Sono- and mechanochemical technologies in the catalytic conversion of biomass.

This tutorial review focuses on the valorisation of biomass by sonochemical and mechanochemical activation. Although several of the examples reported herein rely on the use of model compounds rather than native feedstocks, the conversion of lignocellulosic fractions into valuable compounds is a great opportunity with which to more sustainably exploit natural resources, from environmental, economic and social points of view. The use of non-conventional technologies that generate high-energy microenvironments can improve biomass deconstruction and the accessibility of catalysts, granting higher conversion and selectivity. The critical parameters in sonochemical and mechanochemical conversions have been analysed together with the most common devices and reactors, and the potential of sonocatalysis and mechanocatalysis as emerging tools for both catalytic and biocatalytic biomass conversion will be discussed. A SWOT (strengths, weaknesses, opportunities and threats) analysis will provide an overview of the effective feasibility of these approaches in a biorefinery context. Although these technologies offer indisputable advantages (mild reaction conditions, enhanced reaction rates and mass transfer), their mechanisms and the systematic adjustment of parameters to give optimal outcomes still require further investigation, which will pave the way for reproducible and scalable experiments. Indeed, process scale-up can be accomplished both in batch and flow mode. However, results are not particularly predictable, despite the accurate control of instrumental variables, because of the variability found in biomass sources and the complexity inherent in structures.