Development of novel waste tea-derived activated carbon promoted with SiO2 nanoparticles as highly robust and easily fluidizable sorbent for low-temperature CO2 capture

Waste-derived biomass-based sorbents being employed in many applications, e.g., post-combustion CO2 capture process, are in rising interest. This work investigates the CO2 capture technique by activated carbon (AC) derived from waste tea (WT) biomass. The synthesis protocol consists of carbonization followed by activation with KOH and NaOH, known as chemical activators, utilizing the wet impregnation method. With the aim of developing the AC sorbent fluidizable in fluidized-bed systems, an essential factor in the industrialization of the CO2 capture process, these sorbents are mixed with the easily fluidizable SiO2 nanoparticles (NPs). Prepared samples are characterized via SEM, EDS, BET, FTIR, and TG analysis. Based on the TG analysis assessed in three consecutive adsorption/desorption cycles, 457 %, 141 %, and 69 % higher average CO2 capture capacity is recorded for KOHpromoted AC (2.316 mmol/g) compared to raw waste tea (0.416 mmol/g), NaOH-promoted AC (0.961 mmol/g) and commercial AC (1.370 mmol/g), respectively. Fluidization experiments show that the WT-derived AC mixed with 2.5 wt% SiO2 NPs presents a 45 % higher average bed expansion ratio linked with a homogeneous and bubbleless fluidization regime than its silica-free counterpart, which presents the bubble- and channel-containing bed with a non-uniform regime. This modified sorbent shows a 9% more CO2 capture capacity (2.53 mmol/g) than the WT-derived AC and superior multicyclic stability during 25 multiple adsorption/desorption cycles.