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.

Wet oxidation of biomass for chemical production

Tämän kandidaatintyön tarkoituksena oli tutkia märkähapetusprosessia jätevesien käsittely-menetelmänä ja mahdollisena menetelmänä kemikaalien tuottamiseksi jätevesistä. Erityishuomio on kiinnitetty paperiteollisuudessa syntyviin jätevesiin. Teoriaosassa käsitellään vesikiertoja paperitehtaassa, paperitehtaalla syntyvän jäteveden ominaisuuksia sekä itse märkähapetusprosessia. Märkähapetusprosessissa perehdytään tavalliseen happea käyttävään märkähapetukseen sekä vetyperoksidia käyttävään menetelmään sekä näissä prosesseissa syntyviin väli- ja lopputuotteisiin. Märkähapetus (WO) on terminen hapetusmenetelmä, jolla voidaan käsitellä jätevesiä, jotka ovat liian konsentroituja biologisiin käsittelyihin tai jotka ovat huonosti biohajoavia. Märkähapetuksen tarkoituksena on parantaa molekulaarisen hapen ja orgaanisen aineen välistä kontaktia, jolloin orgaaninen aines pilkkoutuu muodostaen pääasiassa karboksyylihappoja, aldehydejä, hiilidioksidia ja vettä. Märkähapetuksessa hapettavana kaasuna voidaan käyttää joko puhdasta happea tai ilmaa. Vetyperoksidia käyttävässä märkähapetuksessa (WPO) hapettava kaasu on korvattu nestemäisellä vetyperoksidilla. Kokeellisessa osassa tutkittiin orgaanisen aineksen hapetusta käyttäen Fentonin reagenssia, jolloin katalyyttina reaktiossa toimii rautaionit (Fe2+ ja Fe3+) ja hapettimena vetyperoksidi. Hapetettavana jätevetenä käytettiin paperitehtaan hiomolta saatua kiertovettä, TMP-vettä. Hapetuskokeita tehtiin eri vetyperoksidin annoksilla ja katalyytin määrillä eri lämpötiloissa. Hapetuksen jälkeen näytteistä mitattiin kemiallinen hapenkulutus (COD), orgaanisen hiilen kokonaismäärä (TOC) sekä pH. Lisäksi näytteistä määritettiin nestekromatografilla (HPLC) tyypillisten välituotteiden, kuten oksaalihapon, muurahaishapon ja etikkahapon, määrät. Tehdyissä kokeissa COD-arvoja saatiin pienennettyä 50-88 % siten, että suodatetuissa näytteissä muutos oli suurempi kuin suodattamattomissa näytteissä. Lisäksi TOC-arvot laskivat 28-58 %. Tehdyissä kokeissa saatiin myös tuotettua välituotteina karboksyylihappoja, joista etikkahappoa ja oksaalihappoa tuotettiin suurimmat määrät. Myös muurahaishappoa ja meripihkahappoa saatiin tuotettua.

Novel technology for preparation of optically active chemicals

Asymmetric synthesis using modified heterogeneous catalysts has gained lots of interest in the production of optically pure chemicals, such as pharmaceuticals, nutraceuticals, fragrances and agrochemicals. Heterogeneous modified catalysts capable of inducing high enantioselectivities are preferred in industrial scale due to their superior separation and handling properties. The topic has been intensively investigated both in industry and academia. The enantioselective hydrogenation of ethyl benzoylformate (EBF) to (R)-ethyl mandelate over (-)-cinchonidine (CD)-modified Pt/Al2O3 catalyst in a laboratory-scale semi-batch reactor was studied as a function of modifier concentration, reaction temperature, stirring rate and catalyst particle size. The main product was always (R)-ethyl mandelate while small amounts of (S)-ethyl mandelate were obtained as by product. The kinetic results showed higher enantioselectivity and lower initial rates approaching asymptotically to a constant value as the amount of modifier was increased. Additionally, catalyst deactivation due to presence of impurities in the feed was prominent in some cases; therefore activated carbon was used as a cleaning agent of the raw material to remove impurities prior to catalyst addition. Detailed characterizations methods (SEM, EDX, TPR, BET, chemisorption, particle size distribution) of the catalysts were carried out. Solvent effects were also studied in the semi-batch reactor. Solvents with dielectric constant (e) between 2 and 25 were applied. The enantiomeric excess (ee) increased with an increase of the dielectric coefficient up to a maximum followed by a nonlinear decrease. A kinetic model was proposed for the enantioselectivity dependence on the dielectric constant based on the Kirkwood treatment. The non-linear dependence of ee on (e) successfully described the variation of ee in different solvents. Systematic kinetic experiments were carried out in the semi-batch reactor. Toluene was used as a solvent. Based on these results, a kinetic model based on the assumption of different number of sites was developed. Density functional theory calculations were applied to study the energetics of the EBF adsorption on pure Pt(1 1 1). The hydrogenation rate constants were determined along with the adsorption parameters by non-linear regression analysis. A comparison between the model and the experimental data revealed a very good correspondence. Transient experiments in a fixed-bed reactor were also carried out in this work. The results demonstrated that continuous enantioselective hydrogenation of EBF in hexane/2-propanol 90/10 (v/v) is possible and that continuous feeding of (-)-cinchonidine is needed to maintain a high steady-state enantioselectivity. The catalyst showed a good stability and high enantioselectivity was achieved in the fixed-bed reactor. Chromatographic separation of (R)- and (S)-ethyl mandelate originating from the continuous reactor was investigated. A commercial column filled with a chiral resin was chosen as a perspective preparative-scale adsorbent. Since the adsorption equilibrium isotherms were linear within the entire investigated range of concentrations, they were determined by pulse experiments for the isomers present in a post-reaction mixture. Breakthrough curves were measured and described successfully by the dispersive plug flow model with a linear driving force approximation. The focus of this research project was the development of a new integrated production concept of optically active chemicals by combining heterogeneous catalysis and chromatographic separation technology. The proposed work is fundamental research in advanced process technology aiming to improve efficiency and enable clean and environmentally benign production of enantiomeric pure chemicals.

Application of cerium oxide thin films grown by atomic layer deposition for soot removal

The objective of the thesis is to study cerium oxide thin films grown by the atomic layer deposition (ALD) for soot removal. Cerium oxide is one of the most important heterogeneous catalysts and can be used in particulate filters and sensors in a diesel exhaust pipe. Its redox/oxidation properties are a key factor in soot oxidation. Thus, the cerium oxide coating can help to keep particulate filters and sensors clean permanently. The literature part of the thesis focuses on the soot removal, introducing the origin and structure of soot, reviewing emissions standards for diesel particulate matter, and presenting methods and catalysts for soot removal. In the experimental part the optimal ALD conditions for cerium oxide were found, the structural properties of cerium oxide thin films were analyzed, and the catalytic activity of the cerium oxide for soot oxidation was investigated. Studying ALD growth conditions of cerium oxide films and determining their critical thickness range are important to maximize the catalytic performance operating at comparatively low temperature. It was found that the cerium oxide film deposited at 300 °C with 2000 ALD cycles had the highest catalytic activity. Although the activity was still moderate and did not decrease the soot oxidation temperature enough for a real-life application. The cerium oxide thin film deposited at 300 °C has a different crystal structure, surface morphology and elemental composition with a higher Ce3+ concentration compared to the films deposited at lower temperatures. The different properties of the cerium oxide thin film deposited at 300 °C increase the catalytic activity most likely due to higher surface area and addition of the oxygen vacancies.

Methyl and ethyl chloride synthesis in microreactors

Methyl chloride is an important chemical intermediate with a variety of applications. It is produced today in large units and shipped to the endusers. Most of the derived products are harmless, as silicones, butyl rubber and methyl cellulose. However, methyl chloride is highly toxic and flammable. On-site production in the required quantities is desirable to reduce the risks involved in transportation and storage. Ethyl chloride is a smaller-scale chemical intermediate that is mainly used in the production of cellulose derivatives. Thus, the combination of onsite production of methyl and ethyl chloride is attractive for the cellulose processing industry, e.g. current and future biorefineries. Both alkyl chlorides can be produced by hydrochlorination of the corresponding alcohol, ethanol or methanol. Microreactors are attractive for the on-site production as the reactions are very fast and involve toxic chemicals. In microreactors, the diffusion limitations can be suppressed and the process safety can be improved. The modular setup of microreactors is flexible to adjust the production capacity as needed. Although methyl and ethyl chloride are important chemical intermediates, the literature available on potential catalysts and reaction kinetics is limited. Thus the thesis includes an extensive catalyst screening and characterization, along with kinetic studies and engineering the hydrochlorination process in microreactors. A range of zeolite and alumina based catalysts, neat and impregnated with ZnCl2, were screened for the methanol hydrochlorination. The influence of zinc loading, support, zinc precursor and pH was investigated. The catalysts were characterized with FTIR, TEM, XPS, nitrogen physisorption, XRD and EDX to identify the relationship between the catalyst characteristics and the activity and selectivity in the methyl chloride synthesis. The acidic properties of the catalyst were strongly influenced upon the ZnCl2 modification. In both cases, alumina and zeolite supports, zinc reacted to a certain amount with specific surface sites, which resulted in a decrease of strong and medium Brønsted and Lewis acid sites and the formation of zinc-based weak Lewis acid sites. The latter are highly active and selective in methanol hydrochlorination. Along with the molecular zinc sites, bulk zinc species are present on the support material. Zinc modified zeolite catalysts exhibited the highest activity also at low temperatures (ca 200 °C), however, showing deactivation with time-onstream. Zn/H-ZSM-5 zeolite catalysts had a higher stability than ZnCl2 modified H-Beta and they could be regenerated by burning the coke in air at 400 °C. Neat alumina and zinc modified alumina catalysts were active and selective at 300 °C and higher temperatures. However, zeolite catalysts can be suitable for methyl chloride synthesis at lower temperatures, i.e. 200 °C. Neat γ-alumina was found to be the most stable catalyst when coated in a microreactor channel and it was thus used as the catalyst for systematic kinetic studies in the microreactor. A binder-free and reproducible catalyst coating technique was developed. The uniformity, thickness and stability of the coatings were extensively characterized by SEM, confocal microscopy and EDX analysis. A stable coating could be obtained by thermally pretreating the microreactor platelets and ball milling the alumina to obtain a small particle size. Slurry aging and slow drying improved the coating uniformity. Methyl chloride synthesis from methanol and hydrochloric acid was performed in an alumina-coated microreactor. Conversions from 4% to 83% were achieved in the investigated temperature range of 280-340 °C. This demonstrated that the reaction is fast enough to be successfully performed in a microreactor system. The performance of the microreactor was compared with a tubular fixed bed reactor. The results obtained with both reactors were comparable, but the microreactor allows a rapid catalytic screening with low consumption of chemicals. As a complete conversion of methanol could not be reached in a single microreactor, a second microreactor was coupled in series. A maximum conversion of 97.6 % and a selectivity of 98.8 % were reached at 340°C, which is close to the calculated values at a thermodynamic equilibrium. A kinetic model based on kinetic experiments and thermodynamic calculations was developed. The model was based on a Langmuir Hinshelwood-type mechanism and a plug flow model for the microreactor. The influence of the reactant adsorption on the catalyst surface was investigated by performing transient experiments and comparing different kinetic models. The obtained activation energy for methyl chloride was ca. two fold higher than the previously published, indicating diffusion limitations in the previous studies. A detailed modeling of the diffusion in the porous catalyst layer revealed that severe diffusion limitations occur starting from catalyst coating thicknesses of 50 μm. At a catalyst coating thickness of ca 15 μm as in the microreactor, the conditions of intrinsic kinetics prevail. Ethanol hydrochlorination was performed successfully in the microreactor system. The reaction temperature was 240-340°C. An almost complete conversion of ethanol was achieved at 340°C. The product distribution was broader than for methanol hydrochlorination. Ethylene, diethyl ether and acetaldehyde were detected as by-products, ethylene being the most dominant by-product. A kinetic model including a thorough thermodynamic analysis was developed and the influence of adsorbed HCl on the reaction rate of ethanol dehydration reactions was demonstrated. The separation of methyl chloride using condensers was investigated. The proposed microreactor-condenser concept enables the production of methyl chloride with a high purity of 99%.

Deoxygenation of fatty acids for production of fuels and chemicals

The decreasing fossil fuel resources combined with an increasing world energy demand has raised an interest in renewable energy sources. The alternatives can be solar, wind and geothermal energies, but only biomass can be a substitute for the carbon–based feedstock, which is suitable for the production of transportation fuels and chemicals. However, a high oxygen content of the biomass creates challenges for the future chemical industry, forcing the development of new processes which allow a complete or selective oxygen removal without any significant carbon loss. Therefore, understanding and optimization of biomass deoxygenation processes are crucial for the future bio–based chemical industry. In this work, deoxygenation of fatty acids and their derivatives was studied over Pd/C and TiO2 supported noble metal catalysts (Pt, Pt–Re, Re and Ru) to obtain future fuel components. The 5 % Pd/C catalyst was investigated in semibatch and fixed bed reactors at 300 °C and 1.7–2 MPa of inert and hydrogen–containing atmospheres. Based on extensive kinetic studies, plausible reaction mechanisms and pathways were proposed. The influence of the unsaturation in the deoxygenation of model compounds and industrial feedstock – tall oil fatty acids – over a Pd/C catalyst was demonstrated. The optimization of the reaction conditions suppressed the formation of by–products, hence high yields and selectivities towards linear hydrocarbons and catalyst stability were achieved. Experiments in a fixed bed reactor filled with a 2 % Pd/C catalyst were performed with stearic acid as a model compound at different hydrogen–containing gas atmospheres to understand the catalyst stability under various conditions. Moreover, prolonged experiments were carried out with concentrated model compounds to reveal the catalyst deactivation. New materials were proposed for the selective deoxygenation process at lower temperatures (~200 °C) with a tunable selectivity to hydrodeoxygenation by using 4 % Pt/TiO2 or decarboxylation/decarbonylation over 4 % Ru/TiO2 catalysts. A new method for selective hydrogenation of fatty acids to fatty alcohols was demonstrated with a 4 % Re/TiO2 catalyst. A reaction pathway and mechanism for TiO2 supported metal catalysts was proposed and an optimization of the process conditions led to an increase in the formation of the desired products.

Studies in selectivity of lipases in preparation of cyanohydrins, sugar conjugates and secondary alcohols

Biocatalysis can be applied in organic synthetic chemistry to counter challenges posed by increased demands towards chemo-, regio- and stereoselectivity, not forgetting the need for greener chemistry. During the last 30 years, biocatalysis with the use of enzymes as chiral catalysts has become more common in chemistry laboratories and industrial processes. In this thesis, the use of lipases as versatile biocatalysts in the acylation of alcohols is examined both in the light of literature examples and four original publications. In the first part of the work presented in this thesis lipases were utilized in two examples concerning secondary alcohols. First, the kinetic resolution of heterocyclic aromatic secondary alcohols through transesterification was thoroughly examined including the studies of competing hydrolysis and esterification reactions. In another example, lipases were utilized in the formation of a dynamic systemic resolution (DSR) process which in turn was used as a developmental tool in the optimization of the dynamic kinetic resolution (DKR) of five heterocyclic aromatic cyanohydrins in one pot for the preparation of cyanohydrin esters as single enantiomers. In the second part of the work, the regio- and stereoselectivity of lipases was used to form sugar conjugates of glyceric and β-amino acids. The primary hydroxyl groups of methyl α-D-galacto-, -gluco- and -mannopyranosides were now acylated trough lipasecatalyzed transesterification and enantioselective lipase-catalyzed ring-opening of β- lactams, respectively.

Catalytic direct synthesis of hydrogen peroxide in a novel microstructured reactor

The direct synthesis from hydrogen and oxygen is a green alternative for production of hydrogen peroxide. However, this process suffers from two challenges. Firstly, mixtures of hydrogen and oxygen are explosive over a wide range of concentrations (4-94% H2 in O2). Secondly, the catalytic reaction of hydrogen and oxygen involves several reaction pathways, many of them resulting in water production and therfore decreasing selectivity. The present work deals with these two challenges. The safety problem was dealed by employing a novel microstructured reactor. Selectivity of the reaction was highly improved by development a set of new catalysts. The final goal was to develop an effective and safe continuous process for direct synthesis of hydrogen peroxide from H2 and O2. Activated carbon cloth and Sibunit were examined as the catalysts’ supports. Palladium and gold monometallic and palladium-gold bimetallic catalysts were thoroughly investigated by numerous kinetic experiments performed in a tailored batch reactor and several catalyst charachterization methods. A complete set of data for direct synthesis of H2O2 and its catalytic decomposition and hydrogenation was obtained. These data were used to assess factors influencing selectivity and activity of the catalysts in direct synthesis of H2O2 as well as its decomposition and hydrogenation. A novel microstructured reactor was developed based on hydrodynamics and mass transfer studies in prototype microstractural plates. The shape and the size of the structural elements in the microreactor plate were optimized in a way to get high gas-liquid interfacial area and gas-liquid mass transfer. Finally, empirical correlations for the volumetric mass transfer coefficient were derived. A bench-scale continuous process was developed by using the novel microstructral plate reactor. A series of kinetic experiments were performed to investigate the effects of the gas and the liquid feed rates and their ratio, the amount of the catalyst, the gas feed composition and pressure on the final rate of H2O2 production and selectivity.

Increased expression and purification of soluble iron-regulatory protein 1 from Escherichia coli co-expressing chaperonins GroES and GroEL

Iron is an essential metal for all living organisms. However, iron homeostasis needs to be tightly controlled since iron can mediate the production of reactive oxygen species, which can damage cell components and compromise the integrity and/or cause DNA mutations, ultimately leading to cancer. In eukaryotes, iron-regulatory protein 1 (IRP1) plays a central role in the control of intracellular iron homeostasis. This occurs by interaction of IRP1 with iron-responsive element regions at 5' of ferritin mRNA and 3' of transferrin mRNA which, respectively, represses translation and increases mRNA stability. We have expressed IRP1 using the plasmid pT7-His-hIRP1, which codifies for human IRP1 attached to an NH2-terminal 6-His tag. IRP1 was expressed in Escherichia coli using the strategy of co-expressing chaperonins GroES and GroEL, in order to circumvent inclusion body formation and increase the yield of soluble protein. The protein co-expressed with these chaperonins was obtained mostly in the soluble form, which greatly increased the efficiency of protein purification. Metal affinity and FPLC ion exchange chromatography were used in order to obtain highly purified IRP1. Purified protein was biologically active, as assessed by electrophoretic mobility shift assay, and could be converted to the cytoplasmic aconitase form. These results corroborate previous studies, which suggest the use of folding catalysts as a powerful strategy to increase protein solubility when expressing heterologous proteins in E. coli.

Target-directed catalytic metallodrugs

Most drugs function by binding reversibly to specific biological targets, and therapeutic effects generally require saturation of these targets. One means of decreasing required drug concentrations is incorporation of reactive metal centers that elicit irreversible modification of targets. A common approach has been the design of artificial proteases/nucleases containing metal centers capable of hydrolyzing targeted proteins or nucleic acids. However, these hydrolytic catalysts typically provide relatively low rate constants for target inactivation. Recently, various catalysts were synthesized that use oxidative mechanisms to selectively cleave/inactivate therapeutic targets, including HIV RRE RNA or angiotensin converting enzyme (ACE). These oxidative mechanisms, which typically involve reactive oxygen species (ROS), provide access to comparatively high rate constants for target inactivation. Target-binding affinity, co-reactant selectivity, reduction potential, coordination unsaturation, ROS products (metal-associated vsmetal-dissociated; hydroxyl vs superoxide), and multiple-turnover redox chemistry were studied for each catalyst, and these parameters were related to the efficiency, selectivity, and mechanism(s) of inactivation/cleavage of the corresponding target for each catalyst. Important factors for future oxidative catalyst development are 1) positioning of catalyst reduction potential and redox reactivity to match the physiological environment of use, 2) maintenance of catalyst stability by use of chelates with either high denticity or other means of stabilization, such as the square planar geometric stabilization of Ni- and Cu-ATCUN complexes, 3) optimal rate of inactivation of targets relative to the rate of generation of diffusible ROS, 4) targeting and linker domains that afford better control of catalyst orientation, and 5) general bio-availability and drug delivery requirements.

Bio and chemocatalysis for stereo and regioselective one-pot reaction applications

The development of cost efficient, selective and sustainable chemical processes for production of chiral building blocks is of great importance in synthetic and industrial organic chemistry. One way to reach these objectives is to carry out several reactions steps in one vessel at one time. Furthermore, when this kind of one-pot multi step reactions are catalyzed by heterogeneous chemo- and bio-catalysts, which can be separated from the reaction products by filtration, practical access to chiral small molecules for further utilization can be obtained. The initial reactions studied in this thesis are the two step dynamic kinetic resolution of rac-2-hydroxy-1-indanone and the regioselective hydrogenation of 1,2-indanedione. These reactions are then combined in a new heterogeneously catalyzed one-pot reaction sequence enabling simple recovery of the catalysts by filtration, facilitating simple reaction product isolation. Conclusively, the readily available 1,2-indanedione is by the presented one-pot sequence, utilizing heterogeneous enzyme and transition metal based catalysts, transferred with high regio- and stereoselectivity to a useful chiral vicinal hydroxyl ketone structure. Additional and complementary investigation of homogeneous half-sandwich ruthenium complexes for catalyzing the epimerization of chiral secondary alcohols of five natural products containing additional non-functionalized stereocenters was conducted. In principle, this kind of epimerization reactions of single stereocenters could be utilized for converting inexpensive starting materials, containing other stereogenic centers, into diastereomeric mixtures from which more valuable compounds can be isolated by traditional isolation techniques.

Fatty acid ethyl esters production using a non-commercial lipase in pressurized propane medium

The objective of this work is to investigate the production of fatty acid ethyl esters from soybean oil in compressed propane using a non-commercial lipase from Yarrowia lipolytica and two commercial ones as catalysts, Amano PS and Amano AY30. The experiments were performed in the temperature range of 35-65 °C. at 50 bar, enzyme concentration of 5 wt%, oil to ethanol molar ratio of 1:6 and 1:9, and solvent to substrates mass ratio of 2:1 and 4:1. The results indicated that low reaction conversions were generally obtained with the use of commercial and non-commercial lipases in pressurized propane medium. On the other hand, the aspects of low solvent to substrates mass ratio and mild temperature and pressure operating conditions used to produce ethyl esters justify further investigations to improve reaction yields.

The role of organic solvent amount in the lipase-catalyzed biodiesel production

This research note addresses the role of organic solvent amount in the production of fatty acid ethyl esters from soybean oil. N-hexane was chosen as solvent and two commercial immobilized lipases as catalysts, Novozym 435 and Lipozyme IM. The reactions were conducted in 6 hours, varying the solvent to oil ratio from zero to 50 (v/wt) and adopting adopting for Novozym 435: 65 ºC, enzyme concentration (E, wt%) = 5, oil to ethanol molar ratio (R) = 1:10, water addition (H, wt%) = 0, and for Lipozyme IM: 35 ºC, E = 5 wt%, R = 1:3, H = 10 wt%. For Lipozyme IM, an increase in solvent amount is shown to lead to an enhancement of reaction conversion, while a negligible effect was found for Novozym 435. When using 30 mL of solvent the reaction conversions were 88% for Lipozyme IM and 15% for Novozym 435.

The role of metal ions in selective and sustainable processes

Sustainability and recycling are core values in today’s industrial operations. New materials, products and processes need to be designed in such a way as to consume fewer of the diminishing resources we have available and to put as little strain on the environment as possible. An integral part of this is cleaning and recycling. New processes are to be designed to improve the efficiency in this aspect. Wastewater, including municipal wastewaters, is treated in several steps including chemical and mechanical cleaning of waters. Well-cleaned water can be recycled and reused. Clean water for everyone is one of the greatest challenges we are facing today. Ferric sulphate, made by oxidation from ferrous sulphate, is used in water purification. The oxidation of ferrous sulphate, FeSO4, to ferric sulphate in acidic aqueous solutions of H2SO4 over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and several catalysts were screened: active carbon, active carbon impregnated with Pt, Rh, Pd and Ru. Both active carbon and noble metal-active carbon catalysts enhanced the oxidation rate considerably. The order of the noble metals according to the effect was: Pt >> Rh > Pd, Ru. By the use of catalysts, the production capacities of existing oxidation units can be considerably increased. Good coagulants have a high charge on a long polymer chain effectively capturing dirty particles of the opposite charge. Analysis of the reaction product indicated that it is possible to obtain polymeric iron-based products with good coagulation properties. Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60B100°C and 4B10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe2+ to Fe3+ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe2+ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe2+ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe2+ over active carbon and active carbon-noble metal catalysts. Engineering aspects were closely considered and effort was directed to utilizing existing equipment in the production of the new coagulant. Ferrous sulphate can be catalytically oxidized to produce a novel long-chained polymeric iron-based flocculent in an easy and affordable way in existing facilities. The results can be used for modelling the reactors and for scale-up. Ferric iron (Fe3+) was successfully applied for the dissolution of sphalerite. Sphalerite contains indium, gallium and germanium, among others, and the application can promote their recovery. The understanding of the reduction process of ferric to ferrous iron can be used to develop further the understanding of the dissolution mechanisms and oxidation of ferrous sulphate. Indium, gallium and germanium face an ever-increasing demand in the electronics industry, among others. The supply is, however, very limited. The fact that most part of the material is obtained through secondary production means that real production quota depends on the primary material production. This also sets the pricing. The primary production material is in most cases zinc and aluminium. Recycling of scrap material and the utilization of industrial waste, containing indium, gallium and geranium, is a necessity without real options. As a part of this study plausible methods for the recovery of indium, gallium and germanium have been studied. The results were encouraging and provided information about the precipitation of these valuables from highly acidic solutions. Indium and gallium were separated from acidic sulphuric acid solutions by precipitation with basic sulphates such as alunite or they were precipitated as basic sulphates of their own as galliunite and indiunite. Germanium may precipitate as a basic sulphate of a mixed composition. The precipitation is rapid and the selectivity is good. When the solutions contain both indium and gallium then the results show that gallium should be separated before indium to achieve a better selectivity. Germanium was separated from highly acidic sulphuric acid solutions containing other metals as well by precipitating with tannic acid. This is a highly selective method. According to the study other commonly found metals in the solution do not affect germanium precipitation. The reduction of ferric iron to ferrous, the precipitation of indium, gallium and germanium, and the dissolution of the raw materials are strongly depending on temperature and pH. The temperature and pH effect were studied and which contributed to the understanding and design of the different process steps. Increased temperature and reduced pH improve the reduction rate. Finally, the gained understanding in the studied areas can be employed to develop better industrial processes not only on a large scale but also increasingly on a smaller scale. The small amounts of indium, gallium and germanium may favour smaller and more locally bound recovery.

Green diesel synthesis by hydrodeoxygenation of lipids extracted from Chlorella algae in supercritical hexane

Lipids were extracted from Chlorella algae with supercritical hexane. The high lipids yield of approximately 10% was obtained at optimum conditions of 300 rpm stirring speed and 2 h duration compared to the total contents of lipids being 12%. Furthermore, an easiness of hexane recovery may be considered as economically and ecologically attractive. For the first time, in the current work catalytic hydrodeoxygenation (HDO) of Chlorella algal lipids was studied over 5 wt% Ni/H-Y-80 and 5 wt% Ni/SiO2 at 300 C and under 30 bar total pressure in H2. A comparative HDO of stearic acid was carried out under similar conditions. The conversion of lipids was about 35% over 5 wt% Ni/H-Y-80 after 6h, whereas, 5 wt% Ni/SiO2 was totally deactivated after 60 min. The selectivity to hydrocarbons (C15-C18) is 6%. As a comparison, complete conversion of stearic acid over 5 wt% Ni/H-Y-80 was achieved in 6 h. The transformation of lipids proceeded mostly via hydrogenation and hydrolysis with formation of free fatty acid (FFA). The lower activity might be attributed to deactivation of catalysts caused by chlorophylls and carotenoids. Even though the conversion is low, future studies in HDO of lipids extracted from other algae species having higher lipid content could be proposed. Coke resistant catalyst might be considered to improve catalytic activity.