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1.
Preparation of enantiomers using high pressure technologies
Paul Thorey, 2010, doktorska disertacija

Opis: The study of two different methods of obtaining chiral alcohols is proposed herein. The requirement of the relatively new paradigm of green chemistry associated with clean technologies such as biocatalysis or non-conventional solvents, dense gases, was focused at. Indeed, the two methods of production of chiral alcohols were: - the conversion of acetophenone into (R)-1-phenylethanol in dense gases catalysed by Lactobacillus brevis alcohol dehydrogenase and its coenzyme, NADP/H; - the resolution of (±)-trans-1,2-cyclohexanediol by cocrystal formation with tartaric acid followed by supercritical extraction. In both cases high enantiopurities were achieved (ee>99%).
Ključne besede: High-pressure technologies, enantiomers, green chemistry, R-1-phenylethanol, Lactobacillus brevis, alcohol dehydrogenase, NADP, liquid propane, enzyme deactivation, resolution, trans-1, 2-cyclohexanediol, tartaric acid, cocrystal, supercritical carbon dioxide, extraction, X-ray diffraction, differential scanning calorimetry
Objavljeno: 02.02.2011; Ogledov: 1753; Prenosov: 53
.pdf Polno besedilo (6,25 MB)

2.
Characterization of cast Al86Mn3Be11 alloy
Tonica Bončina, Boštjan Markoli, Franc Zupanič, 2009, izvirni znanstveni članek

Opis: An Al86Mn3Be11 alloy cast into copper mould was subjected to metallographic investigation. The as-cast microstructure consisted of a quasicrystalline icosahedral phase (i-phase), Be4AlMn phase and, occasionally, a hexagonal phase. Al-rich solid solution represented the dominant phase. The chemical compositions of phases were determined using AES. The composition of the Be4AlMn slightly deviated from the stoichiometric composition, whereas the composition of the i-phase was approximately Al52Mn18Be30, containing an appreciable amount of Be. The average composition of the hexagonal phase was Al66Mn21Be13. Deep etching and particle extraction provided a deep insight into the three-dimensional morphology of the i-phase and the hexagonal phase, whereas Be4AlMn was slightly attacked by the etchant. The i-phase was present predominantly in the form of dendrites and a rodlike eutectic phase. The hexagonal phase was primarily in the form of hexagonal platelets, whereas Be4AlMn was rather irregular in shape. The morphology of the i-phase can be explained by predominant growth in 3-fold directions and the lowest energy of the 5-fold planes, leading to the faceting and adopting a pentagonal dodecahedron shape. The brightnesses of phases in the backscattered electron images were rationalized by determining their backscattering coefficients. TEM investigation showed considerable phason strain in the i-phase, and the polycrystalline nature of the Be4AlMn phase.
Ključne besede: aluminium alloys, deep etching, metallography, particle extraction, quasicrystal
Objavljeno: 31.05.2012; Ogledov: 827; Prenosov: 2
URL Polno besedilo (0,00 KB)

3.
GRAPE ANTIOXIDANTS - INFLUENCE OF PROCESSING PARAMETERS ON THEIR CONTENT AND ACTIVITY
Iva Ružić, 2012, doktorska disertacija

Opis: Grapes and wine production residuals, containing grape skins, seeds and stems, represent important sources of phenolic compounds. Red wines are rich in phenolic antioxidants while white wines generally show lower (poly)phenolic content and antioxidant activity. The main difference in the production of white and red wines is the fermentation step. The fermentation of red grapes includes maceration, i.e. it takes place in both liquid and solid parts of the grape. In the case of white wines, the must is clarified before the fermentation starts, cultured yeasts are added to convert the must to wine and antioxidant sulfur dioxide is inserted to protect the wine. The objective of the PhD research was to study antioxidant potential of white grape phenolics both in raw material and fermentation products. First, the standards of phenolic compounds commonly found in white grapes and wines were tested for their antioxidant and antiradical activity. All tested compounds except apigenin showed strong antioxidant and antiradical properties. Afterwards, conventional solid-liquid extraction (CE) and pressurized liquid extraction (PLE) of phenolic compounds from grape seeds were performed. The optimal extraction conditions were investigated and extracts were analyzed in order to determine their total phenolic content, individual phenolic compounds and antiradical potential. Two different drying methods (hot air and freeze drying) were applied to the seeds. Solvent efficiencies of water, ethanol and water-ethanol mixtures were compared at different temperatures. In addition, supercritical fluid extraction (SFE) with CO2 was investigated as the technique for the recovery of phenolic compounds and for the pretreatment of white grape seed samples. Both CE and PLE gave extracts rich in phenolic compounds with good antiradical properties and, generally, the best results were obtained with PLE at 130°C. At the end, the influence of maceration process on the content and the activity of grape phenolic antioxidants in white wines was studied. For such a purpose, six commercially available macerated white wines from Italy and Croatia were analyzed. In addition, eight non-macerated wines from the same region and variety were studied and compared to macerated wines. The experiments have shown that the maceration process increases the total phenolic content and antiradical activity of the wine. It enables the production of white wines rich in phenolic compounds and with strong antiradical properties in completely natural way using only the grapes and without addition of any chemical agents.
Ključne besede: white grapes, white wine, maceration, antioxidant activity, polyphenols, extraction, PLE, SFE.
Objavljeno: 05.04.2012; Ogledov: 1555; Prenosov: 63
.pdf Polno besedilo (5,65 MB)

4.
Kinetics of supercritical carbon dioxide extraction of borage and evening primrose seed oil
Petra Kotnik, Mojca Škerget, Željko Knez, 2006, izvirni znanstveni članek

Opis: In the present work, high-pressure extraction of borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) seed oil, containing the valuable -linolenic acid (GLA), has been investigated. Extraction was performed with supercritical carbon dioxide on a semi-continuous flow apparatus at pressures of 200 and 300 bar, and at temperatures of 40 and 60 °C. A constant flow rate of carbon dioxide in the range from 0.17 to 0.20 kgžhwas maintained during extraction. The extraction yields obtained using dense CO2 were similar to those obtained with conventional extraction using hexane as solvent. The composition of extracted crude oil was determined by GCanalysis. The best results were obtained at 300 bar and 40 °C for both seed types extracted, where the quality of oil was highest with regard to GLA content. The evening primrose seed oil extracted with supercritical fluid extraction was particularly rich in unsaturated fatty acidsČ up to 89.7 wt-% of total free fatty acids in the oil. The dynamic behavior of the extraction runs was analyzed using two mathematical models for describing the constant rate period and the subsequent falling rate period. Based on the experimental data, external mass transfer coefficients, diffusion coefficients and diffusivity in solid phase were estimated. Results showed good agreement between calculated and experimental data.
Ključne besede: chemical processing, high pressure technology, supecritical CO2, seed oil extraction, evening primrose, borage, free fatty acids, kinetics, modeling
Objavljeno: 31.05.2012; Ogledov: 869; Prenosov: 6
URL Polno besedilo (0,00 KB)

5.
Isolation of chlorophylls from stinging nettle (Urtica dioica L.)
Maša Hojnik, Mojca Škerget, Željko Knez, 2007, izvirni znanstveni članek

Opis: This study was aimed to assess the feasibility of extracting chlorophylls fromstinging nettle (Urtica dioica L.) by solvent extraction. In preliminary, the investigation concerned three parts of raw material (leaves, stalk and whole plant), different preservation techniques (blanching and drying) and different storage temperatures of preserved material ( |20 C for blanched and 4 C for dried sample). Extracts were analysed for chlorophyll A and chlorophyll B, respectively, by means of HPLC method. Afterwards, optimizationof single-step conventional extraction was carried out by examining the influence of the following process parameters on the extraction yield and isolation efficiency of chlorophylls: type of organic solvent, content of water in ethanol/water mixtures, ratio solvent/material, temperature, time of extraction and pH of the extraction mixture. Furthermore,to improve the yield and/or the selectivity of the extraction, multi-step conventional extraction experiments as well as other solid ]liquid extraction techniques (soxhlet and ultra-sound assisted) were performed and compared. c 2007 Elsevier B.V. All rights reserved.
Ključne besede: chemical processing, extraction, nettle, isolation of chlorophyll, chlorophyll content, solvent extraction
Objavljeno: 31.05.2012; Ogledov: 1043; Prenosov: 7
URL Polno besedilo (0,00 KB)

6.
Supercritical fluid extraction of chammomile flower head flowers: comparison with conventional extraction, kinetics and scale-up
Petra Kotnik, Mojca Škerget, Željko Knez, 2007, objavljeni znanstveni prispevek na konferenci

Opis: Supercritical fluid extraction of chamomile flower heads was performed on semicontinuous extraction apparatus in the lab scale using carbon dioxide as solvent. The results of high pressure experiments were compared with those obtained with Soxhlet extraction, steam distillation and maceration. The obtained extracts were analysed by HPLC on ?-bisabolol, matricine and chamazulene content and by gravimetrical method on essential oil and waxes content. The highest content of active components in extracts and highest extraction yield were obtained using SFE at 250 bar and 40 °C. At this extraction conditions the two step separation was used to optimize the separation of essential oil from unwanted components. Dynamic behaviour of theSFE with single step separation runs were analysed using two mathematical models for describing the constant rate period and subsequent falling rate period. Based on the experimental data, external mass transfer coefficient, diffusion coefficient and diffusivity in solid phase were estimated. Results showed acceptable agreement of calculated and experimental data. Based on theparameters determined in the lab scale, the extraction process was successfully transferred to pilot scale.
Ključne besede: chemical processing, high pressure technology, supercritical extraction, chamomile, matricine, chamazulen, scale-up
Objavljeno: 31.05.2012; Ogledov: 835; Prenosov: 9
URL Polno besedilo (0,00 KB)

7.
Optical properties of plastically deformed copper
J. Trajić, Rebeka Rudolf, Ivan Anžel, M. Romčević, N. Lazarević, M. Mirić, Z. Lazarević, B. Hadžić, Nebojša Romčević, 2010, objavljeni znanstveni prispevek na konferenci

Opis: Pure copper (99.99), prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of 7 cm¡1) and wide ( 40 cm¡1) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen.
Ključne besede: plastically deformed copper, hydrometallurgical extraction of metals
Objavljeno: 31.05.2012; Ogledov: 740; Prenosov: 3
URL Polno besedilo (0,00 KB)

8.
Feature extraction from CAD model for milling strategy prediction
Jože Balič, Simon Klančnik, Simon Brezovnik, 2008, izvirni znanstveni članek

Opis: In this paper we present a procedure of feature determination from a CAD model. From the model we extract information, which has the greatest influence on the technological parameters of treatment and then transform this information into appropriate input data for different intelligent processing strategy prediction systems (for example artificial neural network). With formally complex CAD models, different processing strategies are required on a single workpiece. For this reason we use segmentation as described in this paper, to partition the surface of the CAD model into regions, so that we treat each region as an independent model and determine its features.
Ključne besede: CAD-CAM systems, milling strategies, feature extraction, CAD models, segmentation
Objavljeno: 31.05.2012; Ogledov: 798; Prenosov: 12
URL Polno besedilo (0,00 KB)

9.
Extraction of lutein from Marigold flower petals - Experimental kinetics and modelling
Maša Hojnik, Mojca Škerget, Željko Knez, 2008, izvirni znanstveni članek

Opis: The extraction kinetics behaviour of lutein from Marigold flower petals and simultaneous alkali hydrolysis has been studied. Extraction was carried out by varying following operating conditions: type of organic solvent, temperature, ratio liquid: material, concentration of alkali solution, and particle size of plant material. Experimental extraction curves were analysed with a mathematical model derived from Fick's second law. The extraction of lutein appeared to be governed by slow and fast diffusion processes. Results showed that the intra-particle diffusion was the rate-governing step of the extraction process, and that the chosen model gives very good approximation of experimental data.
Ključne besede: lutein, marigold, conventional extraction, diffusivity, mass transfer
Objavljeno: 31.05.2012; Ogledov: 765; Prenosov: 7
URL Polno besedilo (0,00 KB)

10.
Metallographic techniques for the characterization of quasicrystalline phases in aluminium alloys
Tonica Bončina, Boštjan Markoli, Ivan Anžel, Franc Zupanič, 2008, izvirni znanstveni članek

Opis: Several Al-alloys strengthened by quasicrystalline phases have been developed over the last few years showing the considerable potential for practical application. Therefore there is a strong need for developing new metallographic methods or adapting the traditional ones in order to identify and characterize quasicrystalline phases in a reliable, quick and economical way. This paper describes different techniques: the classical metallographic method, deep etching, particle extraction technique and cross-sectioning using focused ion beam (FIB), and discusses their advantages and disadvantages when identifying quasicrystalline particles. It was discovered that particle extraction techniques are very powerful methods for the identification of phases according to their morphology, and preparation of quality samples for X-ray diffraction (XRD). Transmission electron microscopy (TEM) analyses are also possible provided the extracted particles are thin enough.
Ključne besede: alluminium alloys, quasicrystal, metallography, deep etching, particle extraction
Objavljeno: 31.05.2012; Ogledov: 879; Prenosov: 7
URL Polno besedilo (0,00 KB)

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