Comparative Kinetic Study Research Articles

Comparative Shock Tube and Kinetic Study on High-Temperature Ignition of 2,3-Dihydrofuran and 2,5-Dihydrofuran

The ignition delay times of 2,3-dihydrofuran (23DHF) and 2,5-dihydrofuran (25DHF) were investigated over the temperature range of 1100 to 1635 K with pressure of 1.2, 4, and 10 atm for lean (φ= 0.5), stoichiometric, and rich (φ= 2) fuel/O2/Ar mixtures. 23DHF shows shorter ignition delay times than 25DHF under the above conditions. A modified model (M_Tran model) was presented to improve the prediction of DHF ignition. Kinetic analysis indicated that most 23DHF transforms to cyclopropane carboxaldehyde (CPCA) and further to croton aldehyde (CA) by isomerization while most 25DHF dehydrogenates to furan. Some reactions involving CA and propene show strong sensitivity for 23DHF ignition. Some reactions of furan present strong effect on 25DHF ignition. Ignition delay data between furan, 23DHF, and 25DHF were compared to reveal the effect of number and location of carbon double bonds on the ignition characteristics. The bond dissociation energies of DHF are not as strong as that of furan and are significantly i...

An ignition delay time and kinetic study of 2-methyltetrahydrofuran at high temperatures

Kinetic analyses were performed based on the experimental results of ignition delay times of 2-methyltetrahydrofuran (2-MTHF) using shock tube technique at temperatures of 1050–1800K, equivalence ratios of 0.5–2.0, fuel mole concentrations of 0.25–1.0%, and pressures of 1.2–10atm. A new kinetic model of 2-MTHF oxidation named Mech III was established according to the analysis of simulation using two published models (Mech I from Ravi Fernandes group and Mech II from Battin-Leclerc group) and the experimental data in this work. Comparison between simulation and experimental data indicated that Mech II shows remarkable under-prediction while Mech I gives a good agreement with ignition delay times under most conditions except for underprediction on fuel-rich mixtures at relative low temperature around 1250K. Sensitivity analysis indicated that both models underestimated ignition delay times for the reactions of C0-C4 molecules, so Mech III was formed by introducing such reactions and can demonstrate improved simulation performance under all conditions. Reaction pathway analysis of Mech III showed that 2-MTHF is mainly consumed through fuel decomposition at high temperatures (around 1550K), and H-atom abstraction reactions at lower temperatures (around 1250K), respectively. The comparative experimental and kinetic study between 2-MTHF and 2-methylfuran (MF) indicated that 2-MTHF has higher ignition delay times under the same conditions in this work, while the disparity decreases as the temperature increases, and 2-MTHF produces less soot precursors under high temperature conditions.

Sodiation vs. Lithiation of FePO4: A comparative kinetic study

A comparative study of sodiation and lithiation of FePO4 host material for secondary sodium- and lithium-ion batteries is performed. To ensure the best possible comparability, NaFePO4 based electrodes are prepared by an electrochemical displacement technique using LiFePO4 as the starting material. The electrodes are identical in view of particle size distribution, active material loading, binder, conductive additives, and carbon coating, etc. All differences in the kinetics are exclusively determined by the substitution of the alkali metal cation. Electrochemical impedance spectroscopy is carried out at different temperatures. Kinetic parameters as the exchange current density and the diffusion coefficients of sodium and lithium in the FePO4 host material are obtained by fitting the data to an appropriate equivalent circuit. The study reveals substantially slower intercalation kinetics and larger activation energies for sodiation in comparison to lithiation of FePO4. This is most likely attributed to the different ionic radii and molar masses of sodium and lithium.

Kinetic Study of Copper(II) Simultaneous Extraction/Stripping from Aqueous Solutions by Bulk Liquid Membranes Using Coupled Transport Mechanisms

Heavy metals removal/recovery from industrial wastewater has become a prime concern for both economic and environmental reasons. This paper describes a comparative kinetic study of the removal/recovery of copper(II) from aqueous solutions by bulk liquid membrane using two types of coupled facilitated transport mechanisms and three carriers of different chemical nature: benzoylacetone, 8-hydroxyquinoline, and tri-n-octylamine. The results are analyzed by means of a kinetic model involving two consecutive irreversible first-order reactions (extraction and stripping). Rate constants and efficiencies of the extraction (k1, EE) and the stripping (k2, SE) reactions, and maximum fluxes through the membrane, were determined for the three carriers to compare their efficiency in the Cu(II) removal/recovery process. Counter-facilitated transport mechanism using benzoylacetone as carrier and protons as counterions led to higher maximum flux and higher extraction and stripping efficiencies due to the higher values of both the extraction and the stripping rate constants. Acceptable linear relationships between EE and k1, and between SE and k2, were found.

Sustainable Aromatic Copolyesters via Ring Opening Polymerization: Poly(butylene 2,5-furandicarboxylate-co-terephthalate)s

A series of poly(butylene 2,5-furandicarboxylate-co-terephthalate) copolyesters coPBFxTy covering the whole range of compositions has been prepared via ring opening polymerization (ROP). Cyclic oligomers of butylene 2,5-furandicarboxylate c(BF)n and butylene terephthalate c(BT)n, both mainly consisting of a mixture of dimer, trimer, and tetramer species, were synthesized by the high dilution condensation method. Random copolyesters with the targeted compositions and weight-average molecular weights within the 55 000–80 000 g·mol–1 range were obtained by ROP of c(BF)n/c(BT)n mixtures in periods of time much shorter than those required by melt polycondensation. The thermal properties of these copolyesters were consistent with their compositions and comparable to their isocompositional analogs obtained by polycondensation. A comparative kinetics study of the isothermal crystallization of the homopolyesters and copolyesters differing in composition revealed that the presence of the 2,5-furandicarboxylate units decreased the crystallization rate of PBT. Nevertheless, coPBFxTy copolyesters with moderate contents in BF units were still able to crystallized rapidly from the melt.

A Comparative Study of Growth Kinetics, In Vitro Differentiation Potential and Molecular Characterization of Fetal Adnexa Derived Caprine Mesenchymal Stem Cells.

The present study was conducted with an objective of isolation, in vitro expansion, growth kinetics, molecular characterization and in vitro differentiation of fetal adnexa derived caprine mesenchymal stem cells. Mid-gestation gravid caprine uteri (2–3 months) were collected from abattoir to derive mesenchymal stem cells (MSCs) from fetal adnexa {amniotic fluid (cAF), amniotic sac (cAS), Wharton’s jelly (cWJ) and cord blood (cCB)} and expanded in vitro. These cultured MSCs were used at the 3rd passage (P3) to study growth kinetics, localization as well as molecular expression of specific surface antigens, pluripotency markers and mesenchymal tri-lineage differentiation. In comparison to cAF and cAS MSCs, cWJ and cCB MSCs showed significantly (P<0.05) higher clonogenic potency, faster growth rate and low population doubling (PDT) time. All the four types of MSCs were positive for alkaline phosphatase (AP) and differentiated into chondrogenic, osteogenic, and adipogenic lineages. These stem cells expressed MSC surface antigens (CD73, CD90 and CD105) and pluripotency markers (Oct4, Sox2, Nanog, KLF, cMyc, FoxD3) but did not express CD34, a hematopoietic stem cell marker (HSC) as confirmed by RT-PCR, immunocytochemistry and flow cytometric analysis. The relative mRNA expression of MSC surface antigens (CD73, CD90 and CD105) was significantly (P<0.05) higher in cWJ MSCs compared to the other cell lines. The mRNA expression of Oct4 was significantly (P<0.05) higher in cWJ, whereas mRNA expression of KLF and cMyc was significantly (P<0.05) higher in cWJ and cAF than that of cAS and cCB. The comparative assessment revealed that cWJ MSCs outperformed MSCs from other sources of fetal adnexa in terms of growth kinetics, relative mRNA expression of surface antigens, pluripotency markers and tri-lineage differentiation potential, hence, these MSCs could be used as a preferred source for regenerative medicine.

Comparative study of mechanical properties and damage kinetics of two- and three-dimensional woven composites under high-strain rate dynamic compressive loading

The in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction.

Fluorescence relaxation kinetics of poly(methylphenylsilane) film and nanocomposites.

A comparative study of fluorescence relaxation kinetics of σ-conjugated poly(methylphenylsilane) (PMPS) polymer film and nanocomposites has been performed by ultrafast time-gated fluorescence measurements at various temperatures. Investigations have revealed a fine structure of excitonic σ-σ* band. We attribute this structure to emission from two spatially independent states with different ordering of the polymer chain segments, type gauche and trans conformations. In contrary to a more ordered polymer poly(di-n-hexylsilane), no clear thermochromic transition has been detected in PMPS film; however, the trans band intensity increases with temperature and with excitation wavelength, but it is absent when polymer is incorporated into nanopores of small diameter.

Uncatalyzed and Ruthenium(III) Catalyzed Oxidation of Aspartame by Potassium Permanganate in Aqueous Alkaline Medium: A Comparative Kinetic Study

The reaction kinetics and mechanism of the oxidation of aspartame by permanganate ion in the absence and presence of ruthenium(III) in alkaline media has been studied spectrophotometrically at 298 K and at a constant ionic strength of 1.10 mol·dm−3. The uncatalyzed and catalyzed reaction has a stoichiometry, 1:2 (aspartame: $$ {\text{MnO}}_{4}^{ - } $$ ). The oxidation products, $$ {\text{MnO}}_{4}^{2 - } $$ and 6-benzyl-3-hydroxy-3-methylpiperazine-2,5-dione were characterized by spectral studies. The order with respect to $$ {\text{MnO}}_{4}^{ - } $$ concentration was unity and that of aspartame was less than unity in the uncatalyzed and catalyzed reactions. The alkali KOH concentration was varied and it was found that as the KOH concentration increased, the rate increased with less than unit order in either the absence or presence of catalyst. The order with respect to ruthenium(III) concentration was unity. The species [Ru(H2O)5OH]2+ was found to be the active species of ruthenium(III). The effect of ionic strength and solvent polarity were studied. Based on experimental results suitable mechanisms were proposed. Activation parameters and thermodynamic quantities were determined and discussed.

Comparative Kinetic Study on the Preparation of Poly(Vinyl Acetate) Activated by Microwave and Conventional Heating

Comparative Kinetic Study on the Preparation of Poly(Vinyl Acetate) Activated by Microwave and Conventional Heating

Comparative Kinetic Study of Removal of Pb2+ Ions and Cr3+ Ions from Waste Water using Carbon Nanotubes Produced using Microwave Heating

A comparative study of the removal of Pb2+ ions and Cr3+ ions was conducted to determine the efficiency of carbon nanotubes (CNTs) produced using microwave heating as an adsorbent in removing heavy metal ions from waste water. Optimization of parameters such as adsorbent dosage, pH value, agitation speed, and agitation time was done using the Design Expert software version 6.0. The statistical analysis revealed that optimized conditions for the highest removal for Pb2+ are at pH 4.0, CNTs dosage of 0.09 g, agitation time and speed of 50 min and 150 rpm respectively. Meanwhile, the highest removal Cr3+ ions was observed at pH 8.0, CNTs dosage of 0.09 g, agitation time and speed of 60 min and 150 rpm respectively. For the initial concentration of 2 mg/L, the removal efficiency of Pb2+ ions and Cr3+ ions were 99.9% and 95.5% respectively. The maximum adsorption capacities of both Pb2+ ions and Cr3+ ions onto the CNT were 15.34 mg/g for Pb2+ ions and 24.45 mg/g for Cr3+ ions. Besides that, the Langmuir and Freundlich constants for the removal of Pb2+ ions were 0.073 and 1.438 L/mg while 0.071 and 1.317 L/mg for Cr3+ ions. The statistical analysis proved that the removal of Pb2+ ions and Cr3+ ions fits the Langmuir and Freundlich isotherm models, and both models obeyed the pseudo-second-order.

Comparative kinetic study of the pyrolysis of mandarin and pineapple peel

This study focuses on the pyrolysis processes of fruit peels as energy sources. These pyrolysis processes for mandarin and pineapple peels were analyzed by profiles of conversion vs. temperature and DTG curves. Five kinetic stages were observed, each with a different activation energy calculated by utilizing the Coats and Redfern method and assuming a first order model. The mandarin peel process showed a higher activation energy during the first and second stages of the pyrolysis. Consequently, mandarin peel was selected over pineapple peel for further studies. Other models such as diffusion and nucleation also fitted the data and as a result, the nonlinear integral isoconversional method was implemented to get more accurate activation energies. In the range of 350 and 460°C, there was a rapid decrease in activation energy that was attributed to the radical recombination as the dominant mechanism. Experiments of pyrolysis with the mandarin peel were carried out in the pyrolytic reactor to verify these findings. The pyrolysis oils obtained at 460 and 600°C were analyzed by GC⿿MS and FTIR Spectroscopy. The results showed that the pyrolysis oil obtained at 460°C had a higher average degree of unsaturation. Once the pyrolysis went through temperatures higher than 460°C, the average degree of unsaturation decreased. Although the oil obtained at 460°C showed a higher average degree of unsaturation, it was not enough to show a substantially higher calorific value than the oil obtained at 600°C. The significant difference in the calorific values could be potentially observed in the biochars obtained at the temperatures already mentioned.

Spectrophotometric evaluation of surface morphology dependent catalytic activity of biosynthesized silver and gold nanoparticles using UV–vis spectra: A comparative kinetic study

The development of eco-friendly and cost-effective synthetic protocol for the preparation of nanomaterials, especially metal nanoparticles is an emerging area of research in nanotechnology. These metal nanoparticles, especially silver can play a crucial role in various catalytic reactions. The biosynthesized silver nanoparticles described here was very stable up to 6 months and can be further exploited as an effective catalyst in the chemical reduction of 4-nitrophenol to 4-aminophenol. The silver nanoparticles were utilized as an efficient surface-enhanced Raman scattering (SERS) active substrate using Rhodamine 6G as Raman probe molecule. We have also carried out systematic comparative studies on the catalytic efficiency of both silver and gold nanoparticles using UV–vis spectra to monitor the above reaction spectrophotometrically. We find that the reaction follows pseudo-first order kinetics and the catalytic activity can be explained by a simple model based on Langmuir–Hinshelwood mechanism for heterogeneous catalysis. We also find that silver nanoparticles are more efficient as a catalyst compare to gold nanoparticles in the reduction of 4-nitrophenol to 4-aminophenol, which can be explained by the morphology of the nanoparticles as determined by transmission electron microscopy.

Oxidative Degradation of Atropine Drug by Permanganate Ion in Perchloric and Sulfuric Acid Solutions: A Comparative Kinetic Study

The kinetics of oxidations of atropine (ATR) by permanganate ion in both perchloric and sulfuric acid solutions was studied using spectrophotometric technique at a constant ionic strength of 1.2 moldm-3 and at 25°C. In both acids, the reactions showed a first order dependence with respect to [permanganate], whereas the orders with respect to [ATR] and [H+] were found to be less than unity. The effect of acid concentration suggests that the reactions were acid-catalyzed. Variation of either ionic strength or dielectric constant of the medium had no effect significantly on the oxidation rates. The reactions mechanism adequately describing the kinetic results was proposed. In both acids, the main oxidation products of atropine were identified by spectral and chemical analyses as tropine and phenylmalonic acid. Under comparable experimental conditions, the oxidation rate of atropine in sulfuric acid was approximately three times higher than that in perchloric acid. The reactions constants involved in the different steps of the reactions mechanism have been evaluated. With admiration to the rate-limiting step of these reactions, the activation parameters have been evaluated and discussed.

Oxidation of Caffeine by Permanganate Ion in Perchloric and Sulfuric Acids Solutions: A Comparative Kinetic Study

The kinetics of oxidations of caffeine by permanganate ion in both perchloric and sulfuric acids solutions have been investigated spectrophotometrically at a constant ionic strength of 1.0 mol dm-3 and at 25°C. In both acids, the reaction-time curves were obtained with a sigmoid profile suggesting an autocatalytic effect caused by Mn(II) ions formed as a reaction product. Both catalytic and non-catalytic processes were determined to be first order with respect to the permanganate ion and caffeine concentrations, whereas the orders with respect to [H+] and [Mn(II)] were found to be less than unity. Variation of either ionic strength or dielectric constant of the medium had no significant effect on the oxidation rates. Spectroscopic studies and Michaelis-Menten plots showed no evidence for the formation of intermediate complexes in both acids suggesting that the reactions point towards the outer-sphere pathway. The reactions mechanism adequately describing the kinetic results was proposed. In both acids, the main oxidation products of caffeine were identified as 1,3,7-trimethyluric acid. Under comparable experimental conditions, the oxidation rate of caffeine in perchloric acid was slightly higher than that in sulfuric acid. The constants involved in the different steps of the reactions mechanism have been evaluated. With admiration to the rate-limiting step of these reactions, the activation parameters have been evaluated and discussed.

A Comparative Kinetic Study of Silver(I)-Catalyzed Oxidations of Alanine and Valine by Platinum (IV) in Perchloric and Sulfuric Acids Solutions

The kinetics of oxidations of two aliphatic α-amino acids (AA), namely, alanine and valine by platinum (IV) has been investigated spectrophotometrically in perchloric and sulfuric acids solutions in the presence of silver (I) catalyst at a constant ionic strength of 1.0 mol dm-3 and at 25°C. The reactions were very slow to be measured in the absence of the catalyst. The reactions in both acids showed a first order dependence on both [PtIV] and [AgI], and less than unit order dependences with respect to both [AA] and [H+]. Increasing ionic strength was found to decrease the oxidation rates. Under comparable experimental conditions, the oxidation rates of alanine and valine in perchloric acid solutions were found to be about five times higher than those obtained in sulfuric acid solutions and the oxidation rates of alanine in both acids were found to be higher than those recorded with respect to valine. A plausible oxidations mechanism has been proposed and the rate law expression has been derived. Both spectral and kinetic evidences revealed formation of 1:1 intermediate complexes between AA and AgI in both acids before the rate-controlling step. Then the formed complexes react with the oxidant (PtIV) by an inner-sphere mechanism to give rise to the oxidation products of the amino acids which were identified as the corresponding aldehyde, ammonium ion and carbon dioxide. The activation parameters of the second order rate constants were evaluated and discussed.

Advanced Models for Vibrational and Chemical Kinetics Applied to Mars Entry Aerothermodynamics

The paper presents a comparative study of vibrational-chemical kinetics and heat transfer in carbon dioxide flows under Mars entry conditions for two classes of models: the state-to-state and multitemperature models. The state-to-state approach treats each vibrational state of a molecule as a separate chemical species, thus providing a very detailed flow description. Reduced multitemperature models are based on nonequilibrium quasi-stationary Boltzmann distributions over vibrational energy with vibrational temperatures of different modes. Implementation of multitemperature models requires much less computational effort, making them rather attractive for engineering applications. Simulations have been performed for the upper part of the Mars Pathfinder entry trajectory. Comparisons between different models demonstrate a good agreement for the flowfield variables obtained using the state-to-state and multitemperature approaches, except some discrepancies for the species mole fractions prediction. This conclusion is encouraging for computational fluid dynamics, since it confirms that multitemperature models, while not being so much detailed as state to state, are still able to capture the main peculiarities of thermal and chemical nonequilibrium flows. The transport and thermochemical models have been validated using experimental data obtained in the NASA Hypersonic Pulse ground test facility. It is shown that both state-to-state and advanced multitemperature transport models used in the present simulations provide a better agreement for the heating predictions compared to traditional models.

Identification of Suitable rhizobacterialspecies for Fluoride Contaminated Areas: A Comparative Growth Kinetics Study

Identification of Suitable rhizobacterialspecies for Fluoride Contaminated Areas: A Comparative Growth Kinetics Study

Laser Ignition and Flame Speed Measurements in Oxy-Methane Mixtures Diluted With CO2

Ignition and flame propagation in methane/O2 mixtures diluted with CO2 are studied. A laser ignition system and dynamic pressure transducer are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBVs) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation are recorded by using a high-speed camera in select experiments to visualize the effect of CO2 proportionality on the combustion behavior. The LBV is studied for a range of equivalence ratios (ϕ = 0.8–1.3, in steps of 0.1) and oxygen ratios, D = O2/(O2 + CO2) (26–38% by volume). It was found that the LBV decreases by increasing the CO2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO2 proportionality increases, where it was not possible to obtain LBV due to the deviation from spherical flame shape. Current LBV data are in very good agreement with existing literature data. The premixed flame model from chemkin pro (Reaction Design, 2011, CHEMKIN-PRO 15112, Reaction Design, San Diego, CA) software and two mechanisms (GRI-Mech 3.0 (Smith et al., 1999, “The GRI 3.0 Chemical Kinetic Mechanism,” http://www.me.berkeley.edu/gri_mech/) and ARAMCO Mech 1.3 (Metcalfe et al., 2013, “A Hierarchical and Comparative Kinetic Modeling Study of C1–C2 Hydrocarbon and Oxygenated Fuels,” Int. J. Chem. Kinetics, 45(10), pp. 638–675)) are used to simulate the current data. In general, simulations are in reasonable agreement with current data. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.

Ruthenium(III)-catalyzed oxidation of alginate and pectate biopolymers by chromic acid in aqueous perchlorate solutions: a comparative kinetic study

The kinetics of chromic acid oxidation of alginate and pectate carbohydrate biopolymers in aqueous perchlorate solutions was studied in the absence and presence of ruthenium(III) catalyst at a fixed ionic strength of 2.0 mol dm−3 and a temperature of 298 K. Both uncatalyzed and Ru(III)-catalyzed oxidation reactions were followed spectrophotometrically. Both the reactions exhibited first-order dependence on [Cr(VI)], less than unit order with respect to the biopolymer concentration and fractional second order with respect to [H+]. The catalyzed reactions were first order in [Ru(III)]. No significant effect of ionic strength or dielectric constant of the medium was observed. Addition of Mn(II) inhibited the oxidation. Probable mechanistic schemes for the oxidation reactions are proposed, and the rate laws associated with these mechanisms have been derived. In both cases, the final oxidation products were characterized by spectroscopic data and microanalysis as mono–keto derivatives of the biopolymers. Under comparable experimental conditions, the oxidation rates of alginate were found to be lower than those of pectate for both the uncatalyzed and Ru(III)-catalyzed paths. The activation parameters with respect to the slow step of the mechanisms have been computed.