Technical Feasibility Study on Biofuels Production from Pyrolysis of Nannochloropsis oculata and Algal Bio-oil Upgrading



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Increasing environmental concerns over greenhouse gas emissions, depleting petroleum reserves and rising oil prices has stimulated interest on biofuels production from biomass sources. This study explored on biofuels production from pyrolysis of Nannochloropsis oculata and subsequent bio-oil upgrading by fractional distillation and zeolite upgrading.

The extent of producing biofuels from N. oculata was initially investigated at various pyrolysis temperatures (400, 500 and 600^(0)C) at 100 psig. The distribution of the products significantly varied with temperature. Maximum char and gas yields were achieved at 400^(0)C (52% wt) and 600^(0)C (15% wt), respectively. Liquid production (aqueous and bio-oil) peaked at 500^(0)C (35% wt). The effect of temperature was also tested against product compositions and properties. Mass and energy conversion efficiencies were also estimated to be about 76% and 68%, respectively.

The operating condition for maximum bio-oil production from N. oculata pyrolysis was subsequently determined. Optimum yield was achieved at 5400C and 0 psig where liquid yield was about 43% wt (23% wt bio-oil, 20% wt aqueous) while char and gas yields were about 32 and 12% wt, respectively. The bio-oil obtained has high carbon (72% wt) and hydrogen (10% wt) contents and high energy content (36 MJ/kg). Char and gas also contain considerable energy contents of about 20 MJ/kg and 21MJ/m3, respectively.

Separation of the bio-oil and aqueous liquid product (ALP) components by fractional distillation was then investigated. Heavy distillates has the highest yield (75% wt), followed by light distillates (19% wt). Significant reduction in moisture contents and increase in heating values were observed in the bio-oil distillates. The ALP distillate obtained at 150-1800C was found to contain considerable amounts of acids, esters, amides and lactams and has heating value of about 24 MJ/kg.

Finally, HZSM-5 upgrading was done at various temperatures and reaction times. Reaction temperature greatly affected product yields and upgraded bio-oil composition. The best operating condition was found to be 285^(0)C for 3.5 h, which can produce treated bio-oil with higher hydrocarbons (86%), lower oxygenated (3%) and lower nitrogenous (11%) components. Higher heating value (40 MJ/kg), high carbon (80% wt), and low oxygen (3% wt) contents were also achieved.