Cost-effective carbon-based amine adsorbents for carbon capture: Equilibrium, kinetics and selectivity

The rise in atmospheric CO2 levels is generating alarm with an urgency to develop carbon removal technology. As a promising post-combustion capture method, adsorption process using materials e.g. biochar-based activated carbon (AC) has received increasing attention. Thus, two types of coconut shell (CS) derived ACs that secondary activated by KOH and NaOH are investigated in terms of textural properties, CO2 adsorption behaviors and desorption temperatures. It is demonstrated that KOH shows a better activation effect on capture performance than NaOH, and chemical CS-KOH (CHCS-KOH) could reach the highest BET surface area of 1701.39 m2 g−1 and CO2 uptake of 2.11 mmol g−1 at 0 ℃, 0.15 bar and 4.17 mmol g−1 at 20 ℃, 1 bar, respectively. Dynamic adsorption data are well fitted by a pseudo second-order kinetic model, and the samples could be completely desorbed at 40 ℃. To further explore CO2 uptake and H2O/CO2 adsorption selectivity, amine (PEI/TEPA) modifications are proposed. The results suggest an enhanced adsorption performance of PEI&CHCS-KOH composites under humid flue gas with volume ratio of water in the range of 5–15 vol%, which exhibits the highest promoting effect to 1.81 mmol g−1 at 20 ℃, 0.15 bar with 100% RH 15 vol% H2O for 1 wt% composite. Prominent cost benefit has also been revealed in comparison with PEI&silica gel under the condition of dry and humid conditions, along with superior cyclic stability, which indicates potential application in carbon capture. •An amine-modified composite adsorbent based on AC matrix is developed.•The highest CO2 adsorption uptake of CHCS-KOH is 2.11 mmol g−1.•CO2 adsorption selectivity of the composite is increased by up to 36.09%.•Amine-biochar is cost-effective and promising for post-combustion capture