Effect of Mo content in Mo/Sepiolite catalyst on catalytic depolymerization of Kraft lignin under supercritical ethanol

Abstract

Lignin catalytic depolymerization (LCD) is generally considered as a sustainable and hopeful technology to obtain liquid fuel and high-value aromatic chemicals. However, a controllable and high-efficiency cleavage of lignin interlinkage has been demonstrated to be prominent challenge. Therefore, we report the catalytic depolymerization of Kraft lignin under supercritical ethanol by using a series of as-prepared Mo/sepiolite (SEP) with different Mo content. Mo/SEP catalysts present excellent activity for lignin deploymerization and Mo content significantly affects the conversion of lignin and yields of lignin oil (LO) and petroleum ether soluble product. This is attributed to the synergistically catalyzed effect among L/B acid sites, terminal oxygen and Mo active species. Amongst, 40Mo/SEP shows the highest lignin conversion (98.6%) and LO yield (84.3%) at 290 °C for 3 h, where the yield of PE-soluble product reaching to 70.8% (mainly monomers and dimers). Under these conditions, the obtained LO is mainly consisted of substituted alkylphenols and has a HHV of 34.69 MJ/kg, which is a significant increase from 22.83 MJ/kg of Kraft lignin. According to adequate analyses, the possible mechanism of LCD under supercritical ethanol over 40Mo/SEP was proposed. Wherein, the surface acid sites promote the break of lignin ether linkage (such as C–O bond) and terminal oxygen as hydrogen bond site activates ethanol molecules, then the synergistic effect between L/B acid sites and active Mo species enhance the hydrodeoxygenation and aromatic side-chain isomerization and alkylation reactions.