Esterification of levulinic acid into n-butyl levulinate catalyzed by sulfonic acid-functionalized lignin-montmorillonite complex

In this study,sulfonic acid-functionalized lignin-montmorillonite complex(LMT-SO_(3)H)was pre-pared and employed as an efficient heterogeneous catalyst for the esterification of levulinic acid(LA)into n-butyl levulinate(BL).An intermediate pseudo-butyl levulinate(p-BL)was determined by distilled water treatment and nuclear magnetic resonance(NMR)analysis,and a possible mech-anism for the esterification of LA is proposed.The effects of various process parameters were studied and the results showed that the LMT-SO_(3)H catalyst had the excellent catalytic perfor-mance for esterification of the LA.Under optimum reaction conditions,the yield of BL was 99.3%and the conversion of LA was 99.8%.The LMT-SO_(3)H catalyst exhibited strong acidic sites and high stability even after seven cycles of usage.Furthermore,esterification of the LA with various alcohols over the LMT-SO_(3)H was further investigated.