Alkali Lignin Catalytic Hydrogenolysis with Biofuel Production

Synthesized 5% Pd/Al2O3 and 5% Pd/ATP were used in the hydrogenolysis of lignin in the presence of a solvent of a hydrogen donor, propanol-2, to obtain liquid fuel components. It has been established that the use of Pd-containing alumina-based catalysts makes it possible to obtain phenolic compounds, while in the presence of catalysts based on a polymer matrix from hyperastained polystyrene, the main products are cycloalkanes. In addition, the study of the hydrogenolysis process showed that when using propanol-2 as a solvent, the formation of aromatic compounds is mainly observed, while in the aqueous medium a high yield of phenols is achieved.

The conversion of lignin, the most recalcitrant of the biopolymers, is necessary for a carbon-efficient utilization of lignocellulosic materials. In this context, hydrogenolysis of lignin is a process receiving increasing attention. In this report, the solvent effects on the hydrogenolysis of diphenyl ether and lignin with Raney Ni are addressed. The Lewis basicity of the solvent very much affects the catalytic activity, so Raney Ni in nonbasic solvents is an extremely active catalyst for hydrogenolysis and hydrogenation. In basic solvents, however, Raney Ni is a less active, but much more selective catalyst for hydrogenolysis while preserving the aromatic products. With regard to the reactions with lignin, assessing the complexity of the product mixtures by two-dimensional GC×GC-MS revealed solvent effects on the product distribution. Reaction in methylcyclohexane resulted in cyclic alcohols and cyclic alkanes, whereas reaction in 2-propanol led to cyclic alcohols, cyclic ketones, and unsaturated products. The hydrogenolysis of lignin in methanol, however, produced mostly phenols. Overall, these results demonstrate that the solvent plays a key role in directing the selectivity and, thus, it must be taken into consideration in the design of catalytic systems for conversion of lignin by hydrogenolysis of C-O ether bonds.

The article analyzes published and original data related to the carbon isotopic composition of individual aromatic compounds of fossil organic matter and oil. It has been shown that there is reliable evidence of the intramolecular isotopic heterogeneity of a number of molecules. For example the isotopically depleted carbon of the methyl group of alkylnaphthalenes and the terminal methyl of n-alkanes. The 13C inheritance from the biochemical precursor during the aromatization is also well documented in the example of diterpenes in the series abietic acid — dehydroabietane — simonellite — retene, as well as in the other terpene and steroid series. At the same time, there is evidence of carbon isotopic fractionation during the formation of several aromatic compounds from a single precursor. The increasing aromatization of the prebuild polycyclic structure does not change the 13C value of the molecule, and the formation of aromatic compounds with different numbers of aromatic rings in competing reactions leads to isotope differentiation in accordance with the thermodynamically determined distribution of carbon isotopes. If the suggestion is correct, it is the key to the understanding of specific petroleum aromatic hydrocarbons formation mechanism. It is possible that a comparison of 13C values for pairs of compounds formed during the transformation of one precursor will also provide information on the temperature conditions for the occurrence of the corresponding reactions.

Model combustions are performed in order to simulate a real fire situation. The model used, however, and parameters chosen have a considerable impact on combustion products formed and on their amounts. Formation of hydrocyanic acid from nitrogen-containing molecules was studied. For combustion, the VCI-apparatus (Heraeus) was used. The substances a) linuron, b) triazophos (70% formulation) and c) sheep wool contained 10 to 15% nitrogen. At temperatures of 600 and 950°C, portions in the range of 0.4 to 25 mg were combusted. Formation of aromatic compounds at 950°C was studied for triazophos (70% formulation) and 2-ethylhexyl-thioglycolate.

Excessive consumption of fossil fuel for the production of energy carriers and commodity chemicals caused depletion of fossil fuel resources, environmental pollution, and global warming. Hence, many researchers investigated the production of renewable energy, and chemical commodities from sustainable energy resources, which are abundant and comparably cleaner alternatives to fossil fuel derivatives. Among these renewable resources, lignocellulosic biomass (vegetal cell component including, cellulose, hemicellulose and lignin) appears to be a promising alternative for the production of commodity chemicals and fuels. Lignocellulosic biomass comprises three primary components: cellulose, hemicellulose, and lignin. Lignin, the second principal constituent of biomass after cellulose, is an amorphous polymer made of aromatic monomers. Lignin has been known as the most abundant renewable source of natural building blocks of aromatics and has high potential to serve as a precursor for the production of functionalised aromatics in the petroleum industry. To achieve this goal, many researchers investigated thedepolymerisation of lignin, for the production of monomeric aromatics.This project aims to use lignin as an abundant natural resource for the production of low molecular weight chemical commodities. To achieve this goal, successful fractionation trailed by chemocatalytic upgrading is required to build an effective lignin depolymerisation sequence. Depolymerisation of lignin carried out in this project using two approaches, namely, reductive depolymerisation and fast pyrolysis reaction.To conduct the reductive depolymerisation reaction titanium nitride (TiN) Nano-catalyst supported with copper nanocatalysts used as the catalyst for hydrogenolysis of lignin. In order to investigate the reactivity of TiN supported copper catalyst (TiN-Cu), hydrogenation of benzaldehyde carried out using a series of TiN-Cu and available commercial catalysts. These tests revealed the high activity of TiN particles loaded with 30 Wt. % copper in hydrogenolysis reaction comparable to industrial noble catalysts. Degradation of model compounds with TiN-Cu catalysts carried out to measure the reactivity of lignin and lignin oxide model compounds in the hydrogenation process, which show higher reactivity for selectively oxidised lignin model compounds. In order to promote real lignin sample reactivity during the hydrogenolysis process, selective oxidation of α hydroxyl group of lignin conducted. Selective aerobic oxidation of lignin source carried with HCl/HNO3/TEMPO ((2,2,6,6-Tetramethylpiperidin-1-yl)oxyl) catalyst, and the obtained lignin oxide used for hydrogenation step with TiN-Cu catalyst. High degradation rate for lignin achieved in this process resulting in the production of oligomers consisting of 2 to 3 interconnected aromatic rings and valuable phenolic monomers. The obtained dimers and monomers from hydrogenolysis of lignin, shown high potential to be used as commodity chemicals, such as phenolic precursor for the petrochemical industry.Fast pyrolysis reaction used as the second approach for depolymerisation of lignin. Solvent-assisted fast pyrolysis of lignin shown high selectivity for depolymerisation of lignin toward dimers and trimers with a low amount of oxygen. This process is capable of lowering the aliphatic hydroxyl contents of lignin, along with increasing the amount of single and double bonded aliphatics. The addition of solvent during fast pyrolysis of lignin lowered the molecular weight distribution of the obtained bio-oil (~49-52% decrease) and prohibited the formation of the high amount of char content. The detailed study for cleavage of complex model compounds using Ethanol assisted fast pyrolysis (EAFP) revealed the active sites during this process are the aliphatic hydroxyl groups and etheric linkages. The EAFP of the deuterated lignin model compounds and solvent concluded that the mechanism for cleavage of lignin in the EAFP process involves the formation of a transition state between solvent and oxygen sites of lignin. This transition state involves the cleavage of the etheric site by in situ transfer of hydrogen from ethanol to this linkage.In the final stage of this project, an approach is designed to upgrade industrial available biooils for production of commodity chemicals such as phenolic precursor, and fuel components like BTX (benzene, toluene, and xylene). In this approach, the obtained bio-oils from fast pyrolysis of the tree, hydrogenated in the presence of an industrial catalyst. This process showed a high capacity for lowering the amount of oxygen and resulted in the production of 22% of phenolic monomers, which has high potential to be used as a chemical precursor in the polymer industry. In the other hand, the approach for upgrading the phenolic monomers to a low oxygenated chemical was successful, in which, the fine phenolic monomers such as catechol, anisole, and aliphatic monomers like propanol obtained by the extended HDO reaction.It is believed that the developed method for depolymerisation of lignin to low molecular weight bio-oil and upgrading of the obtained bio-oil can be an effective environmental friendly bioprocess for the production of commodity chemicals and biofuels from lignin.

The present investigation aims at exploring the application of low‐cost catalysts based on smectitic clays to the hydrodeoxygenation (HDO) of Cynara cardunculus derived lignin. Two types of clay minerals, montmorillonite and saponite, are pillared and decorated with suitable metals by means of an optimized process and characterized by X‐ray powder diffraction (XRPD), porosity, scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), Fourier‐transform infrared spectroscopy (FTIR), UV–vis–NIR, Raman, and thermogravimetric analysis (TGA). Alkaline lignin is obtained from steam‐treated cardoon. Lignin depolymerization is conducted in a bench‐scale apparatus under subcritical conditions, at relatively low temperature (320 °C), for 3 h, under 5‐6 MPa of total pressure. Four catalysts are tested, namely, Fe/Al‐pillared montmorillonite (FAMO) and saponite (FASA), and Ni‐exchanged Ni/Al‐pillared montmorillonite (Ni–Ni/AMO) and saponite (Ni–Ni/ASA). Results indicate that mineral clay–based catalysts result effectively in the hydrogenolysis of lignin, producing several low molecular weight aromatics and other species, with overall conversions in the range 60–70%. Montmorillonite‐based catalysts yield the highest substrate conversion, with a prevalence of phenols and substituted phenols, whereas only Ni–Ni/ASA generates a higher abundance of aliphatic hydrocarbons. Overall, data indicate that smectitic clays are promising catalyst supports for products‐oriented HDO of lignin.

Lignin depolymerization has been studied for decades to produce carbon-neutral chemicals/biofuels and biopolymers. Among different chemical reaction pathways, catalytic hydrogenolysis favors reactions under relatively mild conditions, while its yield of bio-oil and high-value aromatic products is relatively high. In this study, the influence of reaction parameters on lignin hydrogenolysis are discussed by chemical process parameter mapping and modeled using three different machine learning algorithms based upon literature experimental data. The best R2 scores for solid residue and aromatic yield were 0.92 and 0.88 for xgboost, respectively. The parameter importance was examined, and it was observed that lignin-to-solvent ratio and average pore size have a larger impact on lignin hydrogenolysis results. Finally, the optimal conditions of lignin hydrogenolysis were predicted by chemical process parameter mapping using the best-fit machine learning model, which indicates that further process improvements can potentially generate higher yields in industrial applications.

Formation of aromatic compounds from condensation reactions of cellulose degradation products

Efficient lignin hydrogenolysis over N-doped macroporous carbon supported Ru catalyst

The catalytic depolymerization of organic solvent lignin with the prepared catalyst 2.5Ru–10Ni/Al-HY was investigated in a high-pressure reactor. Effects of different catalysts, temperature, time, recyclability for catalyst, and solvents on the catalytic performance were explored. The optimal reaction conditions were reaction time 5 h and temperature 280 °C in ethanol solvent. As a result, the highest yield of phenolic monomers was 20.2 wt %, the yield of solid residue was only 4.8 wt %, and the gas products were CH4, C2H6, and CO mainly. With the increase of cycle times, the catalyst had no obvious deactivation, indicating a unique cycle stability. Through NMR characterization of lignin and depolymerization products, it was found that the signals of the original structures (A, B, and C) in lignin disappeared after reaction. According to the analysis of the reaction path, the depolymerization of lignin mainly included the depolymerization of lignin into reaction intermediates and the formation of phenolic compounds by breaking chemical bonds. This research showed a method for preparing phenolic products by the molecular sieve catalyzed depolymerization of lignin.

Catalytic depolymerization of alkaline lignin to value-added phenolic-based compounds over Ni/CeO2-ZrO2 catalyst synthesized with a one-step chemical reduction of Ni species using NaBH4 as the reducing agent

The formation of pyrolytic solid deposit, or coke, in the fuel line can be detrimental to the operation of high-speed aircraft. Yet, the formation of coke from the fuel has not been well characterized. The present study has investigated the relationship between the formation of aromatic compounds and solid deposition for three candidates for high-thermal-stability jet fuels at 482 °C (900 °F) with stressing periods up to 2 h. The fuels include one coal-derived (JP-8C), one paraffinic petroleum-derived (JP-8P), and one naphthenic petroleum-derived (DA/HT LCO). The DA/HT LCO, an extensively hydrotreated light cycle oil where virtually all aromatics have been hydrogenated to cycloalkanes, suppressed the solid deposition to a greater extent than that of the more paraffinic petroleum-derived JP-8P and showed a comparable low solid deposition to that of the coal-derived fuel JP-8C. Both GC/MS and solution-state 13C NMR analysis on the stressed fuels confirmed that the paraffinic content is most likely to crack ...

Catalytic hydrogenolysis of lignin in ethanol/isopropanol over an activated carbon supported nickel-copper catalyst

Lignin depolymerization is crucial for producing fuels and chemicals. Catalytic hydrodeoxygenation offers a distinct method for lignin depolymerization, leading to improved bio-oil conversion yields. This approach involves breaking C-O bonds, hydrogenating rings, and opening rings. In this study, Ru-based bifunctional catalysts with a low Ru metal loading of 0.2 to 0.5 wt.% on tungstated zirconia (Ru/W-Zr-O) were investigated for the ring hydrogenation and hydrogenolysis of lignin model compounds (β-hydroxypropiovanillone and guaiacol) as well as corn stover lignin. The Ru/W-Zr-O catalyst exhibited similar selectivity for ring hydrogenation as the Ru/Al2O3 catalyst. However, Ru/W-Zr-O consistently demonstrated high selectivity for ring-opening hydrogenation products (e.g., linear alkanes) from the model compounds and lignin, particularly in ethanol compared to water. "The highest selectivity towards long-chain alkanes in bio-oil was 79.4%, with an overall lignin conversion rate of 90.6%. By comparing and analyzing experimental data with the activation energies of bonds in lignin model compounds using density functional theory, the reaction mechanism was determined to follow this route: 'aromatics → cyclic hydrocarbon → linear hydrocarbon.' By optimizing the characteristics of bifunctional catalysts and solvents, this work suggests the potential for designing effective catalysts supported on tungstated zirconia for the selective hydrogenolysis of lignin into long-chain alkanes.Graphical

Lignin valorization is strongly dependent on a right strategy for converting lignin into value-added products. Conversion of lignin into monomeric degradation products is one of the important avenues. In this study, chemical mechanisms and monomeric product compositions in hydrolysis (acidic and alkaline), hydrogenolysis, catalytic oxidation, electrochemical oxidation and reduction, photochemical and enzymatic degradation of native and technical lignins, and lignin model compounds are comparatively analyzed. The effect of the structure of a phenylpropane unit in lignin on the chemical reactivity of α-O-4 and β-O-4 bonds in cleavage reactions is also described. Published experimental data suggest some form of activation to be a necessary prerequisite for the splitting of a β-O-4 bond in all chemical reactions under consideration, the nature of which is dependent on the reagents and reaction conditions. Thus, in catalytic oxidation processes, a benzyl hydroxyl group is converted into carbonyl group at the first stage. Chemical transformation involving the α-position in a phenylpropane unit is a usual trigger of further lignin depolymerization. The yield of monomeric products of hydrogenolysis of native lignin is close to the theoretical one, reaching 23% in softwood and 51% in hardwood; in alkaline hydrolysis as well as oxygen and nitrobenzene oxidation of native lignin, the trend is the same that is explained in this study. On the other hand, the yield of monomeric products from isolated samples and technical lignins is much lower. A loss of arylether bonds in the process of lignin separation from wood and in wood pulping explains this difference.