Reductive Catalytic Fractionation Research Articles

Improved Reductive Catalytic Fractionation of Lignocellulosic Biomass through the Application of a Recyclable Magnetic Catalyst.

The reductive catalytic fractionation (RCF) of second generation lignocellulosic biomass is an elegant one-pot process to obtain a highly delignified cellulose pulp, sugar-derived polyols, and depolymerized and stabilized lignin oils. However, the need of noble metal catalysts to prompt the reactions may impact the economic sustainability of the overall "lignin-first" biorefinery if the catalyst recovery and recyclability are not guaranteed. Herein, the use of a novel catalyst based on supported ruthenium over maghemite for the RCF of poplar sawdust is reported for the first time. This material allows us to obtain a pure cellulose pulp with a quantitative magnetic recovery efficiency after the first cycle. The obtained lignin oil is composed by a 12% yield in phenolic monomers (i.e., benzyl alcohol, 4-n-propylguaiacol, and 4-n-propylsyringol), together with dimers and trimers as confirmed by GPC analyses. The catalytic material was found to be stable and recyclable for three reaction cycles with only minor loss of RCF efficiency. On the other hand, the straightforward, lab-scale, magnetic recovery procedure needs to be further improved in the future to ensure quantitative recovery of the catalyst also after several RCF cycles.

Unlocking biomass valorization: Machine Learning insights for Reductive Catalytic Fractionation of cotton stalks

Lignocellulosic biomass valorization has become an intensive area of research due to the importance of renewable nature and availability of biomass. However, biomass fractionation and depolymerization produce numerous datasets, that are difficult to visualise and interpret for the scale-up of the process. Therefore, machine learning algorithms, which can discover hidden patterns in data are applied to these datasets. Reductive Catalytic Fractionation (RCF) of lignocellulosic biomass is an emerging methodology to valorize biomass completely and effectively. Herein, the present work includes the Correlation Analysis and the Principal Component Analysis (PCA) of product distribution obtained from RCF of cotton stalks. Interactions between process variables and delignification (DL), sugar retention (SR), total phenolic monomers (PM), and individual phenolic monomers yield were evaluated. Correlations among DL, SR, and PM yields were also evaluated at different reaction conditions through PCA, which were explained using the reaction mechanism and molecular chemistry of lignin.

Reductive catalytic fractionation of cotton stalks: catalytic strategy for tuning the selectivity of phenolic monomers

Reductive catalytic fractionation of cotton stalks: catalytic strategy for tuning the selectivity of phenolic monomers

Catalytic depolymerization of Camellia oleifera shell lignin to phenolic monomers: Insights into the effects of solvent, catalyst and atmosphere

Camellia oleifera shell (COS) is a renewable biomass resource abundant in lignin with significant potential for producing phenolic monomers. However, the dearth of research has led to considerable resource wastage and environmental pollution. Herein, reductive catalytic fractionation (RCF) of COS was performed using noble metal catalysts in different solvents. An 11.1 wt% yield of phenolic monomers was achieved with 91% selectivity toward propylene-substituted monomers in H2O/EtOH (3:7, v/v) cosolvent under N2 atmosphere. Notably, the highest phenolic monomer yield of 17.0 wt% was obtained with impressive selectivity (86.9%) toward propanol-substituted monomers in the presence of H2. The GPC analysis and 2D HSQC NMR spectra indicated the effective depolymerization of lignin oligomers with catalysts. Phenolic monomers with ethyl, propyl, or propanol side chain could be produced from lignin-derived oligomers through hydrogenolysis, hydrogenation, and decarboxylation reactions. Overall, this study has paved the way for the valorization of COS lignin through the RCF strategy.

Reducing Solvent Consumption in Reductive Catalytic Fractionation through Lignin Oil Recycling.

Reductive catalytic fractionation (RCF) enables the simultaneous valorization of lignin and carbohydrates in lignocellulosic biomass through solvent-based lignin extraction, followed by depolymerization and catalytic stabilization of the extracted lignin. Process modeling has shown that the use of exogenous organic solvent in RCF is a challenge for economic and environmental feasibility, and previous works proposed that lignin oil, a mixture of lignin-derived monomers and oligomers produced by RCF, can be used as a cosolvent in RCF. Here, we further explore the potential of RCF solvent recycling with lignin oil, extending the feasible lignin oil concentration in the solvent to 100 wt %, relative to the previously demonstrated 0-19 wt % range. Solvents containing up to 80 wt % lignin oil exhibited 83-93% delignification, comparable to 83% delignification with a methanol-water mixture, and notably, using lignin oil solely as a solvent achieved 67% delignification in the absence of water. In additional experiments, applying the RCF solvent recycling approach to ten consecutive RCF reactions resulted in a final lignin oil concentration of 11 wt %, without detrimental impacts on lignin extraction, lignin oil molar mass distribution, aromatic monomer selectivity, and cellulose retention. Overall, this work further demonstrates the potential for using lignin oil as an effective cosolvent in RCF, which can reduce the burden on downstream solvent recovery.

Room temperature catalytic upgrading of unpurified lignin depolymerization oil into bisphenols and butene-2

Lignin is the largest source of renewable aromatics on earth. Despite numerous techniques for lignin depolymerization into mixtures of valuable monomers, methods for their upgrading into final products are scarce. The state of the art upgrading methods generally rely on catalytic funneling, requiring high temperatures, catalyst loadings and hydrogen pressure, and lead to the loss of functionality and bio-based carbon content. Here an alternative approach is presented, whereby the target monomers are selectively converted in unpurified mixtures into easily separable final products under mild conditions. We use reductive catalytic fractionation of wood to convert lignin into iso-eugenol and propenyl syringol enriched oil followed by an olefin metathesis to yield bisphenols and butene-2, thus, valorizing all bio-based carbons. To further demonstrate the synthetic utility of the obtained bisphenols we converted them into polyesters with a high glass transition temperature (Tg = 140.3 °C) and thermal stability (Td50% = 330 °C).

Simple building blocks from forestry residues via convergent catalytic pathways

Funneling complex lignocellulose into simple and valuable building blocks has garnered significant interest in the field of biorefinery as a competitor to the petrochemical industry. Reductive Catalytic Fractionation (RCF) of lignocellulose, an innovative biorefinery technology, provides a promising strategy for complete valorization of lignocellulose into various valuable chemicals. In this study, integrated processes utilizing RCF strategies were developed to achieve complete conversion of lignocellulose into various simple and valuable platform chemicals. The core of this system is the flexible use of commercial Ni catalysts including Raney Ni and Ni/SiO2-Al2O3 which brings great benefits for future upscale and industrial applications. Surprisingly, both monomers derived from lignin and high molecular weight fractions could be converted to 4-ethylcyclohexanol while carbohydrate pulp was converted to furfural and 5-methoxymethylfurfural (MMF) in one-pot. MMF could be further upgraded to 2,5-Furandicarboxylicacid (FDCA) via catalytic oxidation by Ru/C catalysts. This work could inspire the development of more sustainable and economically viable biorefinery processes.

Enhanced reductive catalytic fractionation of lignocellulose using a water-resistant RuNiZnOx/Nb2O5 catalyst with synergistic hydrogen spillover and acidic properties

Eco-friendly lignin depolymerization into monomeric phenols in an aqueous system is essential for the sustainable and green valorization of lignocellulosic biomass. However, a major challenge in this process is the development of efficient and stable catalysts for aqueous reductive catalytic fractionation (RCF), as water can cause catalyst deactivation and reduce monomer yields. In this study, a water-resistant RuNiZnOx/Nb2O5 catalyst is developed that demonstrates excellent catalytic activity and stability in aqueous systems, achieving a near-theoretical monomeric phenol yield of 40.1 wt% under reaction conditions of 240℃ and 3 MPa H2 for 4 h. The excellent performance of this catalyst is attributed to the synergistic hydrogen spillover effect between Ni and Ru and the strong acidic properties of ZnO, as revealed by in-situ XPS analysis and NH3-TPD, respectively. This hydrogen spillover effect significantly alters the product composition, promoting the generation of POH-S/G from lignin model compounds. Additionally, screening of the catalyst support materials revealed that Nb2O5 not only enhances Ru dispersion but also improves its stability, resulting in a minor decrease in lignin monomer yield observed after three cycles.

Quantification of Native Lignin Structural Features with Gel‐Phase 2D‐HSQC0 Reveals Lignin Structural Changes During Extraction

AbstractOur ability to study and valorize the lignin fraction of biomass is hampered by the fundamental and still unmet challenge of precisely quantifying native lignin's structural features. Here, we developed a rapid elevated‐temperature 1H−13C Heteronuclear Single‐Quantum Coherence Zero (HSQC0) NMR method that enables this precise quantification of native lignin structural characteristics even with whole plant cell wall (WPCW) NMR spectroscopy, overcoming fast spin relaxation in the gel phase. We also formulated a Gaussian fitting algorithm to perform automatic and reliable spectral integration. By combining HSQC0 measurements with yield measurements following depolymerisation, we can confirm the combinatorial nature of radical coupling reactions during biosynthesis leading to a random sequential organization of linkages within a largely linear lignin chain. Such analyses illustrate how this analytical method can greatly facilitate the study of native lignin structure, which can then be used for fundamental studies or to understand lignin depolymerization methods like reductive catalytic fractionation or aldehyde‐assisted fractionation.

Quantification of Native Lignin Structural Features with Gel-Phase 2D-HSQC0 Reveals Lignin Structural Changes During Extraction.

Our ability to study and valorize the lignin fraction of biomass is hampered by the fundamental and still unmet challenge of precisely quantifying native lignin's structural features. Here, we developed a rapid elevated-temperature 1H-13C Heteronuclear Single-Quantum Coherence Zero (HSQC0) NMR method that enables this precise quantification of native lignin structural characteristics even with whole plant cell wall (WPCW) NMR spectroscopy, overcoming fast spin relaxation in the gel phase. We also formulated a Gaussian fitting algorithm to perform automatic and reliable spectral integration. By combining HSQC0 measurements with yield measurements following depolymerisation, we can confirm the combinatorial nature of radical coupling reactions during biosynthesis leading to a random sequential organization of linkages within a largely linear lignin chain. Such analyses illustrate how this analytical method can greatly facilitate the study of native lignin structure, which can then be used for fundamental studies or to understand lignin depolymerization methods like reductive catalytic fractionation or aldehyde-assisted fractionation.

Reductive catalytic fractionation of lignocellulose over copper phyllosilicate nanotube catalysts

Reductive catalytic fractionation of lignocellulose over copper phyllosilicate nanotube catalysts

Design and Validation of a High-Throughput Reductive Catalytic Fractionation Method

Design and Validation of a High-Throughput Reductive Catalytic Fractionation Method

Uncovering Challenges for Complete Carbohydrate to Bioethanol Utilization in a Reductive Catalytic Fractionation Biorefinery

Uncovering Challenges for Complete Carbohydrate to Bioethanol Utilization in a Reductive Catalytic Fractionation Biorefinery

Hydrodeoxygenation of lignin-derived phenols into cycloalkanes by atomically dispersed Pt-polyoxometalate catalysts

We report atomically dispersed Pt sites anchored on polyoxometalate cesium salts as robust and durable catalysts for upgrading lignin into hydrocarbons at relatively mild conditions. Experimental results and DFT calculations cross-validate the catalytic performance, considering the porosity, acidity, H2 storage capacity, and HOMO-LUMO energy gap of these catalysts. The optimal Pt0.4/CsPW-H2 catalyst enables the hydrodeoxygenation (HDO) of a diverse range of lignin-derived phenolics into hydrocarbons with up to 97% yield at the conditions of 150 °C and 0.1–2 MPa H2. A lignin oil from the reductive catalytic fractionation (RCF) of Eucalyptus wood can be transformed into cyclohexanes with a 32.7 wt% yield under a solvent-free condition. This catalyst demonstrates excellent reusability in the HDO of 4-propyl guaiacol for 20 cycles, achieving a 15095 molpropylcyclohexane molPt−1 total turnover number (TON). This work broadens the horizons of designing highly efficient catalytic systems aimed at sustainably producing liquid fuels from lignin.

Harnessing Atomically Dispersed Cobalt for the Reductive Catalytic Fractionation of Lignocellulose.

The reductive catalytic fractionation (RCF) of lignocellulose, considering lignin valorization at design time, has demonstrated the entire utilization of all lignocellulose components; however, such processes always require catalysts based on precious metals or high-loaded nonprecious metals. Herein, the study develops an ultra-low loaded, atomically dispersed cobalt catalyst, which displays an exceptional performance in the RCF of lignocellulose. An approximately theoretical maximum yield of phenolic monomers (48.3 wt.%) from lignin is realized, rivaling precious metal catalysts. High selectivity toward 4-propyl-substituted guaiacol/syringol facilitates their purification and follows syntheses of highly adhesive polyesters. Lignin nanoparticles (LNPs) are generated by simple treatment of the obtained phenolic dimers and oligomers. RCF-resulted carbohydrate pulp are more obedient to enzymatic hydrolysis. Experimental studies on lignin model compounds reveal the concerted cleavage of Cα-O and Cβ-O pathway for the rupture of β-O-4 structure. Overall, the approach involves valorizing products derived from lignin biopolymer, providing the opportunity for the comprehensive utilization of all components within lignocellulose.

Atmospheric reductive catalytic fractionation of lignocellulose integrated with one-pot catalytic conversion of carbohydrate yielding valuable lignin monomers and platform chemicals from corn straw

Developing a cost-effective and environmentally friendly process for the production of valuable chemicals from abundant herbal biomass receives great attentions in recent years. Herein, taking advantage of the “lignin first” strategy, corn straw is converted to valuable chemicals including lignin monomers, furfural and 5-methoxymethylfurfural via a two steps process. The key of this research lies in the development of a green and low-cost catalytic process utilizing magnetic Raney Ni catalyst and high boiling point ethylene glycol. The utilization of neat ethylene glycol as the sole reactant under atmospheric conditions obviates the need for additional additives, thereby facilitating the entire process to be conducted in glass flasks and rendering it highly convenient for scaling up. In the initial step, depolymerization of corn straw lignin resulted in a monomer yield of 18.1 wt%. Subsequently, in a dimethyl carbonate system, the carbohydrate component underwent complete conversion in a one-pot process, yielding furfural and 5-methoxymethylfurfural as the primary products with an impressive yield of 47.7 %.

Sequential catalytic lignin valorization and bioethanol production: an integrated biorefinery strategy

BackgroundThe effective valorization of lignin and carbohydrates in lignocellulose matrix under the concept of biorefinery is a primary strategy to produce sustainable chemicals and fuels. Based on the reductive catalytic fractionation (RCF), lignin in lignocelluloses can be depolymerized into viscous oils, while the highly delignified pulps with high polysaccharides retention can be transformed into various chemicals.ResultsA biorefinery paradigm for sequentially valorization of the main components in poplar sawdust was constructed. In this process, the well-defined low-molecular-weight phenols and bioethanol were co-generated by tandem chemo-catalysis in the RCF stage and bio-catalysis in fermentation stage. In the RCF stage, hydrogen transfer reactions were conducted in one-pot process using Raney Ni as catalyst, while the isopropanol (2-PrOH) in the initial liquor was served as a hydrogen donor and the solvent for lignin dissolution. Results indicated the proportion of the 2-PrOH in the initial liquor of RCF influenced the chemical constitution and yield of the lignin oil, which also affected the characteristics of the pulps and the following bioethanol production. A 67.48 ± 0.44% delignification with 20.65 ± 0.31% of monolignols yield were realized when the 2-PrOH:H2O ratio in initial liquor was 7:3 (6.67 wt% of the catalyst loading, 200 °C for 3 h). The RCF pulp had higher carbohydrates retention (57.96 ± 2.78 wt%), which was converted to 21.61 ± 0.62 g/L of bioethanol with a yield of 0.429 ± 0.010 g/g in fermentation using an engineered S. cerevisiae strain. Based on the mass balance analysis, 104.4 g of ethanol and 206.5 g of lignin oil can be produced from 1000 g of the raw poplar sawdust.ConclusionsThe main chemical components in poplar sawdust can be effectively transformed into lignin oil and bioethanol. The attractive results from the biorefinery process exhibit great promise for the production of valuable biofuels and chemicals from abundant lignocellulosic materials.

Innovative flow-through reaction system for the sustainable production of phenolic monomers from lignocellulose catalyzed by supported Mo2C.

Molybdenum carbide supported on activated carbon (β-Mo2C/AC) has been tested as catalyst in the reductive catalytic fractionation (RCF) of lignocellulosic biomass both in batch and in Flow-Through (FT) reaction systems. High phenolic monomer yields (34 wt.%) and selectivity to monomers with reduced side alkyl chains (up to 80 wt.%) could be achieved in batch in the presence of hydrogen. FT-RCF were made with no hydrogen feed, thus via transfer hydrogenation from ethanol. Similar selectivity could be attained in FT-RCF using high catalyst/biomass ratios (0.6) and high molybdenum loading (35 wt.%) in the catalyst, although selectivity decreased with lower catalyst/biomass ratios or molybdenum contents. Regardless of these parameters, high delignification of the lignocellulosic biomass and similar monomer yields were observed in the FT mode (13-15 wt.%) while preserving the holocellulose fractions in the delignified pulp. FT-RCF system outperforms the batch reaction mode in the absence of hydrogen, both in terms of activity and selectivity to reduced monomers that is attributed to the two-step non-equilibrium processes and the removal of diffusional limitations that occur in the FT mode. Even though some molybdenum leaching was detected, the catalytic performance could be maintained with negligible loss of activity or selectivity for 15 consecutive runs.

Monolignol Potential and Insights into Direct Depolymerization of Fruit and Nutshell Remains for High Value Sustainable Aromatics.

The inedible parts of nuts and stone fruits are low-cost and lignin-rich feedstock for more sustainable production of aromatic chemicals in comparison with the agricultural and forestry residues. However, the depolymerization performances on food-related biomass remains unclear, owing to the broad physicochemical variations from the edible parts of the fruits and plant species. In this study, the monomer production potentials of ten major fruit and nutshell biomass were investigated with comprehensive numerical information derived from instrumental analysis, such as plant cell wall chemical compositions, syringyl/guaiacyl (S/G ratios, and contents of lignin substructure linkages (β-O-4, β-β, β-5). A standardized one-pot reductive catalytic fractionation (RCF) process was applied to benchmark the monomer yields, and the results were statistically analyzed. Among all the tested biomass, mango endocarp provided the highest monolignol yields of 37.1 % per dry substrates. Positive S-lignin (70-84 %) resulted in higher monomer yield mainly due to more cleavable β-O-4 linkages and less condensed C-C linkages. Strong positive relationships were identified between β-O-4 and S-lignin and between β-5 and G-lignin. The analytical, numerical, and experimental results of this study shed lights to process design of lignin-first biorefinery in food-processing industries and waste management works.

Enhancing the Production of Phenolic Monomers from Reductive Catalytic Fractionation of Biomass over Catalyst of Ni–N-Doped Carbon

Enhancing the Production of Phenolic Monomers from Reductive Catalytic Fractionation of Biomass over Catalyst of Ni–N-Doped Carbon