The effect of nitrogen (III) oxide on direct synthesis of concentrated nitric acid

The effect of nitrogen (III) oxide on the process of dinitrogen tetroxide separation in a dephlegmator during preparation of a "crude mixture" (HNO3–N2O4–N2O3–NO2–NO–H2O) in the production of concentrated nitric acid by direct synthesis was studied in this work. The dependence of crystallization onset on the composition of the N2O4–N2O3 mixture and temperature was determined. The refrigerant capable of maintaining the optimal temperature of the N2O4 extraction was suggested. The absence of nitrogen (III) oxide and nitrogen (I) oxide in the autoclave acid was confirmed.