Bio-oil production by pyrolysis of Azolla filiculoides and Ulva fasciata macroalgae

BACKGROUND AND OBJECTIVES: In this study, the characteristics of biooil samples produced through slow pyrolysis of two different macroalgae, i.e. Azolla ‎filiculoides and Ulva fasciata, at optimized conditions were determined and compared. METHODS: For this purpose, the effects of temperature (300-500 °C), carrier gas flow rate (0.2-0.8 L/min), ‎and heating rate (10-20 °C/min) on the final biooil production were optimized using response ‎surface methodology established by a central composite design. FINDINGS: The highest biooil yield from U. fasciata (34.29%) was obtained at the temperature of 500 °C, ‎‎ nitrogen flow rate of 0.2 L/min, and heating rate of 10 °C/min. As for A. filiculoides feedstock, the highest biooil ‎yield (30.83%) was achieved at the temperature of 461 °C, nitrogen flow rate of 0.5 L/min, and heating rate of 20 °C/min. Both biooil samples contained ‎saturated and unsaturated hydrocarbons. However, the average hydrocarbon chain length was ‎relatively shorter in U. fasciata biooil (C4-C16) than in biooil from A. filiculoides (C6-C24). Although both biooils had almost ‎identical heating values, the U. fasciata bio-oil showed more appropriate properties, i.e. lower viscosity and ‎density. Furthermore, the energy recovery from U. fasciata pyrolysis was calculated as 56.6% which was ‎almost 1.5 times higher than the energy recovery from A. filiculoides pyrolysis. CONCLUSION: The results indicated that U. fasciata biooil, with its superior characteristics, could be proposed as a promising candidate for application in dieselbased automotive industries.