DD288594A5 - PROCESS FOR CLEANING ORGANIC ISOCYANATES OF HYDROLYZABLE CHLORINE COMPOUNDS - Google Patents

Abstract

The invention relates to a process for purifying organic isocyanates of hydrolyzable chlorine compounds, such as tolylene diisocyanate, diphenylmethane diisocyanate and polymethylene polyphenylene polyisocyanate of chlorine-containing compounds. The high purity aromatic isocyanates obtained are used to produce high purity diisocyanates and to produce polyurethane systems with improved processing and product properties. Here, organic isocyanate in the presence of 0.001 to 1 parts by mass in% of ammonium salts 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 impurities; Cleaning; Stripping with inert gas; thermal treatment with ammonium salts as additives}

Description

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 polylsocyanate, 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 usually contain a number of chlorine-containing compounds which are undesirable. Especially in the phosgenation products of aniline-formaldehyde condensation, 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. A part of this compound proves to be relatively stable under the conditions of preparation and remains even after distillation in the isocyanates. It adversely affects the stability, color retention and other properties of the 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, NI 6411863, US 3264336 and DE 2210607 describe treatments with metals, metal oxides and metal salts. These processes lead to a number of technologi see difficulties that offer the separation of metals and 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 arylsulfonic acids and their esters (GB 1458747).

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 2 316 028 formic acid and formamides 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, only the content of easily cleavable chlorine compounds is reduced, which is analytically detected as acidity (see FR 1411934, GB 1015977, US 3,272,425)

 The effectiveness of the thermal treatment can be improved when stripping simultaneously with inert gas and / or inert solvents (US 3219678, BE 659740, GB 1080717, US 3156950, GB1362708, US 3857871, GB 1114690, DD118105, GB 1384065, US4118286).

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

It is further bekaniv., Isocyanates by special distillation techniques (DE 2631168) or crystallization process (DE 1950101, DE 2322574, DE 1938384 and DE 2532722) to clean.

It is clear that the prior art processes have a number of principal disadvantages, especially 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 of minimizing, in particular, the content of chlorine-containing compounds, after an economical purification process from crude isocyanates with a reduced expenditure of time and energy.

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 the object is achieved in that chlorine-containing organic isocyanates are treated thermally with ammonium salts at temperatures of 473 to 513K while passing an inert gas and / or high-boiling solvent. Ammonium salts are to be understood as meaning any salts of ammonia with inorganic or organic acids. In the general formula (NH ₄ I _n X, X represents a mono- or polyvalent radical residue. Examples of X are:

Chloride, carbonate, bicarbonate, sulfate, hydrogen phosphate, oxalate, formate, acetate, tosylate, etc. Particularly preferred are ammonium salts which readily split under the reaction conditions, such as, for example Ammonium carbonates or ammonium carboxylates. The effect of ammonium salts according to the invention was surprising since it had to be assumed that ammonium salts

at elevated temperatures predominantly according to DD 112462 with NCO groups with elimination of isocyanic acid and

Formation of biurets should respond. According to the invention, however, a predominant reaction with chlorine-containing Compounds observed, in particular in the sharp reduction in the content of N, N-disubstituted Carbamoyl chloride detect. The inventive method can be used for the treatment of any organic 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 homologs.

The amount of ammonium salts necessary for the removal of chlorohydro compounds is between 0.001 and

1% by weight in%, preferably between 0.01 and 0.2% by weight in%. As a rule, one chooses the smallest one necessary

Amount to avoid losses of isocyanate or strong viscosity changes. The smallest necessary amount results

from the molar ratios of difficultly hydrolyzable chlorine compounds to ammonium groups, which should be between 20 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 Strip with inert gas until late in 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 498 K, a treatment time of 0.2 to 3 hours can be expected.

The catalytic degradation of chloro compounds can be followed 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 optionally be distilled off from the reaction mixture, one of which may also be distilled off

Further use of the distillation residues is possible. For carrying out the treatment according to the invention, all reactor types of the prior art are suitable in which Temperatures of 473 to 513 K can be 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 also for the cleavage reactors

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 Depending on the type and use, the isocyanate is either distilled or purified to temperatures of about 293

cooled to 333 K to prevent sedimentation.

The erfindungugemäß treated isocyanates are for the preparation of diisocyanates and optionally after Distillation and mixing processes used as a high-quality isocyanate component for Polyurethanansyste ^ /. Especially

suitable is the process for aromatic isocyanates such as diphenylmethane diisocyanate, polymethyl-polyphenylenepolyisocyanate and toluene diisocyanate.

The invention will be explained in more detail by the following embodiments. example 1

250 g of polymethylene polyphenylene polyisocyanate with 70 parts by mass in% diphenylmethane diisocyanate, containing 0.375 parts by weight in% hydrolyslerbares chlorine and 0.105 parts by weight in%, are mixed at 333 K with 0.2 g of ammonium carbonate and then thermally for 30 min at 498 K while passing nitrogen treated. After cooling, the following analytical values are obtained:

0.170 parts by weight in% hydrolyzable chlorine, 0.018 parts by weight in% acidity.

If one uses 0.16g ammonium acetate, one finds:

0.173 parts by weight in% hydrolyzable chlorine, 0.0064 parts by weight in% acidity.

Example 2

250 g of diphenylmethane diisocyanate containing 0.077% by weight of% hydrolyzable chlorine and 0.037% by weight of acidity are violated with 0.1 g of ammonium bicarbonate and thermally treated at 498K for 60 minutes and then the volatile chlorine-containing compounds are removed from COmin at 498K while nitrogen is passed through. Γ lan receives a product with the following data:

0.0083 parts by weight in% hydrolyzable chlorine, 0.0013 parts by weight in% acidity

After vacuum distillation, a diphenylmethane diisocyanate having 0.0016 mass% hydrolyzable chlorine and 0.0009 mass% acidity is obtained.

Claims (2)

1. A process for the purification of organic isocyanates of hydrolyzable chlorine compounds by thermal treatment and stripping with inert gas at a temperature of 473 to 513 K, characterized in that the organic isocyanate in the presence of 0.001 to 1 parts by weight in%
Ammonium salts is subjected to a thermal treatment and then the stripping is carried out by known methods. 2. A process for the purification of organic isocyanates of hydrolyzable chlorine compounds
Claim 1, characterized in that the thermal treatment of the organic
Isocyanates in the presence ν on 0.01 to 0.2 parts by mass in% ammonium salts.