Reaktionen im festen Zustande bei höheren Temperaturen. II. Mitteilung. Reaktionsgeschwindigkeiten exotherm verlaufender Umsetzungen

Koturevic²,

2020

Phytochemical Analysis

Introduction Hypericum perforatum L., Hypericaceae (St John's wort) is a highly familiar plant in the medicinal community which recently showed good antiviral activities including against some types of coronavirus. Objective Establishing the kinetics of isothermal extraction of total hypericin (TH) from the pre‐extracted flowers of H. perforatum flowers. Methods The solvent extraction of TH from the remaining solid residue after the pre‐extraction procedure was performed providing isothermal conditions at the temperature of 313 K, 323 K, and 328 K (±1 K) using ethanol as a solvent. The feasibility of mathematical modelling of the isothermal kinetics of TH extraction was explored applying some of the frequently used kinetic models of solvent extraction: first‐order reaction model, film theory model, unsteady‐state diffusion model, parabolic diffusion model, Elovich's equation. The kinetic complexity was examined using the differential isoconversional method. Results The kinetics of isothermal solvent extraction of TH is a kinetic elementary process with the unique rate‐determining step. It was found that the kinetics of isothermal extraction of TH can be best described employing the theoretical Jander three‐dimensional (3D) diffusional model and its suitability for modelling the investigated extraction was confirmed with statistical parameters [adjusted linear correlation coefficient (R2adj) = 0.998–0.999 and the standard error (SE) = 0.005–0.006]. The values of the model kinetic parameters (rate constant (kM/min‐1), activation energy (Ea = 21.0 ± 4.9 kJ/mol) and pre‐exponential factor (lnA = 3.1 ± 2.2 min‐1) were calculated. Conclusions Based on the model mechanism of the kinetics of the investigated extraction a new mathematical model is suggested and the controlling step of the overall process was found.

α = 1 - {[{(1 - (t \cdot k_{normalM})}^{1 / 2}]}^{3}

where α is extraction degree of TH and k M is the model rate constant of TH extraction from H. perforatum .…”

Section: Resultsmentioning

confidence: 99%

Isothermal kinetics of ethanolic extraction of total hypericin from pre‐extracted Hypericum perforatum flowers

Koturevic²,

2020

Phytochemical Analysis

“…These curves have the same shape, so it was assumed that all of them can be described by the same kinetic model. By using the model fitting method, with great degree of certainty ( ≥ 0.999), it was established that the kinetics of isothermal caffeine extraction under microwave heating can be described by the Jander theoretical kinetic model of three dimensional diffusion [43] which is given by the following equation:…”

Section: Resultsmentioning

confidence: 99%

Isothermal green microwave-assisted extraction of caffeine from guarana: a kinetic study

Koturevic¹,

Green Processing and Synthesis

2017

The kinetics of isothermal green microwave-assisted extraction of caffeine from guarana seed powder with water at a temperature range from 40°C to 60°C was investigated. The caffeine concentration in the water extract was determined by UV-Vis spectrophotometry. By applying the isoconversional method, it was established that the kinetics of the caffeine extraction from the guarana seed powder with microwave heating is an elementary kinetic process. The model fitting method was used to determine the kinetic model of the caffeine extraction under microwave heating. It was found that the kinetics of the caffeine extraction can, under microwave heating, be modeled by the Jander’s model of three dimensional diffusion. The kinetic parameters, activation energy and pre-exponential factor of the caffeine extraction were determined.

“…These curves have an identical shape for all of the investigated temperatures within both heating modes, therefore it was assumed that all of them can be described by the same kinetic model. By using the model fitting method, it was established with a high degree of certainty (≥0.999) that the kinetics of isothermal caffeine extraction under both conventional and microwave heating can be described by Jander theoretical kinetic model (Jander, 1927) of three dimensional diffusion which is given by the following equation: where, k M is the model rate constant of caffeine extraction from guarana seed. When the kinetics of the extraction of caffeine from guarana seed takes place in accordance with the three dimensional diffusion kinetic model, then the dependence of [1 − (1 − ˛) 1/3 ] 2 on time should give straight lines.…”

Section: Resultsmentioning

confidence: 99%

Comparative kinetic analysis of isothermal extraction of caffeine from guarana seed under conventional and microwave heating

Koturevic²,

Chemical Engineering Research and Design

2017

The kinetics of the isothermal extraction of caffeine from the guarana seed powder with water under conventional (CH) and microwave heating (MWH) were investigated. By applying the isoconversional method, it was established that the kinetics of the caffeine extraction under CH and also under MWH is an elementary kinetic process. The model fitting method was used to determine the kinetics model of caffeine extraction. It was found that the kinetics of the caffeine extraction for both heating modes can be described by the Jander's equation. The rate of the extraction of caffeine under MWH is ∼2 times higher than under CH. The values of kinetics parameters (E a and lnA) of the extraction process under MWH are lower than for CH. The established influence of MWH on the kinetics of caffeine extraction is explained with a specific activation mechanism of water molecules and with an increase in the energy of the ground vibration level of resonant oscillator of N 3 -CH 3 band of caffeine molecule ( = 317 cm −1 ) which is caused by the absorption of microwave energy.