Exploratory catalyst screening studies on the liquefaction of model humins from C6 sugars

Abstract

A catalyst screening study is reported on the liquefaction of humins, the solid byproducts from C6 sugar biorefineries for levulinic acid and 5-hydroxymethylfurfural production. Experiments were carried out in a batch reactor using an artificial model of humin derived from glucose with isopropanol (IPA) as the solvent at 400 °C for a 3 h batchtime. Initial studies using noble metal catalysts (Rh, Pt, Pd, Ru) on a carbon support revealed that Pt was the best catalyst in terms of humin conversion (77%) and amounts of alkylphenolics and aromatics in the product oil (GCxGC-FID). Subsequent support screening studies (TiO₂, ZrO₂, CeO₂) were performed using Pt as the active metal and the results were compared with Pt/C. Detailed liquid product analysis (GPC, GC-MS, GCxGC) including blank reactions in the absence of humins revealed that the humins are mainly converted to monomeric alkylphenolics and aromatics oligomers (GPC) and (GC). IPA was shown not to be inert and is converted to acetone and hydrogen, and the latter is the hydrogen source for the various metal catalysed hydrogenolysis and hydro(deoxy)genation reactions. In addition, acetone is converted to aldolcondensation products (like methylisobutylketone, MIBK) and hydrogenation products derived thereof. The best results were obtained with Pt/C when considering humin conversion. However, Pt/CeO₂ was shown to be more attractive when considering the amounts of alkylphenolics in the product oils (20.4 wt% based on humin intake).