10 research outputs found
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<sup>–1</sup> 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 CrCl<sub>3</sub> and MnCl<sub>2</sub> 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 NH<sub>3</sub>‑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 NH<sub>3</sub>-enriched high-temperature
liquid water (HTLW) to address these concerns. Copper catalysts exhibited
excellent performance, and heterogeneous copper catalysts, such as
Cu and Cu<sub>2</sub>O, led to a higher yield of 1,2,4-trifluorobenzene
(89.1%) than homogeneous copper catalysts, such as CuCl<sub>2</sub> 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 Cu<sub>2</sub>O revealed that Cu<sub>2</sub>O has excellent activity maintenance
in NH<sub>3</sub>-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 (FeCl<sub>3</sub>, CrCl<sub>3</sub>, ZnCl<sub>2</sub>, and CuCl<sub>2</sub>) combining three
Brønsted acids (H<sub>2</sub>SO<sub>4</sub>, HCl, and H<sub>3</sub>PO<sub>4</sub>) were evaluated for the decomposition of glucose to
produce levulinic acid (LA). The CrCl<sub>3</sub>–H<sub>3</sub>PO<sub>4</sub> system had a strong synergic catalytic activity for
the decomposition of glucose to LA. The effects of the ratio of CrCl<sub>3</sub> and H<sub>3</sub>PO<sub>4</sub> 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
CrCl<sub>3</sub> in the CrCl<sub>3</sub>–H<sub>3</sub>PO<sub>4</sub> system was 0.4–0.5. To probe the synergic catalysis
mechanism of the CrCl<sub>3</sub>–H<sub>3</sub>PO<sub>4</sub> system, the synergic catalytic activities of CrCl<sub>3</sub>–phosphates
(KH<sub>2</sub>PO<sub>4</sub>, K<sub>2</sub>HPO<sub>4</sub>, and K<sub>3</sub>PO<sub>4</sub>) 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/ZrO<sub>2</sub>, Cu/MgO, and Cu/Al<sub>2</sub>O<sub>3</sub> 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/ZrO<sub>2</sub> was the best. The structures and properties of Cu-based catalysts
are demonstrated by transmission electron microscopy, X-ray diffraction,
H<sub>2</sub> temperature-programmed reduction, N<sub>2</sub> adsorption–desorption,
CO temperature-programmed desorption, and CO<sub>2</sub> temperature-programmed
desorption. The stability of Cu/ZrO<sub>2</sub> is caused by the good
hydrothermal stability and tetragonal phase formation of ZrO<sub>2</sub>, which strongly binds to active Cu. The better activity over Cu/Al<sub>2</sub>O<sub>3</sub> is caused by the larger surface area, higher
Cu dispersion, smaller Cu particle size, and stronger basicity of
Cu/Al<sub>2</sub>O<sub>3</sub>. 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
N<sub>2</sub> 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<sup>+</sup> 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 H<sub>2</sub> or hydrogen donors.
Without the use of hydrogen source, the whole deoxygenation process
became more economical. Moreover, oleic acid can be saturated using
the H<sub>2</sub> 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 CH<sub>3</sub>COOH and CO. The experimental and characterization
results revealed that 30% Ni/AC had a higher adsorption capacity of
CH<sub>3</sub>COOH 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