| 摘要 |
<p>Process for the production of high-purity melamine with high yields by means of pyrolysis of urea at a temperature comprised between 360 and 420 °C and a pressure above 7 MPa in which the products of reaction, comprising a gaseous phase and a liquid phase, are subjected to successive treatments for the purification and recovery of the melamine, characterized by: the liquid phase output from the pyrolysis Reactor containing melamine, non-reacted urea, intermediate oxidized products of pyrolysis (OAT) and products of deammoniating condensation of the melamine (polycondensates), is sent to a downstream reactor (Post-reactor) that operates in substantially equal temperature and pressure conditions to those of the pyrolysis Reactor; the anhydrous gaseous phase coming from the pyrolysis reactor and from Post-reactor, are subjected to washing with molten urea for the recovery of the melamine contained in it as vapor, before being sent back to the urea synthesis plant for the recovery of NH3 and CO2 contained in it; the purified liquid output from the Post-reactor is treated in a Quenching Column at 160-170 °C in the presence of 10% by weight minimum of NH3 in order to eliminate the polycondensates; the Quenching Column output is cooled and a high purity melamine separated by cristallisation from a mother liquor that is direct recycled in an amount of 80% minimum to the Quenching Column, allowing the costless recover of ammonia and melamine; the mother liquor not directly recycled is treated for the separation of OAT and then sent back to the Quenching Column realizing the complete recover of the melamine produced in the reaction system.</p> |
