Patent GB-455865-A (GB)
Title: Improvements in and apparatus for the separation of carbon dioxide and/or hydrogen sulphide from ammonia
IPC: C01B32/50
Filed: 1935-05-01
Abstract: Carbon dioxide is removed from ammonia by washing a gas consisting of or containing the said constituents, e.g. unconverted material from the conversion of ammonium carbamate into urea, with an aliphatic amine which is substituted on the nitrogen atom by one, but only one, hydroxyalkyl group or with a solution of such an amine, at a temperature which is so high that no substantial amount of ammonia is absorbed but which is below the temperature at which the weak gaseous acid is split off from its salt with the amine, the said temperature being at least 70 DEG  C.  Preferably, temperatures above 95 DEG  C., say 100--125 DEG  C., are employed.  Suitable amines include monobutanol amine, monohydroxyethylethylene diamine, monopropanol amine and monoethanol amine.  The weak gaseous acid may be recovered by heating the resulting solution to higher temperatures.  In working up the unconverted ammonium carbamate left in the preparation of urea therefrom under pressure, the unconverted mixture of ammonia and carbon dioxide is separated by the present process, the constituents being compressed again separately from each other in unheated compressors for return to the plant for the preparation of urea.ALSO:Weak gaseous acids, such as carbon dioxide or hydrogen sulphide, are removed from ammonia by washing a gas consisting of or containing the said constituents with an aliphatic amine which is substituted on the nitrogen atom by one but only one hydroxyalkyl group or with a solution of such an amine, at a temperature which is so high that no substantial amount of ammonia is absorbed but which is below the temperature at which the weak gaseous acid is split off from its salt with the amine, the said temperature being at least 70 DEG  C.  Preferably temperatures above 95 DEG  C., say 100--125 DEG C., are employed. Suitable amines include monobutanol amine, monohydroxyethylethylene diamine, monopropanol amine and monoethanol amine.  If the gas mixture contains water vapour, this will be removed in the washing step.  The process may be conducted at atmospheric or elevated pressure.  The weak gaseous acid may be recovered by heating the resulting solution to higher temperatures. The weak gaseous acid thus recovered contains a little ammonia which may be removed therefrom in known manner by washing.  The process may be used for working up the unconverted ammonium carbamate left in the preparation of urea therefrom under pressure, the unconverted mixture of ammonia and carbon dioxide being separated by the present process and compressed again separately from each other in unheated compressors for return to the plant for the preparation of urea.  The process may also be used to separate the gases obtained by heating gas liquor.  If the process for the separation of ammonia and carbon dioxide is conducted under pressure with the employment of monopropanol amine, the ammonia which escapes is free from carbon dioxide; by releasing the pressure while maintaining the temperature further ammonia containing some carbon dioxide is obtained, while the carbon dioxide may be recovered by raising the temperature at atmospheric pressure.