Controlled lignosulfonate depolymerization via solvothermal fragmentation coupled with catalytic hydrogenolysis/hydrogenation in a continuous flow reactor

Sodium lignosulfonate (LS) was valorized to low molecular weight (M-w) fractions by combining solvothermal (SF) and catalytic hydrogenolysis/hydrogenation fragmentation (SHF) in a continuous flow system. This was achieved in either alcohol/H2O (EtOH/H2O or MeOH/H2O) or H2O as a solvent and Ni on nitrogen-doped carbon as a catalyst. The tunability according to the temperature of both SF and catalytic SHF of LS has been separately investigated at 150 degrees C, 200 degrees C, and 250 degrees C. In SF, the minimal M-w was 2994 g mol(-1) at 250 degrees C with a dispersity (D) of 5.3 using MeOH/H2O. In catalytic SHF using MeOH/H2O, extremely low M-w was found (433 mg g(LS)(-1)) with a D of 1.2 combined with 34 mg g(LS)(-1). The monomer yield was improved to 42 mg g(LS)(-1) using dual catalytic beds. These results provide direct evidence that lignin is an unstable polymer at elevated temperatures and could be efficiently deconstructed under hydrothermal conditions with and without a catalyst.