(24a) Activated Carbon from High-Purity Lignin with Controlled Molecular Weight

Over the past decade, the production of biofuels from lignocellulosic biomass has steadily increased to replace fuels from petroleum sources. To make these biofuels cost competitive, it is essential to create products from the “ligno-” components (up to 30% by mass) of the biomass, which requires separating and purifying the byproduct. Activated carbon (AC) is a viable product from the biorefineries since it has a market capacity large enough to consume the necessary amount of lignin produced, and it does not have a stringent requirement for its precursor. However, the relationship between lignin properties and its derived AC properties are not fully understood, especially the effect of lignin molecular weight (MW) and ash content on the key AC properties.

In this work, we use various fractions of ultraclean lignin (from a patented ALPHA process) with different MWs to study how lignin MW and ash content affects the key properties of AC using controlled activation conditions. The pore structure of the ACs were characterized by N₂ adsorption at 77K using BET analysis and the aqueous adsorption capacities were characterized by using iodine number and methylene blue value. The experiment results show the surface area and the adsorption capacities of the ACs increased when using lignin precursors with increased MW, and the purification of the lignin can significant enhance the AC properties. The surface area of the AC from the highest MW lignin can reach to ~1900 m²/g and still has potential to be improved. The high purity and the flexible MW could facilitate the co-produced lignin to produce AC with desired pore structures which can be applied in broad applications. Furthermore, the proposed method in this work for synthesizing AC is not complicated and therefore, is suitable for bulk production.