1. Influence of supercritical carbon dioxide on the activity and conformational changes of α-amylase, lipase, and peroxidase in the solid state using white wheat flour as an exampleMilena Ivanović, Željko Knez, Maja Leitgeb, 2023, original scientific article Keywords: enzyme inactivation, supercritical carbon dioxide, a-amilaze, lipase, antioxidants, horseradish peroxidase, structural changes, CD spectroscopy
Published in DKUM: 22.04.2024; Views: 183; Downloads: 8
 Full text (4,96 MB)
This document has many files! More... |
2. Sustainable processing of materials using supercritical fluids : doktorska disertacijaDragana Borjan, 2022, doctoral dissertation Abstract: Supercritical fluids (SCFs) are powerful solvents with many unique properties. They have great potential for many processes, from extraction to chemical reactions and recycling. Accordingly, phase equilibrium data and thermodynamic and transport properties measurements in systems with a supercritical phase, as well as reliable and versatile mathematical models of the phase equilibrium thermodynamics, are needed for the process design and economic feasibility studies. The dissertation focuses on the benefits of supercritical fluid technology and consists of three main sections.
The first section includes studies of the phase equilibria of the binary gas-alcohol and gas-urea derivatives. The influence of pressure and temperature on the system behaviour (solubility, viscosity, density, interfacial tension, melting point curve) was investigated. Most of the experiments were carried out with a high-pressure optical view cell, with minor modifications of the apparatus and measurement principle to determine mentioned thermodynamic and transport properties.
The second part of the dissertation deals with the recovery of extracts from natural materials. Special interest is oriented towards supercritical fluid extracts, characterised by strong biological activities, especially antimicrobial and antioxidant properties. Supercritical fluid extraction has been performed on a semi-continuous apparatus (at pressures of 150 bar and 250 bar and temperatures of 313.15 K and 333.15 K for oregano extraction; and at pressures of 100 bar and 300 bar and temperatures of 313.15 K and 333.15 K for red beetroot extraction) and various methods such as the microdilution method and the DPPH method were used to determine antimicrobial and antioxidant activity.
In the third part, an overview of different methods for recycling carbon fibre reinforced composites is given, including chemical recycling with supercritical fluids. This field has not been well explored, and the approach is relatively new but very interesting from a sustainable point of view. For an economically feasible process design, the thermodynamic and mass transfer data have to be determined. The principles of the future lab- and pilot-scale operations demand these supporting data be known.
The results obtained in the frame of this study represent the high added value in the scientific field. They are essential to design and modify processes that yield products that cannot be achieved with conventional production processes.
Keywords: supercritical fluids, alcohols, urea, phase equilibria, viscosity, density, interfacial tension, modified capillary method, isolation methods, supercritical fluid extraction, pharmacological activity, carbon fiber reinforced composites, recycling techniques
Published in DKUM: 11.10.2022; Views: 1029; Downloads: 141
Full text (4,64 MB) |
3. High-Perssure process design for polymer treatment and heat transfer enhancementGregor Kravanja, 2018, doctoral dissertation Abstract: The doctoral thesis presents the design of several high-pressure processes involving »green solvents« so-called supercritical fluids for the eco-friendly and sustainable production of new products with special characteristics, fewer toxic residues, and low energy consumption. The thesis is divided into three main parts: polymer processing and formulation of active drugs, measurements of transport properties form pendant drop geometry, and study of heat transfer under supercritical conditions.
In the first part, special attention is given to using biodegradable polymers in particle size reduction processes that are related to pharmaceutical applications for controlled drug release. The PGSSTM micronization process was applied to the biodegradable carrier materials polyoxyethylene stearyl ether (Brij 100 and Brij 50) and polyethylene glycol (PEG 4000) for the incorporation of the insoluble drugs nimodipine, fenofibrate, o-vanillin, and esomeprazole with the purpose of improving their bioavailability and dissolution rate. In order to optimize and design micronization process, preliminary transfer and thermodynamic experiments of water-soluble carriers (Brij and PEG)/ SCFs system were carried out. It was observed that a combination of process parameters, including particle size reduction and interactions between drugs and hydrophilic carriers, contributed to enhancing the dissolution rates of precipitated solid particles.
In the second part, a new optimized experimental setup based on pendant drop tensiometry was developed and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. Droplet geometry was examined by using a precise computer algorithm that fits the Young–Laplace equation to the axisymmetric shape of a drop. The experimental procedure was validated by a comparison of the experimental data for the water-CO2 mixture with data from the literature. For the first time, interfacial tension of CO2 saturated solution with propylene glycol and diffusion coefficients of propylene glycol in supercritical CO2 at temperatures of 120°C and 150°C in a pressure range from 5 MPa, up to 17.5 MPa were measured.
Additionally, the drop tensiometry method was applied for measuring systems that are of great importance in carbon sequestration related applications. The effect of argon as a co-contaminant in a CO2 stream on the interfacial tension, diffusion coefficients, and storage capacity was studied.
In the third part, comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture at high pressures and temperatures was studied. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 °C to 90 °C) and pressures (5 MPa to 30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the heat transfer coefficients (HTC) of supercritical CO2, ethane and their azeotropic mixture in water loop have been measured and compared. A brief evaluation is provided of the effect of mass flux, heat flux, pressure, temperature and buoyancy force on heat transfer coefficients. Additionally, to properly evaluate the potential and the performance of azeotropic mixture CO2-ethane, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system containing exclusively CO2.
Keywords: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients
Published in DKUM: 28.05.2018; Views: 1682; Downloads: 227
Full text (5,51 MB) |
4. Use of non-conventional cell disruption method for extraction of proteins from black yeastsMaja Čolnik, Mateja Primožič, Željko Knez, Maja Leitgeb, 2016, original scientific article Abstract: The influence of pressure and treatment time on cells disruption of different black yeasts and on activities of extracted proteins using supercritical carbon dioxide process was studied. The cells of three different black yeasts Phaeotheca triangularis, Trimatostroma salinum, and Wallemia ichthyophaga were exposed to supercritical carbon dioxide (SC $CO_2$) by varying pressure at fixed temperature (35°C). The black yeasts cell walls were disrupted, and the content of the cells was spilled into the liquid medium. The impact of SC $CO_2$ conditions on secretion of enzymes and proteins from black yeast cells suspension was studied. The residual activity of the enzymes cellulase, $beta$-glucosidase, $alpha$-amylase, and protease was studied by enzymatic assay. The viability of black yeast cells was determined by measuring the optical density of the cell suspension at 600 nm. The total protein concentration in the suspension was determined on UV–Vis spectrophotometer at 595 nm. The release of intracellular and extracellular products from black yeast cells was achieved. Also, the observation by an environmental scanning electron microscopy shows major morphological changes with SC $CO_2$-treated cells. The advantages of the proposed method are in a simple use, which is also possible for heat-sensitive materials on one hand and on the other hand integration of the extraction of enzymes and their use in biocatalytical reactions.
Keywords: P. triangularis, W. ichtyophaga, T. salinum, supercritical carbon dioxide, enzyme activity, cells
Published in DKUM: 10.07.2017; Views: 1546; Downloads: 390
Full text (2,13 MB)
This document has many files! More... |
5. Phase equilibrium measurements and data correlation for the ternary system oleic acid + 1-octanol + carbon dioxideChiara Giulia Laudani, Mateja Primožič, Željko Knez, Maja Leitgeb, 2009, original scientific article Abstract: A study of the high-pressure phase equilibria in the ternary system oleic acid/1- octanol/supercritical CO2 was performed to obtain information for optimization of enzymatic synthesis of n-octyl oleate. Equilibrium data were measured at temperatures of 308.15, 323.15 and 343.15 K over a pressure range from 1 to 25 MPa. Two different apparatuses: a Variable Volume View Cell and a Batch Stirred Tank were used employing synthetic and static-analytic measurement methods, respectively. The measured solubility of dense CO2 in the binary liquid mixture oleic acid/1-octanol covered the range from 0.0781 to 0.7686 of CO2 molar fraction. CO2 solubility increased with increasing pressure up to 10 MPa. At higher pressures, no significant increase was observed. The Soave-Redlich-Kwong equation-of-state (SRK-EoS) with quadratic mixing rules was successfully used for data correlation in the whole P-T-x region studied.
Keywords: data correlation, 1-octanol, oleic acid, supercritical carbon dioxide, Soave-Redlich-Kwong equation-of-state, vapor-liquid equilibria
Published in DKUM: 05.07.2017; Views: 1558; Downloads: 118
Full text (3,35 MB)
This document has many files! More... |
6. Enzymatic esterification of glycerol and stearic acid in non-conventional mediaZsófia Csanádi, Katalin Bélafi-Bakó, Eszter Szentgyörgyi, László Gubicza, Željko Knez, Maja Leitgeb, 2010, original scientific article Abstract: Ionic liquids as trihexyl-tetradecyl-phophonium-dicyanamide (Cyphos 105) and cocosalkyl-pentaethoxi-methyl-ammonium-methosulfate (Ammoeng 100) were applied for the esterification of stearic acid and glycerol using Candida antarctica lipase (Novozyme 435). When only ILs were applied as solvents at 1:15 initial substrate molar ratio the conversion was 76 and 78 % in the case of two kinds of ILs, respectively. Mixed the ILs and supercritical $CO_2$ the conversion reached 79 and 86 %. The conversion was found highest in supercritical $CO_2$, reached 90 %. Moreover formation of glycerol-di-stearate is much lower in the case of ILs comparing with $SCCO_2$.
Keywords: glycerol-mono-stearate, Lipase, ionic liquids, supercritical $CO_2$, carbon dioxide
Published in DKUM: 10.07.2015; Views: 1488; Downloads: 189
Full text (128,92 KB)
This document has many files! More... |
7. |
8. HIGH PRESSURE PHASE EQUILIBRIUM OF THE BINARY SYSTEM TWEEN 80 AND CARBON DIOXIDENatalija 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 in DKUM: 22.04.2014; Views: 2035; Downloads: 89
Full text (2,34 MB) |
9. Thermodynamic properties of coenzyme Q10 in supercritical carbon dioxideDarja 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 in DKUM: 01.06.2012; Views: 1927; Downloads: 146
 Link to full text |
10. Chemical composition of Juniperus communis L. fruits supercritical CO2 extracts: dependence on pressure and extraction timeBranislava 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 in DKUM: 01.06.2012; Views: 2229; Downloads: 56
Link to full text |
