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Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and

a b s t r a c tSugarcane bagasse pretreated with dilute-acid was submitted to an organosolv ethanol process with NaOH under different operational conditions (pretreatment time, temperature, and ethanol concentration) aiming to maximize the glucose yield in the subsequent enzymatic hydrolysis stage. The different pretreatment conditions resulted in variations in the chemical composition of the solid residue as well as in the glucose recovered by enzymatic hydrolysis. All the studied variables presented significant (p < 0.05) influence on the process. The optimum organosolv pretreatment conditions consisted in using 30% (v/v) ethanol at 195 • C, during 60 min. Enzymatic hydrolysis of the residue then obtained produced 18.1 g/l glucose, correspondent to a yield of 29.1 g glucose/100 g sugarcane bagasse. The scale-up of this process, by performing the acid pretreatment in a 10-l semi-pilot reactor fed with direct steam, was successfully performed, being obtained a glucose yield similar to that found when the acid pretreatment was performed in autoclave.

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