Optimization of Alkaline, Acidic, Ionic Liquid and Oxidative Pretreatments for Coconut Waste Conversion into Fermentable Sugars

Cocos nucifera L. is a palm tree of paramount importance in the food and chemistry industries, although over 50% of its biomass is discarded as waste.The aim of the study is to investigate different pretreatments in to coconut husks (CH), based on acid, alkaline, ionic liquid (IL), and peroxidative, in order to produce fermentable sugars.Severity factors were calculated for pretreatments; values ranged from 0.3 to 1.7 for peroxide, from 0.01 to 1.4 for alkaline, from 1.4 to 2.8 for acid and from 2.0 to 3.0 for ionic liquid.Pretreatments were optimized (time and temperature) to maximize the sugar yield and to remove the total lignin after acid hydrolysis.Reducing sugar yield (70%) was higher when CH waste was alkaline-pretreated for 2 h at 76.21 °C.The highest lignin removal rate was recorded when alkaline (21.4%) and peroxide solutions (27.2%) were used.The IL did not increase sugar yield and was not effective in lignin removal.These outcomes were confirmed through infrared spectroscopy, whereas scanning electron microscopy showed increased biomass porosity during alkaline, acid and peroxide pretreatments.The IL showed little and non-significant changes.The crystallinity index notably increased after each pretreatment; besides, it was directly associated with sugar content.