Process for the preparation of urea
AssigneeDsm N.V.
InventorJulius G. T. Van Wijck
Life of this patent
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Abstract
In the present process for the preparation of urea, an off-gas stream released during the synthesis of melamine in a high-pressure melamine process which consists predominantly of ammonia and carbon dioxide, is introduced into at least one high-pressure section of a urea stripping plant and is used in the synthesis of urea. The off-gas stream can be used directly without any further treatment.
Claims13
A process for the preparation of urea in a urea stripping plant having at least one high-pressure section, said high pressure section operating at a pressure of at least 12.5 MPa, wherein said process comprises the step of supplying a gas stream released from a high-pressure process for making melamine, said high-pressure process operating at a pressure at least equal to that of said high pressure section, to at least one high-pressure section of said urea stripping plant without an intermediate adsorption step, wherein said gas stream consists essentially of ammonia and carbon dioxide.
A process for the unified preparation of urea and melamine comprising the steps of:
- feeding a mixture of ammonium carbamate, carbon dioxide, ammonia, and water into a urea synthesis reactor;
- reacting said mixture in said urea synthesis reactor at a pressure of at least about 12.5 MPa and a temperature of at least about 160.degree. C. to form a urea solution containing unreacted ammonium carbamate;
- feeding said urea solution into a stripper, said stripper being operated at a pressure about equal to the pressure in said urea synthesis reactor;
- stripping said urea solution in said stripper using heat and stripping gas to remove substantially all of said unreacted ammonium carbamate from said urea solution, thereby forming a stripped urea solution and a stripped gas stream;
- feeding said stripped gas stream into an ammonium carbamate condenser;
- dehydrating said urea solution to form a urea melt;
- feeding said urea melt and ammonia into a melamine synthesis reactor, said melamine synthesis reactor being operated at a pressure at least equal to the pressure in said urea synthesis reactor and a temperature of at least about 300.degree. C.;
- reacting said urea melt in said melamine synthesis reactor to form a melamine product stream, said melamine product stream;
- separating said melamine product stream into an off gas stream and a melamine melt stream, said off gas stream being obtained at a pressure at least equal to the pressure in said urea synthesis reactor;
- cooling and directly solidifying said melamine melt stream under ammonia pressure to produce a substantially pure dry solid melamine product;
- feeding said off gas stream into said stripper, said stripper being operated at a pressure at least equal to the pressure in said urea synthesis reactor.
Dependencies are inferred from the claim text.