Enhanced production of levulinic acid/ester from furfural residue via pretreatment and two-stage alcoholysis

A two-stage alcoholysis was developed for improved conversion of furfural residue (FR) into levulinic acid (LA) and methyl levulinate (ML). Mixed acids including 0.01 M of H2SO4 and Al2(SO4)3 and methanol/water (50/50 v/v%) were identified as the suitable catalyst and reaction medium. The optimum alcoholysis conditions were 198 °C and 1.5 h for the 1st stage and then 163 °C and 1.3 h for the 2nd stage, and the maximum total yield of LA and ML can reach 25.64%. The reaction kinetics and possible conversion pathways for ML and LA production were proposed. On the basis, HCOOH/H2O2 pretreatment was screened for the pretreatment of FR, which increased the cellulose content of FR from 40.01 to 71.91%. The maximum total yield of LA and ML from pretreated FR was 44.96% under the optimum conditions of 195 °C and 1.9 h for the 1st stage and then 166 °C and 1.1 h for the 2nd stage, which was 16.09% higher than that of isothermal alcoholysis. The reusability tests showed that the Al2(SO4)3 was stable and can be reused at least 5 times. This study developed a new method for high-value utilization of FR and cleaner production of LA and ML.