Adsorption of CO2 from flue gas by novel seaweed-based KOH-activated porous biochars

Recently, environmental problems such as climate change and global warming caused by the greenhouse effect have become a worldwide topic of concern. In this article, two kinds of seaweed porous biochars were prepared by utilizing widely sourced seaweed (sargassum and enteromorpha) using single step KOH activation. The physical and chemical properties of the seaweed porous biochar adsorbents were characterized, and CO2 adsorption performance over seaweed porous biochars was tested in a fixed-bed adsorption system. The textural properties and functional groups of the raw seaweed biochars are significantly improved by KOH activation. The seaweed porous biochars (SCK-800-1 and ECK-800-1) prepared with KOH/biomass weight ratio of 1:1 at 800 °C exhibit the maximum CO2 capacity (reaching 1.05 mmol/g and 0.52 mmol/g at 25 °C, respectively). The adsorption capacity of CO2 decreases with the increase of adsorption temperature, and increases with the increase of CO2 initial concentration. The flue gas components such as O2 and NO do not affect the adsorption capacity of CO2 for SCK-800-1 and ECK-800-1, while SO2 slightly inhibits the CO2 adsorption performance. After ten cycles of adsorption-desorption, the adsorption capacities of seaweed porous biochars only decrease slightly. The pseudo-first order model better fits the experimental data, which demonstrates that the external mass transfer plays a dominant role in CO2 adsorption over two kinds of seaweed porous biochars. The present results may inspire new research interests and provide necessary theoretical guidance for the application and research of seaweed biomass-based biochars for CO2 capture, and effectively expand the utilization of marine biomasss.