Resumen de Lignin depolymerization by supercritical water ultrafast reactions
The necessity of developing sustainable technologies, together with the increasing concern over environmental protection and questions about future availability of petrochemical feedstock have spurred research and development toward new materials from renewable resources environmentally friendly and sustainable. Within this context, lignin, a complex natural polymer obtained as by-product in large quantities in paper industries and modern biorefineries, arises as a promising candidate for these purposes.
The aim of this thesis is to valorize lignin obtaining high value products through an ultrafast and environmentally friendly technology employing supercritical water as solvent and reaction times of milliseconds.
The research started with studying the effect of the parameters that control the depolymerization of lignin: temperature and reaction time. For this study, Kraft lignin as an example of pulp and paper industry by-product was chosen as raw material. At 386ºC and around 200 ms, the highest yield in aromatic monomers was achieved.
The second step of this research consisted in increasing the depolymerization yield by adding NaOH to the supercritical water process. The reaction reached an optimum point at 300 ms with a yield of 60% in aromatic products such as guaiacol, creosol, vanillin and acetovanillone.
In the third part of this thesis, the depolymerization process in alkaline supercritical water was extrapolated to real pulp and biorefinery residues. It was proven that the proposed technology is effective to treat directly industrial black liquors, obtaining a yield higher than 50 wt% in aromatic low molecular weight components.
Finally, as this thesis was focused on the development of a continuous process for its future industrialization, in the fourth chapter, a continuous downstream process for recovering the low molecular weight products from the reaction mixture has been simulated using Aspen HYSYS V10. An economically and energetically feasible strategy was developed in this work.
