Catalytic Depolymerization of a Lignin-Rich Corncob Residue into Aromatics in Supercritical Ethanol over an Alumina-Supported NiMo Alloy Catalyst

Abstract

A one-pot process for the depolymerization of lignin-rich corncob residue (LRCR) is investigated in supercritical ethanol over an alumina supported NiMo (NiMo/Al) alloy catalyst. The LRCR, as a major by-product in corncob enzymatic hydrolysis process, was completely liquefied and effectively transformed into aromatic compounds without the formation of tar or char under optimal reaction condition. Reaction temperature, time, solvent and initial hydrogen pressure have significant effects on the depolymerization of LRCR. The highest overall aromatic yield of 255.4 mg/g LRCR with 57.9 wt % alkylphenols (e.g., 4-ethylphenol, 2,5-diethylphenol and 2,6-diisopropylphenol) was achieved with initial 27.6 bar (gauge) hydrogen in supercritical ethanol at 320 ºC for 7.5 h. The depolymerization of LRCR is also examined over Ni/γ-Al2O3, Mo/γ-Al2O3, and the physical mixture of these two catalysts. The NiMo/Al alloy catalyst exhibits much higher activity than that of other catalysts, and a synergistic effect between Ni and Mo active species is proposed. Furthermore, XRD results show that Mo1.24Ni0.76 alloy is expected to be an important active species for the depolymerization reaction.

Catalytic Depolymerization of Enzymatic Hydrolysis Lignin into Monomers over an Unsupported Nickel Catalyst in Supercritical Ethanol

“…These unsupported nickel catalysts with eliminating the mass transport limitation of the support achieve the complete liquefaction and efficient depolymerization of EHL, obtaining the highest monomer yield of 28.5 wt %, which is much higher than that obtained in previous works. 18,19 The effects of the decomposition temperature and atmosphere of nickel formate on the monomer yield are examined. The roles of ethanol and catalyst as well as the reaction pathway of the primary monomers are also discussed.…”

“…Wang et al 18 employed 5 wt % Ni/C catalyst to depolymerize EHL and obtained an aromatic monomer yield of 12.1 wt % in methanol at 240 °C for 4 h with 3 MPa H 2 . Bai et al 19 reported the depolymerization of EHL with 15 wt % Ni/Al 2 O 3 and obtained an aromatic monomer yield of 10.3 wt % in ethanol at 320 °C for 7.5 h under 2.8 MPa H 2 . Nevertheless, the novel nickelbased catalyst with high activity needs to be further explored in order to obtain higher monomer yield.…”

Unexpected Formation of Organic Siloxanes alongside Ethylphenols in the Catalytic Hydrogenation of Waste Enzymatic Lignin

“…[19] Bai et al reported the depolymerization of lignin-rich corncob residue (LRCR) in supercritical ethanol at 320 C for 7.5 h with a yield of 147.9 mg g À1 (14.79 wt%) for alkylphenol. [20] Jiang et al used isopropanol as solvent and an in situ hydrogen source for the depolymerization of cellulolytic enzyme corn stover lignin and got a highest total monophenols yield of 8.14 wt% over Ni 50 Pd 50 /SBA-15. The yield of phenolic monomers was quite limited though bimetallic supported catalysts were applied.…”

Thermocatalytic Hydrodeoxygenation and Depolymerization of Waste Lignin to Oxygenates and Biofuels in a Continuous Flow Reactor at Atmospheric Pressure

“…The conditions were 27.6 bar of hydrogen in supercritical ethanol at 320 °C for 7.5 h and a NiMo−Al alloy catalyst. 21 As can be seen from previous research, most of the work reporting NiMo or any other catalysts to convert lignin or its monomers focus on high pressure in batch reactors with reaction times exceeding 6 h. Comparatively, for our case, the residence time in a continuous reactor at atmospheric pressure was only 5 s. Hence, in this study, we have focused on the atmospheric pressure, gas-phase conversion of softwood lignin that could be a cost-effective, industrially viable process.…”

“…They obtained 255 mg of aromatics per gram of LRCR with 58% by weight of alkylphenols. The conditions were 27.6 bar of hydrogen in supercritical ethanol at 320 °C for 7.5 h and a NiMo–Al alloy catalyst …”