Lignin-Derived Syringol and Acetosyringone from Palm Bunch Using Heterogeneous Oxidative Depolymerization over Mixed Metal Oxide Catalysts under Microwave Heating

Abstract

Biomass valorization to building block chemicals in food and pharmaceutical industries has tremendously gained attention. To produce monophenolic compounds from palm empty fruit bunch (EFB), EFB was subjected to alkaline hydrothermal extraction using NaOH or K2CO3 as a promotor. Subsequently, EFB-derived lignin was subjected to an oxidative depolymerization using Cu(II) and Fe(III) mixed metal oxides catalyst supported on γ-Al2O3 or SiO2 as the catalyst in the presence of hydrogen peroxide. The highest percentage of total phenolic compounds of 63.87 wt% was obtained from microwave-induced oxidative degradation of K2CO3 extracted lignin catalyzed by Cu-Fe/SiO2 catalyst. Main products from the aforementioned condition included 27.29 wt% of 2,4-di-tert-butylphenol, 19.21 wt% of syringol, 9.36 wt% of acetosyringone, 3.69 wt% of acetovanillone, 2.16 wt% of syringaldehyde, and 2.16 wt% of vanillin. Although the total phenolic compound from Cu-Fe/Al2O3 catalyst was lower (49.52 wt%) compared with that from Cu-Fe/SiO2 catalyst (63.87 wt%), Cu-Fe/Al2O3 catalyst provided the greater selectivity of main two value-added products, syringol and acetosyrigone, at 54.64% and 23.65%, respectively (78.29% total selectivity of two products) from the NaOH extracted lignin. The findings suggested a promising method for syringol and acetosyringone production from the oxidative heterogeneous lignin depolymerization under low power intensity microwave heating within a short reaction time of 30 min.

Catalytic Oxidative Depolymerization of Sodium Lignosulfonate into Valuable Esters over CuxO/m‐Sep Catalyst in H2O Solvent Systems

“…Generally, carrier can provide acid and base active sites, increase the specific surface areas, improve the stability of active components, and reduce the preparation cost of catalyst. For example, CeO 2 , [19] TiO 2 , [20] oyster shells, [21] porous carbons, [22] MOFs, [23] zeolite, [24] and silica [25] have been proved as excellent catalyst carriers in oxidative depolymerization of lignin. Among them, sepiolite (Sep) is a kind of native clay mineral with favourable porosity, alkaline and acidic sites, and good thermal stability, these properties had made it become an excellent adsorption materials and promising catalyst carrier [26] .…”