Catalytic Esterification of Levulinic Acid into the Biofuel n-Butyl Levulinate over Nanosized TiO2 Particles

Abstract

Levulinic esters, synthesized by the esterification of biomass-derived levulinic acid with various alcohols, is an important chemical that plays an essential role in the fields of biomass fuel additives, organic synthesis, and high value-added products. In the present work, the catalytic esterification of levulinic acid with n-butyl alcohol was selected as a typical model reaction to investigate the catalytic performance of an inexpensive commercial catalyst, titanium oxide nanoparticles. The influences of reaction time, reaction temperature, and catalyst loading on the conversion of levulinic acid to n-butyl levulinate were systematically examined through single-factor experiments. Additionally, the optimization of the reaction conditions was further investigated by a Box–Behnken design in response to the surface methodology. The desired product, n-butyl levulinate, with a good yield (77.6%) was achieved under the optimal conditions (reaction time of 8 h, reaction temperature of 120 °C, and catalyst dosage of 8.6 wt.%) when using titanium oxide nanoparticles as catalysts. Furthermore, it was found that addition of water to the catalytic system facilitated the reaction process, to some extent. This study reveals that the nanosized TiO2 material, as an efficient solid acid catalyst, had good catalytic performance and stability for the esterification of levulinic acid after six consecutive uses.

Conversion of Biomass-Derived Molecules into Alkyl Levulinates Using Heterogeneous Catalysts

“…The subsequent protonation and nucleophilic addition via n-butanol facilitated the conversion of α-angelica lactone into pseudo-butyl levulinate. Following a similar process, pseudo-butyl levulinate was converted into an intermediate, I; the literature has reported the formation of pseudo-butyl levulinate [11]. Thereafter, I undergoes ring opening to produce another intermediate, II.…”

“…To increase the rate of the esterification of levulinic acid with n-butanol over commercial TiO2, S. Zhou et al added a small amount of water into the reaction system (Table 1, entry 6) [11]. The increased yield of n-butyl levulinate might be due to the conversion of the surface Lewis acid sites into Brønsted acid sites.…”

“…Other strategies for increasing the rate of the esterification of levulinic acid with alcohols include the desilication of H-ZSM-5 to form mesopores while sacrificing the micropores [29]. Regarding the esterification of To increase the rate of the esterification of levulinic acid with n-butanol over commercial TiO 2 , S. Zhou et al added a small amount of water into the reaction system (Table 1, entry 6) [11]. The increased yield of n-butyl levulinate might be due to the conversion of the surface Lewis acid sites into Brønsted acid sites.…”

“…Fructose can undergo dehydration to form 5-hydroxymethylfurfural, which can be decomposed to form levulinic acid (Figure 1) [5,8,9]. Levulinic acid is a versatile building block for the synthesis of value-added chemicals with extensive applications, and this is attributable to the presence of different functional groups of a ketone carbonyl group and a carboxyl group [10][11][12]. Among the various levulinic acid derivatives, alkyl levulinates are particularly fascinating because of their numerous potential industrial applications as flavoring agents, fragrances, green solvents, and precursors for synthesizing valuable γ-valerolactone [3,13,14].…”

“…Alkyl levulinates exhibit similar physicochemical properties to those of biodiesel composed of fatty acid methyl esters; however, they do not exhibit the principal drawbacks of biodiesel, namely cold flow properties and gum formation [3]. The addition of alkyl levulinates to biodiesel can address these drawbacks because of their properties such as low toxicity, high lubricity, flash point stability, and moderate flow properties under low-temperature conditions [3,11,15]. Alkyl levulinates can be synthesized directly from carbohydrates such as cellulose, glucose, and fructose [16,17].…”