Modelling of rheological behaviour of macaíba pulp at different temperatures

ABSTRACT Fruit pulps undergo temperature variations during processing, leading to viscosity changes. This study aimed to analyse the rheological behaviour of macaíba pulp at different temperatures (10 to 50 ºC, with 5 ºC increments) and speeds (2.5 to 200 rpm, totalling 17 speeds). Experimental measurements were performed in a Brookfield viscometer, fitting the Ostwald-de-Waele, Mizrahi-Berk, Herschel-Bulkley, and Casson models to the experimental data of shear stress as a function of shear rate. Among the models used, the Mizrahi-Berk model (R² > 0.9656 and average percentage deviation - P ≤ 4.1%) was found to best fit the rheogram data. Macaíba pulp exhibited a non-newtonian behaviour and was characterised as pseudoplastic. It showed fluid behaviour indexes below unity under the studied conditions, with decreases in apparent viscosity as temperature and shear rate increased. Such behaviour could be described by the Arrhenius equation. The Mizrahi-Berk and Falguera-Ibarz models (R² > 0.99 and P ≤ 10%) best fitted the data and were used to represent the viscosity behaviour of macaíba pulp. The activation energy values of macaíba pulp ranged between 17.53 and 25.37 kJ mol-1, showing a rheological behaviour like other fruit pulps.

Application Extended Vogel-Tammann-Fulcher Equation for soybean oil

Mathematical models that describe the variation of soybean oil viscosity with temperature according to the recent WLF and VTF (or VFT) equations and traditionally by the Arrhenius equation. The Arrhenius equation shows that the viscosity of the oil is proportional to the absolute temperature and is determined by the activation energy parameter. In Arrhenius' equation the absolute temperature is replaced by T + b where both adjustable T and b are in ° C. The mathematical models described by the equations WLF and VTF, are equal to each other. All three equations are in the same model when used for experimental data of temperature-viscosity dependence, they give exactly the same very high regression coefficient.

SULFONYL CHLORIDES - NOVEL SOURCE OF FREE RADICALS

Novel free radicals source based on sulfonyl chlorides is discovered. The radical mechanism is confirmed by 2,3-dimethyl-2,3-diphenylbutane formation under chlorosulfonated polyethylene heating in the isopropylbenzene solution. Concerted homolytic C-S and S-Cl bond scission of chlorosulfonated polyethylene thermal degradation mechanism proved by kinetic analysis. The proof of the two bonds simultaneous breaking is provided by the threefold activation energy reduction (83 kJ/mol) in comparison to the C-S and C-Cl bond dissociation energy (280 and 286 kJ/mol respectively), the 6 orders lower preexponential factor (2,46 ∙ 10 s) in Arrhenius equation in comparison to one bond cleavage (≈10-10 s) as well as the strongly negative activation entropy value (-134 J/mol∙K).

Some thermodynamic and kinetic properties of H2SO4–H3PO4–H2O–Fe(III) system

The values of the electrode potentials of the redox couple Fe(III) / Fe(II) and the half-wave potentials of the reactions Fe3+ + e– = Fe2+ и Fe2+ — e– = Fe3+ on the cyclic voltammogram of a platinum electrode in acid solutions containing Fe(III) salts have been measured to characterize the oxidizing ability of the H2SO4—H3PO4—H2O—Fe(III) system. The values of these experimentally obtained parameters are close. A decrease in the oxidizing ability of H2SO4 and H3PO4 mixtures containing Fe(III) with an increase in the molar fraction of H3PO4 in them occurs due to the formation of Fe(III) complexes with phosphate anions which are inferior to their hydrate and sulfate complexes in the oxidizing ability. The temperature coefficients of the electrode potential (dE / dt) of the redox couple Fe(III) / Fe(II) in the H2SO4—H2O, H2SO4—H3PO4—H2O and H3PO4–H2O systems were determined experimentally. The diffusion coefficients of Fe(III) in the studied solutions were calculated based on the Randles—Shevchik equation. The temperature dependence of the diffusion coefficients of Fe(III) cations is satisfactorily described by the Arrhenius equation. The parameters of this equation are calculated.

Modified Arrhenius Equation in Materials Science, Chemistry and Biology

The Arrhenius plot (logarithmic plot vs. inverse temperature) is represented by a straight line if the Arrhenius equation holds. A curved Arrhenius plot (mostly concave) is usually described phenomenologically, often using polynomials of T or 1/T. Many modifications of the Arrhenius equation based on different models have also been published, which fit the experimental data better or worse. This paper proposes two solutions for the concave-curved Arrhenius plot. The first is based on consecutive A→B→C reaction with rate constants k1 ≪ k2 at higher temperatures and k1 ≫ k2 (or at least k1 > k2) at lower temperatures. The second is based on the substitution of the temperature T the by temperature difference T − T0 in the Arrhenius equation, where T0 is the maximum temperature at which the Arrheniusprocess under study does not yet occur.

Kinetic Study of Gas Formation in Styrofoam Pyrolysis Process

This research aims to study the reaction kinetics of gas formation in the pyrolysis of styrofoam waste. Pyrolysis of styrofoam waste without a catalyst takes place at a constant temperature of 180°C. In contrast, the pyrolysis of styrofoam waste by adding a zeolite catalyst took place at a constant temperature of 170°C. The amount of styrofoam waste used in this research sample is 200 grams, and the natural zeolite catalyst is 5 grams. Pyrolysis of styrofoam waste without using a catalyst form a gas at a constant temperature of 180°C, the kinetics of the reaction takes place on the zero-order. This result follows the Arrhenius equation K = Ae10617/RT with an activation energy value (Ea) of 1.27x103 kJ.mol-1. Pyrolysis of styrofoam waste by adding a zeolite catalyst to gas formation at a constant temperature of 170°C also takes place on the zero-order. The equation follows Arrhenius K= Ae4711,5/RT and the activation energy value (Ea) is 5.66x102 kJ.mol-1.

Emerging technology approach for extractability and stability of betalains from the peel of beetroot (Beta vulgaris L.)

Betalains are natural color compounds with high water affinity, unstable, and fragile; hence, understanding their thermal tolerance is always beneficial either in manufacturing them or in their application in betalain-rich functional foods for better handling. In our study, the extractability of betalains via microwave-assisted extraction (MAE) from the peel of beetroot was implemented at 100–800 W for 30–150 s with four different solvents. Among the maximum amounts of total betalains (202.08 ± 2.23 mg/100 g FW), betacyanin (115.89 ± 1.08 mg/100 g FW) and betaxanthin (86.21 ± 1.16 mg/100 g FW) were generated by pure water solvent after 150 s of MAE at 800 W. Alternatively, the susceptibility of beetroot peel extracts to processing conditions was investigated by heating them at 30–70 °C, and the thermal instability of betalains was evaluated by half-life (t1/2), temperature quotient (Q10), and activation energy (Ea), using the Arrhenius equation. The resulted retention percentage (R%) proved that ascorbic acid improved the R% of total betalains from 22 to 51% and betacyanin from 3 to 29% and in contrast reduced R% of betaxanthin from 56 to 40% after the heat treatment at 70 °C for 5 h.

Influence of impurities of the transitional metals Fe, Ni, and Co on the hydrolysis kinetics of BH− 4 ions in alkaline solutions

The influence of small amounts of the Fe, Co, and Ni impurities on the spontaneous hydrolytic process of borohydride was studied within a temperature range of 60–100°C. The object under study was a simulated solution containing 9.53 M of OH− ions and 0.14 M of BH− 4 ions, used as a fuel for borohydride fuel cells. The rate constant k of borohydride hydrolysis for a small amount of impurities at different temperature was estimated. The lowest non-accelerating concentrations of the impurities were established (∼10 ppm for iron; ∼1 ppm for cobalt). The strongest accelerating effect on the hydrolysis of BH− 4 ions was rendered by nickel impurities: self-hydrolysis was accelerated by 1.2 times for 1 ppm Ni. The ambiguous trend of the kinetic curves does not allow to accurately estimate the activation energy; however, the increased temperature enhances the catalytic effect of hydrolysis acceleration according to Arrhenius’ equation.

COMPLEX OF NICKEL (II) ION WITH TRYPTOPHAN AS A HOMOGENEOUS CATALYST IN THE DECOMPOSITION REACTION OF CUMENE HYDROPEROXIDE IN AQUEOUS SOLUTION

The formation of Ni2+:Tryptophan (Trp) 1:1 complex, which acts as a model catalyst for decomposition of cumene hydroperoxide (ROOH) in Ni2++Trp+ROOH+H2O system, has been confirmed via kinetic study in aqueous solution at pH>7. The kinetic expression of a single catalytic decomposition reaction of ROOH under the influence of [NiTrp]+ complex was brought out. The temperature dependence of the effective rate constant of ROOH decay (Keff=Kcat[Ni2+]0[Trp]0=const) in the temperature range from 323 to 343 K can be expressed by Arrhenius equation (Eeff is in kJ/mol): Keff=(1.87±0.02)·106exp[–(49.8±0.3)/RT], min –1.

Low Energy Electron Attachment by Some Chlorosilanes

In this paper, the rate coefficients (k) and activation energies (Ea) for SiCl4, SiHCl3, and Si(CH3)2(CH2Cl)Cl molecules in the gas phase were measured using the pulsed Townsend technique. The experiment was performed in the temperature range of 298–378 K, and carbon dioxide was used as a buffer gas. The obtained k depended on temperature in accordance with the Arrhenius equation. From the fit to the experimental data points with function described by the Arrhenius equation, the activation energies (Ea) were determined. The obtained k values at 298 K are equal to (5.18 ± 0.22) × 10−10 cm3·s−1, (3.98 ± 1.8) × 10−9 cm3·s−1 and (8.46 ± 0.23) × 10−11 cm3·s−1 and Ea values were equal to 0.25 ± 0.01 eV, 0.20 ± 0.01 eV, and 0.27 ± 0.01 eV for SiHCl3, SiCl4, and Si(CH3)2(CH2Cl)Cl, respectively. The linear relation between rate coefficients and activation energies for chlorosilanes was demonstrated. The DFT/B3LYP level coupled with the 6-31G(d) basis sets method was used for calculations of the geometry change associated with negative ion formation for simple chlorosilanes. The relationship between these changes and the polarizability of the attaching center (αcentre) was found. Additionally, the calculated adiabatic electron affinities (AEA) are related to the αcentre.