Abstract
Hazelnut shells are an important waste from the hazelnut processing industry that could be valorized in a multi-product biorefinery. Individual or combined pretreatments may be integrated in processes enabling the integral fractionation of biomass. In this study, fractionation methods based on alkaline, alkaline-organosolv, organosolv, or acid-catalyzed organosolv treatments were applied to raw or autohydrolyzed hazelnut shells. A comparative analysis of results confirmed that the highest lignin removal was achieved with the acid-catalyzed organosolv delignification, which also allowed limited cellulose losses. When this treatment was applied to raw hazelnut shells, 65.3% of the lignin was removed, valuable hemicellulose-derived products were obtained, and the cellulose content of the processed solids increased up to 54%. Autohydrolysis of hazelnut shells resulted in the partial solubilization of hemicelluloses (mainly in the form of soluble oligosaccharides). Consecutive stages of autohydrolysis and acid-catalyzed organosolv delignification resulted in 47.9% lignin removal, yielding solids of increased cellulose content (55.4%) and very low content of residual hemicelluloses. The suitability of selected delignified and autohydrolyzed-delignified hazelnut shells as substrates for enzymatic hydrolysis was assessed in additional experiments. The most susceptible substrates (from acid-catalyzed organosolv treatments) reached 74.2% cellulose conversion into glucose, with a concentration of 28.52 g glucose/L.
Highlights
Lignocellulosic biomass (LB) is a key resource for the sustainable manufacture of bio-based chemicals and fuels
In previous studies reported by our research group, 210 ◦ C was identified as the optimal autohydrolysis temperature for producing soluble hemicellulosic oligosaccharides [10]
Hazelnut shells (HS) autohydrolysis assays were performed at 210 ◦ C, and the corresponding autohydrolyzed solids (AS) were selected for assessing the separation of cellulose from lignin
Summary
Lignocellulosic biomass (LB) is a key resource for the sustainable manufacture of bio-based chemicals and fuels. LB can be processed according to the biorefinery concept, which involves consecutive treatment stages to achieve an integral benefit of the feedstock, with minimal or no waste generation [1]. The success of biorefineries depends on the right application of technology methodologies for obtaining multi-products [2]. The contribution of biorefineries to a future bio-economy inspires business opportunities based on product diversification while improving environmental performance [3]. In the field of biomass valorization, the biorefinery acts as a platform for chemicals and energy production through the inclusion of diverse conversion technologies [3,4]. The complexity of biomass utilization lies in both the polymeric nature of its main constituents (cellulose, hemicelluloses, and lignin) and their different chemical reactivities. In the last few decades, several fractionation methods have been developed, as summarized in recent literature reviews [2,5,6,7,8]
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