Reductive Catalytic Depolymerization of Semi-industrial Wood-Based Lignin.

Xiaojia Lu,Lucas Lagerquist,Henrik Grénman,Lionel Estel,Sébastien Leveneur,Kari Eränen,Jarl Hemming,Patrik Eklund

doi:10.1021/acs.iecr.1c03154

Abstract

The current work studies the reductive catalytic depolymerization (RCD) of lignin from a novel semi-industrial process. The aim was to obtain aromatic mono-, di-, tri-, and tetramers for further valorization. The substrate and products were characterized by multiple analytical methods, including high pressure size-exclusion chromatography (HPSEC), gas chromatography–mass spectrometry, GC-flame ionization detector (FID), GC-FID/thermal conductivity detector (TCD), and NMR. The RCD was studied by exploring the influence of different parameters, such as lignin solubility, reaction time, hydrogen pressure, reaction temperature, pH, type and loading of the catalyst, as well as type and composition of the organic/aqueous solvent. The results show that an elevated temperature, a redox catalyst, and a hydrogen atmosphere are essential for the depolymerization and stability of the products, while the reaction medium also plays an important role. The highest obtained mono- to tetramers yield was 98% and mono- to dimers yield over 85% in the liquid phase products. The reaction mechanisms influenced the structure of the aliphatic chain in the monomers, but left the phenolic structure along with the methoxy groups largely unaltered. The current work contributes to the development and debottlenecking of the novel and sustainable overall process, which utilizes efficiently all the fractions of wood, in line with the principles of green engineering and chemistry.

Highlights

One of the leading industrial and societal challenges of the 21st century is the shift from the intensive use of fossil resources to renewables in the production of chemicals, materials, and energy
Lignin is produced in large quantities (>300 billion tons) every year,[4] it has led to limited industrial applications due to its complex and varying molecular structure, broad molecular weight distribution, and variations in the physical−chemical properties.[5]
The solubility of lignin in organic solvents is not predictable, as it is determined by many factors such as chemical structure, molecular weight, and the presence of hydrophilic moieties in the lignin molecule.[23]

Summary

Introduction

One of the leading industrial and societal challenges of the 21st century is the shift from the intensive use of fossil resources to renewables in the production of chemicals, materials, and energy. This shift should be performed in a controlled and sustainable way, following the principles of green chemistry and engineering taking into account the societal and economic aspects. Lignin extracted from biomass is an essential renewable resource in novel biorefinery applications because it could be used to produce aromatic intermediates and fine chemicals, such as vanillin, phenols, guaiacol, eugenol, and so forth,[2,3] provided that efficient depolymerization technologies would exist. The extraction of lignin macromolecules from biomass in its reactive, non-condensed form and their efficient depolymerization methods to produce platform chemicals are the major bottlenecks in lignin utilization, as versatile techniques have already been developed for the further valorization of lignin monomers and dimers.[6−10]

Objectives

Results

Conclusion