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ELECTRIC furnaces, ARC furnaces, DIRECT-fired heaters, ELECTRIC arc, and FURNACES

This work has aimed at evaluating the deoxidation characteristics for Si-Mn in Electric Arc Furnace (EAF) melt shops. A statistical methodology led to the identification of the key EAF tapping process parameters that affect Si and O evolution during secondary refining. A first order kinetic equation estimated the deoxidation constants at the beginning of the ladle furnace process. The experimental values were5,3·10-3 s-1 and 3,6·10-3 s-1 As expected, these values are higher than that estimated for the reduction of the total oxygen content based on the gas injection agitation energy, which was 1,67·10-3 s-1, confirming the importance of the agitation caused by tapping. A model that couples slag and metal composition evolution in special from tapping to arrival at the ladle furnace (LF) was developed. The model confirmed the presence of undissolved slag solid fraction on arrival at the LF and made reasonable prediction for the liquid phase composition. The potential, limitations and applicability of each model are discussed, aiming at defining the next steps for a complete model for ferro-alloys additions to Si-Mn steels. [ABSTRACT FROM AUTHOR]

STABILITY constants, IONIC strength, PERMITTIVITY, OXIDATION kinetics, and HYDROCHLORIC acid

The kinetics of tetrahydrofuran oxidation by sodium N-chloro-p-toluene sulfonamide in the hydrochloric acid medium was studied in this work at 308 K. The reaction rate shows a first-order dependence on [CAT] and fractional-order dependence each on [THF] and [H+]. The derivative rate law, which suitable for experimental results, is Equation 24. The first-order rate constant has been evaluated from the relationship of the plot of Log [CAT] versus Time. The variation of the ionic strength by the addition of sodium perchlorate (NaClO4) and chloride ion on the medium showed no significant effect on the reaction. The reaction rate raised with decreasing dielectric constant (D), while the addition of p-toluene sulfonamide retards the rate of reaction. The oxidation reaction of tetrahydrofuran have been studied at a different temperature, The equilibrium constants for the formation of hypochlorous acid, protonated hydrochlorous acid and protonated hydrochlorous acid-THF complex and its decomposition constant have been estimated. Also, the rate constant for the slow (rate-determining step) and the activation parameter have been calculated. A suitable mechanism for the oxidation reaction of tetrahydrofuran was proposed based on the experimental finding. The mechanism includes the reaction of active species (H2OCl) of the oxidizing agent with the tetrahydrofuran in a fast step to give the complex(X). This complex will then transformed into complex (X̅) in slow step then to γ-butyrolactone in another fast step. [ABSTRACT FROM AUTHOR]

Cinètica, Enzim, and Velocitat de reacció

ADSORPTION capacity, HEAVY metals, AQUEOUS solutions, PHYSISORPTION, and ADSORPTION isotherms

Introduction- Among the heavy metals discharged on water sources the Chromium (VI) and Nickel (II) cause dangerous health effects. Objective- Optimize the effect of the initial concentration of pollutant, temperature and adsorbent dose using residues of the starch obtaining process from hawthorn yam (D. rotundata) in the removal of Chromium (VI) and Nickel (II). Method- The optimization was carried out by applying the Response Surface Methodology (RSM), performing the kinetic and equilibrium study to the optimal condition found, evaluating the fit of the kinetic data to the pseudo-first order, pseudo-second order and Elovich models; those of isotherms to the models of Langmuir and Freundlich. The thermodynamic parameters- Gibbs free Energy (ΔG°), Enthalpy (ΔH°) and Entropy (ΔS°), were calculated using the Van't Hoff graphical method. Results- From the MSR it was found that the optimal conditions for Cr(VI) were 76.6 ° C, 0.14 g and 368.18 ppm, and for Ni (II) 70 °C, 1.19 g and 31.82 ppm. The maximum adsorption capacity was 66.25 mg/g Cr(VI) and 17.67 mg/g Ni(II). The pseudo-second order kinetic model adjusts the adsorption data of Cr(VI) and that of Elovich adjusts the Ni(II) data; on the other hand, the Freundlich isotherm model showed the best adjustment of the adsorption data of the ions under study. The values of ΔG°, ΔS°, and ΔH° established that the process for Cr(VI) is endothermic, not spontaneous, not favorable and reversible; for Ni (II) which is non-spontaneous, exothermic and controlled by physisorption. Conclusions- The residues of the hawthorn yam starch extraction process are an effective adsorbent for the removal of Cr (VI) and Ni (II) present in aqueous solution and the MSR yielded optimal values that serve as the basis for the scalability of the process. [ABSTRACT FROM AUTHOR]

METAL cyanides, THIOUREA, CYANIDES, SUSTAINABLE chemistry, SPECTROPHOTOMETERS, DIFFUSION, and IMPELLERS

In this work, the effect of the agitation speed on the thiourea kinetics with thiourea of gold-floated minerals, the concentration of thiourea (TU) that achieved the greatest recovery of gold from its floated concentrates compared with cyanide was determined, along with the kinetic model that controls leaching with thiourea. For this, a "Suction tube" type Baffled reactor is used with mechanical agitation by means of a vane type impeller. The parameters analyzed were: percentage of solids (15%); TU concentration (1, 3, 6, 9, 12 g / L); stirring speed (420, 490, 560, 700 rpm); reaction time (4 hours); effective reactor capacity (27.1 L). An atomic absorption spectrophotometer is estimated to determine the gold concentration. It was determined that the thiourea concentration of 9 g / L was the one that produced the best gold recovery results. The thiourea leaching process adapts to the kinetic diffusion model through the ash layer as a controlling stage. Thiourea, as a leaching agent of the Au concentrate, has a lower percentage (1.74% less) of recovery of this metal than with cyanide during the leaching process at 240 minutes of stirring at a stirring speed of 700 rpm. [ABSTRACT FROM AUTHOR]

KINETIC control, FLOTATION, CYANIDES, SCANNING electron microscopy, MASS transfer, and FACTORY design & construction

The knowledge of the kinetic control mechanisms of gold leaching in real process conditions is crucial for the correct process design and plant operation. This research evaluated the kinetic control mechanism on the gold leaching with cyanide in alkaline media from a previously floated ore. Before the leaching, a pre-treatment with sodium hypochlorite was carried out to eliminate remaining reagents from the flotation process. After the pre-treatment several leaching experiments were conducted keeping constant the pH, temperature and aeration rate, meanwhile the agitation velocity and cyanide dosage were varied. The analysis of leaching kinetic profiles indicated that the control of the reaction corresponds to the mass transfer in the ash produced by the reaction with two resistances to the leaching process. Furthermore, the analysis was complemented with scanning electron microscopy and x-ray dispersive energy (SEM-EDX) measurements confirming that the leached ore surface do not contain detectable levels of gold. [ABSTRACT FROM AUTHOR]

SAFFLOWER oil, OLIVE oil, CRYSTALLIZATION kinetics, LOW temperatures, ISOTHERMAL processes, and MELTING points

The crystallization behaviors of safflower and olive oils were investigated according to changes in volume and transmitted light intensity during isothermal storage at low temperature. The changes between the oils were significantly different even though their fatty acid compositions were similar, with oleic acid accounting for more than 75% (w/w) of the total oil. It was expected that minor components with high melting points would affect the crystallization behaviors of these oils. The crystallization processes of the oils were then analyzed using a kinetic model in which the oil crystallizes through two different processes. It is suggested that although the crystallization behaviors were apparently different, the crystallization mechanisms of these oils are essentially the same. [ABSTRACT FROM AUTHOR]

SUNFLOWER seed oil, OZONIZATION, CARBONYL compounds, FATTY acids, OXIDATION, and PEROXIDES

Vegetable oils are usually rich in unsaturated fatty acids which are susceptible to oxidation. The oxidation of vegetable oils has been one of the most widely studied fields within lipid chemistry, because it alters their properties and nutritive value, inducing the formation of harmful compounds and off-flavors. Moreover, oxidized vegetable oils display altered physical and chemical properties which are conferred by the newer oxygenated compounds they contain. This is the case of ozonized oils. Ozone is a powerful oxidizing agent that mainly acts on olefinic compounds which generate ozonides and other peroxidic species that can decompose into carbonilic fragments. The action of the oxidant and the later reactions depend on the chemical environment of the reaction as well as the carbonyl termination products resulting from peroxide cleavage. In recent years, sunflower oils with different fatty acid compositions have been developed by breeding and mutagenesis. They displayed higher contents of oleic, stearic or palmitic acids, which mainly alters their triacylglycerol composition. Therefore, four different sunflower oils, common, high oleic, high stearic-high oleic and high palmitic-high oleic, were oxidized with ozone and the progress of the reaction was monitored by measuring the level of oil peroxygenation and the changes in the oils' fatty acid compositions. The peroxidated species formed during ozonation were studied by FT-IR spectroscopy. The main conclusions of this work were that ozonation caused linear oxidation rates that were similar in all the oils assayed. The addition of water accelerated oxidation, which tended to occur in linoleic polyunsaturated fatty acid The FT-IR pointed to the presence of ozonide-derived peroxides as the major oxygenated species. [ABSTRACT FROM AUTHOR]

CORN oil, ANTIOXIDANTS, MICROWAVE cooking, EFFECT of heat on food, OXIDATION, and HEXANAL

Four different corn oil samples including stripped (SCO, Control), refined (RCO), stripped corn oil enriched with rosemary extract (SCO+ROS) and ascorbyl palmitate (SCO+AP) were exposed to microwave (MWH) and conventional heating (CVH). For both heating methods, peroxide value (PV) and conjugated dienes increased at up to 230 °C, at which temperature hexanal (HEX) and conjugated trienes started to increase instead. Kinetic analysis revealed that PV and HEX formation were first ordered and the reaction rate among the samples was as follows: Control > SCO+ROS > RCO > SCO+AP for PV and SCO+ROS > RCO > SCO+AP > Control for HEX. The unsaturated fatty acid contents of CVH and MWH treated samples showed 9.5 and 12.9% reduction in SCO, while they were 2.9 and 7.7% in RCO, 3.6 and 6.1% in SCO+ROS, and finally 4.0 and 4.8% in SCO+AP. It was concluded that MWH led to a more severe deterioration and that the antioxidant activity of ROS was superior to that of AP for both heating methods. [ABSTRACT FROM AUTHOR]

TECHNICAL literature, MICROALLOYING, STEEL, AUSTENITE, MARTENSITE, and DUAL-phase steel

In this work, martensitic kinetic models, available in the technical literature, were studied aiming to model and to predict the austenite to martensite transformation for the USISAR 80T steel, which is a structural, microalloyed, with high hardenability and considered a great weldable steel. Dilatometrictests were performed with a heating rate of 3°C/s until 920°C, with a soaking time of 180 seconds and cooling rates of 25°C/s, 50°C/s, 75°C/s and 100°C/s. One of the studied models showed good agreement with the experimental data for all the employed cooling rates, and it was possible to determinetransformation characteristic constants and suggest a previsibility model for the USISAR 80T steel. [ABSTRACT FROM AUTHOR]

MATHEMATICAL models, HYDROCRACKING, PETROLEUM, DATA modeling, CONCORDANCES, and HYDROCARBONS

The mathematical modeling of hydrocracking reaction of petroleum fractions was carried out considering a pseudohomogeneous phase. The discrete description was used to represent the kinetic of the reactions. One to 6 lumps of pseudocompounds with different reaction routes were used. Data from the oil hydrocarbon hydrocracking of literature were used to obtain the mathematical model parameters. Modeling more than one group or lump was done by automatic successive approach solving the system of equations starting with one lump, then two, then three, and so on, checking that the material balance is satisfied in each case. Findings showed concordance between the models and the experimental data, highlighting the use of six lumps, from whose description it is possible to determine the composition of the hydrocracking products in a detailed and reliable way. [ABSTRACT FROM AUTHOR]

BIOMASS, PYROLYSIS, COAL, BIOCHAR, HEATING, THERMAL analysis, and RENEWABLE energy sources

The objective of this work is to determine the influence of the type of biomass and the heating rate (β) on the pyrolytic decomposition kinetics of Teca and Guachapelí. Experimentally, chemical and energetic biomass were characterized using elemental and immediate analysis and the sample was pyrolyzed using two thermal analysis equipment, one conventional (ATG) and one of simultaneous analysis (ATG, TGD, CDB). The chemical characterization demonstrated the potentialities of biomass as energy sources. The kinetic study carried out identified kinetic models and activation energy values for the devolatilization of hemicellulose, cellulose and lignin for both woods, demonstrating that the F1 model should not be chosen a priori, as the determinant. The influence of the heating rate and the type of biomass on the obtained kinetic results is demonstrated, therefore, results of low to high heating rates should not be extrapolated. [ABSTRACT FROM AUTHOR]

EXTRACTION techniques, ALKYLAMINES, and HYDROXYL group

The immediacy of the problem under study is due to the lack of data on the kinetics of polymer carrier impregnation with extraction agents. The article is aimed at obtaining the kinetic characteristics of the impregnation of a polymeric macroporous carrier--a weakly acidic cation resin with carboxyl groups--with trialkylamine and its solutions in acetone. The integral kinetic curves of the extraction agent adsorption on the carrier were obtained. This allowed estimating the time of equilibrium by the limited solution volume method. This time was 25-30 hours, decreasing with the application of a dilution agent and with the increase in temperature. The kinetic impregnation characteristics were calculated by means of the pseudo-second-order, Elovich, and internal diffusion models. The pseudo-second-order model describes the experimental kinetic data with a high correlation degree (R2 0.995-0.997) and points out that interaction with two sorption centres possibly takes place with the adsorption of a single trialkylamine molecule. The impregnation rate constants via an extraction agent were calculated using all kinetic models. Based on the apparent activation energy magnitude (37±14 kJ/mol), it can be assumed that diffusion is the rate-limiting step of the impregnation process. This article can be useful for creating impregnates containing extraction agents of various classes. [ABSTRACT FROM AUTHOR]

CRYSTALLIZATION, METAL refining, SILICON, HYDROCHLORIC acid, LEACHING, and SOLUBILIZATION

This study aims to evaluate the process of acid leaching, in HCl, for purification of silicon metal, obtained by magnesiothermic reduction of silica and promote greater removal of impurities. The reaction product formed is a powder which is physically and/or chemically bound, with approximately 75% of MgO and approximately 25% of silicon metal, among other elements. Acid leaching is an technique used in the solubilization of oxides by an acid solvent. The silicon metal with purities up to 94% can be obtained in one step. Thus, it has been tested the effect of the following concentration of hydrochloric acid HCl (1, 2, and 3 M), temperature (50, 65, and 80° C) and time (60, 90 and 120 min). The leaching kinetics was studied under non-isothermal condition. After the treatments, it was shown that concentration is the main effect of leaching. In some analyses, it was possible to convert up to 76%, i.e., 99.66% of MgO has been extracted. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the kinetic parameters of the thermal degradation of the pigments extracted from teak leaves at different temperatures (45, 60, 75 and 90 °C) using the kinetic models of order zero, one and two. As a result, the thermal degradation follows first-order kinetics. The rate constants (k) and the halflife times (t½) were determined for each temperature. The activation energy, calculated according to the Arrhenius equation, has a value of 67.6 ± 2,3 kJ/mol. Finally, it was found that the betalains present in the extract of teak leaves are more thermostables than those from beet. [ABSTRACT FROM AUTHOR]

PYROLYSIS, WOOD waste, PYROLYSIS kinetics, AGROFORESTRY, TEAK, and WOOD chemistry

The use of food as a source of energy has been questioned and agroforestry waste shows potential for these purposes. The objective of the work is to realize the chemical and energetic characterization of waste from Ecuador and study the kinetics of its pyrolysis, as an alternative for its use. Elemental, immediate analysis was carried out and thermal analysis techniques were applied. The higher carbon content and lower humidity and ash of Teak, favor its energétic use, with respect to Fernán Sánchez. In addition, its nitrogen and sulfur contents below 1 %, guarantee low NOx and SO2 emissions, reducing its environmental impact. The combined use of TGA, DTG and DSC allows to identify the three stages of pyrolytic cracking, the decomposition of hemicellulose, cellulose and lignin. His kinetic study showed that the first and third stages are determined by diffusive processes fundamentally and in the second, different kinetic models prevail. [ABSTRACT FROM AUTHOR]

Semi-interpenetrated hydrogels (semi- IPN) obtained from acrylamide (AAm) and the biopolymer poly(hydroxybutyrate-cohydroxyvalerate) (P(HB-co-HV)) of different molar mass (Mv) were synthesized. Chemical structure of the synthesized materials was analyzed by using FT-IR spectroscopy. The results suggested the incorporation of P(HBco- HV) within the cross-linked network of the Polyacrylamide (PAAm), which indicated that the semi-IPN hydrogel was synthesized. To confirm this result, semi-IPN dry gel samples were analyzed by differential scanning calorimetry. The swelling behavior of the hydrogels in water was followed gravimetrically and the effect of the percentage composition and percentage of crosslinking reagent (N,N'- methylenebisacrylamide, MBAAm) on the water transport mechanisms was analyzed. Results indicated that the semi-IPN hydrogels swell less than the PAAm hydrogel alone, which was attributed to the hydrophobic nature of the biopolymer incorporated within the crosslinked network of the material. Additionally, the diffusion exponent of the hydrogels (n) was calculated and in all cases, the obtained result was n < 0.50. This fact shows that the diffusion process is less Fickian, which means that the speed of water penetration is lower than the speed of relaxation of the polymer chain. [ABSTRACT FROM AUTHOR]