Biocrude production through hydro‐liquefaction of wood biomass in supercritical ethanol using iron silica and iron beta zeolite catalysts

BACKGROUND: In the production of biofuels from lignocellulosic material, biocrude plays a key role. The present work deals with the biocrude production through hydrothermal liquefaction (HTL) of birch wood in supercritical ethanol over 5 wt% Fe-H-Beta-150 (SiO₂ to Al₂O₃ ratio of 150) or 5 wt% Fe-SiO₂ catalyst.

RESULTS: The liquid and solid products were characterized with various analytical techniques such as gas chromatography mass spectrometry (GC–MS), gas chromatography with a flame ionization detector (GC-FID), size exclusion chromatography (SEC), inductively-coupled plasma mass spectrometry (ICP-MS), powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), and solid-state carbon-13 magic angle spinning nuclear magnetic resonance (¹³C-MAS-NMR), respectively. The results revealed that 5 wt% Fe-H-Beta-150, a strongly Brønsted acidic catalyst, enhanced the biocrude formation when compared with a non-acidic 5 wt% Fe-SiO₂ catalyst. Hemicellulose and lignin degradation occurred resulting in formation of mainly sugars, acids-esters and phenolic compounds in the liquid phase. The gaseous atmosphere of hydrogen also enhanced the degradation of biomass. The biocrude yield from birch was 25wt% over 5 wt% Fe-H-Beta-150. The Brønsted acidic catalyst gave higher dissolution efficiency and its clear catalytic effect was observed in comparison to non-acidic 5 wt% Fe-SiO₂. The degradation level of lignin in the presence of 5 wt% Fe-H-Beta-150 was high 68wt% aromatic products were formed, while only 38wt% was obtained with 5 wt% Fe-SiO₂.

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CONCLUSIONS: Hydrogen atmosphere enhances the fractionation of birch wood when compared to argon atmosphere. The 5wt% Fe-H-Beta-150 catalyst enhanced very strongly the degradation of hemicellulose and lignin in biomass to sugars and acid-esters as well as phenolic compounds, respectively, compared to the non-acidic 5 wt% Fe-SiO₂ catalyst.