Hydrothermal liquefaction of microalgae over transition metal supported TiO₂ catalyst

Hydrothermal liquefaction (HTL) of microalgae Nannochloropsis (NAS) over various transition metal M/TiO₂ (M = Fe, Co, Ni, Mo, and Mn) was investigated. Ni/TiO₂ was the most effective catalyst to improve the yield and quality of biocrude and the liquefaction conversion. Ni/TiO₂ was characterized by XRD, XRF, and XPS. The research of Effect of reaction temperature on HTL of NAS over Ni/TiO₂ suggested that 300 °C led to a maximum biocrude yield of 48.23% and the highest liquefaction conversion of 89.28%. Adding Ni/TiO₂ catalyst reduced the viscosity and provided more light-fraction in biocrude while brought a slight increase in total acid number (TAN). Gas chromatography-mass spectrometry (GC-MS) analysis demonstrated that adding Ni/TiO₂ considerably changed the composition of biocrude and the possible pathways were discussed. Reproduction test showed the Ni/TiO₂ has an excellent reproduction ability in HTL of NAS.