title: Unraveling the Role of Formic Acid and the Type of Solvent in the Catalytic Conversion of Lignin: A Holistic Approach.
abstract: The role of formic acid together with the effect of the solvent type and their synergic interactions with a NiMo catalyst were studied for the conversion of lignin into bio-oil in an alcohol/formic acid media. The replacement of formic acid with H2or isopropanol decreased the oil yield to a considerable degree, increased the solid yield, and altered the nature of the bio-oil. The differences induced by the presence of H2were comparable to those observed in the isopropanol system, which suggests similar lignin conversion mechanisms for both systems. Additional semi-batch experiments confirmed that formic acid does not act merely as an in situ hydrogen source or hydrogen donor molecule. Actually, is seems to react with lignin through a formylation-elimination-hydrogenolysis mechanism that leads to the depolymerization of the biopolymer. This reaction competes with formic acid decomposition, which gives mainly H2and CO2, and forms a complex reaction system. To the best of our knowledge, this is the first time that the distinctive role/mechanism of formic acid has been observed in the conversion of real lignin feedstock. In addition, the solvent, especially ethanol, seems also to play a vital role in the stabilization of the depolymerized monomers and in the elimination/deformylation step.
authors.affiliation: Department of Chemistry, University of Bergen, Allegaten 41, N-5007, Bergen, Norway.
authors.forename: Mikel
authors.initials: M
authors.lastname: Oregui-Bengoechea
authors.affiliation: Chemical and Environmental Engineering Department, University of the Basque Country (UPV/EHU), Alameda Urquijo s/n, 48013, Bilbao, Spain.
authors.forename: Inaki
authors.initials: I
authors.lastname: Gandarias
authors.affiliation: Chemical and Environmental Engineering Department, University of the Basque Country (UPV/EHU), Alameda Urquijo s/n, 48013, Bilbao, Spain.
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Arias
authors.affiliation: Department of Chemistry, University of Bergen, Allegaten 41, N-5007, Bergen, Norway.
authors.forename: Tanja
authors.initials: T
authors.lastname: Barth
mesh_terms: D056804:Biofuels; D002384:Catalysis; D000431:Ethanol; D005561:Formates / Q000737:chemistry*; D006859:Hydrogen; D008031:Lignin / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*
chemical_list: D056804:Biofuels; D005561:Formates; D012997:Solvents; C030544:formic acid; D000431:Ethanol; D006859:Hydrogen; D008031:Lignin
keywords: biomass; heterogeneous catalysis; hydrogen; reaction mechanisms; solvent effects