Biorefining of Lignocellulose into Structural Polymers By Thermochemical Dissolution Processes

Over 181.5 billion tons per year of lignocellulosic biomass is produced each year and such large abundance motivates its use as renewable feedstocks for chemicals.¹ Lignocellulose is a composite material composed of three structural polymers: cellulose (40-60%), hemicellulose (10%-40%), and lignin (15%-30%).² Biorefining pretreatments facilitating the fractionation of lignocellulose into structural polymers is a key step for integrating biogenic feedstocks into chemical supply chains. Current industrial efforts for biorefining have focused on valorizing carbohydrate fractions (e.g., cellulose, hemicellulose) into value-added products (e.g., paper pulp, bioethanol). However, the remaining fraction, lignin, is primarily incinerated to produce low grade heat.² As lignin is the largest biogenic source for aromatics and is rich in chemical functionalities, biorefining processes focusing on the recovery of lignin could expand product lines and the economic competitiveness of biorefineries.

The present research develops a thermochemical dissolution process to rapidly fractionate lignocellulose into cellulosic and lignin-rich product fractions. Lignocellulosic feedstocks are fractionated in batch reactors using commercially available organic bases and polar aprotic solvents. Thermochemical dissolution of lignocellulose proceeds under carbon dioxide atmospheres (2-5 bar), elevated temperatures (150-200 °C), and brief batch holding times (30-60 min), resulting with upwards of 70 wt% lignocellulose dissolution and 90 wt% lignin removal. A suite of solvent candidates are screened for dissolution efficacies and relationships between solvent properties and resultant lignin extractions are offered. Further insights on lignocellulose dissolution are provided by analysis of the residual pulps and regenerated lignins by spectroscopic methods and microscopy. The present research advances a rapid biorefining process consisting of commercial reagents to fractionate lignocellulose into cellulosic and lignin-rich product fractions, both of which can be used downstream as feedstocks for biobased, value-added materials and chemicals.

References

(1) Dahmen, N.; Lewandowski, I.; Zibek, S.; Weidtmann, A. Integrated lignocellulosic value

chains in a growing bioeconomy: Status quo and perspectives. GCB Bioenergy. 2019, 11, 107–117.

(2) Schutyser, W.; Renders, T.; Van den Bosch, S.; Koelewijn, S. F.; Beckham, G. T.; Sels, B. F. Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading. Chem. Soc. Rev. 2018, 47, 852—908.