Influence of butanol isomers on the reactivity of cellulose towards the synthesis of butyl levulinates catalyzed by liquid and solid acid catalysts

Abstract

Butyl esters of levulinic acid form an interesting class of bio-based compounds that can be used, for example, as fuel additives. Their preparation mainly proceeds through the esterification of levulinic acid while the few reported studies on their direct synthesis from cellulose give limited information. In the present work, we studied for the first time in detail the influence of butanol isomers on the non-catalyzed cellulose liquefaction and the acid catalyzed formation of butyl levulinates from cellulose. In the absence of catalysts there was no influence of the alcohol class on liquefaction which reached 70–85% after 2 hours at 300 °C. In the presence of catalysts, we showed that the class of the alcohol had a significant influence on the butyl levulinate yield. With primary alcohols yields of 50% were obtained in the presence of H₂SO₄ (200 °C, 30 min). This level of yield can be considered as very interesting for these kinds of one-pot transformations involving cellulose. With secondary alcohols, yields less than 20% were obtained while no butyl levulinate was formed with tertiary alcohols. We also report for the first time this transformation in the presence of solid acids. Insoluble Cs₂HPW₁₂O₄₀ or sulfated zirconia catalyzed the reaction heterogeneously despite deactivation leading to limited yields of 13% (200 °C, 1 hour). We finally show that water in butanol had an ambivalent role in enhancing the cellulose reactivity but limiting the esterification step and found that 5–7 wt%/butanol of water was the optimum amount.