Abstract: Embodiments pertain to a urea plant and to the operation of a urea plant in a reduced load mode. In embodiments, two evaporators in parallel are used, connected to a finishing section respectively to a melamine plant.

Abstract: A method is disclosed for preparing a metal single-atom catalyst for a fuel cell including the steps of depositing metal single atoms to a nitrogen precursor powder, mixing the metal single atom-deposited nitrogen precursor powder with a carbonaceous support, and carrying out heat treatment. The step of depositing metal single atoms is carried out by sputtering, thermal evaporation, E-beam evaporation or atomic layer deposition. The method uses a relatively lower amount of chemical substances as compared to conventional methods, is eco-friendly, and can produce a single-atom catalyst at low cost. In addition, unlike conventional methods which are limited to certain metallic materials, the present method can be applied regardless of the type of metal.

Abstract: A process is described, having a low-energy consumption and reduced ammonia consumption for the production of high-purity melamine, through the pyrolysis of urea, and the relative plant.

Abstract: Disclosed is an integrated process for the production of urea and melamine, as well as a system for carrying out the process. The invention thereby pertains to an integrated process of the type wherein off-gas obtained from the production of melamine is entered into the process for the production of melamine, by condensation in the presence of water. A typical embodiment thereof is the condensation in the presence of an aqueous carbamate solution obtained from urea recovery. In accordance with the invention, said condensation takes place at a substantially lower pressure than the pressure at which the melamine off-gas is obtained. To this end, the pressure of the off-gas is reduced typically by 2-10 bar. In connection herewith, the system of the invention comprises a pressure reducing unit downstream of an outlet for the melamine off-gas, and upstream of a section for the condensation of the off-gas.

Abstract: An integrated process for the synthesis of urea and melamine, wherein: urea is synthesized with a stripping process in a high-pressure synthesis loop comprising a reactor, a stripper and a carbamate condenser, and the urea solution leaving said stripper is sent to a recovery section to produce a concentrated urea product and a recovered carbamate solution; at least part of said urea product is converted to melamine, and the off-gas from the synthesis of melamine are recycled to the urea synthesis by mixing with the gas phase from the stripper and with said recovered carbamate solution, thus forming a mixed flow which is then condensed in said carbamate condenser, and the condensate is eventually directed to the reactor.

Abstract: A reactor and associated process for the high-pressure synthesis of melamine from urea, comprising a primary step of conversion of the urea into crude melamine inside a first chamber delimited by a shell inside a reactor body and a secondary step of stripping said crude melamine melt inside a second reaction chamber, which is coaxial with and situated outside said first chamber, inside the same reactor body.

Abstract: In an integrated process for urea and melamine production, urea is produced in a urea plant (10) comprising a high pressure urea synthesis section (11) from which an aqueous solution comprising urea, ammonium carbamate and ammonia is obtained and a urea recovery section (21) operating at low pressure, and melamine is produced in a melamine plant (40) wherein off-gases resulting as by-products of the melamine synthesis are discharged from said plant at a medium pressure and recycled to the high-pressure urea synthesis section (11).

Abstract: Process for preparing melamine by converting urea in the presence of a solid catalyst in one reactor or in a plurality of reactors connected in series in the temperature range from 370° C. to 430° C., cooling and filtering the gas formed in the urea conversion, removing the melamine by desublimation and recycling a portion of the gas present after the melamine removal (“cycle gas”) into the reactor or the reactors, which comprises performing all of the above stages at a pressure in the range from 4 bar abs. to 10 bar abs.

Abstract: A system and process for melamine production by gas-phase quenching method and its process are provided. The said system includes a urea scrubber, after which a fluidized bed reactor, a hot-air cooler, a hot-air filter, a crystallizer and a melamine collector are installed in series successively, where the said melamine collector is connected to the said urea scrubber and the said fluidized bed reactor is connected to a carrier gas pre-heater which is connected to a carrier gas compressor; the said system further includes a gas-liquid separator which is connected to the said urea scrubber which is connected to a crystallizer; wherein a cool air blower is provided between the said gas-liquid separator and the crystallizer. The production system of the invention has the advantages of high productivity, stable operation, low energy consumption, low investment and high economic value of tail gas.

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: 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 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: Process for increasing the capacity of an existing urea plant comprising a high-pressure urea synthesis section and one or more recovery sections, wherein next to the existing urea plant a urea production unit, comprising a high-pressure urea synthesis section and a medium-pressure recovery section, is installed, wherein a urea-containing stream is produced from ammonia and carbon dioxide and the urea-containing stream is sent to the existing urea plant where the urea-containing stream is further purified in the low-pressure recovery section.

Abstract: The invention relates to new crystalline modifications of the hydrochloride of 1-[4-(5-cyanoindol-3-yl)butyl]-4-(2-carbamoyl-benzofuran-5-yl)-piperazine, crystalline modification of the dihydrochloride of 1-[4-(5-cyanoindol-3-yl)butyl]-4-(2-carbamoyl-benzofuran-5-yl)-piperazine and amorphous 1-[4-(5-cyanoindol-3-yl)butyl]-4-(2-carbamoyl-benzofuran-5-yl)-piperazine hydrochloride which are suitable in particular for the preparation of solid medicaments for the treatment or prevention of depressive disorders, anxiety disorders, bipolar disorders, mania, dementia, substance-related disorders, sexual dysfunctions, eating disorders, obesity, fibromyalgia, sleeping disorders, psychiatric disorders, cerebral infarct, tension, for the therapy of side-effects in the treatment of hypogonadism, secondary amenorrhea, premenstrual syndrome and undesired puerperal lactation.

Abstract: Systems and methods of producing chemical compounds are disclosed. An example chemical production system includes a combustion chamber having intake ports for entry of a gas mixture. An igniter ignites the gas mixture in the intake chamber to facilitate a reaction at a high temperature and high pressure. A nozzle restricts exit of the ignited gas mixture from the combustion chamber. An expansion chamber cools the ignited gas. The expansion chamber has an exhaust where the cooled gas exits the expansion chamber. A chemical compound product is formed in the expansion chamber.

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 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: It is described the use of urea containing formaldehyde in a process for the production of melamine by the pyrolysis of urea, which can be applied both to a high-pressure process and to a low-pressure 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 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: A low-energy-consumption process is described for the production of high-purity melamine, through the pyrolysis of urea, by the collection and purification of the melamine in aqueous solution produced in the pyrolysis reactor, and its separation by crystallization. The present invention also relates to the equipment for effecting the above process.

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 present invention relates to a non-catalytic process for the preparation of melamine comprising: a) reacting molten urea in a reaction section at a pressure of 4.5 to 15 MPa to produce a reaction mixture containing molten melamine and reaction off-gases; b) vaporizing the molten melamine in said reaction mixture in a vaporization section to produce a gaseous mixture comprising the vaporized melamine and the reaction off-gases at a pressure of 4.

Abstract: Process for preparing melamine by converting urea in the presence of a solid catalyst in one reactor or in a plurality of reactors connected in series in the temperature range from 370° C. to 430° C., cooling and filtering the gas formed in the urea conversion, removing the melamine by desublimation and recycling a portion of the gas present after the melamine removal (“cycle gas”) into the reactor or the reactors, which comprises performing all of the above stages at a pressure in the range from 4 bar abs. to 10 bar abs.

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: In a gas scrubber, a gas stream containing at least one sublimed substance is brought in contact with a liquid or melt stream containing at least one thermally convertible substance, which has a lower temperature than the gas stream. For the intensive and intimate mixing of the gas stream with the liquid or melt stream, an orifice plate with a plurality of holes each surrounded by a retaining edge is provided in the upper part of the gas scrubber, and above the orifice plate inlets for the gas stream and the liquid or melt stream are provided.

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: 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 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 fluidising gas required for creating the fluidised bed.

Abstract: In an integrated process for urea and melamine production, urea is produced in a urea plant (12) comprising a high pressure urea synthesis section (15) and a urea recovery section (16) for separating urea from a carbamate aqueous solution, and melamine is produced in a melamine plant (11) wherein off-gases resulting as byproducts of the melamine synthesis are discharged therefrom at a pressure of at least 2 bar and recycled to the high pressure urea synthesis section (15).

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 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 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: Process for increasing the capacity of a urea plant comprising a compression section, a high-pressure synthesis section, a urea recovery section, in which a urea melt is formed, and optionally a granulation section, the capacity of the urea plant being increased by the additional installation of a melamine plant and the urea melt from the urea recovery section of the urea plant being fed wholly or partly to the melamine plant and the residual gases from the melamine plant being returned wholly or partly to the high-pressure synthesis section and/or the urea recovery section of the urea plant.

Abstract: An integrated process for urea/melamine production. In the process, urea is synthesized from ammonia and carbon dioxide, obtaining molten urea and a gaseous mixture comprising steam and ammonia. The gaseous mixture is condensed, obtaining a cold aqueous ammoniacal solution. Melamine is synthesized from urea with formation of off-gases, comprising ammonia and carbon dioxide. The off-gases are absorbed in at least one fraction of the cold aqueous ammonical solution, with formation of a carbamate aqueous solution. The carbamate aqueous solution is decomposed, obtaining ammonia, carbon dioxide and steam, and a residual aqueous ammoniacal solution. The ammonia and the carbon dioxide are recycled for the urea synthesis. The residual aqueous ammoniacal solution obtained is treated to recover ammonia and carbon dioxide for the urea synthesis.

Abstract: The invention relates to a method for contacting molten urea with a gas stream that contains ammonia and/or carbon dioxide, in which use is made of an additional stream the temperature of which differs from the temperature of the molten urea and/or the gas stream. The additional stream preferably contains ammonia. The method is preferably part of a process for the preparation of 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.