From the Birkeland-Eyde process towards energy-efficient plasma-based NO_X synthesis: A techno-economic analysis

Plasma-based NO_X synthesis via the Birkeland-Eyde process was one of the first industrial nitrogen fixation methods. However, this technology never played a dominant role for nitrogen fixation, due to the invention of the Haber-Bosch process. Recently, nitrogen fixation by plasma technology has gained significant interest again, due to the emergence of low cost, renewable electricity. We first present a short historical background of plasma-based NO_X synthesis. Thereafter, we discuss the reported performance for plasma-based NO_X synthesis in various types of plasma reactors, along with the current understanding regarding the reaction mechanisms in the plasma phase, as well as on a catalytic surface. Finally, we benchmark the plasma-based NO_X synthesis process with the electrolysis-based Haber-Bosch process combined with the Ostwald process, in terms of the investment cost and energy consumption. This analysis shows that the energy consumption for NO_X synthesis with plasma technology is almost competitive with the commercial process with its current best value of 2.4 MJ mol-N^-1, which is required to decrease further to about 0.7 MJ mol-N^-1 in order to become fully competitive. This may be accomplished through further plasma reactor optimization and effective plasma-catalyst coupling.