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1.
Ruihua Guo Chuanguo Ma Shangde Sun Yuxiang Ma 《Journal of the American Oil Chemists' Society》2011,88(4):517-521
A ring-opened product (EPO-HOAc) was prepared using epoxidized palm oil (EPO) and acetic acid (HOAc). The kinetics of the
oxirane cleavage of EPO were investigated at 50, 60, 70, 80, and 90 °C, respectively, in the presence of HOAc. The rate equation
of oxirane cleavage was as follows: r = k[Ep][CH3COOH]1.6 ([Ep] is the molar concentration of oxiranes, [CH3COOH] is the molar concentration of HOAc), and the activation energy of oxirane cleavage was 40.28 kJ mol−1. The structure of EPO-HOAc was confirmed by FT-IR and 1H NMR. The oxidative stability of EPO-HOAc was better than that of palm oil (PO), and the pour point of EPO-HOAc was lower
than that of PO and EPO, which made EPO-HOAc more suitable for biodegradable lubricant materials than PO and EPO. 相似文献
2.
Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry 总被引:1,自引:0,他引:1
C. P. Tan Y. B. Che Man J. Selamat M. S. A. Yusoff 《Journal of the American Oil Chemists' Society》2001,78(11):1133-1138
In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413
K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen
flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation
reaction. From this resulting exotherm, the onset of oxidation time (T
o) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation
of the log (T
o) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based
on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E
a), activation enthalpies (ΔH
‡), and activation entropies (ΔS
‡) for oxidative stability of vegetable oils were calculated. The E
a′, ΔH
‡, and ΔS
‡ for all vegetable oils ranged from 79 to −104 kJ mol−1, from 76 to −101 kJ mol−1, and from −99 to −20 J K−1 mol−1, respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method
for kinetic analysis of lipid oxidation in vegetable oil. 相似文献
3.
Sean F. O’Keefe V. A. Wiley D. Wright 《Journal of the American Oil Chemists' Society》1993,70(9):915-917
Oil was extracted from soybeans, degummed, alkalirefined and bleached. The oil was heated at 160, 180, 200, 220 and 240°C
for up to 156 h. Fatty acid methyl esters were prepared by boron trifluoride-catalyzed transesterification. Gas-liquid chromatography
with a cyanopropyl CPSil88 column was used to separate and quantitate fatty acid methyl esters. Fatty acids were identified
by comparison of retention times with standards and were calculated as area % and mg/g oil based on 17:0 internal standard.
The rates of 18:3ω3 loss and 18:3 Δ9-cis, Δ12-cis, Δ15-trans (18:3c,c,t) formation were determined, and the activation energies were calculated from Arrhenius plots. Freshly prepared soy oil had
10.1% 18:3ω3 and no detectable 18:3c,c,t. Loss of 18:3ω3 followed apparent first-order kinetics. The first-order rate constants ranged from .0018±.00014 min−1 at 160°C to .083±.0033 min−1 at 240°C. The formation of 18:3c,c,t did not follow simple kinetics, and initial rates were estimated. The initial rates (mg per g oil per h) of 18:3c,c,t formation ranged from 0.0031±0.0006 at 160°C to 2.4±.24 at 240°C. The Arrhenius activation energy for 18:3ω3 loss was 82.1±7.2
kJ mol−1. The apparent Arrhenius activation energy for 18:3c,c,t formation was 146.0±13.0 kJ mol−1. The results indicate that small differences in heating temperature can have a profound affect on 18:3c,c,t formation. Selection of appropriate deodorization conditions could limit the amount of 18:3c,c,t produced. 相似文献
4.
Bleaching kinetics of sunflowerseed oil 总被引:1,自引:0,他引:1
Hüseyin Topallar 《Journal of the American Oil Chemists' Society》1998,75(4):531-533
The bleaching process for sunflowerseed oil follows a rate formula, log (A/A
0)=−κ
, according to absorbance measurements. The dark color of crude oil converts to a light color as the absorbance value decreases.
The activation energy E
a was calculated from the Arrhenius equation as 3 kJ, and other activation thermodynamic parameters were determined as ΔS
⊄=−4.4 J K−1, ΔH
⊄=−31.2 J mol−1, and ΔG
⊄=1.6 kJ mol−1. The study showed that the bleaching process was exothermic, presented a decrease of entropy, and was a nonspontaneous process
during activation. 相似文献
5.
Epoxidation of karanja (Pongamia glabra) oil by H2O2 总被引:1,自引:0,他引:1
Vaibhav V. Goud Narayan C. Pradhan Anand V. Patwardhan 《Journal of the American Oil Chemists' Society》2006,83(7):635-640
Epoxidation of karanja oil (KO), a nondrying vegetable oil, was carried out with peroxyacetic acid that was generated in situ from aqueous hydrogen peroxide and glacial acetic acid. KO contained 61.65% oleic acid and 18.52% linoleic acid, respectively,
and had an iodine value of 89 g/100 g. Unsaturated bonds in the oil were converted to oxirane by epoxidation. Almost complete
epoxidation of ethylenic unsaturation was achieved. For example, the iodine value of the oil could be reduced from 89 to 19
by epoxidation at 30°C. The effects of temperature, hydrogen peroxide-to-ethylenic unsaturation ratio, acetic acid-to-ethylenic
unsaturation ratio, and stirring speed on the epoxidation rate and on oxirane ring stability were studied. The rate constant
and activation energy for epoxidation of KO were 10−6 L·mol−1·s−1 and 14.9 kcal·mol−1, respectively. Enthalpy, entropy, and free energy of activation were 14.2 kcal·mol−1, −51.2 cal·mol−1·K−1, and 31.1 kcal·mol−1, respectively. The present study revealed that epoxides can be developed from locally available natural renewable resources
such as KO. 相似文献
6.
Saturated fatty acid adsorption by acidified rice hull ash 总被引:3,自引:0,他引:3
Rice hull ash (RHA) was treated with 1.0 M HNO3 (RHA-A1) and another batch was treated with 14.0 M HNO3 (RHA-A14). RHA-A1 and RHA-A14 had a pH of 6.58 and 6.13, respectively. Adsorption of saturated fatty acids (C8, C10, C12, C14, C16, and C18) was carried out on RHA-A1 and RHA-A14 at 32±1°C. The adsorption data conformed to the Langmuir isotherm. The specific surface
area of RHA-A1 was 183.84 m2 g−1 while that of RHA-A14 was 174.67 m2 g−1. The specific pore volume of RHA-A1 was 0.216 cm3 g−1 while that of RHA-A14 was 0.234 cm3 g−1. The acid-treated ash, RHA-A14 (q
m
=0.43±0.03 mmol g−1 where q
m
is the amount of adsorbate adsorbed to form a monolayer coverage on the ash particles) showed a twofold increase in the adsorption
of fatty acid per gram ash compared to RHA-A1 (q
m
=0.25±0.03 mmol g−1). The free energy of adsorption, ΔG°
ads, was determined to be −7.06±0.10 and −6.75±0.11 kcal mol−1 for RHA-A1 and RHA-A14, respectively. The reduced ΔG°
ads values observed for RHA-A14 were attributed to the electrostatic repulsion of the hydrophobic chain of the fatty acid adsorbed
on adjacent sites and brought into close proximity of each other. The ΔG°
ads values showed that the process of adsorption took place through physisorption on both RHA. 相似文献
7.
p-nitrobenzyl triphenyl phosphonium ylide initiated radical polymerisation of MMA in 1-4 dioxane at 65 ± 1°C for 2 h under
a nitrogen blanket, follows ideal kinetics with bimolecular termination. The overall activation energy and average value of
k
p
2/k
t are 75.7 kJ mol and 1.14 × 102 l mol−1 s−1. FTIR Spectroscopy confirms a band of 1,729 cm−1 of the ester group. 1H NMR and 13C NMR confirms methoxy protons at 3.8 δ ppm and 52 δ ppm, respectively. E.S.R studies confirm a free radical mode of polymerisation. TGDTA analysis confirms the atactic nature
of polymer and its thermal stability up to 120°C. Ylide dissociates to give a phenyl radical which is responsible for polymerisation. 相似文献
8.
Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N2) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide
initial concentration (0.90–3.30 mmol/L), oxide initial surface area (16–143 m2/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by
means of capillary electrophoresis, while iron dissolution was monitored through atomic absorption spectroscopy. Most of Fe(II)
produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments. The hydrosulfide oxidation
by the iron/cerium (hydr)oxide was found to be surface-controlled, with rates (Ri) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: Ri = ki[HS−]t=0−0.5[A]t=0[H+]t=0−0.5
, where ki represents the apparent rate constants for the oxidation of HS− (kHS) or the dissolution of Fe(II) (kFe), [HS−]t = 0 is the initial hydrosulfide concentration, [A]t = 0 is the initial Fe/Ce (hydr)oxide surface area and [H+]t = 0 is the initial proton concentration. The rate constant, kHS, for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 ± 0.65) × 10−4 mol2 L−1 m−2 min−1, with the rate of hydrosulfide oxidation being ca. 10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric
ratio between HS− oxidized and Fe(II) produced; kFe = (3.9116 ± 0.41) × 10−5 mol2 L−1 m−2 min−1). 相似文献
9.
MING CHEN HUI-LAN WANG JING GU GUO-WANG DIAO 《Journal of Applied Electrochemistry》2007,37(3):331-337
The water-soluble p-sulfonated sodium salt of calix[8]arene (III) was synthesized. The product was characterized by FT-IR, NMR and UV–Vis spectra.Then
the electrochemical behaviors of p-sulfonated sodium salt of calix[8]arene in NaAc+HAc (pH = 4) buffer solution was studied. In aqueous solution, p-sulfonated calix[8]arene can be oxidized when the potential is more than 0.7 V vs SCE. It was confirmed that the reaction
was a two-electron irreversible electrochemical reaction. The transfer coefficient, α, was measured as 0.7. At 25°, the diffusion
coefficient of p-sulfonated calix[8]arene was determined as 8.6 × 10−7 cm2 s−1. The diffusion activation energy of p-sulfonated calix[8]arene was 18.9 kJ mol−1 at pH = 4. 相似文献
10.
Karanam Srinivasa Rao Shashi Anand Paladugu Venkateswarlu 《Korean Journal of Chemical Engineering》2010,27(5):1547-1554
Syzygium cumini L. leaf powder and Cd(II) loaded samples were characterized using FTIR and SEM techniques. The biosorption of cadmium ions
from aqueous solution was studied in a batch adsorption system as a function of pH, contact time, adsorbate, adsorbent, anion
and cation concentrations. The biosorption capacities and rates of transfer of cadmium ions onto S. cumini L. were evaluated. The kinetics could be best described by both linear and nonlinear pseudo-second order models. The isothermic
data fitted to various models in the order Freundlich>Redlich-Peterson>Langmuir>Temkin. The maximum adsorption capacity of
S. cumini L. leaves at room temperature was estimated to be 34.54 mg g−1. The negative values of ΔG0 indicated the feasibility of the adsorption process. The endothermic nature was confirmed by the positive value of the enthalpy
change (ΔH0=3.7 kJ mol−1). The positive value of entropy change (ΔS0=16.87 J mol−1 K−1) depicted internal structural changes during the adsorption process. 相似文献
11.
Martin Sterrer Thomas Berger O. Diwald Erich Knözinger Alain Allouche 《Topics in Catalysis》2007,46(1-2):111-119
The adsorption properties of oxygen radicals on the surface of polycrystalline oxides can provide relevant information about
the functionality of specific surface sites in oxidation catalysis. Using electron paramagnetic resonance spectroscopy, we
investigated O2 adsorption at MgO nanocrystal surfaces which were previously enriched with O− radicals i.e. trapped hole centers. On dehydroxylated particle surfaces, two ozonide radical types O
3
−
were isolated as adsorbates and the related energies for O2 adsorption were found to be 55 ± 5 kJ mol−1 and 100 ± 5 kJ mol−1. The respective adsorption sites are assigned to hole centers trapped on oxygen terminated corners and cation vancancies,
respectively.
In addition, O
3
−
ions were also employed as probes for electron trapping sites on partially hydroxylated sample surfaces. Five types of O− radicals emerge from surface colour centre bleaching with N2O, but only two of them adsorb O2 at room temperature. A connection between the well-characterized (H+)(e-) defect – an electron trapped in close vicinity of a nearby proton [Chiesa et al. J. Phys. Chem. B 109 (2005) 7314] – and
one ozonide type which exhibits significant magnetic coupling with an adjacent proton, was established on the basis of their
production parameter dependence. Although the g tensor of an O3
− species reflects the properties of the radical itself rather than the structure of the adsorption site, the related signatures
are proposed to serve also as spectroscopic fingerprints for catalytically relevant surface anion environments. 相似文献
12.
A kinetic study of the reaction between a tocopheroxyl radical and unsaturated fatty acid esters has been undertaken. The
rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl oleate2, ethyl linoleate3, ethyl linolenate4, and ethyl arachidonate5) by the tocopheroxyl radical (5,7-diisopropyltocopheroxyl6) in benzene have been determined spectrophotometrically. The second-order rate constants, k3, obtained are 1.04×10−5 M−1s−1 for2, 1.82×10−2 M−1s−1 for3, 3.84×10−2 M−1s−1 for4, and 4.83×10−2 M−1s−1 for5 at 25.0°C. Thus, the rate constants, kabstr/H, given on an available hydrogen basis are k3/4=2.60×10−6 M−1s−1 for2, k3/2=9.10×10−3 M−1s−1 for3, k3/4=9.60×10−3 M−1s−1 for4, and k3/6=8.05×10−3 M−1s−1 for5. The kabstr/H values obtained for the polyunsaturated fatty acid esters3,4, and5 containing H-atoms activated by two π-electron systems are similar to each other, and are about three orders of magnitude
higher than that for the ethyl oleate2 containing H-atoms activated by a single π-system. From these results, it is suggested that the prooxidant effect of α-tocopherol
in edible oils and fats may be induced by the above hydrogen abstraction reaction. 相似文献
13.
N-vinyl pyrrolidone (NVP) was polymerized in dioxan at 60 ± 0.1°C for 1 h using diphenyl ditelluride as radical initiator.
The system follows ideal kinetics i.e. R
p
α [DPDT]0.5[NVP]. The activation energy and dissociation constant is computed as 46 kJ mol−1 and 1.1 × 10−11 s−1, respectively. The polymer was characterized with the help of FTIR, 1H-NMR, 13C-NMR, ESR spectroscopy. The FT-IR spectrum showed bands at 1660–1680 cm−1 due to combination of >C = O and C–N stretching. The gyromagnetic constant ‘g’ has been computed as 2.2203. The main product of this reaction were poly(N-vinylpyrrolidone)s with phenyl tellanyl ends. The presence of tellurium in polymer is confirmed by ICP analysis. The DSC
shows the T
g
of poly(N-vinylpyrrolidone) is 168°C due to rigid pyrrolidane group. The TGA showed that polymer was stable up to 380°C.The GPC studies
showed that the weight average molecular weight decreases with increase of [DPDT]. 相似文献
14.
F. A. Zaher M. H. El-Mallah M. M. El-Hefnawy 《Journal of the American Oil Chemists' Society》1989,66(5):698-700
The kinetics of oxirane ring cleavage in epoxidized soybean oil have been studied using glacial acetic acid at 60, 70, 80
and 90°C. It was shown that the reaction can be successfully modelled as first order with respect to the epoxide concentration
and second order with respect to acetic acid. The reaction velocity constant at 70°C was found to be 2 × 10−3 1−3 hr−1 mol−2, the frequency factor, A, = 2.321 × 107 hr−1 and the energy of activation, Ea = 15.84 k cal mol−1. The effects of the concentration of acetic acid and the temperature on the net yield of epoxides by in situ epoxidation
were also studied on the basis of the predicted kinetic parameters of the reaction system. 相似文献
15.
Pramod Kandanarachchi Andrew Guo Dmytro Demydov Zoran Petrovic 《Journal of the American Oil Chemists' Society》2002,79(12):1221-1225
The kinetics and mechanism of the hydroformylation of soybean oil by homogeneous ligand-modified rhodium catalysts were investigated
at 70–130°C and 4000–11,000 kPa. The effects of reaction rates on systematic variations in reaction parameters were evaluated
in order to develop an industrial process to convert vegetable oils to polyaldehydes. The activation energies in the presence
of triphenylphosphine (Ph3P) (61.1±0.8 kJ/mol) (mean±SD) and triphenyl phosphite [(PhO)3P] (77.4±5.0 kJ/mol) were determined. The catalyst was deactivated at temperatures higher than 100°C. An evaluation of the
effects of the reaction parameters on initial rates yielded the rate laws for Ph3P {rate=k [olefin][Rh(CO)2Acac]1.1 [Ph3P]−0.5 (pH2+pCO)1.4, where Rh(CO)2Acac is (acetylacetonato)dicarbonylrhodium (I)} and (PhO)3P {rate=[olefin] [Rh(CO)2Acac]1.2 [(PhO)3P]−0.8 (pH2+pCO)0.9 at total pressures lower than 7000 kPa, and rate =[olefin] [Rh(CO)2Acac]1.2 [(PhO)3P]−0.8(pH2+pCO)1.7 at total pressures higher than 7000 kPa}. 相似文献
16.
Zhengyong Liang Bindong Li Chunxu Lü Chao Feng 《Frontiers of Chemical Engineering in China》2008,2(1):59-62
Under the conditions of phase transfer catalysis and nitrobenzene as the solvent, the halogen-exchange fluorination of 2,6-dichlorobenzaldehyde
using KF as fluorinating agent was studied. The kinetics was investigated and the reaction rate constants were obtained under
the optimum conditions of n(KF):n(2,6-dichlorobenzaldehyde): n(Ph4PBr):n(acetone-furan crown ether) = 4:1:0.1:0.05 and temperatures of 433 K, 443 K, 453 K and 463 K. The results illustrated
the activation energy of the first and the second step is 4.57 × 104 J·mol−1 and 3.53 × 104 J·mol−1, respectively. The pre-exponential factor is 4.50 × 105 h−1 and 1.08 × 104 h−1, respectively. Thus a reliable kinetics data could be obtained for further research.
__________
Translated from Chemical Engineering (China), 2007, 35(8): 33–36 [译自: 化学工程] 相似文献
17.
The kinetics of the thermal decomposition reaction of diethylketone triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane,
DEKTP) in ethylbenzene solution were studied in the temperature range of 120.0–150.0 °C and at an initial concentration range
of 0.01–0.10 M. This peroxide was used as a new initiator in methyl methacrylate (MMA) polymerization process at high temperatures
(110.0–140.0 °C) in ethylbenzene solution. The effects of initiator concentration and reaction temperature on the polymerization
rate were investigated in detail. Thus, activation parameters of the solution polymerization process (ΔE
d* = 83.3 kJ mol−1 and ΔE
p* − ΔE
t*/2 = 54.0 kJ mol−1) will be obtained. DEKTP can effectively act as initiator in MMA polymerization and its performance is similar to that presented
by a multifunctional initiator resulting in high-molecular weight polymethylmethacrylate with a high reaction rate. 相似文献
18.
James C. Ewing John P. Cosgrove David H. Giamalva Daniel F. Church William A. Pryor 《Lipids》1989,24(7):609-615
Allylbenzene ozonide (ABO), a model for polyunsaturated fatty acid (PUFA) ozonides, initiates the autoxidation of methyl linoleate
(18∶2 ME) at 37°C under 760 torr of oxygen. This process is inhibited by d-α-tocopherol (α-T) and 2,6-di-ert-butyl-4-methylphenol (BHT). The autoxidation was followed by the appearance of conjugated diene (CD), as well as by oxygen-uptake.
The rates of autoxidation are proportional to the square root of ABO concentration, implying that the usual free radical autoxidation
rate law is obeyed. Activation parameters for the thermal decomposition of ABO were determined under N2 in the presence of radical scavengers and found to be Ea=28.2 ±0.3 kcal mol−1 and log A=13.6±0.2; kd (37°C) is calculated to be (5.1±0.3)×10−7 sec−1. Autoxidation data are also reported for ozonides of 18∶2 ME and methyl oleate (18∶1 ME). 相似文献
19.
Polymerization of methyl acrylate (MA), initiated by p‐acetyl benzylidene triphenylarsonium ylide (p‐ABTAY) in dioxan at (60 ± 1)°C for 1 h, follows nonideal kinetics (Rp ∝ [I]0.21[M]1.40) due to primary radical termination as well as degradative chain transfer reaction. The polymerization proceeded upto 20.49% conversion without gelation and results in the polymer of high molecular weight 98,000. The overall activation energy and the value of kp2/kt are 14 kJ mol–1 and 18.75 × 10–6 L mol–1 s–1, respectively. The ylide dissociates to form phenyl radical, which initiates the polymerization of MA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
20.
Nigerloxin [2-amido-3-hydroxy-6-methoxy-5-methyl-4-(prop-1′-enyl) benzoic acid], a fungal metabolite, is an inhibitor of lipoxygenase
and aldose reductase with free radical-scavenging properties. The interaction of nigerloxin with bovine serum albumin (BSA)
was investigated using fluorescence spectroscopy and circular dichroic measurements. The fluorescence of BSA was quenched
following interaction with nigerloxin, and this property was used to generate a binding constant. The estimated association
constant was 1.01±0.2×106 M−1. Job's method of continuous variation indicated that nigerloxin formed a 1∶1±0.1 complex with BSA. To understand the nature
of the interaction, the variance in the association constant as a function of temperature in the range of 14–45°C was used
to calculate the thermodynamic parameters. The thermodynamic parameters at 27°C derived from the mass action plot and van't
Hoff's plot were as follows: ΔG=−8.2±0.1 kcal/mol, ΔH≈0 kcal/mol, and ΔS=27.5±0.4 cal/mol/K (where ΔG is free energy, ΔH is enthalpy, and ΔS is entropy). Increasing ionic strength did not favor interaction. Circular dichroic measurements revealed that the interaction
of nigerloxin with BSA did not lead to changes in the secondary structure of the protein. The reversibility of the interaction
verified by the dilution method was found to be reversible. These measurements suggest that partial hydrophobic and partial
ionic bonding play a role in the interaction of nigerloxin with BSA. 相似文献