Two-step thermal conversion of oleaginous microalgae into renewable hydrocarbons

• Renewable hydrocarbons were produced via hydrolysis–pyrolysis of algal biomass.
• Microalgal fatty acids were completely and selectively extracted from hydrolysates.
• Recovered fatty acids were free of sulfur and low in salts and nitrogen.
• Pyrolysis of microalgal fatty acids yielded deoxygenated renewable hydrocarbons.

The aim of this study was to evaluate the conversion of microalgal biomass to renewable chemicals and fuels through a two-step reaction and separation process. High density Chlorella protothecoides culture with 40% lipid accumulation (dwb) was produced in 10 L bioreactors and hydrolyzed in batch stainless steel reactors under subcritical conditions. After hydrolysis, fatty acids free of sulfur and low in nitrogen and salts, were recovered by hexane extraction. The fatty acids were pyrolyzed at 410 °C for 2 h under N2 yielding n-alkanes, α-olefins and internal olefins and low molecular weight fatty acids. This study demonstrated the direct conversion of microalgal biomass into valuable platform chemicals and fuels compatible with the existing industrial hydrocarbon infrastructure.