Recent advances in biorefineries based on lignin extraction using deep eutectic solvents: A review

A guide to lignin valorization in biorefineries: traditional, recent, and forthcoming approaches to convert raw lignocellulose into valuable materials and chemicals

“…Partial hydrolysis and degradation of hemicellulose may occur, depending on the properties of the DES. 243,248 Lignin undergoes depolymerization (mainly cleavage of inter-unit ether bonds) and repolymerization pathways similar to those described for the use of ILs. 246,249 Ultimately, the residual content of β-O-4′ linkages and the degree of condensation of the isolated lignin depend on the properties of the solvent and the operating temperature.…”

“…Cellulose can be dissolved in DESs thanks to the formation of extensive hydrogen bonding between the hydrogen bond acceptor of the DES and the hydroxyl groups in cellulose structure. 243,244,248 Additionally, LCCs can be cleaved during pretreatment with DESs, facilitating the solubilization of hemicellulose and lignin. Partial hydrolysis and degradation of hemicellulose may occur, depending on the properties of the DES.…”

“…For instance, one of the most adopted hydrogen bond acceptors, choline chloride, is a common additive used in animal feeds, and urea, a frequently adopted hydrogen bond donor, is used in fertilizers. 243,248 Second, DESs possess a much lower inhibitory effect toward cellulolytic enzymes and fermentative microorganisms, implying that the complete purification of the pulp from the solvent is not necessary after DES pretreatment. 247,248 One drawback of DESs is their high viscosity, which entails high pumping costs.…”

“…243,248 Second, DESs possess a much lower inhibitory effect toward cellulolytic enzymes and fermentative microorganisms, implying that the complete purification of the pulp from the solvent is not necessary after DES pretreatment. 247,248 One drawback of DESs is their high viscosity, which entails high pumping costs. 243 In addition, DESs recycling is challenging and the lack of effective methods represents a prominent limitation to the technoeconomic viability of DESs for biorefinery applications.…”

“…243 In addition, DESs recycling is challenging and the lack of effective methods represents a prominent limitation to the technoeconomic viability of DESs for biorefinery applications. 247,248,253,254 Nevertheless, these green solvents are considered promising candidates for the pretreatment of lignocellulose and for the subsequent valorization of the isolated lignin. 246,247,255,256…”