1. Kinetic modeling of solvent partitioning effect on the production of 5-hydroxymethylfurfural from glucose in biphasic solvent systemHan Xu, Zhihao Bi, Xinyu Cui, Lili Qian, Lingzhao Kong, Niko Samec, Milan Vujanović, Yang Guo, 2025, original scientific article Abstract: The distribution characteristics of 5-hydroxymethylfurfural (5-HMF) in solution significantly affect its yield and separation/purification during its production process from glucose, but there is currently a lack of quantitative correlation with the reaction kinetics. In this paper, a systematic kinetic study was conducted on the catalytic conversion of glucose to 5-HMF using a porous carbon catalyst that possesses both Lewis and Brønsted acid sites in a biphasic solvent system composed of NaCl-H2O and Methyl isobutyl ketone (MIBK). The addition of NaCl was found to enhance the extraction of 5-HMF into the organic phase, with the highest yield of 84.5% achieved under 10 wt% NaCl concentration. Excessive NaCl increases the solubility of 5-HMF in the aqueous phase, thereby causing a reduction in yield. Kinetic study reveals that higher NaCl concentrations suppress glucose isomerization, humins formation, and direct dehydration to 5-HMF. Excess NaCl also facilitated side reactions, such as 5-HMF rehydration. Changes in solubility equilibrium constants and partition coefficient of 5-HMF were positively correlated, and sensitivity analysis highlighted the impact of NaCl on solubility equilibrium of 5-HMF between aqueous and organic phases. By introducing the parameter of polar activation energy (Ec), the impact of NaCl on the rate constants of various reaction pathways was quantified, confirming that NaCl altered the physicochemical properties of solvent and potentially catalyzed the reaction. These findings provide valuable insight into the mechanisms and kinetics of glucose isomerization and dehydration in biphasic solvent systems, laying the foundation for the design and regulation of solvent properties to optimize these reactions.
Keywords: 5-Hydroxymethylfurfural, glucose, solvent, kinetics, catalyst
Published in DKUM: 13.08.2025; Views: 0; Downloads: 2
 Full text (1,55 MB)
This document has many files! More... |
2. The numerical analysis of flame stability in case of premixed hydrogen-air combustionMarc Jaeger, Matjaž Hriberšek, Niko Samec, Yang Guo, Xuebin Wang, Filip Kokalj, 2025, original scientific article Abstract: This study addresses the urgent need for decarbonization of heating sector, focusing on the potential of hydrogen-air combustion in gas condensing boilers. In the field of gas condensing boilers, groups of holes or slits can be used in perforated burner surfaces, providing a possible solution to the challenge of hydrogen air combustion. Real burners are always adjacent to an area with non-existent combustion, which can lead to a disturbed flame pattern. For this reason, a comparison between single-slit and multi-slit perforated flame holders with a significantly reduced structure temperature with a hydrogen-air premix is carried out as part of this study. Using Ansys Fluent, a 2D simulation approach is employed to analyze laminar flame stability behind a perforated flame holder. Inlet conditions consider fully premixed and homogenous distributed mixtures as well as nonhomogeneous premixed mixtures, with variations in pressure, velocity, and mixing degree. The model examines various slit-burner configurations and flashback behaviors based on an actual geometric shape used in a gas heating device. It has been found that with finite multi-slit burners, the bulk flow rates at the critical flashback point are 30–50% higher compared to infinitely symmetrical burners. A further deterioration of 32% is to be expected due to real mixture quality fluctuations and inhomogeneous inflow conditions. Finally, the findings demonstrate the model’s potential for designing efficient surface-stabilized burners and lay the groundwork for future 3D simulations in the pursuit of sustainable heating solutions.
Keywords: hydrogen combustion, flashback, flame stability, perforated flame holder, gas condensing boiler
Published in DKUM: 19.05.2025; Views: 0; Downloads: 6
Full text (6,29 MB)
This document has many files! More... |
3. Enhancing utilization of municipal solid waste bottom ash by the stabilization of heavy metalsFilip Kokalj, Vesna Alivojvodić, Luka Lešnik, Nela Petronijević, Dragana Radovanović, Niko Samec, 2025, original scientific article Abstract: Waste-to-energy (WtE) is a key part of modern waste management. In the European Union, approximately 500 WtE plants process more than 100 million tons of waste yearly, while globally, more than 2700 plants handle over 500 million tons. Roughly 20% of the waste processed is bottom ash (BA). However, this ash can contain heavy metals in concentrations that may render it hazardous. This paper presents a study focusing on stabilizing municipal solid waste incineration BA using simple and industrially viable treatments. The Slovenian WtE plant operator wishes to install the stabilization process; thus, the samples obtained from the plant were treated (1) with a CO2 gas flow, (2) with water spraying, and (3) with a combination of water spraying and a CO2 gas flow under laboratory conditions. Thermodynamic calculations were applied to define potential reactions during the treatment processes in the temperature range from 0 to 100 ◦C and to define the equilibrium composition of the treated ash with additions of CO2 and water. The standard leaching test EN 12457-4 of treated ash shows a reduction of over 40% in barium concentration and over 30% in lead concentration in leachates.
Keywords: heavy metals, waste-to-energy, bottom ash, leachate, reuse
Published in DKUM: 10.03.2025; Views: 0; Downloads: 9
Full text (2,72 MB)
This document has many files! More... |
4. The impact of financial support mechanisms and geopolitical factors on the profitability of investments in solar power plants in SloveniaIztok Gornjak, Filip Kokalj, Niko Samec, 2024, original scientific article Abstract: This article examines the impact of financial support mechanisms and geopolitical factors on the profitability of investments in solar power plants within Slovenia. The European Union’s energy policy prioritizes increases in renewable energy sources, aiming to reduce dependency on unstable and volatile fossil fuel markets. Solar power plants play a vital role in this transition. The energy policy framework also includes mechanisms and support systems to operate such facilities. This article analyzes electricity price trends over the past decade and addresses which support type—guaranteed purchase or operational support—has proven more profitable for investments in solar power plants up to 50 kW in Slovenia, considering economic and geopolitical influences on the electricity market. Although the global energy market has been affected by various significant events in recent years, it was found that the COVID-19 pandemic had minimal impact on the electricity market. In contrast, the onset of the conflict in Ukraine has contributed to rising electricity prices and has influenced the support dynamics essential for the development and sustainability of renewable energy systems. Analyses from the past decade indicate a higher return on investment in solar power plants when operational support mechanisms are chosen over guaranteed purchase support.
Keywords: renewable energy sources, solar power plants, support system, investment profitability factors, electricity price
Published in DKUM: 16.12.2024; Views: 0; Downloads: 12
Full text (4,96 MB)
This document has many files! More... |
5. Povezanost med rakom in onesnaževali, ki nastanejo v procesih sežiga in sosežiga odpadkov: krovni pregled literatureTeja Oblak, Tanja Carli, Vesna Zadnik, Niko Samec, Andreja Kukec, 2023, review article Abstract: Izhodišča: V procesih sežiga in sosežiga odpadkov ter proizvodnje cementa se v okolje sproščajo izpusti, ki vsebujejo različna onesnaževala. Z namenom oceniti povezanost med rakom pri poklicno izpostavljenih in okoliških prebivalcih ter izpostavljenostjo okoljskim onesnaževalom iz sežigalnic, naprav za sosežig in cementarn smo si za cilj zadali izdelavo krovnega pregleda literature. Metode: V krovni pregled literature so bile vključene metaanalize in sistematični pregledi literature v angleščini v obdobju od leta 1980 do leta 2023. Iskanje je bilo izvedeno v štirih podatkovnih zbirkah (PubMed, Scopus, Web of Science, Cochrane Reviews). Kakovost je bila ocenjena z orodjema AMSTAR-2 (metodologija) in GRADE (dokazi). Rezultati: Izmed 7.701 opredeljenih dokumentov jih je bilo v končno analizo vključenih 14 (pet metaanaliz, devet sistematičnih pregledov). Obstajajo nizki do zmerni dokazi o povezanosti med sarkomom mehkih tkiv in ne-Hodgkinovim limfomom z izpostavljenostjo dioksinom v okolici sežigalnic I. generacije, česar študije niso dokazale za sežigalnice naslednjih generacij. Zaenkrat ne razpolagamo z dokazi za sosežig. Pri delavcih v cementarnah I. do II. generacije obstaja nekaj zmernih dokazov o povezanosti med incidenco vseh rakov, pljučnega raka, raka ustne votline in žrela, prostate in želodca z izpostavljenostjo šestvalentnemu kromu. Velika večina dokazov je omejenih zaradi mešanih rezultatov, razlik v tehniki vprašanj, heterogenosti in potencialni pristranosti. Zaključek: Obstajajo omejeni dokazi o povezanosti med rakom in izpostavljenostjo onesnaževalom iz sežigalnic I. in cementarn I. do II. generacije. Za oceno morebitne povezanosti med rakom in onesnaževali iz najsodobnejših naprav za sosežig je smiselno načrtovati ciljane epidemiološke študije in študije notranje izpostavljenosti z uporabo humanega biomonitoringa.
Keywords: rak, odpadki, sežig, sosežig, cementarna, onesnaževala
Published in DKUM: 18.12.2023; Views: 449; Downloads: 33
Full text (193,36 KB)
This document has many files! More... |
6. An analysis of the responsibility for zero wasteIvana Tršelič, Daniel Rolph Schneider, Niko Samec, Filip Kokalj, 2019, original scientific article Abstract: European Union Directive 2008/98/EC sets the priority hierarchy of the prevention of waste, re-using waste, recycling waste, waste recovery, and waste disposal. Although every one of us is in daily contact with waste, we do not have the knowledge that can lead us to the sound management of waste from the beginning, before products are identified as waste. Zero waste is a fundamental concept of the sustainable community of the future. It is a phrase frequently used by politicians seeking to upgrade the municipal solid waste management systems in their communities. In this manner, the responsibility of zero waste is given to the waste management process instead of to householders. Householders then equate waste prevention with recycling and the proper waste management of the collectors, public services, or waste management company. In reality, zero waste starts with each one of us at home. Households should aim to reduce consumption and undertake repairs to extend the life span of products. Behaviour change can only start with knowledge. In reality, waste prevention does not include recycling. Recycling leads to a combined reduction of waste brought to landfill and raw material extraction. The present paper evaluates household waste to clarify the facts. It analyses the composition of three streams: municipal solid waste, separately collected packaging waste, and bulky waste in different regions of Slovenia. The research defines waste into five different categories. The first category is waste that can and should be avoided. The second category is waste that can be re-used. Further on, the research expands by researching the market of the third category that defines recyclables, which waste can be recycled; the last two categories are the waste that we are fighting with at the end of the waste management process, either to make it to the waste-to-energy process or to comply with landfill restrictions. At the end of the research, we summarize the situation of household waste in 2018. Our goal is to reduce the quantity of waste, making only waste that can be recycled. If we consider waste prevention to be a fight against waste, we can put our plan in place by taking the first step: getting to know our enemy.
Keywords: municipal solid waste, zero waste, recycling, lightweight packaging waste, waste management, material recovery
Published in DKUM: 05.12.2023; Views: 397; Downloads: 54
Full text (463,42 KB)
This document has many files! More... |
7. Predelava rudnega ostanka v podjetju Cinkarna Celje d.d. : magistrsko deloJanez Palčnik, 2023, master's thesis Abstract: Skrb za okolje in ekološke regulacije so podjetja v zadnjih letih vzpodbudila v iskanje trajnostnih industrijskih rešitev. Čeravno se zdi, da ekološki oziroma okoljski inženiring in posodabljanje proizvodnje prinašata le veliko investicij ter manjše končne prihodke, ni tako. Z razvojem novih metod in tehnologij je možno v veliki meri enake procese izvesti ceneje, učinkoviteje ter bolj trajnostno naravnano. V magistrskem delu je predstavljen razvoj metode ponovne uporabe odpadnega rudnega ostank, z namenom povečanja učinkovitosti končne proizvodnje pigmentnega titanovega dioksida. Raziskave kažejo, da je možno z relativno ugodnimi in preprostimi postopki iz odpadnega materiala pridobiti med 65 in 75 odstotki titanovega dioksida, ki bi drugače pristal na deponiji, pri čemer se masa končnega odpada zmanjša tudi do 65 odstotkov.
Keywords: titanov dioksid, ponovna uporaba, hidrotermalna sprememba, sulfatni postopek
Published in DKUM: 21.11.2023; Views: 394; Downloads: 0
Full text (4,49 MB) |
8. Small wood pellet boiler 3-D CFD study for improved flue gas emissions employing flue gas recirculation and air stagingFilip Kokalj, Tomas Zadravec, Aleksandar M. Jovović, Niko Samec, 2023, original scientific article Keywords: CFD, combustion, wood pellets, air staging, flue gas recirculation
Published in DKUM: 05.09.2023; Views: 391; Downloads: 17
Full text (1,12 MB)
This document has many files! More... |
9. Ravnanje s plastičnimi odpadki v sistemu krožnega gospodarstva : magistrsko deloEmina Barlović, 2021, master's thesis Abstract: Po svetu in v Evropi se povečuje proizvodnja plastike, posledica česar je povečevanje nastajanja plastičnih odpadkov. Plastični odpadki najpogosteje končajo na odlagališčih ali odvrženi v okolje, kar škodljivo vpliva tako na ljudi kot okolje. Da bi se odpadki v krožnem gospodarstvu izkoristili v kar največji meri, si prizadevajo za njihovo ponovno uporabo in recikliranje. Recikliranje je v veliki meri odvisno od sestave plastičnih odpadkov in ima pogosto določene pomanjkljivosti, zato je trenutno najboljša rešitev ena od oblik energetske predelave. V tem delu so predstavljene prednosti in slabosti predelave plastičnih odpadkov ter možne rešitve, primerjan je sedanji način predelave plastičnih odpadkov v Republiki Hrvaški in Republiki Sloveniji in izbran tehnološki predlog za predelavo plastičnih odpadkov.
Keywords: krožno gospodarstvo, plastični odpadki, recikliranje, energetska predelava
Published in DKUM: 31.05.2021; Views: 1450; Downloads: 157
Full text (1,81 MB) |
10. Predelava in odstranjevanje radioaktivnih odpadkov : magistrsko deloJakov Ivanović, 2021, master's thesis Abstract: V magistrskem delu je pojasnjen pojem radioaktivnosti, radioaktivnih odpadkov in njegova razvrstitev ter viri nastanka. Zaradi številnih lastnosti je potrebno radioaktivne odpadke najprej obdelati na primeren način ter jih na koncu na varen način odložiti. V delu so pojasnjene tehnologije obdelave, ki vključujejo predhodno obdelavo, obdelavo, kondicioniranje in imobilizacijo. Metode odstranjevanja so prikazane glede na razvrstitev radioaktivnih odpadkov. Ob koncu je pojasnjena problematika korozije pri odlaganju radioaktivnih odpadkov v globokih geoloških tvorbah. Prikazani so rezultati raziskave korozije za 3 konkurenčne materiale, ki se uporabljajo za proizvodnjo vsebnikov radioaktivnih odpadkov za globoko geološko odlaganje. Predstavljena je tudi izbira materialov vsebnikov za RAO za prihodnje skupno odlagališče ter primerjana hrvaška in slovenska izbira načinov odstranjevanja odpadkov iz NEK.
Keywords: radioaktivni odpadki, predelava, odstranjevanje, korozija
Published in DKUM: 03.05.2021; Views: 1049; Downloads: 163
Full text (2,84 MB) |
