DD288597A5 - CLEANING PROCEDURE OF ORGANIC ISOCYANATES OF CHLORINE COMPOUNDS - Google Patents

Abstract

The invention relates to a purification process of organic isocyanates of chlorine 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 the process, organic isocyanate is subjected to a thermal treatment in the presence of compounds having a biuret structure at a temperature of 473 to 513 K. The resulting volatile chlorine compounds are then removed by stripping with inert gas. {Organic isocyanates; diisocyanate; Polymethylene polyphenylene polyisocyanate; chlorine-containing impurities; Cleaning; Stripping with inert gas; thermal treatment with biurets}

Description

Characteristics of the 'known prior art,

Organic isocyanates prepared after phosgenation of amines usually 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 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 patents 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 1347,647), sulfuric acid and its esters (GB 1459691) and toluenesulfonic acids and their esters (GB 1458747).

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

Furthermore, it has been found that short-term thermal treatments, while suppressing sedimentation, but only slightly reduces the chlorine-containing compounds. Above all, only the content of easily cleavable chlorine compounds is reduced, which are detected analytically as acidity. (FFt 1411924, GB 1015977, US 3274225) The effectiveness of the thermal processes can be somewhat improved if simultaneously inert gases (US Pat. No. 3,159,050, US Pat. No. 3,219,678, BE 659740, GB 1080717, GB 1362708, GB 1114690, DD 118105, GB 1384065, US Pat. No. 3,857,871 , US 4118286) or special high-boiling solvents (GB 1114690, DD 118105) or are passed through the isocyanates in a suitable form.

It is also known to purify isocyanates by special distillation techniques (DE 2G31168) or by crystallization processes (DE 1950101, DE 2322574, DE 1938384, DE 2532722). It is clear that the processes of the prior art have a number of principal disadvantages, which mainly affect the effectiveness, the technological expenses, the accessibility 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, after an economical purification process from crude isocyanates with reduced expenditure of time and energy, in particular to minimize, in particular, the content of chlorine-containing compounds.

Explanation of the essence of the invention

The object of the invention is to achieve the goal of achieving 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 acidity and hydrolyzable chlorine parameters.

According to the invention the object is achieved in that chlorine-containing organic isocyanates are heated in the presence of compounds having the following biuret structure at temperatures of 4 '3 to 513K.

GO-K]

For the general groups R, H or any aliphatic or aromatic radicals are to be used. It is favorable, if R

is equal to H It is also possible to use biurets which carry free NCO groups in the groups R.

The effect of bluretes according to the invention was surprising insofar as predominant reactions contained NH groups with isocyanate groups had to be assumed. The reduction of the content according to the invention

Chlorine-containing compounds show that at high temperatures also less reactive chlorine compounds, such as N, N-

Disubstituted carbamoyl chlorides, come to the reaction. The inventive method can be used for the treatment of any isocyanates, preferred application

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

Diphenylmethane diisocyanate and its mixtures with homologs. The amount of biurets necessary for the removal of chlorine-containing compounds is between 0.01 and 2 parts by mass Percent. As a rule, one chooses the smallest amount necessary to avoid losses of isocyanate groups. The smallest

The necessary amount results from the molar ratios of the biurets related to the invention to the hardly hydrolyzable chlorine compounds, which should be between 0.05 and 2.

The inventive method is not affected by the presence of hydrogen chloride, but in his Effectiveness increased. It is therefore recommended to remove the contained or formed hydrogen chloride by Stripping with inert gas until the end of the thermal treatment. 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

for example, in diphenylmethane diisocyanate according to conventional methods between 7 and 10 hours. Compared to the

State of the art allows the inventive method a significant reduction in the reaction time. It is located in

general between 0.2 and 6 hours. At a temperature of 498K, a treatment tent of 0.2 to 3 hours can be expected.

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

become. It is also possible, the degradation of special chlorine compounds by spectroscopic methods, for example the

To determine NMR spectroscopy. Compared with most of the prior art processes, the process of the invention offers the advantage that the

used additives may remain in the treated isocyanates. High-purity diisocyanates, for example diphenylmethane diisocyanate, may then be distilled off from the reaction mixture, if desired! also one

Further use of the distillation residues is possible. For carrying out the treatments according to the invention, all reactor types of the prior art are suitable in which Temperatures from 473 to 513K are achieved. When the cleavage reaction and subsequent stripping of the low-boiling Chlorine compounds to be realized in an apparatus can, for example, fumigated stirred tank, bubble bed columns

or sprinkler columns are used. When separating both 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 times in these reactors, the expulsion of the cleavage products takes place in a downstream apparatus. After Cleaning the isocyanate is processed by type and use either by distillation or to temperatures of about 293

cooled to 333 K to prevent sedimentation.

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. Further possibilities of Application consist in the cleaning voi. r-Olymethylene-polyphenylun-polyisocyanate, diphenylmethanediisocyanate, Toluylene diisocyanate and other technical isocyanates. The invention will be explained in more detail by means of subsequent embodiments. Version 1

300g polymethylene polyphenylene polyisocyanate, with 70 parts by mass as a percentage of diphenylmethane diisocyanate containing 0.375 parts by mass in percent hydrolyzable chlorine and 0.105 parts by mass in percent of acidity are ohfie at 498K 20min and 10min while passing nitrogen at 0,152g biuret (NH [CONH _{2] 2} ). After cooling, the polyisocyanate obtained has the following data: 0.202 parts by weight of hydrolyzable chlorine, 0.018 parts by weight of acidity.

Embodiment 2 The procedure is as in Example 1, but uses 0.4 g Tripheny! Biuret and receives the following data: 0.220 parts by mass in percent

hydrolyzable chlorine, 0.013 weight percent acidity.

Embodiment 3

250 g of polymethylene polyphenylene polyisocyanate of Example 1 are mixed with 50 g of diphenylmethane diisocyanate with 5 parts by mass of biuret polyisocyanate and worked as in Example 1. A reaction product with 0.103 parts by mass in percent hydrolyzable chlorine and 0.010 parts by mass in percent acidity.

Claims (2)

Purification method of organic isocyanates of chlorine compounds by thermal treatment and stripping with inert gas at a temperature of 473 to 513 K, characterized in that organic isocyanate in the presence of 0.01 to 2 mass fractions in% of compounds with biuret structure of the thermal treatment is exposed and then the stripping takes place by known methods. Field of application of the invention The invention relates to a process for the purification of 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.