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

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 methanolchloroform 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.