Abstract: The present invention relates to the production and purification of melamine and, in particular, to the purification of a crude melamine product, while minimizing impurities comprising at least one of melem, melam, melon, or ureidomelamine. The crude melamine can be treated with ammonia and a promoter to achieve a very high melamine content in the purified product, at more advantageous conditions, than treatment with ammonia alone. The present invention is also directed to an improved melamine production process that yields melamine with so few impurities that it can be pure enough as to not require an additional purification step.

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: The invention relates to a method for purifying melamine in which impure melamine is heated to a temperature range above 325°C. but lower than the melting point of melamine which depends on the prevailing ammonia pressure. In addition, the impure melamine is held in said temperature range under an ammonia pressure ranging from 1 to 150 bar for a duration lasting from 1 minute up to 20 hours. The melamine is provided in solid form. Afterwards, the melamine is relieved from pressure and cooled in any order.

Abstract: A process for the preparation of pure melamine, in which liquid, ammonia-containing melamine is rapidly depressurized from an ammonia partial pressure p1 between 400 and 50 bar to an ammonia partial pressure p2 between 200 bar and atmospheric pressure, where p1 is always greater than p2, at a temperature which is 0 to 60° C. higher than the melamine solidification point dependent oil the particular prevailing ammonia partial pressure, higher pressures permitting a greater temperature interval from the melamine solidification point than lower pressures, by which means pure melamine separates out in solid form, whereupon, in any sequence, the product is further depressurized if appropriate to atmospheric pressure, cooled to room temperature and the pure melamine is isolated.

Abstract: Process for cooling liquid melamine by mixing with solid melamine or with solid inert substances or with a mixture of solid melamine and solid inert substances.

Abstract: A process for the preparation of pure melamine, in which liquid, ammonia-containing melamine is rapidly depressurized from an ammonia partial pressure p1 between 400 and 50 bar to an ammonia partial pressure p2 between 200 bar and atmospheric pressure, where p1 is always greater than p2, at a temperature which is 0 to 60° C. higher than the melamine solidification point dependent on the particular prevailing ammonia partial pressure, higher pressures permitting a greater temperature interval from the melamine solidification point than lower pressures, by which means pure melamine separates out in solid form, whereupon, in any sequence, the product is further depressurized if appropriate to atmospheric pressure, cooled to room temperature and the pure melamine is isolated.

Abstract: Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the reactor product comprising liquid melamine, CO2 and NH3 to a gas/liquid separator and subsequently transferring the melamine melt coming from the separator to a vessel where the melamine melt is cooled with an evaporating cooling medium, characterized in that, the gas/liquid separation is conducted by addition of 5.10−4-2.10−2 mole of water per mole of melamine.

Abstract: Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt coming from the reactor to a vessel where the melamine melt is cooled with an evaporating cooling medium. The melamine melt comes from the melamine reactor at a temperature between the melting point of melamine and 450° C. and is sprayed into a cooling vessel, via spraying means, and cooled by means of an evaporating cooling medium to form melamine powder. The cooling vessel has an ammonia environment with an increased ammonia pressure. The melamine melt is thereby converted into melamine powder having a temperature of between 200° C. and the solidification point of melamine. The melamine powder is then cooled to a temperature below 200° C. with the powder mechanically agitated and being cooled directly or indirectly, after which the ammonia pressure is released and, if necessary, the melamine powder is cooled further.

Abstract: Process for cooling liquid melamine by mixing with solid melamine or with solid inert substances or with a mixture of solid melamine and solid inert substances.

Abstract: The invention relates to a process for the preparation of melamine from urea by feeding molten urea and hot ammonia gas into a reactor having a pressure within the range 50-150 bar and a temperature within the range 360.degree.-430.degree. C., whereby a reaction product is obtained which contains a liquid melamine melt and a gas mixture. This gas mixture is separated from the liquid melamine melt, and the liquid melamine melt thus obtained is directed to a vaporizer and is vaporized therein, and the melamine-containing gas obtained from the vaporizer is cooled in a quencher, in which case the melamine crystallizes in a very pure state, the purity being typically at minimum 99.9%.

Abstract: Process for the production of highly pure melamine in which an aftertreatment of the melamine is carried out, comprising the stepsa) separating off the NH.sub.3 /CO.sub.2 gas mixture from the liquid melamine, if appropriateb) reducing the CO.sub.2 dissolved in the liquid melamine by introducing gaseous ammoniac) allowing the liquid melamine to remain for a mean residence time of 0 to 8 hours at a temperature between 430.degree. C. and the melting point of melamine and an ammonia partial pressure of 50 to 400 bar andd) slow, controlled cooling by lowering the temperature from the temperature present in a), b) respectively c) to 330.degree. to 270.degree. C. at a cooling rate of up to 150.degree. C.

Abstract: Disclosed is an improved method for separating impurities from a hot synthesis gas mixture which is obtained in the preparation of melamine and urea. The improved separation is achieved by use of filters made of sintered, essentially pure chromium, molybdenum, tungsten, or a mixture of any of these elements.

Abstract: Disclosed are compounds of the formula: ##STR1## or the pharmaceutically acceptable acid addition salts thereof, wherein: R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8 and R.sub.9 are the same or different and represent hydrogen, C.sub.1 -C.sub.6 alkyl, halogen, hydroxy, amino, cyano, nitro, trifluoromethyl, trifluoromethoxy, C.sub.1 -C.sub.6 alkoxy, --O.sub.2 CR', --NHCOR', --COR', --SO.sub.m R', where R' is C.sub.1 -C.sub.6 alkyl and wherein m is 0, 1 or 2; orR.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8 and R.sub.9 independently represent --CONR'R", or --NR'R" where R' and R" independently represent hydrogen or C.sub.1 -C.sub.6 alkyl;R.sub.10 is hydrogen or C.sub.1 -C.sub.

Abstract: A method of purifying melamine produced from urea in a high-pressure, non-catalytic, non-aqueous process is described. In the method impure melamine is heated to a temperature of from about 250.degree. to about 1000.degree. F. under a pressure from about 600 to 3000 psi in the presence of ammonia to provide melamine having a purity of 99.0% or above. The method is economical since chemical treatment and recrystallization steps are not required.

Abstract: The invention relates to a selective removal of impurities from the gas stream leaving a melamine synthesis reactor in the preparation of melamine from urea by means of a treatment with steam at elevated temperature in the presence of a catalyst which is shape-selective. For instance a molecular sieve is chosen.

Abstract: A process for isolating liquid urea and its thermal decomposition products from the off-gas of melamine synthesis, which gas has been freed from melamine by fractional condensation and then been washed with molten urea, wherein the off-gas, containing 2-10 kg of melt per kg of pure gas, is passed at 8-30 m/sec tangentially into the upper part of an axially symmetrical separation zone. As a result of the rotation imparted to the gas/liquid mixture, the two phases are separated from one another, and both pass downward through the separation zone. The gas and liquid are separately taken off at the bottom end of the separation zone. The residence time of the gas mixture in the separation zone is not less than 0.5 second.

Abstract: A method for separating liquid drops of molten urea and/or a molten mixture of urea and its thermal decomposition product from an off gas that has been freed of melamine using at least two gas-liquid separators is disclosed. The method is characterized by filling the gas-liquid separator off stream or at rest with molten urea or a molten mixture of urea and its thermal decomposition product, and at the same time, forcing the molten liquid to flow within said gas-liquid separator to remove undesired melamine iso(cyanurate) therein.

Abstract: Melamine synthesis waste gases are first treated for the removal of melamine by condensation. The waste gases are then treated with urea-containing melts which are cooled indirectly. At least parts of said indirect cooling takes place together with the treatment of the reaction waste gases with the urea-containing melts in a single zone.