One-Step Valorization of Calcium Lignosulfonate To Produce Phenolics with the Addition of Solid Base Oxides in the Hydrothermal Reaction System

A new process, named one-step valorization of calcium lignosulfonate (CSL), has been proposed and used to produce phenolics via the addition of solid base oxides in a hydrothermal reaction system. A series of solid base oxides derived from layered double hydroxides (LDHs) were prepared by introducing ethanol. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses, temperature-programmed desorption of CO2 (CO2-TPD), Brunauer–Emmett–Teller (BET), flame atomic absorption spectrometry (FAAS), and X-ray photoelectron spectroscopy (XPS). Catalytic tests revealed that the liquid yield was approximately 75.82% under the action of NiMgFeOx during CSL depolymerization. Meanwhile, the solid residue accounted for only 19.71%, and the rest of the gaseous product was composed primarily of CO2. In the liquid product, the selectivity of phenolics was approximately 78.75% (24.19% phenol, 46.94% guaiacol, and 7.62% syringol). The gel permeation chromatography (GPC) analysis of the tetrahydrofuran soluble residues showed that CSL was efficiently depolymerized. Moreover, NiMgFeOx was recyclable and exhibited no significant loss of its catalytic activity after four runs.