Porous apatites as novel high temperature sorbents for carbon dioxide

•Synthetic hydroxyapatite as potential new material for CO2 capture at temperature higher than that of CaO based sorbents.•No appreciable decay of the absorbing activity upon several cycles.•The temperature of pre-treatment of porous granules impacts on sorption capacity.•CO2 carrying capacity very close to theoretical limit of 2.6% by mass.•Lower heat for regeneration in comparison with CaCO3 sorbents.

Synthetic hydroxy-apatite was tested as a potential new material for CO2 capture at high temperature, over the operation limit of CaO-based sorbents. Some porous granules of hydroxy-apatite were prepared ad hoc. They were shown to absorb CO2 upon dehydroxylation in the very high temperature range of 900–1200 °C, resulting in A-type carbonated apatite. No appreciable decay of the absorbing capacity was observed with a higher number of absorbing–desorbing cycles, differently from what happens in a conventional chemical sorbent, e.g. calcined natural calcium carbonate. The CO2 carrying capacity was maximum at 1000–1100 °C and very close to the theoretical limit of 2.6% by mass. The macro-granule porosity network appeared to be effective in making the sites available for CO2 capture. At first glance, the process appeared to be chemically controlled. The pre-treatment temperature of the porous granules also had an impact on the sorption capacity. As a first proof of concept, the results obtained by thermogravimetric analysis, and supported by FTIR and XRD analysis, were confirmed by tests carried out in a laboratory-scale reactor, operated as a fixed bed.

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