Steam explosion pretreatment of sugarcane bagasse for bioethanol production

Lignocellulosic biomass is a powerful material for producing sustainable biofuels because it converts into second-generation clean energy capable of coping with the depletion of fossil reserves and rising energy demands. Pretreatment is required in the conversion process to overcome the recalcitrance of the lignocellulosic biomass, accelerate its disintegration into cellulose, hemicellulose, and lignin and obtain an optimal yield of fermentable sugars in the enzymatic hydrolysis. In addition, it should be industrially scalable and capable of improving fuel properties and feedstock processability. Despite its conventionality, steam explosion technology has stood out due to its results and advantages such as wide applicability, high efficiency in the short term, and lack of contamination. This gentle and quick pretreatment combines high-temperature autohydrolysis and structural alteration via explosive decompression. So, steam at high pressure (1-3.5 MPa) and temperature (180-240ºC) are pressed into the cell walls and plant tissues for a duration of seconds (30 s) to several minutes (20 min). The steam explosion method has been one of the most effective especially for the hydrolysis of cellulose from agricultural wastes due to the lower amount of acetyl groups in the composition of hemicellulose. In this aspect, sugarcane bagasse is a promising feedstock for bioethanol production due to its high cellulosic content and high availability. Thereby, by selecting sugarcane bagasse pretreated by steam explosion, it is possible to achieve yields of over 80% depending on the process conditions. The aim of this review was to show the potential application of steam explosion as a thermomechanical pretreatment applied in sugarcane bagasse for bioethanol production considering its high recovery profile and its economic feasibility in a large-scale process. The stages, equipment, variables involved, by-products generated, and advantages and disadvantages of the steam explosion were all considered in this study. Finally, the technique's efficacy with various feedstocks was evaluated, resulting in a novel approach to steam explosion pretreatment.