Effects of Gamma-Valerolactone Assisted Fractionation of Ball-Milled Pine Wood on Lignin Extraction and Its Characterization as Well as Its Corresponding Cellulose Digestion

Muhammad Ajaz Ahmed,Arsalan A Raja,Jae Hoon Lee,Joon Weon Choi

doi:10.3390/app10051599

Abstract

Gamma-valerolactone (GVL) was found to be an effective, sustainable alternative in the lignocellulose defragmentation for carbohydrate isolation and, more specifically, for lignin dissolution. In this study, it was adapted as a green pretreatment reagent for milled pinewood biomass. The pretreatment evaluation was performed for temperature (140–180 °C) and reaction time (2–4 h) using 80% aqueous GVL to obtain the highest enzymatic digestibility of 92% and highest lignin yield of 33%. Moreover, the results revealed a positive correlation (R2 = 0.82) between the lignin removal rate and the crystallinity index of the treated biomass. Moreover, under the aforementioned conditions, lignin with varying molecular weights (150–300) was obtained by derivatization followed by reductive cleavage (DFRC). 2D heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC-NMR) spectrum analysis and gel permeation chromatography (GPC) also revealed versatile lignin properties with relatively high β-O-4 linkages (23.8%–31.1%) as well as average molecular weights of 2847–4164 with a corresponding polydispersity of 2.54–2.96, indicating this lignin to be a heterogeneous feedstock for value-added applications of biomass. All this suggested that this gamma-valerolactone based pretreatment method, which is distinctively advantageous in terms of its effectiveness and sustainability, can indeed be a competitive option for lignocellulosic biorefineries.

Highlights

In the context of the non-sustainable supply of fossil fuels, lignocelluloses have emerged as one potentially suitable option to theoretically swamp the existing petroleum-based fuels [1]. These lignocellulosic substrates are highly likely to shape the future of the bioeconomy given their sustainable supply, relative abundance and readily collectible nature [2]
Pinewood biomass was chosen as a model substrate in this study
To observe the effects of GVL fractionation under different thermal conditions on the milled pinewood composition, a reaction was conducted for 2–4 h in the presence of 80% aqueous GVL with temperature varying from 120 ◦ C to 160 ◦ C

Summary

Introduction

In the context of the non-sustainable supply of fossil fuels, lignocelluloses have emerged as one potentially suitable option to theoretically swamp the existing petroleum-based fuels [1] These lignocellulosic substrates are highly likely to shape the future of the bioeconomy given their sustainable supply, relative abundance and readily collectible nature [2]. These biomasses, in their typical native conformation, are composed of sugar polymers of glucose and xylose and are surrounded by a protective sheath of lignin [3]. The complexity of the cell wall structure, degree of polymerization, cellulose crystallinity, extent of lignification and compositional heterogeneity even within one species of biomass, etc. [6,7] are such major factors

Methods

Results

Conclusion