Willow biomass was subjected to different pretreatment conditions with triethylammonium hydrogen sulfate as solvent, and the produced lignin solutions were treated by oxidation either homogeneously using H2O2 as oxidant or by heterogeneous catalysis using TiO2. Lignin, residual lignin, oil, and the recovered ionic liquid (IL) were characterized in order to determine the effects of each treatment. Lignin was successfully extracted and depolymerized by oxidation and characterized by ATR-IR, HPSEC, and py-GCMS. The obtained oil was characterized by GCMS; it was composed mainly of acids derived from the sugar and lignin fractions, the TiO2 catalyzed oils being richer in phenolic derived compounds than sugar fractions. The final ionic liquid was characterized in order to determine its suitability to be reutilized.