Carbon capture, utilisation, and storage is a key driver to facilitate decarbonization strategies and for meeting
‘Net-Zero’ objectives by 2050. To provide a safe, sustainable, cost-effective method of capturing carbon
dioxide from various industrial processes, both solid and liquid capture agents are used [2]. These capture
materials have their pros and cons relative to one another. However, it is important to assess the performance
of these materials to select suitable candidates for CO2 capture at an industrial scale. There is a need for getting
better insights into these materials, including accurate capture capacity, homogeneity, stability, activity decay,
repeatability and emissions/degradation products. Performance testing/evaluation of carbonation efficiency of
various CO2 capture materials and understanding the degradation products under real process conditions has
a significant impact on the development of next-generation capture technologies. However, there are no
standardised and traceable methods to access these capture materials under relevant capture conditions.
Therefore, there is a need to develop a metrology infrastructure using traceable Primary Reference Materials
(PRMs) to validate various capture materials that are being developed simultaneously to tackle climate change.
Under activity – A3.3.5 of the MetCCUS project, NPL’s Energy Gas Metrology Group has been working towards
developing a traceable capture efficiency testing protocol for CO2 capture materials by using CaO as a
benchmark material. NPL’s traceable PRMs were used to assess the capture efficiency of CaO at this stage,
and the measurement methods developed will be extended to assessing carbon capture capacity of different
CO2 capture materials evolving in the market against the CaO benchmark. The NPL’s materials testing platform
(MTP) consists of a micro-reactor coupled with an online monitoring system that records real-time data from
flue gas (NPL PRMs) interaction with the capture materials. The micro-rector mimics a fixed bed reactor that
can hold solid sorbents starting from a few milligrams to 100 g scale. Liquids CO2 capture solvents can also be
evaluated by swapping the solid sorbent reactor with a reactor vessel that can handle liquids.
CaO is a solid sorbent capable of CO2 uptake and is often used as a benchmark sorbent for CO2 capture
materials. The chemistry of CaO sorbents during carbonation and decarbonation reactions is well known. CaO
chemically combines with CO2 at around 600 °C to form CaCO3 stoichiometrically. The CaO sorbent is
regenerated by thermal decomposition of CaCO3 at around 900 °C to give back CaO and CO2, as shown in
schematic 1 below. According to a recent report, at high temperatures (~ 600 °C), a uniform layer of growth of
CaCO3 occurs over CaO due to a chemical reaction between CaO and CO2 and it was found to be affected by the
concentration of CO2. Therefore, a different CO2 concentration – controlled study would shed more light on
parameters such as capture efficiency/stability of CaO sorbent under different CO2 streams. On repeated
cycling, CaO undergoes agglomeration, which leads to a loss in carbonation efficiency. Various efforts have been made in the recent past to improve the stability and efficiency of CaO through chemical and structural modifications.
Carbon-supported and isomorphous substituted CaO-based hybrid sorbent, reported recently, showed an
increased carbonation efficiency and stability of the sorbent in comparison to pure CaO. This hybrid solid
sorbent had around 65 % of its initial carbonation efficiency retained after 100 carbonation–regeneration
cycles in contrast to the pristine CaO that lost 80 % of its initial carbonation efficiency after 10 carbonation –
regeneration cycles.
