Simultaneous microwave extraction and synthesis of fatty acid methyl ester from the oleaginous yeast Rhodotorula glutinis

Microbial lipids have the potential to substantially reduce the use of liquid fossil fuels, though one obstacle is the energy costs associated with the extraction and subsequent conversion into a biofuel. Here we report a one-step method to produce fatty acid methyl esters (FAME) from Rhodotorula glutinis by combining lipid extraction in a microwave reactor with acid-catalysed transesterification. The microwave did not alter the FAME profile and over 99% of the lipid was esterified when using 25 wt% H₂SO₄ over 20 minutes at 120 °C. On using higher loadings of catalyst, similar yields were achieved over 30 seconds. Equivalent amounts of FAME were recovered in 30 seconds using this method as with a 4 hour Soxhlet extraction, run with the same solvent system. When water was present at less than a 1:1 ratio with methanol, the main product was FAME, above this the major products were FFA. Under the best conditions, the energy required for the microwave was less than 20% of the energy content of the biodiesel produced. Increasing the temperature did not change the energy return on investment (EROI) substantially; however, longer reaction times used an equivalent amount of energy to the total energy content of the biodiesel.