Formation and control of N2O in nitric acid production: Where do we stand today?

Nitric acid production represents the largest source of N2O in the chemical industry, with a global annual emission of 400 kt N2O. The high impact of N2O on the environment as greenhouse gas and stratospheric ozone depletor, and the ongoing agreements and prospective regulations calls for the development of efficient and economical systems for N2O mitigation, but no mature commercial technology is yet available. In this review, the current state-of-the-art for N2O control in the nitric acid manufacture is presented. The formation of N2O and the process are analyzed and several options for reducing its emissions are discussed, depending on the position in the process. Primary abatement options deals with modifications in the ammonia oxidation catalyst, secondary abatement with options between the ammonia converter and the absorber, tertiary abatement with options in the tail-gas upstream of the expander, and quaternary abatement with options in the tail-gas downstream of the expander. The abatement technologies are evaluated based on the technical advantages and disadvantages, and cost efficiency.