process for purifying organic isocyanates of chlorine-containing compounds according to claim 1, characterized in that the thermal treatment of the organic isocyanate in the presence of 0.02 to 0.4 parts by mass in% tetrasubstituted urea.