Direct acid hydrolysis of lignocellulosic and cellulosic biomasses: Zr/P/O system vs. Nb/P/O system

The conversion of lignocellulosic biomass into valuable chemicals is a strategic issue within the framework of the biorefinery concept. 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. Difficulties derive from both the resistant lignin sheath and the tight packing of cellulose chains Tthe catalytic performances of different metallic phosphate systems (Zr/P/O and Nb/P/O) in the heterogeneous catalytic process of direct acid hydrolysis of untreated softwood dust and ball-milled microcrystalline cellulose were investigated. From the tests conducted on both lignocellulose and ball-milled microcrystalline cellulose, it is possible to observe that the two systems allow similar conversion of the lignocellulosic biomass: however, while the ZrPO system is active both in the conversion of cellulosic and hemicellulosic fractions, the NbPO system is active mainly in the conversion of latter fraction. When microwave irradiation was adopted instead of the traditional heating, a significant shortening of the reaction time was reached with similar selectivity results, thus confirming the beneficial role of MW irradiation on biomass hydrothermal conversion. The differences of catalytic performances between the two metal phosphate catalysts can be explained by invoking both the different total concentration and type of acid sites.