Abstract

BALOYI, H.  and  MARX, S.. Preparation of bio-oil from Scenedesmus acutus using thermochemical liquefaction in a 1 L reactor. J. energy South. Afr. [online]. 2021, vol.32, n.2, pp.1-10. ISSN 2413-3051.  http://dx.doi.org/10.17159/2413-3051/2021/v32i2a8903.

Biomass from microalgae is a potential feedstock for biofuels production. It poses no threat to food security as it does not compete with agricultural crops for arable land. Scenedesmus acutus was used as feedstock to produce bio-oil in a large liquefaction reactor. The influence of reaction temperature (280-360ºC), reaction atmosphere (N₂ or CO₂) and solvent on bio-oil yield, C-16 fatty acid yield and oil properties were investigated. Oils were characterised using gas chromatography, Fourier transform infrared (FTIR) spectroscopy and ultimate analysis. Higher bio-oil yields were obtained in a CO₂ atmosphere (250 g.kg^-1 dry microalgae) than in a N2 atmosphere (210g.kg^-1 dry microalgae) whilst higher C16 fatty acid concentrations (600g.kg^-1 bio-oil) were recorded in N2 atmosphere compared to oil prepared in a CO₂ atmosphere (500 g.kg-¹ bio-oil). The oil yield increased to a maximum at 320°C, after which there were no significant changes. Highest bio-oil yields (425 g.kg^-1 dry microalgae) were obtained in ethanol as solvent. FTIR spectroscopy and ultimate analysis showed that proteins present in the feedstock were degraded by breakage of peptide linkages, and nitrogen present in the oils is peptide fragments from protein degradation. The carbon content of all produced oils was high, but the hydrogen content was low, leading to low hydrogen/carbon ratios. Energy consumption and energy efficiency calculations showed that liquefaction in both reaction atmospheres results in a net energy gain, and a CO2 atmosphere is best for high energy efficiency.Highlights • Higher bio-oil yields obtained in a CO₂ atmosphere than N₂. • N₂ atmosphere resulted in a higher C-16 content of the oil than in a CO₂ atmosphere. • Significantly higher bio-oil yields were obtained in ethanol as solvent. • There was a lower energy consumption rate value for oils prepared in a CO₂ atmosphere.

Keywords : microalgae; atmosphere; reaction temperature; yields; C-16 fatty acid.

        · text in English     · English ( pdf )