Solvent free depolymerization of Kraft lignin to alkyl-phenolics using supported NiMo and CoMo catalysts

The catalytic hydrotreatment of Kraft lignin using sulfided NiMo and CoMo catalysts on different acidic
and basic supports (Al2O3, ZSM-5, activated carbon (AC) and MgO-La2O3) was studied in the absence of a
solvent. Experiments were carried out in a batch set-up at a reaction temperature of 350 °C, 4 h and 100
bar initial H2 pressure. The catalysts before and after reaction were characterized by X-ray diffraction,
temperature programmed desorption of ammonia/CO2, BET surface area and scanning electron
microscopy. The liquid products were fractionated and analyzed extensively by different techniques such
as GPC, GC-MS-FID, GC-TCD, FT-IR, 13C-NMR and elemental analyses. Two dimensional gas chromatography
(GC × GC-FID) was applied to identify distinct groups of compounds (aromatics, alkylphenolics,
alkanes) after reaction, and product quantification was performed based on this method. Catalyst activity
is a function of the support and increased in the order Al2O3 < ZSM-5 < AC = MgO-La2O3. In addition, the
support also largely influenced the extent of depolymerization and monomer yield. The highest lignin oil
yields were obtained using the sulfided NiMo supported on activated carbon and MgO-La2O3. The
highest total monomer yield 26.4 wt% on lignin intake, which included 15.7 wt% alkyl-phenolics was
obtained using the sulfided NiMo/MgO-La2O3 catalyst.