Integrated catalytic process for biomass hydrolysis: a comparison of different pretreatments and catalysts

The conversion of lignocellulose biomass into valuable chemicals is one of the pillars of the biorefinery, the aim of which is to develop integrated processes for the transformation of renewables collected from agricultural, forestry and urban waste into “bio-platform molecules”. For these reasons, there is a great interest in developing reusable solid acid catalysts, which are effective in cellulose transformation, in place of the traditional processes that make use of mineral acids. The starting point of the transformation chain is the deconstruction of the lignocellulose and depolymerization of the hemicellulose and cellulose to give monosaccharides, or even transform sugars into other valuable bio-based building blocks. The aim of this work is to compare the performance of metal phosphates catalysts, zirconium and niobium phosphates, in cellulose and lignocellulose (conifer wood sawdust) hydrolysis, after pretreatment of the biomass with different procedures. Two different types of pretreatment were investigated: a mechanical pretreatment, in which the substrate was subjected to a 48-hours treatment in a high-energy ball mill, and a thermal pretreatment, in which biomass was autohydrolyzed at 180°C for 1 hour in a monomodal microwave reactor. Results of tests conducted with metal phosphate catalysts on cellulose and lignocellulose, either as such or after the two different treatments, showed that pretreatments were effective in facilitating the hydrolysis: in particular, with pretreated substrates, we observed an important improvement of catalytic performance. As regards catalytic behaviors, the differences of performances between the two metal phosphates can be explained by invoking both the different total concentration and type of acid sites.