Exploring the reaction conditions for Ru/C catalyzed selective hydrogenolysis of xylitol alkaline aqueous solutions to glycols in a trickle-bed reactor

• Ru/C is an efficient catalyst in continuous xylitol hydrogenolysis in the presence of NaOH.
• A maximum conversion and selectivity to EG was obtained at 200 °C under 60 bar H2.
• These effects confirm the reaction pathways proposed for polyol hydrogenolysis.

The hydrogenolysis of an alkaline aqueous solution of xylitol to mainly ethylene- and propylene-glycols was studied over a Ru/C catalyst in a high pressure fixed-bed reactor run in the trickle-bed mode with co-current downflow of liquid feed and hydrogen. The effects of reaction parameters including H2 pressure (40–80 bar), temperature (190–200 °C) and pH values (NaOH/xylitol molar ratio in the range 0.1–0.2, pH 9–12) and residence time have been explored to increase the selectivity of this reaction to the desired ethyleneglycol product. The activity and final products distribution were much influenced by the hydrogen pressure. An optimum to afford a high conversion and a high selectivity to ethyleneglycol at different space times was found at 60 bar. The effects observed are in agreement with the reaction pathways previously proposed and the relative reaction rates of the dehydrogenation/hydrogenation and base-catalyzed reactions of the intermediates are affected by the hydrogen pressure and the concentration of the alkaline promoter.

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