Synergistic Effect of EtOAc/H2O Biphasic Solvent and Ru/C Catalyst for Cornstalk Hydrolysis Residue Depolymerization

An EtOAc/H₂O biphasic solvent–Ru/C coupling biorefinery process was developed to selectively produce aromatics from cornstalk hydrolysis residue (CHR). In this process, CHR was depolymerized in an ethyl acetate (EtOAc)/H₂O biphasic solvent system over Ru/C catalyst, which produced aromatics and carbohydrates instantly separated by EtOAc and H₂O. Most lignin in CHR was converted to aromatics and nonvolatile fractions, accompanied with partial degradation of cellulose. Optimized results showed that more than 42.7% of aromatics can be obtained under 260 °C for 5 h without external hydrogen pressure. Monophasic and biphasic parallel experimental results show that the strong lignin dissolving ability of the biphasic dissolution/separation system is helpful for aromatics production and separation, which promoted CHR depolymerization over Ru/C. Furthermore, CHR, products, depolymeirzation residue solid (DRS), and catalysts were carefully characterized by gas chromatography (GC-MS), Fourier transform infrared (FT-IR), gel permeation chromatrography (GPC), high-performance liquid chromatrography mass spectrometry (HPLC-MS), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. Results demonstrated that the biphasic solvent–Ru/C coupling process can significantly alleviate repolymerization reactions. Based on these analysis results, the catalytic process in biphasic EtOAc/H₂O was discussed. This work demonstrates that such a green biphasic catalytic/separation coupling system highlights a promising route for efficient biomass degradation and product separation at mild conditions without external hydrogen pressure.