Low-temperature pretreatment by AlCl3-catalyzed 1,4-butanediol solution for producing 'ideal' lignin with super-high content of ß-O-4 linkages.

High contents of internal ß-O-4 linkages in lignin are critical for high-yield production of high-value aromatic monomers by depolymerization. However, it remains great challenge due to lack of suitable protection strategy. In this work, a very effective lignin-first strategy was developed to produce ideal lignin with a super high content of ß-O-4 linkages (up to 72 %) from poplar, in which the pretreatment was undertaken at low temperatures of 90-130 °C with the use of AlCl3-catalyzed 1, 4-butanediol solution. 2D-HSQC NMR spectra revealed that lignin ß-O-4 linkages were protected from etherification of the OH group by 1, 4-butanediol at the α position of lignin aliphatic chains. Besides, the OH groups at the γ position of lignin was also etherified, leading the formation of a structure of Ph-CH=CHCH2O(CH2)4OH. Interestingly, structure protection facilitated the formation of lignin nanoparticles via self-assembly (<100 nm). In addition, it was observed from pyrolysis results that addition of 1, 4-butanediol remarkably protected the structure of lignin by avoiding condensation, promoting the production of aromatics. The cellulose-rich fraction possessed a high cellulose digestibility of 91.64 % by enzymatic hydrolysis at a cellulase dosage of 15 FPU/g cellulose, approximately 6-fold untreated poplar (15.91 %). This low-temperature lignin-first strategy was of great importance for multi-products biorefining lignocellulose because it leads to the production of both lignin with super high content of ß-O-4 linkages for depolymerization and highly digestible cellulose for sugar production.

Advances in organosolv modified components occurring during the organosolv pretreatment of lignocellulosic biomass.

The valorization of organosolv pretreatment (OP) is a required approach to the industrialization of the current enzyme-mediated lignocellulosic biorefinery. Recent literature has demonstrated that the solvolysis happening in the OP can modify the soluble components into value-added active compounds, namely organosolv modified lignin (OML) and organosolv modified sugars (OMSs), in addition to protecting them against excessive degradation. Among them, the OML is coincidental with the "lignin-first" strategy that should render a highly reactive lignin enriched with ß-O-4 linkages and less condensed structure by organosolv grafting, which is desirable for the transformation into phenolic compounds. The OMSs are valuable glycosidic compounds mainly synthesized by trans-glycosylation, which can find potential applications in cosmetics, foods, and healthcare. Therefore, a state-of-the-art OP holds a big promise of lowering the process cost by the valorization of these active compounds. Recent advances in organosolv modified components are reviewed, and perspectives are made for addressing future challenges.

Mild fractionation of poplar into reactive lignin via lignin-first strategy and its enhancement on cellulose saccharification.

The lignin-first biorefinery approach was desirable to produce lignin-derived products by protecting the linkages of lignin and reducing condensation reaction. However, so far lignin-first strategy studies were mainly carried out under harsh conditions, causing serious destruction of lignin structure and reduction of chemically labile linkages, which was not conducive to enhance value of lignin adequately. In this work, mild fractionation of poplar via lignin-first strategy using dioxane/methanol at 80 °C was developed for purposely extracting reactive lignin with a relatively higher yield (>50%), purity (>99%), ß-O-4' linkages and p-hydroxybenzoate group as compared with controlled sample. In addition, glucose yield of cellulose-rich residue under lignin-first strategy was significantly enhanced to 98.57% due to the superior cellulase adsorption abilities, which was obviously higher than the controlled group (53.88%). Overall, this mild lignin-first strategy was promising to fractionate lignocellulose into reactive lignin and fermentable glucose, thereby achieving full utilization of lignocellulose biomass.