Abstract
This work addresses for the first time the study of olive stone (OS) biomass pretreatment by reactive extrusion technology using NaOH as the chemical agent. It is considered as a first step in the biological conversion process of the carbohydrates contained in the material into bio-based products. OS is a sub-product of the olive oil extraction process that could be used in a context of a multi-feedstock and multi-product biorefinery encompassing all residues generated around the olive oil production sector. OS biomass is pretreated in a twin-screw extruder at varying temperatures—100, 125 and 150 °C and NaOH/biomass ratios of 5% and 15% (dry weight basis), in order to estimate the effectiveness of the process to favour the release of sugars by enzymatic hydrolysis. The results show that alkaline extrusion is effective in increasing the sugar release from OS biomass compared to the raw material, being necessary to apply conditions of 15% NaOH/biomass ratio and 125 °C to attain the best carbohydrate conversion rates of 55.5% for cellulose and 57.7% for xylan in relation to the maximum theoretical achievable. Under these optimal conditions, 31.57 g of total sugars are obtained from 100 g of raw OS.
Highlights
IntroductionThe world faces a series of global challenges (climate change, food and energy security, depletion of natural resources, etc.) that require turning upside down the way we produce and consume as a society
The world faces a series of global challenges that require turning upside down the way we produce and consume as a society
The pretreatment of olive stone biomass by alkaline extrusion has been proven to significantly improve the accessibility of cellulolytic enzymes to carbohydrates, while at the same time preventing the degradation of sugars during the process
Summary
The world faces a series of global challenges (climate change, food and energy security, depletion of natural resources, etc.) that require turning upside down the way we produce and consume as a society. The agro-industrial sector produces a series of by-products and wastes that are considered as potential feedstocks for the production of different bio-based products, reinforcing the development of a sustainable bioeconomy. This approach has significant advantages, since these biomass wastes are usually abundant and cheap, have a negative environmental impact and they would otherwise require a disposal system that can this way be avoided. Their revalorization through the conversion to bio-products can solve some of Energies 2020, 13, 4517; doi:10.3390/en13174517 www.mdpi.com/journal/energies
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