Reuse of Ashes from Digestate Solid Fraction as a Catalytic Support for the Conversion of Vegetable Oils in Biofuels

This experimental preliminary study investigates the reuse of ashes from Solid Fraction of Digestate (SFD) to synthesize catalysts for biofuels synthesis from vegetable oils. The digestate derived from anaerobic digestion of pomace, lees and agrifood waste. SFD pellets were incinerated at 700°C to produce ashes. Ashes were washed with HCl solution and optionally converted into zeolites (alkali fusion method followed by hydrothermal synthesis). These three synthesized supports (ashes, washed ashes, and ash-derived zeolites), were impregnated to produce Ni-Mo supported catalysts. Ni-Mo catalysts were comparatively tested by a laboratory-scale batch reactor, performing DeOxygenation (DO) of commercial rapeseed oil into green diesel (40 bar of H2 at room temperature and 320°C). The best DO performances were obtained by the Ni-Mo catalysts supported on SFD ashes washed with HCl (80% oil Conversion and 55.1% Diesel Yield). These performances were also associated with a greater specific surface area of Ni-Mo catalysts supported on SFD ashes washed with HCl than the others in this study. Ni-Mo catalyst from SFD can be of interest for developments in the circular-economy approach.