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Abstract: Ananas je trajnica družine Bromeliaceae, katere plodove konzumirajo po vsem svetu. Velja za eksotično sadje prijetnega okusa in arome, ki se uživa samostojno ali pa se uporablja v različnih produktih. Vendar pa s predelavo ananasa pridelamo tudi velike količine odpadkov, od 25 do 35 % teže sadja, ki lahko povzročajo veliko obremenitev za okolje in onesnaženje. Konvencionalne in nekonvencionalne ekstrakcije so se izkazale kot učinkovite metode za procesiranje odpadkov ananasa. Med nekonvencionalnimi ekstrakcijskimi tehnikami največ zanimanja vzbujajo hidrotermični postopki za procesiranje biomase, saj pri teh postopkih sočasno potekajo reakcije razgradnje odpadne biomase s podkritično vodo in separacijo razgradnih produktov. Podkritična voda se nanaša na tekočo vodo pri temperaturi in tlaku pod kritično točko (Tc = 374,15 ºC, Pc = 22,1 Mpa). Glavni namen magistrske naloge je bil načrtovanje in optimizacija postopka izolacije vrednih spojin iz ananasovih olupkov z uporabo metode odzivinih površin z zasnovo Box-Behnkenovega načrtovanja. Hidrotermično razgradnjo olupkov ananasa smo izvedli pri različnih pogojih, kjer smo spreminjali tri parametre: temperaturo (180, 200, in 220 ºC), čas (15, 30 in 45 min) in razmerje topilo-material (10:1, 20:1 in 30:1 mL/g). Ugotovili smo, da so optimalni pogoji za ekstrakcijo sladkorjev, derivatov sladkorjev, celokupnih ogljikovih hidratov in totalnih fenolov pri temperaturi: 200 ºC, času 30 min in razmerju topilo-material 20:1 mL/g. Največji vpliv na ekstrakcijo vrednih spojin s subkritično vodo imata temperatura in čas, saj se z višanjem temperature ekstrahira večja količina vrednih spojin. Večinoma smo v razgradnih produktih iz odpadnih olupkov ananasa, zaznali visoke vrednosti antioksidativne aktivnosti (od 54,5 do 78 %) ter vsebnosti fruktoze (od 15,10 do 18,20 mg/ g ekstrakta), glukoze (od 14,40 do 18,31 mg/ g ekstrakta) in totalnih fenolov (od 90,50 do 156,90 mg/ g ekstrakta).
Keywords: ekstrakcija s subkritično vodo, ananas (Ananas comosus), analiza razgradnih produktov, HPLC, antioksidativnost, derivati sladkorja
Published in DKUM: 03.03.2025; Views: 0; Downloads: 8
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Abstract: Corncobs are a widespread and renewable by-product of corn cultivation that are typically considered waste or low-value material. Corncobs contain hemicellulose, cellulose, and lignin, which can be converted into valuable products using suitable techniques. Subcritical water is increasingly used as a green medium for the extraction of valuable components from biomass, as it has many advantageous properties (high yield, pure extracts, shorter times) compared to other organic solvents. For this reason, subcritical water was used in this study to extract valuable components from corncobs at different temperatures (150–250 °C) and reaction times (10–60 min). During the decomposition of corncobs, numerous valuable products are formed in the aqueous phase depending on the temperature and reaction time. In addition to sugars and their derivatives, phenolic compounds were also formed, which are of great importance in numerous applications. It was found that at low temperatures (150–170 °C) the hemicellulose in the corncobs begins to decompose and, in particular, the sugars (glucose, xylose, arabinose, and galactose) are initially formed in the aqueous phase. Higher temperatures (200 and 250 °C) are more favorable for the decomposition of corncobs into valuable components. The yield of sugars increases with temperature due to the degradation of the cellulose content of the lignocellulosic biomass. At the same time, several new valuable products (furfural, 5-hydroxymethylfurfural (5-HMF), 1,3-dihydroxyacetone, levulinic acid, and formic acid as well as phenolic components) are formed through the degradation of lignin and the further degradation of sugars. The most important products are certainly the furfurals, which are central platform compounds. The highest furfural content was reached at 200 °C and 60 min and accounted for almost half of all components in the aqueous phase (472.01 ± 5.64 mg/g dry extract). These biomass-derived sugars and derivatives can be used in the production of fuels, pharmaceuticals, biodegradable polymers, and surfactants.
Keywords: corncobs, subcritical water, biomass, valuable compounds, sugar derivates
Published in DKUM: 07.02.2025; Views: 0; Downloads: 5
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Abstract: Uporaba plastike v vsakdanjem življenju drastično raste. Z večanjem količine plastičnih izdelkov se sorazmerno povečuje tudi število plastičnih odpadkov, kar predstavlja velik problem z vidika varovanja okolja. Razgradnja plastike v naravnem okolju je zelo počasen proces, zato raziskovalci iščejo metode za razgradnjo plastičnih mas, z namenom pridobitve dragocenih surovin, ki so primerne za nadaljnjo uporabo. Ena izmed pogosteje uporabljenih plastik je tudi polikarbonat (PC), ki se uporablja za proizvodnjo raznih izdelkov. Namen in cilj diplomskega dela je bil raziskati razgradnjo plastike iz PC v podkritični vodi in ugotoviti, katere uporabne produkte lahko pridobimo iz nje. Za proces razgradnje PC smo uporabili visokotlačni in visokotemperaturni šaržni reaktor. Eksperimente smo izvajali pri temperaturi 250 °C in reakcijskih časih 60 in 120 min, medtem ko smo pri temperaturah 300 in 350 °C reakcije izvajali pri 5, 15, 30, 60 in 120 min. Kot produkte hidrotermične razgradnje smo dobili oljno, plinsko, vodno in trdno fazo. Največji izkoristek oljne faze smo dosegli pri 350 °C po 15 min in je znašal 97,7 %. Pri 250 °C je najvišje izkoristke dosegla trdna faza, ki je predstavljala nerazgrajeno plastiko iz PC, zato se je izkazalo, da je temperatura 250 °C prenizka za uspešno razgradnjo. Analize oljne in plinske faze smo izvedli z metodo plinske kromatografije s plamensko ionizacijskim detektorjem (GC-FID), vodnim fazam smo določili totalni ogljik (TC) s TOC analizatorijem medtem ko smo trdne faze analizirali s Fourierjevo transformacijo z infrardečo spektroskopijo (FTIR). V oljni fazi smo določili tri glavne razgradne produkte: bisfenol A (BPA), 4-izopropilfenol in fenol. Maksimalni izkoristek BPA (40,9 %) smo dosegli pri 250 °C in 120 min, kar lahko pripišemo začetni razgradnji PC v glavni monomer BPA. S podaljševanjem reakcijskega časa in z naraščajočo temperaturo je izkoristek BPA upadal, zaradi pretvorbe v nadaljnje komponente (fenol in 4-izopropilfenol). V plinski fazi so bili poleg CO2 prisotni večinoma alkani in alkeni. Z naraščajočo temperaturo in podaljševanjem reakcijskega časa je naraščalo število prisotnih komponent v plinski mešanici, kot posledica razpada daljših ogljikovodikov na krajše. Ugotovili smo, da je hidrotermična razgradnja PC uspešna metoda in predstavlja alternativni pristop recikliranja plastike iz PC, s katerim lahko pridobimo vredne razgradne produkte, ki so primerni za nadaljnjo uporabo.
Keywords: hidrotermična razgradnja, polikarbonat, podkritična voda, kemijsko recikliranje, BPA
Published in DKUM: 18.09.2024; Views: 0; Downloads: 36
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Abstract: Plastics play a crucial role in our daily lives. The challenge, however, is that they become waste and contribute to a global environmental problem, increasing concerns about pollution and the urgent need to protect the environment. The accumulation and fragmentation of plastic waste, especially micro- and nanoplastics in aquatic systems, poses a significant threat to ecosystems and human health. In this study, the decomposition and fragmentation processes of conventional and biobased plastic waste in simulated water bodies (waters with different pH values) and in real water systems (tap water and seawater) are investigated over a period of one and six months. Three types of plastic were examined: thermoplastic polyethylene terephthalate and thermoset melamine etherified resin in the form of nonwovens and biobased polylactic acid (PLA) in the form of foils. Such a comprehensive study involving these three types of plastics and the methodology for tracking degradation in water bodies has not been conducted before, which underlines the novelty of the present work. After aging of the plastics, both the solid fraction and the leachate in the liquid phase were carefully examined. The parameters studied include mass loss, structural changes and alterations in functional groups observed in the aged plastics. Post-exposure assessment of the fragmented pieces includes quantification of the microplastic, microscopic observations and confirmation of composition by in situ Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. The leachate analysis includes pH, conductivity, turbidity, total carbon and microplastic size distribution. The results highlight the importance of plastic waste morphology and the minor degradation of biobased PLA and show that microfibers contribute to increased fragmentation in all aquatic systems and leave a significant ecological footprint. This study underlines the crucial importance of post-consumer plastic waste management and provides valuable insights into strategies for environmental protection. It also addresses the pressing issue of plastic pollution and provides evidence-based measures to mitigate its environmental impact.
Keywords: polylactic acid, polyethylene terephthalate fabric, melamine etherifed resin fabric, aquatic environment, fragmentation, waste disposal
Published in DKUM: 09.09.2024; Views: 73; Downloads: 23
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Keywords: hydrothermal degradation, waste packing, tetra pak, subcritical water, subcritical waste, chemical recycling, one-stage process, two-stage process, product analysis
Published in DKUM: 16.07.2024; Views: 88; Downloads: 26
Full text (2,12 MB)