Characterization of Organosolv Birch Lignins: Toward Application-Specific Lignin Production.

Petter Paulsen Thoresen,Paul Christakopoulos,Claudia Crestini,Ulrika Rova,Heiko Lange,Leonidas Matsakas

doi:10.1021/acsomega.0c05719

Abstract

Organosolv pretreatment represents one of the most promising biomass valorization strategies for renewable carbon-based products; meanwhile, there is an overall lack of holistic approach to how extraction conditions affect the suitable end-usages. In this context, lignin extracted from silver birch (Betula pendula L.) by a novel hybrid organosolv/steam-explosion treatment at varying process conditions (EtOH %; time; catalyst %) was analyzed by quantitative NMR (1H–13C HSQC; 13C NMR; 31P NMR), gel permeation chromatography, Fourier transform infrared (FT-IR), Pyr-gas chromatography–mass spectroscopy (GC/MS), and thermogravimetric analysis, and the physicochemical characteristics of the lignins were discussed regarding their potential usages. Characteristic lignin interunit bonding motifs, such as β-O-4′, β-β′, and β-5′, were found to dominate in the extracted lignins, with their abundance varying with treatment conditions. Low-molecular-weight lignins with fairly unaltered characteristics were generated via extraction with the highest ethanol content potentially suitable for subsequent production of free phenolics. Furthermore, β-β′ and β-5′ structures were predominant at higher acid catalyst contents and prolonged treatment times. Higher acid catalyst content led to oxidation and ethoxylation of side-chains, with the concomitant gradual disappearance of p-hydroxycinnamyl alcohol and cinnamaldehyde. This said, the increasing application of acid generated a broad set of lignin characteristics with potential applications such as antioxidants, carbon fiber, nanoparticles, and water remediation purposes.

Highlights

A plethora of everyday items are produced from petroleumbased compounds[1] and contribute substantially to the global economy,[2] but the use of nonrenewable carbon resources is the driver behind several negative environmental impacts such as global warming and air pollution.[3]
Characterization of Lignin Samples. 1H−13C Heteronuclear single quantum coherence spectroscopy (HSQC) analysis revealed the most important structural characteristics of lignins originating from the various treatments (Table 1)
Varying treatment conditions during the extraction of lignins by hybrid steam explosion/organosolv processing generate lignins with a wide range of structural and chemical properties

Summary

Introduction

A plethora of everyday items are produced from petroleumbased compounds[1] and contribute substantially to the global economy,[2] but the use of nonrenewable carbon resources is the driver behind several negative environmental impacts such as global warming and air pollution.[3] An often neglected renewable component, at least when compared to the attention that sugar and syngas receives[4] in the transition to a biomassbased society, is lignin, whose production in 2015 reached 100 million tonnes, out of which, only 2% were sold for applications different from energy-production through burning.[5]. Important to note is that the mode of extraction of lignins will affect their final chemistry as both bond cleavage and formation occur to varying extents during the process. The most common methods for lignin extraction were recently reviewed by Wang et al.,[8] where the various extents of bond

Methods

Results

Conclusion