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1.
Uporaba pod- in nadkritične vode za predelavo odpadne plastike
Maja Čolnik, 2021, doktorska disertacija

Opis: Doktorska disertacija obravnava kemijsko razgradnjo najpogosteje uporabljenih plastičnih odpadkov z uporabo pod- in nadkritične vode v uporabne produkte. Doktorsko disertacijo smo razdelili na tri dele. V prvem delu doktorske disertacije smo izvedli hidrotermično razgradnjo brezbarvnih in barvnih odpadnih PET plastenk. Poskuse smo izvajali v visokotemperaturnem in visokotlačnem šaržnem reaktorju pri temperaturah od 250-400 °C in reakcijskem času od 1-30 minut. Pri hidrolizi PET odpadkov so nastali primarni in sekundarni produkti. Glavni produkt razgradnje je bila TPA, ki smo jo po reakciji prečistili in določili izkoristek reakcije. Ugotovili smo, da pri 300 °C in 30 min v podkritični vodi dobimo najvišje izkoristke TPA iz brezbarvnih (90,0 ± 0,4% ) kot tudi iz barvnih (85,0 ± 0,2%) PET odpadnih plastenk. Čistote nastalih TPA smo analizirali s pomočjo HPLC, FTIR in TGA/DSC metod in ugotovili, da so njihove čistote zelo visoke in znašajo med 93-98%. Tekom reakcije so nastajali sekundarni produkti, kot so benzojska kislina, 1,4-dioksan, acetaldehid, IPA in CO2. S pomočjo analiziranih komponent v vodni in plinski fazi smo predpostavili mehanizem razgradnje PET odpadkov. Ocenili smo ekonomski in okoljski vpliv hidrotermične razgradnje PET. Ugotovili smo, da če bi povečali laboratorijski proces na industrijsko merilo, bi na letni ravni dosegli dobiček od prodaje TPA in bi znašal okrog 81 000 €. Pri tem bi kemijsko degradirali skoraj 1400 ton PET odpadkov. Okoljsko analizo hidrotermične razgradnje PET smo izvedli s pomočjo programske opreme OpenLCA in bazo podatkov Ecoinvent 3.6. Ugotovili smo, da so k splošnemu obremenjevanju okolja največ prispevale kategorije morska ekotoksičnost, globalno segrevanje in toksičnost za ljudi. Prav tako smo tekom študije o razgradnji PET odpadkov v podkritični vodi predstavili tudi kinetiko razgradnje kot ireverzibilno zaporedno reakcijo, kjer smo določili, da so reakcije za vse razgradne produkte 1.reda. V drugem delu doktorske disertacije smo v nadkritični vodi degradirali poliolefine (PE in PP). Študirali smo razgradnjo PE in PP odpadne plastike ter za primerjavo degradirali še osnovni LDPE. Prav tako smo spremljali vpliv katalizatorja ocetne kisline na potek, razgradnjo in sestavo nastalih produktov. Eksperimente smo izvajali od 380 °C do 450 °C. Tekom razgradnje so v primeru PP in PE odpadkov nastale štiri faze oljna, plinska, vodna in trdna, med tem ko so v primeru osnovnega LDPE nastale le tri faze. Trdni preostanek pri PP in PE odpadkih smo pripisali razpadu aditivov. Metodo za določevanje lahkih ogljikovodikov in CO2 v plinski mešanici smo tudi razvili in validirali. Plinska faza je vsebovala lahke ogljikovodike (C1 do C6) in CO2, medtem ko oljno fazo po večini sestavljajo nasičeni in nenasičeni alifatski ogljikovodiki, aliciklični ogljikovodiki, aromatski ogljikovodiki in alkoholi. V primeru dodatka ocetne kisline smo ugotovili rahlo povišanje nastanka metana in CO2 v nastali plinski mešanici, zaradi razgradnje ocetne kisline v nadkritični vodi. Z višanjem reakcijskih pogojev je nastajalo manj oljne in več plinske faze. Na osnovi pridobljenih podatkov smo predstavili možen mehanizem razgradnje PP in PE v nadkritični vodi. V tretjem delu doktorske disertacije smo študirali razgradnjo PVC odpadkov v nadkritični vodi pri temperaturi od 400-425 °C in časih od 30-60 min. Ugotovili smo, da PVC odpadki razpadejo na oljno, plinsko, vodno in trdno fazo. Maso kloridnih ionov v vodni fazi smo določili s pomočjo titracijske metode. Pri 400 °C in 30 min smo dobili najvišji izkoristek. Kemijsko sestavo oljne in plinske faze smo določili s pomočjo GC/MS metode. Ugotovili smo, da oljna faza podobno kot pri PE ali PP v glavnem vsebuje nasičene in nenasičene alifatske ogljikovodike, aliciklične ogljikovodike, aromatske ogljikovodike in alkohole. V primeru PVC plastike, pa smo v oljni fazi zasledili še halogenirane ogljikovodike (kloroalkane). Plinska faza je vsebovala le lahke ogljikovodike in CO2.
Ključne besede: Pod- in nadkritična voda, odpadna plastika, kemijsko recikliranje, polietilen tereftalat, polietilen, polipropilen, polivinilklorid, kinetika, tereftalna kislina, benzojska kislina, acetaldehid, 1, 4- dioksan, izoftalna kislina, plini, ogljikovodiki, surovo olje, gorivo
Objavljeno: 11.06.2021; Ogledov: 306; Prenosov: 0
.pdf Celotno besedilo (4,64 MB)

2.
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: 551; Prenosov: 82
.pdf Celotno besedilo (6,32 MB)

3.
FORMULATION, PREPARATION AND CHARACTERIZATION OF NANOEMULSIONS FOR PARENTERAL NUTRITION
Dušica Mirković, 2019, doktorska disertacija

Opis: The aim of this doctoral research was to develop and optimize parenteral nanoemulsions as well as the total parenteral nutrition (TPN) admixture containing a nanoemulsion obtained in the course of the optimization process (hereinafter referred to as optimal nanoemulsion), and to examine their physicochemical and biological quality as well. In addition, the quality of the prepared nanoemulsions was compared with the quality of the industrial nanoemulsion (Lipofundin® MCT/LCT 20%), and, in the end, the TPN admixture initially prepared was also compared with the admixture into which the industrial emulsion was incorporated. Parenteral nanoemulsions that were considered in this dissertation were prepared by the high-pressure homogenization method. This method is the most widely applied method for the production of nanoemulsions due to the shortest length of homogenization time, the best-obtained homogeneity of the product and the smallest droplet diameter. For the nanoemulsion formulation, preparation and optimization purposes, by using, firstly, the concept of the computer-generated fractional design, and, after that, the full experimental design, the assessment of both direct effects of different formulation and process parameters (the oil phase type, the emulsifier type and concentration, a number of homogenization cycles and the pressure under which homogenization was carried out) as well as the effects of their interactions on the characteristics of prepared nanoemulsions was performed. Monitoring the nanoemulsion physical and chemical stability parameters was carried out immediately after their preparation, and then after 10, 30 and 60 days. It included the visual inspection, the measurement of the droplet diameter (the mean and volume droplet diameter), the polydispersity index, the ζ-potential, the pH value, the electrical conductivity, and the peroxide number. After the preparation and after 60 days, the biological evaluation (the sterility test and the endotoxic test) of the prepared nanoemulsions was carried out. As far as the characterization of the TPN admixture is concerned, it included practically the same parameters. The dynamics of monitoring the characteristics of the TPN admixture was determined on the basis of practical needs of hospitalized patients (0h, 24h and 72h). The scope and comprehensiveness of this issue indicated the need to divide the doctoral dissertation into three basic stages. The first stage was preliminary. Using the 24-1 fractional factorial design, nanoemulsions for the parenteral nutrition were prepared. They contained either a combination of soybean and fish oil, or a combination of medium chain triglycerides and fish oil. In addition, the type and the amount of an emulsifier used, a number of high-pressure homogenization cycles, and the homogenization pressure, were also varied. The measurement of the above-mentioned parameters for the industrial nanoemulsion was parallely carried out (Lipofundin® MCT/LCT 20%). The objective of this part of the research was to identify critical numerical factors having the most significant effect on the characteristics that define the prepared parenteral nanoemulsions. Parameters that were singled out as the result of this stage of the research (the emulsifier concentration and a number of homogenization cycles) were used as independent variables in the second stage of the research.
Ključne besede: nanoemulsions, total parenteral nutrition admixtures, high pressure homogenization, design of experiments, optimization, analysis of variance, artificial neural networks
Objavljeno: 07.06.2019; Ogledov: 10962; Prenosov: 0
.pdf Celotno besedilo (2,82 MB)

4.
Formuliranje paracetamola v polimere s superkritičnimi plini
Nina Urbič, 2019, magistrsko delo

Opis: Cilj magistrske naloge je bil določiti topnost učinkovine paracetamol v superkritičnih plinih. V naši raziskavi smo uporabili argon, propan in ogljikov dioksid. V visokotlačni celici smo spreminjali temperaturo in tlak ter spremljali kako se obnaša paracetamol v superkritičnih plinih, ki združujejo lastnosti plinov in tekočin. Paracetamol smo si izbrali zato, ker je ena najbolj razširjenih aktivnih snovi na svetu in jo najdemo v najbolj razširjenih farmacevtskih protibolečinskih izdelkih, ki jih lahko dobimo brez recepta. Topnost paracetamola smo določili s statično – analitično metodo, z jemanjem vzorcev iz zgornje faze, saj je le - ta bogata s plinom. Ugotovili smo, da je topnost paracetamola v vseh treh plinih (argon, propan in ogljikov dioksid) skoraj povsem neodvisna od temperature, narašča pa s tlakom oziroma z višanjem gostote plina. Z uporabo postopka visokotlačne mikronizacije PGSSTM smo paracetamol vezali na biopolimer trilaurin s pomočjo ogljikovega dioksida kot topila. Ogljikov dioksid je deloval kot plastifikator. Molekule plina se z lahkoto vrinejo med verige polimera in povzročijo znižanje viskoznosti polimernega nosilca ter s tem povečajo prosti volumen polimera. S spreminjanjem tlaka ter temperature lahko vplvamo na lastnosti produkta mikronizacije; na porazdelitev por, njihovo velikost in obliko. S pomočjo tehnike PGSSTM smo zmanjšali velikost delcev in tako povečali površino materiala in posledično izboljšali profil raztapljanja učinkovine.
Ključne besede: paracetamol, superkritični plini, biopolimer, ogljikov dioksid, argon, propan
Objavljeno: 02.04.2019; Ogledov: 803; Prenosov: 60
.pdf Celotno besedilo (1,16 MB)

5.
Hidrotermična degradacija polietilena nizke gostote
Blaž Deželak, 2018, magistrsko delo

Opis: V današnjem času težimo k zmanjševanju in ponovni uporabi komunalnih ali industrijskih odpadkov. Polietilen (PE) je eden izmed najpogosteje uporabljenih materialov na svetu in je prisoten v številnih industrijah in segmentih. V zadnjih letih je uporaba plastičnih materialov narasla iz 5 milijonov ton na 100 milijonov ton letno. Največji problem je razkroj plastike, ki povzroča resne okoljske probleme. Razgradnja plastike v subkritični in superkritični vodi je zelo učinkovita metoda za pretvorbo plastičnih odpadkov v širok spekter koristnih produktov, kot so bazne kemikalije, alternativna energija in goriva, specialne kemikalije, brez dragih in pogosto zdravju škodljivih organskih topil. Namen magistrske naloge je bil preučiti hidrotermično degradacijo polietilena nizke gostote (LDPE) v subkritični in superkritični vodi. Eksperimentalni del smo izvedli v visokotlačnem in visokotemperaturnem šaržnem reaktorju v temperaturnem intervalu od 200 do 450 °C. Mešanico LDPE in vode v razmerju 1/5 smo izpostavljali pri reakcijskih časih od 15 min do 120 min. Določali smo vpliv temperature, reakcijskega časa in dodatka katalizatorja ocetne kisline na potek in kinetiko reakcij razgradnje LDPE. Vzorce iz reaktorja smo analizirali in določili produkte degradacije s plinsko kromatografijo in masno spektrometijo (GC/MS). Določili smo še vsebnost celotnega organskega ogljika (TOC). Ugotovili smo, da je pri vseh eksperimentih, ki so bili izvedeni pri temperaturah 425 in 450 °C ter reakcijskem času od 15 - 120 min, prišlo do razgradnje LDPE v subkritični vodi. Razgradne produkte hidrotermične degradacije smo ločili na oljno, plinasto in vodno fazo. Dobljene produkte v oljni in plinski fazi smo analizirali s pomočjo GC/MS, medtem ko smo s TOC analizatorjem določili skupni ogljik v vodni fazi. Ugotovili smo, da je oljna faza v večini sestavljena iz ogljikovodikov (alkanov in alkenov), kjer je prevladoval 2,3-dimetil pentan. Plinasta faza je vsebovala različne pline kot so: dušik, CO2, metan, etan, eten in vse do heksana in heksena. V vodni fazi pa smo določili vsebnost organskih snovi, ki so bile višje pri dodatku katalizatorja ocetne kisline.
Ključne besede: LDPE, hidrotermično utekočinjanje, superkritična voda, razgradni produkti
Objavljeno: 04.12.2018; Ogledov: 623; Prenosov: 0
.pdf Celotno besedilo (2,16 MB)

6.
High-Perssure process design for polymer treatment and heat transfer enhancement
Gregor Kravanja, 2018, doktorska disertacija

Opis: The doctoral thesis presents the design of several high-pressure processes involving »green solvents« so-called supercritical fluids for the eco-friendly and sustainable production of new products with special characteristics, fewer toxic residues, and low energy consumption. The thesis is divided into three main parts: polymer processing and formulation of active drugs, measurements of transport properties form pendant drop geometry, and study of heat transfer under supercritical conditions. In the first part, special attention is given to using biodegradable polymers in particle size reduction processes that are related to pharmaceutical applications for controlled drug release. The PGSSTM micronization process was applied to the biodegradable carrier materials polyoxyethylene stearyl ether (Brij 100 and Brij 50) and polyethylene glycol (PEG 4000) for the incorporation of the insoluble drugs nimodipine, fenofibrate, o-vanillin, and esomeprazole with the purpose of improving their bioavailability and dissolution rate. In order to optimize and design micronization process, preliminary transfer and thermodynamic experiments of water-soluble carriers (Brij and PEG)/ SCFs system were carried out. It was observed that a combination of process parameters, including particle size reduction and interactions between drugs and hydrophilic carriers, contributed to enhancing the dissolution rates of precipitated solid particles. In the second part, a new optimized experimental setup based on pendant drop tensiometry was developed and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. Droplet geometry was examined by using a precise computer algorithm that fits the Young–Laplace equation to the axisymmetric shape of a drop. The experimental procedure was validated by a comparison of the experimental data for the water-CO2 mixture with data from the literature. For the first time, interfacial tension of CO2 saturated solution with propylene glycol and diffusion coefficients of propylene glycol in supercritical CO2 at temperatures of 120°C and 150°C in a pressure range from 5 MPa, up to 17.5 MPa were measured. Additionally, the drop tensiometry method was applied for measuring systems that are of great importance in carbon sequestration related applications. The effect of argon as a co-contaminant in a CO2 stream on the interfacial tension, diffusion coefficients, and storage capacity was studied. In the third part, comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture at high pressures and temperatures was studied. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 °C to 90 °C) and pressures (5 MPa to 30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the heat transfer coefficients (HTC) of supercritical CO2, ethane and their azeotropic mixture in water loop have been measured and compared. A brief evaluation is provided of the effect of mass flux, heat flux, pressure, temperature and buoyancy force on heat transfer coefficients. Additionally, to properly evaluate the potential and the performance of azeotropic mixture CO2-ethane, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system containing exclusively CO2.
Ključne besede: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients
Objavljeno: 28.05.2018; Ogledov: 965; Prenosov: 141
.pdf Celotno besedilo (5,51 MB)

7.
Formation, characterization and application of polysaccharide aerogels
Gabrijela Horvat, 2018, doktorska disertacija

Opis: The aim of this PhD dissertation was to describe and analyze the preparation and characterization of polysaccharide aerogels and their future pharmaceutical and medical application. For the research, we used four types of polysaccharides: pectin, alginate, xanthan and guar. We used two types of pectin, high-methoxyl and low-methoxyl pectin, because of their different gelation mechanisms. The first part of the dissertation describes the preparation and characterization of pure polysaccharide aerogels. First, we prepared pectin spherical aerogels, cross-linked with three different ions, and we investigated their final properties. Later, we developed a new method for the preparation of alginate, pectin, xanthan and guar aerogels. We used only ethanol and no other cross-linkers. Ethanol was removed in the later processes of supercritical drying, and the remaining final material was thus only porous polysaccharide. By this method, we were able to prepare pure xanthan and guar aerogels. Prior to this study, xanthan and guar aerogels were prepared only as composites. Pectin aerogels prepared by the new method have amazing properties. On the other hand, alginate aerogels show poor characteristics, and thus the methods need to be optimised. We tried different alginate viscosities, different alcohols (methanol, ethanol, 1-propanol and 1-butanol), and we investigated longer (24h) and shorter (1h) gel setting times. The second part of this dissertation describes the pharmaceutical and medical applications of prepared aerogels. The release of diclofenac sodium from spherical pectin aerogels was investigated in vitro. Calcium cross-linked aerogels were not able to retain the drug, and its release was immediate. In order to achieve controlled release of diclofenac sodium, zinc ions had to be used as cross-linkers. Later, a low water-soluble drug, nifedipine, was used as a model drug for the monolithic aerogels prepared by the new method. The release of nifedipine from pectin and alginate aerogels was highly increased, compared to the crystalline drug. This result is promising for future evaluation of these materials for increasing the bioavailability of poorly water-soluble drugs. Nifedipine release from xanthan and guar aerogels was prolonged up to two weeks. This result reveals a new perspective on such materials for their potential use in medicine as implants and local drug delivery. According to these results, we then developed a new coating material for medical-grade stainless steel from xanthan and pectin. An aerogel coating was loaded with diclofenac sodium and indomethacin, and their release profiles were investigated in vitro. Electrochemical analysis and cell tests proved the safety of such materials for use in medicine. Using aerogel coatings, the drug can be introduced locally into the body; therefore, the need for intravenous, post-operational treatment is greatly reduced.
Ključne besede: polysaccharides, aerogels, supercritical drying, drug carriers
Objavljeno: 09.04.2018; Ogledov: 1002; Prenosov: 197
.pdf Celotno besedilo (5,84 MB)

8.
Vpliv sestave gojišča na produkcijsko sposobnost seva Streptomyces clavuligerus
Jernej Rotar, 2017, magistrsko delo

Opis: Bakterije Streptomyces clavuligerus v procesu fermentacije sintetizirajo klavulansko kislino, katera učinkovito deluje kot inhibitor β-laktamaze in se uporablja v kombinaciji z antibiotiki kot pomoč pri premagovanju bakterijske odpornosti. Pri tem se pojavlja veliko vprašanj glede vpliva substratov na proizvodnost. Zato je namen te študije izboljšati biosintezo klavulanske kisline, pri čemer se usmerimo k preučevanju vpliva aminokislin in mineralov, ki so ključni gradniki medija za fermentacijo klavulanske kisline. V magistrskem delu na laboratorijskem nivoju eksperimentalno iščemo vpliv sestave gojišča na produkcijsko sposobnost seva ter poskušamo optimizirati gojišče s katerim bi dosegli maksimalno produktivnost. Pri eksperimentalnem delu uporabljamo mikrobiološke in analitske metode. S pomočjo HPLC metode analiziramo vsebnost klavulanske kisline. Rezultati kažejo, da so minerali nepogrešljivi pri biosintezi klavulanske kisline. Železo in cink sta najpomembnejša minerala v fazi produkcije klavulanske kisline. Kalcij in magnezij pa negativno vplivata na produkcijo le te. Ugotovili smo, da dodatek aminokislin k že optimiranemu standardnemu mediju dodatno izboljša produkcijo klavulanske kisline. Dodatek arginina, asparagina, lizina in valina pozitivno vpliva na biosintezo produkta. Manjši pozitiven vpliv imajo tudi treonin, histidin in glicin. Aminokislini metionin in cistein pa negativno vplivata na produkcijo. Najboljše rezultate smo dosegli z dodatkom arginina, in sicer smo z dodatkom 10 mM L-arginina vsebnost izboljšali za 24 %. Dokazali smo, da je produktivnost klavulanske kisline odvisna tudi od same produkcijske zmožnosti bakterij S. clavuligerus, ki se od seva do seva razlikuje.
Ključne besede: klavulanska kislina, Streptomyces clavuligerus, fermentacija, biosinteza, vpliv sestave gojišča, proizvodnost
Objavljeno: 22.11.2017; Ogledov: 1121; Prenosov: 14
.pdf Celotno besedilo (2,20 MB)

9.
Toplotne lastnosti fluidov pri visokih tlakih
Gašper Zajc, 2017, magistrsko delo

Opis: Namen magistrske naloge je bil preučevanje in ovrednotenje toplotnih lastnosti alternativnih nosilcev toplotne energije pri visokih tlakih, kjer smo se podrobneje posvetili ogljikovemu dioksidu in etanu ter njuni azeotropni mešanici. Ti fluidi lahko predstavljajo okolju prijaznejšo alternativo kakor trenutno najbolj razširjeni fluorirani ogljikovodiki. V magistrskem delu smo poleg eksperimentalnega dela v laboratoriju izvajali še razne simulacije v računalniškem programu Aspen Plus V8.8. V eksperimentalnem delu smo postavili delujoč kontinuirni dvocevni toplotni prenosnik, kjer smo merili koeficiente toplotne prestopnosti CO2, etana in njune azeotropne zmesi v odvisnosti od tlaka (od 5 MPa do 30 MPa), temperature (od 20 °C do 65 °C) in pretoka vode (pri 1 L/min in 2 L/min), ki je predstavljala hladen tok v našem protitočnem prenosniku. V drugem delu smo teoretično simulirali obratovanje subkritičnih toplotnih črpalk s CO2 in azeotropno zmesjo CO2 – etan. Opravili smo tudi simulacijo, kjer smo iskali optimalno sestavo azeotropne zmesi, ki bi dajala najvišje izkoristke procesa. Idejna zasnova teh simulacij je nastala zaradi različnih pogojev vrelišča azeotropnih zmesi v razmerju s čistimi snovmi, kar bi lahko potencialno znižalo obratovalne stroške toplotnih črpalk. Glavne ugotovitve so bile: Vsi merjeni visokotlačni fluidi so kazali maksimume toplotne prestopnosti tik nad kritičnimi pogoji. Ti vrhovi so se nato z višanjem tlaka nižali in premikali proti vedno višjim temperaturam. Tvorba teh vrhov je bila posledica specifične toplote fluida, ki je kazala enaka odstopanja nad kritično točko. Ugotovili smo tudi, da azeotropne zmesi tvorijo koeficiente toplotnih prestopnosti med obema komponentama, ki jo sestavljata. Simulativni rezultati analiz obratovanja toplotnih črpalk so kazali potencialne izboljšave izkoristkov procesa z vpeljavo azeotropne zmesi, vendar samo v določenih primerih. Na podlagi znižanja temperature vrelišča azeotropa CO2 – etan smo lahko obratovanje procesa izboljšali na kondenzatorju, vendar smo ga zaradi tega istočasno poslabšali na uparjalniku.
Ključne besede: CO2, etan, azeotrop, toplotni prenosnik, toplotna črpalka, superkritični fluid
Objavljeno: 22.11.2017; Ogledov: 740; Prenosov: 100
.pdf Celotno besedilo (3,62 MB)

10.
Konverzija sladkorjev v subkritični vodi
Karin Hercog, 2017, diplomsko delo

Opis: Namen diplomskega dela je bilo proučiti reakcijske poti razgradnje različnih sladkorjev v subkritični vodi pri danem času, temperaturi in tlaku. Pri tem smo uporabili sedem različnih sladkorjev (celobioza, fruktoza, galaktoza, glukoza, ksiloza, laktoza, saharoza). Vse reakcije smo izvajali v visokotlačnem visokotemperaturnem avtoklavu pri temperaturi 250 ˚C. Reakcije v avtoklavu za posamezni sladkor smo izvajali pri treh različnih časih, 1min, 5min in 15 min. Rezultati pridobljeni s pomočjo eksperimentalnega dela so služili pri proučevanju na katere komponente se uporabljeni sladkorji pri določeni temperaturi, času in tlaku razgradijo, kakšen je posamezen delež sladkorja in ostalih spojin dobljenih pri razgradnji. Reakcijsko zmes, t.j. vodno raztopino sladkorja smo pripravili s pomočjo destilirane vode. Določili smo deleže razgradnih produktov in sicer delež v vodi topnih produktov, delež v acetonu topnih produktov, trdni preostanek ter pline in izgube. Pri eksperimentalnem delu dobljeno vodno in acetonsko fazo smo uporabili za nadaljnje analize, kot sta HPLC analiza in UV-VIS spektrofotoskopija. S pomočjo HPLC smo določili razgradne produkte posameznega sladkorja in njihove deleže glede na celotno maso vzorca. Iz dobljenih rezultatov je razvidno, da sta ena izmed glavnih produktov razgradnje sladkorjev 5-hidroksi metil furfural in furfural. Iz rezultatov je tudi razvidno, da masni delež vodne faze v odvisnosti od časa pada, medtem ko masni delež acetonske faze s časom narašča. S časom se povečuje masa trdnega ostanka in delež nastalih plinov. Delež samega sladkorja v reakciji s časom pada, kar pomeni da se sladkor razgrajuje.
Ključne besede: subkritična voda, ragradnja sladkorjev, celobioza, fruktoza, galaktoza, glukoza, ksiloza, laktoza, saharoza
Objavljeno: 22.11.2017; Ogledov: 757; Prenosov: 81
.pdf Celotno besedilo (1,80 MB)

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