Fractionation of Lignin with Decreased Heterogeneity: Based on a Detailed Characteristics Study of Sequentially Extracted Softwood Kraft Lignin

Rui Liu,Andrey Pranovich,Jarl Hemming,Stefan Willför,Annika Smeds,Luyao Wang,Hongbo Zhang,Chunlin Xu

doi:10.1021/acssuschemeng.1c04725

Rui Liu, Andrey Pranovich + Show 6 more

Open Access

https://doi.org/10.1021/acssuschemeng.1c04725

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Abstract

Industrial lignin fractionation is attracting increasing interest due to its enormous potential in the development of high value-added materials. However, the widely reported fractionation approaches are primarily focused on the separation of fractions with a low polydispersity index (PDI). In this study, based on the detailed characteristic examination of carefully sequential-extracted softwood Kraft lignin fractions, a novel method to isolate lignin fraction with decreased heterogeneity (LGF-dh), was established in consideration of impurities, elemental composition, molar mass distribution, carbohydrate content, functional hydroxyl content, and the content of lignin-relevant aromatic units. To characterize the mentioned properties, an elemental analyzer, SEC-MALS, GC–MS, GC-FID, Py/GC–MS, 31P-NMR, and HSQC-NMR were used to compare the differences of the sequential lignin fractions that were obtained by methyl tert-butyl ether (MTBE), ethyl acetate (EtOAc), ethanol (EtOH), methanol (MeOH), acetone, and dioxane. Moreover, a practical and feasible three-step extraction process was proposed to separate the low heterogeneity lignin fraction from industrial lignin according to the different solubilities of each fraction in the green cosolvent system of EtOH/water, MeOH/water, and acetone/water. Overall, this work presented a comprehensive study on the properties of softwood lignin as well as proposed a feasible and convenient method to reduce the heterogeneity of lignin, which would promote its valorization.

Highlights

Plant biomass is a widely accessible and renewable resource for the development of eco-friendly products, which contribute to minimizing the negative environmental effects caused by waste products from nonrenewable petroleum-based polymers
In order to have a general understanding of the composition of the Kraft lignin (KL), the fundamental properties of the sequentially extracted lignin were discussed in terms of their extractives, elemental content, molar mass distribution, carbohydrate content, functional hydroxyl groups content, and their pyrolysis products
In this study, based on a detailed characteristic examination of sequentially extracted technical softwood lignin fractions by methyl tert-butyl ether (MTBE), EtOAc, ethanol, methanol, acetone, and dioxane, we proposed a feasible and practicable sequential method to isolate lignin with reduced heterogeneity

Summary

Introduction

Plant biomass is a widely accessible and renewable resource for the development of eco-friendly products, which contribute to minimizing the negative environmental effects caused by waste products from nonrenewable petroleum-based polymers. The various reactive functional groups of lignin provide rich active sites ready for further modifications to satisfy the needs of the design of functional materials.[5−8] In addition, its favorable biocompatibility and amphiphilicity make lignin a promising biodegradable natural resource to be applied in the area of biomaterials and nanomedicine.[9−11] More notably, lignin and lignin-based products have generated substantial economic benefits, which has increased with an average annual growth of 2.28% from $599 million to $704 million in the last few years.[1] the large-scale commercial utilization of lignin is still severely limited due to the lack of well-refined industrial lignin with a narrow molecular weight distribution and a relatively uniform chemical structure.[12]

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