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

Carbon capture, utilization, and storage (CCUS), offers a promising avenue for mitigating CO₂ emissions, in which the big challenge is the high CO₂ capture cost. A novel CCUS technology called once-through CO₂ chemical absorption using biogas slurry, could potentially reduce the CO₂ capture cost through decreasing the energy consumption greatly during CO₂ capture. This technology, however, is constrained by the CO₂ absorption capacity of biogas slurry. To enhance the CO₂ capture capacity of this innovative technology, we proposed a method to enhance CO₂ absorption by integrating biochar into biogas slurry. Results indicated that the CO₂ 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 CO₂ 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 CO₂ 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 CO₂ absorption, followed by the EC and BET surface areas of biochar. Increasing the carbonization temperature of biochar could also enhance the CO₂ absorption capacity by biogas slurry. In CO₂-rich biochar-based biogas slurry, CO₂ primarily existed as HCO₃⁻ and carbamate. However, for the influence of the biochar's pore structure, CO₂ in the CO₂-rich biochar-based biogas slurry was more stable than that in CO₂-rich biogas slurry.