Kinetics and Mechanism of Hydrothermal Decomposition of Lignin Model Compounds

The kinetics and underlying mechanisms of the hydrothermal decomposition of the lignin model compounds anisole, diphenyl ether and phenethyl phenyl ether were studied. Whereas diphenyl ether was stable at hydrothermal conditions, anisole and phenethyl phenyl ether underwent hydrothermal decomposition between 260 and 290 °C. Experiments involving different initial reactant concentrations and different batch holding times revealed that hydrolysis of both anisole and phenethyl phenyl ether followed first-order kinetics. Experiments at different temperatures showed that the first-order rate constants displayed Arrhenius behavior, with activation energies of 149.8 ± 16.4 and 143.2 ± 21.0 kJ·mol^–1 for anisole and phenethyl phenyl ether, respectively. A reaction mechanism is proposed for anisole, and reaction pathways for the decomposition of phenethyl phenyl ether are proposed based on the distribution of the products generated by hydrolysis. The reactivity of ether hydrothermal decomposition is discussed by reviewing the published conversion data of other ethers

Crystallization of Asiaticoside from Total Triterpenoid Saponins of <i>Centella Asiatica</i> in a Methanol + Water System

In this contribution, a novel solvent system for the crystallization of asiaticoside from total triterpenoid saponins of <i>Centella asiatica</i> was established by utilizing the difference between the induction periods of madecassoside and asiaticoside. Asiaticoside could be separated from the mixture of asiaticoside and madecassoside by crystallization with about 80% yield and 95% purity. The mechanism behind the significantly different induction periods of asiaticoside and madecassoside in the methanol + water system is also proposed. Crystallization of asiaticoside from total triterpenoid saponins of <i>Centella asiatica</i> achieved a maximum yield of 60% with 70% purity. A recrystallization was carried out to obtain 76% yield with 91% purity. The optimized conditions for the crystallization of asiaticoside from total triterpenoid saponins of <i>Centella asiatica</i> were determined

Microwave-Assisted Oxidative Degradation of Lignin Model Compounds with Metal Salts

A systematic study on microwave-assisted oxidative degradation of lignin model compounds, such as 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol, was performed by evaluating the catalytic activity of 14 types of metal salts. The acidity of each metal salt solution for the oxidative degradation of 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol under the microwave irradiation and conventional heating conditions was measured and compared. The results showed that CrCl₃ and MnCl₂ were the most effective for the degradation of the lignin model compounds. The acidity of metal salt is in favor of the catalytic activity for the degradation of 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol, and microwave irradiation is able to accelerate the degradation rate in a large scale. The possible mechanisms for the degradation of 2-phenoxy-1-phenylethanol, vanillyl alcohol, and 4-hydroxybenzyl alcohol are proposed on the basis of the product distributions

Copper-Catalyzed Decarboxylation of 2,4,5-Trifluorobenzoic Acid in NH₃‑Enriched High-Temperature Liquid Water

1,2,4-Trifluorobenzene, the decarboxylation product of 2,4,5-trifluorobenzoic acid, is an important raw material for synthesizing sitagliptin phosphate, the main medicinal treatment for diabetes. The traditional synthesis suffers from environmental concerns; therefore, in this work, a series of metal catalysts was employed to catalyze the decarboxylation of 2,4,5-trifluorbenzoic acid in NH₃-enriched high-temperature liquid water (HTLW) to address these concerns. Copper catalysts exhibited excellent performance, and heterogeneous copper catalysts, such as Cu and Cu₂O, led to a higher yield of 1,2,4-trifluorobenzene (89.1%) than homogeneous copper catalysts, such as CuCl₂ and CuCl. The effects of catalyst loading and reactant loading on the decarboxylation of 2,4,5-trifluorbenzoic acid were also investigated. Increases in the catalyst and reactant loadings were favorable for the decarboxylation of 2,4,5-trifluorbenzoic acid; however, a high catalyst loading was not favorable. A reusability test with Cu₂O revealed that Cu₂O has excellent activity maintenance in NH₃-enriched HTLW

Synergy of Lewis and Brønsted Acids on Catalytic Hydrothermal Decomposition of Hexose to Levulinic Acid

The mixed-acid systems of four Lewis acids (FeCl₃, CrCl₃, ZnCl₂, and CuCl₂) combining three Brønsted acids (H₂SO₄, HCl, and H₃PO₄) were evaluated for the decomposition of glucose to produce levulinic acid (LA). The CrCl₃–H₃PO₄ system had a strong synergic catalytic activity for the decomposition of glucose to LA. The effects of the ratio of CrCl₃ and H₃PO₄ on glucose, fructose, and 5-hydroxymethylfurfural (5-HMF) decompositions were investigated. The mixed-acid system showed the strongest synergic catalytic activity for glucose, fructose, and 5-HMF decompositions when the ratio of CrCl₃ in the CrCl₃–H₃PO₄ system was 0.4–0.5. To probe the synergic catalysis mechanism of the CrCl₃–H₃PO₄ system, the synergic catalytic activities of CrCl₃–phosphates (KH₂PO₄, K₂HPO₄, and K₃PO₄) systems on glucose decomposition were also evaluated. The possible synergic catalysis mechanisms were proposed. This study provides insights for the synergic catalysis mechanism of hexose conversion to yield LA

Adsorption of Berberine Hydrochloride, Ligustrazine Hydrochloride, Colchicine, and Matrine Alkaloids on Macroporous Resins

This research aims at identifying suitable resin adsorbents for efficient separation and purification of alkaloids from plant materials. The adsorption properties (equilibrium, kinetics, and column breakthrough) of four alkaloid model compounds (berberine hydrochloride, ligustrazine hydrochloride, colchicine, and matrine) on selected macroporous resins were studied. The adsorption equilibrium capacities and desorption ratios of the four model compounds on nine different macroporous resins were measured and compared. It was observed that the resins with a low polarity and high surface area offered a high adsorption capacity for all alkaloids. The pseudo-second-order adsorption rate equation fit well all the kinetic data, and the Langmuir and Freundlich isotherm equations correlate well the adsorption isotherms on the four resins. Among the nine resins studied in this work, the HPD300 resin was identified as the most promising adsorbent for alkaloids separation and purification because of its excellent adsorption and desorption properties for all four alkaloid compounds. The adsorption breakthrough experiment on the HPD300 resin using a mixture solution containing all four model compounds further confirmed the effective separation of alkaloids on the HPD300 resin

Adsorption of Myricetrin, Puerarin, Naringin, Rutin, and Neohesperidin Dihydrochalcone Flavonoids on Macroporous Resins

The adsorption properties (equilibrium, kinetics, and column breakthrough) of five model flavonoids (myricetrin, puerarin, naringin, rutin and neohesperidin dihydrochalcone) on selected macroporous resins were investigated in order to identify a suitable resin adsorbent for effective separation and purification of flavonoids from the extracts of herbal plants. It was observed that the resins with a low polarity and a high specific surface area have high adsorption capacities for all five flavonoids. Both the Langmuir and Freundlich isotherm equations correlate well the adsorption equilibrium data of the five flavonoids on four selected resins, and adsorption enthalpy, entropy, and free energy of the five flavonoids on HPD300 resin were calculated from the adsorption isotherms by the Freundlich equation constants. The pseudo-second-order adsorption rate equation fits the kinetic data on four selected resins better than the pseudo-first-order adsorption rate equation, and the initial adsorption rates were calculated and discussed. The HPD300 resin was selected as the most promising adsorbent for a preliminary separation and purification of flavonoids because of its excellent adsorption/desorption properties including high adsorption rates for all five flavonoids. The adsorption breakthrough experiment with a synthetic flavonoid mixture solution on the HPD300 resin further confirmed that the HPD300 resin can separate the five flavonoids effectively, especially for purifying neohesperidin dihydrochalcone from the flavonoid mixtures

Catalytic <i>In Situ</i> Hydrogenation of Fatty Acids into Fatty Alcohols over Cu-Based Catalysts with Methanol in Hydrothermal Media

The catalytic hydrogenation of fatty acids has witnessed rapid development in recent years. However, the conventional hydrogenation process often requires high-pressure hydrogen. This paper describes a novel protocol to produce fatty alcohols via an <i>in situ</i> hydrogenation of fatty acids in water and methanol using Cu-based catalysts. Cu/ZrO₂, Cu/MgO, and Cu/Al₂O₃ were prepared by the co-precipitation method. All Cu-based catalysts exhibited excellent activity for <i>in situ</i> hydrogenation of fatty acids, and the stability of Cu/ZrO₂ was the best. The structures and properties of Cu-based catalysts are demonstrated by transmission electron microscopy, X-ray diffraction, H₂ temperature-programmed reduction, N₂ adsorption–desorption, CO temperature-programmed desorption, and CO₂ temperature-programmed desorption. The stability of Cu/ZrO₂ is caused by the good hydrothermal stability and tetragonal phase formation of ZrO₂, which strongly binds to active Cu. The better activity over Cu/Al₂O₃ is caused by the larger surface area, higher Cu dispersion, smaller Cu particle size, and stronger basicity of Cu/Al₂O₃. Furthermore, the effects of the reaction time, catalyst loading, methanol loading, carbon number, and types of hydrogen donor on <i>in situ</i> hydrogenation of the fatty acids were investigated to demonstrate the reaction behaviors

Role of Solvent in Catalytic Conversion of Oleic Acid to Aviation Biofuels

The role of solvents in the conversion of oleic acid over Pt/C was studied. Three solvent systems (solvent-free, water, and dodecane systems) were employed for the conversion of oleic acid over Pt/C at 350 °C. Decarboxylation, hydrogen transfer, and aromatization were observed in these three reaction systems. In comparison to the non-solvent reaction system, much slower decarboxylation and aromatization rates and fewer heptadecane and aromatic products were observed in the hydrothermal and dodecane reaction systems. The decarboxylation and aromatization rates and yields of heptadecane and aromatics decreased with increased dodecane loading in the dodecane reaction system, and the decarboxylation and aromatization rates and yields of heptadecane and aromatics significantly decreased with the increase of water in the hydrothermal reaction system. The effects of solvent loading, catalyst loading, and reaction time on the reactions (decarboxylation, hydrogen transfer, and aromatization) were investigated. The reaction behaviors of 1-heptadecene with different solvents were studied, and N₂ adsorption–desorption and thermogravimetric analysis of fresh and spent Pt/C in the three reaction systems were also performed. The results indicate that the competition of dodecane for the Pt/C active sites is mainly responsible for the slow decarboxylation and aromatization rates. In addition to the similar influencing factor to that in the dodecane system, H⁺ released from water and hydrogen bonding, which inhibited the ionization of carboxyl groups, was the key influencing factor for the slower decarboxylation and aromatization rates obtained under hydrothermal conditions

Catalytic Decarboxylation and Aromatization of Oleic Acid over Ni/AC without an Added Hydrogen Donor

Ni/AC (nickel on active carbon) catalysts with different Ni loadings were synthesized and studied for the decarboxylation and aromatization of oleic acid in the absence of H₂ or hydrogen donors. Without the use of hydrogen source, the whole deoxygenation process became more economical. Moreover, oleic acid can be saturated using the H₂ derived from the production of aromatics, which were also considered as the critical component in aviation biofuels. The structure and properties of the catalysts were investigated using X-ray diffraction, transmission electron microscopy, and temperature-programmed desorption of CH₃COOH and CO. The experimental and characterization results revealed that 30% Ni/AC had a higher adsorption capacity of CH₃COOH among the other Ni/AC catalysts and highly dispersed and small Ni particles, providing a heptadecane yield of 40.7%. It also contained 13.8% aromatics, which fulfills the requirement of aviation fuels. This Ni/AC catalyst showed good stability even after being reused thrice