1. Enzyme activity and physiochemical properties of flour after supercritical carbon dioxide processingMaja Leitgeb, Željko Knez, Gordana Hojnik Podrepšek, 2022, original scientific article Abstract: The objectives of this study were to inactivate the enzymes α-amylase, lipase, protease,
and peroxidase in flour with supercritical carbon dioxide (scCO2), and to optimize the enzymatic
treatment conditions. Enzyme inactivation is important, due to the undesirability of certain flour
enzymes that cause adverse reactions during storage as unpleasant rancidity of flour, and, at the
same time, reduce the shelf life of flour. Therefore, crude enzymes and flour were initially exposed
to scCO2 to determine the effect on specific enzyme activity under appropriate conditions. The
activity of the unwanted enzymes lipase and peroxidase decreased under optimal process conditions
of scCO2 exposure, lipase by 30%, and peroxidase by 12%, respectively. It was discovered that the
inactivation of enzymes in wheat flour occurred, where, at the same time, this sustainable method
allows the regulation of enzyme activity in the baking process. Afterwards, the effect of scCO2 on the
physicochemical properties of flour, morphological changes on starch granules, and content of total
lipids was studied. In scCO2-treated white wheat flour, the fat content decreased by 46.15 ± 0.5%,
the grain structure was not damaged, and the bread as the final product had a lower specific surface
volume. Therefore, this could be a promising technology for flour pretreatment, potentially impacting
the prolonging of its shelf-life. Keywords: enzymes, enzyme activity, proteins, supercritical fluids, wheat flour Published in DKUM: 10.04.2025; Views: 0; Downloads: 1
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2. Optimization of the supercritical extraction and decarboxylation process of industrial hempTaja Žitek Makoter, Petra Kotnik, Teo Makoter, Željko Knez, Maša Knez Marevci, 2025, original scientific article Abstract: Cannabinoids are the main active ingredients of Cannabis sativa L., obtained by a suitable extraction method and decarboxylation, in which the acid forms of the cannabinoids are converted into active forms. Supercritical CO2 extraction method and decarboxylation process were optimized for 7 cannabinoids (CBD, CBDA, THC, THCA, CBGA, CBN and CBC). The optimal extraction conditions for all cannabinoids were determined at a temperature of 60 °C and a pressure of 300 bar to 550 bar. At higher temperatures and reaction times, a significant depletion of neutral cannabinoids was observed. The optimal conditions of the decarboxylation process varied depending on the component. For the CBD component, which could be measured in the highest concentrations (560 mg/g), the optimal conditions were 140 °C and 10 min. The study can be an important model for predicting the behavior of cannabinoids under certain parameters. Keywords: supercritical fluids, extraction, cannabinoids, decarboxilation, Cannabis sativa I Published in DKUM: 08.01.2025; Views: 0; Downloads: 7
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3. Suitability of test procedures for determining the compatibility of seal materials with ionic hydraulic fluidsDarko Lovrec, Vito Tič, 2024, original scientific article Abstract: The compatibility of seal materials with the working fluid is crucial for the flawless, energysaving, environmentally sustainable, and safe operation of any technical system. This is especially
true for hydraulic systems operating under high operating pressure. The problem of materials
compatibility comes into play when either a new type of seal material or a new type of fluid comes
into use. The paper discusses the research findings regarding material compatibility testing of new
high-tech ionic hydraulic fluids with commonly used seal materials. Due to the completely different
chemical composition of these new fluids compared to the classical mineral-based oil, for these fluids,
there are no standardized testing procedures. In these cases, we can only lean on the Standards
that apply to classical fluids, which can lead to incorrect results. In the forefront of the paper is the
discrepancy between the results obtained by the standardized test, and the test under real operating
conditions. FKM, an excellent material for seals, proved to be the most suitable in the case of using
ionic hydraulic fluid, according to a standardized test. However, it failed in the comparison test
under real operating conditions, as the cylinder leaked. NBR seals proved to be a better solution.
Keywords: ionic hydraulic fluids, seal material compatibility, static and dynamic test, comparison of results, differences, test suitability Published in DKUM: 10.09.2024; Views: 59; Downloads: 33
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4. 20th European Meeting on Supercritical Fluids : Book of Abstracts2024 Abstract: The 20th European Meeting on Supercritical Fluids (EMSF 2024) was hosted by the Faculty of Chemistry and Chemical Engineering of the University of Maribor from 26 May to 29 May 2024 in Maribor, Slovenia. The EMSF 2024 was a joint event of the International Society for the Advancement of Supercritical Fluids (ISASF) and the European Federation of Chemical Engineering (EFCE) Working Party on High Pressure Technology (WP HPT) Event No. 807. This symposium provided an excellent opportunity for engineers, chemists, physicists, food technologists, and biologists to meet and discuss new ideas, review ongoing challenges, present potential solutions, and identify future issues related to high pressure technologies and supercritical fluids. The aim of the meeting was to deepen connections between researchers, establish new contacts, and promote synergies and partnerships between researchers. The symposium presented the latest advances in high-pressure process technologies that can contribute to the further development of the field. Keywords: supercritical fluids, fundamental data, novel materials, industrial applications, research and development Published in DKUM: 24.07.2024; Views: 161; Downloads: 33
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6. Ionic hydraulic fluids and seal-material compatibilityDarko Lovrec, Roland Kalb, Vito Tič, 2024, original scientific article Abstract: Manufacturers of hydraulic fluids invest a lot of effort and resources in improving their physico-chemical properties, with the goal of getting as close as possible to the properties of an ideal hydraulic fluid. It should be non- flammable, environmentally friendly, sustainable and should have excellent physical and chemical properties. After decades of development in the field of ionic liquids and the search for an ionic liquid suitable for use in hydraulic systems, ionic hydraulic liquids are now already in industrial use, especially on devices that operate in harsh and risky operating conditions. Since ionic hydraulic fluids are a completely new type of hydraulic fluid, one of the issues is their compatibility with the materials present in the hydraulic components, including all the seals. This paper refers to the process of testing the compatibility of hydraulic seal materials with different types of ionic hydraulic fluids according to the standardized percentages and recommendations, with emphasis on changes in the swell, shrinkage and hardness of the seals. The presented results are a useful guide for selecting suitable seal materials in case of using high-tech ionic hydraulic fluids. Keywords: ionic hydraulic fluids, seal material, compatibility, fluid-testing method, test results Published in DKUM: 19.03.2024; Views: 287; Downloads: 24
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7. 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: 143
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8. International Conference Fluid Power 2019 : Conference Proceedings2019 Abstract: The International Fluid Power Conference is a two day event, intended for all those professionally-involved with hydraulic or pneumatic power devices and for all those, wishing to be informed about the ‘state of the art’, new discoveries and innovations within the field of hydraulics and pneumatics. The gathering of experts at this conference in Maribor has been a tradition since 1995, and is organised by the Faculty of Mechanical Engineering at the University of Maribor, in Slovenia. Fluid Power conferences are organised every second year and cover those principal technical events within the field of fluid power technologies in Slovenia, and throughout this region of Europe. This year's conference is taking place on the 19th and 20th September in Maribor. Keywords: fluid power technology, components and systems, control systems, fluids, maintenance and condition monitoring Published in DKUM: 24.02.2020; Views: 1383; Downloads: 48
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9. 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: 245
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10. International conference Fluid power 2017 : September 14th - 15th 2017, Maribor, Slovenia (conference proceedings)2017, proceedings of peer-reviewed scientific conference contributions (international and foreign conferences) Abstract: The International Fluid Power Conference is a two day event, intended for all those professionally-involved with hydraulic or pneumatic power devices and for all those, wishing to be informed about the ‘state of the art’, new discoveries and innovations within the field of hydraulics and pneumatics.
The gathering of experts at this conference in Maribor has been a tradition since 1995, and is organised by the Faculty of Mechanical Engineering at the University of Maribor, in Slovenia. Fluid Power conferences are organised every second year and cover those principal technical events within the field of fluid power technologies in Slovenia, and throughout this region of Europe. This year's conference is taking place on the 14th and 15th September in Maribor.
We wish all participants at the International Conference-Fluid Power 2017 continued successful professional work, and hope that we have yet again added another small piece within the mosaic of fluid power.
Keywords: fluid power technology, components and systems, control systems, fluids, maintenance, monitoring Published in DKUM: 28.09.2017; Views: 1594; Downloads: 186
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