Concentration of dilute nitric acid - by-product of conc nitric acid mfr

摘要

Method of and appts. for concentrating dilute nitric acid obtd. in the mfr. of conc. HNO3 or NO2 from oxides of nitrogen made by oxidising ammonia with air under pressure, whereby oxidised ammonia gases are contacted directly with dilute HNO3 and the hot dilute nitric acid produced is passed into a distillation column. The conc. HNO3 forms gas the bottom end of the distillation column and the dilute HNO3 formed in the vapour is recycled to contact the incoming oxidised ammonia gases. The heat in the nitric acid is used efficiently, the dilute HNO3 appearing at the bottom of the distillation columns is concentrated and the water, product of the ammonium oxidation reaction is eliminated.