Upgrading of bio-oil and aqueous liquid product from pyrolysis of microalgae (Nannochloropsis oculata) by fractional distillation

Abstract

The liquid product (bio-oil and aqueous) from pyrolysis of biomass such as microalgae contains a wide variety of compounds which makes it a potential source of biofuels and bio-chemicals. However, its complex composition limits its direct use as such. In this paper, fractional distillation at atmospheric conditions was explored as a technique to upgrade the quality of the pyrolyticbio-oil and aqueous liquid product (ALP) distillate fractions. By fractional distillation, the liquid product components were separated to relatively simpler distillate fractions which were then analyzed in terms of moisture, energy content, elemental and chemical compositions to assess their potential uses as fuel substitute or source of bio-chemicals. Fractional distillation of algal bio-oil resulted to 19% wt light fractions (BF1 and BF2), 7% wt middle fractions (BF3 and BF4), 51% wt heavy fraction (BF5) and 23% wt non-distillate residue. BF1 and BF2 were found to be comparable to diesel and BF6 to heavy fuel oil using van Krevelen diagram. For the ALP, the distillate fraction obtained at 150-180 o C (AF5) was found to have a heating value (about 24 MJ/kg) which is higher than methanol and wood-derived bio-oils. It was also found to contain various components such as carboxylic acids and carboxylate esters which could be further processed to produce value-added chemicals. The separation factor, β, showed that complete separation can be achieved by fractional distillation for some compounds such as high molecular weight olefins and naphthenes.