共查询到20条相似文献,搜索用时 93 毫秒
1.
Oils were extracted from the seeds of rubber [Hevea brasiliensis (Kunth) Muell. Arg.] and melon (Colocynthis vulgaris Schrad) using different solvents at varying temperatures. The objective was to determine temperature coefficients (n) for
enhanced oil removal and the enthalpy changes accompanying the extraction process.
Values of n, obtained from the slopes of the plots of the natural logarithm of equilibrium oil yield vs T/10, were on the
order of 1.10, showing that oil, yield increased by a factor of about 1.10 for every 10° rise in temperature. Also, n values
were used to predict oil yields at other temperatures by knowing the oil yield at a given temperature.
Enthalpy changes (ΔH) in the extraction of both oils were determined using the Arrhenius equation. The ΔH values obtained
were in the range of 4–13.5 kJ mol−1, indicating the physical nature of oil extraction by a solvent. 相似文献
2.
Bo Lin Liting Yang Honghai Dai Aihua Yi 《Journal of the American Oil Chemists' Society》2008,85(2):113-117
The kinetics of the oxirane cleavage of epoxidized soybean oil (ESO) by methanol (Me) without a catalyst was studied at 50,
60, 65, 70 °C. The rate of oxirane ring opening is given by k[Ep][Me]2, where [Ep] and [Me] are the concentrations of oxiranes in ESO and methanol, respectively and k is a rate constant. From the temperature dependence of the kinetics thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), free energy of activation (ΔF) and activation energy (ΔE
a) were found to be 76.08 (±1.06) kJ mol−1, −118.42 (±3.12) J mol−1 k−1, 111.39 (±2.86) kJ mol−1, and 78.56 (±1.63) kJ mol−1, respectively. The methoxylated polyols formed from the oxirane cleavage reaction , were liquid at room temperature and had
three low temperature melting peaks. The results of chemical analysis via titration for residual oxiranes in the reaction
system showed good agreement with IR spectroscopy especially the disappearance of epoxy groups at 825, 843 cm−1 and the emergence of hydroxy groups at the OH characteristic absorption peak from 3,100 to 3,800 cm−1. 相似文献
3.
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
4.
The extraction of Mg2+ from ammonium dihydrogen phosphate (MAP) solution by extractant (D2EHPA) and its mixture, including acidic extractant (HEHPEHE),
alkaline extractant (TOA) and neutral extractant (TBP) respectively, is investigated. The good extraction selectivity of Mg2+ with D2EHPA from ammonium dihydrogen phosphate solution is verified, which is found to be associated with the cation exchange
and chelation capability of D2EHPA on the basis of its molecular structure. The related thermodynamic data are also obtained
in terms of experimental results as follows: the extraction enthalpy is 2.659×10−2 (J·mol−1·K−1), the free energy is 1.501×103 (J·mol−1) and the entropy is 4.441 (J·mol−1). Meanwhile, the major influencing factors, such as the initial pH, the initial concentration of extractant, phase ratio
and the extraction temperature on the extraction ratios of Mg2+, are studied, and the optimal process conditions are obtained. As shown in the extraction experiments for practical MAP solution,
superior grade MAP can be obtained by three levels of extraction under optimal condition. 相似文献
5.
Corn oil was extracted from whole ground corn using ethanol as the solvent. The yield of oil was measured as a function of
temperature, time of extraction, solvent-to-solids ratio, and ethanol concentration. Optimal conditions were a solvent-to-solids
ratio of 4 mL/g corn, an ethanol concentration of 100%, 30 min of extraction time, and a temperature of 50°C. Under these
conditions, a single batch extraction yielded ≈3.3 g oil/100 g corn, equivalent to 70% extraction efficiency. A three-stage
extraction, where the same corn was exposed to fresh ethanol, resulted in a yield of ≈4.5 g/100 g corn (2.5 lb/bu of corn),
equivalent to 93% recovery of the oil in corn. When anhydrous ethanol was used to repeatedly extract fresh corn, moisture
was absorbed linearly by ethanol from the corn in successive stages, which, in turn, decreased oil yield and increased nonoil
components in the extract. 相似文献
6.
Few data are available for diffusion coefficients measured in industrial copper electrolytes. In the present work the influence
of copper concentration (19.9–58.1 g dm−3), temperature (20–60°C) and concentrations levelling agents i.e. animal glue (0–5 mg dm−3) and thiourea (0–5 mg dm−3) on diffusion coefficients of copper was studied in industrial copper refinery electrolytes. Chronoamperometry at ultramicroelectrodes
was used as an electrochemical technique. Apparent bulk diffusion coefficients were calculated on the basis of the theory
of electrochemical nucleation on disc-shaped ultramicroelectrodes. Increasing copper concentration decreased the apparent
bulk diffusion coefficient of copper and diffusion coefficients followed the Arrhenius temperature relationship. The experimental
activation energy was 26.8 kJ mol−1. The influence of levelling agents on diffusion coefficients was not strong in the studied concentration range of animal
glue and thiourea. 相似文献
7.
Ryan Doell Samir K. Konar David G. B. Boocock 《Journal of the American Oil Chemists' Society》2008,85(3):271-276
The kinetic parameters of a truly homogeneous base-catalyzed transmethylation of soybean oil at four temperatures from 23
to 50 °C have been determined for the first time. The addition of oxolane, as well as a high methanol/oil molar ratio (27:1),
was used to achieve and maintain a monophasic system throughout the reactions. Second order rate constants were determined
in terms of the concentrations of the mechanistic reactants, which were the glycerides and methoxide ions (and not methanol).
Doubling the methoxide concentration increased the reaction rate twofold. At 23 °C the rate constants for the conversion of
triglycerides to diglycerides, diglycerides to monoglycerides, and monoglycerides to glycerol were 6.3, 15.3 and 13.0 L mol−1 min−1, respectively. These increased to 54.2, 136 and 139 L mol−1 min−1 at 50°C. These latter values (adjusted to 60 °C) were 65, 770 and 190 times larger, respectively, than values cited previously
(and adjusted to the methoxide basis) for a transmethylation of Pongamia oil, which was also claimed to be homogeneous. Activation
energies for all three steps were the same (63 kJ mol−1). Pre-exponential factors showed that in diglycerides and triglycerides the second and third ester chains sterically hindered
the attack of methoxide ions on the ester carbonyl groups. 相似文献
8.
Methanol electrooxidation was investigated on Pt–Ru electrocatalysts supported on glassy carbon. The catalysts were prepared
by electrodeposition from solutions containing chloroplatinic acid and ruthenium chloride. Bulk composition analysis of the
Pt–Ru catalyst was performed using an X-ray detector for energy dispersive spectroscopy analysis (EDX). Three different compositions
were analyzed in the range 0–20 at.% Ru content. Tafel plots for the oxidation of methanol in solutions containing 0.1–2 M
CH3OH, and in the temperature range 23–50 °C showed a reasonably well-defined linear region. The slope of the Tafel plots was
found to depend on the ruthenium composition. The lower slope was determined for the Pt catalyst, varying between 100 and
120 mV dec−1. The values calculated for the alloys were higher, ranging from 120 to 140 mV dec−1. The reaction order for methanol varies from 0.5 to 0.8, increasing with the ruthenium content. The activation energy calculated
from Arrhenius plots was found to change with the catalyst composition, showing a lower value around 30 kJ mol−1 for the alloys, and a higher value, of 58.8 kJ mol−1, for platinum. The effect of ruthenium content is explained by the bifunctional reaction mechanism. 相似文献
9.
K. P. Yadava B. S. Tyagi V. N. Singh 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1991,51(1):47-60
The removal of Pb(II) from aqueous solution by adsorption on china clay and wollastonite is an attractive process. The amount of Pb(II) removed by adsorption is highly dependent on the temperature of the adsorbate solution and favours low temperature. The equilibrium times were noted, i.e. 90 min for china clay and 120 min for wollastonite. The various rate parameters of the adsorption process have been determined at different temperatures. The activation energies were determined and found to be ?5.345 kJ mol?1 and ?8.730 kJ mol?1 for Pb(II)-china clay and Pb(II)-wollastonite systems, respectively. The adsorption isotherm was measured experimentally at various temperatures. The negative values of enthalpy change (ΔH = ?77.95 kJ mol?1 and ?16.40 kJ mol?1 for china clay and wollastonite, respectively) indicate the exothermic nature of the adsorption processes for both systems. The isosteric heats of the adsorption process have been determined at various surface coverages of the adsorbents used. The various thermodynamic parameters have been calculated to elucidate the mechanism involved in the adsorption process. 相似文献
10.
Takuma Katase Kuniaki Murase Tetsuji Hirato Yasuhiro Awakura 《Journal of Applied Electrochemistry》2007,37(3):339-344
The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf2N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that
the diffusion coefficient of Cu(I) ions in TMHA-Tf2N containing 12 mmol dm−3 Cu(I) ions was 1.2 × 10−6 cm2 s−1 and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I
−/I
3− at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity
of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10−5 cm2 s−1 at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO4 solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution
with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol−1 in the ionic liquid solution. 相似文献
11.
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
12.
A new type of poly(vinyl alcohol)(PVA)/peat/organoclay composite beads was prepared. This composite bead was a porous spherical
particle with a diameter of 3.0–5.0 mm and a porosity of about 50%. The oragnoclay is prepared by hexadecyl trimethyl ammonium
bromide (HDTMA) exchanged clay. The dynamic adsorption behavior between methyl ethyl ketone (MEK) and this composite bead
was investigated. The adsorption process occurs in two stages with external mass transport occurring in the early stage and
intraparticle diffusion occurring in the later stage. The rate of MEK diffusion in the external mass transport process and
the intraparticle diffusion process in the adsorption temperature 20–35 °C was 3.28–76.98 × 10−8 cm2/s and 1.62–3.17 × 10−7 cm2/s, respectively. The rate of MEK diffusion in both processes was concentration independent, and it increased with increasing
the adsorption temperature. Langmuir isotherm adsorption model was more suitable for describing the adsorption equilibrium
of MEK. The calculated Q values in the adsorption temperature 20–35 °C were 5.90–22.78 mg/g composite bead. The adsorption
capacity of this composite bead increased with increasing the adsorption temperature. The adsorption process was physical
adsorption, endothermic and non-spontaneous process. 相似文献
13.
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
14.
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
15.
Chuanshang Cai Honghai Dai Rongsheng Chen Caixia Su Xiaoya Xu Shi Zhang Liting Yang 《European Journal of Lipid Science and Technology》2008,110(4):341-346
In the present work, the kinetics of the epoxidation of soybean oil (SBO) by peroxyacetic acid (PAA) generated in situ in the presence of sulfuric acid as the catalyst was studied at various temperatures (45, 65 and 75 °C). It was found that epoxidation with almost complete conversion of unsaturated carbon and negligible oxirane cleavage can be attained by the in situ technique. The rate constant for epoxidation of SBO was found to be of the order of 10–6 mol–1s–1 and the activation energy of epoxidation is 43.11 kJ/mol. Some thermodynamic parameters: enthalpy, entropy and free activation energy of 40.63 kJ/mol, –208.80 J/mol and 102.88 kJ/mol, respectively, were obtained for the epoxidation of SBO. The kinetic and thermodynamic parameters of epoxidation obtained from this study indicate that an increase in the process temperature would increase the rate of epoxide formation. The epoxidation of corn oil and sunflower oil were also investigated under the same conditions. The results show that the reaction rate is in the order of soybean oil > corn oil > sunflower oil. 相似文献
16.
《分离科学与技术》2012,47(10):1448-1455
The article describes transport of Pb(II) through bulk liquid membrane (BLM) containing calix[6]arene hexaester derivative (1) as a carrier. The effect of various parameters such as temperature, carrier concentration, stirring speed and type of solvent on the Pb(II) transport efficiency of the carrier through BLM was evaluated. The activation energy values for the extraction and re-extraction were found as 56.33 kJ mol?1 and 14.79 kJ mol?1, respectively. These values demonstrate that the process is diffusionally controlled by Pb(II). Observations indicate that the membrane entrance and exit rate constants (k1, k2) increase with increasing stirring speed as well as carrier concentration and decrease with increasing temperature. The effect of solvent on k1 and k2 was found to be in the order of CH2Cl2 > CHCl3 > CCl4. 相似文献
17.
Kinetics of the Chemical Dissolution of Vanadium Pentoxide in Acidic Bromide Solutions 总被引:2,自引:0,他引:2
A novel vanadium bromide redox flow battery employing a vanadium bromide electrolyte in both half-cells has been proposed.
Preparation of the electrolyte for this redox cell requires the chemical dissolution of vanadium pentoxide powder in the acidic
bromide supporting electrolyte. In this study, the kinetics of the chemical dissolution process were investigated and a second
order surface controlled reaction is reported with rate equation given by: Rate = 5 × 10−4(l mol−1 s−1)[Br−]2 at 25 °C and an activation energy of 37.2 kJ mol−1. 相似文献
18.
A. R. Kamali J. Fahim 《International Journal of Self-Propagating High-Temperature Synthesis》2009,18(1):7-10
Addressed is the effect of ball milling on aluminothermic reduction of TiO2. In 0.5-h milled 3TiO2 + Al mixtures, a two-step reaction was found to yield TiAl and Ti3Al. Upon an increase in the milling time (to 20 h), a one-step reaction yielded TiAl. The activation energy for TiAl formation
was 75 kJ mol−1 for 0.5-h milled samples and 33 kJ mol−1 for 20-h milled samples.
The article is published in the original. 相似文献
19.
Waheed A. Badawy Rabab M. El-Sherif Hassan Shehata 《Journal of Applied Electrochemistry》2007,37(10):1099-1106
The electrochemical behavior, especially the corrosion and passivation, of a Cu–Al bronze was investigated. Conventional electrochemical
techniques including open-circuit potential, anodic polarization, cyclic voltammetry and electrochemical impedance spectroscopy
were used. It was found that the addition of chloride ion up to 0.15 M in 0.5 M Na2SO4 solution decreases the corrosion rate due to the formation of CuCl, whereas at higher concentration of the chloride ion,
the corrosion rate increases due to the formation of the soluble CuCl2−. The activation energy was found to be 10 kJ mol−1. This value indicates that the corrosion process is under diffusion control. The impedance measurements showed that the passive
film can be represented by a duplex layer, a relatively thick porous outer film on top of a thin compact layer. An equivalent
circuit was used to explain and analyze the impedance data. The model includes another R-C combination and Warburg impedance
in addition to the simple Randles cell to account for the spontaneously formed passive film and the diffusion phenomena. 相似文献
20.
Natividad Ortega Laura Sez David Palacios María D. Busto 《International journal of molecular sciences》2022,23(12)
The behavior against temperature and thermal stability of enzymes is a topic of importance for industrial biocatalysis. This study focuses on the kinetics and thermodynamics of the thermal inactivation of Lipase PS from B. cepacia and Palatase from R. miehei. Thermal inactivation was investigated using eight inactivation models at a temperature range of 40–70 °C. Kinetic modeling showed that the first-order model and Weibull distribution were the best equations to describe the residual activity of Lipase PS and Palatase, respectively. The results obtained from the kinetic parameters, decimal reduction time (D and tR), and temperature required (z and z’) indicated a higher thermal stability of Lipase PS compared to Palatase. The activation energy values (Ea) also indicated that higher energy was required to denature bacterial (34.8 kJ mol−1) than fungal (23.3 kJ mol−1) lipase. The thermodynamic inactivation parameters, Gibbs free energy (ΔG#), entropy (ΔS#), and enthalpy (ΔH#) were also determined. The results showed a ΔG# for Palatase (86.0–92.1 kJ mol−1) lower than for Lipase PS (98.6–104.9 kJ mol−1), and a negative entropic and positive enthalpic contribution for both lipases. A comparative molecular dynamics simulation and structural analysis at 40 °C and 70 °C were also performed. 相似文献