Hydrothermal processes for conversion of lignocellulosic biomass to value-added compoundsTanja 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: 363; Prenosov: 61
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Subcritical water as a green medium for extraction and processing of natural materialsMatej 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: 1128; Prenosov: 184
Celotno besedilo (3,71 MB)
The influence of enzymatic treatment on wool fibre properties using PEG-modified proteasesSuzana Jus
, Marc Schroeder
, Georg M. Gübitz
, Elisabeth Heine
, Vanja Kokol
, 2007, izvirni znanstveni članek
Opis: The main contribution of the presented work was to introduce the use of proteases modified with the soluble polymer polyethylene glycol (PEG) in the bio-finishing process of wool fibres, to target enzyme action to the outerparts of wool fibres, i.e. to avoid the diffusion and consequent destroying of the inner parts of the wool fibre structure, in the case of native proteases using. Different proteolytic enzymes from Bacillus lentus and Bacillus subtilis in native and PEG-modified forms were investigated and their influence on the modification of wool fibres morphology surface, chemical structure, as well as the hydrolysis of wool proteins, the physico-mechanical properties, and the sorption properties of 1:2 metal complex dye during dyeing were studied. SEM images of wool fibres confirmed smoother and cleaner fibre surfaces without fibre damages using PEG-modified proteases. Modified enzyme products have a benefit effect on the wool fibres felting behaviours (14%) in the case when PEG-modified B. lentus is used, without markedly fibre damage expressed by tensile strength and weight loss ofthe fibre. Meanwhile the dye exhaustion showed slower but comparable level of dye uptake at the end of the dyeing.
Ključne besede: volnena vlakna, proteolitski encimi, encimske modifikacije, sorpcija barve, morfologija vlaken, wool fibres, proteolytic enzymes, enzyme modification, felting, dye sorption, protein hydrolysis, XPS-analysis, fibre morphology
Objavljeno: 01.06.2012; Ogledov: 2024; Prenosov: 91
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In-situ investigation of sucrose hydrolysis - successful link between design of experiment, RC1 and reactIR systemKatja Zajšek
, Andreja Goršek
, 2008, izvirni znanstveni članek
Opis: The main purpose of this work was combining the modern laboratory equipment (RC1 reaction calorimeter and ReactIRTMiC10 reaction analysis system) and the concept of the Taguchi fs design of experiment to determine the relative influence of important process parameters affecting the sucrose hydrolysis. The reaction was catalyzed by strong acidic cation-exchange resin Amberlite IR-120 in H+ form. Four process parameters, including reaction temperature (.), sucrose mass concentration (fÁS), catalyst mass concentration (fÁC) and the rotational frequency of the stirrer (fm) at four levels were considered in this study. Relative contributions of the proposed influencing process parameters on hydrolysis time were estimated by analysis of the variance (ANOVA). The results showed that . had a substantial effect on the reaction time (78,3 %), the fm and fÁC had a smaller ones (7,9 % and 6,4 %, respectively), meanwhile the remain fraction to 100 % represents error (7,4 %). The optimum conditions, where the time required for complete sucrose hydrolysis would be the shortest, are: .= 79 Ključne besede: sucrose hydrolysis, catalyst, Taguchi method, in-situ FTIR, reaction calorimeter RC1
Objavljeno: 31.05.2012; Ogledov: 1673; Prenosov: 59
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Analysis of reactive dyestuffs and their hydrolysis by capillary electrophoresisAlenka Ojstršek
, Aleš Doliška
, Darinka Fakin
, 2008, izvirni znanstveni članek
Opis: The objective of the presented research was to examine the potential of capillary electrophoresis (CE) for the analysis of structurally different reactive dyestuffs, their activation and posterior hydrolysis, with special focus on optimization of the working conditions. Preliminary, the effect of various additives to the background electrolyte on the resolution improvements versus migration time of Reactive Black 5 as a model dyestuff was investigated. Based on these results, the electropherograms of eight commercially interesting reactive dyestuffs of various chemical structures and their converted forms upon alkaline pH were carried-out. In order to examine the behavior of the reactive dyestuff during the dyeing process, the dye-bath absorbance was monitored throughout the Reactive Black 5 exhaustion, and the conversion of the dye's form was highlighted using the CE technique. The obtained results unequivocally prove that CE could offer a fast and efficient detection method of structurally different reactive dyestuffs, as well as their hydrolysis products in the dye-baths and effluents later on.
Ključne besede: capillary electrophoresis, dyes, hydrolysis
Objavljeno: 31.05.2012; Ogledov: 1414; Prenosov: 58
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