One-pot depolymerization of forest residues to potential aviation fuel over hybrid zeolite – N-doped activated carbon supported NiMo catalyst

Abstract

In this work, sawdust and bark are depolymerized by catalytic reductive liquefaction using a bimetallic NiMo catalyst, with the aim to generate bio-fuel components in a single reaction step, that potentially could be used to produce sustainable aviation fuel (SAF). The hybrid support Zeolite Y combined with N-doped on activated carbon (YNAC) was synthesized from zeolite Y (silica/alumina ratio, SAR = 80) and N-doped activated carbon (NAC). The effect of temperature, pressure, and catalyst loading were systematically investigated to obtain conditions favorable for the yield and quality of the liquid product. The result at 400 °C, 20 bar H₂ (at room temperature), 4 h residence time with 30 wt% catalyst loading of NiMo@YNAC (75:25) showed the lowest solid yields, which was 3.9 wt% when using sawdust. The solid yield increased to 18.2 wt% when using bark and was intermediate (8.4 wt%) when using a sawdust/bark blend with 8/2 wt ratio. Sawdust was mainly converted into a liquid product consisting of cycloalkanes (C₄-C₇) (48.1 wt%), aromatics (2.1 wt%), phenolic compounds (15.8 wt%), and a heavy oil fraction (9.2 wt%). Meanwhile, bark was converted into similar compounds, however, with higher yields of mainly naphthenic and biphenyl components. The catalytic activity of NiMo on other supports such as ɤ-Al₂O₃, ZrO₂, TiO₂, and CeO₂ were also examined at the same conditions as NiMo@YNAC (75:25). Moreover, acidic washing of the bark was very beneficial resulting in that the solid yield significantly decreased, from 18 % to 6 %, while the bio-oil yield was improved (from 78 % to 91 %). The results showed that the NiMo@YNAC (75:25) catalyst with high deoxygenation and hydrogenation effects is a promising candidate for depolymerization of biomass into biofuels.