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Hydrothermal processes for conversion of lignocellulosic biomass to value-added compounds
Tanja Milovanović, 2020, doktorska disertacija

Opis: 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.
Ključne besede: Subcritical water, biomass, biowaste, extraction, hydrothermal degradation, hydrolysis, bioactive compounds.
Objavljeno: 16.10.2020; Ogledov: 326; Prenosov: 55
.pdf Celotno besedilo (6,32 MB)

On-line condition monitoring and evaluation of remaining useful lifetimes for mineral hydraulic and turbine oils
Vito Tič, Darko Lovrec, 2017, znanstvena monografija

Opis: 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.
Ključne besede: Hydraulic and turbine oils, degradation mechanisms, on-line condition monitoring, test methods, remaining useful lifetime
Objavljeno: 22.12.2017; Ogledov: 925; Prenosov: 248
.pdf Celotno besedilo (7,75 MB)
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Low temperature impact toughness of the main gas pipeline steel after long-term degradation
P. O. Maruščak, Irina Danyliuk, R.T. Biščak, Tomaž Vuherer, 2014, izvirni znanstveni članek

Opis: 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.
Ključne besede: impact toughness, fracture, damage, gas pipeline, steel, degradation
Objavljeno: 03.04.2017; Ogledov: 666; Prenosov: 327
.pdf Celotno besedilo (699,32 KB)
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Subcritical water as a green medium for extraction and processing of natural materials
Matej Ravber, 2016, doktorska disertacija

Opis: 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.
Ključne besede: Subcritical water, Biowaste, Extraction, Hydrolysis, Antioxidants, Hydrothermal degradation.
Objavljeno: 16.06.2016; Ogledov: 1104; Prenosov: 183
.pdf Celotno besedilo (3,71 MB)

Case study of the sonochemical decolouration of textile azo dye Reactive Black 5
Simona Vajnhandl, Alenka Majcen Le Marechal, 2007, izvirni znanstveni članek

Opis: The decolouration and mineralization of reactive dye C.I. Reactive Black 5, a well-known representative of non-biodegradable azo dyes, by means of ultrasonic irradiation at 20, 279 and 817 kHz has been investigated with emphasis on the effect of various parameters on decolouration and degradation efficiency. Characterization of the used ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using Fricke and iodine dosimeter. Experiments were carried out with low frequency probe type, and a high-frequency plate type transducer at 50, 100 and 150 W of acoustic power and within the 5-300 mgžL initial dye concentration range. Decolouration, as well as radical production, increased with increasing frequency, acoustic power, and irradiation time. Any increase in initial dye concentration results in decreased decolouration rates. Sonochemical decolouration was substantially depressed by the addition of 2-methyl-2-propanol as a radical scavenger, which suggests radical-induced reactions in the solution. Acute toxicity to marine bacteria Vibrio fischeri was tested before and after ultrasound irradiation. Under the conditions employed in this study, no toxic compounds were detected after 6 h of irradiation. Mineralization of the dye was followed by TOC measurements. Relatively low degradation efficiency (50% after 6 h of treatment) indicates that ultrasound is rather inefficient in overall degradation, when used alone.
Ključne besede: textile industry, wastewater treatment, textile dyeing, reactive dyes, azo dyes, decoloration, ultrasound, degradation, decoloration kinetics, oxidizing species
Objavljeno: 01.06.2012; Ogledov: 1495; Prenosov: 72
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Ultrasound in textile dyeing an the decolouration/mineralization of textile dyes
Simona Vajnhandl, Alenka Majcen Le Marechal, 2005, pregledni znanstveni članek

Opis: In recent decades ultrasound has established an important place in different industrial processes such as the medical field, and has started to revolutionize environmental protection. The idea of using ultrasound in textile wet processes is not a new one. On the contrary there are many reportsfrom the 1950s and 1960s describing the beneficial effects of ultrasound in textile wet processes. The aim of this paper is to review some fundamentals of ultrasound, its broad application and gather some new researchand studies regarding ultrasound application in textile wet processes,with the emphasis on textile dyeing and the decolouration/mineralization of textile wastewaters.
Ključne besede: textile industry, textile dyes, wastewater, decoloration, degradation, ultrsound
Objavljeno: 01.06.2012; Ogledov: 1231; Prenosov: 33
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