Hydrodeoxygenation of Propylphenols on a Niobia-Supported Platinum Catalyst : Ortho, Meta, Para Isomerism, Reaction Conditions, and Phase Equilibria

Abstract

The alkylphenols found in liquefied lignocellulose could become a source of bio-based aromatic hydrocarbons for fuel components. In the hydrodeoxygenation (HDO) of alkylphenols, hydroxyl groups must be removed while avoiding the hydrogenation of the aromatic ring. Here, the HDO of propylphenols is studied using a Pt/Nb2O5 catalyst and n-tetradecane solvent. HDO experiments are performed using different reaction conditions of batch residence time (0–161 min gcat greactant −1), pressure (20–30 bar H2), and temperature (300–375 °C). HDO is studied with ortho-, meta-, and para-propylphenol. The influence of vapor–liquid equilibrium and chemical equilibrium are assessed using thermodynamic calculations. Almost full deoxygenation is attained in the experiments; the main products are propylbenzene and propylcyclohexane. The study finds that, of the isomers, 4-propylphenol is the most favorable for forming propylbenzene (77% maximum selectivity), whereas 2-propylphenol is the least favorable (55% maximum selectivity). Additionally, the reactivity of propylbenzene in the test conditions is detrimental to its selectivity after 5 min gcat greactant −1. Finally, the temperature at which the process favors propylbenzene is found to shift as a function of pressure; at 20 bar, propylbenzene is favored at 350 °C and at 30 bar, it is favored at 375 °C.