Catalytic cracking of sterol-rich yeast lipid

Microbial lipids offer a promising feedstock for renewable biofuels. However, one of the major concerns with their conversion from lipids into suitable fuels is the high sterol content of the lipid. This is especially problematic for lipids obtained from oleaginous yeasts, as there are some indications that the sterol content could inhibit catalyst performance during hydrotreating. In this investigation a sterol-rich model feedstock (a 50:50 mixture of cholesterol and rapeseed oil, “RC50”) and an unrefined microbial lipid derived from the oleaginous yeast Metschkownia pulcherrima were converted to a diesel-like fuel in a single step via catalytic cracking. Far from reducing catalyst performance the cracking of the sterol groups liberated hydrogen, resulting in a reduction in the olefin content as well as an increase in the aromatic content of the fuel. The cracking of RC50 over Pd/C resulted in a fuel with a comparable product distribution to ultra-low sulphur diesel (ULSD), with high levels of linear alkanes and approximately 10 wt% aromatics. Cracking of unrefined yeast lipid over Pd/C was shown to result in an energy dense, hydrocarbon fuel suitable for marine applications (unblended) or a road transport fuel at 50% v/v blends with ULSD.