Fragmentation route of doubly ionized benzene, aniline, and nitroanilines monomers using a novel protocol from density functional theory and QTAIM

The possibility of finding the fragmentation routes by theoretical methods led us to compare the molecular ions between neutral molecules of benzene, aniline, and o-, m-, and p-nitroaniline, using the density functional theory (DFT), under an aug-cc-pVDZ base set and a B3LYP exchange-correlation functional. After determining the structure and electronic energy of neutral and doubly ionized species, we used a new protocol based on analyzing Wiberg's binding indexes and the quantum theory of atoms in Bader molecules (QTAIM). The charge transfer and electronic distribution in aromatic monomers indicate the possibility of fragment formation in at least two pairs of carbon-carbon (CC) atoms. They show the possible loss of the -CNH₂ and -NO₂ groups in the aniline and nitroaniline molecules doubly ionized.

Techno-economic optimization of a process superstructure for lignin valorization

Lignin, the most abundant aromatic biopolymer on Earth, is often considered a biorefinery by-product, despite its potential to be valorized into high-added-value chemicals and fuels. In this work, an integrated superstructure-based optimization model was set up and optimized using mixed-integer non-linear programming for the conversion of technical lignin to three main biobased products: aromatic monomers, phenol-formaldehyde resins, and aromatic aldehydes/acids. Several alternative conversion pathways were simultaneously compared to assess the profitability of lignins-based processes by predicting the performance of technologies with different TRL. Upon employing key technologies such as hydrothermal liquefaction, dissolution in solvent, or high-temperature electrolysis, the technical lignins could have a market value of 200 €/t when the market price for aromatic monomers, resins, and vanillin is at least 2.0, 0.8, and 15.0 €/kg, respectively. When lower product selling prices were considered, the aromatic monomers and the resins were not profitable as target products.

Catalytic hydrogenolysis of alkali lignin in supercritical ethanol over copper monometallic catalyst supported on a chromium-based metal-organic framework for the efficient production of aromatic monomers

The catalytic hydrogenolysis of lignin has been reported as an effective approach for lignin depolymerization owing to its high efficiency for aromatic monomer production. In this study, a series of copper monometallic catalysts over an MIL-101(Cr) support were synthesized and used for the catalytic hydrogenolysis of alkali lignin using supercritical ethanol. First, the optimal copper catalyst for lignin hydrogenolysis was selected. Subsequently, the reaction conditions for catalytic hydrogenolysis were systematically optimized to maximize the total monomer yield. The optimal conditions were determined to be 6 h of reaction time, 20 min of sonication pretreatment, 50% catalyst loading, and 5% lignin loading. Under these conditions, an aromatic monomer yield of 38.5% was obtained; this depolymerized lignin stream, which is mainly composed of G-type monomers, can serve as a promising aromatic feedstock and carbon source for further microbial upgrading and bioconversion to produce various value-added products.

Performance of three delignifying pretreatments on hardwoods: hydrolysis yields, comprehensive mass balances, and lignin properties

BACKGROUND

In this work, three pretreatments under investigation at the DOE Bioenergy Research Centers (BRCs) were subjected to a side-by-side comparison to assess their performance on model bioenergy hardwoods (a eucalyptus and a hybrid poplar). These include co-solvent-enhanced lignocellulosic fractionation (CELF), pretreatment with an ionic liquid using potentially biomass-derived components (cholinium lysinate or [Ch][Lys]), and two-stage Cu-catalyzed alkaline hydrogen peroxide pretreatment (Cu-AHP). For each of the feedstocks, the pretreatments were assessed for their impact on lignin and xylan solubilization and enzymatic hydrolysis yields as a function of enzyme loading. Lignins recovered from the pretreatments were characterized for polysaccharide content, molar mass distributions, β-aryl ether content, and response to depolymerization by thioacidolysis.

RESULTS

All three pretreatments resulted in significant solubilization of lignin and xylan, with the CELF pretreatment solubilizing the majority of both biopolymer categories. Enzymatic hydrolysis yields were shown to exhibit a strong, positive correlation with the lignin solubilized for the low enzyme loadings. The pretreatment-derived solubles in the [Ch][Lys]-pretreated biomass were presumed to contribute to inhibition of enzymatic hydrolysis in the eucalyptus as a substantial fraction of the pretreatment liquor was carried forward into hydrolysis for this pretreatment. The pretreatment-solubilized lignins exhibited significant differences in polysaccharide content, molar mass distributions, aromatic monomer yield by thioacidolysis, and β-aryl ether content. Key trends include a substantially higher polysaccharide content in the lignins recovered from the [Ch][Lys] pretreatment and high β-aryl ether contents and aromatic monomer yields from the Cu-AHP pretreatment. For all lignins, the ¹³C NMR-determined β-aryl ether content was shown to be correlated with the monomer yield with a second-order functionality.

CONCLUSIONS

Overall, it was demonstrated that the three pretreatments highlighted in this study demonstrated uniquely different functionalities in reducing biomass recalcitrance and achieving higher enzymatic hydrolysis yields for the hybrid poplar while yielding a lignin-rich stream that may be suitable for valorization. Furthermore, modification of lignin during pretreatment, particularly cleavage of β-aryl ether bonds, is shown to be detrimental to subsequent depolymerization.