Hydrothermal decomposition of waste multilayer packaging

V letu 2020 smo v Sloveniji pridelali več kot milijon ton odpadkov. Skoraj 30 % odpadkov predstavlja odpadna embalaža raznih produktov. Poznamo različne vrste embalaže: papirnato, stekleno, kovinsko, plastično, leseno in večslojno. Večslojni embalaži lahko rečemo tudi sestavljena. Ena izmed najpogosteje uporabljenih in dobro poznanih večslojnih embalaž je tudi tetrapak embalaža. Tetrapak embalaža je sestavljena iz papirja/kartona, polietilena (PE) in aluminija. Problem recikliranja tetrapak embalaže je v tem, da njenih sestavnih delov ni mogoče enostavno ločiti z mehanskimi metodami. Uporaba pod- in nadkritičnih fluidov v različnih kemijskih procesih je vse pogostejša. Zaradi svoje dostopnosti in nizke cene je kot medij za uporabo v nadkritičnih procesih vse pogosteje uporabljena voda. V tem magistrskem delu smo preučevali razgradnjo odpadne tetrapak embalaže s pod- in nadkritično vodo v visokotlačnem in visokotemperaturnem šaržnem reaktorju pri temperaturi od 300 °C do 450 °C ter v časovnem obdobju med 15 in 60 min. Reakcije smo izvajali v eni in v dveh stopnjah. Razmerje odpadni materil/voda je bilo 1 g/10 mL. Nastale produkte v štirih fazah (plinski, vodni, oljni in trdni) smo analizirali s različnimi tehnikami (FTIR, TC, GC/MS, HPLC). Enostopenjsko hidrotermično razgradnjo odpadne tetrapak embalaže smo izvedli pri temperaturi 425 °C oz. 450 °C in reakcijskem času 15 min ali 60 min. Ugotovili smo, da z višanjem temperature in daljšanjem reakcijskega časa narašča izkoristek oljne faze. Najvišji izkoristek oljne faze smo dobili pri temperaturi 450 °C in reakcijskem času 60 min in je znašal 60,7 %. V drugem delu smo izvedli dvostopenjsko hidrotermično razgradnjo odpadne tetrapak embalaže. Prvo stopnjo smo izvedli v podkritični vodi pri temperaturi 250 °C oz. 300 °C in reakcijskem času 30 oz. 60 min. Najvišji izkoristek vodne faze (18,0 %) smo določili pri temperaturi razgradnje 250 °C in reakcijskem času 60 min, najvišji izkoristek oljne faze (35,1 %) pa pri temperaturi razgradnje 300 °C in času 60 min. Drugo stopnjo razgradnje, kjer smo uporabili trdni preostanek iz prve stopnje, smo opravili pri temperaturi 425 oz. 450 °C in reakcijskem času 15 min. Najvišji izkoristek oljne faze po obeh stopnjah skupaj (65,5 %) dobimo pri vzorcu, ki smo ga v prvi stopnji razgradili pri temperaturi 300 °C in reakcijskem času 60 min, v drugi stopnji pa pri temperaturi 450 °C in reakcijskem času 15 min. Oljni fazi smo določili kemijsko sestavo in ugotovili, da je sestavljena iz nasičenih in nenasičenih alifatskih ogljikovodikov, aromatskih spojin, ketonov, alkoholov in amidov. Analizirali smo tudi vodno fazo, v kateri so bili prisotniglukoza, fruktoza, celobioza, gliceraldehid, anhidrid glukoze, levulinska kislina, furfural in 5-hidroksimetilfurfural. Plinska faza je vsebovala CO2 in ogljikovodike med C1-C6. Po razgradnji tetrapaka je kot trdni preostanek nastal aluminijev prah obdan s tanko plastjo PE.In 2020, Slovenia produced more than one million tonnes of waste. Packaging of various products accounts for nearly 30% of waste. Various types of packaging include paper, glass, metal, plastic, wood, and multilayer packaging. Multilayer packaging is also known as composite packaging. Tetra Pak® is one of the most widely used and well-known multilayer packaging. Tetra Pak® packaging consists of paper/cardboard, polyethylene (PE) and aluminium. The problem with recycling Tetra Pak® lies in the fact that its components cannot be easily separated by mechanical processing. The use of sub- and supercritical fluids for various chemical processes has become increasingly important method in recent times. Due to its accessibility and low price, water is being more and more frequently used as a medium in supercritical processes. In this master’s thesis we studied the decomposition of waste Tetra Pak® packaging with sub- and supercritical water in a high-pressure and high-temperature batch reactor, at temperatures from 300 °C to 450 °C and a reaction time of 15 to 60 min. Reactions were performed in one and two stages. The ratio material/water was 1 g/10 mL. Degradation products in four phases (gas, aqueous, oil and solid) were analysed by various techniques (FTIR, TC, GC/MS, HPLC). One-stage hydrothermal decomposition of waste Tetra Pak® packaging was performed at a temperature of 425 ° C or 450 ° C and a reaction time of 15 min and 60 minutes. We found out that as the temperature and the reaction time increase, the yield of the oil phase increases. The highest oil yield was obtained at 450 °C and a reaction time of 60 min and it was 60.7 %. In the second part, we performed a two-stage hydrothermal decomposition of waste Tetra Pak®. The first stage was performed in subcritical water at a temperature of 250 °C or 300 °C and a reaction time of 30 or 60 min. The highest yield of the aqueous phase (18.0%) was determined at a decomposition temperature of 250 °C and a reaction time of 60 min, while the highest oil yield (35.1%) was found at a decomposition temperature of 300 °C and a time of 60 min. The second stage of decomposition, where we used the solid residue from the first stage, was performed at a temperature of 425 or 450 °C and a reaction time of 15 min. The highest oil yield after both steps together (65.5%) was obtained for the sample, which was decomposed in the first stage at 300 °C over the period of 60 min, and in the second stage at 450 ° C and over the period of 15 min. The chemical composition of the oil phase was determined and it was found that it is composed of saturated and unsaturated aliphatic hydrocarbons, aromatic compounds, ketones, alcohols and amides. We also analyzed the aqueous phase in which following compounds were present: glucose, fructose, cellubiose, glyceraldehyde, glucose anhydride, levulinic acid, furfural, and 5-hydroxymethylfurfural. The gas phase contained CO2 and hydrocarbons between C1-C6. After decomposition, the solid residue was formed as an aluminium powder, which was surrounded by a thin layer of PE

Adsorption of metal ions on slag

Onesnaževanje z odpadnimi vodami predstavlja velik delež onesnaževanja narave. V teh odpadnih vodah se pogosto nahajajo tudi težke kovine, ki jih moramo zaradi ogrožanja okolja, živali in ljudi iz vode odstraniti. Kot poceni metoda za odstranjevanje težkih kovin iz vode, se je uveljavila adsorpcija. V iskanju učinkovitih ter poceni adsorbentov, se je dobro izkazala tudi žlindra, ki je stranski produkt pri proizvodnji jekla. V diplomskem delu predstavljamo rezultate raziskave adsorpcijskih lastnosti bele žlindre. Žlindri smo najprej določili specifično površino BET, volumen por, premer por, velikost delcev in zeta potencial. Nadalje smo preučevali vpliv pH in koncentracije na adsorpcijo železovih, bakrovih in svinčevih ionov. Hkrati smo preučili še medsebojni vpliv izbranih ionov na adsorpcijo. Preučevali smo učinkovitost in kapaciteto adsorpcije in iz rezultatov ugotovili, da pH minimalno vpliva na adsorpcijo bakra in železa, svinec pa ima adsorpcijski maksimum pri pH 7. Pri preiskovanju vpliva koncentracije smo ugotovili, da učinkovitost adsorpcije s koncentracijo narašča za svinec, na baker in železo pa skoraj ne vpliva, saj je bila učinkovitost v območju koncentracij od 1 mM do 13 mM 100 %. Medsebojni vpliv ionov daje pozitivne rezultate na učinek adsorpcije.Waste water pollution represents a substantial share in environmental pollution. Quite often, waste waters contain heavy metals – and because they pose a threat to the environment, animals and humans, their removal from water is necessary. Adsorption has become a widely used and inexpensive method for removing heavy metals from water. In search for efficient and inexpensive adsorbents, slag, a steel-making by-product, has performed rather well. The present diploma thesis presents the findings of the study of white slag adsorption properties. First, specific surface area BET of slag was determined as well as pore volume, pore diameter, particle size and zeta potential. The next step was the determination of how pH and concentration affect the adsorption of iron, copper and lead ions. The interaction of the selected ions and their impact on the adsorption process was also studied. The results of adsorption efficiency and capacity reveal that the pH has minimal effect on the adsorption of copper and ironfor lead the adsorption maximum is at pH 7. Higher concentrations resulted in better adsorption efficiency for lead but hardly affected the adsorption of copper and iron – the efficiency range being from 1 mM to 13 mM 100%. The interaction of ions positively affects the adsorption efficiency

Comparative study of hydrothermal decomposition of virgin and recycled polypropylene

Plastics are widely used due to their versatile properties and numerous applications. However, the proper management of plastic waste is a major challenge, even though it is recyclable. The process of repeated recycling can cause the quality of the material to decrease as unwanted contaminants and pollutants increase. This can affect the chemical recycling of plastics at the end of their life and the recovery of secondary products that can be used in other applications. In this study, the chemical degradation of virgin polypropylene (vPP) and recycled polypropylene (rPP) was investigated in supercritical water at a temperature of 450 °C and a reaction time of 15 to 240 min. The oil phase was the primary decomposition product and was obtained in high yield, which reached a maximum after 30 min of reaction time and was 96.9 % for vPP and 94.5 % for rPP. The results of our study show that there are some differences in the product composition depending on which material (vPP or rPP) is chemically recycled

Evaluation of the impact and fracture toughness of a nanostructured bainitic steel with low retained austenite content

The impact and fracture toughness of a nanostructured, kinetically activated bainitic steel was determined using Standard methods. Prior to testing, the steel was quenched in oil and aged naturally for a period of 10 days in order to obtain a fully bainitic microstructure with a retained austenite content below 1%, resulting in a high hardness of 62HRC. The high hardness originated from the very fine microstructure of bainitic ferrite plates formed at low temperatures. It was determined that the impact toughness of the steel in the fully aged condition improved remarkably, whereas the fracture toughness was in line with expectations based on the extrapolated data available in the literature. This suggests that a very fine microstructure is most beneficial to rapid loading conditions, whereas material flaws such as coarse nitrides and non-metallic inclusions are the major limitation for obtaining a high fracture toughness