Session: 06-03 Novel Reactors and Processes

Paper Number: 117211

117211 - Solar Thermal Ammonia Production via Metal Nitride Looping 

Ammonia is produced worldwide on a massive scale due its utility as a chemical intermediate and to its critical importance for use as, and in, fertilizers that underpin modern agricultural practices and the societies dependent on them.  The widely practiced Haber-Bosch process for producing ammonia requires high pressures and is energy and carbon dioxide intensive; the hydrogen feed stock is sourced from methane via reforming, and the nitrogen is produced by removal of oxygen from air in the form of carbon dioxide after combustion of additional methane.  We have investigated an alternate, potentially more sustainable, route to ammonia wherein nitrogen is produced from air utilizing a solar thermochemical metal-oxide based process. Ammonia is subsequently produced from this nitrogen and renewably sourced hydrogen using a somewhat analogous two-stage nitride-based cycle.  In the first step of the cycle, hydrogen reacts with metal nitride particles to produce ammonia, resulting in a reduced (nitrogen deficient) metal nitride. In the second step, the nitride is regenerated for reuse through reaction with nitrogen. The net result is ammonia produced from sunlight, air, and (green) hydrogen, while the metal oxide and nitride particles are recycled. An overview of the entire process and economic analysis will be presented. However, the bulk of the presentation will focus on the novel ammonia production cycle.  A rationale for identifying nitrides of interest will be introduced. Binary nitrides, i.e., those containing only one metal and nitrogen, are generally unsuitable. Ternary or quaternary nitrides offer more options and flexibility. Experimental results for synthesizing and characterizing several series of relevant ternary and quaternary nitrides will be discussed. The nitride looping reaction chemistry has been convincingly demonstrated in our laboratories using a ternary CoMo formulation.  This nitride can be repeatedly cycled between 662 and 331 (Co:Mo:N) compositions.  The results of reaction and kinetic studies will be presented.

Presenting Author: James Miller Arizona State University

Presenting Author Biography: Dr. James E. Miller (Jim) retired from Sandia National Laboratories in 2017 after 25 years of service. He is currently a Professor of Practice in the School of Sustainability at Arizona State University. As a chemical engineer he has directed his research efforts towards energy, materials, and chemical processing spanning topics from heterogeneous catalysis to desalination. For more than a decade now his efforts have been primarily focused on high temperature thermochemical processes, for example water and carbon dioxide splitting for the production of hydrogen or synthesis gas, thermochemical energy storage, and other processes such as ammonia synthesis. Dr. Miller has co-authored over 120 technical documents, holds 16 patents, and is the recipient of two R&D 100 Awards. Dr. Miller received his B.S. in Chemical Engineering from Texas A&M University in 1986, and his Ph.D. in Chemical Engineering from the University of Texas at Austin in 1992.