Solid Adsorption Challenges Chemical Absorption for Post-combustion Carbon Capture – Capture Technical Session at Cambridge Biannual

Written by Xiaobo Luo from the University of Hull whose attendance at the UKCCSRC Biannual Meeting in Cambridge in April 2014 was supported by the UKCCSRC ECR Meeting Fund. This report covers the presentations given by Dr Hao Liu, Professor Colin Snape and Professor Joe Wood as part of the Capture Technical Session on Solid Adsorption at the UKCCSRC Biannual in Cambridge, 2-3 April 2014. The other two presentations in the session were by Dr Tina  Düren and Professor Fredrik Glasser 

IPCC’s new report, Climate Change 2013: The Physical Science Basis, lists the evidences of climate change from observations of the atmosphere and surface growing significantly during recent years. But CCS commercial deployments are still struggling about the readiness of candidate technologies. The state-of-the-art amine scrubbing technology for carbon capture from fossil fuel fired power plants incurs substantial energy penalty which can reach up to 37% in the case of coal-fired power plants. Consequently, alternative cost-effective capture technologies have to be developed. At the UKCCSRC biannual meeting in Cambridge 2-3 April 2014, several presentations were delivered to update the research progresses on solid adsorption.

The innovation centre of CCS in University of Nottingham did lots of studies on solid adsorption. Dr Hao Liu made a presentation about solid adsorbents looping technology. Solid adsorbents looping is widely recognized as having the potential to be a viable next generation capture technology compared to the aqueous amine scrubbing process, offering potentially significantly improved capture efficiency at reduced energy penalty, lower capital and operational costs and smaller plant footprints. His team conducted the experiments to study the PEI-silica adsorbent in a bubbling fluidized bed (BFB). The process simulations were also carried out under the conditions of 40% PEI loading and sweeping gas with H₂O and N₂. Compared to MEA-based absorption, the efficiency (LHV) penalty reduces 2.4% when it integrated with NGCC power plants. The main contributor is lower regeneration heat requirement. Another exciting experiment they are working on is CO₂ capture from ambient air using solid adsorbents looping technology, although in an early stage.

However, the success of the solids looping technology is largely determined by the successful development of superior adsorbent materials. Professor Colin Snape  in University of Nottingham leads a team investigating performance enhanced activated spherical carbon adsorbents for CO₂ capture (EPSRC Project: EP/G063176/1: Innovative Adsorbent Materials and Processes for Integrated Carbon Capture and Multi-pollutant Control for Fossil Fuel Power Generation). The efficacy of KOH activation in improving the CO₂ capture of a range of spherical carbon materials (carbon beads) has been investigated. KOH activation significantly improves CO₂ adsorption. At 25^oC and a CO₂ partial pressure of 0.15 bar, the CO₂ uptakes for the best-performing KOH-activated carbon beads investigated were found to be around 2 times higher for phenolic resin (PR) derived carbons (1.89 mmol/g) and about 3 times higher for polyacrylonitrile (PAN)-based carbon (2.34 mmol/g) than their respective steam activated carbons. The substantially enhanced performance of the carbon materials for CO₂ capture augurs extremely for their applications in solids looping technology for the post-combustion carbon capture, due to their fast adsorption kinetics, low heat of adsorption and excellent mechanical strength. 

In the following section, Professor Joe Wood, from University of Birmingham, made a presentation on the studies of hydratalcite clays for CO₂ adsorption (EPSRC Project: EP/G061785/1: Step Change Adsorbents and Processes for CO₂ Capture). The presentation gave examples of work carried out to develop ‘step change’ adsorbents based upon amine modified layered double hydroxides (LDHs). Synthesis methods involved exfoliation and grafting of amine molecules to the LDH/hydrotalcite clays. The materials were characterized by a range of characterisation techniques. Carbon dioxide adsorption was studied using thermogravimetric analysis (TGA) and fixed bed breakthrough experiments. Modelling of temperature swing adsorption process was carried out using gProms software and fitted to experimental breakthrough curves. The work reports the optimal prearation conditions and adsorption uptakes of CO₂ and makes recommendations for future scale up and industrial adsorber design.