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 WOx 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 WOx 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 WOx. HPLC-visible WOx, 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 WOx and Ni, showing that Ni promotes WOx 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.