DD286934A7 - PROCESS FOR CLEANING ORGANIC ISOCYANATES FROM CHLORINE-CONTAINING COMPOUNDS - Google Patents

Abstract

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. In this case, organic isocyanate is exposed in the presence of 0.01 to 1.0% hydrogen chloride as a catalyst at a temperature of 473 to 513 K of 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; Catalyst hydrogen chloride}

Description

Field of application of the invention

The invention relates to a purification process of organic isocyanates, such as tolylene diisocyanate, diphenylmethane diisocyanate and Polymethyien polyphenylenpolyisocyanat 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 Verarboitungseipenschaften.

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. Thus, in the patent specifications DE 1,138,040; DE 1,286,025; NL 6,411,863; No. 3,264,336 and DE 2,210,607 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 or metal compounds from the isocyanates or the limited usability of metal-containing isocyanates and metal-containing distillation residues. Similar limitations are found in the use of other additives such as imidazole (GB 1,347,647), sulfuric acid and its esters (GB 1,459,691) and toluenesulfonic acids and doron esters (GB 1,458,747).

It is known from the patent specification DE 1.240.849 to eliminate the content of hydrolyzable chlorine by a chloride hydrolysis carried out in a specific manner. In DE 2,316,028 formic acid and formamide are recommended for the same purpose, but only tested for their usefulness in tolylene diisocyanate.

Furthermore, short-time thermal treatments (FR 1,411,934, GB 1,015,977, US 3,2 / 4,225) have been found to prevent the formation of sediment but to have insignificant effects on other contaminants. The effectiveness of the temperature treatments can be improved by stripping simultaneously with inert gases and / or inert solvents (US 3,219,678; BE 659,740; GB 1,080,717; US 3,156,950; GB 1,362,708; US 3,857,871: GB 1,114 .690; DD 118.105; GB 1.384.065; US 4.118.286).

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

It is furthermore known to purify isocyanates by means of special distillation techniques (DE 2,631,168) or crystallization processes (DE 1,950,101, DE 2,322,574, DE 1,938,384 and DE 2,532,722).

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 the Zie! on the basis of an economic purification process from crude isocyanates with reduced expenditure of time and energy especially to minimize the content of chlorine-containing compounds waitestgehend.

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 in the presence of hydrogen chloride as a catalyst at a temperature of 473 to 513 K heated and then removed at these temperatures, the hydrogen chloride by passing an inert gas and / or a high-boiling inert solvent.

Although the process according to the invention can be used for the treatment of any isocyanates, the preferred field of application is isocyanates, which may contain thermally poorly degradable secondary carbamoyl chlorides, such as diphenyltranediisocyanate and its mixtures with homologous polyisocyanates.

The amount of hydrogen chloride necessary for the catalytic removal of chlorine-containing compounds is between 0.01 and 1%, preferably 0.02 and 0.2%. As a rule, one chooses the smallest amount necessary for catalysis, since the hydrogen chloride must be removed again. For the introduction of hydrogen chloride, various methods are applicable.

It is also possible to introduce gaseous hydrogen chloride at any temperatures. It is also possible to add compounds which split off hydrogen chloride, for example carbamoyl chlorides of primary amines or chlorination products.

A specific embodiment is the generation of hydrogen chloride in the isocyanate, for example by the addition of a small amount of compounds which hydrolyze chlorine-containing compounds to hydrogen chloride, such as, for example, water or formic acid.

Furthermore, it is also possible to supply the isocyanate with a small amount of aqueous hydrochloric acid or a solvent saturated with hydrogen chloride.

It is important that the catalytically active hydrogen chloride remains within the limits of the invention during the treatment. For this purpose, it is favorable to carry out an analytical control of the chlorine values during the reaction time.

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 favorable to proceed according to a specific temperature program. Dio treatment time is generally between 7 to 10 hours according to conventional methods. Compared to the prior art, the method according to the invention allows a significant reduction in the reaction time. The treatment line is reduced to 0.2 to 6 hours. It is about 0.3 to 3 hours at a thermal treatment of 493 K. Dor catalytic degradation of chlorine compounds can be traced by the determination of acidity and hydrolyzable chlorine. It is possible to determine the degradation of special chlorine compounds, for example by NMR spectroscopy.

The catalytic effect of hydrogen chloride according to the invention was surprising insofar as previously only the catalytic removal of chlorine-containing compounds with strongly acidic metal halide succeeded. Moreover, in most processes, conditions were predominantly chosen that caused rapid removal of hydrogen chloride.

Compared to the use of metal halides, the inventive method has the advantage that the catalyst hydrogen chloride can be easily removed by stripping after the thermal treatment with an inert gas at a temperature of 473 to 513 K. High-purity diisocyanates, for example 4,4'-diphenylmethane diisocyanate, can then optionally be distilled off from the reaction mixture, it being also possible to use the Dostillationsrückstandes. For carrying out the HCl-catalyzed cleavage of chlorine precursors, all types of renatures of the prior art are suitable in which temperatures of 473 to 513 K are reached. If the cleavage reactions and the subsequent stripping off of the low-boiling chlorine compounds in an apparatus are to be realized, for example, gassed stirred tanks, bubble bed columns or sprinkling columns can be used. Upon separation of the two process stages, flow reactors, such as shell-and-tube heat exchangers, double-walled tubes and others, can also be used for the cleavage reactions. After a sufficient residence time in these reactors, the removal of the cleavage products takes place in a downstream apparatus. After purification, the isocyanate is either processed by distillation or cooled to temperatures of about 293 to 333 K, depending on the type and intended use, in order to prevent sedimentation.

The isocyanates treated according to the invention are used for the preparation of diisocyanates and optionally after distillation and mixing processes as high-quality isocyanate components for polyurethane systems. The process is particularly suitable for aromatic isocyanates, such as methylene diphenyl diisocyanate, polymethylene polyphenylene polyisocyanate and toluene diisocyanates.

The invention will be explained in more detail by means of subsequent embodiments.

Embodiment 1

0.15 g of hydrogen chloride are introduced into 250 g of diphenylmethane diisocyanate (acidity 0.037%, hydrolyzable chlorine 0.077%) at 353 K and heated to 498 K with stirring for 60 minutes. Then it is also stripped with nitrogen at 498 K for 60 min. After this treatment, the following chlorine values are found:

Acidity = 0.0004%

hydrolyzable chlorine = 0.0079%

Embodiment 2

250 g of diphenylmethane diisocyanate of Example 1 are heated for 60 minutes at 498K and an adjusted content of 0.028% hydrogen chloride. It is then stripped with nitrogen at 498 K for 60 minutes. The following chlorine words are obtained:

Acidity = 0.0032%

hydrolyzable chlorine = 0.0170%

Implementation Bills 3

300 g of a polymethylene polyphenylene polyisocyanate containing 0.377% hydrolyzable chlorine and 0.076% acidity, are mixed at 8OK with 0.2 ml of 36% hydrochloric acid, heated for 15 min to 225K and then 15min at 498K while reading through nitrogen. After this treatment, 0.012% is found for the acidity and 0.203% for the hydrolyzable chlorine.

Working without aqueous hydrochloric acid and initiating nitrogen at 498K for 30 min gives the following data:

Acidity = 0.01 β%

hydrolyzable chlorine - 0.327%

Embodiment 4

25Og of diphenylmethane diisocyanate of Example 1 are heated with 10 g of diphenylmethane diisocyanate (containing 2.39% MCI in the form of the primary carbamoyl chloride) for 60 min at 498 K and then while passing nitrogen through the contained and formed hydrogen chloride in the course of 60min at 498K removed. A diisocyanate is obtained with the following data:

Acidity = 0.0017%

hydrolyzable chlorine = 0.0073%

Implementation Bills 5

The procedure is as in Example 4, but using only 3 g of diphenylmethane diisocyanate with 2.39% HCl and heated to 513K for 30 min.

It is then removed with nitrogen at 513 K hydrogen chloride for 60 min. Data received:

Acidity = 0.0041%

hydrolyzable chlorine = 0.0128%

Exemplary embodiments

In 250 g of diphenylmethane diisocyanate {acidity 0.0091%, hydrolyzable chlorine 0.046%) is added at 473K 0.12% water based on diphenylmethane diisocyanate. After a reaction time of 120 minutes at this temperature, during which the acidity (HCI content) increases to 0.0203%, nitrogen is introduced over 60 minutes to remove the hydrogen chloride formed. After this treatment, 0.0010% is obtained for acidity and 0.0037% for hydrolyzable chlorine. If you work without water and initiate nitrogen at 473 K for 240min, you will get the following data: Acidity = 0.0011%

hydrolyzable chlorine = 0.0067%

Claims (2)

1. purification process of organic isocyanates of chlorine-containing compounds by thermal treatment and stripping, characterized in that organic isocyanate is exposed in the presence of 0.01 to 1.0% hydrogen chloride as catalyst at a temperature of 473-513 K of the thermal treatment and then the Stripping by known methods takes place. 2. purification process of organic isocyanates according to claim 1, characterized gekennozichnet that the thermal treatment of the organic isocyanate in the presence of 0.02 to 0.2% hydrogen chloride takes place.