CS227246B1 - Process for producing cyanuric acid - Google Patents

Abstract

A method of producing cyanuric acid by pyrolysis of urea, consisting in continuously feeding urea into the reaction space, where a reservoir of already produced cyanuric acid is formed, mixing it with the cyanuric acid present and passing the resulting mixture through the reaction space at a temperature of 160 to 300 °C. The loose powdery product is continuously removed. The ratio between the amount of urea fed and the amount of cyanuric acid retained in the reaction mixture is in the range of 1:2 to 1:9. The process enables continuous production of cyanuric acid in a relatively simple device with a high degree of automation.

Description

The invention relates to the continuous preparation of cyanuric acid by pyrolysis of urea.

Practically the only industrially used process for the production of cyanuric acid is the pyrolysis of urea in the temperature range of 160 to 300 ° C. The sum equation of this reaction is relatively simple,

NH ₂ -CO-NH ₂ O

II

H N ^x C 4 NH 4 O = c. _N .c = o

H

OH = * Ϊ -C

The HO OH + 3 NH ₃ mechanism is disproportionately complex. In fact, the reaction undergoes a series of biuret, triuret, ammelide, melamine, and other formation processes. However, the yield of the reaction is influenced by the temperature and the time for which the pyrolysis is carried out. From a chemical point of view, the reaction is relatively well developed and does not cause any particular problems. However, the behavior of the reaction mixture during pyrolysis is complicated. The urea first melts into a well-flowing melt and solidifies again according to the degree to which the reaction has reached the reaction. The solidifying reaction mass creates hard, very tight crusts on the vessel walls. Since the reaction is not yet complete when the mixture solidifies, and the mixture needs to be heated further, the deposited crust will deteriorate heat transfer and make the reaction difficult.

In practice, therefore, a number of different methods are used to prevent these difficulties. The pyrolysis is carried out, for example, in a high-boiling solvent, in a metal melt, in recycled crude cyanuric acid. For the pyrolysis, urea cyanurate is used, which is prepared in advance from cyanuric acid and urea. The reaction is carried out in a fluidized bed, optionally divided into several stages and each stage carried out in a separate apparatus.

All these processes have advantages, but also disadvantages, consisting mainly in the use of excipients, in the increased need for material handling, in the complexity of the machinery, increased energy consumption, hatching technology, etc.

Many of these drawbacks can be overcome by utilizing the proposed continuous process for producing cyanuric acid according to the present invention.

The urea entering continuously into the reaction is metered at a suitable rate into a reaction space heated to 160-300 ° C, in which a portion of the resulting pruritic cyanuric acid is retained by a suitably designed overflow. The size of the containment exceeds two to nine times the amount of fresh urea dosed, so that at the point where the urea enters the reactor, the mixture remains in a passive state and does not stick to the reaction vessel walls.

With a suitably designed stirrer, the reaction mixture is moved along the length of the reactor at such a rate that at the end of the reactor the reaction is complete and the crude cyanuric acid is continuously discharged in bulk. The urea may be fed to the reactor optionally in admixture with an inert substance, which may be cyanuric acid.

This solution makes it possible to produce cyanuric acid continuously on a relatively simple machine with maximum utilization of consumed energy, low labor intensity, small built-up area, high degree of automation and in stable quality.

The following examples illustrate embodiments of the invention.

He did

Urea was fed continuously at a rate of 0.3 kg / h into a reactor containing 2.5 kg of retained crude cyanuric acid heated to 270 ° C. The crude product was continuously removed from the reactor after a steady-state run of 78% by weight. cyanuric acid.

Example 2

A urea melt was continuously fed at a rate of 0.3 kg / h to the reactor containing the crude cyanuric acid retainer heated to 245 ° C. A crude mixture containing 82 wt.% Was obtained continuously from the reactor. cyanuric acid.

Example 3

A 2: 1 mixture of cyanuric acid and urea was continuously charged to a reactor containing a 2.5 kg crude cyanuric acid retainer heated to 260 ° C. A crude mixture containing 80 wt. cyanuric acid.

Example 4

0.6 kg / h of a 9: 1 mixture of cyanuric acid and urea was continuously fed to the 250 ° C reactor. A mixture containing 85 wt% cyanuric acid was continuously withdrawn from the reactor.

Claims (1)

SUBJECT OF THE INVENTION Process for the production of cyanuric acid by pyrolysis of urea, characterized in that the urea is continuously fed into the reaction space, where the cyanuric acid formed is retained, with which the urea is mixed and the resulting pasty consistency is passed through the reaction space at 60 to 300 ° C. to give a free-flowing powdered product, wherein the ratio between the amount of urea fed and the amount of cyanuric acid retained in the reaction mixture is in the range of 1: 2 to 1: 9.