| | SLO | ENG | Cookies and privacy

Bigger font | Smaller font

Search the digital library catalog Help

Query: search in
search in
search in
search in
* old and bologna study programme

Options:
  Reset


1 - 10 / 13
First pagePrevious page12Next pageLast page
1.
Preparation of enantiomers using high pressure technologies
Paul Thorey, 2010, dissertation

Abstract: 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%).
Keywords: 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
Published: 02.02.2011; Views: 2065; Downloads: 66
.pdf Full text (6,25 MB)

2.
Enzyme-catalyzed reactions in different types of high-pressure enzymatic reactors
Mateja Primožič, Maja Leitgeb, Muzafera Paljevac, Željko Knez, 2006, original scientific article

Abstract: The enzyme-catalyzed hydrolysis of carboxy-methyl cellulose (CMC) was performed in three different types of reactors; in a batch stirred-tank reactor (BSTR) operating at atmospheric pressure, in a high-pressure batch stirred-tank reactor (HP BSTR) and in a high-pressure continuous tubular-membrane reactor (HP CTMR). In the high-pressure reactors aqueous SC C02 was used as the reaction medium. The aim of our research was optimization of the reaction parameters for reaction performance. All the reactions were catalyzed by cellulase from Humicola insolens. Glucose production in the high-pressure batch stirred-tank reactor was faster than in the BSTR at atmospheric pressure. The optimal temperature for the reaction performed in the BSTR at atmospheric pressure was 30°C, while the optimal temperature for the reaction performed in SC C02 was 32°C. The influence of the application of tubular ceramic membranes in the high-pressure reaction system was studied on the model reaction of CMC hydrolysis at atmospheric pressure and in SC C02. The reaction was catalyzed by cellulase from Humicola insolens covalently linked to the surface of the ceramic membrane. The hydrolysis of CMC in SC C02 and at atmospheric pressure was performed for a long time period. The reaction carried out in SC C02 was more productive than the reaction performed at atmospheric pressure.
Keywords: chemical processing, enzymatic reaction, cellulase, supercritical carbon dioxide, high-pressure batch reactor, high-pressure membrane reactor
Published: 31.05.2012; Views: 1135; Downloads: 163
.pdf Full text (454,51 KB)
This document has many files! More...

3.
4.
Supercritical fluids as solvents for enzymatic reactions
Maja Leitgeb, Mateja Primožič, Željko Knez, 2007, review article

Abstract: Enzymes may act in different solvent systems. Water as the solvent in vivo may be replaced partially or mostly with other solvents, such as micro-emulsions, organic solvents, reversed micelles, ionic liquids and supercritical fluids (SCFs).Several types of enzymatic reactions were performed in SCFs. Influence of SCFs on enzyme stability and activity is presented on different examples; on different reaction systems (hydrolysis, transesterification...) and on the use of non-immobilized (Subtilisin carlsberg, Aspergillus niger...) as well as immobilized enzymes. Several types of high-pressure enzymatic reactors (batch-, stirred-tank-, extractive semibatch-, recirculating batch-, semicontinuous flow-, continuous packed-bed-, and continuous-membrane reactors) have been used for the performance of enzymatic reactions. In the studies on stability of biocatalysts in a high-pressure batch-stirred tank reactor changes in biocatalysts activity due to pressurization/depressurization steps were observed. Interesting alternative to overcome this inconvenience is the use of the high-pressure continuous membrane reactors, where just single compression and expansion step is necessary.
Keywords: enzymatic reactions, supercritical carbon dioxide, high-pressure, enzyme stability, high-pressure reactors
Published: 31.05.2012; Views: 1299; Downloads: 51
.pdf Full text (177,49 KB)
This document has many files! More...

5.
6.
Lipase-catalyzed transesterification of (R,S)-1-phenylethanol in SC $CO_2$ and in SC $CO_2$/ionic liquid systems
Muzafera Paljevac, Željko Knez, Maja Leitgeb, 2009, original scientific article

Abstract: Commercial immobilized lipase B from Candida antarctica (CALB) was successfully applied to catalyzing the transesterification of (R,S)-1-phenylethanol in supercritical carbon dioxide and in supercritical carbon dioxide/ionic liquid biphasic system. Firstly, the variables affecting the performance of CALB in transesterification reactions in supercritical carbon dioxide, such as CALB concentration, temperature and pressure, were studied. An increase in the conversion and in the reaction rate was observed as the CALB/substrate ratio, temperature and pressure, were increased from 4.3 to 19.9, from 40 °C to 80 °C and from 8 MPa to 10 MPa, respectively. Further increase in temperature from 80 °C to 120 °C and pressure from 10 MPa to 30 MPa resulted in lower conversion and lower initial reaction rate. Furthermore, different vinyl esters were used as acyl donors for CALB-catalyzed transesterification of (R,S)-1-phenylethanol in supercritical carbon dioxide. The highest initial reaction rate was attained with vinyl butyrate, although 50% conversion was attained faster when vinyl acetate was used as acyl donor. Secondly, in transesterification of (R,S)-1-phenylethanol, performed in supercritical carbon dioxide/ionic liquid biphasic system, influence of concentration of 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF$_4$] was studied. The addition of 50 mmol (70% w/w reaction mixture) of [bmim][BF$_4$] to the reaction system gave the best result in terms of transesterification rate.
Keywords: candida antarctica lipase B, transesterification, (R, S)-1-phenylethanol, ionic liquids, vinyl acetate, supercritical carbon dioxide
Published: 31.05.2012; Views: 1396; Downloads: 42
.pdf Full text (446,49 KB)
This document has many files! More...

7.
Chemical composition of Juniperus communis L. fruits supercritical CO2 extracts: dependence on pressure and extraction time
Branislava Barjaktarović, Milan Sovilj, Željko Knez, 2005, original scientific article

Abstract: 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.
Keywords: chemical processing, high pressure technology, CO2, supercritical fluid extraction, pressure, extraction time, Juniperus communis, oxygenated terpenes, juniper berry oil, carbon dioxide
Published: 01.06.2012; Views: 1114; Downloads: 29
URL Link to full text

8.
Thermodynamic properties of coenzyme Q10 in supercritical carbon dioxide
Darja Pečar, Valter Doleček, 2007, original scientific article

Abstract: The densities of coenzyme Q10 in supercritical carbon dioxide were measured at 308.15, 313.15, 323.15 and 333.15 K and in the pressure range from 10 to 40 MPa with the vibrating tube densimeter. The reliability of the technique has been verified in our previous works and in the present work it was checked comparing our experimental densities of pure carbon dioxide with literature data. The partial molar volumes, isothermal compressibilities, isobaric thermal expansivities, internal pressures and cluster sizes were calculated from obtained densities.
Keywords: koenzim Q10, density measurements, partial molar volume, isothermal compressibility, isobaric thermal expansivity, internal pressure, supercritical carbon dioxide
Published: 01.06.2012; Views: 934; Downloads: 51
URL Link to full text

9.
HIGH PRESSURE PHASE EQUILIBRIUM OF THE BINARY SYSTEM TWEEN 80 AND CARBON DIOXIDE
Natalija Novak, 2014, undergraduate thesis

Abstract: In the frame of the diploma thesis we researched the phase equilibrium of the binary system Tween 80 and CO2. Equilibrium compositions of the system have been determined with a static analytical method at temperature 40, 60 and 80 °C and pressures up to 300 bar. The obtained data was plotted in isothermal diagrams where mass percentage is presented as a function of pressure. In this work also the viscosity of Tween 80 was determined in the temperature range between 20 and 80°C and shear rates up to 180 s-1. The measurements were obtained by using coaxial cylinder and compared with available literature data.
Keywords: supercritical fluids, phase equilibrium, carbon dioxide, Tween 80
Published: 22.04.2014; Views: 986; Downloads: 41
.pdf Full text (2,34 MB)

10.
Search done in 0.26 sec.
Back to top
Logos of partners University of Maribor University of Ljubljana University of Primorska University of Nova Gorica