CO2 capture by adsorption on biomass-derived activated char: A review.

Carbon capture and storage has been recognized as the most promising method for CO2 control. Among the many sorbents, char derived from pyrolysis and hydrothermal carbonization (HTC) of biomass have demonstrated excellent CO2 adsorption capability. This paper reviews the different parameters to produce a higher yield of biochar and hydrochar suitable for carbon sequestration. The mechanism of physisorption and chemisorption is briefly presented. The different kinetic models, diffusion models to describe adsorption mechanism, and adsorption isotherms for CO2 uptake from biomass-derived hydrochar are reviewed. The different factors that affect the CO2 uptake are the type of activation, surface area and porosity, the ratio of activation agent to char, activation temperature, adsorption pressure and temperature, additives, and other physicochemical properties. The optimal conditions for CO2 uptake with chemical activation of KOH is a KOH/char ratio of 2-3, activation temperature of 700 °C, and an adsorption temperature below 50 °C.