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1.
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: 1089; Prenosov: 30
URL Povezava na celotno besedilo

2.
Particle formation using supercritical fluids
Željko Knez, 2006, pregledni znanstveni članek

Opis: Particle formation and the design of solid particles and powdery composites with unique properties is at the moment one of major the developments of supercritical fluid (synonyms: dense gases, dense fluids, high pressure) applications. Conventional well-known processes for the particle-size redistribution of solid materials are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, in recrysfallization processes the product is contaminated with solvent and waste solvent streams are produced. The application of supercritical fluids may overcome the drawbacks of conventional processes, and powders and composites with special characteristics can be produced. Several processes for the formation and design of solid particles using dense gases have been studied intensively. The unique thermodynamic and fluid-dynamic properties of supercritical fluids can also be used for the impregnation of solid particles, for the formation of solid powderous emulsions, particle coatings, e.g. for the formation of solids with unique properties for use in different applications. This review will focus on the fundamentals and on recent advances of particle formation and design processes using supercritical fluids on their applications and the technological advantages and disadvantages of various processes.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno: 31.05.2012; Ogledov: 1246; Prenosov: 28
.pdf Celotno besedilo (514,21 KB)
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3.
The lipase-catalyzed synthesis of fatty acid fructose esters in organic media and in supercritical carbon dioxide
Saša Šabeder, Maja Leitgeb, Željko Knez, 2006, izvirni znanstveni članek

Opis: Sugar fatty acid esters are biodegradable surface active compounds in foodstuffs and cosmetics or pharmaceuticals. They have potential in replacing pollutant chemically synthesized surfactants. The enzymatic synthesis of fructose palmitate catalyzed by Candida antarctica B lipase was performed in different organic media in a batch react at atmospheric pressure. The influence of the organic solvent and temperature on the esterification was studied. Since supercritical carbon dioxide (SC CO2) has several advantages over organic solvents, such as high reaction rate, high mass transfer, non-toxicity, non flammability and low price, it was also chosen as a reaction medium for fructose palmitate production. The influence of temperature on immobilized lipase activity was studied at 10 MPa and the results were compared to the results obtained from reactions performed at atmospheric pressure under the same reaction conditions. The highest conversion (67%) was obtained after 24 hours of reaction in SC C02 at 80°C. A change of the particle size distribution and morphology of the untreated lipase and lipase treated with 2-methyl 2-butanol and SC C02 was observed. This article was presented at 1st SEECChE, held in Belgrade, September 25-28, 2005
Ključne besede: chemical processing, high pressure technology, supercritical CO2, lipase catalyzed syntheses, esterification, fructose palmitate, biocatalysts, lipase, Candida antarctica B
Objavljeno: 31.05.2012; Ogledov: 1341; Prenosov: 99
.pdf Celotno besedilo (392,53 KB)
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4.
Proteinase-catalyzed hydrolysis of casein at atmospheric pressure and in supercritical media
Mateja Primožič, Maja Leitgeb, Željko Knez, 2006, izvirni znanstveni članek

Opis: In the presented work, reaction parameters for hydrolysis of casein, catalyzed by Carica papaya latex at atmospheric and high pressure, were optimized. Casein is a remarkably efficient nutrient, supplying not only essential amino acids, but also some carbohydrates, calcium, phosphorus and therefore is very important for the food industry. Different reaction parameters such as temperature, stirring rate, casein and enzyme concentration were studied to found the optimal conditions for the reaction. Reactions were performed at atmospheric pressure; an influence of temperature/pressure on the casein hydrolysis in supercritical carbon dioxide (SC CO2) was also investigated to improve the reaction rates. Higher conversions were achieved when the reactions were performed in SC CO2, even though casein was not soluble in this medium.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, enzymatic reactions, proteinase, Carica papaya latex
Objavljeno: 31.05.2012; Ogledov: 934; Prenosov: 13
URL Povezava na celotno besedilo

5.
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: 1050; Prenosov: 18
URL Povezava na celotno besedilo

6.
Influence of temperature and pressure during PGSS[sup]TM micronization and storage time on degree of crystallinity and crystal forms of monostearate and tristearate
Zoran Mandžuka, Željko Knez, 2008, izvirni znanstveni članek

Opis: For controlling the degree of crystallinity and crystal form during particle formation using supercritical fluids, knowledge of pressure influence on solid-liquid-gas (S-L-G) equilibrium and solubility data of the system is crucial. S-L-G equilibrium data were determined in pressure range from 50 to 600 bar for systems monostearate/CO2 and tristearate/CO2 using a high-pressure view cell. Results showed a temperature minimum for both systems.The solubilities of CO2 in liquid glycerides were high: maximum solubilities, which were determined at temperatures 70 and 90 °C and pressure range from 50 to 450 bar, were from 50 to 90 mol%. Physical characteristics of micronized monostearate and tristearate samples were studied in detail after micronization and after 3 months of storage at 20 °C.
Ključne besede: chemical processing, high pressure technology, supercritical fluids, micronization, fine particles, Particles from Gas Saturated Solution, degree of crystallinity
Objavljeno: 31.05.2012; Ogledov: 1929; Prenosov: 23
URL Povezava na celotno besedilo

7.
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: 1042; Prenosov: 28
URL Povezava na celotno besedilo

8.
Influence of the aromatic ring substituents on phase equilibria of vanilins in binary system with CO2
Mojca Škerget, Lucija Čretnik, Željko Knez, Maja Škrinjar, 2005, izvirni znanstveni članek

Opis: Solid-liquid phase transitions of vanillin, ethylvanillin, o-vanillin and o-ethylvanillin in presence of compressed CO2 were determined with the modified capillary method. Furthermore, the solubilities of the above mentioned vanillins in supercritical CO2 were measured at 313.2, 333.2 and 353.2 K and in the pressure range 8-30 MPa using a static-analytic method. The experimental equilibrium solubility data have been fitted to the Peng-Robinson equation in combination with two parameter van der Waals mixing rules and binary parameters were determined from the best fit. Results showed that the phase equilibria of vanillins in dense CO2 are influenced by the position of the hydroxyl group bound to the aromatic ring. Under the pressure of CO2 the melting point depression and also the solubility of both o-vanillins was higher than those of p-vanillins. Oppositely, the alchoxy group (methoxy or ethoxy) showed no significant influence on the solubility of vanillins.
Ključne besede: chemical processing, high pressure technology, CO2, phase equilibria, vanillin isomers, data, ring substituents
Objavljeno: 01.06.2012; Ogledov: 1153; Prenosov: 27
URL Povezava na celotno besedilo

9.
Phase equilibira of permethrin and dicofol with carbon dioxide
Petra Kotnik, Amra Perva-Uzunalić, Mojca Škerget, Željko Knez, 2005, izvirni znanstveni članek

Opis: The solubilities of pesticides (permethrin and dicofol) in CO2 were measured by a static-analytic method at pressures ranging from 10.0 MPa to 25.0 MPa andtemperatures of 293.2 K, 303.2 K, and 313.2 K. Due to the nonconventional shape of some solubility isotherms, solid-liquid transitions of pesticides under pressure of CO2 were determined using a modified capillary method. Sincethe solubilities depend on solvent density, the experimental binary solid-fluid equilibrium data were correlated as a function of solvent density by two different models.
Ključne besede: chemical processing, high pressure technology, CO2, pesticides, phase equilibria, solubility
Objavljeno: 01.06.2012; Ogledov: 948; Prenosov: 20
URL Povezava na celotno besedilo

10.
Comparison of the esterification of fructose and palmitic acid in organic solvent and supercritical carbon dioxide
Saša Šabeder, Maja Leitgeb, Željko Knez, 2005, izvirni znanstveni članek

Opis: Sugar fatty acid esters are nonionic surfactants, which are used for personal care products, cosmetic applications, and as emulsifiers for food. In recent years, enzymatic synthesis of sugar fatty acid esters is attracting keen attention as a new manufacturing method for future application. Reaction parameters of lipase-catalyzed synthesis of fructose fatty acid esters in organic solvent were optimized in a batch reactor at atmospheric pressure. Optimum conditions for reaction performed in organic solvent at atmospheric pressure were 10% (wžw of substrates) of lipase from Candida antarctica B, 12.14% (wžw of reaction mixture) of molecular sieves at 60 C, and stirring rate of 600 rpm. Esterification of fructose and palmitic acid was performed insupercritical carbon dioxide with and without addition of cosolvent (organicsolvent) at 60 C. Effect of pressure on enzyme activity was studied.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, esterification, organic solvent, lipase catalysed synthesis, fructose fatty esters, Candida antarctica B, enzyme activity
Objavljeno: 01.06.2012; Ogledov: 1113; Prenosov: 23
URL Povezava na celotno besedilo

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