•Deep eutectic solvents was used for biomass and lignin depolymerization.•Oxalic acid and formic acid DES gave the highest lignin yields.•Microwave heating promoted selective bond cleavage during ...lignin depolymerization.•MD simulations show that certain bonds stretch more during microwave irradiation.
Biomass deconstruction and lignin depolymerization was performed using three different deep eutectic solvents. Various temperature (110°, 130°, and 150 °C) and time (1, 5, 10, 15 min) conditions were tested in a 2450 MHz microwave reactor. Oxalic acid (130 °C, 15 min) and formic acid DES (150 °C, 15 min) gave the highest lignin yield. Microwave heating reduced the processing time significantly. NMR characterization shows that microwave heating promotes selective bond cleavage during lignin depolymerization and has a narrow molecular weight distribution compared to conventional heating techniques. Molecular dynamic simulations showed that certain lignin bonds are stretched under the electric field imparted during microwave irradiation, increasing its probability of breaking.
Lignin, the planet's most abundant renewable source of aromatic compounds, is difficult to degrade efficiently to welldefined aromatics. We developed a microwave‐assisted catalytic Swern oxidation ...system using an easily prepared catalyst, MoO2Cl2(DMSO)2, and DMSO as the solvent and oxidant. It demonstrated high efficiency in transforming lignin model compounds containing the units and functional groups found in native lignins. The aromatic ring substituents strongly influenced the selectivity of β‐ether phenolic dimer cleavage to generate sinapaldehyde and coniferaldehyde, monomers not usually produced by oxidative methods. Time‐course studies on two key intermediates provided insight into the reaction pathway. Owing to the broad scope of this oxidation system and the insight gleaned with regard to its mechanism, this strategy could be adapted and applied in a general sense to the production of useful aromatic chemicals from phenolics and lignin.
Quick and easy: An effective and efficient method was developed for the oxidation and cleavage of lignin model compounds using easily prepared and environmentally friendly MoO2Cl2(DMSO)2 as catalyst under microwave irradiation. Owing to the broad scope of this oxidation system and the insight gleaned with regard to its mechanism, this strategy could be adapted and applied in a general sense to the production of useful aromatic chemicals from phenolics and lignin.
A heterogeneous catalyst system, employing Au nanoparticles (NPs) and Li-Al (1 : 2) layered double hydroxide (LDH) as support, showed excellent activity in aerobic oxidation of the benzylic alcohol ...group in β-O-4 linked lignin model dimers to the corresponding carbonyl products using molecular oxygen under atmospheric pressure. The synergistic effect between Au NPs and the basic Li-Al LDH support induces further reaction of the oxidized model compounds, facilitating facile cleavage of the β-O-4 linkage. Extension to oxidation of γ-valerolactone (GVL) extracted lignin and kraft lignin using Au/Li-Al LDH under similar conditions produced a range of aromatic monomers in high yield. Hydrolysis of the Au/Li-Al LDH oxidized lignin was found to increase the degree of lignin depolymerization, with monomer yields reaching 40% for GVL extracted lignin. Based on these results, the Au/Li-Al LDH + O
catalyst system shows potential to be an environmentally friendly means of depolymerizing lignin to low molecular weight aromatics under mild conditions.
Lignin, a major component of lignocellulosic biomass, is crucial to plant growth and development but is a major impediment to efficient biomass utilization in various processes. Valorizing lignin is ...increasingly realized as being essential. However, rapid condensation of lignin during acidic extraction leads to the formation of recalcitrant condensed units that, along with similar units and structural heterogeneity in native lignin, drastically limits product yield and selectivity. Catechyl lignin (C-lignin), which is essentially a benzodioxane homopolymer without condensed units, might represent an ideal lignin for valorization, as it circumvents these issues. We discovered that C-lignin is highly acid-resistant. Hydrogenolysis of C-lignin resulted in the cleavage of all benzodioxane structures to produce catechyl-type monomers in near-quantitative yield with a selectivity of 90% to a single monomer.
As we work to transition the modern society that is based on non‐renewable chemical feedstocks to a post‐modern society built around renewable sources of energy, fuels, and chemicals, there is a need ...to identify the renewable resources and processes for converting them to platform chemicals. Herein, we explore a strategy for utilizing the p‐hydroxybenzoate in biomass feedstocks (e. g., poplar and palm trees) and converting it into a portfolio of commodity chemicals. The targeted bio‐derived product in the first processing stage is p‐hydroxybenzamide produced from p‐hydroxybenzoate esters found in the plant. In the second stage a continuous reaction process converts the p‐hydroxybenzamide to p‐aminophenol via the Hofmann rearrangement and recovers the unreacted p‐hydroxybenzamide. In the third stage the p‐aminophenol can be acetylated to form paracetamol, which is readily isolated by liquid/liquid extraction at >95 % purity and an overall p‐hydroxybenzamide‐to‐paracetamol process yield of ~90 %. We explore how utilization of protecting groups alters the challenges in this process and expands the portfolio of possible products to include p‐(methoxymethoxy)aniline and N‐acetyl‐p‐(methoxymethoxy)aniline. These target compounds could become value‐added renewably‐sourced platform chemicals that could be used to produce biodegradable plastics, pigments, and pharmaceuticals.
Paracetamol can be produced from p‐hydroxybenzamide at >95 % purity in 90 % yield. Aqueous ammonia treatment of poplar or oil palm empty fruit bunches forms p‐hydroxybenzamide. Under continuous processing conditions, a Hofmann rearrangement converts p‐hydroxybenz‐amide to p‐aminophenol, then liquid/liquid extraction combined with acid/base chemistry and acetylation purifies, forms, and isolates paracetamol.
Lignin is a crucial component of plant matter; however, it is also largely responsible for the recalcitrance of lignocellulosic biomass when subjected to pretreatment processes. Lignin is generated ...in large volumes as a waste product from paper and pulping industry as well as cellulosic biorefineries. As a result, lignin valorization is critical to the successful implementation of cellulosic biofuels. To this end, we investigated interactions between three ionic liquids (ILs) and the lignolytic enzyme laccase toward biocatalytic lignin conversion to aromatic monomers. Laccase exhibited minimal loss of activity in 10% diethylamine hydrogensulfate (DEAHSO4). Changes in V max and K m of laccase with respect to IL concentration indicate that DEAHSO4 is a noncompetitive inhibitor, whereas cholinium lysinate (ChLys) and C2C1ImOAc are mixed inhibitors. Docking simulations suggested that ChLys and C2C1ImOAc disrupt residues leading to the active site. Experiments with a β-O-4′ linked model dimer revealed that laccase in C2C1ImOAc and ChLys requires the presence of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to oxidize the β-O-4′ linkage, leading to polymerization of the model dimer. Alkaline lignin treated with laccase, ABTS, and the aqueous ILs (AILs) showed few structural changes, although the lignin was partially solubilized and converted to degradation products. The major products obtained from alkaline lignin were vanillin, acetosyringone, syringaldehyde, and acetovanillone. The results of this study provide, for the first time, an in-depth explanation of the interactions between laccase and AILs for the purpose of lignin valorization.
The Cover Feature shows that three steps are key in capturing p‐hydroxybenzamide and converting it into paracetamol from a waste stream produced from the ammonia pretreatment of biomass, e.g., poplar ...trees or oil palm empty fruit bunches. The pretreated biomass is converted into renewably sourced fuels (e.g., isobutanol and sustainable aviation fuel). The p‐hydroxybenzamide (yellow bottles) is converted in a continuous process to p‐aminophenol (purple bottle), a precursor to paracetamol (red bottle), plastics, ink, and other products. This result is a portfolio of sustainably sourced commodity chemicals that could add value to a biorefinery. More information can be found in the Research Article by S. D. Karlen and co‐workers.
Ionic liquid (IL) treatment of lignin is a promising strategy to producing nonpetroleum-based polyols for diverse polyurethane (PU) applications. Herein, IL 1-butyl-3-methylimidazolium (BMIMBr) was ...employed to treat organosolv hardwood (OS-HW) and softwood (OS-SW) lignins, as well as kraft softwood (Kr-SW) lignin. Phosphorus nuclear magnetic resonance spectroscopy (31P NMR) and gel permeation chromatography (GPC) analyses revealed the highest impacts of BMIMBr treatment on OS-HW lignin, where BMIMBr-treated OS-HW lignin showed 40% increase in hydroxyl content and 20% decrease in molecular weight. By contrast, compositional changes to OS-SW and Kr-SW after BMIMBr treatment were not detected. BMIMBr treatment of OS-HW lignin increased its reactivity with isocyanate by 42%, and X-ray photoelectron spectroscopy (XPS) analysis of BMIMBr-treated OS-HW lignin after washing confirmed the potential to recover the IL. Together, these results demonstrate the efficacy of IL treatment in improving the applicability of certain lignins as polyol alternatives.
Selective oxidation of lignin's β-aryl ether units combined with secondary chemical treatment for depolymerization can generate valuable oxygen-rich aromatics. Although there have been many reports ...of the successful oxidative depolymerization of lignin, an accurate assessment of the merits of each method is hampered by the wide array of lignins used. Here, we test a selection of literature methods for secondary lignin depolymerization using a common set of lignin substrates. In an initial step, the lignins were oxidized using 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)/
tert
-butyl nitrite (
t
BuONO)/O
2
. The oxidized lignins were then subjected to a variety of depolymerization methods, the yield of aromatic monomers being quantified and compared to lignin depolymerized using an Au/Li-Al LDH catalyst followed by hydrolysis without prior C
α
-OH oxidation. The Au/Li-Al LDH system gave the highest monomer yield for the untreated lignins, moreover, for DDQ-oxidized lignins, the Au/Li-Al LDH method produced similar monomer yields with high selectivity towards aromatic acids and aldehydes.
DDQ oxidized lignins were used as substrates to assess the effectiveness of secondary depolymerization methods for the production of aromatics.
The cell walls of leaf base tissues of the Canary Island date palm (Phoenix canariensis) contain lignins with the most complex compositions described to date. The lignin composition varies by tissue ...region and is derived from traditional monolignols (ML) along with an unprecedented range of ML conjugates: ML-acetate, ML-benzoate, ML-p-hydroxybenzoate, ML-vanillate, ML-p-coumarate, and ML-ferulate. The specific functions of such complex lignin compositions are unknown. However, the distribution of the ML conjugates varies depending on the tissue region, indicating that they may play specific roles in the cell walls of these tissues and/or in the plant's defense system.
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