Antiikin pedagoginen perintö

Kirjallisuusarvostelu

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%.

CO2:n adsorptio Loviisan voimalaitoksen päästöilmasta 14C-päästöjen määrittämiseksi

Tämän kandidaatintyön tavoitteena oli selvittää mahdollisuuksia 14C:n kemiallisten muotojen eriyttämiseen käyttäen Loviisan voimalaitoksella olemassa olevaa näytteenkeräyslaitteistoa. Lisäksi tarkoituksena oli selvittää parhaiten tähän käyttötarkoitukseen soveltuva zeoliittityyppiä tyypeistä 4A, 5A ja 13X. Työn kirjallisessa osassa käsitellään ydinvoimalaitoksen C14-päästöjä keskittyen pääosin Loviisan VVER-laitokseen. Adsorption osalta esitellään kaupallisesti käytettyjä adsorptiomateriaaleja ja paneudutaan adsorptioon fysikaalisena ja kemiallisena ilmiönä. Lisäksi esitellään kahden desorptiomenetelmän perusperiaatteet. Kirjallisen osan lopussa kootaan tutkimukseen vaikuttavia tekijöitä ja esitellään aiemmin käytössä ollut näytteenkeräyslaitteisto. Kokeellisessa osassa esitellään työssä käytetyt laitteistot. Lisäksi on kuvattu mittausten suoritus nestetuikelaskurilla. Tämän jälkeen työssä esitellään mittaustuloksien käsittely ja näin saadut tulokset.

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.

Analysis and modelling of chemical looping combustion process with and without oxygen uncoupling

Effective control and limiting of carbon dioxide (CO₂) emissions in energy production are major challenges of science today. Current research activities include the development of new low-cost carbon capture technologies, and among the proposed concepts, chemical combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) have attracted significant attention allowing intrinsic separation of pure CO₂ from a hydrocarbon fuel combustion process with a comparatively small energy penalty. Both CLC and CLOU utilize the well-established fluidized bed technology, but several technical challenges need to be overcome in order to commercialize the processes. Therefore, development of proper modelling and simulation tools is essential for the design, optimization, and scale-up of chemical looping-based combustion systems. The main objective of this work was to analyze the technological feasibility of CLC and CLOU processes at different scales using a computational modelling approach. A onedimensional fluidized bed model frame was constructed and applied for simulations of CLC and CLOU systems consisting of interconnected fluidized bed reactors. The model is based on the conservation of mass and energy, and semi-empirical correlations are used to describe the hydrodynamics, chemical reactions, and transfer of heat in the reactors. Another objective was to evaluate the viability of chemical looping-based energy production, and a flow sheet model representing a CLC-integrated steam power plant was developed. The 1D model frame was succesfully validated based on the operation of a 150 kWth laboratory-sized CLC unit fed by methane. By following certain scale-up criteria, a conceptual design for a CLC reactor system at a pre-commercial scale of 100 MWth was created, after which the validated model was used to predict the performance of the system. As a result, further understanding of the parameters affecting the operation of a large-scale CLC process was acquired, which will be useful for the practical design work in the future. The integration of the reactor system and steam turbine cycle for power production was studied resulting in a suggested plant layout including a CLC boiler system, a simple heat recovery setup, and an integrated steam cycle with a three pressure level steam turbine. Possible operational regions of a CLOU reactor system fed by bituminous coal were determined via mass, energy, and exergy balance analysis. Finally, the 1D fluidized bed model was modified suitable for CLOU, and the performance of a hypothetical 500 MWth CLOU fuel reactor was evaluated by extensive case simulations.

Development of an HTR-10 model in the Serpent reactor physics code

The use of exact coordinates of pebbles and fuel particles of pebble bed reactor modelling becoming possible in Monte Carlo reactor physics calculations is an important development step. This allows exact modelling of pebble bed reactors with realistic pebble beds without the placing of pebbles in regular lattices. In this study the multiplication coefficient of the HTR-10 pebble bed reactor is calculated with the Serpent reactor physics code and, using this multiplication coefficient, the amount of pebbles required for the critical load of the reactor. The multiplication coefficient is calculated using pebble beds produced with the discrete element method and three different material libraries in order to compare the results. The received results are lower than those from measured at the experimental reactor and somewhat lower than those gained with other codes in earlier studies.

Spatial modeling techniques for mapping and characterization of acid sulfate soils

Acid sulfate (a.s.) soils constitute a major environmental issue. Severe ecological damage results from the considerable amounts of acidity and metals leached by these soils in the recipient watercourses. As even small hot spots may affect large areas of coastal waters, mapping represents a fundamental step in the management and mitigation of a.s. soil environmental risks (i.e. to target strategic areas). Traditional mapping in the field is time-consuming and therefore expensive. Additional more cost-effective techniques have, thus, to be developed in order to narrow down and define in detail the areas of interest. The primary aim of this thesis was to assess different spatial modeling techniques for a.s. soil mapping, and the characterization of soil properties relevant for a.s. soil environmental risk management, using all available data: soil and water samples, as well as datalayers (e.g. geological and geophysical). Different spatial modeling techniques were applied at catchment or regional scale. Two artificial neural networks were assessed on the Sirppujoki River catchment (c. 440 km2) located in southwestern Finland, while fuzzy logic was assessed on several areas along the Finnish coast. Quaternary geology, aerogeophysics and slope data (derived from a digital elevation model) were utilized as evidential datalayers. The methods also required the use of point datasets (i.e. soil profiles corresponding to known a.s. or non-a.s. soil occurrences) for training and/or validation within the modeling processes. Applying these methods, various maps were generated: probability maps for a.s. soil occurrence, as well as predictive maps for different soil properties (sulfur content, organic matter content and critical sulfide depth). The two assessed artificial neural networks (ANNs) demonstrated good classification abilities for a.s. soil probability mapping at catchment scale. Slightly better results were achieved using a Radial Basis Function (RBF) -based ANN than a Radial Basis Functional Link Net (RBFLN) method, narrowing down more accurately the most probable areas for a.s. soil occurrence and defining more properly the least probable areas. The RBF-based ANN also demonstrated promising results for the characterization of different soil properties in the most probable a.s. soil areas at catchment scale. Since a.s. soil areas constitute highly productive lands for agricultural purpose, the combination of a probability map with more specific soil property predictive maps offers a valuable toolset to more precisely target strategic areas for subsequent environmental risk management. Notably, the use of laser scanning (i.e. Light Detection And Ranging, LiDAR) data enabled a more precise definition of a.s. soil probability areas, as well as the soil property modeling classes for sulfur content and the critical sulfide depth. Given suitable training/validation points, ANNs can be trained to yield a more precise modeling of the occurrence of a.s. soils and their properties. By contrast, fuzzy logic represents a simple, fast and objective alternative to carry out preliminary surveys, at catchment or regional scale, in areas offering a limited amount of data. This method enables delimiting and prioritizing the most probable areas for a.s soil occurrence, which can be particularly useful in the field. Being easily transferable from area to area, fuzzy logic modeling can be carried out at regional scale. Mapping at this scale would be extremely time-consuming through manual assessment. The use of spatial modeling techniques enables the creation of valid and comparable maps, which represents an important development within the a.s. soil mapping process. The a.s. soil mapping was also assessed using water chemistry data for 24 different catchments along the Finnish coast (in all, covering c. 21,300 km2) which were mapped with different methods (i.e. conventional mapping, fuzzy logic and an artificial neural network). Two a.s. soil related indicators measured in the river water (sulfate content and sulfate/chloride ratio) were compared to the extent of the most probable areas for a.s. soils in the surveyed catchments. High sulfate contents and sulfate/chloride ratios measured in most of the rivers demonstrated the presence of a.s. soils in the corresponding catchments. The calculated extent of the most probable a.s. soil areas is supported by independent data on water chemistry, suggesting that the a.s. soil probability maps created with different methods are reliable and comparable.

Intensification of Operation of Inclined Plate Settler at Fertilizer Plant

Fertilizer plant’s process waters contain high concentrations of nitrogen compounds, such as ammonium and nitrate. Phosphorus and fluorine, which originate from phosphoric acid and rock phosphate (apatite) used in fertilizer production, are also present. Phosphorus and nitrogen are the primary nutrients causing eutrophication of surface waters. At fertilizer plant process waters are held in closed internal circulation. In a scrubber system process waters are used for washing exhaust gases from fertilizer reactors and dry gases from granulation drums as well as for cooling down the fertilizer slurry in neutralization reactor. Solids in process waters are separated in an inclined plate settler by gravitational sedimentation. However, the operation of inclined plate settler has been inadequate. The aim of this thesis was to intensify the operation of inclined plate settler and thus the solids separation e.g. through coagulation and/or flocculation process. Chemical precipitation was studied to reduce the amount of dissolved species in process waters. Specific interest was in precipitation of nitrogen, phosphorus, and fluorine containing specimens. Amounts of phosphorus and fluorine were reduced significantly by chemical precipitation. When compared to earlier studies, annual chemical costs were almost eight times lower. Instead, nitrogen compounds are readily dissolved in water, thus being difficult to remove by precipitation. Possible alternative techniques for nitrogen removal are adsorption, ion exchange, and reverse osmosis. Settling velocities of pH adjusted and flocculated process waters were sufficient for the operation of inclined plate settler. Design principles of inclined plate settler are also presented. In continuation studies, flow conditions in inclined plate settler should be modelled with computational fluid dynamics and suitability of adsorbents, ion exchange resins, and membranes should be studied in laboratory scale tests.

Ydinvoimalaitos AES-2006:n reaktorin painesäiliön rakenne, materiaalivalinta, valmistustekniikka ja asennus

Tässä kandidaattityössä on käsitelty Rusatom Overseas Oy:n toimittaman ydinvoimalaitoksen AES-2006 reaktoripiiriin kuuluvan painesäiliön ominaisuuksia, materiaalivalintoja ja niiden kriteerejä, reaktorin valmistusmenettelyä ja sen asennusvaiheita mukaan lukien pääkiertoputkiston hitsaus julkisesti saatavilla olevan materiaalin pohjalta. Tässä kandidaatintyössä on kuvattu AES-2006 ydinvoimalaitoksen kehityshistoria ja lueteltu sen keskeisimmät eroavuudet edeltäjistään. Työn keskeisessä osassa on tarkastettu VVER-1200 reaktorin painesäiliön toimittajan ilmoittaman teräksen koostumus ja tärkeimpien seosaineiden vaikutus painesäiliöön ja koko voimalaitoksen käyttöikään. Tämän jälkeen on käsitelty reaktorin painesäiliön valmistustekniikkaa ja asennusta reaktorirakennuksessa. Johtopäätöksissä on vedetty yhteen tulokset ja otettu kantaa vertailukelpoiseen painesäiliöteräkseen ja sen ominaisuuksiin. Tärkeimmiksi seikoiksi nousevat tässä työssä seosaineiden myönteinen ja kielteinen vaikutus koko ydinvoimalaitoksen käyttöikään, ja ko. seosaineiden hallinnan tärkeys valmistus- ja asennusvaiheissa.

Radioaktiivisen päästön ennustaminen valmiustilanteessa

Ydinvoimaloissa käytetään toiminnallisia syvyyssuuntaisia puolustustasoja ydinturvallisuuden varmistamiseksi. Puolustuksen viidennessä ja viimeisessä tasossa pyritään lieventämään vakavan onnettomuuden ympäristövaikutuksia ja väestöön kohdistuvaa säteilyaltistusta. Suojelutoimien onnistumisen kannalta on tärkeää pystyä arvioimaan etukäteen radioaktiivisen päästön suuruus ja ajankohta mahdollisimman tarkasti. Tässä diplomityössä on esitelty radioaktiivisen päästön suuruuteen ja ajankohtaan vaikuttavat ilmiöt sekä niihin liittyvät merkittävät epävarmuudet. Ydinvoimalaitosten turvallisuusjärjestelmien osalta tarkastelun kohteena ovat suomalaiset käynnissä olevat reaktorit Olkiluoto 1 & 2 sekä Loviisa 1 & 2. Kaikissa Suomen laitoksissa on käytössä vakavan onnettomuuden hallintaan soveltuvia järjestelmiä ja toimintoja. Työssä etsittiin tietoa eri maiden radioaktiivisen päästön ennustamiseen käytettävistä ohjelmista. Eri mailla on eri toimintaperiaatteilla ja laajuuksilla toimivia ohjelmia. Osassa työkaluja käytetään ennalta laskettuja tuloksia ja osassa onnettomuustilanteet lasketaan onnettomuuden aikana. Lisäksi lähivuosina Euroopassa on tavoitteena kehittää yhteistyömaille yhteisiä valmiuskäyttöön soveltuvia ohjelmia. Työssä kehitettiin uusi valmiustyökalu Säteilyturvakeskuksen käyttöön Microsoft Excelin VBAohjelmoinnin avulla. Valmiustyökalu hyödyntää etukäteen laskettujen todennäköisyyspohjaisten analyysien onnettomuussekvenssejä. Tällöin valmiustilanteessa laitoksen tilanteen kehittymistä on mahdollista arvioida suojarakennuksen toimintakyvyn perusteella. Valmiustyökalu pyrittiin kehittämään mahdollisimman helppokäyttöiseksi ja helposti päivitettäväksi.

Johdon tehtävien merkitys muutosprosessin toteuttamisessa työntekijöiden kokemana - Case: Forssan seudun hyvinvointikuntayhtymä

Sosiaali- ja terveyspalveluiden järjestämisessä Suomessa ollaan muutoksen äärellä. Muutoksilla pyritään palvelujen saatavuuden ja saavutettavuuden turvaamiseen sekä lähipalveluiden varmistamiseen. Nämä muutokset haastavat sosiaali- ja terveydenhuollon johtamistyön muutosprosessien hallintaan. Muutosjohtamisen keskiössä ovat muutosjohtamisen tehtävät ja muutosprosessien onnistuminen, jotta toivotut muutokset saadaan käytäntöön. Tämän tapaustutkimuksen tavoitteena oli selvittää, miten muutosprosessissa johtamisen erilaiset tehtävät ovat yhteydessä muutoksen toteutumiseen, miten tiedottaminen onnistuu muutosprosessissa ja miten työntekijät ovat kokeneet muutosjohtamisen muutosprosessin aikana. Tutkimustapauksena toimi 1.1.2014 Forssan seudun hyvinvointikuntayhtymässä toteutettu organisaatiomuutos. Tutkimuksen kohdejoukkona olivat kliinistä työtä tekevät hoitotyöntekijät. Tutkimus toteutettiin sekä kvantitatiivista että kvalitatiivista tutkimusotetta käyttäen. Empiirinen tutkimusaineisto kerättiin kyselylomakkeella. Kysely lähetettiin 12 eri yksikön hoitotyöntekijöille (N=440) Forssan seudun hyvinvointikuntayhtymässä ja vastausprosentiksi saatiin 44 %. Kvantitatiivinen aineisto kerättiin kyselylomakkeella strukturoiduilla väittämillä ja kvalitatiivinen aineisto kerättiin kyselylomakkeen avoimilla ja puolistrukturoiduilla kysymyksillä. Strukturoidut kysymykset analysoitiin SPSS -ohjelman avulla ja avoimet ja puolistrukturoidut kysymykset analysointiin sisällönanalyysillä. Tutkimuksen tulokset osoittivat, että työntekijöiden kokemukset johdon ja esimiesten toiminnasta muutosprosessissa olivat samansuuntaisia. Työntekijät pitivät tärkeänä, että muutoksen välttämättömyys perustellaan hyvin ja muutoksen tavoitteet esitellään selkeästi. Muutokseen valmistautumiseen tulee varata riittävästi aikaa ja muutos tulee suunnitella hyvin. Työntekijöiden näkemyksen mukaan osallistavien ryhmien kautta olisi ollut mahdollista osallistua muutoksen tekemiseen ja kokea vastuuta muutoksen tekemisestä. Työntekijät odottivat, että johto ja esimiehet palkitsevat heitä muutosprosessissa joustavuudesta ja jaksamisesta. Tulosten perusteella tiedottamisessa ja viestinässä muutosprosessissa tulee kiinnittää huomiota tiedon oikea-aikaisuuteen sekä sen sisältöön. Lisäksi on tärkeää järjestää mahdollisuus lisäinformaation antamiseen. Tiedottamisen ja viestinnän muutosprosessissa koettiin olevan erittäin tärkeä tiedon siirtymisen ja muutosmyönteisyyden kannalta. Tehdyn tapaustutkimuksen perusteella voidaan todeta, että johtamisen tehtävillä voidaan selittää lähes puolet muutoksen onnistumisesta sekä johtajuuden tehtävillä lähes neljännes muutoksen onnistumisesta. Johtamisen tehtävillä on enemmän vaikutusta muutoksen onnistumiseen kuin johtajuuden tehtävillä.

Analysis of PACTEL small break LOCA experiment using TRACE

A small break loss-of-coolant accident (SBLOCA) is one of problems investigated in an NPP operation. Such accident can be analyzed using an experiment facility and TRACE thermal-hydraulic system code. A series of SBLOCA experiments was carried out on Parallel Channel Test Loop (PACTEL) facility, exploited together with Technical Research Centre of Finland VTT Energy and Lappeenranta University of Technology (LUT), in order to investigate two-phase phenomena related to a VVER-type reactor. The experiments and a TRACE model of the PACTEL facility are described in the paper. In addition, there is the TRACE code description with main field equations. At the work, calculations of a SBLOCA series are implemented and after the calculations, the thesis discusses the validation of TRACE and concludes with an assessment of the usefulness and accuracy of the code in calculating small breaks.