Experimental investigation on fast pyrolysis of freshwater algae. Prospects for alternative bio-fuel production

Abstract

Several technologies have been developed with the aim of obtaining fuels from algae. In the present work, the fast pyrolysis of three different types of microalgae (Botryococcus braunii, Spirulina platensis, and Pithophora sp.) is investigated focusing on the quality and yield of the liquid product as a potential biofuel. The characterization of microalgae shows an elevated content of lipids in Botryococcus braunii, higher levels of proteins in Spirulina, and an equal number of proteins and carbohydrates in Pithophora sp. A fixed bed reactor, connected to a vacuum system, and nitrogen as inert gas flow are used in the pyrolysis experiments at 300, 400, 500, and 600 °C. At 500 °C, Botryococcus braunii produces the maximum amount of pyrolytic oil (65% yield) while Spirulina and Pithophora sp. affords the greatest amount at 600 °C, in 45% and 28% yield, respectively. Gas chromatography-mass spectrometry (GC–MS) analysis of the Botryococcus braunii-derived oils shows a high content of long-chain derivatives of alcohols, carboxylic acids, and unsaturated hydrocarbons. On the other hand, Spirulina-derived oil consists mostly of nitrogenated compounds while oil from Pithophora sp. is composed of oxygenated and/or nitrogenated products, depending on the reaction temperature. The measured higher heating value (HHV) of Botryococcus braunii-derived oil produced at 500 °C is 45 MJ/kg and this bio-oil could be used as a feedstock for fuel production after chemical upgrading to decrease the oxygen content (6.59 wt%).