Lignocellulosic Glycols: Recovery of Lignin, Glycols, and Tungsten Catalyst from Hydrogenolysis Effluent

The literature shows the possibility to produce ethylene glycol via catalytic hydrogenolysis over tungsten and nickel catalysts at good yields (∼35 wt %) from deashed lignocellulosic biomass that, thereby, still retains its lignin. This approach still requires purging the solubilized lignin from the recycle loop to avoid accumulation in the system while retaining glycols and the tungsten catalyst. We investigate here the selective removal of the lignin by liquid–liquid extraction with guaiacol, by cold-water precipitation (CWP), or by a combination of both. These approaches allow removal of more than 90% of the solubilized lignin, depending on the solvent or the water-effluent ratio. The distillation resistance of the resulting aqueous and organic streams appears to be prohibitive due to their high dilution. However, complementary experiments in semibatch mode show room to increase the glycol concentration to an affordable level. Finally, we examined the integration of liquid–liquid extraction into the hydrogenolysis step by feeding guaiacol under biphasic conditions, which achieved good glycol yield and efficient lignin removal but suffered from significant degradation of the guaiacol solvent to phenol and cyclohexanol.