1. Correlating nickel functionalities to selectivity for hydrogen peroxide electrosynthesisMiha Nosan, Dušan Strmčnik, Vasiliy Brusko, Maria Kirsanova, Matjaž Finšgar, Ayrat M. Dimiev, Boštjan Genorio, 2023, izvirni znanstveni članek Ključne besede: nickel oxide, heat-treated graphene oxide, selectivity, oxygen reduction reaction, peroxide formation
Objavljeno v DKUM: 10.05.2024; Ogledov: 231; Prenosov: 10
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3. Liquefaction, cracking and hydrogenation of microalgae biomass resources to ▫$CO_2$▫ negative advanced biofuels : mechanisms, reaction microkinetics and modellingDana Marinič, Miha Grilc, Brigita Hočevar, Florian Delrue, Blaž Likozar, 2023, izvirni znanstveni članek Opis: Deoxygenation of triglycerides is one of the crucial pathways for the production of oxygen-free hydrocarbons and biofuels that are fully compatible with conventional internal combustion engines. The one-step liquefaction and hydrotreatment of Chlorella sorokiniana microalgae was investigated in a three-phase slurry reactor. The production of diesel-like hydrocarbons was successfully accomplished over sulfide form of NiMo/Al2O3 catalyst under hydrogen atmosphere. The present work contains a comprehensive investigation of the temperature and hydrogen pressure influence on the final product composition. The highest yield of C18 and C16 (26.1% and 10.7%, respectively) was reached by increasing the reaction temperature to 350 °C and hydrogen pressure to 50 bar, while at milder conditions (200 °C and 20 bar) the products appeared only in trace concentrations. In order to obtain an accurate kinetic model, reaction mechanism was first needed to be determined based on experimentally obtained products and intermediates. A simplified reaction pathway contains liquefaction, hydrogenolysis, hydrodeoxygenation, decarboxylation and decarbonylation. The model comprises mass transfer phenomena involved in the liquefaction process, the mass transfer of hydrogen from gas to liquid phase, adsorption, desorption and surface reaction kinetics. The lowest rate constant was calculated for the microalgae conversion to triglycerides (k0 = 1.93 × 10−6 min−1), indicating slow liquefaction.
Ključne besede: Microalgae, Biofuel, Liquefaction, Hydrodeoxygenation, One-pot reaction
Objavljeno v DKUM: 17.07.2023; Ogledov: 390; Prenosov: 32
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4. Development of a methodology to calibrate a pedestrian microsimulation model : doctoral dissertationChiara Gruden, 2022, doktorska disertacija Opis: Walking, as a mode of transport, is becoming widespread, in a world, where urban conglomerates are broadening and becoming denser. Modern lifestyle trends on a side, and eco-friendly policies on the other, push people into walking habits, increasing the need for a suitable, attractive, accessible, connected and safe walking infrastructure. To reach such a result, it is necessary to understand, what are the needs of the users of this infrastructure, taking into consideration the behavioral specificities and the safety needs of pedestrians. In this process pedestrian microsimulation models, surrogate safety techniques, and technologies able to measure specific traits of pedestrian dynamics play a central role. The firsts allow to reproduce repeatedly in a virtual environment a specific infrastructure and to study the response of pedestrians. Nevertheless, to be accurate and efficient, they need to go through long and tedious calibration and validation processes, that are often seen as an important limitation by technicians. Surrogate safety techniques are methods, that are based on the concept, that it is possible to predict the safety level of a location, using near accidents. The main advantage of such techniques is that they are proactive. Till this moment, these techniques have been mainly applied to on-field measurements and are primarily centered on motorized road users. Less interest has been shown for vulnerable road users, especially for pedestrians, who have been less extensively studied. Finally, an element that could highly affect pedestrian safety is their reaction time. Nevertheless, its measurement has long been a big issue. Eye-tracking technology could be one of the solutions, allowing to analyze the directions and objects fixated by pedestrians. These listed issues are also the topics that are addressed by this research work. Focusing on the study of the action of pedestrians while crossing the road on an unsignalized crosswalk set on a roundabout entry leg, the dissertation thesis aims at studying the crossing time, reaction time and surrogate safety aspects typical of pedestrians at the recalled location. The main purpose of the research work is to develop a methodology to calibrate pedestrian Social Force Model at a selected location, using a specifically formulated neural network as a tool to fine-tune model's behavioral parameters. Eight parameters have been chosen to be fine-tuned, five of those are related to pedestrian behavior and three of them are related to car-following behavior. After the selection of input parameters, a feedforward network has been formulated. Its application in the framework of the whole calibration process has brought to considerably positive results, finding a combination of input parameters that improved the performance of the microsimulation model of 37 % in comparison to the default one. The outputs of the calibrated model have been used to calculate three measures of surrogate safety, and also in this case results demonstrated an improvement in the calculation of surrogate safety measures when using the calibrated outcomes in comparison to their calculation on the “default” model outputs. Finally, reaction time measurement and prediction have been addressed by the thesis, in order to be able to describe pedestrian crossing action in its completeness. Quantitative eye-tracking outputs have been the starting point for the calculation of pedestrian reaction time at different locations, and they allowed to create a database of behavioral, geometric, regulatory and flow characteristics, which was the foundation for the formulation of a new prediction model for pedestrian reaction time. The prediction model, which consists of a cascade-correlation neural network, gave a good response to the learning and generalization steps, turning a 74 % correlation between the measured reaction time values and the predicted ones, and being able to follow the variability of these values.
Ključne besede: pedestrian, microsimulation model, calibration, neural network, surrogate safety indicators, reaction time.
Objavljeno v DKUM: 03.10.2022; Ogledov: 873; Prenosov: 105
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5. Modified coefficient of subgrade reaction to laterally loaded pilesAyhan Gurbuz, 2018, izvirni znanstveni članek Opis: An accurate prediction of the load capacity of a laterally loaded pile at a permissible displacement is an important concern at the design stage. In contrast to many sophisticated methods, Broms’ method based on moment equilibrium has been preferred by engineers to predict the load capacities of laterally loaded piles due to both its simplicity and because it is established on a way of hand calculation. However, Broms’ method typically overestimates a pile’s lateral load capacity as it requires a constant coefficient of horizontal subgrade reaction (nh) into analyses, regardless of the magnitude of the pile’s top displacement. In this study, modified coefficients of subgrade reactions(nh*) that are sensitive to the pile’s top displacement in cohesionless soils are first proposed to improve the performance level of Broms’ method for the prediction of the load capacity of a laterally loaded pile as the pile’s top displacement increases. The modified values of nh* are calibrated using 45 independently free-head, single-driven, full-scale pile tests from 23 sites in cohesionless soils. It is demonstrated that Broms’ method with nh* would correctly estimate a pile’s lateral load-deflection behavior with accuracy levels similar to more complicated methods.
Ključne besede: Broms' method, coefficient of horizontal subgrade reaction, p-y curves, strain wedge model
Objavljeno v DKUM: 11.10.2018; Ogledov: 1380; Prenosov: 616
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6. Reactive sintering of $MnZn$ ferritesTomaž Kosmač, Mihael Drofenik, 2001, izvirni znanstveni članek Opis: Reaction-formed $MnZn$ ferrite was prepared and the decrease in shrinkage after sintering due to the volume expansion accompanying iron oxidation was studied.
Green compacts consisting of the milled raw oxides $Fe_2O_3$, $Mn_3O_4$, $ZnO$ and metallic iron powder were sintered at 1350 °C in air. During the first hold at 800 °C, $Fe$ was oxidized to $\alpha-Fe_2O_3$ and $Zn$ ferrite was formed. Above 1300 °C the reaction bonding was completed and $MnZn$ ferrite, exhibiting a relatively low shrinkage, was formed. The chemical reactions involved during reaction bonding were associated with a volume expansion and porosity formation, compensating for the shrinkage on sintering. Intensive milling decreases the porosity after sintering but induces the oxidation of iron, and partially removes the shrinkage compensation caused by the presence of metallic iron.
Ključne besede: reaction-forming, $MnZn$ ferrite, inorganic technology, ferrite ceramics, reaction bonded ceramics, sintering, iron oxides, iron
Objavljeno v DKUM: 25.08.2017; Ogledov: 1182; Prenosov: 112
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7. Calorimetric insight into coupling between functionalized primary alkyl halideand vinylic organocuprate reagent : experimental determination of reaction enthalpies in the synthesis of (R)-ethyl 3-(tert-butyldimethylsilyloxy)hex-5-enoate - a key lactonized statinside chain precursorZdenko Časar, Marko Tramšek, Andreja Goršek, 2010, izvirni znanstveni članek Opis: The first calorimetric study of coupling between organocuprate, derived from Grignard reagent (vinyl magnesium chloride), and primary alkyl halide (e.g. (S)-ethyl 3-(tert-butyldimethylsilyloxy)-4-iodobutanoate) has been conducted. This transformation is paramountly important for efficient preparation of (R)-ethyl 3-(tert-butyldimethylsilyloxy)hex-5-enoate – a key lactonized statin side chain precursor. The results obtained give thorough calorimetric insight into this complex low-temperature synthesis as well as a new understanding of the suggested reductive elimination of the final intermediates in the coupling reaction. Namely, the surprising unexpected spontaneous three-step exothermal event has been observed during controlled progressive heating of the mixture of the final intermediates to the room temperature. This phenomenon confirms that coupling between functionalized primary alkyl halide and vinylic organocuprate reagent is not a simple $S_N2$ substitution reaction. The presented study provides among others the first reported values of reaction enthalpies and corresponding adiabatic temperature rises of reaction mixture for all exothermic events that occurred in the (R)-ethyl 3-(tert-butyldimethylsilyloxy)hex-5-enoate synthesis. The obtained results ensure consequential thermal process safety knowledge which can be incorporated into safe process scale-up as well as design of reactor system with sufficient cooling capacity for industrial production of (R)-ethyl 3-(tert-butyldimethylsilyloxy)hex-5-enoate. Moreover, the results provide a basic guidance for other organocuprate coupling reaction systems.
Ključne besede: Grignard reagents, organocuprates, coupling reaction, reaction calorimetry, statins
Objavljeno v DKUM: 17.08.2017; Ogledov: 1134; Prenosov: 105
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8. Enzymatic fatty ester synthesisSimona Pečnik, Željko Knez, 1992, izvirni znanstveni članek Opis: Fatty ester synthesis with immobilized 1,3-specific lipase from Mucor Miehei is described. 1,2-Isopropylidene glycerol was peoduced by condensation of glycerol with acetone was esterified with oleic acid in the presence of a Mucor Miehei lipaze (Lipozyme TM) to obtain 1,2 isopropylidene- 3-oleoyl glycerol. The effects of various process parameters (temperature and pressure)and various ratios (enzyme/substrate) have been investigated to determine optimal conditions for the esterification process. The highest conversion of oleic acid (80% w/w) was obtained at 55 oC and 57.057 bar, while the optimal addition of lipase to substrate was determined to be 0,096 g per gram of reaction mixture. The esterification can be modelled successfully as a reverse second order reaction. Thermodynamic properties of the reaction system at 55 oC and 0.057 bar were also determined. Activation energy was 20.82 kJ/mole, entropy of activation -0,26 kJ/(Kmole) and free energy of activation was 103.32 kJ/mole.
Ključne besede: chemical engineering, biotechnology, esterification, syntheses, esters, enzymes, lipase, Mucor miehei, reaction kinetics, reaction thermodynamics, 1, 2-isopropylidene-3-oleoyl glycerol
Objavljeno v DKUM: 06.06.2012; Ogledov: 2549; Prenosov: 98
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10. In-situ investigation of sucrose hydrolysis - successful link between design of experiment, RC1 and reactIR systemKatja Zajšek, Andreja Goršek, 2008, izvirni znanstveni članek Opis: The main purpose of this work was combining the modern laboratory equipment (RC1 reaction calorimeter and ReactIRTMiC10 reaction analysis system) and the concept of the Taguchi fs design of experiment to determine the relative influence of important process parameters affecting the sucrose hydrolysis. The reaction was catalyzed by strong acidic cation-exchange resin Amberlite IR-120 in H+ form. Four process parameters, including reaction temperature (.), sucrose mass concentration (fÁS), catalyst mass concentration (fÁC) and the rotational frequency of the stirrer (fm) at four levels were considered in this study. Relative contributions of the proposed influencing process parameters on hydrolysis time were estimated by analysis of the variance (ANOVA). The results showed that . had a substantial effect on the reaction time (78,3 %), the fm and fÁC had a smaller ones (7,9 % and 6,4 %, respectively), meanwhile the remain fraction to 100 % represents error (7,4 %). The optimum conditions, where the time required for complete sucrose hydrolysis would be the shortest, are: .= 79 Ključne besede: sucrose hydrolysis, catalyst, Taguchi method, in-situ FTIR, reaction calorimeter RC1
Objavljeno v DKUM: 31.05.2012; Ogledov: 2533; Prenosov: 72
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