Catalytic pyrolysis of nutrient-stressed Scenedesmus obliquus microalgae for high-quality bio-oil production

Abstract

Pyrolysis of nutrient-stressed Scenedesmus obliquus microalgae over various supported metal M/Fe3O4-HZSM-5 catalysts (M = Zr, W, Co and Mo) was investigated at a temperature of 500 °C and catalyst to biomass ratio of 1:1. The synthesized catalysts were characterized using XRD, TGA and HRSEM/EDS. The influence of temperature (400 °C, 500 °C, 600 °C and 700 °C) and catalyst to biomass ratio (0.25:1, 0.5:1 and 1:1) on pyrolysis product yield was also investigated. The results showed that all the supported metal catalysts during pyrolysis promote aromatization and acid ketonization of bio-oils. The total amounts of acids present in pyrolytic bio-oil significantly decreased from 26.68% (non-catalytic) to between 0.58 and 9.68% (catalytic). Also, production of 2-pentanone was observed to increase from ∼10% (non-catalytic) to 27.36–53.90% (catalytic). In terms of energy recovery, Co/Fe3O4-HZSM-5 had about 40% energy recovery, which was the highest while the least performing catalyst was W/Fe3O4-HZSM-5 with 24.18% energy recovery in bio-oil. Overall, Co/Fe3O4-HZSM-5 catalyst showed better activity in enhancing the bio-oil quality and yield; it had the lowest nitrogen content (4.77 wt%) and highest bio-oil yield (17.73 wt %) as well as highest HHV (39.12 MJ/kg) which is almost similar to that of crude petroleum.