Hydrothermal upgrading of water-insoluble algal biocrude over γ-Al2O3 supported multi-metallic catalysts

The hydrothermal liquefaction (HTL) of microalgae can produce a water-insoluble biocrude as well as other by-products, and is a promising technology for crude bio-oil (biocrude) production. This work explored for the first time the catalytic hydrothermal upgrading (at 400 degrees C with H-2 for 1 h or 4 h) of the water-insoluble biocrude over gamma-Al2O3 supported NiMoW, NiCoMo, CoMoW and CoNiMoW catalysts synthesized in our lab. The results show that CoMoW/gamma-Al2O3 both for 1 h and 4 h supported high upgraded oil yields (over 70 wt.%). The upgraded oil by CoNiMoW/gamma-Al2O3 for 4 h had the highest C (78.6 wt.%) and H (9.4 wt.%) contents and heating value (38.7 MJ/kg). CoMoW/gamma-Al2O3 (3 wt.% CoO, 10 wt.% MoO3 and 14 wt.% WO3) for 1 h was a good option and could lead to equivalent levels of C, H contents and HHV but the lowest O content (6.31 wt.%) of upgraded oil, in comparison with all gamma-Al2O3 supported multi-metallic catalysts for 4 h. It significantly increased the alkane content and decreased the O-containing compound content by the catalytic hydrodeoxygenation of organic acids and by the dehydration of amides. Both CoMoW/gamma-Al2O3 and CoNiMoW/gamma Al2O3 for 4 h performed well in converting high-boiling-point macromolecules to comparatively lower-molecular-weight compounds.