Enhancing Aromatic Production from Reductive Lignin Disassembly: in Situ O-Methylation of Phenolic Intermediates

Abstract

ABSTRACT:The selective conversion of lignin into aromatic compounds has the potential to serve as a "green" alternative to the production of petrochemical aromatics. Herein, we evaluate the addition of dimethyl carbonate (DMC) to a biomass conversion system that uses a Cu-doped porous metal oxide (Cu 20 PMO) catalyst in supercritical methanol (sc-MeOH) to disassemble lignin with little to no char formation. While Cu 20 PMO catalyzes C-O hydrogenolysis of aryl-ether bonds linking lignin monomers, it also catalyzes arene methylation and hydrogenation, leading to product proliferation. The MeOH/DMC co-solvent system significantly suppresses arene hydrogenation of the phenolic intermediates responsible for much of the undesirable product diversity via Omethylation of phenolic -OH groups to form more stable aryl-OCH 3 species. Consequently, product proliferation was greatly reduced and aromatic yields greatly enhanced with lignin models, 2-methoxy-4-propylphenol, benzyl phenyl ether, and 2-phenoxy-1-phenylethan-1-ol. In addition, organosolv poplar lignin (OPL) was examined as a substrate in the MeOH/DMC co-solvent system. The products were characterized by nuclear magnetic resonance spectroscopy ( 31 P, 13 C, and 2D 1 H-13 C NMR) and gas chromatography-mass spectrometry techniques. The co-solvent system demonstrated enhanced yields of aromatic products. INTRODUCTION.

Conversion of Lignin Models by Photoredox Catalysis

“…[13] Moreover, the b-O-4 linkage has the propensity to undergo structuralc hange during traditional depolymerization, whichi st he main cause of lignin's recalcitrance to upgrading. [15] Furthermore, reductiveb ond cleavage usually requires an external hydrogen source such as hydrogen gas that originates from fossil resources, [16] which is not ag reen approach. For instance, the high temperatures (> 80 8C) can cause dearomatization and deoxygenation of lignin and the proliferation of oxygen-containing products.…”

“…[14] Functional groups such as the free phenolsa nd g-alcohols commonly present in lignin are less tolerated in transitionmetal-catalyzed reactions owing to excessive oxidation andundesired bond cleavage. [15] Furthermore, reductiveb ond cleavage usually requires an external hydrogen source such as hydrogen gas that originates from fossil resources, [16] which is not ag reen approach.…”

Ethanol: A Promising Green Solvent for the Deconstruction of Lignocellulose

“…[65] The idea of using protection and stabilization reagents may inspiref uture researchi nto the deconstruction of lignin in ethanol for higher yields of monomers. Barret et al used dimethyl carbonate as a cosolventt os uccessfully promote the yields of the stable, depolymerized aromatic speciesu pon disassembling lignin in supercritical alcohol with CuMgAl catalyst.…”

“…Barret et al used dimethyl carbonate as a cosolventt os uccessfully promote the yields of the stable, depolymerized aromatic speciesu pon disassembling lignin in supercritical alcohol with CuMgAl catalyst. [65] The idea of using protection and stabilization reagents may inspiref uture researchi nto the deconstruction of lignin in ethanol for higher yields of monomers. [66] Deeper insights into the reaction mechanisms during lignocellulosed econstruction reactions in ethanol are needed.…”

Investigation of the Reaction Pathways of Biomass‐Derived Oxygenate Conversion into Monoalcohols in Supercritical Methanol with CuMgAl‐Mixed‐Metal Oxide

“…[1][2][3] Ar ecent approachf irst proposed by Ford and co-workersi nvolves the supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHDO)o fb iomass into monoalcohols and cyclohexyl alcohols with aC uMgAlc atalyst. [4][5][6][7][8] This process has an umber of advantages including very high yields (up to 121 wt %d ue to methanol incorporation and complete conversion of biomasst op roducts)o ff uel range alcohols, all reactions occurinasinglereactor,and it utilizes all fractionso fb iomass including the energy-rich lignin fraction.T he alcohol products could either potentiallyb eu sed directly as af uelo ru pgraded by condensation or oligomerization. [9][10][11] Other biomass conversion processes like enzymatic hydrolysis, supercritical water hydrolysis, or aqueous-phase hydrodeoxygenation require separate depolymerization and sugar conversion steps that lead to lower yields and higher processing costs.…”