Nowadays, hexitols from the hydrogenation of biomass have achieved a good piece of attention because they are versatile compounds with a wide range of uses. In essence, the conversion of biomass into sugar alcohols with supported metal catalysts is a two-step reaction. First, biomass is hydrolysed to sugars over acid or acidified supports and then hydrogenated into the sugar alcohols by supported metal catalysts under H2 pressure. However, hydrolysis of cellulose has remained a challenge. Therefore, supercritical water (SCW) appears as a very interesting alternative to overvome this problem. SCW has been demonstrated to be an excellent solvent and reaction medium to improve the cellulose hydrolysis selectivity into glucose by controlling the reaction time. In this sense, it is able to achieve higher hexitols (sorbitol and mannitol) yield using SCW as a pretreatment of cellulose before the hydrogenation process than carrying out a one-step reaction from cellulose untreated (Figure 1).
In both cases, Ru/MCM-48 has been used as catalysts improving hexitols selectivity in this reaction. SCW pretreatment was carried out by ultra-fast hydrolysis (UFH) of cellulose, where the reactor works with SCW and residence time of 20 ms. Finally, products from UFH of cellulose and untreated cellulose were hydrogenated into hexitols in a commercial reactor Berghof BR-25 (Scheme 1).
Alberto Romero – Project Cathycel CTQ2011-27347