Biomass-derived porous carbons have recently gained much attention for carbon dioxide (CO2) adsorption. In this work, RSS were used as a precursor to prepare highly porous activated carbon (AC). RSSAC was synthesized through the conventional two-stage chemical activation as well as through a new three-stage chemical activation process. RSS were activated with K2CO3 under different ratios and carbonized at 500 °C, 600 °C, and 700 °C for different activation times. AC was carefully characterized using thermogravimetric analysis (TGA), elemental composition analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and CO2 adsorption capacity using HPVA II to obtain AC with higher adsorption capacity towards CO2 capture. The SEM images of RSSAC revealed a highly porous structure. From the elemental composition analysis, carbon (77) and oxygen (18) were the major elements found in RSSAC. The yield of the activation process decreased with a higher ratio of K2CO3. A maximum yield of 81.84 was obtained at 500 °C and 1:1 ratio. The highest CO2 adsorption capacity of 60.06 mg/g was obtained for AC3(700) prepared by three-stage activation. From these findings, it can be concluded that the three-stage activation is an effective method for producing AC with higher adsorption capacity towards CO2 and that RSSAC can serve as a suitable adsorbent for CO2 capture. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.