Post-combustion CO₂ capture by formic acid-modified CaO-based sorbents

The performance of CaO-based sorbents modified with formic acid in both its liquid and vapor phase has been investigated for high-temperature post-combustion CO₂ capture in calcium-looping cycles. The treatment of limestone with aqueous solutions containing 10 or 30vol% formic acid was found to promote crystal growth. By contrast, higher acid concentrations produced smaller crystals. However, all sorbents modified by acid solutions had almost identical reductions of 44% and 46% in surface area and pore volume (determined by N₂ adsorption), respectively, relative to the parent material. Despite the low porosity, limestone (fine powder) treated with 10% acid solution displayed the highest CO₂ capture capacity in the first cycle with a capture of 0.6g CO₂/g sorbent compared to 0.49g/g for untreated powder material. By 20 cycles, the modified sorbent still captured 67.4% more CO₂ than the natural sorbent captured under similar conditions. Relatively low concentration formic acid solution improved the CO₂ capture capacity of CaO-based sorbents better than treatment with acid vapor due to the limited acidification achieved by vapor phase treatment.