Production of liquefied fuel from depolymerization of kraft lignin over a novel modified nickel/H-beta catalyst

Advances in Heterogeneous Catalysts for Lignin Hydrogenolysis

Lignin is the main component of lignocellulose and the largest source of aromatic substances on the earth. Biofuel and bio-chemicals derived from lignin can reduce the use of petroleum products. Current advances in lignin catalysis conversion have facilitated many of progress, but understanding the principles of catalyst design is critical to moving the field forward. In this review, the factors affecting the catalysts (including the type of active metal, metal particle size, acidity, pore size, the nature of the oxide supports, and the synergistic effect of the metals) are systematically reviewed based on the three most commonly used supports (carbon, oxides, and zeolites) in lignin hydrogenolysis. The catalytic performance (selectivity and yield of products) is evaluated, and the emerging catalytic mechanisms are introduced to better understand the catalyst design guidelines. Finally, based on the progress of existing studies, future directions for catalyst design in the field of lignin depolymerization are proposed.

Microwave-assisted depolymerization of lignin with synergic alkali catalysts and a transition metal catalyst in the aqueous system

In this study, synergic alkali catalysts (NaOH + NaAlO2) and Ni/ZrO2 were used for microwave-assisted lignin depolymerization.

Mild depolymerization of the sinocalamus oldhami alkali lignin to phenolic monomer with base and activated carbon supported nickel-tungsten carbide catalyst composite system

In this study, the sinocalamus oldhami alkali lignin was depolymerized into phenolic products in a combined system by using the composite alkali and Ni-W₂C/activated carbon (AC) as catalysts. FT-IR, GPC, TG, 2D-HSQC and GC-MS were used to analyze the composition, structure and distribution of degradation products, and the synergistic effect of metal and alkali catalysts on the depolymerization of lignin was also studied. The results showed that Ni-W₂C/AC and composite alkali could effectively improve the catalytic degradation efficiency of lignin under mild conditions, 94.4% of lignin was converted and 17.18% of phenolic monomers were obtained under 260 °C for 5 h. In this composite system, the synergism of the basic sites, the metal active sites and the Lewis acid sites could promote the cleavage of C-O bonds in the lignin molecule and lower the char formation during the base-catalyzed solvolysis. Phenolic monomers were mainly composed of phenol, 2-methyl-phenol and p-cresol etc.

Advances in Versatile Nanoscale Catalyst for the Reductive Catalytic Fractionation of Lignin

In the past five years, biomass-derived biofuels and biochemicals were widely studied both in academia and industry as promising alternatives to petroleum. In this Review, the latest progress of the synthesis and fabrication of porous nanocatalysts that are used in catalytic transformations involving hydrogenolysis of lignin is reviewed in terms of their textural properties, catalytic activities, and stabilities. A particular emphasis is made with regard to the catalyst design for the hydrogenolysis of lignin and/or lignin model compounds. Furthermore, the effects of different supports on the lignin hydrogenolysis/hydrogenation are discussed in detail. Finally, the challenges and future opportunities of lignin hydrogenolysis over nanomaterial-supported catalysts are also presented.

Selective production of phenolic monomers via high efficient lignin depolymerization with a carbon based nickel-iron-molybdenum carbide catalyst under mild conditions

Lignin is an abundant renewable source of bio-aromatics and its valorization is of great importance. In this work, an efficient non-precious carbon based metal-Mo₂C catalytic system for selective production of phenolic monomers (PMs) from organosolv lignin depolymerization is proposed. With the optimized catalyst of Ni-Fe-Mo₂C, 89.56% of liquefaction and 35.53% of PMs yields were achieved under 260 ℃ for 4 h with water-methanol (4:1 v/v) solvent. Characterization of the catalysts shows that the induction of Ni-Fe species was favor for the formation of β-Mo₂C, and efficiently promoted the lignin liquefaction. The decoration of Ni/Fe can also change the side chain hydrogenolysis ability of the catalyst and exhibite high yield for 4-ethylphenol (14.77%) production. Methanol, used as co-solvent, was found to play an important role in PMs production and lignin depolymerization. These results demonstrated that the Ni-Fe-Mo₂C catalytic system has potential to produce valuable phenolic monomers from lignin under mild conditions.

Solvolysis of Kraft Lignin to Bio-Oil: A Critical Review

Lignin, a component of lignocellulosic biomass, is abundant and is produced extensively as a waste product of the Kraft pulping process, lignin obtained from this process is called Kraft lignin (KL). Lignin’s three-dimensional structure composed of aromatic alcohols (monolignols) makes it a potential source of renewable aromatic chemicals or bio-oil, if depolymerized. Among all the depolymerization methods for KL, solvolysis is the most popular, showing consistently high bio-oil yields. Despite the large number of studies that have been carried out, an economically feasible industrial process has not been found and comparison among the various studies is difficult, as very different studies in terms of reaction media and catalysts report seemingly satisfactory results. In this review, we compare and analyze KL solvolysis studies published, identify trends in bio-oil composition and give a comprehensive explanation about the mechanisms involved in the processes. Additional commentary is offered about the availability and future potential of KL as a renewable feedstock for aromatic chemicals, as well as logistical and technical aspects.

Cleavage of aryl-ether bonds in lignin model compounds using a Co-Zn-beta catalyst

Efficient cleavage of aryl-ether linkages is a key strategy for generating aromatic chemicals and fuels from lignin. Currently, a popular method to depolymerize native/technical lignin employs a combination of Lewis acid and hydrogenation metal. However, a clear mechanistic understanding of the process is lacking. Thus, a more thorough understanding of the mechanism of lignin depolymerization in this system is essential. Herein, we propose a detailed mechanistic study conducted with lignin model compounds (LMC) via a synergistic Co-Zn/Off-Al H-beta catalyst that mirrors the hydrogenolysis process of lignin. The results suggest that the main reaction paths for the phenolic dimers exhibiting α-O-4 and β-O-4 ether linkages are the cleavage of aryl-ether linkages. Particularly, the conversion was readily completed using a Co-Zn/Off-Al H-beta catalyst, but 40% of α-O-4 was converted and β-O-4 did not react in the absence of a catalyst under the same conditions. In addition, it was found that the presence of hydroxyl groups on the side chain, commonly found in native lignin, greatly promotes the cleavage of aryl-ether linkages activated by Zn Lewis acid, which was attributed to the adsorption between Zn and the hydroxyl group. Followed by the cobalt catalyzed hydrogenation reaction, the phenolic dimers are degraded into monomers that maintain aromaticity.

Rational production of highly acidic sulfonated carbons from kraft lignins employing a fractionation process combined with acid-assisted hydrothermal carbonization

Highly acidic lignin-derived sulfonated carbons (LDSCs) were produced from hardwood and softwood kraft lignins under mild conditions by applying fractionation and/or pre-carbonization treatments combined with acid-assisted hydrothermal carbonization. The use of lignin fraction with higher amount oxygen, obtained from the fractionation process, resulted in carbon with the highest density of surface acid groups and improved catalytic activity. The LDSCs were successful tested in the dehydration reaction of fructose to obtain 5-hydroxymethylfurfural, and the best catalyst can be recycled without loss in its catalytic activity after perform a simple regeneration process. In contrast, the pre-carbonization step, commonly performed in several works, resulted in LDSCs with low acidity. A simple and optimized methodology for obtaining LDSCs under mild conditions was developed, and the correlations between the preparation method and the physicochemical and catalytic properties established in this work may be extendible to other starting materials for rational sulfonated carbons production.

High performance of Mo-promoted Ir/SiO2 catalysts combined with HZSM-5 toward the conversion of cellulose to C5/C6 alkanes

In this study, the Mo-promoted Ir/SiO₂ (Ir-MoO_x/SiO₂) catalysts combined with the zeolite HZSM-5 were used for the direct conversion of microcrystalline cellulose (MCC) to liquid fuel (C₅/C₆ alkanes) in n-dodecane/H₂O system. A synergistic effect was formed between the partially reduced MoO_x species and the Ir particles, which effectively promoted the catalytic activity of Ir/SiO₂ catalyst. When the Mo/Ir molar ratio was 0.5, a high yield of C₅/C₆ alkanes (91.7%) was achieved at 210 ℃ for 12 h. In addition, the main component of C₅/C₆ alkanes was n-hexane, which was proven to be obtained by the hydrogenolysis of the key intermediate, sorbitol, formed from the hydrolysis and hydrogenation of MCC.

Efficient depolymerization of Kraft lignin to liquid fuels over an amorphous titanium-zirconium mixed oxide supported partially reduced nickel-cobalt catalyst

A series of non-precious metal/metal oxide nickel-cobalt catalysts was prepared for a highly efficient depolymerization of Kraft lignin (KL) into liquid fuels using amorphous TiZr-oxide (Ti_1-yZr_yO₂) as a carrier. The effects of Ni-NiO_x, Co-CoO_x, NiCo-NiCoO_x, NiCoO_x and NiCo catalysts supported on amorphous TiZr-oxide carrier on KL depolymerization were investigated. It was found that the NiCo-NiCoO_x/Ti_1-yZr_yO₂ catalyst is optimal for converting KL to petroleum ether (PE)-soluble product (mainly composed of monomers and dimers) in an 80.2% high yield at 320 °C for 24 h, with excellent reusability and a low formation of char. Under these conditions, the higher heating value (HHV) increased from 25.11 to 33.89 MJ/kg. A meticulous study on NiCo-NiCoO_x/Ti_1-yZr_yO₂ catalysts revealed that the synergistic effect among Lewis acid sites, basic sites and metal active sites played an important role in obtaining high yields of monomers and low rates of char formation during lignin conversion.

Ethanol/1,4-dioxane/formic acid as synergistic solvents for the conversion of lignin into high-value added phenolic monomers

In this study, a mixture solvent of ethanol/1,4-dioxane/formic acid (FA) is firstly reported to efficaciously depolymerize industrial lignin to produce high-value added phenolic monomers, in which 1,4-dioxane acts as lignin solvent, ethanol acts as solvent, reactant and in situ hydrogen donor, and FA acts as acid catalyst and in situ hydrogen donor. The effects of solvent composition and reaction conditions on the lignin conversion and product yields were explored, resulting in a low residue yield of 6.57% and a high phenolic monomers yield of 22.4% at 300 °C for 2 h when Kraft lignin was depolymerized in the mixture solvent of ethanol/1,4-dioxane/FA (10:10:2, v/v). Moreover, possible reaction mechanism on lignin depolymerization in the mixture solvent was illustrated, suggesting a favorable synergistic effect among the three components of the mixture solvent. In addition, the satisfactory applicability of the mixture solvent was approved through the feedstock adaptability and recyclability experiments.