Biodiesel production from Rhodosporidium toruloides by acidic ionic liquids catalyzed hydrothermal liquefaction

Hydrothermal liquefaction (HTL) has been proved to be an efficient method to disrupt cell walls and extract lipids from oleaginous yeast. However, many steps are needed for converting bio-oil into fatty acid methyl esters after HTL. Herein, acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO₄]) was introduced as the catalyst in HTL to convert oleaginous yeast Rhodosporidium toruloides to biodiesel in one step. [Bmim][HSO₄] has dual effects on cell wall disruption and transesterification in reactions. As a result, the biodiesel yield achieved as high as 15.1 ± 3.2 % in optimal condition. The biodiesel was composed of long chain fatty acid methyl esters, and the higher heating value was 40.62 ± 0.05 MJ·kg^-1. After the catalyst recycled 4 times, the catalytic efficiency still kept at 62.8 ± 2.1 %. The results indicated catalytic HTL was a direct and efficient method for biodiesel production from Rhodosporidium toruloides.