Green ammonia production via microalgae steam catalytic gasification process over LaFeO3 perovskite

Abstract

Ammonia (NH3) is a potential carbon-free energy carrier. This study proposed a green route for NH3 production via microalgae steam catalytic gasification process over LaFeO3 perovskite. The experiments of pyrolysis, catalytic pyrolysis, steam gasification, and steam catalytic gasification were compared in a fixed bed reactor. Compared with pyrolysis, steam is introduced as the gasifying agent for reforming volatile-N and gasifying char-N during steam gasification, thus promoting the fuel-nitrogen transfer into the gas phase. Synergistic effects of steam and LaFeO3 are able to promote the hydrogenation of char-N, the decomposition of proteins, and the deamination of amides, resulting in a remarkable release of NH3. More importantly, steam and LaFeO3 can significantly promote the conversion of HCN into NH3, which will enhance the selectivity of NH3. Proper steam concentration can provide considerable amounts of H radicals for enhanced NH3 production, whereas excessive steam is likely to facilitate the NH3 conversion to H2. Gasification temperature exerts positive effects on the NH3 yield at 700–800 °C, but further increase in temperature causes a reduction in NH3 production, as a result of its decomposition into N2. The highest conversion of nitrogen into NH3 (55.98 wt%) is obtained at 800 °C with a steam concentration of 54 vol% and the catalyst-to-feedstock ratio of 1. Moreover, the LaFeO3 perovskite also exhibits desirable stability during the long-term cycling both in the activity and structure aspect.