Kinetic Studies on Both Synthesis of Methacrolein Catalyzed by an Ionic Liquid and Catalyst Deactivation

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 C₁₀ fuel precursors and separation of C₁₀ products and 2,3-butanediol from fermentation broth were achieved in one-pot with ethanolammonium butyrate (EOAB) and K₂HPO₄ as SOE reagents and catalysts. The SOE and reaction conditions such as the concentrations of EOAB and K₂HPO₄, reaction temperature and time were optimized. When the system was composed of 6 wt% EOAB-44 wt% K₂HPO₄ and the mixture was stirred for 6 h at 200 rpm, 40 ℃, the yield of C₁₀ 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 C₁₀ product formation was the key step for aldol condensation reaction.

CONCLUSIONS

With EOAB and K₂HPO₄ 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 C₁₀ 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.

Catalytic Synthesis of Methacrolein via the Condensation of Formaldehyde and Propionaldehyde with L-Proline Intercalated Layered Double Hydroxides

Aldol condensation reactions are very important C–C coupling reactions in organic chemistry. In this study, the catalytic performance of layered double hydroxides (LDHs) in the aldol condensation reaction of formaldehyde (FA) and propionaldehyde (PA) was investigated. The MxAl-LDHs (denoted as re-MxAl–LDHs; M = Ca and Mg; X = 2–4), as heterogeneous basic catalysts toward the aldol condensation reaction, were prepared via a two-step procedure. The catalyst exhibited a high PA conversion (82.59%), but the methacrolein (MAL) selectivity was only 36.01% due to the limitation of the alkali-catalyzed mechanism. On this basis, the direct intercalation of L-proline into LDHs also has been investigated. The influences of several operating conditions, including the temperature, reaction time, and substrate content, on the reaction results were systematically studied, and the optimized reaction conditions were obtained. The optimized Mg3Al–Pro-LDHs catalyst exhibited a much higher MAL selectivity than those of re-MgxAl–LDHs.