Integrated absorption-mineralisation for low-energy CO2 capture and sequestration

The high energy penalty of absorbent regeneration remains the most critical challenge hindering the large-scale application of amine-based carbon dioxide (CO2) capture. To overcome this challenge, we developed an integrated CO2 absorption-mineralisation (IAM) process in which the amine sorbent can be regenerated by a chemical method rather than the traditional thermal method. We investigated the technical feasibility of IAM and the associated mechanisms by adding calcium oxide or fly ash into CO2-loaded amine solutions, including the five commonly used amines: monoethanolamine, diethanolamine, piperazine (PZ), N-methyldiethanolamine and 2-amino-2-methy-1-propanol. The performance stability of the optimised amine was verified in multicycle experiments. We also investigated the technical feasibility of IAM in practical applications using fly ash as a feedstock for absorbent regeneration. The CO2 absorption and mineralisation experiments were performed in a bubble column and a stirred reactor respectively. Acid titration was used to measure the CO2-loading of solid and liquid sample. FT-IR spectroscopy was used to analyse the species changes in the amine solutions during regeneration. The crystalline phases present in fresh and carbonated fly ash samples were determined by X-ray diffraction analysis. The results indicate that CO2 absorbed by the five amine solutions was sequestered into carbonate precipitates at a moderate temperature (40 °C) and the amine absorbents were regenerated after carbonation reactions. PZ exhibited the largest cyclic loading (0.72 mol/mol) and regeneration efficiency (91%) among the five amines. PZ also achieved stable cyclic loading, regeneration efficiency and kinetic performance over five cycles of IAM experiments. When the industrial waste, fly ash was used, PZ displayed a cyclic loading of 4.2 mol/mol, lower than that of CaO but still 1.1 times higher than that of the thermal regeneration-based process. Compared with the traditional thermal regeneration-based CO2 capture, the IAM process has great advantages in energy reduction and capital savings due to a larger cyclic CO2 capacity, a requirement for less energy for amine regeneration and no need for CO2 compression and pipeline transport. This technology has great potential for industrial applications, particularly with CaO-containing wastes, such as fly ash and other alkaline wastes.