Multiscale analysis of lignocellulose recalcitrance towards OrganoCat pretreatment and fractionation

Dennis Weidener,Sabine K Dietrich,Pablo Domínguez De María,Holger Klose,Murali Dama,Walter Leitner,Benedict Ohrem,Markus Pauly,Philipp M Grande

doi:10.1186/s13068-020-01796-8

Abstract

BackgroundBiomass recalcitrance towards pretreatment and further processing can be related to the compositional and structural features of the biomass. However, the exact role and relative importance to those structural attributes has still to be further evaluated. Herein, ten different types of biomass currently considered to be important raw materials for biorefineries were chosen to be processed by the recently developed, acid-catalyzed OrganoCat pretreatment to produce cellulose-enriched pulp, sugars, and lignin with different amounts and qualities. Using wet chemistry analysis and NMR spectroscopy, the generic factors of lignocellulose recalcitrance towards OrganoCat were determined.ResultsThe different materials were processed applying different conditions (e.g., type of acid catalyst and temperature), and fractions with different qualities were obtained. Raw materials and products were characterized in terms of their compositional and structural features. For the first time, generic correlation coefficients were calculated between the measured chemical and structural features and the different OrganoCat product yields and qualities. Especially lignin-related factors displayed a detrimental role for enzymatic pulp hydrolysis, as well as sugar and lignin yield exhibiting inverse correlation coefficients. Hemicellulose appeared to have less impact, not being as detrimental as lignin factors, but xylan-O-acetylation was inversely correlated with product yield and qualities.ConclusionThese results illustrate the role of generic features of lignocellulosic recalcitrance towards acidic pretreatments and fractionation, exemplified in the OrganoCat strategy. Discriminating between types of lignocellulosic biomass and highlighting important compositional variables, the improved understanding of how these parameters affect OrganoCat products will ameliorate bioeconomic concepts from agricultural production to chemical products. Herein, a methodological approach is proposed.

Highlights

Biomass recalcitrance towards pretreatment and further processing can be related to the compositional and structural features of the biomass
Many factors have been related to the recalcitrance of the plant cell walls: Changes in the celluloses degree of polymerization, its crystallinity, and pore size can interfere with the hydrogen-bond network of the fibers and are believed to facilitate accessibility of degrading enzymes [6]
We investigated the relationship between the plant wall composition of ten different lignocellulosic materials and its role in an acidic pretreatment, using OrganoCat as prototypical approach for full valorization

Summary

Introduction

Biomass recalcitrance towards pretreatment and further processing can be related to the compositional and structural features of the biomass. Lignocellulosic biomass (or the plant cell wall) is the most abundant renewable resource on earth It is mainly composed of polysaccharides—such as cellulose and various hemicelluloses—and the aromatic macromolecule lignin. Weidener et al Biotechnol Biofuels (2020) 13:155 as cellulose fibrils embedded in a matrix of non-cellulosic polysaccharides and lignin providing strength and mechanical support to the plant [2] This complex structural and compositional nature of the material often hampers an efficient fractionation, a phenomenon known as recalcitrance. Despite many studies on lignocellulose recalcitrance, it is still unclear how the structural and chemical features hamper a successful and efficient biomass pretreatment [5]. Hemicelluloses are amorphous and are relatively well hydrolyzed by, e.g., dilute acids in pretreatment processes [5] These hemicelluloses represent a physical barrier limiting accessibility of the cellulosic fiber. A reduced acetyl content in corn stover seems to improve effectiveness of these enzymes [11], but might still depend strongly on the chemical structure of xylan and/or the interaction with other wall polymers [5]

Methods

Results

Conclusion