US 12,391,655 B1
Melamine process with a two-stage purification of melamine offgas
Simone Gamba, Pagazzano (IT)
Assigned to Casale SA, Lugano (CH)
Appl. No. 18/710,989
Filed by Casale SA, Lugano (CH)
PCT Filed Oct. 5, 2023, PCT No. PCT/EP2023/077650
§ 371(c)(1), (2) Date May 16, 2024,
PCT Pub. No. WO2024/074656, PCT Pub. Date Apr. 11, 2024.
Claims priority of application No. 22200402 (EP), filed on Oct. 7, 2022; and application No. 23158350 (EP), filed on Feb. 23, 2023.
Int. Cl. C07D 251/60 (2006.01)
CPC C07D 251/60 (2013.01) 20 Claims
 
1. A process for the synthesis of melamine including the steps of:
reacting a feed stream of urea melt under non-catalytic high pressure melamine synthesis conditions to generate a raw melamine product and an offgas comprising ammonia and carbon dioxide,
subjecting said offgas to a purification process by washing the offgas with urea melt, to obtain a purified offgas and a urea melt containing ammonia and melamine precursors, wherein the purification process includes a first purification step performed in a first purification stage and a second purification step performed in a second purification stage,
wherein said purification steps are carried out in sequence so that the offgas from the melamine synthesis is subject to the first purification step and the so obtained partially purified gas is further processed in the second purification step,
wherein:
during said first purification step, the offgas is contacted with urea melt comprising a recirculated urea melt containing ammonia and melamine precursors, said recirculated urea melt being withdrawn from the first stage and reintroduced in the same first stage,
wherein said recirculated urea melt, before being reintroduced in the first stage, is cooled in a shell and tube heat exchanger to a temperature not less than 165° C.