1. Kinetic modeling of solvent partitioning effect on the production of 5-hydroxymethylfurfural from glucose in biphasic solvent systemHan Xu, Zhihao Bi, Xinyu Cui, Lili Qian, Lingzhao Kong, Niko Samec, Milan Vujanović, Yang Guo, 2025, original scientific article Abstract: The distribution characteristics of 5-hydroxymethylfurfural (5-HMF) in solution significantly affect its yield and separation/purification during its production process from glucose, but there is currently a lack of quantitative correlation with the reaction kinetics. In this paper, a systematic kinetic study was conducted on the catalytic conversion of glucose to 5-HMF using a porous carbon catalyst that possesses both Lewis and Brønsted acid sites in a biphasic solvent system composed of NaCl-H2O and Methyl isobutyl ketone (MIBK). The addition of NaCl was found to enhance the extraction of 5-HMF into the organic phase, with the highest yield of 84.5% achieved under 10 wt% NaCl concentration. Excessive NaCl increases the solubility of 5-HMF in the aqueous phase, thereby causing a reduction in yield. Kinetic study reveals that higher NaCl concentrations suppress glucose isomerization, humins formation, and direct dehydration to 5-HMF. Excess NaCl also facilitated side reactions, such as 5-HMF rehydration. Changes in solubility equilibrium constants and partition coefficient of 5-HMF were positively correlated, and sensitivity analysis highlighted the impact of NaCl on solubility equilibrium of 5-HMF between aqueous and organic phases. By introducing the parameter of polar activation energy (Ec), the impact of NaCl on the rate constants of various reaction pathways was quantified, confirming that NaCl altered the physicochemical properties of solvent and potentially catalyzed the reaction. These findings provide valuable insight into the mechanisms and kinetics of glucose isomerization and dehydration in biphasic solvent systems, laying the foundation for the design and regulation of solvent properties to optimize these reactions.
Keywords: 5-Hydroxymethylfurfural, glucose, solvent, kinetics, catalyst
Published in DKUM: 13.08.2025; Views: 0; Downloads: 3
 Full text (1,55 MB)
This document has many files! More... |
2. Countermovement jump in female sprinters : kinetic parameters and asymmetryNikola Prvulović, Milan Čoh, Dražen Čular, Mario Tomljanović, Goran Sporiš, Suzana Žilič Fišer, 2022, original scientific article Abstract: Analyzing asymmetry from biomechanical parameters of the lower extremities has become a standard practice for accurate assessment of athletic performance, injury prevention, and
rehabilitation. The aims of this study were (1) to determine differences between explosive strength
and asymmetry of the lower extremities using kinetic parameters of the CMJ jump test in young
female athletics, and (2) to investigate correlation between speed and asymmetry, as speed and
kinetic parameters. The two groups of nine female sprinters (mean ± SD; G1-age 15.6 ± 1.34 years,
height 170.1 ± 0.57 cm, body mass 62.54 ± 7.73 kg, and BMI 21.6 ± 2.05; G2-age 16.2 ± 1.3 years,
height 168.4 ± 0.61 cm, body mass 57.69 ± 3.12 kg, and BMI 20.37 ± 1.38) performed the CMJ test
without using an arm swing, as well as a 100 m test. Two tensiometric platforms were used for the
kinetic parameters and asymmetry. Asymmetry was calculated by an AI equation, and the values of
the takeoff velocities and jump height parameters were obtained by integral formula and the trapezoidal rule of impulse-momentum methods. The results show differences in four kinetic parameters:
height (G1- 26.82 ± 3.56 cm, vs. G2- 17.45 ± 2.01 cm), concentric impulse, (G1- 96.05 ± 16.95 N·s, vs.
G2- 68.41 ± 4.77 N·s), takeoff velocity, (G1- 2.29 ± 0.14 m/s, vs. 1.83 ± 0.12 m/s), and concentric
velocity, m/s (G1- 1.5 ± 0.175 m/s, vs. 1.17 ± 0.122 m/s), as well as a negative strong and very
strong correlation between asymmetry and kinetic parameters for three parameters: Peak Force
(G1- r = −0.878, and all subjects r = −0.633), Eccentric Impulse of left leg (G1- r = −0.865) and
Concentric Impulse of right leg (G2- r = −0.878), (p <.05). The younger sprinters did not show the
principle of muscle activation in the form of a longer preparatory phase of contact time, eccentric
and concentric phase, as well as a force impulse that is optimal. There was no correlation between
asymmetry and sprint performance.
Keywords: asymmetry, kinetics, explosive strength, sprint, athletics
Published in DKUM: 01.04.2025; Views: 0; Downloads: 6
Full text (277,80 KB)
This document has many files! More... |
3. Kinetic modelling of catalytic 5-hydroxymethylfurfural hydrogenation to value-added chemicals : doctoral dissertationBrett Pomeroy, 2024, doctoral dissertation Abstract: Lignocellulosic biomass has been widely recognized as a renewable feedstock that has enormous potential for the production of bio-based fuels and platform chemicals. Obtained from the dehydration of sugars, 5-hydroxymethylfurfural (HMF) in particular has received extensive consideration due to its diverse functionality and versatility. However, despite its potential, major technical and economic challenges still need to be addressed before HMF valorization technologies can be competitive with current processes that rely on fossil fuels.
This doctoral study specifically focuses on the catalytic hydrogenation of HMF into various platform chemicals while utilizing nickel-based catalysts. The overall goal of this dissertation is to advance these technologies through innovative catalyst design and catalyst characterization techniques that allowed for a systematic investigation into the major catalyst surface properties that influence activity and product selectivity. Various characterization techniques were applied to acquire relevant catalyst surface and structural properties including temperature-programmed reduction, temperature-programmed desorption, X-ray powder diffraction, and transition electron microscopy, N2 physisorption, and diffuse reflectance infrared Fourier transform spectroscopy. A detailed kinetic model was also established that takes into account the number of metallic active sites that provides comparative kinetic parameters to better understand catalyst activity.
The main discoveries obtained during this doctoral thesis include the determination of the critical influence that the support material has on catalyst activity and tuning the reaction network. Particularly, it was found that carbon as a relatively neutral support was effective for hydrodeoxygenation, however, an alumina support was necessary to activate the furan ring and facilitate ring saturation and ring opening reactions. The solvent system was also found to be impactful where incorporating water as a co-solvent completely eliminated all dehydration side reactions. Structural-activity correlations indicate that both acid and basic active sites could play a pivotal role in dictating between the two competing reactions of ring saturation and ring opening. The results presented in this doctoral dissertation provide crucial details for more optimal catalyst design and operating conditions for the effective conversion of 5-hydroxymethylfurfural via hydrogenation for the purpose of advancing sustainable bio-based chemical production.
Keywords: biomass, catalysis, kinetics, hydrogenation, 5-hydroxymethylfurfural
Published in DKUM: 19.09.2024; Views: 0; Downloads: 19
Full text (12,16 MB) |
4. |
5. Kinetics study of hydrothermal degradation of PET waste into useful productsMaja Čolnik, Darja Pečar, Željko Knez, Andreja Goršek, Mojca Škerget, 2022, original scientific article Abstract: Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 °C and 350 °C) and reaction times from 1 to 240 min. PET waste was decomposed in subcritical water (SubCW) by hydrolysis to terephthalic acid (TPA) and ethylene glycol (EG) as the main products. This was followed by further degradation of TPA to benzoic acid by decarboxylation and degradation of EG to acetaldehyde by a dehydration reaction. Furthermore, by-products such as isophthalic acid (IPA) and 1,4-dioxane were also detected in the reaction mixture. Taking into account these most represented products, a simplified kinetic model describing the degradation of PET has been developed, considering irreversible consecutive reactions that take place as parallel in reaction mixture. The reaction rate constants (k1–k6) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.
Keywords: PET waste, subcritical water, kinetics, degradation, TPA
Published in DKUM: 18.09.2023; Views: 645; Downloads: 237
Full text (2,22 MB)
This document has many files! More... |
6. The curing of diallylterephthalate determination of the kinetic triplet A, Ea,app, ƒ(α) using the isoconversional methodDušan Klinar, Janvit Golob, Matjaž Krajnc, 2003, original scientific article Abstract: Allyl polymers are important materials for the production of high performance ophthalmic lenses by free-radical bulk polymerization in the casting process. Isoconversional model-free analysis was applied to the isothermal and nonisothermal curing of diallylterephthalate performed by DSC at different sets of heating rates. The results of the kinetic analysis in a form of kinetic triplet $(Ea, A, ƒ(α))$ present the variation of the Arrhenius parameters with the calculation method, reaction extent, process mode and heating rates applied. This variation is a sign of the complex and multi-step reaction mechanism. Such a mechanism was approximated with one step $(1-α)^n$ reaction model. With the isokinetic relationship - IKR (compensation effect) in the form of $lnA=aEa,app+b$ it was found out that the isothermal and nonisothermal IKR lines converge to different singular points. From the correlation procedure with the experimental data isothermal narrowest point – NPI was selected as a common point. The curing process in the isothermal and nonisothermal process conditions, respectively, was successfully simulated with the obtained kinetic parameters. The possible alternative reaction paths and the partial diffusion control of the curing process are the reasons for the limiting usage of the model-free kinetic analysis method. This method was mainly used as a preliminary step for further analysis with other methods.
Keywords: DSC, DAT, curing kinetics, compensation effect
Published in DKUM: 29.08.2017; Views: 1505; Downloads: 108
Full text (158,92 KB)
This document has many files! More... |
7. Saponification reaction system : a detailed mass transfer coefficient determinationDarja Pečar, Andreja Goršek, 2015, original scientific article Abstract: The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate.
This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures.
The results indicated an important role of reliable kinetic model, as significant difference in $k_La$ product was obtained with extended and simple approach.
Keywords: chemical kinetics, mass transfer, saponification, heterogeneous system
Published in DKUM: 25.08.2017; Views: 1794; Downloads: 232
Full text (156,61 KB)
This document has many files! More... |
8. Kinetic studies of catalytic ozonation of atrazineBrigita Tepuš, Marjana Simonič, 2008, original scientific article Abstract: The aim of our work was to degrade atrazine by the ozone treatment of both a model and the original drinking water samples, using Pt-catalyst, and to evaluate the performance of this catalyst. The rate constant for the reaction of atrazine with ozone was determined in the model water sample. The activation energies and the reaction orders of ozone decomposition were determined in both the model and the drinking water samples. Ozone treatment using Pt-catalyst has some influence on the loss of atrazine in the sources of drinking water. The concentration of some metabolites in the model and drinking water was observed during ozone treatment. The toxicity of atrazine to crustacean Daphnia magna in the original drinking water and in the ozone treated water samples was also assessed.
Keywords: ozone, Pt-catalyst, atrazine, water treatment, waste water, kinetics
Published in DKUM: 05.07.2017; Views: 1352; Downloads: 88
Full text (185,82 KB)
This document has many files! More... |
9. Denitrification of spent regenerated brine using molassesBrigita Tepuš, Marjana Simonič, Aleksandra Petrovič, Jasmina Filipič, 2014, original scientific article Abstract: Spent BRINE from the regeneration of exhausted resins has to be properly treated before its disposal. The heterotrophic denitrification of regenerated brine was studied in present work. Molasses which served as a carbon source has until now not been applied during brine denitrification. The nitrate and nitrite consumptions were observed according to different ratios between total organic carbon and nitrate (TOC / NO3 ratios) and the influence of NaCl was studied during batch experiments. This work ascertained that molasses is a very good source of carbon, and no addition of other nutrients is necessary. The complete nitrate removal from regenerated brine could be achieved using molasses.
Keywords: nitrate, denitrification, regeneration brine, molasses, kinetics
Published in DKUM: 05.07.2017; Views: 1326; Downloads: 424
Full text (1,15 MB)
This document has many files! More... |
10. A kinetic study on drinking water denitrification using a membrane bioreactorAleksandra Petrovič, Andreja Goršek, Marjana Simonič, 2015, original scientific article Abstract: This study determines the basic parameters of Monod kinetics for microbial growth within a membrane bioreactor using the Zenon ZeeWeed 10 MBR system. The influent nitrate concentration was kept at 70 ± 2 mg L-1 NO3ˉ. During the experiments a constant concentration of activated sludge was maintained at approximately 0.76 g L-1 under anoxic conditions. Sucrose was added to the activated sludge as a carbon source. The Monod kinetic parameters were calculated by numerical interpolation, by considering experimental data. The maximum specific growth rate of the biomass was determined to be 0.31 h-1, half-saturation constant 5.4 mg L-1, and yield coefficient 0.35 mg biomass mg-1 COD. Afterwards, a dynamic simulation was performed within the calculated parameters. The dynamic concentration profiles for substrate and biomass were determined at different dilution rates within the range of 0.8 to 5 d-1.
Keywords: kinetics, denitrification, drinking water, membrane bioreactor, sucrose
Published in DKUM: 03.04.2017; Views: 1837; Downloads: 430
Full text (1,68 MB)
This document has many files! More... |
