CO2 absorption performance of biogas slurry enhanced by biochar as a potential solvent in once-through CO2 chemical absorption process

• Wood biochar showed the least CO 2 absorption enhanced in biogas slurry, followed by C3 and highest in C4 plant biochar. • Elevated pH in biogas slurry and biochar's total pore volume are key to enhance CO 2 absorption. • In biochar-based biogas slurry, CO 2 mainly exists as HCO 3 − and carbamate, showing more stability than in biogas slurry. Carbon capture, utilization, and storage (CCUS), offers a promising avenue for mitigating CO 2 emissions, in which the big challenge is the high CO 2 capture cost. A novel CCUS technology called once-through CO 2 chemical absorption using biogas slurry, could potentially reduce the CO 2 capture cost through decreasing the energy consumption greatly during CO 2 capture. This technology, however, is constrained by the CO 2 absorption capacity of biogas slurry. To enhance the CO 2 capture capacity of this innovative technology, we proposed a method to enhance CO 2 absorption by integrating biochar into biogas slurry. Results indicated that the CO 2 absorption capacity of biogas slurry improved by biochar varied with the type of biochar adopted. Among all the investigated biochar, the wood biochar like sea buckthorn and sand willow exhibited the lowest CO 2 capture enhancement, with 0.82±0.19 mmol/g and 0.81±0.30 mmol/g, respectively. Biochar from C4 plants like corn stalks and cobs demonstrated the highest enhancement, with 2.11±0.24 mmol/g and 2.47±0.86 mmol/g, respectively. The enhancement driven by C3 plant biochar like millet stalks and shells was intermediate, with 1.62±0.47 mmol/g and 1.62±0.46 mmol/g, respectively. The primary factor for promoting CO 2 absorption in the biochar-based biogas slurry was the increase in pH of biogas slurry. The total pore volume of biochar was the principal material property that enhanced CO 2 absorption, followed by the EC and BET surface areas of biochar. Increasing the carbonization temperature of biochar could also enhance the CO 2 absorption capacity by biogas slurry. In CO 2 -rich biochar-based biogas slurry, CO 2 primarily existed as HCO 3 − and carbamate. However, for the influence of the biochar's pore structure, CO 2 in the CO 2 -rich biochar-based biogas slurry was more stable than that in CO 2 -rich biogas slurry.