Cellulose Recovery from Agri-Food Residues by Effective Cavitational Treatments

Abstract

Residual biomass from agri-food production chain and forestry are available in huge amounts for further valorisation processes. Delignification is usually the crucial step in the production of biofuels by fermentation as well as in the conversion of cellulose into high added-value compounds. High-intensity ultrasound (US) and hydrodynamic cavitation (HC) have been widely exploited as effective pretreatment techniques for biomass conversion and in particular for cellulose recovery. Due to their peculiar mechanisms, cavitational treatments promote an effective lignocellulosic matrix dismantling with delignification at low temperature (35–50 °C). Cavitation also promotes cellulose decrystallization due to a partial depolymerization. The aim of this review is to highlight recent advances in US and HC-assisted delignification and further cellulose recovery and valorisation.

Lignin as a Natural Carrier for the Efficient Delivery of Bioactive Compounds: From Waste to Health

“…Furthermore, traditional methodologies are often time-consuming and employ toxic or dangerous organic solvents, meaning that it is important to use alternative methods for sustainable practice. Green methods include extractions using recyclable deep eutectic solvents and ionic liquids [ 31 ], electric fields, cavitation (acoustic and hydrodynamic cavitation) [ 28 ], subcritical and supercritical solvent conditions, enzymes, microwaves and green solvents [ 32 ], including eco-solvents such as glycerol and limonene and natural solvents (e.g., vegetable oils, bioethanol).…”

“…When ultrasound waves in the range of 20–150 kHz are applied to a liquid medium, the physical effects of cavitation, such as shockwaves and microjets, are predominant. On the other hand, ultrasound frequencies in the range of 150–2000 kHz mainly cause chemical effects due to the formation of hydroxyl radicals (HO·) in the local hotspots generated by cavitation [ 28 ]. The release of local pressure and the generation of oxidizing radicals can be exploited to disintegrate and depolymerize the macromolecular structure of lignin to obtain particles on a nanoscale level.…”

“…However, a pretreatment step is mandatory due to the strong physical and chemical interactions between hemicellulose, cellulose, and lignin. Choosing a suitable sustainable biomass pretreatment method is therefore of crucial importance as it should not excessively increase costs [ 28 , 29 ]. This review presents the state of the art of lignin-derived nanoparticles for use in drug-delivery applications.…”

Mechanochemical Applications of Reactive Extrusion from Organic Synthesis to Catalytic and Active Materials

“…However, the presence of almost 19% lignin means that it is recalcitrant to direct enzymatic hydrolysis and further fermentation to bioethanol [55]. While a range of physical, chemical, and mechanical treatments, biopretreatments, and combined treatments have recently been reported in the literature [56], mechanical treatment is preferable because of its mild and almost solventless conditions and energy savings. Due to these favorable features, an ever-growing number of research studies have been published on the effectiveness of extrusion in producing fermentable sugars from a wide range of lignocellulosic biomasses.…”

Separation of Lignocellulose and Preparation of Xylose from Miscanthus lutarioriparius with a Formic Acid Method

“…Hemicellulose can be used to produce products such as xylose, furfural, xylitol, and xylo-oligosaccharides, and it can be further derived into biofuels, bio-based materials, and chemicals [2][3][4]. In nature, cellulose, hemicellulose, and lignin are combined with each other and closely linked to form complex supramolecular complexes, which makes lignocellulose difficult to effectively degrade and utilize; meanwhile, the enzymatic hydrolysis of cellulose largely depends on the adsorption of enzymes on the substrate, while lignin can irreversibly adsorb enzymes, leading to enzyme inactivation [5]. In order to realize the conversion of lignocellulosic resources to biomass energy, the separation of cellulose and hemicellulose from lignocellulose by efficient technology is key to improve the bioconversion efficiency.…”