Abstract
Lignin is a natural biopolymer present in lignocellulosic biomass. During paper pulp production with the Kraft process, it is solubilized and degraded in Kraft lignin and then burned to recover energy. In this paper, the solvolysis of Kraft lignin was studied in water and in water/alcohol mixtures to produce oligomers and monomers of interest, at mild temperatures (200–275 °C) under inert atmosphere. It was found that the presence of alcohol and the type of alcohol (methanol, ethanol, isopropanol) greatly influenced the amount of oligomers and monomers formed from lignin, reaching a maximum of 48 mg·glignin−1 of monomers with isopropanol as a co-solvent. The impact of the addition of various solid catalysts composed of a metal phase (Pd, Pt or Ru) supported on an oxide (Al2O3, TiO2, ZrO2) was investigated. In water, the yield in monomers was enhanced by the presence of a catalyst and particularly by Pd/ZrO2. However, with an alcoholic co-solvent, the catalyst only enhanced the formation of oligomers. Detailed characterizations of the products with FTIR, 31P-NMR, 1H-NMR and HSQC NMR were performed to elucidate the chemical transformations occurring during solvolysis. The nature of the active catalytic specie was also investigated by testing homogeneous palladium catalysts.
Highlights
Published: 21 July 2021Lignocellulose is one of the most abundant sources of renewable carbon on earth
Lignocellulose appears to be vital for the production of chemicals with a reduced carbon footprint compared to fossil resources
We were able to see the effect of different systems of water and alcohol as a co-solvent for the conversion of a Kraft lignin under sub-critical conditions (225 ◦ C, 40 bar) in a batch reactor
Summary
Lignocellulose is one of the most abundant sources of renewable carbon on earth It has been identified as a renewable source of energy and chemicals, and is used as is in various applications from energy to animal feed, being as well an ideal candidate for replacing some of our chemical needs from the petroleum chain. In this approach, lignocellulose appears to be vital for the production of chemicals with a reduced carbon footprint compared to fossil resources. Hemicelluloses and lignin are dissolved and degraded in liquid phase, called black liquor, as sugars, organic acids and Kraft lignin. This black liquor is concentrated and burnt to Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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