Power-to-chemicals: Low-temperature plasma for lignin depolymerisation in ethanol

How to Survive at Point Nemo? Fischer-Tropsch, Artificial Photosynthesis, and Plasma Catalysis for Sustainable Energy at Isolated Habitats

Inhospitable, inaccessible, and extremely remote alike the famed pole of inaccessibility, aka Point Nemo, the isolated locations in deserts, at sea, or in outer space are difficult for humans to settle, let alone to thrive in. Yet, they present a unique set of opportunities for science, economy, and geopolitics that are difficult to ignore. One of the critical challenges for settlers is the stable supply of energy both to sustain a reasonable quality of life, as well as to take advantage of the local opportunities presented by the remote environment, e.g., abundance of a particular resource. The possible solutions to this challenge are heavily constrained by the difficulty and prohibitive cost of transportation to and from such a habitat (e.g., a lunar or Martian base). In this essay, the advantages and possible challenges of integrating Fischer-Tropsch, artificial photosynthesis, and plasma catalysis into a robust, scalable, and efficient self-contained system for energy harvesting, storage, and utilization are explored.

Recent progress of low-temperature plasma technology in biorefining process

In recent years, low-temperature plasma-assisted processes, featuring high reaction efficiency and wide application scope, have emerged as a promising alternative to conventional methods for biomass valorization. It is well established that charged species, chemically energetic molecules and radicals, and highly active photons playing key roles during processing. This review presents the major applications of low-temperature plasma for biomass conversion in terms of (i) pretreatment of biomass, (ii) chemo fractionation of biomass into value-added chemicals, and (iii) synthesis of heterogeneous catalyst for further chemo-catalytic conversion. The pretreatment of biomass is the first and foremost step for biomass upgrading to facilitate raw biomass transformation, which reduces the crystallinity, purification, and delignification. The chemo-catalytic conversion of biomass involves primary reactions to various kinds of target products, such as hydrolysis, hydrogenation, retro-aldol condensation and so on. Finally, recent researches on plasma-assisted chemo-catalysis as well as heterogeneous catalysts fabricated via low-temperature plasma at relatively mild condition were introduced. These catalysts were reported with comparable performance for biomass conversion to other state-of-the-art catalysts prepared using conventional methods.

Enhanced oxidative depolymerization of lignin in cooperative imidazolium-based ionic liquid binary mixtures

The aerobic oxidation of lignin model 2-phenoxyacetophenone (2-PAP) in cooperative ionic liquid mixtures (CoILs) with 1-ethyl-3-methylimidazolium acetate ([C₂C₁im]OAc) and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([B_ZC₁im]NTf₂) was investigated. Complete degradation of 2-PAP was achieved with [C₂C₁im]OAc/[B_ZC₁im]NTf₂ molar ratio (R_IL) of 1/1 and 1/2 at 100 °C for 2 h. The conversion and product yields from CoILs were higher than those in pure ILs, indicating the cooperative effects of [C₂C₁im]OAc/[B_ZC₁im]NTf₂ on cleaving aryl-ether bonds. [C₂C₁im]OAc promoted the catalytic cleavage of aryl-ether bonds and solvation, and [B_ZC₁im]NTf₂ induced the formation of alkyl radicals and enhanced the product selectivity. Accordingly, the highest conversion of alkali lignin (79.8%) was obtained with R_IL of 5/1 at 100 °C for 2 h, and phenol monomers (306 mg/g) were selectively produced. The CoILs exhibited good catalytic capacities for oxidative depolymerization of lignin, which strongly depends on the changes in intermolecular interactions and structural organization with varying R_IL.

A mechanistic study on electro-Fenton system cooperating with phangerochate chrysosporium to degrade lignin

The combined catalytic system of Electro-Fenton (E-Fenton) and Phanerochaete chrysosporium (P. chrysosporium) was constructed in liquid medium with additional potential to overcome the limitations of lignin degradation by white rot fungi alone. To further understand the mechanism of synergistic catalysis, we optimized the optimum potential for lignin catalysis by P. chrysosporium and built synergistic versus separate catalyses. After 48 h of incubation, the optimum growth environment and the highest lignin degradation rate (43.8%) of P. chrysosporium were achieved when 4 V was applied. After 96 h, the lignin degradation rate of the cocatalytic system was 62% (E-Fenton catalysis alone 22% and P. chrysosporium catalysis alone 19%), the pH of the growth maintenance system of P. chrysosporium was approximately 3.5, and the lignin peroxidase (LiP) and manganese-dependent peroxidase (MnP) enzyme activities, were significantly better than those of the control. The qPCR results indicated that the expression of both MnP and LiP genes was higher in the cocatalytic system. Meanwhile, FTIR and 2D-HSQC NMR confirmed that the synergistic catalysis was effective in breaking the aromatic functional groups and the side chains of the aliphatic region of lignin. This study showed that the synergistic catalytic process of electro-Fenton and P. chrysosporium was highly efficient in the degradation of lignin. In addition, the synergetic system is simple to operate, economical and green, and has good prospects for industrial application.

The combined catalytic system of Electro-Fenton (E-Fenton) and Phanerochaete chrysosporium (P. chrysosporium) was constructed in liquid medium with additional potential to overcome the limitations of lignin degradation by white rot fungi alone.

Cleavage via Selective Catalytic Oxidation of Lignin or Lignin Model Compounds into Functional Chemicals

Lignin, a complex aromatic polymer with different types of methoxylated phenylpropanoid connections, enables the sustainable supply of value-added chemicals and biofuels through its use as a feedstock. Despite the development of numerous methodologies that upgrade lignin to high-value chemicals such as drugs and organic synthesis intermediates, the variety of valuable products obtained from lignin is still very limited, mainly delivering hydrocarbons and oxygenates. Using selective oxidation and activation cleavage of lignin, we can obtain value-added aromatics, including phenols, aldehydes, ketones, and carboxylic acid. However, biorefineries will demand a broad spectrum of fine chemicals in the future, not just simple chemicals like aldehydes and ketones containing simple C = O groups. In particular, most n-containing aromatics, which have found important applications in materials science, agro-chemistry, and medicinal chemistry, such as amide, aniline, and nitrogen heterocyclic compounds, are obtained through n-containing reagents mediating the oxidation cleavage in lignin. This tutorial review provides updates on recent advances in different classes of chemicals from the catalytic oxidation system in lignin depolymerization, which also introduces those functionalized products through a conventional synthesis method. A comparison with traditional synthetic strategies reveals the feasibility of the lignin model and real lignin utilization. Promising applications of functionalized compounds in synthetic transformation, drugs, dyes, and textiles are also discussed.

Characterization of lignin streams during ionic liquid/hydrochloric acid/formaldehyde pretreatment of corn stalk

This work investigated the role of formaldehyde (FA) in lignin anti-condensation during corn stalk pretreatment based on 1-butyl-3-methylimidazolium chloride ([C₄C₁im]Cl)/hydrochloric acid (HCl). As a result of the aldolization reactions between FA and lignin, the condensation of lignin fragments was inhibited, and lignin remained in soluble fragmental molecules. Characterizations on the compositional and structural changes of lignin and its degraded products during pretreatment (80 °C-100 °C, 2-5 h) with FA addition in comparison with those in DO/HCl/FA or [C₄C₁im]Cl/HCl were conducted. Results revealed that the structural features of lignin were affected by FA addition and solvent type. In the [C₄C₁im]Cl/HCl/FA system, FA stabilization was unfavorable for the cleavage of β-O-4' bonds and lignin with low S/G ratio (3.4) and high molecular weight (Mw = 9920 g·mol^-1) was extracted. The compositions of degraded products were considerably affected by FA addition.