doctoral disertation
Tanja Milovanović (Author), Mojca Škerget (Mentor), Željko Knez (Co-mentor)

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;

Data

Language: English
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: [T. Milovanović]
UDC: [66.061.3+66.094.941]:547.458(043.3)
COBISS: 33266691 Link will open in a new window
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Other data

Secondary language: Slovenian
Secondary title: Hidrotermični procesi za konverzijo lignocelulozne biomase v produkte z višjo dodano vrednostjo
Secondary abstract: V doktorski disertaciji smo preučevali subkritični vodni proces razgradnje lignocelulozne biomase za pridobitev spojin z visoko dodano vrednostjo. Doktorska disertacija je razdeljena na štiri osrednja poglavja. V prvem in drugem delu disertacije smo preučevali vzorčne spojine (standarde celuloze in sladkorja ter kostanjeve tanine), z namenom razumeti procese pridobivanja spojin iz biomase. Razgradnjo celuloze in različnih sladkorjev smo izvedli v šaržnem reaktorju s subkritično vodo. Glavne faze, kot so v vodi topna frakcija, v acetonu topna frakcija in trdni ostanek, so bile ločene in analizirane. Analiza vodotopne faze je bila izvedena z metodo HPLC, opremljeno z UV in RI detektorjem, medtem ko je bila v acetonu topna faza celuloze analizirana z metodo GC-MS. Skupna vsebnost sladkorja je bila določena s kolorimetrično metodo fenol-žveplove kisline. Lastnosti trdega ostanka, pridobljenega iz celuloze, kot so: specifična površina, volumen por in premer por, pa so bile določene z adsorpcijsko metodo plina. Vodotopna faza je v večini sestavljena iz sladkornih monomerov in monomernih razgradnih produktov, kot so 5-hidroksimetilfurfural (5-HMF), furfural, eritroza, sorbitol, 1,6-anhidroglukoza, glikolaldehid, glicerlaldehid, 1,3-dihidroksiaceton, piruvaldehid , levulinske, mlečne, oksalne in jantarne kisline, medtem ko je fazo topno v acetonu, ki se imenuje tudi bio olje, sestavljajo furani, fenoli, karboksilne kisline, aldehidi, ketoni in visoko molekularne spojine. Na osnovi dobljenih rezulatov smo predlagali reakcijski mehanizem celuloze in sladkorjev v subkritični vodi. Rezultate hidrotermalne razgradnje celuloze in sladkorja smo uporabili za preučitev industrijsko zanimivih izdelkov, kot je obdelava papirnih odpadkov s subkritično vodo. Določeni so bili optimalni pogoji (temperatura in reakcijski čas), ki so nam dali največji izkoristek danih kemikalij (furfural, 5-HMF, levulinska kislina). %Lubje sladkega kostanja (Castanea Sativa) vsebuje veliko taninov in različnih fenolnih spojin, ki jih je mogoče uporabiti v farmacevtske, kozmetične, prehranske ter medicinske namene. V drugem delu disertacije smo uporabili izvleček sladkih kostanjevih taninov in lubje kostanjov, ki so zelo bogati z bioaktivnimi spojinami in zanimivi za predelavo s subkritičnim vodnim procesom. Spektrofotometrične metode smo uporabili za določitev skupne vsebnosti taninov, fenolov in ogljikovih hidratov ter antioksidativne aktivnosti. Identificirane spojine so elaginska in galna kislina, elagitanini (veslalagin, kastalagin, 1-o-galol castalagin, veskalin in kastalin), sladkorji (maltoza, glukoza, fruktoza in arabinoza) in derivati sladkorja (5-HMF, furfural in levulinska kislina). Rezultate, pridobljene s hidrotermalno hidrolizo, smo primerjali z rezultati kisle hidrolize. Nazadnje je bila izvedena optimizacija reakcijskih parametrov subkritičnih vodnih procesov, da bi dobili produkt, ki je zelo bogat z ellaginsko kislino. V tretjem delu disertacije je opisana ekstrakcija s subkritično vodno divjega kostanja (Aesculus hippocastanum), ki ga sestavljajo semena, semenska lupina, lubje in listi. Smo odkrili v ekstraktih različne spojine, kot so escini, eskulin, fraksin, fenolne spojine (klorogenska, neoklorogenska in galna kislina) in furfurali (5-hidroksimetifurfural, furfural in metilfufrual) in jih količinsko ovrednostili s pomočjo metode HPLC. V zadnjem delu disertacije je predstavljena primerjalna študija ekstrakcije kakavove lupine, z uporabo zelenih metod (superkritični CO2 in subkritična voda) in konvencionalne metode (ekstrakcija Soxhleta s heksanom in ekstrakcija s 50% acetonom), za pridobivanje bioaktivnih spojin. S HPLC smo dokazali obstoj metilksantinov, fenolnih spojin, sladkorjev, derivatov sladkorjev, masnih kislin.
Secondary keywords: biomasa;subkritična voda;biološki odpadki;ekstrakcija;hidrotermalna razgradnja;hidroliza;bioaktivne spojine;doktorske disertacije;Lignocelulozna biomasa;Disertacije;Razgradnja;
Type (COBISS): Doctoral dissertation
Thesis comment: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages: XVI, 138 str.
ID: 11835371