US 4,565,867 A · Anhydrous high-pressure melamine synthesis

Abstract

This high-pressure, high-temperature anhydrous process prepares melamine from urea. It is a primary object of the present invention to provide a highly energy-efficient and improved continuous process for the production of melamine from urea which utilizes a simplified process to produce and recover a high-grade (96 to 99.5% purity) melamine as a dry powder directly from liquid melamine melt. Molten urea is supplied to a reactor maintained at high temperature (700.degree. to 800.degree. F.) and high pressure (1700 to 2200 psig) whereby melamine, CO.sub.2, and NH.sub.3 are formed. The reactor effluent stream containing liquid melamine, CO.sub.2, and NH.sub.3 is transferred to a gas separator where CO.sub.2 and NH.sub.3 containing melamine are separated and cycled to a scrubber unit for scrubbing with molten urea reactant to remove the melamine before transfer of the CO.sub.2 and NH.sub.3 gases at high pressure to an adjacent urea plant for utilization in producing urea. The melamine liquid product is transferred from the gas separator to a collecting tank maintained at a pressure of less than about 615 psig and from about 120.degree. to 260.degree. F. where the liquid melamine is immediately contacted with, or quenched with a liquid, preferably liquid ammonia. The melamine separates as a dry powder which requires no further processing, having a purity in the range of 96 to 99.5%, useful in applications including fertilizer and resin manufacture. This process is highly cost efficient.

Claims16

Dependent claims

A continuous process for producing melamine from urea comprising pyrolyzing urea in a reactor at a pressure at from about 1500 to 2500 psig and at a temperature at from about 670.degree. to 800.degree. F. to produce a reaction product containing liquid melamine, CO.sub.2 and NH.sub.3 ;

transferring, under pressure, said reaction product as a mixed stream to a separator unit;
maintaining said separator unit at substantially the same pressure and temperature as said reactor;
separating said reaction product in said separator unit into CO.sub.2 and NH.sub.3 offgases containing melamine vapors and liquid melamine;
simultaneously transferring
(a) said CO.sub.2 and NH.sub.3 offgases containing melamine at a temperature and pressure substantially the same as said temperature and pressure of said separator unit to a scrubber unit and scrubbing said off-gases with molten urea to preheat said urea and cool said offgases and remove therefrom said melamine, and thereafter removing NH.sub.3 and CO.sub.2 gases from said scrubber unit at a temperature of from about 350.degree. to about 450.degree. F. and feeding said preheated molten urea containing said melamine to said reactor, and
(b) said liquid melamine to a product cooling unit;
and depressurizing and quenching said liquid melamine with a liquid medium which will form a gas at the temperature of said liquid melamine in said product cooling unit to produce a commercially useful solid melamine product, without washing or further purification.

4 more elements

A plant-system for producing melamine from urea comprising as the essential components of said plant-system a reactor unit;

a separator unit;
a scrubber unit, and a product cooling unit,
said reactor unit including:
means for heating and maintaining said reactor to a temperature of from about 670.degree. F. to about 800.degree. F.;
means for pressurizing said unit to from about 1500 to 2500 psig and pyrolyzing urea to produce liquid melamine, CO.sub.2 and NH.sub.3, and means for continuously transferring under said temperature and pressure conditions liquid melamine, CO.sub.2 and NH.sub.3 as a mixed stream to said separator unit;
said separator unit including:
means for maintaining said separator at substantially the same temperature and pressure as said reactor;
means for receiving and separating under said temperature and pressure conditions said stream of liquid melamine, NH.sub.3 and CO.sub.2, and means for continuously transferring said CO.sub.2 and NH.sub.3 offgases containing melamine vapors to said scrubber, and means for continuously transferring said liquid melamine to said product cooling unit;
said scrubber unit including:
means for receiving molten urea;
means for receiving said offgases containing said melamine from said separator unit at said temperature and pressure conditions of said separator unit;
means for contacting said molten urea with said offgases containing melamine to scrub said melamine from said CO.sub.2 and NH.sub.3 gases and preheating said urea, and means for continuously transferring said molten urea containing said scrubbed melamine to said reactor;
said product cooling unit including:
means for receiving said liquid melamine from said separator unit;
means for depressurizing and quenching said liquid melamine with a liquid medium which will form a gas at the temperature of said liquid melamine, and collecting said melamine without washing or further purification as a solid at from about 96 to 99.5% melamine.

12 more elements

Dependencies are inferred from the claim text.

Anhydrous high-pressure melamine synthesis

Life of this patent

Anhydrous high-pressure melamine synthesis

Life of this patent

Abstract

Claims16