| | SLO | ENG | Piškotki in zasebnost

Večja pisava | Manjša pisava

Iskanje po katalogu digitalne knjižnice Pomoč

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju

Opcije:
  Ponastavi


1 - 9 / 9
Na začetekNa prejšnjo stran1Na naslednjo stranNa konec
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: 2219; Prenosov: 81
.pdf Celotno besedilo (6,25 MB)

2.
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: 1348; Prenosov: 29
URL Povezava na celotno besedilo

3.
Chemical composition of Juniperus communis L. fruits supercritical CO2 extracts: dependence on pressure and extraction time
Branislava Barjaktarović, Milan Sovilj, Željko Knez, 2005, izvirni znanstveni članek

Opis: Ground fruits of the common juniper (Juniperus communis L), with a particle size range from 0.2500.400 mm, forming a bed of around 20.00 +/- 0.05 g, were extracted with supercritical CO2 at pressures of 80,90, and 100 bars and at a temperature of 40 De. The total amount of extractable substances or global yield (mass of extract/mass of raw material) for the supercritical fluid extraction process varled from 0.65 to 4.00"10 (wt). At each Investigated pressure, supercriticaI CO2 extract fractions collected In successive time intervals over the course of the extraction were analyzed by capillary gas chromatography, using flame ionization (GO-FIO) and mass spectrometric detection (GC-MS). More than 200 constituents were detected In the extracts, and the contents of 50 compounds were reported in the work. Dependence of the percentage yields of monoterpene, sesquiterpene, oxygenated monoterpene, and oxygenated sesquiterpene hydrocarbon groups on the extraction time was investigated, and conditions that favored the yielding of each terpene groups were emphasized. At all pressures, monoterpene hydrocarbons were almost completely extracted from the berries in the first 0.6 h. It was possible to extract oxygenated monoterpenes at 100 bar in 0.5 h and at 90 bar in 1.2 h. Contrary to that, during an extraction period of 4 h at 80 bar, it was possible to extract only 75% of the maximum yielded value of oxygenated monoterpene at 100 bar. Intensive extraction of sesquiterpenes could be by no means avoided at any pressure, but at the beginning of the process (the first 0.5 h) at 80 bar, they were extracted about a and 3 times slower than at 100 and 90 bar, respectively. Oxygenated sesquiterpenes were yielded at fast, constant extraction rates at 100 and 90 bar In 1.2 and 3 h, respectively. This initial fast extraction period was consequently foIlowed by much slower extraction of oxygenated sesquiterpenes.
Ključne besede: chemical processing, high pressure technology, CO2, supercritical fluid extraction, pressure, extraction time, Juniperus communis, oxygenated terpenes, juniper berry oil, carbon dioxide
Objavljeno: 01.06.2012; Ogledov: 1282; Prenosov: 35
URL Povezava na celotno besedilo

4.
Separation of parthenolide from feverfew: performance of conventional and high-pressure extraction techniques
Lucija Čretnik, Mojca Škerget, Željko Knez, 2005, izvirni znanstveni članek

Opis: In present work the extraction of feverfew flower heads was performed using supercritical carbon dioxide at pressures from 200 to 800 bar and at temperatures of 40, 60 and 80 °C. For comparison, the conventional extractionswith organic solvents have been performed. Dry feverfew flower heads were used as starting material. Supercritical fluid extraction (SFE) wasperformed using a semi continuous flow apparatus in a laboratory and pilot scale. The influence of process parameters on the total yield and amount of parthenolide isolated was investigated. Dynamic behaviour of the extraction runs followed by single-step separation was analysed by a mathematical model for initial constant rate extraction period and the subsequent time-dependant diffusion controlling mass transfer rate period. In order to concentrate the obtained extract in parthenolide, a two-step separation was employed.
Ključne besede: chemical processing, high pressure extraction, conventional extraction, supercritical CO2, parthenolide, feverfew, extraction rate, mass transfer
Objavljeno: 01.06.2012; Ogledov: 1239; Prenosov: 74
URL Povezava na celotno besedilo

5.
Extraction of phenolic compounds from elder berry and different grape marc varieties using organic solvents and/or supercritical carbon dioxide
Tünde Vatai, Mojca Škerget, Željko Knez, 2009, izvirni znanstveni članek

Opis: Optimal operating conditions for the extraction of phenolic compounds from grape marc and elder berry have been investigated. The aim was to obtain extracts with high anthocyanin content, which show stability during storage and would be potentially interesting for commercial applications as natural colorants. For this purpose three varieties of grape marc, native to Slovenia (Refošk, Merlot and Cabernet), were studied. The results were compared with the extraction of elder berry, which is known for its high anthocyanin content. Single-step batch extractions were performed with ethanol, ethyl-acetate and acetone in different ratios with water. Temperatures of 20 °C, 40 °C and 60 °C were applied. Influence of the change in pH values of the extraction media was investigated regarding the yield and degradation of anthocyanins. Two-step extractions, combining supercritical fluid extractions (SFE) and conventional batch extractions, were applied. The most efficient conventional solvents in single-step extractions were mixtures of organic solvent and water at 60 °C. Pre-treatment of the natural material with supercritical CO2 (with or without ethanol as co-solvent) improved the extraction of polyphenols from the grape marc. This method provides an alternative to the pre-treatment of the plant materials, replacing toxic organic solvents (e.g. hexane). Acidified extraction media resulted in higher anthocyanin content in the extracts. However, the degradation of the anthocyanins during storage was higher, which led to the loss of the intensive colour. The addition of a commercially available rosemary extract to the extraction solvent improved the stability of the grape marc extract during storage.
Ključne besede: extraction, organic solvents, supercritical CO2, anthocyanins, grape marc, elder berry, natural colorant
Objavljeno: 01.06.2012; Ogledov: 1175; Prenosov: 90
URL Povezava na celotno besedilo

6.
Isolation and Characterisation of Flavonoids From Citrus Peels
Katja Makovšek, 2013, doktorska disertacija

Opis: Citrus flavonoids are very interesting for food and pharmaceutical industry since they possess many antioxidant properties and biological activities. Mandarin peels represent an important source of hesperidin and polymethoxy flavones nobiletin and tangeretin. Pommelo peels represent an important source of naringin that can be used as precursor for naringin dihdydro-2,3-chalcone artificial sweetener. Since pommelo peels possess good antioxidant and antimicrobial properties, their extracts are very interesting products for food industry. Therefore isolation of flavonoid from mandarin and pommelo peels is an important topic of investigations. The investigation of the doctoral dissertation is divided in four parts. The first part is focused on the determination of the optimal conditions for the isolation of hesperidin and naringin from mandarin and pommelo peels by conventional extraction. The optimal conditions and the influence of extraction parameters are determined by Taguchi methodology. Very good isolation efficiency of hesperidin, 61.3 mg HES from 1 g of mandarin peels, was obtained by 70 % acetone solution and extraction conditions: 60 °C, 90 min, material to solvent ratio 1/50 g/mL and 3 stages of extraction. The highest amount of naringin, 32.8 mg NAR were isolated from 1 g of material at conditions: conventional extraction, 120 min, albedo, 60 % ethanol, material to solvent ratio 1/50 g/mL and 60 °C. The simple procedure of conventional extraction shows results comparable to more sophisticated methods such as extraction with microwave and ultrasound. Taguchi experimental design was proved to be an efficient methodology to determine the optimal conditions and the parameters that significantly influence product properties. The second part of the investigation focuses on the characterization of mandarin and pommelo peel extracts and their antioxidant properties. Radical scavenging activity against DPPH and antioxidant capacity of lipid soluble and water soluble compounds were determined for mandarin and pommelo extracts. Taguchi experimental design was applied for determination of the influence of extraction parameters on antioxidant properties. The optimal conditions to prepare extracts with high antioxidant properties were also determined. In the third part the investigation focuses on the concentration and separation of citrus flavonoids by extraction with supercritical fluids. Supercritical CO2 was applied for the separation of polymethoxylated flavones (PMF) and flavanone glycoside from mandarin peels. The optimal conditions and the parameter influence on the separation were determined by using Taguchi experimental design. The influence of supercritical fluid extraction parameters on material pre-treatment and isolation of flavonoids was studied. These investigations show that supercritical CO2 is a potential solvent for isolation and separation of PMF from mandarin peels. The fourth and last part of the investigation focuses on the concentration of flavonoids in extract solutions. Since membrane separation processes are very interesting concentration methods in industry, microfiltration, ultrafiltration, nanofiltration and revese osmosis were used for concentration of mandarin and pommelo peel extract solutions. Microfiltration and ultrafiltration could be used in the separation steps after extraction, since they did not influence the amount of dry material and valuable compounds in tested solutions. Reverse osmosis and nanofiltration were shown as useful methods for separation of solvent from extract solutions.
Ključne besede: Flavonoids, hesperidin, naringin, citrus peels, mandarin (Citrus reticulata), pommelo (Citrus maxima), conventional extraction, supercritical fluid extraction, membrane separation processes, Taguchi experimental design
Objavljeno: 22.04.2013; Ogledov: 2705; Prenosov: 330
.pdf Celotno besedilo (10,49 MB)

7.
“Thermodynamic and physical properties for high pressure process design”
Maša Knez Hrnčič, 2014, doktorska disertacija

Opis: The thesis is comprised of three main categories. The first part of dissertation covers investigations of phase equilibria of compounds from natural materials in conventional and also non conventional supercritical fluids. In details, the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion) is investigated, quantitative and qualitative analyses to evaluate and identify compounds contained after performing preliminary extraction experiments from different natural tissues are presented. The impact of operating parameters (pre-treatment of the raw material with SFE; different extraction solvents: propane, CO2, non conventional SCFs; different extraction temperatures and pressures) on extraction kinetics is observed. Following substances were taken into consideration: vanillins, caffeine, carnosoic acid extract and lecithin. Second part of dissertation covers studies of phase equilibria of the systems bio oil/gas, which is crucial in biorefinery process design. In this part of dissertation, which covers studies of phase equilibria of binary and ternary systems, the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion) for binary system bio oil/supercritical fluid (bio oil/CO2) and (bio oil/H2) was studied. Additionally, phase behaviour of ternary systems of (bio oil/diesel/CO2) and (bio oil/tail water/CO2) under the impact of pressure and/or temperature is observed. These data are of a high importance for bio refineries as an important part of necessary sustainable development. In recent years, studies on biodiesel synthesis have focused on development of process intensification technologies to resolve some of these issues. Fundamental data to design fractionation process of components of bio oil are crucial for an efficient hydrogenation process of bio oil. In the third part of dissertation observation of phase equilibria and determination of the parameters like diffusion coefficient, density and viscosity for the systems polymer/CO2 at elevated pressures is investigated. An overview of different methods applied to determine the parameters like diffusion coefficient, density and viscosity of the systems polymer (PEG)/CO2 at elevated pressures is offered. Observation of phase equilibria of the binary system PEG/CO2, determination of the impact of pressure and/or temperature on the system behaviour (miscibility, solubility, phase inversion), determination of thermodynamically and physically properties of the system with new applicative methods and finally, comparison of the results obtained by different methods is provided. The interfacial tension (IFT) at the (PEG)/CO2 interface has been determined by using an experimental technique developed to study the interfacial interactions of the liquids in equilibrium with gas in a glass-windowed equilibrium cell by the means of Capillary Rise (CR) method. Advantages and disadvantages of methods that were applied are exposed and discussed.
Ključne besede: phase equilibria, natural materials, conventional and non conventional supercritical fluids, extraction, bio oil, data for biorefinery process design, systems polymer (PEG)/CO2, diffusion coefficient, density, viscosity, surface tension, Capillary Rise (CR) method.
Objavljeno: 28.10.2014; Ogledov: 1594; Prenosov: 236
.pdf Celotno besedilo (4,46 MB)

8.
Extraction of lutein diesters from tagetes erecta using supercritical $CO_2$ and liquid propane
Mojca Škerget, Miran Bezjak, Katja Makovšek, Željko Knez, 2010, izvirni znanstveni članek

Opis: The efficiency of high pressure extraction of lutein diesters from marigold (Tagetes erecta) flower petals has been investigated. The solvents used for extraction were supercritical carbon dioxide and liquid propane. Operating parameters were 300 bar and 40, 60 and 80 °C for $CO_2$ and 100, 150, 200 bar and 40 and 60 °C for propane, respectively. The influence of process parameterson the total yield of extraction and content of lutein diesters in the extracts was investigated. The results show, that solvent power of propanefor lutein diesters is approximately 3.5 times higher than of $CO_2$. The calculation procedure based on the Fick's second law was applied to determine the diffusivities of lutein diesters during extraction from marigold flower petals for both extraction stages: a constant rate stage followed by a stage of decreasing rate. The mathematical model based on the Fick's second law well described the experimental extraction results.
Ključne besede: lutein diesters, Tagetes errecta, extraction, supercritical $CO_2$, subcritical propane
Objavljeno: 10.07.2015; Ogledov: 739; Prenosov: 49
.pdf Celotno besedilo (156,17 KB)
Gradivo ima več datotek! Več...

9.
OLEORESINI IZ RDEČE PEKOČE PAPRIKE - EKSTRAKCIJA IN UPORABA
Jana Simonovska, 2016, doktorska disertacija

Opis: Pepper (Capsicum annuum L.) as widely distributed vegetable crop in the world is an excellent source of nutritive and biologically active compounds. The characteristic compounds, capsaicinoids and carotenoids, highlight the importance of the red hot pepper varieties and their oleoresin extracts in the food and pharmaceutical industry. In the Ph.D. thesis was studied the possibility for a separate and integral utilization of the red hot pepper for obtaining the oleoresins from pericarp, placenta, seeds and stalk. Pre-treatment of the raw material (drying, separation of anatomical structures i.e. pericarp, placenta and seeds, and determination of theirs physico-chemical characteristics and determination of the he characteristic bioactive compounds: capsaicinoids, carotenoids and volatiles was studied, also. The second part of the Ph.D. thesis was focused of the determination of the optimal conditions for isolation of the bioactive capsaicinoids and coloured compounds, through comparative following of the thermodynamical parameters by application of organic solvents and supercritical fluids. Influence of the working parameters: temperature, time, pressure, solid to liquid phase ratio, density, type of solvents, and particle size of raw material on the yield of extract and content of capsaicinoids, colour compounds and volatiles was studied. Modelling of the experimental phase data by application of mathematical methods was performed. Re-utilization of seed and stalk from red hot pepper in form of extracts for development of new formulations as edible films, biopesticides and nanoemulsions was studied, also.
Ključne besede: red hot pepper, pericarp, placenta, seed, stalk, extraction, sub- and supercritical fluids, bioactive compounds, volatiles, re-utilization, edible films, biopesticides, nanoemulsions
Objavljeno: 08.11.2016; Ogledov: 1017; Prenosov: 85
.pdf Celotno besedilo (4,71 MB)

Iskanje izvedeno v 0.31 sek.
Na vrh
Logotipi partnerjev Univerza v Mariboru Univerza v Ljubljani Univerza na Primorskem Univerza v Novi Gorici