Dissertation
CHEMICAL LOOPING OF MANGANESE TO SYNTHESIZE AMMONIA AT ATMOSPHERIC PRESSURE
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004393
Handle:
https://hdl.handle.net/2376/118879
Abstract
Synthetic ammonia (NH3) enables the production of about half of the food we eat. Synthetic NH3 and chemicals such as urea derived from NH3 are mostly used for fertilization in agriculture. NH3 is currently almost exclusively produced based on fossil fuels, consuming about 2% of the world's energy budget. Industrial NH3 is produced by the Haber–Bosch process (gas-phase heterogeneous catalysis at ~300 atm and ~500°C, hydrogen gas (H2) from natural gas via reforming, nitrogen gas (N2) from air) which consumes about 525-750 kg natural gas per 1000 kg of NH3. Research is presented here towards a sustainable synthesis of NH3 based on chemical looping by using Manganese (Mn) to activate dinitrogen to form Mn-nitride. Then the NH3 is harvested by contacting Mn-nitride with renewable H2 at atmospheric pressure. The incentive for this is to enable a smaller scale, robust, and technologically simple NH3 synthesis process at the tonne per day scale driven by intermittent renewable electricity used for electrolysis of water. Avoiding the high-pressure requirement of the conventional Haber-Bosch process may also render chemical looping useful where large capital expenses required for Haber-Bosch plants are challenging to secure.
Chemical looping ammonia synthesis (CLAS) at atmospheric pressure using Mn to activate dinitrogen is here enhanced by a sodium-containing promoter. The addition of NaOH as an alkali-containing promoter significantly improves yield and kinetics of chemical looping of Mn for NH3 synthesis. Morphology changes were detected during the Mn nitridation, which yielded a coherent picture of nitridation of solid Mn. The evolution of three distinct regions in the solid during nitridation of Mn with time was quantified and reduced to a simple design equation. Kinetics and mass transfer via diffusion of N in Mn were explored experimentally as well to enable process modeling and design. Mathematical models to make quantitative predictions of N penetration in Mn and the N concentration profile in the solid for a model gas-solid nitridation reaction with different controlling mechanisms are critically evaluated. The N diffusion coefficient (DN) and reaction rate coefficient, k were estimated.
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Details
- Title
- CHEMICAL LOOPING OF MANGANESE TO SYNTHESIZE AMMONIA AT ATMOSPHERIC PRESSURE
- Creators
- Wrya Aframehr
- Contributors
- Peter H Pfromm (Advisor)Bernard J Van Wie (Committee Member)Manuel Garcia-Perez (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Chemical Engineering and Bioengineering, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 143
- Identifiers
- 99900883136701842
- Language
- English
- Resource Type
- Dissertation