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The curing of diallylterephthalate determination of the kinetic triplet A, Ea,app, ƒ(α) using the isoconversional method
Dušan 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: 29.08.2017; Views: 797; Downloads: 86
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Saponification reaction system
Darja 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: 25.08.2017; Views: 724; Downloads: 86
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Kinetic studies of catalytic ozonation of atrazine
Brigita 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: 05.07.2017; Views: 505; Downloads: 67
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Denitrification of spent regenerated brine using molasses
Brigita 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: 05.07.2017; Views: 568; Downloads: 313
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A kinetic study on drinking water denitrification using a membrane bioreactor
Aleksandra 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: 03.04.2017; Views: 859; Downloads: 305
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Manipulation of chitosan binding on the polyethylene terephthalate (PET) surface and study of coatings on poultry meat shelf life-time
Tina Tkavc, 2014, doctoral dissertation

Abstract: The aim of this study was to activate inert PET surfaces in order to introduce the surfaces’ carboxyl groups and to obtain its hydrophilic character, which was important for the chitosan bonding to it. Films where chitosan was attached to the PET could be used as active packaging material for food like fresh poultry meat. For PET activation two advanced and environmentally friendly techniques were used: 1) O2 plasma activation; and 2) CO2 plasma activation. Differently treated PET foils deposited on Au quartz crystals (model studies - adsorption and desorption) and real films were characterized. Later on, real films were studied in the terms of carboxylic/amino group content, hydrophobic/hydrophilic character, surface composition and adsorption/desorption of chitosan onto/from the surface. Results clearly showed that the use of both surfaces’ activation processes increased the ability of PET foils to adsorb chitosan, but CO2 plasma gave a higher concentration of carboxyl groups on the PET surface and consequently, due to the chemical bonding the chitosan layers were more stable. Even though CO2 plasma pre-treated PET foils gave better results during the experimental work, we could not avoid layer by layer adhesion of chitosan which resulted in non-bound molecules. Pre-treated foils and with chitosan functionalized foils were tested preliminarily with ASTME E1 (2002) microbiological tests. Functionalized CO2 plasma pre-treated foils gave the broadest spectra of antimicrobial activity, and therefore they were chosen for further microbiological analyses, where chitosan`s influence on inoculated poultry models towards selected standard strains, typical for poultry meat, was being tested. By determining the MIC (minimal inhibitory concentration) for selected microorganisms we have proven, that chitosan possesses antimicrobial properties at low concentrations. During the transfer of the experiment to a larger scale (food models, which are a very complex environment), it has been shown that on PET bonded chitosan did not have the inhibitory effect to that extent, with the exception of Staphylococcus aureus, as was expected. Similar results were expressed using both these methods: Colony count technique and real-time PCR. In the end, the organoleptic properties of the chicken models exposed to foils have shown that chitosan changes the color and taste of meat immediately after exposure, but samples were staying edible longer. Therefore, functionalized PET, which has an inhibitory influence towards variety of microorganisms, may be applied as an active packaging system for poultry meat after some optimization of the coating procedure in binding chitosan onto the PET surfaces.
Keywords: PET/chitosan/antimicrobial packaging/adsorption-desorption kinetics/microbiological tests
Published: 22.10.2014; Views: 1627; Downloads: 153
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Enzymatic fatty ester synthesis
Simona Pečnik, Željko Knez, 1992, original scientific article

Abstract: 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.
Keywords: chemical engineering, biotechnology, esterification, syntheses, esters, enzymes, lipase, Mucor miehei, reaction kinetics, reaction thermodynamics, 1, 2-isopropylidene-3-oleoyl glycerol
Published: 06.06.2012; Views: 1576; Downloads: 74
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A novel metalloprotease from Bacillus cereus for protein fibre processing
Fernanda de Sousa, Suzana Jus, Anita Erbel, Vanja Kokol, Artur Cavaco-Paulo, Georg M. Gübitz, 2007, original scientific article

Abstract: A novel protease produced by Bacillus cereus grown on wool as carbon and nitrogen source was purified. B. cereus protease is a neutral metalloprotease with a molecular mass of 45.6 kDa. The optimum activity was at 45 °C and pH 7.0. The substrate specificity was assessed using oxidized insulin B-chain and synthetic peptide substrates. The cleavage of the insulin B-chain was determined to be Asn3, Leu6, His10-Leu11, Ala14, Glu21, after 12 h incubation. Among the peptide substrates, the enzyme did not exhibit activity towards ester substrates; with p-nitroanilide, the kinetic data indicate that aliphatic and aromatic amino acids were the preferred residues at the P1 position. For furylacryloyl peptides substrates, which are typical substrates for thermolysin, the enzyme exhibited high hydrolytic activity with a Km values of 0.858 and 2.363 mM for N-(3-[2-Furyl]acryloyl)-Ala-Phe amide and N-(3-[2-Furyl]acryloyl)-Gly-Leu amide, respectively. The purified protease hydrolysed proteins substrates such as azocasein, azocoll, keratin azure and wool.
Keywords: textile finishing, enzymatic modification, wool fibre, enzymes, Bacilus cereus, specificity, kinetics, metalloprotease
Published: 01.06.2012; Views: 1359; Downloads: 82
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Case study of the sonochemical decolouration of textile azo dye Reactive Black 5
Simona Vajnhandl, Alenka Majcen Le Marechal, 2007, original scientific article

Abstract: The decolouration and mineralization of reactive dye C.I. Reactive Black 5, a well-known representative of non-biodegradable azo dyes, by means of ultrasonic irradiation at 20, 279 and 817 kHz has been investigated with emphasis on the effect of various parameters on decolouration and degradation efficiency. Characterization of the used ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using Fricke and iodine dosimeter. Experiments were carried out with low frequency probe type, and a high-frequency plate type transducer at 50, 100 and 150 W of acoustic power and within the 5-300 mgžL initial dye concentration range. Decolouration, as well as radical production, increased with increasing frequency, acoustic power, and irradiation time. Any increase in initial dye concentration results in decreased decolouration rates. Sonochemical decolouration was substantially depressed by the addition of 2-methyl-2-propanol as a radical scavenger, which suggests radical-induced reactions in the solution. Acute toxicity to marine bacteria Vibrio fischeri was tested before and after ultrasound irradiation. Under the conditions employed in this study, no toxic compounds were detected after 6 h of irradiation. Mineralization of the dye was followed by TOC measurements. Relatively low degradation efficiency (50% after 6 h of treatment) indicates that ultrasound is rather inefficient in overall degradation, when used alone.
Keywords: textile industry, wastewater treatment, textile dyeing, reactive dyes, azo dyes, decoloration, ultrasound, degradation, decoloration kinetics, oxidizing species
Published: 01.06.2012; Views: 1492; Downloads: 72
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Thread loadings in different measuring positions on the sewing machine
Darja Žunič-Lojen, Jelka Geršak, 2005, original scientific article

Abstract: The knowledge of sewing thread tension determined at different measuring locations on the sewing machine is the basis for the definition of the loading magnitudes acting during the stitch formation process and the locations at which they appear, concerning the stitch cycle or the main shaft turn of the sewing machine. During the stitch formation process the sewing thread is exposed to the highest tension in the region between the tension regulator and the thread take-up lever, following by tension in the region between the take-up lever and the needle and in the region in front of the tension regulator. Dynamic tension and tension force are also dependent on stitch velocity.
Keywords: textile industry, sewing, kinetics of sewing, thread, dynamic thread loadings
Published: 01.06.2012; Views: 1512; Downloads: 75
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