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Method for producing pure melamine

A pure melamine, melamine technology, used in organic chemistry and other directions

Active Publication Date: 2007-04-04
UREA CASALE SA
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0006] The disadvantage of this method is that there is still a considerable amount of CO in the melamine suspension or solution taken out of the quench cooler. 2

Method used

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  • Method for producing pure melamine

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Embodiment 1

[0032] NaOH consumption in the melamine process according to the prior art

[0033] The crude melamine melt produced in the reactor is separated from the reaction off-gas, followed by passing the melamine melt through NH 3 Instead, it is processed and then sent to a quencher. Since the melamine melt contains 1.5% by weight of CO 2 , so 15 kg of CO per ton of melamine melt 2 Introduced into the quench cooler.

[0034] The melamine melt is brought into contact with a liquid containing NaOH in a quench cooler. NaOH reacts with the CO present according to the following reaction equation 2 The reaction produces Na 2 CO 3 , so it cannot be used for the expected pH-raising effect of by-product decomposition.

[0035]

[0036] because each mole of CO 2 2 moles of NaOH are required, so 54.5 kg of 50% NaOH is required per tonne of melamine melt from the synthesis section, just to consume the CO carried into the quench by the melamine melt 2 .

[0037] The decomposition ...

Embodiment 2

[0040] NaOH consumption in the process according to the invention

[0041] The melamine melt produced by the high pressure process is separated from the reaction off-gas and treated with gaseous ammonia before quenching to substantially remove dissolved CO from the melamine melt 2 . The melamine melt thus treated was fed into a quench cooler at a temperature of 350° C. and a pressure of 150 bar. Quenching was performed at 200°C using boiler feed water. Add 3 tons of quenching water per ton of melamine melt to obtain a melamine solution with a concentration of 25% by weight melamine. The NH was then stripped from the melamine solution at 200 °C with steam 3 and CO 2 . The solution containing 25% by weight of melamine was diluted with the recovered crystallization mother liquor to a melamine concentration of 8% by weight, wherein the temperature of the solution was cooled to 130°C. Add 45.5 kg of 50% NaOH solution per ton of melamine melt to decompose by-products in the me...

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Abstract

The invention relates to a method for producing pure melamine by preparing a melamine melt, which is obtained in a high pressure process and from which the reaction gases are removed. Said method is characterised in that the melamine melt is quenched by water with a purity in excess of 95 wt. %, that NH3 and CO2 are subsequently removed from the obtained melamine solution and that alkali is added to said melamine solution and the mixture is then left to rest, whereby pure melamine is obtained by crystallisation. Thus a melamine can be obtained with the same quality as that produced in known comparative methods, using smaller quantities of alkali.

Description

technical field [0001] This application relates to a process for the manufacture of pure melamine. Background technique [0002] In the high-pressure process for the manufacture of melamine, the urea melt and any The selected gaseous ammonia is converted into liquid melamine and waste gas. The reaction waste gas is mainly composed of ammonia and carbon dioxide, and contains a small amount of gaseous melamine. The liquid crude melamine contains, besides unreacted urea, by-products such as melem, melam or other condensation products of melamine, which are not desired in the final product and must therefore be removed. The removal of melamine by-products from melamine takes advantage of the known fact that the by-products and water are preferably hydrolyzed in the presence of a base to form carbonylaminotriazine compounds such as cyanuramide and cyanuramide. They remain in solution during the subsequent crystallization of melamine, thereby selectively crystallizing pure mela...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C07D251/60C07D251/62
CPCC07D251/60C07D251/62
Inventor 沃尔夫冈·吕克
Owner UREA CASALE SA
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