Pretreatment greatly facilitates ethyl levulinate production from catalytic alcoholysis of Napier grass stem

Abstract

The inhibition effect of impurities in the raw lignocellulosic biomass greatly impedes its direct acid-catalyzed alcoholysis process to produce downstream chemicals. Previous literatures widely investigated the inhibition problems of lignin content and cellulose crystallite in the raw biomass for the production of alkyl levulinate (AL), while the effect of inorganic matters on this process only received cursory attention. In this contribution, the vital importance of ash removal in raw material for efficient catalytic alcoholysis of cellulose fraction been highlighted. Moreover, it has been found that the facile pretreatment of Napier grass stem greatly facilitates the acid-catalyzed alcoholysis of its cellulose fraction towards ethyl levulinate (EL), a versatile commodity chemical. EL yield as high as 72.1 % can be accomplished from the NaOH-pretreated Napier grass stem in ethanol/γ-valerolactone co-solvent medium over Al(OTf)3 at 170 ℃ for 150 min, which is almost ten times that from the pristine one in ethanol medium. It is also interesting to note that a facile and green water prewashing treatment can efficiently remove the inorganic component of the raw biomass, which thus largely promotes the conversion of Napier grass stem to EL. The activation energies of cellulose degradation and glucopyranoside alcoholysis after pretreatment decreased to 62.4 kJ/mol and 68.6 kJ/mol, respectively. This work presents a highly-reliable strategy for valorizing grass lignocellulosic feedstock to produce bio-based ester compounds.