1. Kinetics study of hydrothermal degradation of PET waste into useful productsMaja Čolnik, Darja Pečar, Željko Knez, Andreja Goršek, Mojca Škerget, 2022, original scientific article Abstract: Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 °C and 350 °C) and reaction times from 1 to 240 min. PET waste was decomposed in subcritical water (SubCW) by hydrolysis to terephthalic acid (TPA) and ethylene glycol (EG) as the main products. This was followed by further degradation of TPA to benzoic acid by decarboxylation and degradation of EG to acetaldehyde by a dehydration reaction. Furthermore, by-products such as isophthalic acid (IPA) and 1,4-dioxane were also detected in the reaction mixture. Taking into account these most represented products, a simplified kinetic model describing the degradation of PET has been developed, considering irreversible consecutive reactions that take place as parallel in reaction mixture. The reaction rate constants (k1–k6) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.
Keywords: PET waste, subcritical water, kinetics, degradation, TPA
Published in DKUM: 18.09.2023; Views: 213; Downloads: 12
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2. Degradation of polyvinyl chloride (PVC) waste with supercritical waterMaja Čolnik, Petra Kotnik, Željko Knez, Mojca Škerget, 2022, original scientific article Abstract: 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.
Keywords: polyvinyl chloride, supercritical water, chemical recycling, plastic waste
Published in DKUM: 18.09.2023; Views: 183; Downloads: 11
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3. Chemical recycling of polyolefins waste materials using supercritical waterMaja Čolnik, Petra Kotnik, Željko Knez, Mojca Škerget, 2022, original scientific article Abstract: 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.
Keywords: polypropylene, polyolefins, supercritical water, plastics waste, chemical recycling
Published in DKUM: 18.09.2023; Views: 178; Downloads: 9
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4. Green techniques for preparation of red beetroot extracts with enhanced biological potentialDragana Borjan, Vanja Šeregelj, Darija Cör Andrejč, Lato Pezo, Vesna Tumbas Šaponjac, Željko Knez, Jelena J. Vulić, Maša Knez Marevci, 2022, original scientific article Abstract: 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.
Keywords: red beetroot, supercritical fluid extraction, antioxidant activity, anti-inflammatory activity, antihyperglycemic activity, chemometric approach
Published in DKUM: 18.08.2023; Views: 153; Downloads: 11
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5. P-x,y equilibrium data of the binary systems of 2-propanol, 1-butanol and 2-butanol with carbon dioxide at 313.15 K and 333.15 KDragana Borjan, Maša Knez Marevci, Željko Knez, 2022, original scientific article Abstract: The ability to predict the behaviour of high-pressure mixtures of carbon dioxide and alcohol is important for industrial purposes. The equilibrium composition of three binary carbon dioxide-alcohol systems was measured at temperatures of 313.15 K and 333.15 K and at pressures of up to 100 bar for carbon dioxide-2-propanol, up to 160 bar for carbon dioxide-1-butanol and up to 150 bar for carbon dioxide-2-butanol. Different equilibrium compositions of carbon dioxide in alcohols were observed despite their similar molecular weight (M2-propanol = 60.100 g mol−1, M1-butanol = 74.121 g mol−1 and M2-butanol = 74.122 g mol−1) and place in the functional hydroxyl group (first or second carbon molecule). It is assumed that the differences in the phase equilibria are due to different vapor pressures, polarities and solute-solute interactions.
Keywords: high-pressure phase equilibrium, carbon dioxide, 2-propanol, 1-butanol, 2-butanol
Published in DKUM: 17.08.2023; Views: 124; Downloads: 11
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6. Determination of viscosity, density and interfacial tension of the carbon dioxide–isopropanol, argon–isopropanol, sulphur hexafluoride–isopropanol binary systems at 313.15 K and 333.15 K and at elevated pressuresDragana Borjan, Maja Gračnar, Željko Knez, Maša Knez Marevci, 2022, original scientific article Abstract: Viscosity, density, and interfacial tension of three binary systems (carbon dioxide–isopropanol, argon–isopropanol, and sulphur hexafluoride–isopropanol) were measured at temperatures of 313.15 K and 333.15 K and at pressures up to 100 bar for carbon dioxide, and for argon and sulphur hexafluoride up to 500 bar. A vibrating tube densimeter method has been used for density measurements and a variable-volume high-pressure optical view cell with some modifications for the other measurements. The results showed that pressure does not have a high impact on viscosity. Density is found to be a linear function of pressure and temperature and the densities of the investigated binary systems increase with pressure and decrease with temperature. Interfacial tension decreased with the elevated pressure at a constant temperature for all the investigated systems. Accurate prediction of thermodynamic and mass transfer data is fundamental in various engineering and industrial operations to design processes with a higher yield of targeted compounds.
Keywords: viscosity, interfacial tension, carbon dioxide, argon, suplhur hexafluoride, isopropanol
Published in DKUM: 17.08.2023; Views: 147; Downloads: 11
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7. Hop (Humulus lupulus L.) essential oils and xanthohumol derived from extraction process using solvents of different polarityKatja Bizaj, Mojca Škerget, Iztok Jože Košir, Željko Knez, 2022, original scientific article Abstract: This study evaluates the content of essential oils (EOs) and prenylated flavonoid Xanthohumol (XN) in extracts of Slovenian hops, cultivar Aurora, obtained by using fluids of different polarity. It is a continuation of our previous work, investigating the extraction of bitter acids from hops. Extraction was conducted semi-continuously, using sub- and supercritical fluids of different polarity, i.e., carbon dioxide (CO2) and propane as non-polar and dimethyl ether (DME) as the polar solvent. The experiments explored a temperature range between 20 °C and 80 °C and pressures ranging from 50 bar to 150 bar. The content of XN in extracts was analysed using high-performance liquid chromatography and experiments demonstrated the largest concentration of XN was obtained using DME. In order to analyse the EO components in extracts, connected with a distinct odour, the steam distillation of extracts was performed and GC analysis was employed. Hop oil derived from CO2 extracts at specific conditions, had the highest relative concentration of linalool, β-caryophyllene and α-humulene, and oil derived from propane extracts had the highest content of all other five selected components (myrcene, geraniol, farnesene, α-selinene and δ-cadinene). The relative content of the investigated EO components in DME extracts was similar to that in propane extracts.
Keywords: hop extract, hop essential oils, flavonoids, carbon dioxide, propane, dimethyl ether
Published in DKUM: 17.08.2023; Views: 114; Downloads: 10
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8. Antioxidant, antibacterial, antitumor, antifungal, antiviral, anti-inflammatory, and nevro-protective activity of Ganoderma lucidum : an overviewDarija Cör Andrejč, Željko Knez, Maša Knez Marevci, 2022, review article Abstract: Ganoderma lucidum is a very medicinal mushroom that has been utilized in Oriental medicine for many years. It has a wide range of pharmacological and therapeutic properties, and has been used for many years as a health promoter. It contains various biologically active compounds that improve the immune system and have antioxidant, antitumor, anti-inflammatory, antifungal, and antimicrobial properties. Active compounds include triterpenoids and polysaccharides, as well as proteins, lipids, phenolics, sterols, etc. In the following review, we summarize briefly their biological activities, such as antioxidant, anti-bacterial, anti-fungal, antitumor, anti-viral, and anti-inflammatory activity. Although Ganoderma has a number of medicinal effects that have been confirmed by the in vitro and in vivo studies summarised in this review, there are some limitations. Clinical trials face mainly a lack of pure constituents. Accurate identification of the compounds obtained is also problematic. In addition, most of the included studies were small, and there were concerns about the methodological quality of each study. Studies have shown that Ganoderma has valuable potential for the prevention and treatment of cancer. In any case, G. lucidum cannot be used as first-line therapy for cancer.
Keywords: Ganoderma lucidum, bioactive function, active compounds, polysaccharides, triterpenoids
Published in DKUM: 16.08.2023; Views: 96; Downloads: 12
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9. The effect of drying methods and extraction techniques on oleuropein content in olive leavesDarija Cör Andrejč, Bojan Butinar, Željko Knez, Kaja Tomažič, Maša Knez Marevci, 2022, original scientific article Abstract: Increased demand for olive oil has caused higher quantities of byproducts in olive processing, such as olive leaves, olive skins, and vegetation water. It is well known that olive leaves contain several phenolic compounds, including secoiridoids. Oleuropein is the major secoiridoid in olive leaves. Oleuropein has been found to exhibit antioxidative, antimicrobial, antiviral, and antiatherogenic activities. We studied the effect of extraction techniques and drying methods on oleuropein content in olive leaves of Istrska belica and Lecino cultivar. Three different procedures of drying were used: at room temperature, at 105 °C, and freeze drying. Ethanol-modified supercritical extraction with carbon dioxide, conventional methanol extraction, and ultrasonic extraction with deep eutectic solvent were performed. Antioxidant activity was determined, as well as methanolic and supercritical extracts. The presence of olive polyphenols was confirmed by the HPLC method.
Keywords: olive leaves, drying, different extraction techniques, oleuropein
Published in DKUM: 10.08.2023; Views: 113; Downloads: 11
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10. Molekularni in celični odziv na oksidativni stres, hipoksijo in naravne antioksidante, pridobljene s konvencionalno in superkritično ekstrakcijo, pri akutni in kronični mieloični levkemiji in vitro : doktorska disertacijaStaša Jurgec, 2023, doctoral dissertation Abstract: Akutna mieloična levkemija (angl. Acute Myeloid Leukemia, AML) in kronična mieloična levkemija (angl. Chronic Myeloid Leukemia, CML) sta skupini hematoloških rakov, za kateri je značilna nekontrolirana delitev krvnih celic mieloične linije. Kljub napredku v poznavanju genetskih dejavnikov in molekularnih mehanizmov, ki lahko privedejo do AML in CML, so trenutno razpoložljivi načini zdravljenja nezadostni. Za boljše razumevanje patofiziologije nastanka in razvoja AML in CML smo v doktorski nalogi proučili uravnavanje celične redoks homeostaze pri tej skupini rakov. V prvem delu doktorske naloge izvedli meta-analizo transkriptomskih podatkov iz 4 študij CML in 1 študije AML. V drugem delu smo na celičnih linijah AML HL-60 in KASUMI1 in celičnih linijah CML K562 in Ku812F natančneje proučili vpliv oksidativnega stresa, povzročenega z vodikovim peroksidom, hipoksije in naravnih ekstraktov origana, konoplje in brusnice, pridobljenih s hladno maceracijo, ekstrakcijo z ultrazvokom in superkritično tekočinsko ekstrakcijo, na molekularnem in celičnem nivoju. Z meta-analizo transkriptomskih podatkov smo med prvimi 100 najbolj diferencialno izraženimi geni identificirali gen za nekodirajočo RNA LINC01554 in dva pseudogene RPS27AP20 in FAM133CP, ki predhodno še niso bili povezani z AML in CML, in potrdili, da se AML in CML razlikujeta v izražanju genov, poveznih z uravnavanjem redoks homeostaze. Izpostavitev oksidativnemu stresu je znižala celično rast/proliferacijo pri proučevanih celičnih linijah, pri tem pa je bil vpliv večji pri celičnih linijah AML kot CML. Oksidativni stres je še znižal metabolno aktivnost celice pri celičnih linijah AML in jo povišal pri celičnih linijah CML. Ugotovljene razlike v celični rasti/proliferaciji in metabolizmu med AML in CML v pogojih oksidativnega stresa so bile posledica zmanjšanega preživetja celičnih linij AML v primerjavi s celičnimi linijami CML in ne spremenjenega celičnega cikla. Na molekularnem nivoju so se proučevane celične linije razlikovale v izražanju AQP1, 3, 8, 9 in 11, SOD1, CAT in AATF. Tretiranje z ekstrakti je v pogojih oksidativnega stresa znižalo celično rast/proliferacijo pri celičnih linijah HL-60, KASUMI1 in K562 in povišalo količino reaktivnih kisikovih in dušikovih spojin (ROS/RNS) pri celični liniji HL-60 oziroma znižalo njihovo količino pri celični liniji KASUMI1. Ekstrakti niso vplivali na celično rast/proliferacijo pri celični linji Ku812F in na količino ROS/RNS pri celičnih linijah K562 in Ku812F. Znižana celična rast v prisotnosti oksidativnega stresa in ekstraktov je bila posledica zmanjšanega preživetja celic in ne spremenjenega celičnega cikla. Tretiranje z ekstrakti brusnice je povišalo izražanje SOD1 pri celični liniji Ku812F, v prisotnosti oksidativnega stresa in specifičnih ekstraktov pa smo ugotovili še razlike v izražanju SOD1, NQO1 in PRDX1 med proučevanimi celičnimi linijami. Hipoksija je znižala celično rast/proliferacijo pri vseh proučevanih celičnih linijah, pri tem pa so bile celične linije AML bolj dovzetne za vplive hipoksije kot celične linije CML. Še več, hipoksija je specifično znižala metabolizem celice pri celičnih linijah AML. Znižana rast/proliferacija in metabolizem celičnih linij AML v primerjavi s celičnmi linijami CML v hipoksiji sta bila posledica zmanjšanega preživetja in ne spremenjenega celičnega cikla.
Rezultati doktorske naloge kažejo, da se AML in CML razlikujeta v molekularnem in celičnem odzivu na dejavnike, ki vplivajo na celično redoks homeostazo. Molekularni mehanizmi, ki omogočajo večjo dovzetnost AML za ROS/RNS, ki vodijo v znižanje celične rasti/proliferacije in preživetja celic, bi lahko v prihodnje predstavljali potencialne klinične tarče za nadzorovanje in zdravljenje te bolezni.
Keywords: AML, CML, oksidativni stres, hipoksija, naravni ekstrakt, RT-qPCR
Published in DKUM: 19.07.2023; Views: 284; Downloads: 31
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