Biorefineries are industrial facilities where biomass is converted into chemicals, fuels and energy. The use of lignocellulose as raw material implies the development of pretreatments to reduce its recalcitrant character prior to the processes that lead to the synthesis of the products of interest. These treatments are based on physico-chemical processes where it is necessary to use acids, bases, oxidants, and high pressure and temperature conditions that lead to the depolymerization of lignocellulose at the expense of generating a series of streams that must be treated later or to the production of by-products. In recent years, mechanochemistry is becoming relevant in the design of processes that help in the depolymerization of lignocellulose. These mechanochemical processes are being used in combination with chemicals and/or enzymes, allowing the use of minor loads of reagents or enzymes. In this review, the advances achieved in the use of mechanochemistry for treating lignocellulosic biomass or cellulose will be presented, with special emphasis on how these mechanochemical processes modify the structure of lignocellulose and help subsequent treatments. It will focus on using ball milling or extrusion, ending with a section dedicated to future work needed to implement these technologies at the industrial level.

In the present work, a series of catalysts based on aluminum and zirconium oxides was studied for the transformation of glucose into 5-hydroxymethylfurfural. These catalysts were characterized by using experimental techniques, such as X-ray diffraction, N₂ adsorption–desorption at −196 °C, X-ray photoelectron spectroscopy, temperature-programmed desorption of NH₃ and CO₂, and scanning transmission electron microscopy. The catalytic behavior in glucose dehydration was evaluated in a water-methyl isobutyl ketone biphasic system, in the presence of CaCl₂, in order to minimize losses due to unwanted secondary reactions. High glucose conversion and 5-hydroxymethylfurfural (HMF) yield values were obtained in the presence of an Al(Zr)O_x catalyst with an Al:Zr molar ratio of 7:3, reaching 97% and 47%, respectively, at 150 °C after 120 min. Under tested conditions, this catalyst retained most of its catalytic activity for four reuses.

Nb-based catalysts supported on porous silica with different textural properties have been synthesized, characterized, and tested in the one-pot reaction of furfural to obtain valuable chemicals. The catalytic results reveal that the presence of fluoride in the synthesis, which limits the growing of the porous silica, limits diffusional problems of the porous silica, obtaining higher conversion values at shorter reaction times. On the other hand, the incorporation of NbO_x species in the porous silica provides Lewis acid sites and a small proportion of Brönsted acid sites, in such a way that the main products are alkyl furfuryl ethers, which can be used as fuel additives.

In this work, acidic ion-exchange resins with strong Brönsted sulphonic groups were assessed in the catalytic etherification of the platform molecule 5-(hydroxymethyl)furfural (HMF) to 5-(ethoxymethyl)furfural (EMF), a biofuel with an energy density close to that of gasoline (30 MJ/L) which also reduces emissions of NO_x and SO_x and solid particles respect to fossil-derived fuels. Catalytic performance was optimized modifying experimental parameters such as reaction time, temperature, and concentration of reagent employed. This process was carried out in batch reactors using ethanol 96% as solvent. Among different cation-exchange resins tested, Purolite CT275DR provided the fastest HMF conversion together with Purolite PD206, and the highest selectivity to EMF, achieving above 70% selectivity at 100 °C. Over time, strong acid sites favoured product hydrolysis opening the furan ring originating ethyl levulinate (EL) to the detriment of EMF selectivity. Purolite CT275DR was also utilised to realize the transformation from sugars directly to EMF in the same reaction medium, in a one-pot process, obtaining relevant results from fructose (37% HMF yield, 21% EMF yield after 5 h), but originating selectively ethylglucosides and ethylgalactosides in the presence of glucose and galactose, respectively, due to the absence of necessary Lewis acid sites to isomerize aldose and proceed with dehydration.