Surface kinetics and transport phenomena modelling for furfural hydrotreatment over Pd/C in isopropanol and tetrahydrofuran

Abstract

Extensive experimental and computational study of hemicellulose-derived furfural hydrogenation, hydrodeoxygenation, oligomerisation and etherification has been conducted over Pd/C catalyst. In-situ reduction of PdO surfaces was observed, forming predominately Pd(111). Tetrahydrofurfuryl alcohol was observed as the main product. Selected solvent (solventless conditions, tetrahydrofuran, isopropanol), atmosphere (nitrogen, hydrogen), temperature (100–200 °C), pressure (25–75 bar) and stirring speed were varied. A micro-kinetic model was developed incorporating thermodynamics (hydrogen solubility), mass transfer, adsorption, desorption and surface reactions. The above-listed phenomena and their contribution to the surface coverages, TOF’s and global reaction rates were studied. Approximately 66% of active sites were estimated to be covered by the solvent, 5% by furanic species, while hydrogen coverage was low and limiting. Both furfural ring and aldehyde group hydrogenation have low activation energies (19.1 kJ mol−1and 23.5 kJ mol−1), although subsequent hydrogenation of tetrahydrofurfural (Ea=42.5 kJ mol−1) is preferred at higher temperatures compared to furfuryl alcohol (Ea=24.0 kJ mol−1) hydrogenation. Complete hydrogenation can be achieved at room temperature, while deoxygenation becomes considerable above 150 °C (Ea = 59.6 kJ mol−1), leading to complete conversion in most tests, yielding up to 77% tetrahydrofurfuryl alcohol at 75 bar in isopropanol.