Lignin heterogeneity, including complex chemical structure and wide molecular-weight distribution, results in the inhomogeneous and modest performance of lignin, which substantially restricts its value-added applications. For an evaluation of the effects of lignin heterogeneity on the self-assembly nanosizing behaviors, three lignin fractions subdivided from enzymatic hydrolysis lignin (EHL) were used as the raw material for lignin micro-/nanoparticles (LMNPs) preparation, and afterward, the properties of these obtained LMNPs were compared. The three lignin fractions (denoted as F1, F2, and F3) presented reduced heterogeneity compared to the parent EHL, and a gradual increasing of molecular weight accompanied by decreasing hydrophilic group content were found from F1 to F3. The LMNPs prepared from the three fractions exhibited totally different morphologies: F1 mostly formed incomplete spherical particles with large size (450–650 nm), F3 produced only small compact nanoparticles (about 50 nm) with a quite uniform size distribution, and then two distinct particles with a large hollow structure (500–700 nm) and a small compact structure (100–250 nm) were fabricated using F2 as the raw materials. Among the three fractions, F3 showed the highest yield, and the obtained F3 nanoparticles exhibited excellent water dispersion stability because of their small/uniform particles size and high negative zeta potential. The formation mechanism of different nanosizing behaviors among the three lignin fractions was proposed on the basis of the nanoemulsion formed by amphiphilic low-molecular-weight lignin and the hydrophobic aggregation of high-molecular-weight lignin. Overall, this work demonstrates that lignin heterogeneity has significant effects on the self-assembly nanosizing behaviors of lignin, and the nanoparticle properties can be substantially improved using fractionated lignin with high molecular weight.

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This work presents a novel and green lignin-based nanocomposite and highlights the synergism of lignin's multiple functions (surfactant, sacrificial template, and reducing agent) in the material preparation process.

7In this study, air, steam and CO 2 -enhanced gasification of rice straw was simulated using 8 Aspen PlusTM simulator and compared in terms of their energy, exergy and environmental 9 impacts. It was found that the addition of CO 2 had less impact on syngas yield compared with 10 gasification temperature. At lower CO 2 /Biomass ratios (below 0.25), gasification system 11 efficiency (GSE) for both conventional and CO 2 -enhanced gasification was below 22.1%, and 12 CO 2 -enhanced gasification showed a lower GSE than conventional gasification. However at 13 higher CO 2 /Biomass ratios, CO 2 -enhanced gasification demonstrated higher GSE than 14 conventional gasification. For CO 2 -enhanced gasification, GSE continued to increase to 15 58.8% when CO 2 /Biomass was raised to 0.87. In addition, it was found that syngas exergy 16 increases with CO 2 addition, which was mainly due to the increase in physical exergy. 17Chemical exergy was 2.05 to 4.85 times higher than physical exergy. The maximum exergy 18 efficiency occurred within the temperature range of 800 o C to 900 o C because syngas exergy 19 peaked in this range. For CO 2 -enhanced gasification, exergy efficiency was found to be more 20 sensitive to temperature than CO 2 /Biomass ratios. In addition, the preliminary environmental 21 analysis showed that CO 2 -enhanced gasification resulted in significant environmental benefits 22 compared with stream gasification. However improved assessment methodologies are still 23 needed to better evaluate the advantages of CO 2 utilization. 24

Lignin heterogeneity, involving complex structure and high polydispersity, is a key challenge that restricts its value-added applications. Fractionation of heterogeneous lignin into several homogeneous subdivisions is an attractive and practical strategy to overcome this limitation. In this work, γ-valerolactone (GVL), a sugar-derived product, was used as a green solvent for lignin fractionation when mixed with water. The enzymatic hydrolysis lignin (EHL) was subdivided into three different fractions (F1, F2, and F3) by dissolving it completely in 60% aqueous GVL and then following gradient precipitation in 40%, 30%, and 5% aqueous GVL solutions, sequentially. Detailed characterization techniques were conducted to provide a comprehensive evaluation of the three obtained lignin fractions. Moreover, the proposed fractionation mechanism was further investigated on the basis of Kamlet−Taft parameters. The gel permeation chromatography (GPC) analyses showed that the three fractions presented lower polydispersity than the parent EHL and, furthermore, a gradual decreasing molecular weight due to the different solubility of various molecular weight lignins in aqueous GVL solvents. The structural analyses revealed that with the decrease of molecular weight, the guaiacyl unit content in lignin fractions decreased, with significant increases of functional groups (i.e., aromatic/aliphatic hydroxyl and carboxyl groups). The solvent recycling study showed that the aqueous GVL had a high recovery, and the recycled GVL had the same lignin fractionation performance as fresh GVL. Overall, compared with traditional fractionation using multiple organic solvents, the present work provides a green and efficient route to fractionate lignin and, therefore, significantly decreases its molecular weight polydispersity and structural heterogeneity.