Effect of palladium-doped magnetite nanoparticles in the hydrothermal liquefaction of biomass to bio-oil

In this work, the mixed spent grain biomass, a mixture of maize and barley, was used as a feedstock for bio-oil production through hydrothermal liquefaction (HTL) in the presence of palladium-doped magnetite nanoparticle catalysts. The palladium-doped magnetite nanoparticles were synthesized by the co-precipitation process and characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray diffraction techniques. A maximum bio-oil yield of 61.3% was obtained using palladium-doped magnetite particles compared to 46.31% obtained in the absence of the catalyst. The elemental analysis of bio-oil showed an increase in elemental carbon from 55.07 wt% for uncatalyzed liquefaction to 76.47 wt% for Pd-doped magnetite nanoparticle-catalysed liquefaction. Similarly, the elemental hydrogen increased from 5.32 wt% for uncatalyzed to 7.63 wt% for Pd-doped magnetic nanoparticle catalysed liquefaction. The elemental analysis further indicated improved bio-oil quality, with a reduction in oxygen content from 36.52 wt% to 14.33 wt% and nitrogen from 2.51 wt% to 1.32 wt%. The GC-MS showed an increase of hydrocarbons from 60.45% for uncatalyzed liquefaction to 88.03% for Pd-doped magnetite nanoparticle catalysed liquefaction. Furthermore, the bio-oil produced in the presence of Pd-doped magnetite nanoparticles showed that physical properties were within acceptable limits compared to the crude bio-oil standard. The application of palladium-doped magnetite nanoparticles in the HTL of mixed spent grain biomass increases the yield of bio-oil and improves its quality, thus increasing its energy performance. This provides a potential pathway to produce a high-quality bio-oil suitable for blending or direct use in existing fuel systems.