A facile method for char elimination during base-catalyzed depolymerization and hydrogenolysis of lignin

- Organosolv lignin was extracted and structurally characterized for depolymerization.
- Lignin depolymerization was achieved by a synergic catalyst of NaOH and Ru/C.
- The structural characteristics of the degraded lignins were deeply investigated.
- The thermal degradation kinetics of the degraded lignins were also evaluated.
- This proposed process extends the depolymerization of lignin in aqueous NaOH system.

Lignin is a renewable source of phenolic compounds for the possible replacement of fossil fuels. However, severe char formation induced by the repolymerization is a crucial challenge for current lignin utilization. Herein, an efficient base-catalyzed depolymerization and in situ hydrogenolysis process of organosolv lignin depolymerization and char elimination was implemented using the synergic catalyst of NaOH and different hydrogenation catalysts. NMR (2D-HSQC and 31P NMR), TG and GPC techniques were elaborately used to characterize the partly degraded lignin (DL) after catalytic hydrocracking. Meanwhile, the monomeric compounds were characterized and quantified by GC-MS technique. Under an optimal condition with the synergic catalyst of 0.025 mol NaOH coordinated with 5% Ru/C at 260 °C, a low yield of char (6.4%) and high yield of water-soluble fraction (95.4%), including 24.3% degraded lignin, 44.6% water-soluble product and 26.5% oil-soluble product, could be obtained. Additionally, the content of acetic acid was significantly high in the monomeric fraction among all degraded compounds of lignin. Furthermore, the DL exhibits excellent thermal stability, which can be suitable for developing lignin-based flame resistant material. In short, this proposed process extends the depolymerization methodology of lignin in aqueous NaOH system.

The proposed lignin depolymerization process will be beneficial for the future utilization of this sustained and energy-potential aromatic material173