DE1768804A1 - Process for the production of autocondensation products of urea and for their separation from the resulting mixtures - Google Patents

Description

PATENT LAWYERS

Dr. D. Thomsen H. Tiedtke G. Bulling

Dipl.-Chem. Dipl.-Ing. Dipl.-Chem.

case B.2o 3 ^ 5 eooo Munich 2

VAL 33

TELEPHONE 0811/22 68 94

TELEGRAM ADDRESS: THOPATENT

MONKS

^{2 J} Uli 1968

Imperial Chemical Industries Limited London (Great Britain)

Process for the production of autocondensation products of urea and their Separation from the resulting mixtures

The invention relates to the pyrolysis of urea and to the production and separation thereof Autocondensation products, in particular biuret, made therefrom. The manufacture of such auto-condensation products, in particular Biuret, is generally made by heating urea in a reaction vessel or rows of reaction vessels at temperatures between about 130 ° and 210 ° C in carried out in such a way that biuret is formed with evolution of ammonia. This reaction progresses at higher levels Temperatures continue faster, but when biuret is formed, it reacts with the urea that has not yet been converted

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with formation of triuret and cyanuric acid. It is therefore common to use the molten mass (consisting of urea, Biuret, triuret and cyanuric acid) from the reaction vessel or vessels if the content of Biuret, triuret and cyanuric acid in it is in a favorable order of magnitude and these three components so far as possible from the unreacted urea that goes to the reaction vessel or to the reaction vessels in the circuit is returned to separate.

The standard method of separation is to dissolve the molten mixture in water, to cool it to crystallize out the biuret, triuret and cyanuric acid (which are less soluble than hernia), to filter the biuret, triuret and cyanuric acid, to filter the water content of the reduce Hernstoffiltrats by evaporation and attributed this circulated to the reaction vessel and the reaction vessels. The main shortcomings of this method are:

(a) The entire biuret cannot be crystallized out by cooling. For example, about 30% of the biuret leaving the reaction vessel or vessels can be returned to them with the urea filtrate,

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and the presence of that substantial amount of biuret in the return fluid promotes the formation of larger amounts of triuret and cyanuric acid.

(b) Some urea goes through hydrolysis during the Evaporation stage lost.

It has been found that these disadvantages can be overcome by the invention, through which a method for Separation of urea from a mixture of urea and its autocondensation products, in particular biuret, Triuret and cyanuric acid is created in which the mixture is dissolved in water, the solution with a complex-forming gown is treated that is capable of forming an insoluble complex with the tissue at the solution temperature, and this insoluble complex is separated from the solution in which the autocondensation products remain dissolved. After the insoluble complex has been separated from it, the autocondensation products can pass out of the solution known processes are crystallized out. The center forming the complex is preferably one that the severed insoluble complex back to urea and complexing agent can be decomposed by subsequent heating can.

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Of the compounds which are known to form insoluble complexes with urea, saturated straight-chain hydrocarbons or hydrocarbon derivatives are preferably used. When using such hydrocarbons or hydrocarbon derivatives, the stability of the complex increases with increasing molecular weight and decreases with increasing temperature. Therefore, when the separation of the urea is to be carried out at high temperatures (e.g., about 5o ° or 60 ⁰ C), it is advisable to have a complexing agent with a high molecular weight to use, which increases in any case the efficiency of the separation.

The invention also provides a method for producing autocondensation products from urea, in particular Biuret, triuret and cyanuric acid created by the pyrolysis of urea in one or more reaction vessels, in which the molten mixture (containing urea, biuret, triuret and cyanuric acid) from the reaction vessel or is withdrawn from the reaction vessels, the mixture is dissolved in water, a complexing agent is added to the solution that is capable of forming an insoluble complex with the dissolved urea, which precipitates, the insoluble one The complex is separated from the solution and the autocondensation products (especially triuret and cyanuric acid)

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be crystallized from the solution. The severed one insoluble complex is preferably recycled to the process.

An embodiment of the invention is illustrated in Figure 1 of the drawings. The pulp is pyrolyzed in a reaction vessel or a series of reaction vessels 1 to form a molten mixture of urea and its condensation products (mainly biuret with about triuret and cyanuric acid). The molten mixture is withdrawn into a dissolving and complexing tank 2, wherein the mixture is dissolved in water and a complexing agent (e.g., a paraffin) is added to form an insoluble complex with the pulp which precipitates. (Two separate tanks, one for solution and another for complex formation, can be useful instead of the tank 2 shown). The insoluble complex and the solution are sent to a centrifuge 3 where they are separated, the insoluble complex being sent to a decomposer 4 where it is decomposed by heat into urea and complexing agent. These are separated, wherein the urea to the reaction vessel or the reaction vessels 1 and the complex forming agent is recycled to the solvent and complex formation tank 2 in the circulation (In fact, the decomposer k Not necessarily required.; The insoluble

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borrowed complex can directly to the reaction vessel or to the Reaction vessels 1 are returned in the circuit, where the temperature is high enough to cause the decomposition, the complexing agent is allowed to remain in the reaction vessel (s) 1, and when the molten mixture containing a complexing agent is withdrawn into the solution and the complexing tank 2 the complex-forming agent re-forms with the urea to form the insoluble complex). fresh urea is added to the insoluble complex before it is sent to the decomposer 4, however, the fresh urea could obviously be transferred directly to the reaction vessel or vessels 1 in the same way are fed.

The solution from der.Zentrifuge 3 becomes a crystallization vessel 5 where the dissolved biuret (and other autocondensation products) are crystallized and then to the centrifuge 6, where these separated from the solution 'are dried in a dryer 7 and recovered. the remaining solution that still contains some biuret and other auto-condensation products and possibly containing some urea, the centrifuge 6 becomes the solution and complexing tank 2 returned in the cycle.

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From the above it appears that only urea (with complexing agent) to the decomposer 4 and the The reaction vessel or the reaction vessels 1 is returned in the circuit; no biuret is returned there, and consequently there is a decrease in the amount of triuret and cyanuric acid formed therein. Furthermore, the urea complex is returned to the decomposer 4 in solid form, whereby the costly and laborious evaporation step of the known separation processes and loss of urea is avoided by hydrolysis that occurs in the process.

The invention also provides a method for producing autocondensation products from urea, in particular Biuret, triuret and cyanuric acid, created by the pyrolysis of urea in one or more reaction vessels, in which the molten mixture (containing urea, biuret, triuret and cyanuric acid) from the reaction vessel or the reaction vessels is withdrawn, the mixture is dissolved in water, the autocondensation products (containing Biuret, triuret and cyanuric acid) crystallized out of the solution and separated off, to the separated urea containing solution is added a complexing agent which is suitable with the dissolved urea a

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to form insoluble complex, which precipitates, the insoluble complex is separated from the solution, the complex to urea and complexing agent decomposed by heating and the urea to the reaction vessel or to the Reaction vessels and the complex-forming agent are recycled to the complex-forming stage.

Another embodiment of the invention is shown in FIG. 2 of the drawing. As in Fig. 1, the melted Mixture (containing urea biuret, triuret and cyanuric acid) withdrawn from the reaction vessel or the reaction vessels 1 and dissolved in water in a solution tank 8. The resulting solution is in a crystallization vessel 9 for crystallization the autocondensation products (biuret, triuret and cyanuric acid) treated, which are separated in centrifuge Io, in dried in a dryer 11 and recovered. The separated urea-containing solution becomes a complexing tank 12 passed, to which a complexing agent is added which is suitable with the urea one To form insoluble complex, which precipitates and is separated in centrifuge 13. The separated solution (which is still somewhat Biuret, triuret and cyanuric acid and possibly some urea) is recycled to the solution tank 8, while the separated insoluble complex is passed to a decomposer 14, where it by the action of

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Heat decomposes and separates back to urea and complexing agent. The separated urea is returned to the reaction vessel or vessels 1 in the circuit, and the separated complex-forming agent is returned to the complex formation tank 12 in the circuit. As shown, fresh urea is added to the complex, before the latter to the decomposer 14 g * overall forwards, but obviously could be the fresh urea in the same manner directly to the reaction vessel or the reaction vessels 1 are introduced.

As in the case of FIG. 1, no biuret (or other autocondensation products) is returned to the reaction vessel or vessels 1 in the circuit. Any biuret that has not crystallized out and has been separated off by centrifuge Io is removed from centrifuge 13 and recycled to solution tank 8, whereby it passes through reaction vessel or vessels 1 and reduces the amount of triuret and cyanuric acid formed therein returned to the decomposer Ik in solid form, which avoids the costly and laborious evaporation stage of the known separation processes and the loss of urea due to hydrolysis.

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Claims (9)

Claims 1) Process for separating urea from a mixture of urea and its autocondensation products, in particular biuret, triuret and cyanuric acid, characterized in that the mixture is dissolved in water, the Solution treated with a complexing agent which is suitable 'at the temperature of the solution with the urea to form an insoluble complex and separate the insoluble complex from the solution in which the autocondensation products remain loosened. 2) Method according to claim 1, characterized in that the autocondensation products are crystallized from the solution, after the insoluble complex has been separated therefrom. 3) Method according to one of the preceding claims, characterized in that the separated insoluble Complex decomposed by heating back to urea and complexing agent. 4) Process for the production of auto-condensation pro- 109882/1909 17688CK A4 - «- urea products, especially biuret, triuret and cyanuric acid by the pyrolysis of urea in one or more reaction vessels, characterized in that the molten Mixture (containing urea, biuret, triuret and cyanuric acid) from the reaction vessel or vessels withdraws, the mixture dissolves in water, a complexing agent is added to the solution, which is suitable with the dissolved urea to form an insoluble complex, which precipitates, separating the insoluble complex from the solution and the auto-condensation products (especially biuret and cyanuric acid) crystallize out of the solution. 5) Method according to claim 4, characterized in that the separated insoluble complex is heated decomposed back to urea and complex-forming agent and returned to the process in the ^ cycle. 6) Process for the production of autocondensation products of urea, in particular biuret, triuret and cyanuric acid by the pyrolysis of urea in one or more reaction vessels, characterized in that the molten The mixture (containing urea, biuret, triuret and cyanuric acid) is withdrawn from the reaction vessel or vessels, the mixture dissolves in water, the autocondensation products (containing biuret, triuret and cyanuric acid) from the Solution crystallized out and separated off to the separated 109882/1909 BATH Al - ta - urea-containing solution, a complex-forming agent is added i which is suitable, one containing the dissolved urea
to form insoluble complex, which precipitates, separates the insoluble complex from the solution - _t the complex decomposed by heating · to urea and complex-forming agent and the urea to the reaction vessel or vessels
and returning the complexing agent to the complexing step. 7) Method according to one of the preceding claims, characterized in that there is a complex-forming agent uses a saturated, straight-chain hydrocarbon or a saturated straight-chain hydrocarbon derivative, 8) Method according to one of the preceding claims, characterized in that paraffin is used as a complex-forming agent. 9) Method according to one of the preceding claims, characterized in that the complex-forming agent used is one having a high molecular weight . 109882/1909 BATH ORIGINAL Al Blank page