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1.
Modified coefficient of subgrade reaction to laterally loaded piles
Ayhan 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: 11.10.2018; Ogledov: 658; Prenosov: 329
.pdf Celotno besedilo (735,27 KB)
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2.
Reactive sintering of $MnZn$ ferrites
Tomaž 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: 25.08.2017; Ogledov: 544; Prenosov: 72
.pdf Celotno besedilo (441,54 KB)
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3.
Calorimetric insight into coupling between functionalized primary alkyl halideand vinylic organocuprate reagent
Zdenko 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: 17.08.2017; Ogledov: 601; Prenosov: 55
.pdf Celotno besedilo (206,94 KB)
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4.
Enzymatic fatty ester synthesis
Simona 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: 06.06.2012; Ogledov: 1626; Prenosov: 76
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5.
Optimal reactor systems for Van de Vusse reaction scheme with multicomponent feed
Duško Bikić, Branko Butinar, Peter Glavič, 2002, izvirni znanstveni članek

Opis: In the present paper, product yield in the Van de Vusse reaction scheme with multicomponent feed has been studied. The optimal reactor structures have been found by investigating optimality conditions. The optimum product yield and criteria for selecting an appropriate reaction system have been obtained as functions of kinetic parameters. On the basis of optimization results the parameter space has been classified into regions indicating optimum reactor structure.
Ključne besede: optimal reactor structure, optimum product yield, multicomponent feed, parameter space, Van der Vusse reaction
Objavljeno: 01.06.2012; Ogledov: 1813; Prenosov: 96
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6.
In-situ investigation of sucrose hydrolysis - successful link between design of experiment, RC1 and reactIR system
Katja 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: 31.05.2012; Ogledov: 1700; Prenosov: 60
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7.
Enzyme-catalyzed reactions in different types of high-pressure enzymatic reactors
Mateja Primožič, Maja Leitgeb, Muzafera Paljevac, Željko Knez, 2006, izvirni znanstveni članek

Opis: The enzyme-catalyzed hydrolysis of carboxy-methyl cellulose (CMC) was performed in three different types of reactors; in a batch stirred-tank reactor (BSTR) operating at atmospheric pressure, in a high-pressure batch stirred-tank reactor (HP BSTR) and in a high-pressure continuous tubular-membrane reactor (HP CTMR). In the high-pressure reactors aqueous SC C02 was used as the reaction medium. The aim of our research was optimization of the reaction parameters for reaction performance. All the reactions were catalyzed by cellulase from Humicola insolens. Glucose production in the high-pressure batch stirred-tank reactor was faster than in the BSTR at atmospheric pressure. The optimal temperature for the reaction performed in the BSTR at atmospheric pressure was 30°C, while the optimal temperature for the reaction performed in SC C02 was 32°C. The influence of the application of tubular ceramic membranes in the high-pressure reaction system was studied on the model reaction of CMC hydrolysis at atmospheric pressure and in SC C02. The reaction was catalyzed by cellulase from Humicola insolens covalently linked to the surface of the ceramic membrane. The hydrolysis of CMC in SC C02 and at atmospheric pressure was performed for a long time period. The reaction carried out in SC C02 was more productive than the reaction performed at atmospheric pressure.
Ključne besede: chemical processing, enzymatic reaction, cellulase, supercritical carbon dioxide, high-pressure batch reactor, high-pressure membrane reactor
Objavljeno: 31.05.2012; Ogledov: 1494; Prenosov: 273
.pdf Celotno besedilo (454,51 KB)
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