Optimization of alkaline pretreatment for the co-production of biopolymer lignin and bioethanol from chestnut shells following a biorefinery approach

Abstract

Among lignocellulosic materials, chestnut shells (CNS) are a rejected feedstock from agro-food industry with promising possibilities as a suitable raw material to be used in a biorefinery scheme. The aim of this work was to optimize the alkaline delignification of CNS for the co-production of lignin and bio-ethanol. Under the optimal conditions (7.2% NaOH, 80 °C and 30 min), 92.6% of delignification was achieved, and 60.5% of glucan was recovered. This delignified solid was subjected to a simultaneous saccharification and fermentation using Saccharomyces cerevisiae, reaching an ethanol production of 14.6 g/L (ethanol conversion of 97%). Furthermore, the lignin extracted from CNS was characterized for the first time in terms of the chemical composition (pyrolysis-GC/MS), molecular weight distribution (HPSEC), thermal stability (TGA), structural properties and functional groups (FTIR and NMR) and total phenolic content (Folin-Ciocalteu). A preliminary economic analysis demonstrated that the co-production of lignin is the key factor in the profitability of the CNS biorefinery, and that alkaline delignification could be a suitable revalorization strategy of this unexploited residue.