Reactivity-guided experimental design and severity factor development for optimizing the chemical activation of hydrolysis lignin into CO2-adsorbing carbons

Hydrolysis lignins (HL) produced from cellulosic ethanol biorefineries can be transformed into high-value activated carbons (ACs) for capturing CO2, offering more lucrative options compared to using them as combustion fuels. Maximizing gravimetric yield and CO2 adsorption performance of ACs made from lignin through chemical activation requires a thorough understanding and control of lignin's reactivity under activation conditions. This study introduces a methodological framework that merges analytical thermobalance reactivity assessments with experimental design principles to simultaneously optimize AC yield and CO2 adsorption during the chemical activation of hydrolysis lignin with K2CO3 in a batch, gram-scale furnace. Using this structured strategy revealed ways to minimize the activator amount and temperature needed, while still achieving high gravimetric yields and high CO2 uptake. Furthermore, building on a solid-state kinetic model describing the chemical activation of polyphenols with K2CO3, we propose a new chemical activation severity factor (SCA) that combines temperature, K2CO3-to-lignin ratio, and reaction time into a single metric that correlates with the CO2 adsorption performance of ACs derived from hydrolysis lignin. The results demonstrate that reactivity tests and chemical activation models from analytical thermobalance experiments can guide the design of lignin-based activated carbons in a more systematic, engineering-driven manner rather than relying on trial-and-error approaches.