Carbon Dioxide Capture Using Amine Functionalized Hydrothermal Carbons from Technical Lignin

Amine scrubbing is the most optimized and widely researched post combustion carbon dioxide capture technology till date. However, amine scrubbing remains costly because of high energy inputs during the regeneration stage. Although less researched, “solid sorbents” such as zeolite, active carbon, carbon coke, metal–organic frameworks and mesoporous silica are currently under development for CO2 capture as potential alternatives to amine scrubbers. In this study, sorbents were synthesized from carbonaceous materials (CMs) obtained from hydrothermally treated (350 °C) lignin, a waste material from forest biorefineries. CMs were activated with potassium hydroxide (KOH) at 800 °C to improve their textural properties and finally functionalized with polyethyleneimine (PEI) to also improve its CO2 capture properties. This study evaluated synergistic effect of these two treatments on adsorption capacity of CO2. Activation increased surface area of CMs from 2.8 to 1341 m2 g−1. CO2 capacities of 2 mmol g−1 (L350 PEI 5%) and 1.53 mmol g−1 (L350) could be reached at 30 °C, due to improved textural and chemical properties of the samples. Optimal PEI loading was determined to be 5%, after which CO2 sorption decreased with further additions of PEI. This was ascribed to blockage of the micro-pores in the activated samples at high PEI impregnation. Also, activated samples showed faster adsorption kinetics compared to PEI functionalized activated samples. The feasibility of using waste lignin with improved surface area and surface functionalities as alternative materials for CO2 adsorption was demonstrated.