DD288596A5 - PROCESS FOR CLEANING ORGANIC ISOCYANATES OF CHLORINE COMPOUNDS - Google Patents

Abstract

The invention relates to a process for the purification 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. Here, organic isocyanate in the presence of 0.005 to 2 parts by weight in% trialkyl phosphates at a temperature of 437 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; trialkyl}

Description

Field of application of the invention

The invention relates to a process for the purification of organic isocyanates, such as toluene 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. A part of these compounds proves to be relatively stable under the conditions of preparation and ve ι remains also nar.h a distillation in the isocyanates. It adversely affects the stability, color retention and other properties of isocyanates.

Therefore, there has 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 processes lead to a number of technological difficulties relating to the separation of the metals and metal compounds from the isocyanates or the limited usability of metal-containing isocyanates or metal-containing distillation residues.

Similar restrictions 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 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 2316028 formic acid and formamido are recommended for the same purpose, but tested only for use in toluene diisocyanate.

Furthermore, it has been found that while short term thermal Behani suppress the sediment formation, but only slightly reduce the content of chlorine-containing compounds. Regulator is thereby reduced only the content of easily cleavable chlorine compounds, 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 special distillation techniques (DE 2631168) or crystallization processes (DE 1950101, DE 2322574, DE 19383Ö4 and DE 2532722).

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.

t aim 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 heated with trialkyl phosphates of general structure I at temperatures of 473 to 513K optionally with passing an inert gas and / or in the presence of a high-boiling solvent.

RO - ^ - P = O RO S ^

As trialkyl phosphates, any substances with alkyl, cycloalkyl, aralkyl or other groups R are to be used. Especially

preferred are small chain length alkyl groups, e.g. Methyl and ethyl, it can be assumed that

Trialkylphosphate with chlorine-containing compounds in isocyanates with elimination of low-boiling reaction products

react.

The amount of trialkyl phosphates to be used depends on the content of hydrolyzable chlorine compounds. you

generally selects 0.005 to 2 parts by mass in percent. Preferably, the smallest necessary amount is used to

To avoid yield losses. The addition of the trialkyl phosphates can be arbitrary and throughout the technological Temperature range from 313 to 513 K. 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

Ciphenylmethane diisocyanate and its mixtures with homologs. The treatment according to the invention of chlorine-containing isocyanates is carried out at a temperature of 473 to 513K. Under certain circumstances, it may be beneficial to proceed after a certain temperature. 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. The temperature of 498 K can be expected with a treatment time of 0.2 to 3 hours.

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.

If appropriate, high-purity diisocyanates, for example diphenylmethane diisocyanate, can be obtained from the reaction mixture.

are distilled off, with a 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 of 473 K to 513 K can be achieved. When the cleavage reaction and subsequent stripping of the

light-boiling chlorine compounds in an apparatus are to be realized, for example, fumigated Rülirkessel,

Bubble bed columns or sprinkler columns are used. When separating both process stages are for the Cleavage reactions also flow reactors, such as tubular heat exchangers, jacketed pipes and other usable. After appropriate residence times in these reactors, the removal 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 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 a high-quality isocyanate component for polyurethane systems. Especially

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

Embodiment 1

250g of diphenylmethane diisocyanate containing 0.077 parts by weight of hydrolyzable chlorine and an acidity of 0.037 parts by weight in percent are treated at 498K for 2 hours with 0.2 g of triethyl phosphate. Subsequently, in the course of 1 hour at 498 K, the volatile chlorine compounds are removed by passing nitrogen through. There remains a product containing 0.0092 percent by weight of cololyacyl chloride and 0.0015 percent by weight of acidity. In the vacuum distillation, a pure white diphenylmethane-4,4'-diisocyanate is obtained (HyCl: 0.0018 parts by weight in percent, acidity: 0.0010 parts by weight in percent).

Aus'ührungsbelsplel 2

300 g polymethylene polyphenylene polyisocyanate 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 heated with 0.3 g of triethyl for 30 min at 498 K while passing nitrogen and then cooled. A polyisocyanate having the following values is obtained: hydrolyzable chlorine: 0.151 parts by weight in percent, acidity: 0.009 parts by weight in percent, η = 18OmPa s.

Embodiment 3

250 g of diphenylmethane diisocyanate containing 0.059 parts by mass of hydrolyzable chlorine and having an acidity of 0.021% by mass are treated with 0.25 g of triethyl phosphate at 483 K for 2.5 h. This is followed by a fast

Cooling to 333 to 343 K and an after-reaction at this temperature. A modified diphanylmethane-4,4'-

Diisocyanate with the following values: hydrolyzable chlorine: 0.0130 parts by mass in%, acidity: 0.0018 parts by mass in percent.

Claims (2)

1. A process for the purification of organic isocyanates of chlorine compounds by thermal
Treatment and stripping with inert gas at a temperature of 473 to 513K, thereby
characterized in that organic isocyanates in the presence of 0.005 to 2 parts by mass in% of trialkyl phosphates are subjected to the thermal treatment and then the
Stripping by known methods takes place. 2. A process for purifying organic isocyanates of chlorine compounds according to claim 1, characterized in that trialkyl phosphates are used in an amount which is about 0.01 to 1 parts by mass in% of the isocyanate used correspond.