An innovative two-step catalytic process for the conversion of kraft lignin to biofuels

Abstract

Valorisation of lignins to biofuels and biobased chemicals is of high interest to stimulate the necessary transition from a fossil-based to a biobased economy. This study presents the experimental validation of the ABC-Salt process for the conversion of a Kraft lignin (Lignoboost) into hydrocarbon-rich liquids in a two-step approach: (i) hydrodepolymerization in cresol with a Zn-based salt catalyst (ZnCl 2 , KCl, and NaCl (44.3: 41.9: 13.8 mol%)), and (ii) a two-step catalytic hydrotreatment with a commercial NiMo-based catalyst. The hydrodepolymerization was conducted in a continuous stirred-tank reactor at 340 °C and 125 bar, yielding 95 wt% lignin oil with minimal char formation (<2 wt%) over nearly 100 h on stream. Among Zn salts tested (ZnCl 2 , ZnS, ZnO), ZnCl 2 showed the highest catalytic efficiency, reducing molecular weight from 1600 Da to about 600 Da. After desalting, the hydrodepolymerization oil was hydrotreated in a packed-bed reactor (275–425 °C, 200 bar) to hydrocarbons with an oxygen content <0.5 wt%, also with minimal carbon loss. At optimized conditions, a high overall carbon yield of lignin to hydrocarbons of approximately 87%C, corresponding to 55 wt% based on the weight of the lignin input, was obtained. The final hydrocarbon product was fractionated by distillation, and the fractions were analyzed using CHN, GC–MS, GCxGC-ToF, NMR, GPC, and dedicated ASTM methods to assess fuel properties. Dedicated TEA and LCA were performed on the integration of the ABC-salt process with a pulp and paper mill, and a net production cost of 1.66 € 2020 /L Fuel was calculated, with lignin as the highest cost contributor. The global warming potential savings were determined to range from 72% to 89% compared to fossil fuels.