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1.
Hydrothermal processes for conversion of lignocellulosic biomass to value-added compounds
Tanja 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: 16.10.2020; Views: 319; Downloads: 55
.pdf Full text (6,32 MB)

2.
Subcritical water as a green medium for extraction and processing of natural materials
Matej 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: 16.06.2016; Views: 1100; Downloads: 182
.pdf Full text (3,71 MB)

3.
Extraction of curcuminoids with subcritical water
Ignacio Macicior Borregón, 2015, undergraduate thesis

Keywords: subcritical water, extraction, curcuma
Published: 06.11.2015; Views: 989; Downloads: 46
.pdf Full text (1,47 MB)

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