In a commercial process for the production of adipic acid, cyclohexanone and cyclohexanol are oxidized with nitric acid to form adipic acid. A by-product of the reaction is N.sub.2 O. N.sub.2 O has recently been identified as gas that if released to the atmosphere acts as an ozone depletion gas and as a global warming gas. Efforts are underway in the chemical industry to significantly reduce the amount of N.sub.2 O that is released to the atmosphere.
Japanese Patent Application Publication S61-257940 discloses a process for the conversion of off-gas from the production of adipic acid by nitric acid oxidation, wherein the off-gas is heated in a heat exchange unit to raise the temperature sufficiently high that the N.sub.2 O decomposes to form NO, nitrogen, and oxygen. The patent application points out that if the reaction were conducted catalytically, then the products of the reaction would be nitrogen and oxygen, but very little NO.
One of the problems with the process described in this Japanese publication is that the heating of the off-gas to reaction temperature by a heat exchanger and the decomposition reaction both take place in the same reactor. Since the decomposition reaction is highly exothermic the temperature in the chamber will exceed about 1000 to 1300 degrees C. Such high temperatures require ceramic equipment or equipment made from very expensive metals.
Burton D. Fine et al in "The Yield of Nitric Oxide from Premixed Flames of Hydrogen and Hydrocarbons with Nitrous Oxide" NASA Technical Note D-1736, 5/63 discloses premixing gases containing N.sub.2 O with various fuels and igniting the mixture.
European Patent Application 93400042.3, published Aug. 11, 1993, discloses the conversion of N.sub.2 O to NO by injecting dinitrogen oxide either into a flame or into the hot gases issuing from the flame.
The present invention provides an improved process for the decomposition of N.sub.2 O contained in an off-gas from nitric acid oxidation to produce adipic acid. The process can be operated in an efficient manner with modestly priced equipment. The stream exiting the reactor is relatively high in NO concentration, and is diluted only minimally by combustion products of the combustible gas used to heat the off-gas to its combustion temperature. When dilution is minimized, the NO yield (moles of NO produced per mole of N.sub.2 O fed) is unexpectedly high, and the higher concentration of NO produced can be economically recovered in a commercial absorption tower.