1. Hop (Humulus lupulus L.) essential oils and xanthohumol derived from extraction process using solvents of different polarityKatja Bizaj, Mojca Škerget, Iztok Jože Košir, Željko Knez, 2022, izvirni znanstveni članek Opis: This study evaluates the content of essential oils (EOs) and prenylated flavonoid Xanthohumol (XN) in extracts of Slovenian hops, cultivar Aurora, obtained by using fluids of different polarity. It is a continuation of our previous work, investigating the extraction of bitter acids from hops. Extraction was conducted semi-continuously, using sub- and supercritical fluids of different polarity, i.e., carbon dioxide (CO2) and propane as non-polar and dimethyl ether (DME) as the polar solvent. The experiments explored a temperature range between 20 °C and 80 °C and pressures ranging from 50 bar to 150 bar. The content of XN in extracts was analysed using high-performance liquid chromatography and experiments demonstrated the largest concentration of XN was obtained using DME. In order to analyse the EO components in extracts, connected with a distinct odour, the steam distillation of extracts was performed and GC analysis was employed. Hop oil derived from CO2 extracts at specific conditions, had the highest relative concentration of linalool, β-caryophyllene and α-humulene, and oil derived from propane extracts had the highest content of all other five selected components (myrcene, geraniol, farnesene, α-selinene and δ-cadinene). The relative content of the investigated EO components in DME extracts was similar to that in propane extracts.
Ključne besede: hop extract, hop essential oils, flavonoids, carbon dioxide, propane, dimethyl ether
Objavljeno v DKUM: 17.08.2023; Ogledov: 355; Prenosov: 47
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2. Extraction of lutein diesters from tagetes erecta using supercritical $CO_2$ and liquid propaneMojca 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 v DKUM: 10.07.2015; Ogledov: 1504; Prenosov: 137
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3. Silica aerogels as support for lipase catalyzed esterifications at sub- and supercritical conditionsZoran Novak, Maja Leitgeb, Vlasta Krmelj, Željko Knez, 2003, izvirni znanstveni članek Opis: The enzymes (lipases from Candida rugosa and porcine pancreas) were immobilized on silica aerogels by sol-gel procedure followed by supercritical drying with CO2. Such immobilized enzymes were used as biocatalysts for esterification in supercritical CO2 and near critical propane at 40 °C and 100 bar. It was found out that the initial reaction rates in propane rose two to three times in comparison with the same reaction, catalyzed by free lipase. SC CO2 deactivated the non-immobilized lipase in reaction mixture while with the immobilized enzyme the conversion was 35%. The initial reaction rates in propane were 20 times higher than in water medium due to the properties of propane as a medium for esterification of fatty acids.
Ključne besede: chemical processing, biotechnology, esterification, immobilization of enzymes, supercritial CO2, propane, lipases, supercritical CO2 drying
Objavljeno v DKUM: 01.06.2012; Ogledov: 1868; Prenosov: 29
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4. An approach to calculate thermodynamic properties of mixtures including Propane, n-Butane, and IsobutaneJurij Avsec, Koichi Watanabe, 2005, izvirni znanstveni članek Opis: This paper discusses a mathematical model for computing the thermodynamic properties of propane, n-butane, isobutane, and their mixtures, in the fluid phase using a method based upon statistical chain theory. The constants necessary for computations such as the characteristic temperatures of rotation, electronic state, etc. and the moments of inertia are obtained analytically applying a knowledge of the atomic structure of the molecule. The paper presents a procedure for calculating thermodynamic properties such aspressure, speed of sound, the Joule-Thomson coefficient, compressibility, enthalpy, and thermal expansion coefficient. This paper will discuss, for the first time, the application of statistical chain theory for accurate properties of binary and ternary mixtures including propane, n-butane, and isobutane, in their entire fluid phases. To calculate the thermodynamic properties of Lennard-Jones chains, the Liu-Li-Lu model has been used. The thermodynamic properties of the hydrocarbon mixtures are obtained using the one-fluid theory.
Ključne besede: statistical thermodynamics, chain theory, mixtures, transport properties, hydrocarbons, isobutane, n-butane, propane, refrigerants
Objavljeno v DKUM: 01.06.2012; Ogledov: 2154; Prenosov: 106
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5. Statistical approach to calculate thermodynamic properties for propaneJurij Avsec, K. A... Watanabe, 2005, izvirni znanstveni članek Opis: The paper describes a mathematical model to compute equilibrium thermodynamic properties in the fluid phase of pure hydrocarbons with the aid of classical thermodynamics and statistical associating chain theories. In the present paper thermodynamic properties for propane, as an example of hydrocarbon substances, are calculated. To calculate the thermodynamic properties of real fluids, models based on the Lennard-Jones intermolecular potential were applied. To calculate the thermodynamic properties of real fluids with the aid of classical thermodynamics, Miyamoto-Watanabe (MW) equations, developed in terms of the Helmholtz energy were used. Analytical results obtained by statistical thermodynamics are compared with the MW model and show relatively good agreement.
Ključne besede: statistical thermodynamics, propane, thermodynamic properties, SAFT model, chain theory
Objavljeno v DKUM: 01.06.2012; Ogledov: 1917; Prenosov: 85
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6. Preparation of enantiomers using high pressure technologiesPaul 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 v DKUM: 02.02.2011; Ogledov: 3039; Prenosov: 139
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