1. Chemical decomposition of thermosetsVasil Handjiski, 2024, undergraduate thesis Abstract: This bachelor thesis depicts the chemical degradation of polyurethane and melamine formaldehyde, which are representatives of thermosets. A high–pressure reactor was used to perform chemical degradation. The effectiveness of the chemical degradation of the selected thermosets was monitored by measuring pH, total organic carbon (TOC) and total nitrogen (TN) of the liquid residues. The remaining solid material was characterized by infrared spectroscopy and the mass loss was determined. Using these analytical methods, it was concluded that the chemical degradation depends on the temperature and the duration of the reactions as well as the reaction medium. It was found that “white liquor” is a more effective medium for the chemical degradation of polyurethane and melamine formaldehyde than water.
Keywords: chemical degradation, polyurethane, melamine formaldehyde, FTIR
Published in DKUM: 22.10.2024; Views: 0; Downloads: 0 |
2. Energy storage potential of used electric vehicle batteries for supporting renewable energy generation in IndiaRajat Chauhan, Ram Santran, Matevž Obrecht, Rhythm Singh, 2024, original scientific article Abstract: As electric vehicle (EV) batteries degrade to 80 % of their full capacity, they become unsuitable for electric vehicle propulsion but remain viable for energy storage applications in solar and wind power plants. This study aims to estimate the energy storage potential of used-EV batteries for stationary applications in the Indian context. To estimate the renewable energy generation and used-EV capacity, the study adopted International Energy Agency (IEA) and International Council on Clean Transportation (ICCT) growth scenarios for renewable energy growth and electric vehicle growth, respectively. Battery degradation models for popular battery chemistries in electric vehicle mobility, namely Lithium Iron Phosphate, Lithium Manganese Oxide, and Nickel Manganese Cobalt, are employed to estimate reusable battery capacity. The first life for these battery chemistries, for mobility applications, ranges from 3.5 to 7 years. Results indicate an estimated storage potential of 1300–1870 GWh in used electric vehicle batteries in India by 2038. This is equivalent to 17 % – 39 % of average daily energy generation from solar and wind power plants in various scenarios by the year 2038. This research contributes to SDG-7 by facilitating clean energy accessibility through renewable energy storage and supports emission reduction efforts in transportation and energy sectors, thereby fostering sustainable cities (SDG-11).
Keywords: used-EV batteries, battery degradation, renewable energy, energy storage, battery capacity, Li-ion batteries
Published in DKUM: 09.08.2024; Views: 104; Downloads: 9
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3. Degradation of waste tetra pak packaging with hydrothermal treatment in sub-/supercritical waterMihael Irgolič, Maja Čolnik, Petra Kotnik, Mojca Škerget, 2024, original scientific article 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: 11
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4. Comparative study of hydrothermal decomposition of virgin and recycled polypropyleneMihael Irgolič, Maja Čolnik, Petra Kotnik, Lidija Čuček, Mojca Škerget, 2023, original scientific article Abstract: 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.
Keywords: virgin polypropylene, plastics, chemical degradation, chemical recycled
Published in DKUM: 18.04.2024; Views: 235; Downloads: 5
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5. 3D-printed collagen–nanocellulose hybrid bioscaffolds with tailored properties for tissue engineering applicationsAndreja Dobaj-Štiglic, Florian Lackner, Chandran Nagaraj, Marco Beaumont, Matej Bračič, Isabel Duarte, Veno Kononenko, Damjana Drobne, Balaraman Madhan, Matjaž Finšgar, Rupert Kargl, Karin Stana-Kleinschek, Tamilselvan Mohan, 2023, original scientific article Keywords: assays, degradation, porosity, scaffolds, 3D printing
Published in DKUM: 09.04.2024; Views: 238; Downloads: 17
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6. 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: 645; Downloads: 60
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7. Hydrothermal processes for conversion of lignocellulosic biomass to value-added compounds : doctoral disertationTanja Milovanović, 2020, doctoral dissertation Abstract: In this doctorial dissertation subcritical water processes of lignocellulosic biomass to obtain value-added compounds are studied. The doctorial dissertation is divided into four main parts. In the first and second part of dissertation, model compounds (standards of cellulose and sugars and chestnut tannins) were primarly used in order to better understand processes of real biomass material.
The degradation of cellulose and different sugars was performed in batch reactor with subcritical water. The different reaction temperatures and times were used. The main phases, such as water-soluble fraction, acetone-soluble fraction and solid residue were separated and analysed. The analysis of water-soluble phase was done by HPLC equipped with UV and RI detector, while acetone-soluble phase of cellulose was analysed by GC-MS. Total sugar content was determined by the phenol-sulphuric acid colorimetric method. The properties of char, obtained using cellulose as a treated material, such as: specific surface area, pore volume and pore diameter were determined by gas adsorption method. A water-soluble phase mainly consists of sugar monomers and monomer degradation products such as 5-hydroxymethylfurfural (5-HMF), furfural, erythrose, sorbitol, 1,6-anhydroglucose, glycolaldehyde, glycerlaldehyde, 1,3-dihydroxyacetone, pyruvaldehyde, formic, levulinic, lactic, oxalic and succinic acids, while acetone-soluble phase, referred to also as bio-oil, consists of furans, phenols, carboxylic acids, aldehydes, ketones and high molecular compounds. The reaction mechanism of cellulose and sugars in subcritical water has been proposed based on the obtained results. Furthermore, the results from cellulose and sugar hydrothermal degradation were utilized in further work to determine which industrially interesting products could be obtained by hydrothermal processing of paper waste in subcritical water. The optimum conditions ( temperature and reaction time), which gave us the highest yield of base chemicals (furfural, 5-HMF, levulinic acid) were determined.
Sweet chestnut (Castanea Sativa) bark contains high level of tannins and various phenolic compounds which can be utilized in pharmaceutical, cosmetic, nutritional and medical purposes. The sweet chestnut tannins extract and sweet chestnut bark were used as materials highly rich in bioactive compounds for subcritical water processes which are presented in the second part of doctorial dissertation, respectively. The spectrophotometric methods were used to determine total tannins, phenols and carbohydrates content and antioxidant activity. The identified compounds were ellagic and gallic acid, ellagitannins (vescalagin, castalagin, 1-o-galloyl castalagin, vescalin and castalin), sugars (maltose, glucose, fructose and arabinose) and sugar derivatives (5-HMF, furfural and levulinic acid). The results obtained from hydrothermal hydrolysis were compared to results from acid hydrolysis. Finally, the optimization of reaction parameters of subcritical water processes has been done aiming to obtain the product highly rich in ellagic acid.
Subcritical water extraction of horse chestnut (Aesculus hippocastanum) parts such as seeds, seed shell, bark and leaves was described in the third chapter of dissertation. The detected compounds in extracts, such as escins, esculin, fraxin, phenolic compounds (chlorogenic, neochlorogenic and gallic acids) and furfurals (5-hydroxymethyfurfural, furfural, and methylfufrual) are quantified using HPLC.
The last part of dissertation proposes extraction of cocoa shell using green technologies (supercritical CO2 and subcritical water extraction) and also conventional methods (Soxhlet extraction with hexane and extraction with 50 % acetone) to obtain bioactive compounds in order to compare the results. The detected compouns were methylxanthines, phenolic compounds, sugars, fatty acids.
Keywords: Subcritical water, biomass, biowaste, extraction, hydrothermal degradation, hydrolysis, bioactive compounds.
Published in DKUM: 16.10.2020; Views: 1774; Downloads: 163
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8. On-line condition monitoring and evaluation of remaining useful lifetimes for mineral hydraulic and turbine oilsVito Tič, Darko Lovrec, 2017, scientific monograph Abstract: Condition monitoring of hydraulic and turbine oils, and especially their remaining useful life, is becoming an important strategic business advantage for plant owners, which benefits in environment protection and cost reduction.
This monograph discusses the problem of condition monitoring of hydraulic fluids throughout their life-cycles. Particular emphasis is placed on assessing mineral-based oils’ conditions and their remaining useful lifetimes quantitatively. Practicality and usefulness are vital when developing and deploying various methods for condition monitoring systems within industrial environments. Therefore, it is important to know the oil degradation mechanisms and influencing factors, commonly used laboratory methods and oil ageing tests, as well as, for on-line condition monitoring system design, the available sensors with all their characteristics and restrictions.
The proposed approach is based on a novel method for testing the durability and oxidation stability of different hydraulic and turbine oils. The developed mathematical model is based on data from previously conducted oil-ageing tests for the assessment of an oil's condition and its remaining useful lifetime. The method can also be used for comparison of different oils and selection of a more adequate oil with high oxidation stability and long service-lifetime.
Keywords: Hydraulic and turbine oils, degradation mechanisms, on-line condition monitoring, test methods, remaining useful lifetime
Published in DKUM: 22.12.2017; Views: 1777; Downloads: 430
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9. Low temperature impact toughness of the main gas pipeline steel after long-term degradationP. O. Maruščak, Irina Danyliuk, R.T. Biščak, Tomaž Vuherer, 2014, original scientific article Abstract: The correlation of microstructure, temperature and Charpy V-notch impact properties of a steel 17G1S pipeline steel was investigated in this study. Within the concept of physical mesomechanics, the dynamic failure of specimens is represented as a successive process of the loss of shear stability, which takes place at different structural/scale levels of the material. Characteristic stages are analyzed for various modes of failure, moreover, typical levels of loading and oscillation periods, etc. are determined. Relations between low temperature derived through this test, microstructures and Charpy (V-notch) toughness test results are also discussed in this paper.
Keywords: impact toughness, fracture, damage, gas pipeline, steel, degradation
Published in DKUM: 03.04.2017; Views: 1497; Downloads: 444
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10. Subcritical water as a green medium for extraction and processing of natural materialsMatej Ravber, 2016, doctoral dissertation Abstract: In this doctoral dissertation, the application of subcritical water as a green medium for
the extraction and processing of natural materials is presented. The work is divided into three
main parts. In the first part, subcritical water is proposed as a solvent for the simultaneous
extraction of oil- and water-soluble phase from oily seeds. The extraction parameters, such as
temperature, time and material to solvent ratio that yield the highest amounts of both phases
are examined. The quality of both obtained phases is examined. The characteristics of oils
obtained using subcritical water is compared to that obtained using a conventional method.
The second part of this work proposes subcritical water as an efficient solvent for the
isolation of bioactive phenolic compounds from wood waste, that is produced by the forestry
industry. Different wood fractions are firstly extracted in batch-mode and the fraction with the
highest amounts of bioactive compounds is determined. Next, semi-continuous operation is
applied, where the effects of different extraction parameters are studied on the extraction yield
and quality of the extract. The effect of temperature and ethanol addition to the subcritical
water on the content of single phenolic compounds identified in the extracts is observed.
Lastly, the cost of manufacturing of such a product is estimated by evaluating the economics
of different pilot- and industrial-scale processes operating at optimal conditions determined
on the laboratory scale.
The last part proposes the use of subcritical water as an efficient hydrolytic medium
for glycoside bonded antioxidants, specifically those found in waste agro-industrial sources.
Effect of temperature, treatment time, concentration and the atmosphere used for establishing
the pressure in the reactor are first studied on a model glycoside compound - rutin and the
optimal combination of reaction parameters are established for the batch-mode reactor. The
degradation products of the model compound are identified and the concentration/time profiles
of their degradation are observed. Furthermore, the reaction kinetics explaining the
degradation of the rutin standard are evaluated. In the next step, the method is implemented
on a real glycosides-containing extract. The extract is hydrolyzed at conditions obtained from
the first step and the free aglycone is obtained at the highest yields possible. Lastly, the process
is upgraded to continuous operation and the final hydrolyzed high-purity product is recovered.
Keywords: Subcritical water, Biowaste, Extraction, Hydrolysis, Antioxidants, Hydrothermal degradation.
Published in DKUM: 16.06.2016; Views: 1904; Downloads: 230
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