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Selective catalytic tailoring of the H unit in herbaceous lignin for methyl p-hydroxycinnamate production over metal-based ionic liquids

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      Abstract

      Selective catalytic tailoring of herbaceous lignin for the production of methyl p-hydroxycinnamate (MPC).

      Abstract

      Selective valorization of lignin to achieve high value and commodity chemicals is attracting increasing attention. In this work, an efficient and reusable metal-based ionic liquid (MBIL) was developed for the selective tailoring of p-coumaric acid ester ( pCA), a typical p-hydroxyphenyl (H) unit, into methyl p-hydroxycinnamate (MPC). Under optimized conditions and in the presence of catalyst [Bmim][FeCl 4], a volatile aromatic product of 10.5 wt% was obtained, of which, 70.5% separated as pure MPC with an isolated yield of 71.1 mg g −1. FT-IR, 13C NMR, ANO and 2D HSQC demonstrated that the H unit was preferentially tailored from lignin, of which, 86.0 wt% of the H structure unit is cut off from lignin, with 70.6% being selectively converted to MPC. Further investigation demonstrated that MBIL prefers to tailor ester bonds compared to ether bonds using model compounds, and the superior catalytic ester bond cleavage performance exhibited by [Bmim][FeCl 4] can be ascribed to the relatively narrow energy gap between the lignin ester bond and [FeCl 4] anion and to the comparatively low absolute binding energy between the cation and anion through DFT calculations.

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      The catalytic valorization of lignin for the production of renewable chemicals.

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        Catalytic Transformation of Lignin for the Production of Chemicals and Fuels.

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          Formic-acid-induced depolymerization of oxidized lignin to aromatics.

          Lignin is a heterogeneous aromatic biopolymer that accounts for nearly 30% of the organic carbon on Earth and is one of the few renewable sources of aromatic chemicals. As the most recalcitrant of the three components of lignocellulosic biomass (cellulose, hemicellulose and lignin), lignin has been treated as a waste product in the pulp and paper industry, where it is burned to supply energy and recover pulping chemicals in the operation of paper mills. Extraction of higher value from lignin is increasingly recognized as being crucial to the economic viability of integrated biorefineries. Depolymerization is an important starting point for many lignin valorization strategies, because it could generate valuable aromatic chemicals and/or provide a source of low-molecular-mass feedstocks suitable for downstream processing. Commercial precedents show that certain types of lignin (lignosulphonates) may be converted into vanillin and other marketable products, but new technologies are needed to enhance the lignin value chain. The complex, irregular structure of lignin complicates chemical conversion efforts, and known depolymerization methods typically afford ill-defined products in low yields (that is, less than 10-20wt%). Here we describe a method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid that results in more than 60wt% yield of low-molecular-mass aromatics. We present the discovery of this facile C-O cleavage method, its application to aspen lignin depolymerization, and mechanistic insights into the reaction. The broader implications of these results for lignin conversion and biomass refining are also considered.
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            Author and article information

            Affiliations
            [1 ]School of Chemistry and Chemical Engineering
            [2 ]State Key Laboratory of Pulp and Paper Engineering
            [3 ]South China University of Technology
            [4 ]Guangzhou 510640
            [5 ]China
            [6 ]Beijing Key Laboratory of Ionic Liquids Clean Process
            [7 ]Institute of Process Engineering
            [8 ]Chinese Academy of Sciences
            [9 ]Beijing 100190
            [10 ]National Engineering Research Centre of Chemical Fertilizer Catalyst
            [11 ]School of Chemical Engineering
            [12 ]Fuzhou University
            [13 ]Fuzhou 350002
            Journal
            GRCHFJ
            Green Chemistry
            Green Chem.
            Royal Society of Chemistry (RSC)
            1463-9262
            1463-9270
            2018
            2018
            : 20
            : 16
            : 3743-3752
            10.1039/C8GC01252K
            © 2018

            http://rsc.li/journals-terms-of-use

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            Self URI (article page): http://xlink.rsc.org/?DOI=C8GC01252K

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