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Chemicals from Paraffin Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
The technical production of urea is based on the reaction of ammonia with carbon dioxide. The reaction occurs in two steps: ammonium carbamate is formed first, followed by a decomposition step of the carbamate to urea and water. The first reaction is exothermic and the equilibrium is favored at lower temperatures and higher pressures. Higher operating pressures are also desirable for the separation absorption step that results in a higher carbamate solution concentration. A higher ammonia ratio than stoichiometric is used to compensate for the ammonia that dissolves in the melt. The reactor temperature ranges between 170°C and 220°C (340°F–395°F) at a pressure of about 3,000 psi. The second reaction represents the decomposition of the carbamate. The reaction conditions are 200°C (390°F) and 450 psi: 2NH3+CO2→H2NCOONH4H2NCOONH4→H2NCONH2+H2O
Methanation
Published in Martyn V. Twigg, Catalyst Handbook, 2018
In an ammonia plant methanation is the final stage in the purification of the synthesis gas in which small concentrations of carbon monoxide and carbon dioxide (0.1–0.5%) are removed catalytically by reaction with hydrogen. The synthesis catalyst is extremely susceptible to the presence of carbon oxides, so much so that its long-term activity is adversely affected unless they are reduced to very low levels (see Section 8.5.2.). In some plants the presence of carbon dioxide in the synthesis gas can also lead to the formation of ammonium carbamate (NH4COONH2) where the make-up gas meets ammonia-containing circulating gas, forming a solid deposit which can restrict the gas flow and/or foul the compressor. Ammonium carbamate is also known to cause stress corrosion cracking at critical points in the synthesis-gas compressor.
Natural and Process Compressors
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
A related process often accompanying the production of ammonia is urea which is made from ammonia and CO2. The ammonia and CO2 are fed into the reactor at high pressure and temperature, and the urea is formed in a two-step reaction, first producing ammonium carbamate and then urea. The urea contains unreacted NH3 and CO2 and ammonium carbamate. As the pressure is reduced and heat applied, the ammonium carbamate decomposes to NH3 and CO2 which are then recycled. The urea solution is then concentrated and granulated for use as fertilizer and chemical feedstock.
Carbon-dioxide capture, storage and conversion techniques in different sectors – a case study
Published in International Journal of Coal Preparation and Utilization, 2023
Another application for this captured CO2 is in the production of urea, the world’s most widely produced nitrogen fertilizer. Urea is a fertilizer, feed supplement, and a raw material for polymers and pharmaceuticals. A colorless crystalline material melts at 132.7°C (271°F) and decomposes prior to boiling. It is manufactured industrially by reacting ammonia with CO2. Ammonia and CO2 react to make ammonium carbamate, which is subsequently dehydrated to form urea.