Thermodynamics of metal reactants for ammonia synthesis from steam, nitrogen and biomass at atmospheric pressure

• Published in: AIChE journal Vol. 58; no. 10; pp. 3203 - 3213
• Main Authors: Michalsky, Ronald, Pfromm, Peter H.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-10-2012; Wiley; American Institute of Chemical Engineers
• Subjects: Ammonia; Applied sciences; Atmospheric pressure; Catalysis; Catalytic reactions; Chemical engineering; Chemical reactions; Chemical synthesis; Chemistry; Exact sciences and technology; fertilizer; fossil fuel; General and physical chemistry; low pressure; Reactors; Simulation; solar energy; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; thermochemical reaction cycle; Thermodynamics; Cartography; Gibbs free energy; Catalytic reaction; Fertilization; Atmospheric pressure; Carbon dioxide; ammonia; Reforming; Biomass; low pressure; Water vapor; fertilizer; Fertilizers; Hydrolysis; thermochemical reaction cycle; Solar energy; Production; Fossil fuel; Thermodynamic properties; Natural gas
• ISSN: 0001-1541; 1547-5905
• DOI: 10.1002/aic.13717

Catalytic ammonia synthesis at approximately 30 MPa and 800 K consumes about 5% of the global annual natural gas production causing significant CO2 emissions. A conceptual solar thermochemical reaction cycle to produce NH3 at near atmospheric pressure without natural gas is explored here and compared to solar thermochemical steam/air reforming to provide H2 used in the Haber‐Bosch process for NH3 synthesis. Mapping of Gibbs free energy planes quantifies the tradeoff between the yield of N2 reduction via metal nitridation, and NH3 liberation via steam hydrolysis vs. the temperatures required for reactant recovery from undesirably stable metal oxides. Equilibrium composition simulations suggest that reactants combining an ionic nitride‐forming element (e.g., Mg or Ce) with a transition metal (e.g., MgCr2O4, MgFe2O4, or MgMoO4) may enable the concept near 0.1 MPa (at maximum 64 mol % yield of Mg3N2 through nitridation of MgFe2O4 at 1,300 K, and 72 mol % of the nitrogen in Mg3N2 as NH3 during hydrolysis at 500 K). © 2011 American Institute of Chemical Engineers AIChE J, 58: 3203–3213, 2012