Year: 2012
Type: dissertation
Abstract: Approximately 45% of the global hydrogen production (from fossil fuels such as natural gas or coal totaling 2% of the global energy generation) is absorbed as feedstock in the synthesis of over 130 million metric tons ammonia (NH 3 ) annually.To achieve food security for a growing world population and to allow for additional uses of the nitrogen-fertilizer for production of bioenergy feedstock or as combustion fuel or H 2 carrier -demand for NH 3 is projected to increase.This work pursues the synthesis of ammonia at atmospheric pressure and without fossil fuel.Conceptually, concentrated solar radiation is utilized to transfer electrons from the lattice oxygen of a transition metal oxide to the metal ion.This yields a metallic reactant that provides the reducing power for the subsequent six-electron reductive cleavage of N 2 forming a transition metal nitride.In a second reaction, the generated lattice nitrogen is hydrogenated with hydrogen from H 2 O to NH 3 .This furnishes the transition metal oxide for perpetuated NH 3 synthesis.Theory and experimentation identified manganese nitride as a promising reactant with fast diffusion characteristics (8 ± 4 x 10 -9 cm 2 s -1 apparent nitrogen diffusion constant at 750°C) and efficient liberation of 89 ± 1 mol% nitrogen via hydrolysis at 500°C.Opposed to only 2.9 ± 0.2 mol% NH 3 from manganese nitride, 60 ± 8 mol% of the nitrogen liberated from molybdenum nitride could be recovered as NH 3 .Process simulation of a Mo-based NH 3 synthesis at 500-1200°C estimates economically attractive production under fairly conservative process and market conditions.To aid the prospective design of a Mn or Mo-based reactant, correlating the diffusion constants for the hydrolysis of seven nitrides with the average lattice nitrogen charge (9.96-68.83%,relative to an ideal ionic solid) indicates the utility of first-principle calculations for developing an atomic-scale understanding of the reaction mechanism in the future.
Author: Michalsky, Ronald
Institution: Technische Hochschule Mittelhessen
Language: English
Subfield: Catalysis
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W189031346