In the conversion of biomass resources to biofuels, three challenges must be met. The first challenge is the recalcitrance of lignocellulose and the reticular connection of lignin. The second challenge is the uncertain chemical constituents contained in biomass.The third and the most important challenge is the heterogeneity of biomass reaction systems. Ultrasonic energy provides a special physicochemical environment for processing biomass systems. However, critical assessment of ultrasound-assisted pretreatments and reactions of biomass for producing biofuels is needed to consider the role and mechanism of ultrasonic intensification and how it can be used advantageously in future biorefineries.
Dr. LUO Jia and Prof. FANG Zhen of Xishuangbanna Tropical Botanical Garden (XTBG) reviewed progress in ultrasound-assisted pretreatments and reactions of biomass materials. They described and critically evaluated recent applications of ultrasonic energy in the pretreatment and conversion of lignocelluloses, biodiesel and microalgae. They also introduced the potential of ultrasound for other related biomass processing (emulsification, demulsification and aggregation) and in-situ process monitoring. They discussed and analyzed key issues as well.
They concluded that the introduction of ultrasonic energy played a positive influence on the pretreatment and thermochemical/biochemical conversion of biomass. The current barriers that hinder the large-scale application of ultrasonic energy could be those at the scientific level (such as the real mechanism of ultrasonic intensification and its integration with chemical energies), those at the engineering level (such as the improvement of ultrasonic reactor design and parameter optimization) and those at the economic level (such as the improvement of energy efficiency and lowering the cost for ultrasonic operation and the catalysts). Therefore, ultrasound-assisted processes are needed to be further studied both at the fundamental level and at the applicable level to realize practical ultrasonic systems.