The process in order to recover the gaseous ammonia, an aqueous solution containing ammonia and carbon dioxide

摘要

In the manufacture of nitriles by ammoxidation of hydrocarbons with molecular O2 in the presence of NH3, the off-gas containing NH3 and CO2 is scrubbed with water, and air and/or O2 is passed through the solution to desorb NH3, the resulting mixture of NH3, air and/or O2 being recycled for further ammoxidation of hydrocarbons. Reference is made to the production of benzonitrile from toluene and of phthalonitriles from xylene.ALSO:PICT:1072293/C1/1 Ammonia is recovered from an aqueous solution containing NH3 and CO2, the molar ratio of NH3: CO2 being, more than two, by passing through the solution a desorption gas, which does not react with NH3 and CO2, at a temperature below 60 DEG C. and above the freezing point of said solution and thus desorbing NH3 gas free from CO2. In one embodiment, an NH3/CO2 solution produced by scrubbing a gaseous NH3 / CO2 mixture formed in urea synthesis, or in the manufacture of nitriles from hydrocarbons by ammoxidation, is fed through line 6 into top plate 3 of desorption column 1 and is contacted with ascending desorption gas, e.g. O2 or N2, or a mixture of these such as air, thereby desorbing part of its NH3 content. The desorbed NH3 and desorption gas leave by line 7 and may be recycled to the ammoxidation reactor. The NH3-depleted solution descends via the plates below, e.g. bubble cap plates to the bottom of the column and is removed by line 4. The whole or part of the solution on a plate may be removed from the column and heated in a heater 2 to maintain the desired column temperature, or alternatively an interior heater is provided. The NH3/CO2 solution and desorption gas may be pre-heated. Column pressure is usually atmospheric but can be elevated or reduced. A counter current pipe system and an agitation mixing system are other desorption means specified.