One-pot synthesis of fuel precursor from acetoin fermentation broth using ionic liquid-based salting-out extraction system.

Background: The development of biofuels, especially liquid hydrocarbon fuels, has been widely concerned due to the depletion of fossil resources. In order to obtain fuel precursors, the reaction of C-C bond formation is usually carried out with biomass derived ketones/aldehydes as reactants. Acetoin and 2,3-butanediol are two platform chemicals, which are co-existed in fermentation broth and traditionally separated by distillation, and then acetoin could be use as C4 building block to prepare hydrocarbon fuels. In order to mitigate the process complexity, direct aldol condensation reaction of acetoin in fermentation broth was studied in this work.
Results: A one-pot process of product separation and acetoin derivative synthesis was proposed based on salting-out extraction (SOE). Aldol condensation reaction of acetoin and 5-methyl furfural in different SOE systems was compared, and the results showed that the synthesis of C ₁₀ fuel precursors and separation of C ₁₀ products and 2,3-butanediol from fermentation broth were achieved in one-pot with ethanolammonium butyrate (EOAB) and K ₂ HPO ₄ as SOE reagents and catalysts. The SOE and reaction conditions such as the concentrations of EOAB and K ₂ HPO ₄ , reaction temperature and time were optimized. When the system was composed of 6 wt% EOAB-44 wt% K ₂ HPO ₄ and the mixture was stirred for 6 h at 200 rpm, 40 ℃, the yield of C ₁₀ products was 80.7%, and 95.5% 2,3-butanediol was distributed to the top EOAB-rich phase. The exploration of reaction mechanism showed that an imine intermediate was rapidly formed and the subsequent C ₁₀ product formation was the key step for aldol condensation reaction.
Conclusions: With EOAB and K ₂ HPO ₄ as SOE reagents and catalysts, one-pot synthesis of fuel precursor from acetoin fermentation broth was achieved without prior purification. A yield of 80.7% for C ₁₀ products was obtained which was accumulated at the interface of two aqueous-phase, and 95.5% 2,3-BD was distributed to the top EOAB-rich phase. This work provides a new integration process of product separation and derivative synthesis from fermentation broth based on ionic liquid SOE.
(© 2023. The Author(s).)