Water in the washing solvent after deep eutectic solvent pretreatment affects properties of lignocellulose nanofibrils

Microwave-assisted deep eutectic solvents (DES) pretreatment of control and transgenic poplars for boosting the lignin valorization and cellulose bioconversion

Elucidating the structural characteristics and changes of lignin during biorefining is considerably important for lignin valorization. To examine the structural transformations of lignin under deep eutectic solvent (DES) pretreatments, the double enzymatic lignin (DEL) isolated from Eucalyptus was pretreated with DES (ChCl/lactic acid, 1:10) under the conditions of 60–140 °C for 6 h. The structural transformations of lignin during the DES pretreatment have been investigated by quantitative 13C NMR, two-dimensional-heteronuclear single quantum correlation (2D-HSQC) NMR, 31P NMR, gel permeation chromatography (GPC), and scanning electron microscopy (SEM) techniques and the lignin degradation products recovered after DES pretreatment have been analyzed by gas chromatography–mass spectrometry (GC–MS) technique. NMR results demonstrated that the dissociation of aryl ether linkage (i.e., β–O–4) is dominant during the DES pretreatment, which is in line with the increased content of phenolic hydroxyl in these lignins. In addition, the decreased aliphatic hydroxyl groups suggested that the acylation or dehydration of aliphatic hydroxyl groups occurred as the pretreatment temperature elevated. Based on the results observed, possible pathways for chemical transformations of lignin were proposed. Furthermore, it was found that DES pretreatment also resulted in a homogeneous lignin morphology, facilitating the formation of lignin nanoparticles. In short, unmasking the lignin chemistry during the DES pretreatment will facilitate the optimization of the pretreatment process and production of homogeneous nanosized lignin particles with preferable chemical reactivity from parent lignin in the current biorefinery process.

Electro-driven deep eutectic solvent pretreatment of wheat straw with enhancive component fractionation and hydrogen evolution at room temperature

In this study, in order to overcome the recalcitrance of sunflower stalk bark (SSB) residues, three kinds of pretreatment methods, i.e., dilute acid pretreatment, alkaline pretreatment, and deep eutectic solvent (DES) pretreatment, were employed to pretreat the SSB material. The effects of the different pretreatment methods for enzymatic hydrolysis efficiency and sugar recovery were evaluated. The enzymatic hydrolysis yield (EHY) of SSB after dilute sulfuric acid, NaOH, and DES pretreatment could be improved from 15.2% to 26.8%, 96.7%, and 93.3%, respectively. Among the three pretreatment methods, dilute acid could effectively decompose hemicellulose while preserving more lignin in the pretreated solids, and it could only enhance EHY within a limited range (< 30%). Compared with dilute sulfuric acid pretreatment, NaOH and choline chloride/lactic acid pretreatments could effectively remove not only hemicellulose but also lignin. Results showed that satisfactory EHY (> 90%) was observed in both alkaline and DES pretreated SSB solids. Besides, DES method was much more efficient in the extraction of lignin (95%) compared with NaOH pretreatment (80.2%). Lignin could be recovery by DES pretreatment as value-added by-product from SSB and was more environmentally friendly and sustainable during production. Finally, under the condition of 1:10 (w/w) solid to DES solution and 150°C pretreatment temperature, the mass balance of DES-150°C showed that 28.1g glucose was obtained from 100g SSB, and the glucose recovery yield was 77.6% of theoretical, demonstrating the potential of environmentally friendly DESs in biorefinery.

Due to its low cost and green nature, pretreatment of lignocelluloses using deep eutectic solvents (DESs) is a promising approach for dissociation of lignocelluloses and extraction of lignin. However, pureChCl/glycerol DES has been found to be ineffective for this purpose. In this work, we develop a strategy of introducing Lewis acids (AlCl3, FeCl3, FeCl2, ZnCl2, and CuCl2) into ChCl/glycerol for efficient pretreatment of hybrid Pennisetum energy grass in order to produce high-purity and antioxidative lignin. Furthermore, the structural characteristics of the regenerated lignin isolated using the DES pretreatment were comprehensively investigated. The results revealed that the FeCl3-catalyzed DES pretreatment facilitated fractionation of the regenerated lignin. It was observed that the amount of ether linkages in the regenerated lignin decreased gradually with increasing pretreatment severity. Furthermore, it was found that the amount of phenolic hydroxyl groups in the regenerated lignin was sharply increased. The regenerated lignin isolated after the DES pretreatment showed excellent antioxidant activity. It is concluded that a deep understanding of the fundamental chemistry of lignin during the Lewis acid-catalyzed DES pretreatment will be beneficial for the optimization of the pretreatment process.

Pretreatment is an important step to reduce the recalcitrance factors in biomass for effective biomass utilization. In particular, the choice of processing solvents in the pretreatment influences the quantity and quality of the final products. Although conventional organosolv pretreatments are effective, they are typically performed under harsh conditions. Compared to those approaches, recent studies have shown that the use of Deep Eutectic Solvents (DES) made up of a hydrogen bond donor and acceptor at the eutectic point can be a promising alternative as biomass processing solvents because of their good thermal stability and compatibility with natural components. In this study, DES pretreatment was applied to corn stover, which is the largest agricultural residue in the United States. The performance of the pretreatments was assessed by measuring the removal of xylan and lignin from the corn stover, as well as the production of glucose and xylose by subsequent enzymatic hydrolysis. The results indicated that the DES pretreatment resulted in significantly higher delignification rates (75%) than an organosolv pretreatment (35%) at the same processing temperature. The DES pretreatment also resulted in a more effective conversion of glucan (81%) and xylan (56%) than the organosolv pretreatment. The results indicated that DES pretreatment is a promising processing strategy for biomass utilization.

Ultrafast fractionation of wild-type and CSE down-regulated poplars by microwave-assisted deep eutectic solvents (DES) for cellulose bioconversion enhancement and lignin nanoparticles fabrication

Evaluation of deep eutectic solvent pretreatment towards efficacy of enzymatic saccharification using multivariate analysis techniques

Ultrafast alkaline deep eutectic solvent pretreatment for enhancing enzymatic saccharification and lignin fractionation from industrial xylose residue

Preparation of high yield lignin-containing cellulose nanofibrils from alkaline peroxide mechanical pulp by deep eutectic solvents pretreatment.

Multivariate analysis of the process of deep eutectic solvent pretreatment of lignocellulosic biomass

Acid/alkali-catalyzed deep eutectic solvent pretreatment of corn straw for enhanced biohydrogen production

Utilization of guaiacol-based deep eutectic solvent for achieving a sustainable biorefinery

Establishing the constitutive relationship between deep eutectic solvents pre-treatment extent, cellulose structure characteristics, and dissolution efficiency in lyocell processing.

Insights into the poplar cell wall deconstruction following deep eutectic solvent pretreatment for enhanced enzymatic saccharification and lignin valorization