Fractionation of lignin using organic solvents: A combined experimental and theoretical study

Veerapandian Ponnuchamy,Oihana Gordobil,René Herrera Diaz,Anna Sandak,Jakub Sandak

doi:10.1016/j.ijbiomac.2020.11.139

Abstract

Refining of industrial lignin to produce homogeneous fractions is essential for high-value applications. However, the understanding of key interactions between a variety of solvents with lignin polymer is still uncertain. In this work, single-step fractionation of industrial hardwood kraft lignin (HKL) using organic solvents of different polarities – ethanol, acetone, diethyl ether and hexane – was investigated by combining an experimental and theoretical approach. Experimental results revealed that higher polarity solvents (ethanol and acetone) exhibited higher solubility yield compared to moderate and low polarity solvents. The chemical differences between lignin fractions were proven by pyrolysis gas chromatography mass spectrometry and near infrared spectroscopy. Density functional theory (DFT) results indicated that ethanol presented higher interaction energy followed by acetone, diethyl ether and hexane, which was consistent with experimental findings. Hydrogen bond and non-covalent interaction results from DFT demonstrated that the predominant interaction was found for high polarity of ethanol over other solvents and γ-OH in the lignin model is the key site.

Highlights

Reduction and revalorization of industrial by-products is an environmental and social challenge
Conclusions based on the Density functional theory (DFT) calculation were consistent with the experimental results, where both methods found that ethanol makes stronger interaction with lignin, which eventually facilitates greater solubility
Experimental results have shown that ethanol and acetone drive demethoxylation reaction, which can be compared to the DFT-optimized isolated lignin model with different solvent environments where we have found some significant changes in the structural bond parameters with ethanol and acetone environments

Summary

Introduction

Reduction and revalorization of industrial by-products is an environmental and social challenge. Kraft pulping process is the standard method for delignification of wood to convert it to paper pulp. This industrial process annually produces a large kraft lignin-rich residual stream that is typically combusted, resulting in low-value utilization [1]. It is still difficult to understand lignin chemistry and structure-properties relationships. This industrial waste has revealed high potential for numerous applications, and over the years, kraft lignin has been evaluated as a renewable source for the production of fine chemicals and gaseous products

Methods

Results

Conclusion