Pulsed corona discharge as an advanced oxidation process for degradation of organic

Advanced oxidation processes (AOPs) have been studied and developed to suffice the effective removal of refractory and toxic compounds in polluted water. The quality and cost of wastewater treatment need improvements, and electric discharge technology has a potential to make a significant difference compared to other established AOPs based on energy efficiency. The generation of active oxidant species such as ozone and hydroxyl radicals by high voltage discharge is a relatively new technology for water treatment. Gas-phase pulsed corona discharge (PCD), where a treated aqueous solution is dispersed between corona-producing electrodes free of the dielectric barriers, was developed as an alternative approach to the problem. The short living radicals and ozone formed in the gas phase and at the gas-liquid interface react with dissolved impurities. PCD equipment has a relatively simple configuration, and with the reactor in an enclosed compartment, it is insensitive towards gas humidity and does not need the gas transport. In this thesis, PCD was used to study and evaluate the energy efficiency for degrading various organic compounds, as well as the chemistry of the oxidation products formed. The experiments investigate the aqueous oxidation of phenol, humic substances, pharmaceutical compounds (paracetamol, ibuprofen, indomethacin, salicylic acids, -estradiol), as well as lignin degradation and transformation to aldehydes. The study aims to establish the influence of initial concentration of the target pollutant, the pulsed discharge parameters, gas phase composition and the pH on the oxidation kinetics and the efficiency. Analytical methods to measure the concentrations of the target compounds and their by-products include HPLC, spectrophotometry, TOC and capillary electrophoresis. The results of the research included in this summary are presented in the attached publications and manuscripts accepted for publication. Pulsed corona discharge proved to be highly effective in oxidizing each of the target compounds, surpassing the closest competitor, conventional ozonation. The increase in oxidation efficiencies for some compounds in oxygen media and at lower pulse repetition frequencies shows a significant role of ozone. The role of the ·OH radicals was established in the surface reactions. The main oxidation products, formation of nitrates, and the lignin transformation were quantified. A compound specific approach is suggested for optimization of the PCD parameters that have the most significant impact on the oxidation energy efficiency because of the different characteristics and responses of the target compound to the oxidants, as well as different admixtures that are present in the wastewater. Further studies in the method’s safety (nitration and nitrosation of organic compounds, nitrite and nitrate formation enhancement) are needed for promoting the method.

Effects of Dietary Fat Oxidation Products and Flavonols on Lipoprotein Oxidation

Various studies suggest that oxidative modifications of low density lipoprotein (LDL), and also other lipoproteins, have an important role in the development of atherosclerosis. In addition to the oxidation products formed endogenously, oxidised triacylglycerols (TAG) and oxysterols in the diet contribute to the oxidised lipoproteins found in circulation. However, studies on both the effect of oxidised dietary lipids on lipoprotein lipid oxidation and the reactions that modify oxidised fat after ingestion have been scarce. Studies on the effects of dietary antioxidants on the lipid oxidation in vivo and the risk of atherosclerosis have been inconclusive. More clinical trials are needed to test the importance of lipoprotein oxidation as a cardiovascular risk factor in humans. In the recent years, various methods have been optimised and applied to the analysis of lipid oxidation products in vivo, and information on the molecular structures of oxidised lipids in plasma, lipoproteins and atherosclerotic plaques has started to accumulate. However, specific structures of oxidised TAG molecules present in these tissues and lipoprotein fractions have not been investigated earlier. In the orginal research in this thesis, an approach based on highperformance liquid chromatographyelectrospray ionisationmass spectrometry (HPLCESIMS) and baseline diene conjugation (BDC) methods was used in order to investigate lipid oxidation level and oxidised TAG molecular structures in pig and human lipoproteins after dietary interventions. The approach was optimised with human LDL samples, which contained various oxidation products of TAG. LDL particles of hyperlipidaemic subjects contained an elevated amount of conjugated dienes. In the pig studies, several oxidised TAG structures with hydroxy, keto, epoxy or aldehydic groups were found in chylomicrons and VLDL after diets rich in sunflower seed oil. Also, the results showed that oxidised sunflower seed oil increased the oxidation of lipoprotein lipids and their TAG molecules. TAG hydroperoxides could be detected neither in the small intestinal mucosa of the pigs fed on the oxidised oil nor in their chylomicrons or VLDL.6 In the clinical studies, dietary flavonol aglycones extracted from sea buckthorn berries did not have an effect on lipoprotein lipid oxidation and other potential risk factors of atherosclerosis, but their absorption was demonstrated. Oil supplementation seemed to increase the bioavailability of the flavonols. Oxidised TAG molecules were detected in LDL particles of the subjects after both flavonol and control diets.

Wet oxidation of recalcitrant lignin waters: Experimental and kinetic studies

The dissertation is based on four articles dealing with recalcitrant lignin water purification. Lignin, a complicated substance and recalcitrant to most treatment technologies, inhibits seriously pulp and paper industry waste management. Therefore, lignin is studied, using WO as a process method for its degradation. A special attention is paid to the improvement in biodegradability and the reduction of lignin content, since they have special importance for any following biological treatment. In most cases wet oxidation is not used as a complete ' mineralization method but as a pre treatment in order to eliminate toxic components and to reduce the high level of organics produced. The combination of wet oxidation with a biological treatment can be a good option due to its effectiveness and its relatively low technology cost. The literature part gives an overview of Advanced Oxidation Processes (AOPs). A hot oxidation process, wet oxidation (WO), is investigated in detail and is the AOP process used in the research. The background and main principles of wet oxidation, its industrial applications, the combination of wet oxidation with other water treatment technologies, principal reactions in WO, and key aspects of modelling and reaction kinetics are presented. There is also given a wood composition and lignin characterization (chemical composition, structure and origin), lignin containing waters, lignin degradation and reuse possibilities, and purification practices for lignin containing waters. The aim of the research was to investigate the effect of the operating conditions of WO, such as temperature, partial pressure of oxygen, pH and initial concentration of wastewater, on the efficiency, and to enhance the process and estimate optimal conditions for WO of recalcitrant lignin waters. Two different waters are studied (a lignin water model solution and debarking water from paper industry) to give as appropriate conditions as possible. Due to the great importance of re using and minimizing the residues of industries, further research is carried out using residual ash of an Estonian power plant as a catalyst in wet oxidation of lignin-containing water. Developing a kinetic model that includes in the prediction such parameters as TOC gives the opportunity to estimate the amount of emerging inorganic substances (degradation rate of waste) and not only the decrease of COD and BOD. The degradation target compound, lignin is included into the model through its COD value (CODligning). Such a kinetic model can be valuable in developing WO treatment processes for lignin containing waters, or other wastewaters containing one or more target compounds. In the first article, wet oxidation of "pure" lignin water was investigated as a model case with the aim of degrading lignin and enhancing water biodegradability. The experiments were performed at various temperatures (110 -190°C), partial oxygen pressures (0.5 -1.5 MPa) and pH (5, 9 and 12). The experiments showed that increasing the temperature notably improved the processes efficiency. 75% lignin reduction was detected at the lowest temperature tested and lignin removal improved to 100% at 190°C. The effect of temperature on the COD removal rate was lower, but clearly detectable. 53% of organics were oxidized at 190°C. The effect of pH occurred mostly on lignin removal. Increasing the pH enhanced the lignin removal efficiency from 60% to nearly 100%. A good biodegradability ratio (over 0.5) was generally achieved. The aim of the second article was to develop a mathematical model for "pure" lignin wet oxidation using lumped characteristics of water (COD, BOD, TOC) and lignin concentration. The model agreed well with the experimental data (R2 = 0.93 at pH 5 and 12) and concentration changes during wet oxidation followed adequately the experimental results. The model also showed correctly the trend of biodegradability (BOD/COD) changes. In the third article, the purpose of the research was to estimate optimal conditions for wet oxidation (WO) of debarking water from the paper industry. The WO experiments were' performed at various temperatures, partial oxygen pressures and pH. The experiments showed that lignin degradation and organics removal are affected remarkably by temperature and pH. 78-97% lignin reduction was detected at different WO conditions. Initial pH 12 caused faster removal of tannins/lignin content; but initial pH 5 was more effective for removal of total organics, represented by COD and TOC. Most of the decrease in organic substances concentrations occurred in the first 60 minutes. The aim of the fourth article was to compare the behaviour of two reaction kinetic models, based on experiments of wet oxidation of industrial debarking water under different conditions. The simpler model took into account only the changes in COD, BOD and TOC; the advanced model was similar to the model used in the second article. Comparing the results of the models, the second model was found to be more suitable for describing the kinetics of wet oxidation of debarking water. The significance of the reactions involved was compared on the basis of the model: for instance, lignin degraded first to other chemically oxidizable compounds rather than directly to biodegradable products. Catalytic wet oxidation of lignin containing waters is briefly presented at the end of the dissertation. Two completely different catalysts were used: a commercial Pt catalyst and waste power plant ash. CWO showed good performance using 1 g/L of residual ash gave lignin removal of 86% and COD removal of 39% at 150°C (a lower temperature and pressure than with WO). It was noted that the ash catalyst caused a remarkable removal rate for lignin degradation already during the pre heating for `zero' time, 58% of lignin was degraded. In general, wet oxidation is not recommended for use as a complete mineralization method, but as a pre treatment phase to eliminate toxic or difficultly biodegradable components and to reduce the high level of organics. Biological treatment is an appropriate post treatment method since easily biodegradable organic matter remains after the WO process. The combination of wet oxidation with subsequent biological treatment can be an effective option for the treatment of lignin containing waters.

Aqueous photocatalytic oxidation of steroid estrogens

Concerns have increased regarding the detection of endocrine-disrupting compounds in the effluents of sewage treatment plants (STPs). These compounds are able to disrupt normal function of the endocrine system of living organisms even at trace concentrations. Natural and synthetic steroid estrogens (SEs) are believed to be responsible for the majority of the endocrine-disrupting effects. Municipal sewage, the main source of SEs in the environment, is a complex mixture of a wide range of pollutants at concentrations much higher than those of SEs. Low concentrations of SEs in the presence of copollutants thus make their removal problematic. The main objectives of the present work were to study the potential of photocatalytic oxidation (PCO) to effectively treat SE-containing aqueous solutions and to identify the optimum conditions for such treatment. The results showed that SEs can be effectively degraded photocatalytically. Due to the adsorption properties of SEs on the TiO2 photocatalyst surface alkaline medium was found to be beneficial for SE oxidation despite the presence of co-pollutants in concentrations characteristic for the sanitary fraction of municipal sewage. The potential of PCO to selectively oxidise SEs was examined in the presence of copollutants of the sanitary fraction of sewage - urea, saccharose and human urine. The impact of ethanol, often used as a solvent in the preparation of SE stock solutions, was also studied and the results indicated the need to use organic solvent-free solutions for the study of SE behaviour. Photocatalytic oxidation of SEs appeared to be indifferent towards the presence of urea in concentrations commonly found in domestic sewage. The effect of other co-pollutants under consideration was far weaker than could be expected from their concentrations, which are from one hundred to a few thousands times higher than those of the SEs. Although higher concentrations can dramatically slow down the PCO of SEs, realistic concentrations of co-pollutants characteristic for the sanitary fraction of domestic sewage allowed selective removal of SEs. This indicates the potential of PCO to be a selective oxidation method for SE removal from the separate sanitary fraction of municipal sewage.

Perfluorattuja yhdisteitä sisältävien jätevesien puhdistus- ja analyysimenetelmät

Perfluoratut alkyyliyhdisteet eli PFAS-yhdisteet ovat synteettisiä orgaanisia yhdisteitä, joissa on fluorattu hiiliketju. Hiilen ja fluorin väliset vahvat sidokset ovat muodostuneet ongelmaksi jätevedenpuhdistamoilla, sillä yhdisteet eivät hajoa puhdistamoilla käytössä olevilla vedenpuhdistusmenetelmillä. Yhdisteitä kertyy luontoon jätevesien mukana. Kandidaatintyössä on vertailtu yhdisteitä sisältävien vesien käsittelymenetelmiä parhaiten soveltuvan menetelmän löytämiseksi. Menetelmien kustannuksia tai soveltuvuutta vedenpuhdistamomittakaavan prosessiksi ei ole arvioitu. Lisäksi työssä on koottu yhdisteitä sisältävien jätevesien analysointiin sopivia analyysimenetelmiä. Soveltuvat puhdistus- ja analyysimenetelmät on esitelty uusien tieteellisten artikkelien pohjalta. Mahdollisia erotusmenetelmiä ovat membraanierotus ja sorptio. Membraaneista soveltuvimpia ovat nanosuodatus- ja käänteisosmoosimembraanit, joilla erottuvat jopa 0,0001 μm:n kokoiset partikkelit. PFAS-yhdisteet voidaan erottaa sorptiolla muun muassa aktiivihiileen. Yhdisteiden rakenne hajoaa nykyaikaisilla hapetusmenetelmillä ja polttamalla lietteen mukana. Hapettaminen permanganaatin avulla ei tuottanut hyvää tulosta, mutta fotokemiallisella hapetuksella ja alhaisen lämpötilan plasmatekniikalla (NTP) yhdisteiden rakenne hajosi lähes kokonaan. Fotokemiallinen hapetus onnistui erityisesti perfluorokarboksyylihapoilla, joiden rakenne hajosi jopa kolmessa tunnissa. Yleisimmin käytetty analyysimenetelmä on nestekromatografin ja massaspektrometrin yhdistelmä (LC-MS/MS) ja matriisivaikutus minimoidaan tyypillisesti kiinteäfaasiuutolla (SPE). Työssä esitellyistä käsittelymenetelmistä parhaiten soveltuva on NTP-menetelmä, koska sillä saatiin tutkimusten mukaan hajotettua yhdisteiden rakenne muita menetelmiä lyhyemmässä ajassa ja se soveltuu parhaiten kaikille PFAS-yhdisteille. NTP-menetelmässä ei tarvita katalyyttiä tai lisäkemikaaleja. Voimakkaana hapettimena toimivat epästabiilit hydroksyyliradikaalit, jotka syntyvät koronapurkauksen kautta. Koronapurkauksessa muodostuu myös otsonia ja lisäksi vapaa happi voi tehostaa hapettumista. Menetelmässä muodostuvien hajoamistuotteiden hallinta vaatii lisätutkimusta. Mahdollinen hallintakeino voisi olla esimerkiksi hapettumisessa vapautuvien fluoridi-ionien saostaminen. Muodostuvien hajoamistuotteiden toksisuutta voitaisiin tarkkailla biosensorilla.

Oxidation of Aqueous Thiosulfate Solutions by Pulsed Corona Discharge

The aim of this Master’s thesis focused on the oxidation of sodium thiosulfate using non thermal plasma technology as an advance oxidation process (AOP). By using this technology we can degrade certain toxic chemical compounds present in mining wastewaters as pollutants. Different concentrations of thiosulfate and pulse frequencies were used in the PCD experiments and the results in terms of various delivered energies (kWh/m3) and degradation kinetics were compared. Pulsed corona discharge is an energy efficient process compared to other oxidation processes using for the treatment of waste water pollutants. Due to its simplicity and low energy costs make it attractive in the field of waste water treatment processes. This technology of wastewater treatment has been tested mainly on pilot scale level and in future the attempts are to be focus on PCD investigations on larger process scale. In this research work of oxidation of thiosulfate using pulsed corona discharge, the main aim of this research was to study degradation of a studied toxic and not environmental friendly chemical compound. The focus of this research was to study the waste waters coming from the gold mines containing leachate compound thiosulfate. Literature review contained also gold leaching process when cyanide is used as the leachate. Another objective of this work was to compare PCD process with other processes based on their energy efficiencies. In the experimental part two concentrations of sodium thiosulfate, 1000ppm and 400ppm, were used. Two pulse generator frequencies of 833 and 200 pulses per second (pps) were used. The chemical analyses of the samples taken during semi-batch PCD oxidation process were analyzed by ion chromatographic (IC). It is observed after the analyses that among different frequencies and concentrations, the most suitable ones for the process is 200pps and 1000ppm respectively because the pollutants present in the waste water has more time to react with the OH radicals which are the oxidants and the process is energy efficient compared to other frequencies.

Ultrasound-assisted electrochemical treatment of wastewaters containing organic pollutants by using novel Ti/Ta2O5-SnO2 electrodes

Advanced oxidation processes (AOPs) are modern methods using reactive hydroxyl radicals for the mineralization of organic pollutants into simple inorganic compounds, such as CO2 and H2O. Among AOPs electrochemical oxidation (EO) is a method suitable for coloured and turbid wastewaters. The degradation of pollutants occurs on electrocatalytic electrodes. The majority of electrodes contain in their structure either expensive materials (diamond and Pt-group metals) or are toxic for the environment compounds (Sb or Pb). One of the main disadvantages of electrochemical method is the polarization and contamination of electrodes due to the deposition of reaction products on their surface, which results in diminishing of the process efficiency. Ultrasound combined with the electrochemical degradation process eliminates electrode contamination because of the continuous mechanical cleaning effect produced by the formation and collapse of acoustic cavitation bubbles near to the electrode surface. Moreover, high frequency ultrasound generates hydroxyl radicals at water sonolysis. Ultrasound-assisted EO is a non-selective method for oxidation of different organic compounds with high degradation efficiencies. The aim of this research was to develop novel sustainable and cost-effective electrodes working as electrocatalysts and test their activity in electrocatalytic oxidation of organic compounds such as dyes and organic acids. Moreover, the goal of the research was to enhance the efficiency of electrocatalytic degradation processes by assisting it with ultrasound in order to eliminate the main drawbacks of a single electrochemical oxidation such as electrodes polarization and passivation. Novel Ti/Ta2O5-SnO2 electrodes were developed and found to be electrocatalytically active towards water (with 5% Ta content, 10 oxide film layers) and organic compounds oxidation (with 7.5% Ta content, 8 oxide film layers) and therefore these electrodes can be applicable in both environmental and energy fields. The synergetic effect of combined electrolysis and sonication was shown while conducting sonoelectrochemical (EO/US) degradation of methylene blue (MB) and formic acid (FA). Complete degradation of MB and FA was achieved after 45 and 120 min of EO/US process respectively in neutral media. Mineralization efficiency of FA over 95% was obtained after 2 h of degradation using high frequency ultrasound (381, 863, 1176 kHz) combined with 9.1 mA/cm2 current density. EO/US degradation of MB provided over 75% mineralization in 8 h. High degradation kinetic rates and mineralization efficiencies of model pollutants obtained in EO/US experiments provide the preconditions for further extrapolation of this treatment method to pilot scale studies with industrial wastewaters.

Kloorifenoleja sisältävien jätevesien AOP-käsittely

Kirjallisuustyössä tutkittiin tehostetun hapetuksen menetelmiä (engl. Advanced Oxidation Processes, AOPs) kloorifenolien käsittelyssä. Tutkittava aine valittiin US EPA:n (United States Environmental Protection Agency) ympäristölle haitallisten aineiden listalta. Työssä tutkitut AOP-menetelmät olivat otsonointi kasvatetussa pH:ssa, O3/H2O2-prosessi, fotolyyttinen otsonointi (O3/UV), H2O2/UV-prosessi ja Fenton-prosessi (H2O2+Fe2+). AOP-käsittelyssä OH-radikaalien oletetaan pääosin aiheuttavan epäpuhtauksien hapettumisen. Kirjallisuustyössä tutkittiin OH-radikaaleihin vaikuttavien parametrien, kuten pH:n, lämpötilan sekä hapettimien ja hapetettavan aineen konsentraatioiden vaikutusta kloorifenolien hapetusprosessissa. Työn tarkoituksena oli selvittää tehokkain AOP-käsittely kloorifenoleja sisältävien jätevesien käsittelylle. AOP-käsittelyjen tehokkuutta verrattiin hajoamisnopeusvakioiden, puoliintumisaikojen sekä hapettimen kemikaalikulutuksen ja kustannuksen perusteella. Fenton-prosessin ja otsonoinnin pH:ssa 9 todettiin olevan tehokkaimpia menetelmiä kloorifenolien hapetuksessa. Fenton-prosessin hapetusnopeus oli tehokkaampaa 4-CP:n ja 2,4-DCP:n hapetuksessa, kun taas otsonointi pH:ssa 9 hapetti nopeammin 2,3,4,6-TeCP:n ja 2,4,6-TCP:n. Kustannustehokkuuden perusteella Fenton-prosessi oli otsonointia tehokkaampi. Parhaan menetelmän valinta kloorifenoleiden poistamiseksi oli vaikeaa, sillä useissa tutkimuksissa oli tutkittu vain yhtä menetelmää. Lisäksi eri tutkimuksissa käytetyt prosessiolosuhteet olivat erilaiset, joka hankaloitti tutkimusten vertailua. Lopullinen AOP-menetelmän valinta tulisikin suorittaa vasta laboratoriotutkimusten jälkeen.

Mäskin sisältämän ligniinin modifiointi PCD-hapetuksella

Teoriaosassa tutkittiin mäskin muodostumista oluentuotantoprosessissa, ligniiniä ja sen pilkkoutumista hapetuksella, eri kehittyneitä hapetusmenetelmiä ja hapetuksella saatavia potentiaalisia pääkomponentteja. Kehittyneissä hapetusmenetelmissä keskityttiin pääasiassa pulssitettuun koronapurkaukseen perustuvaan PCD-menetelmään (Pulsed Corona Discharge). Tutkittavana pääkomponenttina toimi glyoksyylihappo. Työn kokeellisessa osassa tutkittiin mäskistä erotetun ligniinin pilkkoutumista PCD-hapetuksella. Tässä menetelmässä hapetus perustuu sähköpurkauksen aikana syntyvien hydroksyyliradikaalien ja otsonin muodostumiseen, jotka voivat toimia hapettimina. Kokeissa käytettiin oluentuotannosta saatua mäskiä, josta ligniiniä liuotettiin natriumhydroksidi-vesi-liuoksen avulla uuttamalla.. Tämän jälkeen liuosta käsiteltiin PCD laitteistossa. PCD-käsiteltyä tuotetta analysoitiin mittaamalla ligniinin ja aldehydien pitoisuudet siitä spektrofotometrin avulla. Työn tarkoituksena on tutkia PCD hapetusmenetelmän soveltuvuutta mäskin sisältämän ligniinin muokkaamiseen siten, että siitä syntyvää tuotetta voitaisiin käyttää jossakin muussa sovelluksessa, kuten esimerkiksi lääkkeiden raaka-aineena lääketeollisuudessa. PCD hapetusmenetelmä on koronasähköpurkauksiin perustuva laite, jota käytetään pääasiassa vedenpuhdistuksessa hajoittamaan haitallisia orgaanisia yhdisteitä. Tämän työn perusteella ligniiniä hajosi, aldehydejä muodostui ja hapetusnäytteiden pH laski hapetusajan kasvaessa. Tämä viittasi vahvasti glyoksyylihapon muodostumiseen PCD-laitteistossa.

Combination of pulsed corona discharge with TiO2 photocatalysis: verification of hypothesis

The oxidation potential of pulsed corona discharge concerning aqueous impurities is limited in respect to certain refractory compounds. This may be enhanced in combination of the discharge with catalysis/photocatalysis as developed in homogeneous gas-phase reactions. The objective of the work consists of testing the hypothesis of oxidation potential enhancement in combination of the discharge with TiO2 photocatalysis applied to aqueous solutions of refractory oxalate. Meglumine acridone acetate was included for meeting the practical needs. The experimental research was undertaken into oxidation of aqueous solutions under conditions of various target pollutant concentrations, pH and the pulse repetition rate with plain electrodes and the electrodes with TiO2 attached to their surface. The results showed no positive influence of the photocatalyst, the pollutants were oxidized with the rate identical within the accuracy of measurements. The possible explanation for the observed inefficiency may include low UV irradiance, screening effect of water and generally low oxidation rate in photocatalytic reactions. Further studies might include combination of electric discharge with ozone decomposition/radical formation catalysts.

Formation of nitrates in water in presence of formate and oxalate treated with pulsed corona discharge (PCD)

Tavallisten hapetusmenetelmien sijasta kehittyneitä hapetusmenetelmiä (AOP) on kehitetty yhä enemmän, jotta hapetusprosessista tulisi kannattavampi, tehokkaampi, ympäristöystävällisempi ja sitä voitaisiin hyödyntää laajalti eri paikoissa. Uusi teknologia, joka käyttää otsonia ja hydroksyyliradikaalia sähköimpulssien kanssa, on yksi mahdollinen tehokkaampi vedenkäsittelymentelmä. Kyseistä menetelmää kutsutaa pulsed corona discharge (PCD) -menetelmäksi, joka käyttää prosessissa muodostuvia otsonia ja hydroksyyliradikaalia hapettavina tekijöinä. Tässä työssä tutkittiin nitraatin muodostumista vedessä, kun vettä käsiteltiin PCD-laitteessa ja, kun oksalaatti- ja formaatti-ioneja oli sekoittuneina veteen. Nitraatteja muodostuu PCD–laitteessa veteen, kun ilman typpi reagoi hapettimina toimivien otsonin ja hydroksyyliradikaalin kanssa. Aiemmissa tutkimuksissa nitraatin muodostumisen on todistettu parantuvan, kun karboksyylihapot muurahais- ja oksaalihappo ovat sekoittuneina veteen. Tässä tutkimuksessa tarkoituksena oli tutkia, miten formaatti- ja oksalaatti-ionien, joiden pitoisuudet olivat 0 ppm, 50 ppm ja 100 ppm, läsnäolo vedessä vaikuttaa nitraatin muodostumiseen. PCD-kokeista saadut näytteet analysoitiin ionikromatografilla. Kyseisessä tutkimuksessa nitraatin muodostuminen oli samansuuruista jokaisessa kokeessa hapetusajan kasvaessa samalla, kun otettujen näytteiden pH-arvot laskivat. Tuloksena voitiin pitää sitä, ettei formaatti- tai oksalaatti-ioneilla ollut vaikutusta nitraatti-ionien muodostumiseen.

Kinetics of selective oxidation of lactose to lactobionic acid over Pd-active carbon catalyst

Laktoosi eli maitosokeri on tärkein ainesosa useimpien nisäkkäiden tuottamassa maidossa. Sitä erotetaan herasta, juustosta ja maidosta. Laktoosia käytetään elintarvike- ja lääketeollisuuden raaka-aineena monissaeri tuotteissa. Lääketeollisuudessa laktoosia käytetään esimerkiksi tablettien täyteaineena. Hapettamalla laktoosia voidaan valmistaa laktobionihappoa, 2-keto-laktobionihappoa ja laktuloosia. Laktobionihappoa käytetään biohajoavien pintojen ja kosmetiikkatuotteiden valmistuksessa, sekä sisäelinten säilöntäliuoksissa, joissa laktobionihappo estää happiradikaalien aiheuttamien kudosvaurioiden syntymistä. Tässä työssä laktoosia hapetettiin laktobionihapoksi sekoittimella varustetussa laboratoriomittakaavaisessa panosreaktorissa käyttäenkatalyyttinä palladiumia aktiivihiilellä. Muutamissa kokeissa katalyytin promoottorina käytettiin vismuttia, joka hidastaa katalyytin deaktivoitumista. Työn tarkoituksena oli saada lisää tietoa laktoosin hapettamisen kinetiikasta. Laktoosin hapettumisessa laktobionihapoksi havaittiin selektiivisyyteen vaikuttavan muunmuassa reaktiolämpötila, paine, pH ja käytetyn katalyytin määrä. Katalyyttiä kierrättämällä eri kokeiden välillä saatiin paremmat konversiot, selektiivisyydet ja saannot. Parhaat koetulokset saatiin hapetettaessa synteettisellä ilmalla 60 oC lämpötilassa ja 1 bar paineessa. Tehdyissä kokeissa pH:n säätö tehtiin manuaalisesti, joten pH ei pysynyt koko ajan haluttuna. Laktoosin konversio oli parhaimmillaan 95 %. Laktobionihapon suhteellinen selektiivisyys oli 100% ja suhteellinen saanto 100 %. Kinetiikan matemaattinen mallinnus tehtiin Modest-ohjelmalla käyttäen kokeista saatuja mittaustuloksia.Ohjelman avulla estimoitiin parametreja ja saatiin matemaattinen malli reaktorille. Tässä työssä tehtiin kineettinen mallinnus myös ravistelureaktorissa tehdyille laktoosin hapetuskokeille, missä pH pysyi koko ajan haluttuna 'in-situ' titrauksen avulla. Työn yhteydessä selvitettiin myös mahdollisuutta käyttää monoliittikatalyyttejä laktoosin hapetusreaktiossa.

Gas-phase photocatalytic oxidation of volatile organic compounds

Substances emitted into the atmosphere by human activities in urban and industrial areas cause environmental problems such as air quality degradation, respiratory diseases, climate change, global warming, and stratospheric ozone depletion. Volatile organic compounds (VOCs) are major air pollutants, emitted largely by industry, transportation and households. Many VOCs are toxic, and some are considered to be carcinogenic, mutagenic, or teratogenic. A wide spectrum of VOCs is readily oxidized photocatalytically. Photocatalytic oxidation (PCO) over titanium dioxide may present a potential alternative to air treatment strategies currently in use, such as adsorption and thermal treatment, due to its advantageous activity under ambient conditions, although higher but still mild temperatures may also be applied. The objective of the present research was to disclose routes of chemical reactions, estimate the kinetics and the sensitivity of gas-phase PCO to reaction conditions in respect of air pollutants containing heteroatoms in their molecules. Deactivation of the photocatalyst and restoration of its activity was also taken under consideration to assess the practical possibility of the application of PCO to the treatment of air polluted with VOCs. UV-irradiated titanium dioxide was selected as a photocatalyst for its chemical inertness, non-toxic character and low cost. In the present work Degussa P25 TiO2 photocatalyst was mostly used. In transient studies platinized TiO2 was also studied. The experimental research into PCO of following VOCs was undertaken: - methyl tert-butyl ether (MTBE) as the basic oxygenated motor fuel additive and, thus, a major non-biodegradable pollutant of groundwater; - tert-butyl alcohol (TBA) as the primary product of MTBE hydrolysis and PCO; - ethyl mercaptan (ethanethiol) as one of the reduced sulphur pungent air pollutants in the pulp-and-paper industry; - methylamine (MA) and dimethylamine (DMA) as the amino compounds often emitted by various industries. The PCO of VOCs was studied using a continuous-flow mode. The PCO of MTBE and TBA was also studied by transient mode, in which carbon dioxide, water, and acetone were identified as the main gas-phase products. The volatile products of thermal catalytic oxidation (TCO) of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Continuous PCO of 4 TBA proceeded faster in humid air than dry air. MTBE oxidation, however, was less sensitive to humidity. The TiO2 catalyst was stable during continuous PCO of MTBE and TBA above 373 K, but gradually lost activity below 373 K; the catalyst could be regenerated by UV irradiation in the absence of gas-phase VOCs. Sulphur dioxide, carbon monoxide, carbon dioxide and water were identified as ultimate products of PCO of ethanethiol. Acetic acid was identified as a photocatalytic oxidation by-product. The limits of ethanethiol concentration and temperature, at which the reactor performance was stable for indefinite time, were established. The apparent reaction kinetics appeared to be independent of the reaction temperature within the studied limits, 373 to 453 K. The catalyst was completely and irreversibly deactivated with ethanethiol TCO. Volatile PCO products of MA included ammonia, nitrogen dioxide, nitrous oxide, carbon dioxide and water. Formamide was observed among DMA PCO products together with others similar to the ones of MA. TCO for both substances resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide and water. No deactivation of the photocatalyst during the multiple long-run experiments was observed at the concentrations and temperatures used in the study. PCO of MA was also studied in the aqueous phase. Maximum efficiency was achieved in an alkaline media, where MA exhibited high fugitivity. Two mechanisms of aqueous PCO – decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite - lead ultimately to carbon dioxide, water, ammonia and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. This finding helped in better understanding of the gasphase PCO pathways. The PCO kinetic data for VOCs fitted well to the monomolecular Langmuir- Hinshelwood (L-H) model, whereas TCO kinetic behaviour matched the first order process for volatile amines and the L-H model for others. It should be noted that both LH and the first order equations were only the data fit, not the real description of the reaction kinetics. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation.

Catalysis by gold for biomass transformations

The development of new technologies to supplement fossil resources has led to a growing interest in the utilization of alternative routes. Biomass is a rich renewable feedstock for producing fine chemicals, polymers, and a variety of commodities replacing petroleumderived chemicals. Transformation of biomass into diverse valuable chemicals is the key concept of a biorefinery. Catalytic conversion of biomass, which reduces the use of toxic chemicals is one of the important approaches to improve the profitability of biorefineries. Utilization of gold catalysts allows conducting reactions under environmentally-friendly conditions, with a high catalytic activity and selectivity. Gold-catalyzed valorization of several biomass-derived compounds as an alternative approach to the existing technologies was studied in this work. Isomerization of linoleic acid via double bond migration towards biologically active conjugated linoleic acid isomers (CLA) was investigated. The activity and selectivity of various gold catalysts towards cis-9,trans-11-CLA and trans-10,cis-12-CLA were investigated in a semi-batch reactor, showing that the yield of the desired products varied, depending on the catalyst support. The structure sensitivity in the selective oxidation of arabinose was demonstrated using a series of gold catalysts with different Au cluster sizes in a shaker reactor operating in a semibatch mode. The gas-phase selective oxidation of ethanol was studied and the influence of the catalyst support on the catalytic performance was investigated. The selective oxidation of the lignan hydroxymatairesinol (HMR), extracted from the Norway spruce (Picea abies) knots, to the lignan oxomatairesinol (oxoMAT) was extensively investigated. The influence of the reaction conditions and catalyst properties on the yield of oxoMAT was evaluated. In particular, the structure sensitivity of the reaction was demonstrated. The catalyst deactivation and regeneration procedures were studied. The reaction kinetics and mechanism were advanced.

Development of an environmentally friendly method of starch oxidation by hydrogen peroxide and a complex water-soluble Iron catalyst

Oxidized starch is a key component in the paper industry, where it is used as both surfacing sizer and filler. Large quantities are annually used for this purpose; however, the methods for the oxidation are not environmentally friendly. In our research, we have studied the possibility to replace the harmful oxidation agents, such as hypochlorite or iodates and transition metal catalysts, with a more environmentally friendly oxidant, hydrogen peroxide (H2O2), and a special metal complex catalyst (FePcS), of which only a small amount is needed. The work comprised batch and semi-batch studies by H2O2, ultrasound studies of starch particles, determination of low-molecular by-products and determination of the decomposition kinetics of H2O2 in the presence of starch and the catalyst. This resulted in a waste-free oxidation method, which only produces water and oxygen as side products. The starch oxidation was studied in both semi-batch and batch modes in respective to the oxidant (H2O2) addition. The semi-batch mode proved to yield a sufficient degree of substitution (COOH groups) for industrial purposes. Treatment of starch granules by ultrasound was found to improve the reactivity of starch. The kinetic results were found out to have a rather complex pattern – several oxidation phases were observed, apparently due to the fact that the oxidation reaction in the beginning only took place on the surface, whereas after a prolonged reaction time, partial degradation of the solid starch granules allowed further reaction in the interior parts. Batch-mode experiments enabled a more detailed study of the mechanisms of starch in the presence of H2O2 and the catalyst, but yielded less oxidized starch due to rapid decomposition of H2O2 due to its high concentrations. The effect of the solid-liquid (S/L) ratio in the reaction system was studied in batch experiments. These studies revealed that the presence of the catalyst and the starch enhance the H2O2 decomposition.