Abstract
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.
Highlights
The Brazilian coconut industry operates at large scale (2.34 millions of tons of fruits) and it generates approximately 900 thousand tons of unused coconut husks (CH).[1]
Lignocellulosic coconut husks are a prominent agroindustrial byproduct that can be beneficial to the production of value-added conversion products due to high concentrations of fermentable sugars
The pretreatments increased by three times the reducing sugar yield (70.0%) of CH samples in comparison to coconut samples that were not subjected to pretreatments (32.2%)
Summary
The Brazilian coconut industry operates at large scale (2.34 millions of tons of fruits) and it generates approximately 900 thousand tons of unused coconut husks (CH).[1]. Biomass fractionation into its main components is a process of paramount importance that can be achieved through different pretreatments.[5,6] Pretreatment disrupts the recalcitrance of the lignocellulosic biomass structure by separating lignin from cellulose This process increases the proportion of amorphous cellulose, since it is more susceptible to acid/enzymatic hydrolysis, changes intra and inter-molecular hydrogen bonds, and enables biomass dissolution.[7]. Hydrolysis yield is estimated at 20% of the theoretical value when no pretreatment is adopted.[8] many methods
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