Ethylene Glycol from Lignocellulosic Biomass via Hydrogenolysis: Deactivation and Recycling of W and Ni Catalysts

This work investigates the stability and recyclability of the W and Ni catalysts used during the hydrogenolysis of deashed lignocellulosic biomass for the production of ethylene glycol. Hydrogenolysis experiments were conducted in a 45 mL autoclave reactor using pinewood as feedstock at 245 °C and 60 bar of H₂ for 1–2 h. Sodium polytungstate and Raney nickel were employed as catalysts, with active WO_x species derived from sodium polytungstate. Catalyst stability was evaluated through four consecutive hydrogenolysis cycles performed in the same reactor. Three key findings have been identified: (i) both catalysts retain activity across multiple cycles when kept in the reactor, (ii) XRF analysis has shown that WO_x is predominantly dissolved in the liquid phase and must be recovered for reuse, and (iii) guaiacol-based extraction selectively removes UV-active species that are likely lignin-derived while preserving soluble WO_x. HPLC-visible WO_x, although a minor species, may serve as a proxy for catalytic activity, appearing in equilibrium with other soluble and potentially active forms. The interaction between WO_x and Ni, showing that Ni promotes WO_x loss through unknown mechanisms, possibly involving surface deposition or complexation with sugars, was further examined. Across the four-cycle study, an ethylene glycol yield of approximately 19 wt % was obtained, demonstrating consistent catalytic performance. These findings provide an improved understanding of catalyst behavior and offer a practical route for catalyst recovery and management in EG production.