Thermal and Catalytic Fast Pyrolysis of Oily Extracts of Microalgae: Production of Biokerosene

Abstract

Three different microalgae species, Desmodesmus sp., Nannochloropsis oculata and Halamphora coffeaeformis were grown under controlled conditions. The resulting dry biomass was characterized by TG-DTA (thermogravimetry-differential thermal analysis) and extracted with three solvents having different polarities. The extracts gross mass yields varied from 2% using n-hexane to 23% (or 74% when subtracting the volatiles and ashes) when using methanol-chloroform whatever the microalgae species. Fourier transform infrared (FTIR) spectra of all extracts suggested the presence of fatty esters and acids. The extracts were pyrolyzed at 600 °C, using a micro pyrolizer coupled to a gas chromatograph-mass spectrometer (GC-MS), without and with γ-alumina as catalyst. Hydrocarbons concentrations varied respectively from 92% in the better case to 46% in the worst case. The C9-C15 fraction of these hydrocarbons, potentially useful for biokerosene formulation, was object of detailed analysis. In this fraction, nitrogenous products had concentrations always lower than 0.1%. The main hydrocarbons produced were linear 1-alkenes for thermal pyrolysis whereas for pyrolysis with γ-alumina, linear 1-alkenes and also alkenes isomers and linear alkanes, together with cyclic and aromatic compounds were observed for all microalgae species, but in different proportions. The C9-C15 fraction of pyrolyzed extracts can be considered as precursor for biokerosene or direct “drop in” fuel for kerosene petroleum fraction.