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Carbonization of Class G well cement containing metakaolin under supercritical and saturated environments
Gregor Kravanja, Željko Knez, 2023, izvirni znanstveni članek

Ključne besede: well cement, carbonization, metakaolin, supercritical CO2, gas saturated solution, CaCo3
Objavljeno v DKUM: 15.04.2024; Ogledov: 143; Prenosov: 13
.pdf Celotno besedilo (14,25 MB)
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Degradation of polyvinyl chloride (PVC) waste with supercritical water
Maja Čolnik, Petra Kotnik, Željko Knez, Mojca Škerget, 2022, izvirni znanstveni članek

Opis: The chemical degradation of PVC waste in SCW between 400 and 425 °C and reaction times from 30 to 60 min was studied. The PVC waste in SCW decomposed into the gas, oil, water soluble, and solid phases. The highest yield of the gas and oil phases was achieved at the temperature of 425 °C after 60 min. By increasing the reaction time at 400 °C, the yield of chloride ions in the aqueous phase increased and reached the maximum at 60 min. The gas and oil phases contained many valuable compounds similar to crude oil. Alkanes and chloroalkanes; alkenes, alicyclic, and aromatic hydrocarbons; as well as alcohols were the main groups of hydrocarbons in the oil phase, while the gas phase contained only light hydrocarbons (C1–C6), CO2, and small amounts of H2. This confirmed that the largest chlorine content remains in the aqueous phase and does not pass into the gas phase. It can be concluded that SCW presents effective decomposition media for plastic waste.
Ključne besede: polyvinyl chloride, supercritical water, chemical recycling, plastic waste
Objavljeno v DKUM: 18.09.2023; Ogledov: 468; Prenosov: 21
.pdf Celotno besedilo (1,09 MB)
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Chemical recycling of polyolefins waste materials using supercritical water
Maja Čolnik, Petra Kotnik, Željko Knez, Mojca Škerget, 2022, izvirni znanstveni članek

Opis: In the following work, the hydrothermal degradation of polypropylene waste (PP) using supercritical water (SCW) has been studied. The procedure was carried out in a high-pressure, high-temperature batch reactor at 425 °C and 450 °C from 15 to 240 min. The results show a high yield of the oil (up to 95%) and gas (up to 20%) phases. The gained oil phase was composed of alkanes, alkenes, cycloalkanes, aromatic hydrocarbons, and alcohols. Alkanes and alcohols predominated at 425 °C and shorter reaction times, while the content of aromatic hydrocarbons sharply increased at higher temperatures and times. The higher heating values (HHVs) of oil phases were in the range of liquid fuel (diesel, gasoline, crude and fuel oil), and they were between 48 and 42 MJ/kg. The gas phase contained light hydrocarbons (C1–C6), where propane was the most represented component. The results for PP degradation obtained in the present work were compared to the results of SCW degradation of colored PE waste, and the potential degradation mechanism of polyolefins waste in SCW is proposed. The results allowed to conclude that SCW processing technology represents a promising and eco-friendly tool for the liquefaction of polyolefin (PE and PP) waste into oil with a high conversion rate.
Ključne besede: polypropylene, polyolefins, supercritical water, plastics waste, chemical recycling
Objavljeno v DKUM: 18.09.2023; Ogledov: 504; Prenosov: 16
.pdf Celotno besedilo (3,44 MB)
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Green techniques for preparation of red beetroot extracts with enhanced biological potential
Dragana Borjan, Vanja Šeregelj, Darija Cör Andrejč, Lato Pezo, Vesna Tumbas Šaponjac, Željko Knez, Jelena J. Vulić, Maša Knez Marevci, 2022, izvirni znanstveni članek

Opis: Red beetroot is well known for its high proportion of betalains, with great potential as functional food ingredients due to their health-promoting properties. The objective of this study was to investigate the influence of processing techniques such as Soxhlet, cold, ultrasound and supercritical fluid extraction on the betalains content and its antioxidant, anti-inflammatory and antihyperglycemic activities. Whilst Soxhlet extraction with water has provided the highest yield, the highest content of total phenolics was found in an extract prepared using Soxhlet extraction with 50% ethanol. Amongst eight phenolic compounds detected in the extracts, protocatechuic acid was the most abundant. The concentrations of total phenolics ranged from 12.09 mg/g (ultrasound extraction with 30% methanol) to 18.60 mg/g (Soxhlet extraction with 50% ethanol). The highest anti-inflammatory activity was observed for cold extraction with 50% methanol extract. The high radical scavenging activity of supercritical fluid extracts could be a consequence of nonphenolic compounds. The chemometrics approach was further used to analyse the results to find the “greenest” method for further possible application in the processing of beetroot in the food and/or pharmaceutical industry. According to the standard score, the best extraction method was determined to be Soxhlet extraction with 50% ethanol.
Ključne besede: red beetroot, supercritical fluid extraction, antioxidant activity, anti-inflammatory activity, antihyperglycemic activity, chemometric approach
Objavljeno v DKUM: 18.08.2023; Ogledov: 392; Prenosov: 29
.pdf Celotno besedilo (944,05 KB)
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Sustainable processing of materials using supercritical fluids : doktorska disertacija
Dragana Borjan, 2022, doktorska disertacija

Opis: 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.
Ključne besede: 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
Objavljeno v DKUM: 11.10.2022; Ogledov: 947; Prenosov: 133
.pdf Celotno besedilo (4,64 MB)

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BIOAEROGELS: PROMISING MATERIALS FOR IMPREGNATION OF DRUGS : diploma thesis dissertation
Jorge Rodríguez Antolín, 2020, diplomsko delo

Opis: The following work examines the possibility of impregnating chosen model drug into bioaerogels to obtain final formulation with added value. The drug used in this study was esomeprazole, used to treat acid-related diseases. In the first part of the work, bioaerogels were prepared. Polysaccharide aerogels are lightweight biocompatible and biodegradable materials, suitable for applications in pharmaceutical industry. For this purpose, three different cores were prepared: pectin, alginate and their mixture, followed by coating with chitosan layer. The production of the bioaerogels follows a sol-gel synthesis and supercritical drying technique. All samples were characterised, and optimisation was performed based on examined properties. Aerogels having a pectin core and chitosan coating showed the highest surface area and the highest adsorption capacity. In the second part, the impregnation of esomeprazole was performed using two different methods: supercritical impregnation and diffusion via sol-gel synthesis. For supercritical impregnation, supercritical carbon dioxide was used as a solvent for impregnation of the drug. In the diffusion method, the model drug was added during sol-gel synthesis using ethanol as solvent. Finally, complete characterisation of prepared formulation followed by drug release studies was performed. The study showed successful impregnation of esomeprazole using either carbon dioxide or ethanol as a solvent. Bioaerogels proved to be promising as carriers for achieving the optimal release of the chosen drug.
Ključne besede: Bioaerogels, polysaccharides, supercritical impregnation, diffusion method, esomeprazole
Objavljeno v DKUM: 09.07.2020; Ogledov: 888; Prenosov: 54
.pdf Celotno besedilo (1,28 MB)

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