Over the last 5-6 years, teams from Newcastle University and Durham University have worked to produce the first thermodynamically reversible chemical reactor- AKA the memory reactor. It overcomes the equilibrium constraints that usually limit reversible chemical reactions, in this case, being used to produce pure hydrogen. The team visited ISIS to examine the structure of the materials at the heart of the reactor using neutrons, testing an experimental set up designed by final year PhD student Dan Telford.
Industrial production of hydrogen is key to the long-term goal of sustainable, low emission fuels and power production. There are various methods of producing hydrogen on an industrial scale, from electrolysis to anaerobic digestion of biomass and steam-methane reforming of natural gas. These techniques have varying environmental impacts and there is a need to develop methods of hydrogen production that are both efficient and sustainable.
The reversible water-gas shift reaction is used to produce hydrogen in industry by the conversion of carbon monoxide and water vapour to carbon dioxide and hydrogen. While hydrogen is produced by the reaction, it is equilibrium limited and only 50% efficient, typically producing mixtures of the four gases in a 1:1:1:1 ratio. The perfect reactor would overcome the normal rules of thermodynamics by increasing the effective equilibrium constant to a number of choice, therefore producing more hydrogen in the product mix.
The team has developed a chemical looping memory reactor made of a non-stochiometric perovskite, which acts as an oxygen carrier material. The material enables an oxidising and a reducing reaction, with one reactant and one product entering/exiting at either end of the reactor. At the oxidising end, H2O enters, reacts with the oxygen-carrier material (which becomes oxidised) and exits as H2 at the reducing end. Once water reduction to hydrogen is complete, CO is fed into the reactor to reduce the oxygen carrier material and exits as CO2 at the oxidising end.
At Polaris, the team used neutrons to examine the structure of the perovskite bed material, primarily to look at its oxygen composition. If they know how much oxygen is in the material at different stages along the reactor bed, they can better understand how to optimise the reactor. They also wanted to examine the potential of alternative oxygen carrier materials for use in memory reactors.
The reactor is a pipe structure that allows reactant gases to be fed in at either end and flow along it. As the fixed neutron beam can’t probe the entire length of the pipe, joint ISIS and Newcastle University PhD student Daniel Telford designed a solution that allows the entire reactor bed to be examined using neutrons at different stages. Rather than one long pipe, the reactor is constructed of multiple smaller pipes, which can be connected or disconnected in different orders, with one section in the neutron beam while the others remain outside. It sounds relatively simple, but, as Dan tells us, has been “a really long time coming”. He credits the collaboration between various ISIS teams: design engineers, the sample environment design team, and the pressure and furnace team who helped complete the set up. After various setbacks and delays on their beam time, Dan explains that “It’s very rewarding to see something we spent so long designing being assembled here. It is thankfully coming together quite straightforwardly”.
Dan Telford with the experimental set up he designed.
With the increasing interest in hydrogen as an energy source, particularly in the transition to Net Zero, development of methods such as this which produce sustainable ‘blue’ hydrogen will play a key role. For now, the team is excited to be working on the project at ISIS and putting Dan’s set-up into play.
