Catalytic hydrothermal liquefaction of Spirulina platensis for biocrude production using Red mud

In this work, catalytic hydrothermal liquefaction of Spirulina platensis using red mud as a heterogeneous catalyst was studied. Red mud, a waste by-product of the Bayer process and its activated form, were used to study the influence of catalyst on biocrude yield and quality. The experimental study was carried out in a batch reactor with a feedstock slurry loading from 10 to 30 wt.%. A maximum yield of bio-crude about 27.5 wt.%, 35 wt.% and 40.7 wt.% for non-catalytic hydrothermal liquefaction and catalytic hydrothermal liquefaction using red mud and activated red mud, respectively at a temperature of 300 °C, 20% slurry concentration and 30 min was obtained. FT-IR and TGA were used to characterize bio-crude from catalytic hydrothermal liquefaction of spirulina. Further, the biocrude was analysed to identify its component using GC-MS. It was found that nitrogen-containing compounds were not much pronounced in biocrude from catalytic hydrothermal liquefaction. To maximise the biocrude yield, the various process conditions such as temperature (250–350 °C), reaction time (20–60 min), slurry concentration (10–30%) and catalyst-to-biomass ratio (1:2–1: 4) were investigated. When the excess of the catalyst was added, a slight increase in biocrude yield was found. For the temperature above 300 °C, the biocrude yield did not improve much. The algal slurry concentration of above 20% led to a decrease in biocrude yield.