Conversion and upgrading of microalgal lipids as a potential feedstock for sustainable aviation fuel production

Abstract

Microalgae are widely recognised as a promising feedstock for sustainable aviation fuel (SAF). However, their utilisation in hydroprocessed esters and fatty acids (HEFA) pathways is constrained by the compositional complexity and elevated impurity levels of crude microalgal lipid extracts, which are incompatible with hydrotreating requirements. This study presents a sequential acid-catalysed transesterification and vacuum distillation approach for producing fatty acid methyl esters (FAME) from crude microalgal lipids and evaluating changes in product composition and impurity characteristics relevant to HEFA applications. Crude microalgal lipids were reacted with methanol in the presence of mineral acids, and the effects of catalyst type, acid loading, temperature, and water addition on conversion behaviour were systematically evaluated. Sulphuric acid delivered the highest FAME yield of 0.21 g/g crude microalgal lipid at 6 wt% acid loading, 10 wt% water, and 50 °C. The resulting FAME profiles were consistently dominated by C16–C20 fatty acids, indicating that product composition is primarily governed by the intrinsic characteristics of the microalgal feedstock. Subsequent vacuum distillation increased FAME content from 58.2 to 87.0 wt% and reduced impurity levels. Across the overall process, total metals and non-metals were reduced by approximately 95 and 91%, respectively, relative to the crude microalgal lipid feedstock. Overall, the combined conversion and upgrading approach can improve the quality of microalgal-derived FAME while significantly reducing impurities, strengthening its potential as a feedstock for HEFA-based SAF production.