Effect of Chlorella vulgaris growing conditions on bio-oil production via fast pyrolysis

Microalgae have been recognized as one of the most promising biomass sources of energy, in particular for bio-fuels production. In this paper the production of bio-oil from a fast growing microalgae species with low lipids content is proposed. The influence of both the cultural medium and the reaction conditions on bio-oil yields and quality is investigated performing fixed and fast pyrolysis tests on Chlorella vulgaris grown in complete and nitrogen starved medium. Nitrogen starvation leads to a higher lipids amount in the biomass, increasing its calorific value. Fast pyrolysis of nitrogen starved microalgae is proposed to achieve high bio-oil yield and quality. In this case, experiments have pointed out a maximum bio-oil yield of about 72% mass on dry basis at 400 degrees C. Bio-oil products were characterized on the basis of GC-MS, elemental analysis and calorific content. In particular, the GC-MS analysis accounts for an oily fraction of the bio-oil formed by several hydrocarbons as well as oxygenated and nitrogenous species, including indoles, fatty acids and alcohols. The bio-oil produced from nitrogen starved biomass exhibits higher amount of fatty acids and lower amount of nitrogenous species, resulting in an improved quality. Furthermore, the higher lipids amount of the nitrogen starved biomass leads to a major carbon content in the bio-oil and thus to a slight increase of its calorific value. For all the experimental tests the energy consumption ratio was calculated, and fast pyrolysis of nitrogen starved biomass has proved to be the most convenient process in the energetic valorization of microalgae. (C) 2013 Elsevier Ltd. All rights reserved.