| 摘要 |
In a process for the synthesis of urea from carbon dioxide and ammonia at least part of one or both of these reactants, prior to being introduced into the autoclave in which they are treated to produce urea, is obtained from a solution thereof, which is treated with a non-volatile chemical reducing agent to remove free oxygen before or during the extraction from the solution of the said reactant or reactants. The reducing agent may be added to the solution of reactants or, alternatively, said solution may be passed over a solid reducing agent. Specified reducing agents are pyrogallol, alkali hydrosulphites, ferrous, manganous, cuprous and titanous salts or hydroxides, and metals such as copper, iron and zinc. The process may be applied to the deoxygenation of (1) carbon dioxide extracted from flue gas by absorption in alkali carbonate or ethanolamine solution; (2) carbon dioxide obtained by conversion of water-gas, followed by absorption in water under pressure; and (3) recycled carbon dioxide and ammonia dissolved in water or introduced into an inert oil to form a suspension of ammonium carbamate. |
