PNNL

Abstract

Efficient cleavage of ß-O-4 bonds in lignin to high-yield aromatic compounds for the potential production of fuels and chemicals is vital for the economics of the modern biorefinery industry. This work is distinct in that a detailed mechanistic analysis of the reaction pathways of veratrylglycero-ß-guaiacyl ether (VGE) catalyzed by transition-metal-free solid acid zeolite in aqueous conditions at high hydrogen pressure has been performed. VGE degradation produced high monomers yields (~87%), including guaiacol (48.2%), 1-(3,4-dimethoxyphenyl) ethanol (10.3%), 1-(3,4-dimethoxyphenyl)-2-propanol (6.1%), 3,4-dimethoxyphenylpropanol (4.7%), 3,4-dimethoxycinnamyl alcohol (4.1%), and 1,2-dimethoxy-4-propylbenzene (2%). The products were identified and confirmed by the in-situ solid-state magic angle spinning (MAS) 13C NMR in real-time conditions and the two-dimensional gas chromatography (GC×GC). A variety of products reveal the crucial role of hydrogen, water, and acid sites for heterolytic cleavage of the ß-O-4 bond in VGE. Decarbonylation, hydrogenolysis, hydrogenation, and dehydration reaction pathways are proposed and further validated using first-principles calculations. Keywords: acid catalysis, ß-O-4 cleavage mechanism, in-situ solid-state NMR, comprehensive two-dimensional gas chromatography, phenolic monomers