Direct Conversion of the Oleaginous YeastRhodosporidium diobovatumto Biodiesel Using the Ionic Liquid [C₂mim][EtSO₄]

Abstract

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 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 [C2mim­[EtSO4]/g yeast, and 65 °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.

The Oleaginous Red YeastRhodotorula/Rhodosporidium: A Factory for Industrial Bioproducts

“…Interestingly, it has been reported that up to 70% of the cost to make biodiesel could be accrued after the production of the cell biomass, when chemical methods of extracting TAGs are used [80]. This is a costly process that requires the complete drying of biomass, full chemical diffusion of solvent into the cells [81], yeast cell wall disruption, and lipid extraction [2].…”

“…This same method was effective for R. diobovatum and was optimized to produce 97.1% conversion of maximum FAME yields in 2.5 hours at 65°C. They did note a loss of ~40% of their KOH catalyst but conclude that switching from a homogenous to a heterogeneous catalyst could mitigate this [80]. Therefore, research is ongoing to develop R. diobovatum as top biofuel production species.…”

Efficient Extraction of a Docosahexaenoic Acid (DHA)-Rich Lipid Fraction from Thraustochytrium sp. Using Ionic Liquids

“…Ionic liquids (ILs) have been shown to increase the lipid extraction efficiency from microalgae by dissolving both dry and wet microalgae under relatively mild conditions (80–140 °C) with and without a co-solvent ( Table 1 ) [ 1 , 30 , 31 ]. ILs are often described as “green” designer solvents with many desirable physical-chemical properties such as great thermal stability, low melting points, and negligible vapor pressure [ 32 ]. In bioprocessing, ILs are best known for the capability of some ionic liquids to solvate highly recalcitrant biopolymers like cellulose [ 33 , 34 , 35 ].…”

Ionic Liquids in Biomass Processing

“…The synergetic effect of combining IL – methanol solvent and microwave heating produced biodiesel in 42 % yield based on dry biomass weight . The direct conversion of wet oleaginous yeast biomass to fatty acid biodiesel using 1‐ethyl‐3‐methylimidazoliumethylsulfate and KOH is also known . Some of the more recent (after 2012) applications of ILs in biodiesel synthesis are shown in Table .…”