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1.
2.
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: 1091; Prenosov: 30
URL Povezava na celotno besedilo

3.
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: 1051; Prenosov: 18
URL Povezava na celotno besedilo

4.
Concentration of free fatty acids in rapeseed oil
Petra Kotnik, Mojca Škerget, Željko Knez, 2012, objavljeni znanstveni prispevek na konferenci

Ključne besede: materials, methods, vegetable oils
Objavljeno: 01.06.2012; Ogledov: 908; Prenosov: 12
URL Povezava na celotno besedilo

5.
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: 949; Prenosov: 20
URL Povezava na celotno besedilo

6.
Phenols, proanthocyanidins, flavones and flavonols in some plant materials and their antioxidant activities
Mojca Škerget, Petra Kotnik, Majda Hadolin Kolar, Andreja Rižner Hraš, Marjana Simonič, Željko Knez, 2005, izvirni znanstveni članek

Opis: Methanol extracts prepared from five plant materials native to the Mediterranean area, namely olive tree (Olea europaea) leaf, St. John's wort (Hypericum perforatum), hawthorn (Crataegus laevigata), oregano (Origanum vulgare) and laurel leaf (Lauris nobilis), were examined for their phenolic components. Total phenolic content was determined by the Folin-Ciocalteu method. The content of proanthocyanidins in acid-hydrolysed extracts was determined spectrophotometrically. The contents of free flavones (apigenin andluteolin) and flavonols (kaempferol, myricetin and quercetin) were determined by HPLC analysis. The time of hydrolysis of flavones, flavonols andproanthocyanidins was optimised. Antioxidant activities of apigenin, luteolin, kaempferol, myricetin, quercetin and of plant extracts were examined. Antioxidative activities were studied in sunflower oil at 98 °C, by measuring peroxide value, and in an aqueous emulsion system of -carotene and linoleic acid by measuring the absorbance of the sample. Among flavones and flavonols investigated, only myricetin inhibited oxidation of sunflower oil. All other flavones and flavonols showed pro-oxidative activity. Oppositely, in the emulsion system, only apigenin showed pro-oxidative activity while otherflavones and flavonols and plant extracts inhibited oxidation of -carotene.
Ključne besede: chemical processing, extraction, plant material, fenolic content, hidrolysis, antioxidants, flavones, flavonols, proanthocyanidines, oils, emulsions
Objavljeno: 01.06.2012; Ogledov: 1232; Prenosov: 41
URL Povezava na celotno besedilo

7.
Preparation of WO[sub]3 aerogel catalysts using supercritical CO[sub]2
Zoran Novak, Petra Kotnik, Željko Knez, 2004, izvirni znanstveni članek

Opis: Single tungsten oxide aerogels (WO3), binary oxide aerogels (WO3-Al2O3) and ternary oxide aerogels (WO3-SiO2-Al2O3) were prepared using standard sol-gel route. Tungsten oxide tetraethoxide (WO(OCH2CH3)4) was used as the sol-gel precursor. The excellent properties of the gels obtained by the sol-gel synthesis were preserved upon supercritical drying with CO2. After supercritical drying at 40 °C and 100 bar, all aerogels were calcined to 800 °C. The influence of the synthesis parameters on the catalytic activity of WO3as supported on silica andžor alumina aerogels was investigated through thetransformation of N-(phosphonomethyl)iminodiacetic acid to N-(phosphonomethyl)glycine. Despite including WO3 into single and mixed silicaand alumina aerogels, high specific surface areas (284-653 m2 g-1) were preserved. Higher conversion was obtained for catalysts with higher ratios of WO3 in the mixed silica-alumina aerogels that were calcined at 800 °C.
Ključne besede: chemical processing, aerogels, catalysts, tungsten oxides, preparation of aerogels, characterisation of aerogels, supercritical CO2, supercritical drying, high pressure technology
Objavljeno: 01.06.2012; Ogledov: 1087; Prenosov: 19
URL Povezava na celotno besedilo

8.
Phase equilibria in systems containing [alpha]-tocopherol and dense gas
Mojca Škerget, Petra Kotnik, Željko Knez, 2003, izvirni znanstveni članek

Opis: Solubility of ▫$alpha$▫-tocopherol in CO2 and propane was determined at temperatures 303, 313, 333 and 353 K and over a pressure range from 79 to 286 bar for CO2 and 16 to 112 bar for propane. A static-analytic method was applied. The solubility of ▫$alpha$▫-tocopherol in dense CO2 under the conditions investigated was in the range of 0.2-17.0 mg/g CO2. The maximal solubilities of ▫$alpha$▫-tocopherol in propane were approximately up to ten times higher than in CO2 and were in the range from 38.9 to 171.9 mg/g propane. Phase equilibrium data for Milk Thistle seed oil in supercritical CO2 were determined at temperatures 313, 333 and 353 K and pressures ranging from 100 to 300 bar. The oil was previously additionally vitaminized and contained 1.9 wt.% of ▫$alpha$▫-tocopherol and 1.7 wt.% of free fatty acids (FFA). The solubility of oil in CO2 was in the range from 1.3 to 17.9 mg/g CO2. The distribution coefficients of ▫$alpha$▫-tocopherol and FFA between light and heavy phase were determined on a solvent free basis. The obtained separation factors increased with temperature and pressure to approximately 160-200 bar and decreased with a further increase of pressure.
Ključne besede: chemical processing, supercritical fluids, phase equilibria, separation factors, vitamin E, CO2, dense gases
Objavljeno: 01.06.2012; Ogledov: 940; Prenosov: 16
URL Povezava na celotno besedilo

9.
Načrtovanje visokotlačne separacije maščobnih kislin iz rastlinskih olj
Petra Kotnik, 2014, doktorska disertacija

Opis: Predstavljeno delo obravnava raziskave na področju faznih ravnotežij, ekstrakcije in frakcioniranja maščobnih kislin v rastlinskih oljih, obogatenih s prostimi maščobnimi kislinami (FFA) pri visokih tlakih v inertnem mediju, kot je ogljikov dioksid (CO2). Podatki so ključni za nadaljnje načrtovanje visokotlačnih separacijskih procesov, saj pripomorejo k izboljšanju določenih industrijskih procesov v smeri okoljevarstva in kvalitete proizvodov. Baze podatkov že vsebujejo podatke faznih ravnotežij za sistem rastlinska olja – CO2. Zaradi širokega izbora rastlinskih olj, ki se danes nahajajo na tržišču, podatki o faznih ravnotežjih za vsa olja niso dostopni. Predvsem v literaturi ni podatkov za fazna ravnotežja pri tlakih višjih od 350 bar in podatkov o faznih inverzijah v sistemih rastlinsko olje – CO2. Delo je tako omejeno na tri rastlinska olja, ki so komercialno dostopna, to so repično olje, olje koruznih kalčkov in olje boraga. Olja so predhodno obdelana s postopkom umiljenja in na ta način obogatena s prostimi maščobnimi kislinami. Meritve faznih ravnotežij in opazovanja faznih inverzij so izvedena na sistemih FFA-obogateno repično olje – CO2, FFA-obogateno olje koruznih kalčkov – CO2 in FFA-obogateno olje boraga – CO2 v območju tlakov med 100 in 550 bar in temperaturah 35, 45, 65 in 85 °C. Vsebnost maščobnih kislin smo določili s plinsko kromatografijo in na podlagi dobljenih rezultatov določili porazdelitvene koeficiente in separacijske faktorje. Raziskave visokotlačne ekstrakcije olja iz semen s CO2 smo izvedeli na dveh naravnih materialih z visoko vsebnostjo prostih maščobnih kislin, to so semena boraga (Borago officinalis L.) in semena nočnega svetlina (Oenthera biennis L.) pri tlaku 200 in 300 bar in temperaturah 40 in 60 °C. Ekstrakcijske krivulje smo ovrednotili z dvema matematičnima modeloma, ki kar najbolje opišeta potek ekstrakcijske krivulje v območju stacionarnega prenosa snovi in v območju nestacionarnega prenosa snovi. Zaključek raziskave predstavlja frakcioniranje repičnega olja v smeri izolacije -linolenske kisline in koncentriranja FFA in -sitosterola v oljih. Pri koncentriranju FFA smo uporabili dva postopka, prvi je superkritična ekstrakcija v dveh stopnjah, ki daje zadovoljive rezultate v primerjavi s konvencionalno metodo kolonske kromatografije.
Ključne besede: fazno ravnotežje, ekstrakcija, separacija, ogljikov dioksid, rastlinska olja, proste maščobne kisline, beta-sitosterol, gamma-linolenska kislina
Objavljeno: 12.06.2014; Ogledov: 1173; Prenosov: 156
.pdf Celotno besedilo (2,97 MB)

10.
Preventiva samomora pri mladostnikih
Petra Kotnik, 2014, diplomsko delo/naloga

Opis: Samomor je vzrok številnim smrtim. Zasledimo ga v različnih literaturah, tako strokovnih, kot laičnih. Samomor predstavlja zelo visoko smrtnost v svetu. Zaradi samomora ljudje umirajo, tako kot za ostalimi boleznimi, ki ogrožajo prebivalstvo. Velik problem je samomor med mladimi, ki so občutljiva skupina, ki samomorilne namene kažejo z drugačnimi znaki, kot odrasle in starejše osebe. Tako kot strokovnjaki bi tudi laiki morali poznati vzroke, dejavnike tveganja in nasploh poznati starostne skupine ljudi, kako se v takih situacijah obnašajo. S tem bi naredili prvi korak k preprečevanju samomora. V diplomskem delu so predstavljene različne starostne skupine, iz česar je razvidno, da mladostniki samomorilne namene sporočajo s svojim vedenjem. Pri mladostnikih je veliko tudi samomorilnih misli, več kot pri ostalih odraslih osebah. Iz literature je razvidno, da so depresivne motnje najpogostejši vzrok samomora pri mladih, simptomi depresije prepoznamo lahko že pri otrocih. Predstavljeni so vzroki samomora, zgodovina samomora, sociološki pogled na samomor in preventiva s strani medicinske sestre. Ugotovili smo, da se ves proces preventive samomora začne s pogovorom in poslušanjem bolnika, medicinska sestra pa je tista, ki je z bolnikom največ v stiku in si najprej pridobi njegovo zaupanje. Preventivno lahko delujejo tudi vsi ostali, najbolj pomembno pa je biti seznanjen o samomoru, o čemer se še premalo govori.
Ključne besede: samomor, mladostnik, samomorilne misli, depresija, sociološki pogled na samomor, preventiva samomora, medicinska sestra.
Objavljeno: 18.07.2014; Ogledov: 1089; Prenosov: 206
.pdf Celotno besedilo (1,34 MB)

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