Towards Lignin-Derived Chemicals Using Atom-Efficient Catalytic Routes

Abstract

Efficient valorization of lignin into fuels and chemicals will boost the lignocellulose biorefinery industry and reduce our dependence on fossil fuel feedstocks. Selective cleavage/conversion of lignin into specific monomers is the utmost goal in current biorefinery research; this can be achieved by controlling the catalyst properties and reaction conditions. Atom-efficient catalytic routes can play a significant role in converting lignin monomers into desirable products. Lignocellulose fractionation methodology, product separation technology, and process mass efficiency are also important for lignin biorefineries. Lignin is a potential non-fossil resource of diverse functionalized phenolic units. The most important lignin-derived monomers are 4-alkylphenols, 4-hydroxybenzaldehydes, 4-hydroxybenzoic acids, and 4-hydroxycinnamic acids/esters. Efficient transformation of lignin and/or its monomers into valuable aromatics and their derivatives is crucial, not only for a sustainable lignocellulose biorefinery, but also to reduce our dependence on fossil feedstocks. This review provides a concise account of the recent advances in lignocellulose fractionation/lignin depolymerization processes towards lignin-derived monomers. Subsequently, numerous potential atom-efficient catalytic routes for upgrading lignin monomers into drop-in chemicals and new polymer building blocks are discussed. Lignin is a potential non-fossil resource of diverse functionalized phenolic units. The most important lignin-derived monomers are 4-alkylphenols, 4-hydroxybenzaldehydes, 4-hydroxybenzoic acids, and 4-hydroxycinnamic acids/esters. Efficient transformation of lignin and/or its monomers into valuable aromatics and their derivatives is crucial, not only for a sustainable lignocellulose biorefinery, but also to reduce our dependence on fossil feedstocks. This review provides a concise account of the recent advances in lignocellulose fractionation/lignin depolymerization processes towards lignin-derived monomers. Subsequently, numerous potential atom-efficient catalytic routes for upgrading lignin monomers into drop-in chemicals and new polymer building blocks are discussed. used for holding a solid catalyst during the reaction in an autoclave reactor so that efficient catalyst’s recovery/reusability can be achieved when one of the products is a solid (here: pulp). an insoluble residue obtained after the two-step acid hydrolysis of lignocellulose with 72 wt% H2SO4 at room temperature ca. 20°C as well as with 3–4 wt% H2SO4 for a few hours at high temperatures ca.120°C. obtained from kraft pulping process (also known as sulfate pulping process) that involves fractionation of lignocellulose into cellulose, hemicellulose, and lignin in the presence of a hot mixture of aqueous NaOH and Na2S solution. in the paper industry, organosolv is a pulping process that uses an organic solvent to solubilize lignin and hemicellulose, giving pure cellulose fibers from woody lignocellulose. a chemical process for producing pulp from woody lignocellulose using NaOH solution. In this process, anthraquinone is used as a pulping additive that will help to prevent carbohydrate degradation so that it can be efficiently converted into useful molecules and fuels like glucose and bioethanol. a chemical reaction involving the transfer of simple alkyl groups, such as methyl or ethyl from preferably one organic compound to another, especially between benzene rings, to produce valuable chemicals.