Efficient synthesis of C15 fuel precursor by heterogeneously catalyzed aldol-condensation of furfural with cyclopentanone

Abstract

The aldol-condensation reaction of biomass-derived furfural and cyclopentanone coupled with hydrogenation/hydrodeoxygenation is a promising route for the production of renewable high-quality diesel or jet fuel. In this paper, we focus on the heterogeneously catalyzed aldol condensation of furfural with cyclopentanone, in order to maximize the yield of 2,5-bis(2-furylmethylidene)cyclopentan-1-one (F₂C, a C₁₅ fuel precursor). Experiments were conducted over a series of solid-base catalysts and it was found that potassium fluoride impregnated alumina shown the highest catalytic efficiency. We further investigated the effect of different parameters on the performance of KF/γ-Al₂O₃, including KF loading amount, solvent, reaction time and temperature. Over KF/γ-Al₂O₃ with a 33% KF loading amount, the aldol reaction achieved an F₂C molar yield up to 95.4% at 333 K within 2 h. Under the nearly optimal condition, the separated solid product is almost F₂C with a purity of 100%, providing a high-quality biofuel precursor for the next processing step.

Scheme 1. Comparison of the obtained fuel products using different ketones as second reactants.

Fig. 1. Conversions of furfural (white bar), yields (grey bar) and selectivities (black bar) of F₂C over different solid-base catalysts. Reaction conditions: 333 K, 2 h; 1.92 g furfural, 0.84 g cyclopentanone (furfural/cyclopentanone mole ratio 2 : 1), 40 mL methanol and 0.2 g catalyst were used in each reaction; the KF loading of KF/γ-Al₂O₃ was 20 wt%.

Fig. 2. CO₂-TPD curves of different solid-base catalysts.

Fig. 3. XRD patterns of γ-Al₂O₃ and KF/γ-Al₂O₃.

Scheme 2. Proposed pathway for the furfural–cyclopentanone aldol condensation over KF/γ-Al₂O₃.

Fig. 4. Conversions of furfural () and yields of F₂C () over different loading amount KF/γ-Al₂O₃. Reaction conditions: 333 K, 2 h; 1.92 g furfural, 0.84 g cyclopentanone (furfural/cyclopentanone molar ratio 2 : 1), 0.2 g catalyst and 40 mL ethanol were used in each reaction.

Fig. 5. Furfural conversions () and F₂C yields () over 33 wt% KF/γ-Al₂O₃ at different reaction temperatures. Reaction conditions: 2 h; 1.92 g furfural, 0.84 g cyclopentanone (furfural/cyclopentanone molar ratio 2 : 1), 0.2 g catalyst and 40 mL methanol were used in each reaction.

Fig. 6. Furfural conversion () and F₂C yield () over 33 wt% KF/γ-Al₂O₃ as a function of reaction time. Reaction conditions: 333 K; 1.92 g furfural, 0.84 g cyclopentanone (furfural/cyclopentanone molar ratio 2 : 1), 0.2 g catalyst and 40 mL methanol were used in each reaction.

Fig. 7. Conversions of furfural (white bar), yields (grey bar) and selectivities (black bar) of F₂C over recycled 33 wt% KF/γ-Al₂O₃. Reaction conditions: 333 K, 2 h; 1.92 g furfural, 0.84 g cyclopentanone (furfural/cyclopentanone molar ratio 2 : 1), 0.2 g catalyst and 40 mL methanol were used in each reaction.