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1.
A comparative study was carried out in order to evaluate the kinetics of the formation of a number of primary and secondary oxidation products during oxidation of olive oil in the Rancimat test at 100–130 °C. There were good correlations between the Rancimat index (OSI) and stability indices (IP) measured in the Rancimat test with no significant differences in kinetic parameters calculated from them. Mean values of the temperature coefficient, Q10 number, activation energy (Ea), frequency factor (A), and free energy of activation (ΔG++) for olive oil oxidation were calculated to be ?3.44 × 10?2°C?1, 2.21, 98.91 kJ/mol, 12.17 × 1012 h?1, and 128.25 kJ/mol, respectively. Each unit change in Ea was accompanied by an average 1.43 × 1012 change in A, indicating a higher contribution for factor A than for Ea to the olive oil stability. The Ea and A correlated well with the values of enthalpy and entropy, respectively. The values of OSI or IP could be described well by the ΔG++ values. Kinetic data indicated that olive oil stability is more affected by the indigenous antioxidants than by the fatty acid composition.  相似文献   

2.
Oxidation kinetics of the triacylglycerols (TAGs) and fatty acid methyl esters (FAMEs) of sesame, olive, and canola oils were studied in the presence of the different concentrations of sesamol (0.1%–0.16%) at 60, 80, and 100°C. Sesamol increased the temperature coefficient, TC, and Q10 number of the TAGs more significantly compared to the FAMEs. All the sesamol-added TAG and FAME systems, respectively, of the olive, canola, and sesame oils, respectively, exerted increased values of the Arrhenius (activation energy, Ea, and frequency factor, A) and Eyring (enthalpy, ΔH++, and entropy, ΔS++) equation parameters. Sesamol improved the Gibbs free energy (ΔG++) of the activated complex formation in the canola, sesame, and olive systems, respectively, and the effect was greater in the FAMEs.  相似文献   

3.
Accelerated oxidation tests, such as the determination of the induction period, increase the lipid oxidation rate by exposing a food to elevated temperatures, in the presence of excess quantities of air or oxygen. In addition to the well‐founded oxidative stability index (OSI) method, an innovative and promising technique is the oxidation test (OXITEST) reactor. A new analytical method was developed with OXITEST to oxidize vegetable oils. At a preliminary stage of the investigation, the induction periods of sunflower and extra‐virgin olive oil obtained by the OXITEST reactor were plotted against temperature, on the basis of the Arrhenius law; the activation energy and the frequency factor of lipid oxidation were calculated and resulted in 98.61 kJ/mol and 2.33×1010 s–1, respectively, for sunflower oil and 106.48 kJ/mol and 6.27×1010 s–1, respectively for extra‐virgin olive oil. The new oxidative technique was employed to determine the induction periods of vegetable oils; the results obtained were well correlated with those achieved with OSI technology, with a Pearson correlation coefficient r = 0.9785 (p <0.05) for oilseeds and palm oil and r = 0.9501 (p <0.05) for extra‐virgin olive oils.  相似文献   

4.
The oxidation kinetics of the purified triacylglycerols of olive, canola, and fish oils as affected by different concentrations of hydroxytyrosol were studied at 60–100 °C. On average, hydroxytyrosol improved the temperature susceptibility (temperature coefficient, TC, and Q10 number) of olive oil, whereas opposite results were observed for canola and fish oils. Despite the results observed in canola and fish oils, hydroxytyrosol caused much greater changes in the Arrhenius equation parameters (activation energy, Ea, and frequency factor, A) for the oxidation of olive oil. On the whole, the highest increase in the Gibbs free energy, ΔG++, of the activated complex formation as affected by the antioxidant was for olive (9.7%), canola (8.9%), and fish (5.7%) oils, respectively.  相似文献   

5.
This work reports the adsorption of strontium from aqueous solutions onto activated carbon. Various factors such as pH, initial concentration of strontium, particle size and temperature were considered. The optimum conditions obtained were: pH value = 4.0, contact time = 8 h, initial concentration of Sr(II) = 100 mg/l, particle size = 270 μm and temperature of 293.15 K. The adsorption of strontium(II) on activated carbon follows pseudo-first order kinetics and the energy of activation Ea calculated using the Arrehenius equation was found to be 3.042 kJ/mol.The adsorption isotherms could be fitted by the Langmuir model with the maximum adsorption capacity Qo being 5.07×10–4 mol/g at 293.15 K. A dimensionless separation factor RL was used to judge the favourable adsorption. The values of the mass transfer coefficient βL (cm/s) at different temperatures indicated that the velocity of mass transfer of Sr(II) ions onto activated carbon was slow. The intraparticle diffusion mechanism is of great importance in determining the overall rate of removal and the negative entropy of activation ΔS# value 145.13 J/mol K, reflects that no significant change occurs in the internal structure of activated carbon during adsorption of strontium(II). The Gibbs free energy ΔG°ads values range from –36.61 kJ/mol to –41.75 kJ/mol at 293.15–333.15 K, which show the physical adsorption properties of activated carbon and indicate the feasibility of the process.  相似文献   

6.
《分离科学与技术》2012,47(4):705-722
Abstract

The sorption behavior of 3.18×10?6 mol l?1 solution of Tm(III) metal ions onto 7.25 mg l?1 of 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated at different temperatures i.e. 303 K, 313 K, and 323 K. The maximum equilibration time of sorption was 30 minutes from pH 7.5 buffer solution at all temperatures. The various rate parameters of adsorption process have been investigated. The diffusional activation energy (ΔEads) and activation entropy (ΔSads) of the system were found to be 22.1±2.6 kJ mol?1 and 52.7±6.2 J mol?1 K?1, respectively. The thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were calculated and interpreted. The positive value of ΔH and negative value of ΔG indicate that sorption is endothermic and spontaneous in nature, respectively. The adsorption isotherms such as Freundlich, Langmuir, and Dubinin–Radushkevich isotherm were tested experimentally at different temperatures. The changes in adsorption isotherm constants were discussed. The binding energy constant (b) of Langmuir isotherm increases with temperature. The differential heat of adsorption (ΔHdiff), entropy of adsorption (ΔSdiff) and adsorption free energy (ΔGads) at 313 K were determined and found to be 38±2 kJ mol?1, 249±3 J mol?1 K?1 and –40.1±1.1 kJ mol?1, respectively. The stability of sorbed complex and mechanism involved in adsorption process has been discussed using different thermodynamic parameters and sorption free energy.  相似文献   

7.
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   

8.
Two new highly stable energetic salts were synthesized in reasonable yield by using the high nitrogen‐content heterocycle 3,4,5‐triamino‐1,2,4‐triazole and resulting in its picrate and azotetrazolate salts. 3,4,5‐Triamino‐1,2,4‐triazolium picrate (1) and bis(3,4,5‐triamino‐1,2,4‐triazolium) 5,5′‐azotetrazolate (2) were characterized analytically and spectroscopically. X‐ray diffraction studies revealed that protonation takes place on the nitrogen N1 (crystallographically labelled as N2). The sensitivity of the compounds to shock and friction was also determined by standard BAM tests revealing a low sensitivity for both. B3LYP/6–31G(d, p) density functional (DFT) calculations were carried out to determine the enthalpy of combustion (ΔcH (1) =−3737.8 kJ mol−1, ΔcH (2) =−4577.8 kJ mol−1) and the standard enthalpy of formation (ΔfH° (1) =−498.3 kJ mol−1, (ΔfH° (2) =+524.2 kJ mol−1). The detonation pressures (P (1) =189×108 Pa, P (2) =199×108 Pa) and detonation velocities (D (1) =7015 m s−1, D (2) =7683 m s−1) were calculated using the program EXPLO5.  相似文献   

9.
Thermoplastic elastomeric hydrogenated styrene—butadiene (HSBR) elastomer was prepared by diimide reduction of styrene-butadiene rubber in the latex stage. The products were characterized by infrared, 1H-NMR, 13C-NMR spectroscopy, and differential scanning calorimetry (DSC). The standard free energy change, ΔG0 at 298°K is −44.7 × 104 kJ/mol, indicating that the formation of HSBR is thermodynamically feasible. The value of heat change of the reaction at constant volume, ΔUT is −41.6 × 104 kJ/mol. The effect of different reaction parameters on the level of hydrogenation, calculated from nuclear magnetic resonance spectroscopy, was also investigated. The degree of hydrogenation increases with the increase in reaction time, temperature, the concentration of reactants and catalyst. A maximum of 94% hydrogenation was obtained under the following conditions: time, 4 h; temperature, 45 ± 2°C; pH, 9.36; cupric sulphate (CuSO4 · 5H2O) catalyst concentration, 0.0064 mmol; hydrazine concentration, 0.20 mol; and hydrogen peroxide concentration, 0.26 mol. The diimide reduction of SBR is first-order with respect to olefinic substrate, and the apparent activation energy is 9.5 kJ/mol. The glass transition temperature increases with the increase in saturation level due to development of crystalline segments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1151–1162, 1997  相似文献   

10.
BACKGROUND: This paper describes the modeling of the kinetics of thermal inactivation of transglutaminase (TGase) from a newly isolated Bacillus circulans BL32, isolated from the Amazon environment. The purified enzyme was incubated at temperatures ranging from 30 to 70 °C and values of the thermodynamic inactivation parameters, such as activation energy (ΔE), activation enthalpy (ΔH), activation entropy (ΔS), and free energy (ΔG) for thermal inactivation, were calculated. RESULTS: The kinetics of TGase thermo‐inactivation followed a Lumry–Eyring model. The enzyme was very stable up to 50 °C, with approximately 50% of activity remaining after heating for 12 h. It was completely inactivated by incubation at 70 °C for 2 min. ΔE for TGase was 350.5 kJ mol?1. ΔH and ΔS for thermo‐inactivation of the TGase were 347.8 kJ mol?1 and 744 J mol?1 K?1 at 50 °C, respectively. Dynamic light scattering measurements suggest that the thermal inactivation of this microbial TGase can be partially attributed to the formation of aggregates. CONCLUSION: These results provide useful information about the thermal characteristics of the microbial TGase from B. circulans BL32 and indicate that this enzyme could be a good candidate for industrial applications. Copyright © 2009 Society of Chemical Industry  相似文献   

11.
In the present work, the impact of microwave pretreatment on the thermal degradation of color (chlorophylls) in mustard greens was studied. The drying experiments were conducted in the range of temperatures from 50 to 80°C. The degradation in the levels of chlorophylls has been quantified using Hunter color values (L*, a*, and b*) and calculating total color difference (ΔE). From the color results, the changes in color values (L*, a*, and b*) were observed as inappreciable, and changes in ΔE were found to be increased during drying. Analysis of kinetic data displayed a first-order reaction kinetics for chlorophyll degradation. Arrhenius equation was used to calculate the activation energies for rate constants, and it has been varied from 13.3 to 27.4?kJ/mol. Thermodynamic parameters, enthalpy of activation (ΔH#), and entropy activation (ΔS#) were found to be in the range of 1.40–2.63?J/mol and ?293 to ?305?J/mol?·?K, respectively. The data from the present work revealed that the microwave pretreatment of mustard greens remarkably influenced the retention of chlorophylls in the final dehydrated powder.  相似文献   

12.
The kinetics of ytterbium(III) extraction from sulfate medium with Cyanex 923 in heptane has been investigated with a constant interfacial cell with laminar flow, which aimed to identify the extraction regime, reaction zone and rate equations. It was found that the extraction rate of ytterbium(III) increased linearly with stirring speed and specific interfacial area. The activation energy Ea (9.56 kJ mol?1), activation enthalpy ΔH± (7.05 kJ mol?1), activation entropy ΔS±298 (?0.31 kJ mol?1) and Gibbs free energy of activation ΔG±298 (98.3 kJ mol?1) were calculated from the dependence of extraction rate on temperature. The experiential rate equations were obtained by investigating the influence of the concentration of various species on the extraction rate. A diffusion regime has been deduced from evidence of the linear dependence of extraction rate on stirring speed and the low value of the activation energy. The liquid–liquid interface is most probably the reaction zone in view of the linear dependence of extraction rate on specific interfacial area, the high interfacial activity and low water‐solubility of extractant. Thus the mass transfer rate is controlled by interfacial film diffusion of species. Copyright © 2007 Society of Chemical Industry  相似文献   

13.
To date, most studies of the thermodynamic properties of organic aerosols have utilized test aerosols generated by spray atomization followed by a diffusion drying step. Some evidence points to possible biases in measured thermodynamic properties stemming from the presence of residual solvent (water or alcohol) in the dried aerosol. In the current study we compared measurements of thermodynamic properties of organic aerosols generated by atomization of aqueous solutions to those generated by homogeneous condensation using a modified Sinclair-La Mer generator. In particular, using the Integrated Volume Method (Saleh et al. 2008 Saleh, R., Walker, J. and Khlystov, A. 2008. Determination of Saturation Pressure and Enthalpy of Vaporization of Semi-Volatile Aerosols: The Integrated Volume Method. J. Aerosol Sci., 39: 876[Crossref], [Web of Science ®] [Google Scholar]), we measured and compared the saturation pressure (P sat ) at 298 K and enthalpy of vaporization (ΔH) of C-6 (adipic) and C-9 (azelaic) dicarboxylic acid aerosol generated using these techniques. We found that P sat and ΔH exhibited no statistically significant difference across the tested aerosol generation methods, indicating that any residual solvent carried by the particles had no impact on the measurements. For adipic acid, we obtained P sat of 3.3 × 10?5 (±0.9 × 10?5) Pa and ΔH of 132 (±8) kJ/mol with atomization, and P sat of 4.2 × 10? 5 (±2.2 × 10?5) Pa and ΔH of 126 (±21) kJ/mol with homogeneous condensation; for azelaic acid, we obtained P sat of 1.4 × 10?5 (±0.5 × 10?5) Pa and ΔH of 145 (±15) kJ/mol with atomization, and P sat of 0.9 × 10? 5 (±0.3 × 10? 5) Pa and ΔH of 158 (±17) kJ/mol with homogeneous condensation. In addition, SEM images of the acids generated by the two methods showed no obvious difference in surface morphology.  相似文献   

14.
The voltammetric behavior of naphthoquinone in the presence of free fatty acids (FFA) at the polypyrrole (PPy)‐modified electrode was investigated in an ethanol/1,2‐dichloroethane (3 : 1) solution containing 0.1 M LiClO4. A well‐defined new reduction peak appeared at a more positive potential and was higher than that obtained at the bare Pt electrode. Based on the fact that the new reduction peak current showed a good correlation with the concentration of fatty acids, an electroanalytical method for the acid value (AV) of vegetable oils was developed using the PPy‐modified electrode in linear potential sweep voltammetry. The experimental parameters were optimized to obtain a sensitive voltammetric response in this work. A linear calibration graph was obtained in the concentration range of 5.0×10–6–6×10–3 M for FFA (R = 0.993), with a sensitivity of 2.41×10–2 A L/mol and a detection limit of 1.2×10–6 M (S/N = 3). Each assay of vegetable oil sample took about 80 s. The developed method is applied to the AV determination of six commercial vegetable oils. The results well agreed with those obtained by the titration method. Compared to the conventional titration method, the proposed method is superior in sensitivity and accuracy and requires a small amount of vegetable oil sample, with no pretreatment.  相似文献   

15.
The polymerization of 2-vinylpyridine (2VP) in dimethylformamide (DMF) with azobisisobutyronitrile (AIBN) as initiator was studied with a differential scanning calorimeter. By taking an appropriate amount of AIBN and after correction for its decomposition, the following values could be obtained: Heat of polymerization ΔHp,o = ?68 ± 4 kJ/mol; overall Arrhenius activation parameters Ea = 90.0 ± 4 kJ/mol and ln A = 24 ± 1.0 (A = 2.6 × 1010 dm3/2/mol1/2. s).  相似文献   

16.
Some thermodynamic and explosive properties of the recently reported 1‐azido‐2‐nitro‐2‐azapropane (ANAP) have been determined in a combined computational ab initio (MP2/aug‐cc‐pVDZ) and EXPLO5 (Becker–Kistiakowsky–Wilson's equation of state, BKW EOS) study. The enthalpy of formation of ANAP in the liquid phase was calculated to be ΔfH°, ANAP(l)=+297.1 kJ mol−1. The heat of detonation (Qv), the detonation pressure (P), and the detonation velocity of ANAP were calculated to be Qv=−6088 kJ kg−1, P=23.8 GPa, D=8033 m s−1. A mixture of ANAP and tetranitromethane (TNM) was investigated in an attempt to tailor the impact sensitivity of ANAP, but results obtained indicate that the mixture is almost as sensitive as pure ANAP. On the other hand, ANAP and TNM were found to be chemically compatible (1H, 13C, 14N NMR; DSC) and a 1 : 1 mixture (by weight) of both components was calculated to have superior explosive properties than either of the individual components: Qv=−6848 kJ kg−1, P=27.0 GPa, D=8284 m s−1.  相似文献   

17.
Analyses of the isothermal and nonisothermal melt kinetics for syndiotactic polystyrene have been performed with differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The regime II→III transition, at a crystallization temperature of 239°, is found. The values of the nucleation parameter Kg for regimes II and III are estimated. The lateral‐surface free energy, σ = 3.24 erg cm?2, the fold‐surface free energy, σe = 52.3 ± 4.2 erg cm?2, and the average work of chain folding, q = 4.49 ± 0.38 kcal/mol, are determined with the (040) plane assumed to be the growth plane. The observed crystallization characteristics of syndiotactic polystyrene are compared with those of isotactic polystyrene. The activation energies of isothermal and nonisothermal melt crystallization are determined to be ΔE = ?830.7 kJ/mol and ΔE = ?315.9 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2528–2538, 2002  相似文献   

18.
Adsorption of proteins on solid surfaces is widely studied because of its importance in various biotechnological, medical, and technical applications, e.g., biosensors, cardiovascular implants, and chromatography. Adsorption thermodynamics has been studied on the microbeads of N,N′‐diethylaminoethyl (DEAE) Dextran anion exchanger for the human serum albumin (HSA) at 25, 30, 35, 40, and 45°C. As a result, some thermodynamic parameters like Freundlich constants, thermodynamic equilibrium constant (KD), standard free energy changes (ΔGassoc), standard entropy changes (ΔSassoc), and standard enthalpy change (ΔHassoc) have been evaluated. Using the linear Van't Hoff plot, ΔHassoc value of the system for the interaction of bovine serum albumin (BSA)‐adsorbed crosslinked DEAE dextran microbeads was determined as 20.650 kJ/mol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3942–3947, 2006  相似文献   

19.
The two‐dimensional coordination polymer cadmium phosphate with the morphology of rectangle layers was prepared by solid‐state template reaction at room temperature, and was characterized by XRD, FTIR, and TEM techniques. The as‐synthesized sample is a layered cadmium phosphate material, in which the structure is poly (CdPO4?) anion framework with ammonium ions and water species residing in the space between the layers, and cadmium ions are coordinated by the phosphate oxygen atoms. This article also presents the adsorption of Pb(II) ions from aqueous solution on the as‐synthesized coordination polymer cadmium phosphate, and the results showed that this inorganic polymer adsorbent had good adsorption capacity. It could reach to the saturation adsorption capacity within an hour, and its excellent adsorption capacity for Pb(II) was 5.50 mmol/g when the initial solution concentration was 1.68 × 103 μg/mL at T = 278K. Moreover, the adsorption kinetics and adsorption isotherms were studied, it revealed that the adsorption kinetics can be modeled by pseudo second‐order rate equation wonderfully. The apparent activation energy (Ea), ΔG, ΔH, and ΔS were 3.16 kJ mol?1, ?13.97 kJ mol?1, ?11.84 kJ mol?1, and 7.66 J mol?1 K?1, respectively. And it was found that Langmuir equation could well interpret the adsorption of the as‐synthesized coordination polymer cadmium phosphate for Pb(II) ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

20.
The aggregation behavior of a di‐ and tri‐block copolymers of type PEO‐PBO, PEO‐PBO‐PEO, surface‐active ionic liquid (SAIL) of type 4‐dodecyl‐4‐methylmorpholinium chloride [C12mmor][Cl], and 1‐dodecyl‐1‐methylpyrrolidinium chloride [C12mpyrr][Cl]) in water as well as in 10 mM of a poorly water soluble dexamethasone (dex) aqueous solution was studied by determining the critical micelle concentrations using drug solubilization, surface tension, and isothermal titration calorimetry (ITC) methods. ITC measurements were also made on solutions prepared by mixing the micellar aqueous solutions of copolymers and simple aqueous solutions of SAIL across the mole fractions at three different temperatures (298.15, 308.15, and 318.15 K). The thermodynamic parameters, namely Gibbs free energy (ΔGm), enthalpy (ΔHm), and entropy (ΔSm), of micellization were calculated, and it was observed that the negative ΔGm and positive ΔSm for the mixture solutions increase with the increase in mole fraction of SAIL. Otherwise, the micellization is reported to be a spontaneous and highly entropy‐driven process. The dex‐solubilized micellar solutions were mixed with agar to obtain standing gels. The gel samples were dry‐cast into thin films, and the release of dex from films by simple dilution was monitored by UV measurements. The drug release data was fitted to several mechanistic models, and it was inferred that the release mechanism for dex from thin films is non‐Fickian for mixtures and Fickian in copolymer or SAIL micellar aqueous solutions. The transport of dex is diffusion‐controlled with diffusivities of 5.8–12 × 10?11 m2 s?1 for copolymer micelles, 5–11 × 10?11 m2 s?1 for micelles of SAIL, and 3–14 × 10?11 m2 s?1 for the mixed micelles of copolymer and SAIL in aqueous media.  相似文献   

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