Production of nitrogen tetroxide

Claim 1

A PROCESS FOR PRODUCTION OF NITROGEN TETROXIDE OF AT LEAST 99.5% NITROGEN TETROXIDE CONCENTRATION WHICH COMPRISES COOLING A GAS MIXTURE CONTAINING PRIMARILY NITROGEN AND LESSER AMOUNTS OF NITRIC OXIDE, NO2 OXYGEN AND WATER VAPOR OBTAINED FROM THE CATAKYTIC OXIDATION OF AMMONIA TO CONDENSE A MAJOR PORTION OF THE WATER THEREFROM, SEPARATING THE GAS MIXTURE FROM THE CONDENSATE AND INTRODUCING THE GAS MIXTURE AS THE SOLE REACTANTS INTO AN OXIDATION ZONE, PASSING THE GAS MIXTURE CONTAINING NITROGEN, NITRIC OCIDE, NO2, OXYGEN AND RESIDUAL WATER VAPOR THROUGH SAID OXIDATION ZONE TO OXODIZE THE NITRIC ACID BY THE CONTAINED OXYGEN TO INCREASE MATERIALLY ITS NO2 CONTENT, WITHDRAWING THE GAS MIXTURE OF INCRESED NO2 CONTENT FROM THE OXIDATION ZONE AND INTRODUCING SAID GAS MIXTURE INTO A LOWER PORTION OF AN ABSORPTION ZONE, INTRODUCING CONCENTRATED NITRIC ACID OF ABOUT 85-95% ACID CONCENTRATION INTO AN UPPER PORTION OF THE ABSORPTION ZONE, SELECTIVELY ABSORBING THE NO2 OF THE GAS MIXTURE BY THE NITRIC ACID IN STAGES WITHIN THE ABSORPTION ZONE BY PASSING SAID GAS MIXTURE UPWARDLY WITHIN SAID ABSORPTION ZONE IN INTIMATE COUNTERCURRENT CONTACT IN THE STAGES WITH CONCENTRATED NITRIC ACID PASSING DOWNWARDLY THEREIN AT A T EMPERATURE OF ABOUT 20*-50*C. AND UNDER PRESSURE, WITHDRAWING A MIXTURE OF NITRIC ACID, NO2 AND WATER FROM A LOWER PORTION OF THE ABSORPTION ZONE, RECIRCULATING A PORTION OF THE LAST-MENTIONED WITHDRAWN MIXTURE, AFTER COOLING BY INDIRECT HEAT EXCHANGE, INTO THE