Uncovering the realistic potential of chemical looping ammonia production routes
Why is this research needed?
Scaled ammonia production has led to mass manufacturing of fertilisers, which has been a key factor enabling population growth. Currently, almost all ammonia is produced using fossil fuels and its production accounts for 1.3% of global greenhouse gas emissions. To meet the net-zero target by 2050, either this emission will need to be captured, instead of releasing to the atmosphere (blue ammonia production), or an entirely new process based on 100% renewable resources needs to be developed (green ammonia production). Whilst the latter is a long-term aspiration, it is difficult to achieve in the immediate future, and the blue ammonia route will need to be an intermediate step towards achieving fully sustainable ammonia production. However, these emerging technologies can increase the cost of ammonia production by 10-100%, according to a recent study by the International Energy Agency.
One simple way to realise blue ammonia production is to retrofit existing production facilities with carbon capture equipment. However, this may not be the most economical and environmentally friendly approach. Recently, a new approach known as chemical looping ammonia production (CLAP) has been proposed, compatible with both the blue and green ammonia routes. This technology uses a solid intermediate to synthesise ammonia via multiple reaction steps. The advantage is that a good ammonia yield can be obtained at lower operating pressures, compared to the conventional process operated at 150 bar or more. The ability to lower the pressures can potentially reduce the cost of ammonia production, but this has largely remained as speculation and no rigorous studies have been performed to date to verify this.
Our project aims to study the economic and environmental feasibility and sustainability of this chemical looping ammonia production approach, against the retrofitting of existing NH3 production technology with a carbon capture facility. The work will evaluate the cost and energy demand of these two routes and identify favourable operating conditions for the chemical looping ammonia production route, along with suitable solid intermediates that can be used to realise the process. This information will then be used as part of the lifecycle analysis of the production methods to study their environmental impact from production of raw materials through to the use of final products and disposal of any wastes. Importantly, the input parameters for process and environmental assessments will be based on experimental results, which will verify whether the thermodynamic assumptions about common CLAP materials are realistic.
What is this research investigating?
The primary objective of this work is to examine the economic and environmental feasibility and sustainability of chemical looping ammonia production (CLAP) using metal nitrides and metal imides. CLAP shows promise for high NH3 production rates at low pressures, exceeding the performance of the classical Haber-Bosch process. However, the full potential of CLAP remains unassessed. Therefore, we will undertake economic, environmental and technical assessment for CLAP processes by:
- Experimentally verifying the thermodynamic and kinetic assumptions for the four most promising CLAP materials, identified in our earlier work among imides and nitrides;
- Constructing process flow sheets of a commercial ammonia production plant and a CLAP-based plant, each producing 500k tonne NH3/y, with and without carbon capture;
- Performing techno-economic analysis and life cycle analysis of the two types of plants, investigating different process configurations.
What does the research hope to achieve?
The outcome of this work will benefit academic and industrial research in blue ammonia production and related areas (in particular, ammonium nitrate and urea production, and to some extent, blue hydrogen production). The proposed work will serve to verify key thermodynamic properties of metal nitrides and metal imides required for a viable chemical looping ammonia production process, which could focus the direction for future research on novel materials for this application. It will also inform policymaking at local and national levels by providing evidence of viability (or otherwise) of different options for ammonia production. The outcome will be disseminated as open-access research papers so that the methodology and results are available to the wider community without unnecessary barriers. Research models and data generated from this project will be stored in university-managed storage space, which is available to other users free of charge.
The research assistants for this project are current PhD students, and they will benefit through this project from further development of their skills and experience in materials synthesis, experiments for assessing materials performance, process modelling, techno-economic analysis and life cycle analysis, and their application to a pressing industrial problem. They will also have the opportunity to present their work in national and international forums, including UKCCSRC meetings. In addition, as part of a small team with a flat management structure, the RAs will also have exposure to project management, which will aid them to develop their own research work and proposals when they complete their PhD research and move forward to be independent researchers.
This research is ongoing. Outputs will be shared below as they become available.