Abatement technologies for N2O emissions in the adipic acid industry

Abstract

Adipic acid (AA) is the main intermediate in nylon 6, 6 that is manufactured by polymerization condensation of AH salt (hexamethylenediammonium adipate). Adipic acid is also an intermediate in the production of polyester-polyol, a material used in polyurethane.

Annual production capacity of AA for 1998 was estimated to be 2.3 million metric tons and about 80% of that AA is used to manufacture nylon 6, 6. Almost all AA is produced by nitric acid oxidation of KA oil, a mixture of cyclohexanone and cyclohexanol.

The reaction of nitric acid oxidation unavoidably generates nitrous oxide. The N₂O emission coefficient for Japan's AA plant is approximately 0.25 kg-N₂O/kg-AA. If the N₂O output from all adipic acid plants is calculated using the N₂O emission coefficient described above and the world's AA production capacity then we obtain a figure of 576,250 metric tons per year, but if we calculate only that which will be clearly reduced by 1999–2000, a reduction of ca. 80% has already been achieved. This is because the N₂O abatement equipment of the major AA manufacturers is scheduled to have completed startup by 1999–2000.

The main technologies used to reduce nitrous oxide in the adipic acid industry are catalytic decomposition and thermal destruction. These methods convert nitrous oxide into nitrogen and oxygen. Catalytic decomposition operates at about 500°C and thermal destruction operates at and over 1000°C. Using these reduction technologies allows the adipic acid manufacturers to reduce N₂O emissions by 90% or more.