Lignin: An Experimental Study

Lignin is a naturally abundant and renewable precursor with a potential to be used in the production of both chemicals and materials. As many lignin conversion processes suffer from significant productions of solid wastes in the form of hydrochars, this study focused on transforming hydrochars into magnetic activated carbons (MAC). The hydrochars were produced via hydrothermal treatment of lignins together with formic acid. The activation of the hydrochars was performed chemically with KOH. A focus was held on optimizing the MACs as adsorbents for CO2. MACs are potentially relevant to carbon capture and storage (CCS) and gas purification processes. In general, the MACs had high specific surface areas (up to 2875 m2/g), high specific pore volumes,

Most of the remaining lignin is used for deriving low-value products or in narrow market segments.7 However, there is a high potential to use lignin as a precursor for renewable chemicals and materials, and, consequently, lignin is researched for a future use in biorefineries3,4 and materials production. The structure and chemistry of lignin, and the different approaches to lignin depolymerization/repolymerization, depend both on the particular wood and the processes used for lignin separation.8 Attempts to produce liquid fuels and chemicals from lignin often suffer from large side-product streams of solid waste.5,6,9 By transforming these solid wastes into functional materials would add value to the lignin and reduces its environmental footprint. These wastes, e.g., have the potential to be used as a precursor for renewable functional materials such as activated carbons

However, the small particle size also makes the separation of PACs from liquids much more difficult than the separation of GACs.27

Magnetic activated carbons (MACs) may allow for new usage of ACs in various processes. MACs and other porous materials with magnetic properties have previously been produced.28–31 Chemical co-precipitation29,32–35 with paramagnetic or ferromagnetic compounds is a promising approach. Ball milling36 and impregnation37,38 can also be used to introduce such compounds with magnetic properties into the ACs. Suspended powdered MACs may be separated from liquids with a use of external magnetic fields.29,30

In this study, solid by-products from the conversion of lignin into biooil6,9 were used to produce MACs with magnetic properties from iron-containing nanoparticles. The MACs could be optimized to either contain very high large ultramicropore volumes or have very large surface