Kinetics of oxidation of biodiesel from soybean oil mixed with TBHQ: determination of storage time

Synthetic antioxidants are an alternative to prevent or retard the degradation of biofuels made from vegetable oils. In this study, it was evaluated the oxidative stability of B100 soybean oil biodiesel, in the presence of tercbutylhydroquinone (TBHQ). The results showed that the induction period, that precedes the seeding process, was delayed in the presence of the antioxidant. Moreover, the obtained results suggest that the B100 biodiesel containing TBHQ can present a storage time at 25 ºC, three times longer than the estimated time for the pure B100.

Hydrogels of cellulose acetate crosslinked with pyromellitic dianhydride: part I: synthesis and swelling kinetics

This work describes the synthesis of hydrogels of cellulose acetate (AC) crosslinked with 1,2,4,5-benzenotetracarboxylic dianhydride (PMDA). The crosslinking reaction was monitored by FTIR. Analysis of aromatic fragments from the alkaline hydrolysis of the gels by UV spectroscopy indicated that an increase in the stoichiometric ratio of dianhydride resulted in higher degrees of crosslinking. The non-porous nature of the gels was confirmed by analysis of nitrogen adsorption. Water absorption isotherms showed that as the temperature and degree of crosslinking increased, the percentage of water absorbed at equilibrium (%Seq) also increased. The hydrogels presented second order swelling kinetics.

Treated domestic sewage: kinetics of Escherichia coli and total coliform inactivation by oxidation with hydrogen peroxide

Hydrogen peroxide has been used for decades in developed countries as an oxidizing agent in the treatment of water, domestic sewage and industrial effluents. This study evaluated the influence of the concentration of H2O2 and pH on the inactivation of Escherichia coli cells and the disinfection of sewage treated. The results showed that the inactivation rate increased with pH and H2O2. The presence of other contaminants dissolved in the effluent is probably the cause of these differences, because E. coli inactivation in synthetic wastewater was found to be much faster than in the real treated domestic sewage.

Adsorção do corante Reativo Azul 19 em solução aquosa por lama vermelha tratada quimicamente com peróxido de hidrogênio

Adsorption of Reactive Blue 19 dye onto activated red mud was investigated. Red mud was treated with hydrogen peroxide (LVQ) and heated at both 400 ºC (LVQ400) and 500 ºC (LVQ500). These samples were characterized by pH, specific surface area, point of zero charge and mineralogical composition. Adsorption was found to be significantly dependent on solution pH, with acidic conditions proving to be the most favorable. The adsorption followed pseudo-second-order kinetics. The Langmuir isotherm was the most appropriate to describe the phenomenon of dye removal using LVQ, LVQ400 and LVQ500, with maximum adsorption capacity of 384.62, 357.14 and 454.54 mg g-1, respectively.

PRACTICAL STOCHASTIC MODEL FOR CHEMICAL KINETICS

The Practical Stochastic Model is a simple and robust method to describe coupled chemical reactions. The connection between this stochastic method and a deterministic method was initially established to understand how the parameters and variables that describe the concentration in both methods were related. It was necessary to define two main concepts to make this connection: the filling of compartments or dilutions and the rate of reaction enhancement. The parameters, variables, and the time of the stochastic methods were scaled with the size of the compartment and were compared with a deterministic method. The deterministic approach was employed as an initial reference to achieve a consistent stochastic result. Finally, an independent robust stochastic method was obtained. This method could be compared with the Stochastic Simulation Algorithm developed by Gillespie, 1977. The Practical Stochastic Model produced absolute values that were essential to describe non-linear chemical reactions with a simple structure, and allowed for a correct description of the chemical kinetics.

Photoinhibition of Photosystem II. Kinetics, Photoprotection and Mechanism

Photosystem II (PSII) is susceptible to light-induced damage defined as photoinhibition. In natural conditions, plants are capable of repairing the photoinhibited PSII by on-going degradation and re-synthesis of the D1 reaction centre protein of PSII. Photoinhibition is induced by both visible and ultraviolet light and photoinhibition occurs under all light intensities with the same efficiency per photon. In my thesis work, I studied the reaction kinetics and mechanism of photoinhibition of PSII, as well as photoprotection in leaves of higher plants. Action spectroscopy was used to identify photoreceptors of photoinhibition. I found that the action spectrum of photoinhibition in vivo shows resemblance to the absorption spectra of manganese model compounds of the oxygen evolving complex (OEC) suggesting a role for manganese as a photoreceptor of photoinhibition under UV and visible light. In order to study the protective effect of non-photochemical quenching, the action spectrum was measured from leaves of wild type Arabidopsis thaliana and two mutants impaired in nonphotochemical quenching of chlorophyll a excitations. The findings of action spectroscopy and simulations of chlorophyll-based photoinhibition mechanisms suggested that quenching of antenna excitations protects less efficiently than would be expected if antenna chlorophylls were the only photoreceptors of photoinhibition. The reaction kinetics of prolonged photoinhibition was studied in leaves of Cucurbita maxima and Capsicum annuum. The results indicated that photoinhibitory decrease in both the oxygen evolution activity and ratio of variable to maximum fluorescence follows firstorder kinetics in vivo. The persistence of first-order kinetics suggests that already photoinhibited reaction centres do not protect against photoinhibition and that the mechanism of photoinhibition does not have a reversible intermediate. When Cucurbita maxima leaves were photoinhibited with saturating single-turnover flashes and continuous light, the light response curve of photoinhibition was found to be essentially a straight line with both types of illumination, suggesting that similar photoinhibition mechanisms might function during illumination with continuous light and during illumination with short flashes.

About the kinetics and mechanism of the reactions of 4-(2-pyridylazo)-resorcinol, with Zn2+, Cu2+ and Zn2++Cu2+ equimolar mixtures, in aqueous solutions

The kinetics and mechanism of the reactions between 4(2pyridylazo)-resorcinol and Zn2+, Cu2+ and Zn2++Cu2+ equimolar mixtures were studied. The reactions were performed in aqueous solution (pH = 8.5, borate buffer) and monitored spectrophotometrically at 500 nm using stopped-flow technique. Spectral and kinetic data indicate that the Zn2++Cu2+ equimolar mixture behaves as an unique species and it can be attributed to the interactions of Zn2+ and of Cu2+ with water molecules in the aqueous solution. A mechanism is proposed and the rate constants are calculated.

Sorption kinetics and intrapaticulate diffusivity of As(III) bioremediation from aqueous solution, using modified and unmodified coconut fiber

The pollution and toxicity problems posed by arsenic in the environment have long been established. Hence, the removal and recovery remedies have been sought, bearing in mind the efficiency, cost effectiveness and environmental friendliness of the methods employed. The sorption kinetics and intraparticulate diffusivity of As (III) bioremediation from aqueous solution using modified and unmodified coconut fiber was investigated. The amount adsorbed increased as time increased, reaching equilibrium at about 60 minutes. The kinetic studies showed that the sorption rates could be described by both pseudo-first order and pseudo-second order process with the later showing a better fit with a value of rate constant of 1.16 x 10-4 min-1 for the three adsorbent types. The mechanism of sorption was found to be particle diffusion controlled. The diffusion and boundary layer effects were also investigation. Therefore, the results show that coconut fiber, both modified and unmodified is an efficient sorbent for the removal of As (III) from industrial effluents with particle diffusion as the predominant mechanism.

Polarographic study and electrode kinetics of [Zn(II) - antibiotics - cephaloglycin] system vis a vis kinetics of electrode reactions

Electrode kinetics and complex formation of Zn(II) using doxycycline, chlortetracycline, oxytetracycline, tetracycline, minocycline, amoxicillin, chloramphenicol and cephaloglycin were reported at pH = 7.30 ± 0.01 in = 1.0 molL-1 NaClO4 used as supporting electrolyte at 25.0°C. Kinetic parameters viz. transfer coefficient (α), degree of irreversibility (λ) and rate constant (k) were determined. The study showed that 'Transition state' behaves between reactant (O) and product (R) response to applied potential. The stability constants varied from 2.14 to 10.31 showing that these drugs or their complexes could be used against Zn toxicity.

Comparison of the dehydration kinetics of solid state compounds of 2-methoxybenzylidenepyruvate with some divalent metal ions

Divalent metal complexes of ligand 2-methoxybenzylidenepyruvate with Fe, Co, Ni, Cu and Zn as well as sodium salt were synthesized and investigated in the solid state. TG curves of these compounds were obtained with masses sample of 1 and 5mg under nitrogen atmosphere. Different heating rates were used to characterize and study these compounds from the kinetic point of view. The activation energy and pre-exponential factor were obtained applying the Wall-Flynn-Ozawa method to the TG curves. The obtained data were evaluated and the values of activation energy (Ea / kJ mol-1) was plotted in function of the conversion degree (α). The results show that due to mass sample, different activation energies were obtained. The results are discussed mainly taking into account the linear dependence between the activation energy and the pre exponential factor, where was verified the effect of kinetic compensation (KCE) and possible linear relations between the dehydrations steps of these compounds.

Raw water use charge reduction for the rural sector in the PCJ Watershed

The deficient environmental preservation on agricultural properties has reflected in great soil losses for erosion and the high rate of sedimentation. Therefore, this work brings the application of software to demonstrate that planters can get benefits by the conservationist practices. The benefits will be obtained from the environment aspect (erosion and sedimentation control), as well as economical aspect (financial incentives). A proposal has been created by the Technical Chamber of Rural Water Use and Conservation (CT-Rural) to estimate the reduction in raw water use charge for the rural water users of the PCJ Watershed - this reduction is being possible since January 2007, at the PCJ Committee. The software develops a simple relationship, so that if the rural conservationist action goes more efficient, such as if the conserved rural area goes larger, then the reduction value will bring better benefits for the rural water users. Within the purposes of this study, there is the idealization of mechanisms that may support specific management matters related to the water users of federal rivers from the rural sector of PCJ Watershed.

Decomposition kinetics of gaseous ozone in peanuts

This study was conducted to evaluate the decomposition kinetics of gaseous ozone in peanut grains. This evaluation was made with 1-kg peanut samples, moisture contents being 7.1 and 10.5% wet basis (w.b.), placed in 3-liter glass containers. The peanut grains were ozonated at the concentration of 450 µg L-1, at 25 and 35 ºC, with gas flow rates of 1.0 and 3.0 L min-1. Time of saturation was determined by quantifying the residual concentration of ozone after the gas passed through the grains to constant mass. The decomposition kinetics of ozone was evaluated after the grain mass was ozone-saturated. For the peanut grains whose moisture content was 7.1% (w.b.), at 25 and 35ºC and with flow rates of 1.0 and 3.0 L min-1, the values obtained for time of saturation of gaseous ozone ranged between 173 and 192 min; the concentration of saturation was approximately 260 µg L-1. For the grains whose moisture content was 10.5% (w.b.), a higher residual concentration of gaseous ozone was obtained at 25 ºC, that of 190 µg L-1. As regards the half-life of ozone, the highest value obtained was equivalent to 7.7 min for grains ozonated at 25 ºC, while for those with moisture content of 10.5% at 35 ºC, half-life was 3.2 min. In the process of ozone decomposition in peanut grains, temperature was concluded to be the key factor. An increase of 10 ºC in the temperature of the grains results in a decrease of at least 43% in the half-life of ozone.

KINETICS OF MASS LOSS OF ARABICA COFFEE DURING ROASTING PROCESS

ABSTRACT Roasting is one of the most complex coffee processing steps due to simultaneous transfers of heat and mass. During this process, beans lose mass because of fast physical and chemical changes that will set color and flavor of the commercial coffee beverage. Therefore, we aimed at assessing the kinetics of mass loss in commercially roasted coffee beans according to heating throughout the processing. For that, we used samples of 350-g Arabica coffee processed grains with water content of 0.1217 kga kg-1, in addition to a continuous roaster with firing gas. The roaster had initial temperatures of 285, 325, 345 and 380 °C, decreasing during the process up to 255, 285, 305 and 335 °C respectively. Mass loss was calculated by the difference between grain weight before and after roasting. We observed a linear variation directly dependent on roaster temperature. For each temperature during the process was obtained a constant mass loss rate, which was reported by the Arrhenius model with r2 above 0.98. In a roaster in non-isothermal conditions, the required activation energy to start the mass loss in a commercial coffee roasting index was 52.27 kJ mol -1.

Design of Pulsed Electroacoustic Measurement System for Space Charge Characterisation

Pulsed electroacoustic (PEA) method is a commonly used non-destructive technique for investigating space charges. It has been developed since early 1980s. These days there is continuing interest for better understanding of the influence of space charge on the reliability of solid electrical insulation under high electric field. The PEA method is widely used for space charge profiling for its robust and relatively inexpensive features. The PEA technique relies on a voltage impulse used to temporarily disturb the space charge equilibrium in a dielectric. The acoustic wave is generated by charge movement in the sample and detected by means of a piezoelectric film. The spatial distribution of the space charge is contained within the detected signal. The principle of such a system is already well established, and several kinds of setups have been constructed for different measurement needs. This thesis presents the design of a PEA measurement system as a systems engineering project. The operating principle and some recent developments are summarised. The steps of electrical and mechanical design of the instrument are discussed. A common procedure for measuring space charges is explained and applied to verify the functionality of the system. The measurement system is provided as an additional basic research tool for the Corporate Research Centre of ABB (China) Ltd. It can be used to characterise flat samples with thickness of 0.2–0.5 mm under DC stress. The spatial resolution of the measurement is 20 μm.

Kinetics of epsilon antitoxin antibodies in different strategies for active immunization of lambs against enterotoxaemia

Enterotoxaemia, a common disease that affects domestic small ruminants, is mainly caused by the epsilon toxin of Clostridium perfringens type D. The present study tested four distinct immunization protocols to evaluate humoral response in lambs, a progeny of non-vaccinated sheep during gestation. Twenty-four lambs were randomly allocated into four groups according to age (7, 15, 30 and 45 days), receiving the first dose of epsilon toxoid commercial vaccine against clostridiosis with booster after 30 days post vaccination. Indirect ELISA was performed after the first vaccine dose and booster to evaluate the immune response of the lambs. Results showed that for the four protocols tested all lambs presented serum title considered protective (≥0.2UI/ml epsilon antitoxin antibodies) and also showed that the anticipation of primovaccination of lambs against enterotoxaemia conferred serum title considered protective allowing the optimization of mass vaccination of lambs.