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

In this study, the characteristics of bio-oil samples produced through slow pyrolysis of two different macroalgae, i.e. Azolla filiculoides and Ulva fasciata, at optimized conditions were determined and compared.

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 bio-oil production were optimized using response surface methodology established by a central composite design.

The highest bio-oil 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 bio-oil 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 bio-oil samples contained saturated and unsaturated hydrocarbons. However, the average hydrocarbon chain length was relatively shorter in U. fasciata bio-oil (C4- C16) than in bio-oil from A. filiculoides (C6-C24). Although both bio-oils 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.

The results indicated that U. fasciata bio-oil, with its superior characteristics, could be proposed as a promising candidate for application in dieselbased automotive industries.