Development of absorbent materials in ammonia synthesis

Lead Research Organisation: University of Oxford
Department Name: Oxford Chemistry

Abstract

The Haber process is currently used to produce ammonia, an essential feedstock for the fertilizer industry that feeds 48% of the world's population. However, high temperatures and pressure are necessary and many recycle steps are needed meaning it is an energy intensive and expensive process that can only feasibly occur on a large scale.
It would be of great benefit if ammonia could be produced under milder conditions. This would create the possibility of smaller scale ammonia production, which would allow fertilizers to be produced at point of use. Lower temperature and pressures mean that it is feasible that the system could be powered by renewable energy, such as wind or solar power. This changes the process from an environmentally unfriendly process to one that is carbon emission free. This movement away from fossil fuels is both economic and environmentally friendly.
One possible method of achieving ammonia production at mild conditions is the use of absorbents. The produced ammonia is absorbed and so removed from the reaction, which forces the equilibrium towards producing more products. This gives higher yields of ammonia despite the less favorable conditions.
There are a number of factors that will be considered when developing the new absorbent. The absorbent must have a high ammonia capacity. As stationary applications are being targeted, capacity by volume is most important although good capacity by weight would be beneficial. The strength of the ammonia absorbent interaction must also be considered. This should be strong enough to ensure equilibrium is shifted but not so strong as to make removing the ammonia difficult. Another consideration is the ability of the ammonia to diffuse through the absorbent. It must be possible for the ammonia to travel through the pores easily to ensure the maximum capacity is achieved.
The main aims of the project are a greater understanding of how ammonia interacts with an absorbent leading to development of a new ammonia absorbent for use in ammonia production.
Many novel research methods will be used in achieving these aims. A variety of syntheses will be used to prepare the absorbents. Varied characterization will be utilized including a number of novel techniques. It is also hoped that synchrotron experiments will give new information about how the ammonia molecules order within the absorbents. NEXAFS will also be used to understand the bonding in the absorbent and the effect this has on the ammonia storage mechanism.
This project falls within the EPSRC Physical Sciences research area and is jointly funded by Siemens.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1811580 Studentship EP/N509711/1 01/10/2016 31/03/2020 Kirsty Jane Purchase
 
Description The research has so far mainly focused on two areas; layered materials and zeolites.

Alternatives to MgCl2 (currently the most commonly used ammonia adsorbent) have been explored and studied. As MgCl2 is a layered material, other layered materials were studied. The structure of these materials and the nature of the ammonia-absorbent interactions and how these vary with material have been investigated. Adsorption capacity and rate experiments have been carried out and how these vary with temperature studied. Synchrotron studies have been carried out on these materials.

A variety of zeolites have also been studied with the aim of achieving fast, stable, high temperature ammonia adsorption to overcome the deficiencies of MgCl2 in these areas. Synchrotron x-ray diffraction has been used to find the location of ammonia adsorption sites and to understand more about the nature of the bonding interactions. A variety of metals have been loaded on the zeolites and the effect these metals have on the ammonia adsorption studied.
Exploitation Route Research in the above mentioned areas is continuing.
Sectors Agriculture, Food and Drink,Chemicals,Energy,Environment,Transport