Abstract: Plant for the synthesis of melamine starting from urea, wherein the stream of offgas containing NH3 and CO2 produced by the synthesis of melamine is converted into urea in a dedicated urea plant.

Abstract: A process for the purification of a melamine melt (5) containing melamine and by-products, comprising the steps of: (a1) quenching of said melamine melt; (a2) decomposition of by-products with alkali, providing an alkaline aqueous solution of melamine (26); (b) stripping of said alkaline aqueous solution of melamine (26); (c) crystallization of melamine with a first alkali-containing solution (6b) and separation of solid melamine (7) from a mother liquor (8); (d) treatment of said mother liquor, providing a waste water stream (11) containing carbonates; (e) decomposition of at least part of the carbonates contained in said waste water stream (11) into carbon dioxide and alkali, providing a second alkali-containing aqueous solution (30); (f) recycle of at least part of said alkali-containing aqueous solution (30) to at least one of said steps (a1), (a2) and (c).

Abstract: Reactor for the synthesis of melamine from urea, in accordance with the high-pressure non-catalytic process, comprising: a vertical reactor body (1), at least one inlet (2) for the urea melt, a set of heating elements (3), and a central duct (7), said set of heating elements (3) being arranged inside said central duct.

Abstract: Reactor for the synthesis of melamine from urea, in accordance with the high-pressure non-catalytic process, comprising: a vertical reactor body (1), at least one inlet (2) for the urea melt, a set of heating elements (3), and a central duct (7), said set of heating elements (3) being arranged inside said central duct.

Abstract: The present invention relates to a method for recycling water in a melamine production process comprising—a wet process comprising the steps of aqueous treatment of a melamine melt from a melamine synthesis plant with an aqueous alkali containing solution and crystallization for producing solid melamine and a triazine containing alkaline mother liquor,—a wastewater treatment process comprising the steps of thermal treatment of said triazine containing alkaline motor liquor, and—a recycling process, whereby at least parts of the thermally treated alkaline mother liquor are being recycled to the wet process.

Abstract: The present invention concerns process for obtaining melamine at high purity characterized by comprising the steps of:—quenching a melamine melt, deprived of off-gases of the melamine synthesis and containing melamine impurities such as ammeline, ammelide and polycondensates, with an aqueous solution comprising ammonia under conditions such to substantially convert polycondensates into melamine, obtaining a melamine solution substantially free of polycondensates, recovering melamine from said melamine solution by melamine crystallization, obtaining melamine crystals and a melamine crystallization mother liquor,—treating said crystallization melamine mother liquor under conditions such to convert at least a portion of its ammeline content into ammelide and melammine, obtaining a treated mother liquid having at least a reduced ammeline content.

Abstract: A high-pressure melamine reactor is provided. The high-pressure melamine reactor comprising at least one horizontal reactor body having a bottom and a top side with at least one dome integrally formed on the top side of the reactor body. The at least one horizontal reactor body comprises at least two compartments separated by at least one baffle, in particular an overflow baffle. The at least one dome is solely located above at least one of the compartments serving as melamine synthesis unit, wherein the at least one compartment serving as melamine synthesis unit comprises at least one heating element.

Abstract: A process for high-pressure, liquid phase conversion of urea into melamine is disclosed, where molten urea is fed to a first reaction zone (S1) where the melamine melt is under mechanical agitation, and a heat input (Q1) is provided to maintain the endothermic reaction, and the liquid is then passed to a second reaction zone (S2) kept at a lower temperature and where further agitation is provided. Embodiments of plants adapted to carry out the process are also disclosed, including multiple stirred reactors in cascade and a single reactor with multiple internal compartments defining said first and second reaction zones.

Abstract: Melamine is a common industrial chemical contaminant which should be absent from food and feed supplies due to melamine's toxicity. Provided is a method to assess the presence of melamine in samples prepared from compositions. The method may include using a microbial enzyme called melamine deaminase which hydrolyzes melamine to ammeline and ammonia. The method may include assessing the presence of any ammonia produced from an enzymatic reaction between the sample and the enzyme.

Abstract: A process for the continuous production of melamine from urea by means of a fluidized-bed reactor, wherein process gas guided in the process circuit is used as fluidizing gas and wherein the temperature of the process gas at the inlet of the conveying means for the fluidizing gas is adjusted by adjusting the mixing ratio of a process gas stream guided over a scrubber and of a process gas stream guided past the scrubber.

Abstract: A process for the preparation of melamine by decomposition of urea with the use of a catalyst, the catalyst comprising a) 10-90% by weight of zeolite, b) 10-90% by weight of a matrix comprising silica, alumina, silicon aluminum oxides and/or clay minerals, and c) 0-10% by weight of additives and the total content of nickel and vanadium in the catalyst being less than 500 ppm.

Abstract: A melamine skeleton-bearing organosilicon compound has a film forming ability, water solubility and compatibility with resins. It is prepared by reacting cyanuric chloride with a primary and/or secondary amine compound and neutralizing with a base.

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 is described for drying melamine wet cakes, comprising the steps of: a) providing a turbo-dryer (T) comprising a cylindrical tubular body (1) having a heating jacket (4), inlets and outlets (5, 6) and a bladed rotor (7) rotatably supported therein; b) feeding a continuous flow of a melamine wet cake into the turbo-dryer (T), the internal wall (9) of which is maintained at a temperature of at least 220° C.; c) feeding a continuous flow of a gas selected from air or nitrogen into the turbo-dryer (T); d) subjecting the flow of melamine wet cake to the mechanical action of the bladed rotor (7) rotating at a speed of at least 200 rpm, with consequent centrifugation of the wet cake against the heated wall (9), thus causing the instantaneous evaporation of the water contained into the cake, and transport of the latter towards the outlet (6); e) continuously discharging, after an average residence time of less than 1 minute, a flow of melamine crystals having a humidity content of less than 0.1%.

Abstract: The invention concerns a method for producing melamine by dissolving urea, in which solid, liquid or gaseous media other than the gas mixture consisting of the components formed during the reaction is used to desublime the melamine from the gas phase.

Abstract: The invention relates to a method for producing melamine by decomposing urea inside a fluidised bed reactor, during which the hot reaction gas is cooled inside a gas cooler, and the obtained heat is directly used for pre-heating the fluidizing gas required for creating the fluidized bed.

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 characterized 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 crystallization. Thus a melamine can be obtained with the same quality as that produced in known comparative methods, using smaller quantities of alkali.

Abstract: The invention relates to a method for treating triazine-containing water of a melamine plant. The method is characterized in that the water containing ionic and non-ionic triazines in a dissolved form is fed to at least one membrane filtration unit, the water is separated into an ionic triazine-rich fraction and a non-ionic triazine-rich fraction in the membrane filtration unit, whereupon the ionic triazine-rich fraction is discharged and the non-ionic triazine-rich fraction is redirected into the melamine plant. The inventive method allows a great portion of the melamine contained in the triazine-containing water to be redirected into the process while the yield is increased along the entire melamine process. Furthermore, the need for fresh water in the wet part of the melamine plant is decreased. The disclosed method can be carried out continuously and in liquid phase.

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: Process for the preparation of melamine, comprising a first mixing step in which at least two melamine-containing flows, originating from at least two different processes for the preparation of melamine, are brought into contact with each other, with a mixture being formed. In one embodiment, at least one melamine-containing flow contains melamine from a low-pressure gas-phase process for the preparation of melamine and at least one melamine-containing flow contains melamine from a high-pressure liquid-phase process for the preparation of melamine.

Abstract: The invention is directed to a process for the preparation of melamine connected through a carbamate concentration unit, comprising a desorption column in which a gas stream, comprising ammonia, carbon dioxide and water is generated, with a process for the preparation of urea, comprising a heat exchanger wherein a urea containing stream is present, wherein the gas stream, comprising ammonia, carbon dioxide and water, is send to the heat exchanger, wherein heat is exchanged with the urea containing stream and the gas stream, comprising ammonia, carbon dioxide and water is cooled and at least partially condensed to obtain an ammonium carbamate solution that is send to the process for the preparation of urea.

Abstract: The invention relates to a device for thermally purifying waste water, comprising a tank through which waste water can flow. The inventive device is characterized by having at least one flow guiding means for guiding the waste water inside the tank in an essentially meandering manner, and by having at least one heating means inside the tank for regulating a predetermined temperature.

Abstract: The invention relates to a method and a device for producing melamine by means of the thermal conversion of urea. The invention is characterized in that: a) urea is reacted to form melamine at least partially under reaction conditions wherein an educt, an intermediate and/or an end product are present in a supercritical state; and b) the mixture consisting of at least one educt, an intermediate and/or an end product essentially forms a homogeneous phase and all educts, intermediates, and/or end products are in a complete solution. The single-phase reaction results in an especially efficient reaction.

Abstract: The invention relates to a high pressure method for producing pure melamine by pyrolyzing urea in a vertical synthesis reactor. The synthesis reactor has three stages above one another: a) in the first stage, the smaller portion of the total amount of urea is introduced into the central tube of a first tank reactor forming a first melamine-containing reaction medium; b) in the second stage, the first melamine-containing reaction medium and the larger portion of the total amount of urea is introduced into the central tube of a second tank reactor forming a second melamine-containing reaction medium; c) in the third stage, the second melamine-containing reaction medium is introduced into a vertical tubular flow reactor forming a raw melamine melt that is processed to obtain pure melamine.

Abstract: A two-stage process is provided for purifying off-gases from a high-pressure melamine plant. In the first stage, the off-gases are contacted with a recirculated urea melt containing melamine precursors and NH3. In the second stage, the off-gases are contacted with a fresh urea melt.

Abstract: The present invention relates to a process for the catalytic preparation of melamine by decomposition of urea over particular solid catalysts using a main reactor and an after-reactor. A catalyst having a low Lewis acidity is used in the main reactor and a catalyst having an equal or preferably higher Lewis acidity is used in the after-reactor.

Abstract: The invention relates to a process for preparing melamine, comprising a cooling step from which a mixture H2O containing NH3, CO2 and H2O is released, wherein: the mixture and a flow of liquid NH3 are fed to an absorption section; the mixture and the flow of liquid NH3 in the absorption section are contacted with each other, with gaseous NH3 and an ammonium carbamate solution being formed; the gaseous NH3 and the ammonium carbamate solution are separately discharged from the absorption section, wherein a part of the discharged ammonium carbamate solution is returned to the cooling step and a part of the removed gaseous NH3 is liquefied and returned to the absorption section.

Abstract: The invention relates to a method for producing melem-free melamine by means of aqueous processing of a melted mass of melamine which is obtained using a high-pressure method. According to the inventive method, the melted mass of melamine is quenched by means of an aqueous solution containing alkalis, following the isolation of the off-gases, and is directly transferred into an aqueous alkaline melamine solution, out of which the melamine is then crystallized. The invention thus enables melamine to be obtained, with a melam content of less than 1000 ppm and a melem content of less than 50 ppm. The invention also relates to a quenching agent.

Abstract: Process for cooling and crystallizing solid melamine from the gaseous phase or from melamine melts as they develop in technical processes used to produce melamine, characterized in that the melamine-containing process gases or melamine melts are introduced into liquid, organic phase at high pressure, said phase comprising polyvalent alcohols such as ethylene glycol, glycerine or their homologous series or of amines such as ethanol amines or a mixture of both groups. The advantage this process is that the hot melamine is cooled very quickly without forming thermal decomposition products and that during quenching no reaction of the melamine with the solvent occurs, the formation of higher deammoniation products such as melam and melem is prevented and higher deammoniation products of the melamine such as melam and melem, are partially converted back into melamine.

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: The invention relates to a method for producing pure melamine in a high-pressure method. According to said method, in the first stage, the melamine melt is brought into contact with hot NH3 and NH3 from the second stage and in the second step is brought into contact with cold NH3 in such a way that it is cooled to a temperature, which is 1–30° C. above the pressure-dependent melting point of the melamine, before being optionally rested in a third stage and subsequently treated in various ways.

Abstract: A process for the production of melamine by pyrolysis of urea in a high-pressure reactor having a vertical central pipe is provided. The melamine flows upwards into the reactor from below, mixes in the lower part of the reactor with a urea melt, and optionally NH3, introduced into the reactor from below, and emerges from the central pipe in the upper part of the central pipe. Part of the melamine formed flows downward in the annular space between the central pipe and reactor wall, and the remainder is expelled for further work-up. The off-gases are removed at the top of the reactor. A reactor for carrying out the process is also provided.

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: A process for purifying gaseous melamine containing ammonia is provided. The method comprises partly condensing the gaseous melamine-containing ammonia to form melamine in liquid NH3 and purified NH3 gas. The melamine and purified NH3 gas are taken off.

Abstract: A process for preparing melamine by pyrolysis of urea in a high-pressure process, in which urea is reacted together with NH3 to give melamine and the melamine melt formed is fed together with further urea to a cooling reactor, with the melt being cooled to a temperature which is 1-50° C., preferably 1-30° C., above the melting point of the melamine, which is dependent on the prevailing NH3 pressure. Introduction of NH3 in countercurrent drives out the CO2 formed, after which the melamine melt is worked up in any appropriate way.

Abstract: A method for purifying melamine comprising impurities like ureido-melamine, oxotriazines, melam, melem, comprises the step of putting into contact at a temperature comprised between 340° C. and 410° C. and at a pressure comprised between 8 and 17 MPa a melamine melt with a bed of a catalyst thus obtaininig melamine with a purity of at least 99%.

Abstract: Process for preparing melamine from urea at elevated temperature and in the presence of a catalyst, in which a gaseous product stream is obtained which is contacted with a liquid coolant in a cooling zone and in which a proportion of the concentrated aqueous carbamate solution from the absorption zone is returned to the cooling zone.

Abstract: A process for producing melamine crystals at high pureness is distinguished by the fact that it comprises a crystallisation step of a flow comprising substantially pure melt melamine by cooling with liquid ammonia and a thickening step of the resulting suspension of melamine crystals in liquid ammonia by separation of a portion of the liquid ammonia present in said suspension, whereby the liquid ammonia separated in said thickening step is reused as coolant in the crystallisation step.

Abstract: A process for the production of melamine by pyrolysis of urea in a high-pressure reactor having a vertical central pipe is provided. The melamine flows upwards into the reactor from below, mixes in the lower part of the reactor with a urea melt, and optionally NH3, introduced into the reactor from below, and emerges from the central pipe in the upper part of the central pipe. Part of the melamine formed flows downward in the annular space between the central pipe and reactor wall, and the remainder is expelled for further work-up. The off-gases are removed at the top of the reactor. A reactor for carrying out the process is also provided.

Abstract: The invention relates to a method for producing pure melamine. According to this method, the melamine melt, which is produced from urea in a high-pressure process, is cooled and ammonia is added until it reaches a temperature of approximately 1 to 50° C. above the melting temperature of the melamine as dependent on the respective pressure of ammonia and then either a) quenched with water or an aqueous solution or suspension containing ammonia and/or melamine so that the melamine solidifies or b) quenched with cold liquid or gaseous ammonia, so that the melamine solidifies, the melamine then being cooled further with water or an aqueous solution or suspension containing ammonia and/or melamine and c) the melamine is then isolated.

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: A method for purifying melamine comprising impurities like ureido-melamine, oxotriazines, melam, melem, comprises the step of putting into contact at a temperature comprised between 340° C. and 410° C. and at a pressure comprised between 8 and 17 MPa a melamine melt with a bed of a catalyst thus obtaining melamine with a purity of at least 99%.

Abstract: Process for the preparation of melamine comprising a reaction step, a gas/liquid separation step in which a melamine melt is separated from off-gases, a stripping step and a cooling step, in which the stripping step is carried out at a pressure of between 5 MPa and 17 MPa and a temperature of between 330° C. and 450° C. and in which the melamine melt obtained in the preceding steps is pressurised in the cooling step to a pressure of between 15 and 35 MPa, with the pressure in the cooling step being higher than the pressure in the stripping step and with the temperature in the cooling step being adjusted between the melting point of the urea melt at the prevailing pressure and 365° C.

Abstract: Process for preparing melamine from urea at elevated temperature and in the presence of a catalyst, in which a gaseous product stream is obtained which is contacted with a liquid coolant in a cooling zone and that the temperature in the scrubbing section is lowered by applying an extra cooling step.

Abstract: A process for producing melamine crystals at high pureness is distinguished by the fact that it comprises a crystallisation step of a flow comprising substantially pure melt melamine by cooling with liquid ammonia and a thickening step of the resulting suspension of melamine crystals in liquid ammonia by separation of a portion of the liquid ammonia present in said suspension, whereby the liquid ammonia separated in said thickening step is reused as coolant in the crystallisation step.

Abstract: The invention relates to a method for producing solid melamine by expanding liquid, ammoniacal melamine which is mixed with excess ammonia, whereby a dispersion is produced. Said dispersion is expanded, optionally after it has been held under ammonia pressure, whereby solid melamine is deposited. The solid melamine is optionally held under ammonia pressure. Expansion is then optionally carried out in any particular order, along with cooling to room temperature and the pure melamine is isolated.

Abstract: The invention relates to a method for producing urea. According to said method, the off-gases which originate from a melamine plant and essentially consist of NH3 and CO2 are introduced into the high-pressure zone of the urea plant by means of ejectors.

Abstract: Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt to an expansion vessel where the melamine melt is cooled by incorporated ammonia. Excess ammonia gas is added to the melamine melt to produce a gas/liquid mixture having a mass ratio of at least 0.01. This two-phase mixture is then sprayed via a spraying means into an expansion vessel, the expansion vessel having an ammonia environment with a reduced ammonia pressure. The melamine melt is cooled and solidified by the expansion and evaporation of the incorporated ammonia to form melamine powder. The melamine melt is thereby directly converted into a melamine powder after which the melamine powder is cooled further and the ammonia pressure is released.

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: A method for the production of melamine from urea via a high-pressure non-catalytic process in which molten urea is reacted to produce melamine, carbon dioxide, and ammonia, the by-product gases are separated from the melamine melt, and the melamine melt is treated with ammonia in a liquid-filled column to remove dissolved carbon dioxide, the treated melamine melt being solidified to produce high-purity melamine. In the liquid-filled column, or bubble column, the melamine melt is treated with between 0.02 and 3 tons of ammonia per ton of melamine, the bubble column being operated at a pressure of between 1 and 40 MPa and at a temperature between the melting point of melamine at prevailing pressure and 450° C., with the residence time of the melamine melt in the bubble column being between 1 minute and 10 hours.