Catalytic Liquefaction of Humin Substances from Sugar Biorefineries with Pt/C in 2-Propanol

The catalytic liquefaction of humins, the solid byproduct from the conversion of C6 sugars (glucose, fructose) to 5-hydroxymethylfurfural (HMF) and levulinic acid (LA), using a supported Pt/C catalyst in isopropanol (IPA) as the solvent was investigated. At bench mark conditions (400 °C, 7 h, 27 wt % catalyst on humin intake, 21 wt % humin on total intake (IPA and humins)), about 60% of the humins was converted to a humin oil. This oil was analyzed in detail (GC-MS, GCxGC-FID, GPC) and shown to consist of a mixture of monomers and oligomers belonging to various product classes (alkylphenolics, aromatics, aliphatic hydrocarbons). IPA was shown to be reactive under the prevailing reaction conditions and acts as a hydrogen donor for the humin depolymerization/hydrodeoxygenation reactions. A systematic study according to a central composite design (19 experiments) was performed to optimize the reaction conditions (T, humin intake, catalyst intake, and batch time) to obtain the highest humin conversion and alkylphenolics yield. The highest humin conversion was 72%, whereas the highest amount of alkylphenolics was 14% (based on GC detectables in the liquid phase after reaction). A reaction network is proposed based on structural proposals for humins and the main reaction products.