Carbon from Lignin and Sodium Lignosulfonate ，need to make clear the Applications for lignin and lignosulfonates are limited today due to the undefined structure and varying properties of the substance. However, lignin, as the second most abundant bio-resource besides cellulose and the bio-resource with one of the highest natural carbon contents, has the potential to act as a precursor for carbon materials.
We have applied a Kraft lignin and a sodium lignosulfonate with the cross-linker toluene-2,4-diisocyanate. The reaction mixture was molded to form small cylindrical shaped paddings.
Cross-linked lignin-polyurethane and lignosulfonate-polyurethane networks were analyzed via elemental analysis and thermogravimetric analysis and finally carbonized. The carbon material was analyzed for its BET surface area and its surface structure via scanning electron microscopy. Surface areas between 70 and 80 m²·g−1 could be reached. Moreover, the material was tested for its adsorption potential of crude oil from water and could take up to twice its own weight.
For better understanding of the core chemistry of the cross-linking reaction, we have studied the reaction with model substances to define the reactive groups and the influence of sulfonate groups in the cross-linking reaction of lignin and lignosulfonates with toluene-2,4-diisocyanate.
Carbon materials were produced via isocyanate cross-linking of lignin and lignosulfonate and a subsequent carbonization reaction. For the cross-linking reaction, it was shown with model substances that without a catalyst, lignin predominately cross-links via its aliphatic OH groups, while sulfonate groups of lignosulfonates act as a catalyst.
The model reaction studies could confirm former studies on the reactivity of OH groups and different isocyanates . It could also be shown that the H-lignin model would be more reactive than the G- and S-lignin models.
The cross-linking degree constitutes the final surface area and structure, while intermediate cross-linking results in the highest surface areas and roughest structures.
Lignosulfonates form nano-sized salt crystals on its surface after carbonization, which absorb water and causes sinking. In contrast, Kraft lignin polyurethanes float in water and have a good ability to adsorb crude oil.