Abstract: The present invention relates to an improved process for the purification of melamine obtained by synthesis from urea which comprises the following steps: a) bringing raw melamine containing impurities of polycondensates and other by-products of the synthesis reaction, into solution, obtaining a solution/suspension in which the insoluble products are dispersed; b) subjecting the solution/suspension thus obtained to treatment to remove the CO2 dissolved, reducing its concentration to values lower than 0.5% by weight; c) treating the solution/suspension obtained in step b), having a content of CO2 lower than 0.5% by weight, with ammonia in a quantity ranging from 1 to 15%, preferably from 3 to 9% by weight, at a temperature ranging from 110 to 180° C., preferably from 130 to 140° C.; d) putting the solution leaving step c) in contact with a solid catalyst, under the same conditions as step c). The present invention also relates to the equipment for effecting said process.

Abstract: The present invention relates to an improved process for the purification of melamine obtained by synthesis from urea which comprises the following steps: a) bringing raw melamine containing impurities of polycondensates and other by-products of the synthesis reaction, into solution, obtaining a solution/suspension in which the insoluble products are dispersed; b) subjecting the solution/suspension thus obtained to treatment to remove the CO2 dissolved, reducing its concentration to values lower than 0.5% by weight; c) treating the solution/suspension obtained in step b), having a content of CO2 lower than 0.5% by weight, with ammonia in a quantity ranging from 1 to 15%, preferably from 3 to 9% by weight, at a temperature ranging from 110 to 180° C., preferably from 130 to 140° C.; d) putting the solution leaving step c) in contact with a solid catalyst, under the same conditions as step c). The present invention also relates to the equipment for effecting said process.

Abstract: A process for the production of high-purity melamine by pyrolysis of urea at high pressure, wherein the liquid phase output from the pyrolysis reactor is sent to a downstream post-reactor, and wherein the anhydrous gaseous phase from the pyrolysis reactor and from the post-reactor are subjected to washing with molten urea for the recovery of the melamine. The purified liquid exiting the post-reactor is treated in a quenching column, in order to eliminate polycondensates, while the quenching column output is cooled. A high purity melamine is then separated by crystallization from a mother liquor, the greater part of which is recycled to the quenching column, thereby enabling a costless recovery of ammonia and melamine. The remaining mother liquor is treated for the separation of oxidized products of pyrolysis and is then sent back to the quenching column, thereby realizing the complete recovery of the melamine.

Abstract: In the oxidation process of aromatic hydrocarbons to produce the corresponding aromatic acids and anhydrides, such as isophthalic and terephthalic acid and their homologous products, by catalytic oxidation in the presence of acetic acid as reaction medium, the water, by-product of the oxidation reaction, is separated from the acetic acid to be recycled by means of azeotropic/extractive distillation, using, as modifying solvent of their relative volatility, the same aromatic hydrocarbon fed to the oxidation reaction.

Abstract: The process to recover both melamine and oxyaminotriazines (OAT) from the mother liquors of melamine crystallisation comprising the following steps: a) addition to a melamine and OAT containing aqueous solution at high temperature of an alkaline agent until the solution pH reach a value equal or higher than 11; b) most of melamine crystallisation by solution cooling; c) separation and recovery of precipitated melamine; d) acidification of the obtained solution, after precipitated melamine separation, in order to reach a pH of about 7; e) the suspension obtained in d) above after precipitated melamine recovery, is subject to filtration according to tangential filtration technique obtaining a clear permeate which contains as a solution all melamine which did not precipitate in step b) and a retentate comprising of OAT dispersion; f) OAT deprived mother liquors from e) are recycled to row melamine solution preparation step; in such a way almost the total amount of melamine, which did not precipitate in step b),

Abstract: 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.

Abstract: A process for the purification of melamine, deriving from urea, according to a high pressure non catalytic process, by means of polycondensates and other by-products transformation, which by-products derive from the melamine synthesis comprosing the following steps: dissolving in water the raw liquid melamine containing polycondensates and other melamine synthesis by-products, subjecting such solution to a treatment capable to remove dissolved CO2 limiting its concentration to a value lower than 0.5 wt. %, submitting raw melamine solution, to the action of ammonia, in an amount of 5 to 25 wt. %, at a temperature of 100 to 250° C. and leaving the mixture to react for some minutes, recoving a solution having polycondensates concentration lower than 1000 ppm, typically less than 100 ppm.

Abstract: The process to recover both melamine and oxyaminotriazines (OAT) from the mother liquors of melamine crystallisation comprising the following steps: a) addition to a melamine and OAT containing aqueous solution at high temperature of an alkaline agent until the solution pH reach a value equal or higher than 11; b) most of melamine crystallisation by solution cooling; c) separation and recovery of precipitated melamine; d) acidification of the obtained solution, after precipitated melamine separation, in order to reach a pH of about 7; e) the suspension obtained in d) above after precipitated melamine recovery, is subject to filtration according to tangential filtration technique obtaining a clear permeate which contains as a solution all melamine which did not precipitate in step b) and a retentate comprising of OAT dispersion; f) OAT deprived mother liquors from e) are recycled to row melamine solution preparation step; in such a way almost the total amount of melamine, which did not precipitate in step b),

Abstract: High pressure melamine manufacturing process starting from urea with high yields and conversion rates characterized in that it comprises the following steps: a) urea is fed to a reactor essentially containing molten melamine, which reactor operates in continuous and is kept at a temperature in the range of 360 to 420° C. under a pressure higher than 7×103 KPa and preferably 8×103 to 9×103 KPa, while a vigorous mixing is provided by evolving gases; b) liquid reaction product is recovered containing 85 to 95%, preferably 88 to 93% melamine and a gaseous phase is removed containing essentially CO2 and NH3; c) liquid phase collected in b) is continuously fed, together with fresh NH3 to a tubular reactor, in which the essentially whole volume is occupied by the liquid phase (plug flow reactor) without any mixing of the reaction product with reactant nor the intermediate products (no “back mixing”), kept at a temperature of 360 to 450° C.

Abstract: The present invention relates to a method for the wet purification of gaseous mixtures containing detergent powders in suspension with 18-22 wt. % sodium chloride in aqueous solution.