Solventless hydrodeoxygenation of isoeugenol and dihydroeugenol in batch and continuous modes over a zeolite-supported FeNi catalyst

Abstract

A low-cost bimetallic bifunctional 5–5 wt% FeNi/H-Beta-300 catalyst was investigated in solventless hydrodeoxygenation of lignin-derived model compounds isoeugenol or dihydroeugenol in batch and continuous modes. The catalyst was characterized in detail by laser diffraction, scanning electron microscopy–energy-dispersive X-ray microanalysis, inductively coupled plasma–optical emission spectrometry, transmission electron microscopy, Fourier-transform infrared spectroscopy with pyridine, X-ray diffraction, Mössbauer spectroscopy, X-ray absorption spectroscopy, hydrogen temperature programmed reduction, nitrogen physisorption, thermogravimetric analysis, oxygen temperature-programmed oxidation, organic elemental analysis, soluble coke extraction with dichloromethane, and Raman spectroscopy. The composition of the reaction mixture was analysed by GC-FID, GC-MS, SEC and Karl-Fischer titration, while microGC-TCD was used for the analysis of the gas phase. Selectivity of 80% to the desired oxygen-free compounds was obtained at ca. 80% of the initial dihydroeugenol conversion with 0.3 g of catalyst at 300 °C and 30 bar of hydrogen with a residence time of 12 min. Catalyst deactivation occurred via aliphatic coke formation which resulted not only in a decrease in conversion but also significant selectivity changes with increasing time-on-stream. The apparent activation energy of dihydroeugenol hydrodeoxygenation in solventless isoeugenol hydrodeoxygenation was calculated to be 6.3 kJ mol⁻¹ ascribed to both external mass transfer limitations of hydrogen dissolved in dihydroeugenol and by rapid catalyst deactivation in the initial isoeugenol hydrogenation. The spent catalyst was successfully regenerated by coke oxidation and subsequently reused.