Direct Conversion of the Oleaginous Yeast Rhodosporidium diobovatum to Biodiesel Using the Ionic Liquid [C2mim][EtSO4]

In this study, the direct conversion of wet oleaginous yeast biomass to fatty acid methyl esters (FAME) using base transesterification in the presence of an ionic liquid was optimized. The ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate, was used to facilitate this process and improved the yields of FAME transesterified directly from wet biomass using potassium hydroxide (KOH) as a catalyst. Factorial screening was first used to identify critical factors affecting the FAME transesterification yield, and subsequently, response surface methodology was employed to study the interaction of methanol, KOH, and temperature on reaction yield. The optimized conditions for dried biomass were found to be 16.9 g methanol/g yeast, 0.056 g KOH/g yeast, 2 g [C(2)mim[EtSO4]/g yeast, and 65 degrees C, which yielded 97.1% conversion of the maximum FAME yield in only 2.5 h. The optimized system was further studied to observe the reaction profiles and FAME yield over time from both dry yeast and fresh wet yeast biomass containing varying degrees of water (from 65 to 80 wt %). The ionic liquid was found to improve total overall yield of FAME (96.9 +/- 0.4%) compared to the negative control without ionic liquid (69.6 +/- 5.0%) when wet yeast was used. While all the ionic liquid was recovered from the reaction, it contained only 59.3% of the catalyst, suggesting a heterogeneous catalyst may be more appropriate in future work.