Evaluating the effects of temperature on pressurized pyrolysis of Nannochloropsis oculata based on products yields and characteristics

• N. oculata is a suitable feedstock for pyrolysis due to high volatile matter.
• Temperature effects on product yields and properties during pressurized pyrolysis.
• Algal bio-oil has high energy content and has similar composition as diesel fuel.
• Suitability of char as a fuel was based on Van Krevelen diagram.
• Gas from pyrolysis of N. oculata has high percentage of combustible hydrocarbons.

Biofuels derived from pyrolysis of microalgae can be potential alternatives for petroleum-derived fuels. Pyrolysis is an easily controllable thermochemical conversion process that yields energy fuels such as bio-oil, char and combustible gases. Microalgae is a very promising feedstock for this process since it has high lipid content, grows faster than lignocellulosic biomass, has high productivity and high photosynthetic efficiency. Several reaction parameters including temperature could affect the yield and quality of biofuels from pyrolysis. This paper aimed to evaluate the effect of temperature during pyrolysis of Nannochloropsis oculata using a pressurized fixed-bed batch-type reactor. Based on the results, the distribution of the products significantly varied with pyrolysis temperature, and the pyrolysis process can be manipulated to favor one of its products. Bio-oil with high heating value (HHV) of about 38 MJ/kg, due to its high carbon (76wt%) and hydrogen (11wt%) contents, and low oxygen content (7wt%), can be produced from N. oculata. It also consists mainly of saturated (34.95%) and unsaturated aliphatics (34.43%), and aromatics (14.19%) ranging from C8 to C21, which is comparable to diesel fuel. The HHV of the char (27 MJ/kg) and gas (27 MJ/m3) were also relatively high. Based on their heating values (HHV) and compositions, the char, bio-oil and gas produced from pyrolysis of N. oculata can be potentially used as alternative sources of energy. Mass and energy conversion efficiencies of the process were also estimated to be approximately equal to 76% and 68%, respectively.