Syngas production from NH3 and CO2 through chemical looping ammonia cracking - reverse water gas shift

Abstract

Ammonia (NH3) offers benefits over molecular hydrogen as an energy vector because it can be liquefied, transported, and stored more easily using the existing infrastructure. NH3 can react with CO2 to produce syngas (H2 +CO) as a feedstock for circular chemical production. In the conventional process design, this involves: 1) cracking of NH3 to N2 and H2, 2) subsequent product gas separation, and 3) CO production through the reverse water gas shift (RWGS) reaction. Herein, a novel approach referred to as “NH3-RWGS” is presented, which integrates these three steps into a two-reactor process utilizing the chemical-looping principle. In the first reactor, NH3 is cracked over a catalytically active bed material, and H2 reacts further with the metal oxide bed material, producing H2O and N2 as gaseous products and reduced metal oxide/metal. This reduced metal oxide is then moved to the second reactor, where it reacts with CO2 or a mixture of CO2 and H2O, forming CO and H2 as the desired product gas and the re-oxidized metal oxide, which is returned to the first reactor. This process can be favorably implemented in two gas–solid countercurrent flow moving beds. Herein, the underlying design principles are developed, and the maximum achievable gas conversion with an iron-based bed material is established. The feasibility of the underlying chemistry was demonstrated using a supported Fe/MgAl2O4 bed material that exhibited fast kinetics and cyclic stability for the relevant reactions.