Multiscale analysis of lignocellulose recalcitrance towards OrganoCat pretreatment and fractionation

Abstract

Background: Biomass 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. Results: The 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. Conclusion: These 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.

Recent advances in the valorization of plant biomass

“…To solve these problems, OrganoCat was recently proposed, which is similar to Organosolv but employs a biphasic solvent system (oxalic acid and 2-methyltetrahydrofuran); nevertheless, it was developed based on mature acid pretreatment [ 65 ]. In other words, OrganoCat is an improvement of the mature acid pretreatment method, in which oxalic acid and 2-methyltetrahydrofuran (2-MeTHF) are applied as a catalyst and an extractive phase for hydrolysing amorphous hemicellulose and extracting lignin in situ from the reactive phase, respectively, resulting in three produce streams, namely cellulose-rich solid pulp, organic phase-containing lignin, and acid-containing aqueous phase-containing hemicellulose [ 66 , 67 ]. To date, this technology has been studied on several different types of biomass feedstocks, but the treatment effect on each biomass feedstock varies greatly.…”

“…For instance, rice straw seemed to be well suited for OrganoCat, which was accompanied by 98.99% cellulose recovery, 88.79% hemicellulose solubilization, and 71.46% lignin removal after OrganoCat treatment [ 68 ]. By contrast, OrganoCat does not have much effect on eucalyptus, and only low amounts of lignin and sugars can be extracted [ 66 ]. As a method designed for refinery applications, OrganoCat has some promising characteristics, such as easy and effective fractioning, fewer sugar degradation products, and more efficient recovery efficiency, which result in minimized energy and mass consumption [ 69 ].…”

“…In addition, during the OrganoCat process, lignin can be extracted in situ from the reactive phase by the 2-MeTHF phase, therefore, maintaining the low concentration and structural integrity of lignin and reducing the occurrence of condensation reactions while retaining a higher number of aryl ether linkages, which is more beneficial for lignin valorization [ 66 ]. Surprisingly, the monomer composition of lignin from different lignocellulosic feedstocks showed different changes after the OrganoCat process, among which those from beech wood and Miscanthus were not changed.…”

Fractionation of Lignocellulosic Biomass using the OrganoCat Process

“…A typical set of conditions for the lignocellulose pretreatment and fractionation process OrganoCat (OrganoCat) uses 0.1 M FDCA as a catalyst, a biomass loading of 100 g L -1 (beech wood, compared to the aqueous phase), 1 h of reaction time and 160 °C as the reaction temperature. The composition of beech wood has been published elsewhere 21 (~48% cellulose, 27% hemicellulose, 26% lignin). Figure 1 shows the extracted hemicellulose hydrolysate with this set of conditions as well as longer reaction time (3 h) and lower temperature (140 °C).…”

“…to have a beneficial effect as well 22 . Due to the variety in composition, however, the process needs optimization, depending on the different feedstocks 21 . Considering the overall process performance, downstream purification of the separated fractions must be considered, which is why selectivity plays a major role.…”