Slurry hydroprocessing of solid technical lignins and lignin-derived bio-oils with transition metal sulfide catalysts: From batch to continuous processing

The current study demonstrates an efficient strategy for slurry hydroprocessing of solid technical lignins and lignin-derived bio-oils. Semibatch hydroprocessing experiments were performed in a lab-scale 1 L reactor using three technical lignins, and bio-oils (Lignol®)derived by derivatisation from two of these lignins. Four different supported molybdenum or tungsten catalysts, as well as an unsupported molybdenum-based catalyst formed in-situ from a lipophilic molybdenum salt, were tested for the hydroprocessing of lignin bio-oils. All tested supported catalysts exhibited good hydrotreating activity with an overall deoxygenation degree over 80%. The molybdenum-based catalysts yielded fractions with slightly lower oxygen content but higher acidity and a broader boiling-point distribution than the tungsten-based alternatives. The unsupported catalyst showed superior activity with a hydrodeoxygenation degree of 90%. Conversion into bio-oils significantly increased lignin reactivity. Potential chemical differences due to lignin origin appeared secondary to factors, such as sugars or ash content. The process was scaled up to a continuous slurry hydroprocessing process with two different molybdenum-based catalysts, and over 20 kg of lignin-containing feedstock (30 wt% lignin) was processed successfully with each catalyst, achieving up to 87% oxygen removal. Characterisation of the fresh and spent catalyst revealed no indications of significant deactivation when lignin-derived bio-oils were used.