[diss] Kemian tekniikan korkeakoulu / CHEM

Permanent URI for this collectionhttps://aaltodoc.aalto.fi/handle/123456789/51

Browse

Browsing [diss] Kemian tekniikan korkeakoulu / CHEM by Issue Date

Filter results by year or month
Now showing 1 - 20 of 654
  • Kamfenilonitutkimuksia
    (1911-05-24) Hintikka, S. V. (Sulo Viljo)
     Doctoral dissertation (monograph)
  • The effect of tempering on the toughness of hardened steel
    (1966) Pietikäinen, Juha
     Kemian ja materiaalitieteiden tiedekunta | Doctoral dissertation (monograph)
    The effect of tempering upon the toughness of hardened steel has been investigated. A steel having the nominal analysis: 0.35 % C, 1.5 % Si, 20 % Ni was chosen for this work. The analysis was mainly chosen with the objectives in mind that the Ms temperature should be low enough to ensure that no tempering will occur on quenching, and that the carbides produced on tempering might precipitate each within its own particular tempering temperature range. Test bars made of the investigated steel were austenitized and quenched in liquid nitrogen, with subsequent isothermal tempering at various temperatures in the range Tt = -110 to 450 °C. The structures of the heat-treated specimens were examined by x-rays and by electron microscopy, using both the replica and thin foil technique. Changes occurring in the structures during the tempering process were followed with the aid of a dilatometer. The principal part of the work consists of mechanical tests, for which a torsion testing machine was designed and built. The machine was so designed that the true stress vs. true strain diagram could be readily obtained with its aid. The experimental conditions, including speed of rotation (n) and testing temperature (Tk), were variable within wide limits. In the mechanical tests performed, the speed of rotation was varied within the range of n = 0.00135 to 640 r.p.m. The testing temperatures were: Tk = -110, +25 and +95 °C. The deformed structures were also examined by electron microscopy.
  • Inherent safety in process plant design : an index-based approach
    (1999-05-08) Heikkilä, Anna-Mari
     Doctoral dissertation (monograph)
    An inherently safer design is one that avoids hazards instead of controlling them, particularly by reducing the amount of hazardous material and the number of hazardous operations in the plant. Methods developed to date have largely been for the evaluating the safety of a proposed design. In the future the emphasis will be more and more on the synthesis of an inherently safer plant. At the moment it seems that the best practice is not adopted quickly enough by the potential practitioners. The aim of this work is to try to reduce this hinder by presenting an improved method for inherently safer design. In this thesis an Inherent Safety Index for conceptual chemical process design is presented. This is required, since inherent safety should be considered in the early phases of design when the major decisions on the chemical process are made. The presented methodology allows such a consideration since the index is based on the knowledge available in the preliminary process design stage. The total index is divided into Chemical and Process Inherent Safety Index. The previous is formed of subindices for reaction heats, flammability, explosiveness, toxicity, corrosiveness and chemical interaction. The latter is formed of subindices for inventory, process temperature, pressure and the safety of equipment and process structure. The equipment safety subindex was developed based on accident statistics and layout data separately for isbl and osbl areas. The subindex for process structure describes the safety from the system engineering's point of view. It is evaluated by case-based reasoning on a database of good and bad design cases i.e. experience based information on recommended process configurations and accident data. This allows the reuse of existing design experience for the design of new plants, which is often neglected. A new approach for computerized Inherent Safety Index is also presented. The index is used for the synthesis of inherently safer processes by using the index as a fitness function in the optimization of the process structure by an algorithm that is based on the combination of an genetic algorithm and case-based reasoning. Two case studies on the synthesis of inherently safer processes are given in the end.
  • Interactions between cationic starch and anionic surfactants
    (2001-03-02) Merta, Juha
     Doctoral dissertation (article-based)
    The interactions between cationic starch (CS) and anionic surfactants and their mixtures were studied by using surface tension, solution viscosity and dynamic light scattering (DLS) measurements. The composition and structure of the complexes of CS and surfactants were studied by using phase equilibrium determination, small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) measurements. Critical association concentrations (cac) are well below the critical micellisation concentrations (cmc) of the surfactants. Associative phase separation occurs in extremely dilute systems when the charge ratio between the surfactants and the polymer is close to one. The effect of mixing on micellisation of the binary surfactant solution can be described by taking into account the effects of the volume difference between the hydrocarbon chains. The separated phase is a hydrophobic, viscous, gel-like complex containing less than 60 w% of water. With mixed surfactants, the more surface-active component is enriched in the complex phase. The gel is dissolved entirely or partly when excess surfactant is added with charge reversal mechanism. The mixed micelles of alkanoates are prolate ellipsoids with the longer-chain surfactant enriched in the end-cups of the ellipsoid. In dilute solutions CS molecules have a helical conformation. The core of CS/surfactant aggregates is formed by surfactant monomers and the surrounded shell by CS-chains. The structure of the complexes in dilute solutions resembles the inclusion complexes of amylose and surfactants. The charge neutralized CS-surfactant complexes consists of lyotropic liquid crystalline phase. The mesophases are the same as the pure surfactants form without any added polymer (hexagonal, lamellar or cubic), but they form with CS at lower surfactant concentrations. The gel-like CS-surfactant complex phases have high viscosity and elasticity. Their rheological behaviour is described by the Hershel-Bulkley model.
  • Computational analysis of protein function : lipases and A-kinase anchoring proteins
    (2001-03-16) Herrgård, Sanna
     Doctoral dissertation (article-based)
    In this thesis, normal mode analysis, electrostatic calculations, and sequence-based bioinformatics methods were applied to investigate protein sequence-structure-function relationship. Two different protein families were studied: a family of fungal lipases (the Rhizomucor miehei lipase or RmL family), and a family of adapter proteins called A-kinase anchoring proteins (AKAPs). The RmL family is well conserved, and three-dimensional structures for several members of this family are known. The AKAP family is a functionally, but not structurally, related protein family that consists of multi-domain proteins whose domain architectures are not well understood. In the first part of this thesis, lipase structure-function relationship was investigated using two complementary methods: normal mode analysis and electrostatic calculations. Normal mode analysis was applied to characterize the collective motions in RmL; a global breathing motion as well as local loop motions were shown to be associated with the conformational change. The electrostatic calculations yield a detailed description of the role of electrostatic interactions in the RmL structure, function, and stability. Two main results were obtained in this study. First, the key residues that affect the lid stability were identified. Second, a network of electrostatic interactions was discovered. This network is an important feature of the lipase structure, since it connects the active site to the mobile lid region. The network was observed to be conserved in the RmL family and their homologues. In the second part of the thesis, the sequence-function relationship of an AKAP from Caenorhabditis elegans (AKAPCE) was studied using sequence-based bioinformatics methods. The domain architecture of AKAPCE reveals that it shares two domains with SARA (Smad anchor for receptor activation), which is an adapter protein involved in the TGFβ signaling pathway. One of the domains, FYVE, is well characterized, whereas the other one, a TGFβ receptor binding domain, has not been characterized earlier. The existence of these two domains in AKAPCE leads us to propose a novel AKAP function as a TGFβ receptor binding protein.
  • Expression, purification and characterization of fungal and viral recombinant proteins
    (2001-03-22) Vihinen, Helena
     Doctoral dissertation (article-based)
    This work reports the production of recombinant yeast and viral proteins in a number of diverse in vivo model systems for enzymatic and structural studies. In the first part Hsp150Δ peptide, a derivative of the yeast (Saccharomyces cerevisiae) secretory heat-shock protein Hsp150, was investigated for its ability to act as a carrier in transporting the ectodomain of rat nerve growth factor (NGFRe) out from the yeast cell. The Hsp150Δ-NGFRe fusion protein was efficiently secreted into the growth medium, where it constituted the majority of total secreted proteins. Inhibition experiments with purified Hsp150Δ-NGFRe showed that Hsp150Δ did not prevent NGFRe from folding into a ligand-binding conformation. Circular dichroism (CD) analysis revealed that the Hsp150Δ-carrier did not have any specific secondary structure, which was also suggested by NMR analysis of a synthetic polypeptide corresponding to the repetitive consensus sequence of subunit II of Hsp150. These findings suggest that Hsp150Δ can successfully act as a carrier for foreign proteins, such as NGFRe, made and secreted by S. cerevisiae. The second part of this study involved the expression and purification of an RNA animal virus, Semliki Forest virus (SFV), nonstructural proteins (Nsp1-4) using a number of in vivo protein expression systems. To ensure quantities large enough for structural and enzymatic studies of the Nsps, each of them was expressed either in bacteria (Escherichia coli) or in insect cells (Sf9). All the proteins were expressed in high quantities (10-100 mg/l), and purified by affinity and size exclusion chromatography under nondenaturing or denaturing conditions. Independent of the expression system used, all the partially purified Nsps aggregated and precipitated either upon concentration, dialysis, storing or thawing. No detergents were found that could alleviate the aggregation problem or assist in the purification process. Despite the unsuccessful purification of Nsps for structural studies, the expression and partial purification of Nsp1 and Nsp3 permitted biochemical characterization of their enzyme activities and posttranslational modifications. Point mutational analysis of the Nsp1 methyltransferase domain revealed that residue His38 was essential for the guanylyltransferase activity of Nsp1. Furthermore, residues Asp64 and Asp90 were found to be important for the methyltransferase activity of Nsp1. Phosphorylation sites in Nsp3 were determinated by point mutational analysis, electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) as well as by phosphopeptide mapping and Edman sequencing. A phosphorylated domain (aa 320-368) was located in the C-terminal, non-conserved region of Nsp3, where 12 serines and 4 threonines could be modified by phosphates. The phosphorylation of Nsp3 seemed not to affect the membrane association or the localization of Nsp3 in either transfected or infected cells. Furthermore, Nsp3 phosphorylation deficient mutant viruses were capable of replication in infected mammalian cells a similar manner to the wild type SFV, but their neuropathogenicity in adult mice was greatly reduced.
  • Lactic acid based poly(ester-urethane) : modification via copolymerization, chain linking and blending
    (2001-05-11) Kylmä, Janne
     Doctoral dissertation (article-based)
    The properties of biodegradable lactic acid based poly(ester-urethanes), PEU, were chemically and physically modified and the structure-property relationships investigated. The heat resistance of PEU was improved by copolymerization of lactic acid with DL-mandelic acid. The glass transition temperature of poly(L-lactic acid-co-DL-mandelic acid-urethanes) showed a marked increase with increased mandelic acid composition. Molecular weight depression was attributed to the steric hindrance of the bulky phenyl group of mandelic acid. Novel biodegradable and thermoplastic poly(ester-urethane) elastomers were synthesized by the copolymerization of lactic acid and ε-caprolactone. Properties, such as glass transition temperature and mechanical properties were strongly dependent on the composition of the copolymer. Small amounts of ε-caprolactone increased the strain of PEU, and at higher caprolactone content the poly(L-lactic acid-co-ε-caprolactone-urethane), P(LA/CL)U, exhibited elastomeric properties, having lower strength but significant elongation. The rheological properties of PEU were enhanced by modification of the structure of the polymer chains. An increase in the amount of 1,6-hexamethylene diisocyanate (HMDI) as a chain extender caused branching, which was revealed by the broadened MWD and increased shear thinning at low frequencies. The chain linking technology for lactic acid prepolymers was further developed with the use of highly effective carboxyl and hydroxyl reactive chain extenders. Reaction between 2,2'-bis(2-oxazoline) (BOX) and the carboxyl groups of the lactic acid oligomer led to a hydroxyl terminated prepolymer with low acid value, which provided a significant increase in molecular weight in the HMDI linking reaction. The introduction of oxamide groups into the polymer structure increased the chain stiffness, which was detected in enhanced mechanical properties and an increase in the glass transition temperature. The impact strength of poly(ester-urethane) was significantly improved by blending. The toughening was achieved with a finely dispersed P(LA/CL)U or copoly(L-lactide/ε-caprolactone) elastomer phase in the matrix PEU. Tensile modulus and strength showed a downward trend as a function of rubber content but remained at an acceptable level. Good compatibility and interactions at the rubber-matrix interface were observed. The relationship between phase separation and mechanical properties of rubber-toughened blends was investigated. Composition of the elastomer, i.e. ε-caprolactone content, was found to determine the formation of the heterophase structure. The degree of crosslinking in the P(LA/CL)U rubber was another important factor in the impact modification. Furthermore, the balance between impact strength and stiffness of the poly(ester-urethane) composites was considerably improved by the addition of particulate or fibrous fillers as a third component.
  • Calculation of multicomponent mass transfer between dispersed and continuous phases
    (2001-06-15) Alopaeus, Ville
     Doctoral dissertation (article-based)
    In many industrially important unit operations, mass transfer between dispersed and continuous phases takes place. The accurate and fast solution of the mass transfer model equations is essential in order to design these unit operations accurately. The mass transfer rate between phases is calculated in two parts. The first part is to solve the interphasial mass transfer fluxes. With multicomponent systems, this is best done with the Maxwell-Stefan diffusion model along with a mass transfer model. The other part is to calculate the mass transfer area between the phases. This can be done with population balance models, preferably with a flow model that discriminates various regions of the modeled system. The flow model is needed if the phenomena affecting the development of the mass transfer area are not homogeneous in separate parts of the considered region. The mass transfer rate needed in the material balances is then a product of the mass transfer fluxes and the mass transfer area. The mass transfer calculations with the Maxwell-Stefan model leads to complicated matrix function calculations. This is very time consuming because these models need to be solved many times during the solution of a unit operation or reactor model. Two simplifications to these complicated functions are presented in this work. The first is a method to calculate general matrix functions related to the multicomponent mass transfer models approximately. It is based on the fact that the diffusion coefficient matrices have larger diagonal than off-diagonal elements. The other approximation is a linearization of the high flux correction. The applicability of these two approximations, along with other modeling aspects, is considered with a distillation tray model. An approximation was also presented in this work for calculating diffusion, and further the mass transfer coefficients, within spherical particles. A population balance approach is used with a stirred tank flow model to calculate drop size distributions in liquid-liquid dispersions. In order to test the applicability of the flow model with population balances, drop size distributions are measured and the drop breakage and coalescence function parameter values are estimated. The inhomogeneous character of the dispersion in a stirred tank can be used in the parameter estimation process.
  • Pathways of glycine betaine synthesis in two extremely halophilic bacteria, Actinopolyspora halophila and Ectothiorhodospira halochloris
    (2001-10-26) Nyyssölä, Antti
     Doctoral dissertation (article-based)
    Glycine betaine is a solute which is able to restore and maintain the osmotic balance of living cells. In this thesis, the glycine betaine synthesis in two extremely halophilic bacteria Actinopolyspora halophila and Ectothiorhodospira halochloris is investigated. A. halophila synthesized remarkably high intracellular concentrations of glycine betaine. The highest glycine betaine concentration, determined at 24% (w/v) NaCl, was 33% of the cellular dry weight. The data presented in this work indicate that the de novo synthesis of glycine betaine proceeds via the threefold methylation of glycine. S-adenosylmethionine acts as the methyl group donor in the reactions. The genes encoding this pathway were cloned and successfully expressed in Escherichia coli. In E. halochloris, glycine sarcosine N-methyltransferase (GSMT) and sarcosine dimethylglycine N-methyltransferase (SDMT) catalyze the reaction sequence. In A. halophila all three methylation reactions appear to be catalyzed by a fusion protein. The methyltransferases from the two bacteria show high sequence homology. Furthermore, it was demonstrated that in addition to the glycine methylation pathway, A. halophila has the ability to oxidize choline to glycine betaine. Choline was first oxidized to betaine aldehyde in a reaction in which H2O2-generation and oxygen consumption are coupled. Betaine aldehyde was oxidized further to glycine betaine in a reaction in which NAD(P)+ was reduced. The GSMT and SDMT of E. halochloris were expressed in E. coli, purified, and some of their enzymatic properties were characterized. Both enzymes had high substrate specificity and pH optima near physiological pH. No evidence of cofactors was found. The enzymes showed Michaelis-Menten kinetics for their substrates. The apparent Km and Vmax values were determined for all substrates, when the other substrate was present in saturating concentrations. Both enzymes were strongly inhibited by the reaction product S-adenosylhomocysteine. Glycine betaine inhibited the methylation reactions only at high concentrations. Finally, it was demonstrated that the expression of the E. halochloris methyltransferase genes in E. coli results in glycine betaine accumulation and improves salt tolerance.
  • Size control of sawn timber by optical means in breakdown saw machines
    (2001-11-23) Vuorilehto, Jaakko
     Doctoral dissertation (monograph)
    The thesis investigates optical measuring and statistical data processing, and presents a method to understand and reduce sawing variation by examination of sawn timber sizes. Continuous timber size control offers improved opportunities for analysing saw machines or even individual sawblades. The thesis is illustrated with seven saw machine case studies that relate to the development of the technique. Log and cant breakdown is examined in single- and double-arbor circular saws and bandsaws. The first analysis of each saw machine is made in normal production, and the second using a controlled benchmarking test. A total of 44350 logs were sawn in the study. The behaviour of a saw machine is described using such descriptors as total, within-board and between-board standard deviations, and sawblade bend. Based on observations in benchmarking, an equation y=αeβx±R, where α and β are constants, R the process reproducibility, and x a variable that expresses sawing time and saw load, can be established for each of the saw machine descriptors. An example is the total standard deviation descriptor function s=0.21e0.58x±0.11, established for a single-arbor circular saw in a 4-piece saw set-up. The method will help a sawmill to establish descriptors and equations used to describe the behaviour of their saw machines, to baseline saw machine performance and to compare it to best practices in the industry. The descriptors may be used to establish current, short- or long-term capabilities and characteristics. The method can be used to examine various production conditions and tooling, such as effects of log size, feed speed, and sawing time. Other factors include saw speed, sawblade parameters, operation of setworks and feedworks, and effects of seasons. The results of the study show that sawblade behaviour, feedworks and work piece holding problems, and previous saw machines may be causes of large sawing variation.
  • From biomass to fuels : hydrotreating of oxygen-containing feeds on a CoMo/Al2O3 hydrodesulfurization catalyst
    (2001-11-30) Viljava, Tuula-Riitta
     Doctoral dissertation (article-based)
    Biomass is a renewable alternative to fossil raw materials in the production of liquid fuels and chemicals. Liquefied biomass contains an abundance of oxygen-containing molecules that need to be removed to improve the stability of the liquids. A hydrotreating process, hydrodeoxygenation (HDO), is used for the purpose. Hydrodeoxygenation is similar to the hydrodesulfurization (HDS) process used in oil refining, relying upon a presulfided CoMo/γ-Al2O3 catalyst. The stability of the sulfided catalyst is critical in HDO because biocrudes usually do not contain the sulfur compounds needed to maintain the sulfidation of the catalyst. The aim of this work was to examine the role of sulfur in maintaining the activity of the HDO catalyst. Sulfur was introduced as an organic sulfur-containing co-reactant or as a sulfur substituent in an oxygen-containing reactant molecule as a way of simulating mixed feeds composed of biocrudes and conventional crudes, or it was introduced as a low molecular weight sulfiding agent. In addition, the stability of the sulfided catalyst against changes in the feed composition was studied to find out whether the activity of the catalyst could be maintained by carrying out HDO alternately with HDS. Simultaneous HDO and HDS was studied in a batch reactor with model compounds having a sulfur-containing (mercapto or methylmercapto) and an oxygen-containing (hydroxyl or methoxy) substituent in the same molecule, and with binary mixtures of mono-substituted benzene compounds. In both cases, the reactions of the oxygen-containing substituents were strongly suppressed as long as a sulfur-containing functionality was present. HDS reactions of mercapto and methylmercapto groups were either enhanced or retarded in the presence of oxygen-containing functionality. HDS was enhanced when the oxygen-containing substituent was located in para-position to the sulfur substituent thereby increasing the electronegativity of the sulfur atom and thus facilitating the adsorption of the reactant on the active site of the catalyst. Otherwise, the HDS rate declined due to strong competitive adsorption of the oxygen-containing compounds on the active sites of the catalyst, and due to the formation of less reactive sulfur compounds via methyl transfer from the methoxy groups to sulfur. In conclusion, simultaneous hydrotreating of sulfur- and oxygen-containing feeds leads to strong suppression of oxygen removal reactions and usually also to a decrease in the efficiency of sulfur removal. The effect of low molecular weight sulfiding agents, H2S and CS2, on HDO of phenol and anisole was studied first in a batch and then in a flow reactor to see whether the addition of sulfiding agents might improve the stability of the presulfided catalyst without decreasing the rate and without affecting the selectivity of HDO. The HDO rate of phenol decreased noticeably in the presence of CS2 in the batch reactor, and the selectivities of the HDO reaction paths were changed: the hydrogenation-hydrogenolysis route was less sensitive to the sulfur compound than was the CArom-O hydrogenolysis path. At higher concentrations of the sulfiding agent, also the hydrogenation route became inhibited. With anisole, there was an increase in the rate of demethylation to phenol, but oxygen removal was virtually unaffected. In the flow reactor studies, the formation of hydrogenated HDO products of phenol remained constant up to the highest concentration of H2S in the feed, but a dramatic decrease in the yield of the aromatic reaction product occurred already at low concentrations of H2S. Selective inhibition of one of the HDO paths confirmed the presence of at least two kinds of active sites on the catalyst. This means that addition of an inhibitor can be used to adjust the product distribution of HDO in process scale. However, the presulfided catalyst deactivated with time on stream also in the presence of sulfiding agents. Finally, the stability of the presulfided catalyst against changes in the feed composition was studied in a flow reactor. HDO of phenol and HDS of benzothiophene were carried out alternately in periods of four to eight hours. In this way, the deleterious effect of the competition of HDO and HDS was almost totally avoided and the stability of the catalyst during HDO was improved. The lengths of the HDO and HDS periods now need to be optimized.
  • Deposition of binary and ternary oxide thin films of trivalent metals by atomic layer epitaxy
    (2001-12-07) Nieminen, Minna
     Doctoral dissertation (article-based)
    The atomic layer epitaxy (ALE) technique was used to grow thin films of binary metal oxides Al2O3, Ga2O3 and La2O3, and ternary metal oxides LaNiO3, LaCoO3, LaAlO3, and LaGaO3. In addition, another type of mixed-oxide, viz. phosphorus-doped Al2O3 was studied. The binary oxides Ga2O3 and La2O3 and all the ternary oxides were deposited by the ALE method for the first time. New ALE processes were developed for the undoped and doped Al2O3 films. The thin films were characterized by a wide range of methods for structural and surface analysis, including XRD, FTIR, XPS, AFM, XRF, RBS, TOF-ERDA, and SIMS. A review of previous work on these trivalent metal oxide thin films is presented by way of background. The Al2O3 and Ga2O3 films deposited from metal beta-diketonates and ozone were of high quality: stoichiometric, uniform, dense, and free of any significant contamination. However, the La2O3 films contained an excess of oxygen, due to the carbonate-type impurity that was detected. All Al2O3 and Ga2O3 films were amorphous, but polycrystalline, cubic La2O3 was formed at temperatures above 300 °C. Hexagonal La2O3 film was obtained by annealing the as-deposited amorphous and cubic La2O3 films. Simultaneously, the carbon content in the films was reduced. In contrast to the stable Al2O3 and Ga2O3 films, the cubic and hexagonal La2O3 films were chemically unstable and reacted with ambient air, transforming to LaO(OH) and La(OH)3, respectively. The perovskite-type oxides LaNiO3, LaCoO3, LaAlO3, and LaGaO3 were deposited using metal beta-diketonates and ozone as precursors. No optimal ALE process could be demonstrated for the LaNiO3 and LaCoO3 films, which were non-uniform in thickness and either consisted of separate oxide layers or contained an excess of the transition metal. The LaAlO3 and LaGaO3 film growth, in contrast, was well-controlled yielding stoichiometric, uniform, and smooth films, demonstrating the potential of the ALE technique for producing the more complex ternary oxide films. All the as-deposited ternary oxide films were amorphous but crystallized with cubic structure when post-annealed ex situ. After annealing high-quality, epitaxial LaAlO3 and LaGaO3 films were obtained on lattice-matched perovskite-type substrates while randomly or slightly oriented films were obtained on non-lattice matched substrates. The films were relatively pure and only small amounts of common impurities, carbon and hydrogen, were detected. Phosphorus-doped Al2O3 films were deposited from AlCl3, P2O5 or trimethylphosphate, and water. The phosphorus content could be controlled by the phosphorus doping ratio: when the P/Al atomic ratio was below 1.0, the films consisted of both Al2O3 and AlPO4, whereas above that they contained predominantly AlPO4. Phosphorus was uniformly distributed when the phosphorus content exceeded 5 at.%, and it was enriched on the film/substrate interface when the content was lower.
  • Development of low-temperature deposition processes by atomic layer epitaxy for binary and ternary oxide thin films
    (2002-03-08) Putkonen, Matti
     Doctoral dissertation (article-based)
    Atomic layer epitaxy (ALE) method was employed for the study of growth of binary and ternary metal oxide thin films. As background for the study, the basic principles of the ALE method are presented together with a review of existing ALE deposition processes and precursors for oxide thin films. The suitability of β-diketonate type precursors (M(thd)3 M=Sc,Y,La; thd = 2,2,6,6-tetramethylheptanedione) and ozone were studied for ALE depositions of Group 3 oxides, namely Sc2O3, Y2O3 and La2O3. All three oxides could be deposited by a self-limiting ALE process once a suitable deposition temperature was identified. The optimal deposition temperature was found to depend on the position of the self-limiting deposition region, but also on the impurity content, which increases at low deposition temperatures. Deposition rate of Sc2O3 was considerably higher from organometallic precursor, (C5H5)3Sc, than from β-diketonate precursor (0.75 Å(cycle)-1 vs. (0.125 Å(cycle)-1). In a second set of experiments, the suitability of the ALE processes developed was tested for the deposition of ternary thin films, namely yttria-stabilised zirconia (YSZ) and lanthanum aluminate. Before these processes were applied, study was made of the deposition of ZrO2 from β-diketonate and organometallic precursors at 200-500 °C. Furthermore, ALE deposited MgO films were tested for their suitability as buffer layers between silicon substrate and LaAlO3 film. Crystalline YSZ films were obtained regardless of the yttrium to zirconium ratio, whereas the LaAlO3 films were crystalline only after annealing at 900 °C.
  • Process development for mannitol production by lactic acid bacteria
    (2002-04-12) Weymarn, Niklas
     Doctoral dissertation (monograph)
    D-Mannitol (here: mannitol) is a naturally occurring sugar alcohol with six carbon atoms. It is only half as sweet as sucrose. However, mannitol and other sugar alcohols exhibit reduced caloric values compared to the respective value of most sugars, which make them applicable as sweeteners in so-called "light" foods. Moreover, sugar alcohols are metabolized independently of insulin and are thus also applicable in diabetic food products. Besides applications in the food industry, mannitol is also used in the pharmaceutical industry. In medicine, mannitol is used to decrease cellular edema (excessive accumulation of fluid) and increases the urinary output. In this doctoral thesis, the development of a new bioprocess for the production of mannitol is described. For this purpose, aspects such as strain selection, choice of process method, optimization of process parameters, scale-up, and metabolic engineering were studied. At present, mannitol is produced commercially by catalytic hydrogenation of fructose-containing syrups. The existing chemical production methods are, however, characterized by several drawbacks. The uppermost being that when fructose is catalytically hydrogenated only about 50 % of it is converted into mannitol, whereas the rest is converted into another sugar alcohol, sorbitol. In addition, ultra-pure (expensive) raw materials (fructose and hydrogen gas) are required for efficient conversion. When more cost-effective raw materials, such as glucose-fructose syrups are used as starting material for catalytic hydrogenation, the main product is sorbitol and mannitol is formed as a by-product. Hence, mannitol production becomes very dependent on the market demand of sorbitol. Furthermore, mannitol is relatively difficult to purify from sorbitol. In addition, ion exchange is required for removal of the metal catalyst from the production solution. This results in even higher production costs and decreased yields. The microbial mannitol production process described in this thesis is based on high cell density cultures of slowly growing heterofermentative lactic acid bacteria. The bioconversion of fructose to mannitol was performed in a slowly agitated membrane cell-recycle bioreactor equipped with pH and temperature control. Neither aeration nor nitrogen flushing of the bioconversion medium was required, which drastically lowers the investment costs of such a plant. An important detail in the new bioprocess was the re-use of cell biomass in successive bioconversions. In a semi-continuous production experiment, the initial cell biomass provided stable mannitol productivities and yields for at least 14 successive batches. Moreover, using a simple purification protocol comprising cooling crystallization of a supersaturated solution and crystal recovery by means of drum centrifugation, high yields of high-purity (>98 %) mannitol crystals were obtained. Moreover, in scale-up trials the microbial mannitol production process was successfully run at a small pilot-scale (100 L). The yield of crystalline mannitol from the initial sugar consumed in the bioprocess was about 52 % (w/w). This compares favorably to a commercial chemical process with a yield of about 39 %. Hence, under optimized conditions the best production strain (Leuconostoc mesenteroides) converted up to 95 % (mol/mol) of fructose consumed into mannitol. Unfortunately, this is only achieved when a significant amount of glucose is co-metabolized by the cells. The catabolism of glucose enables cofactor regeneration in the cells and is thus, essential for the bioconversion of fructose to mannitol. Moreover, some mannitol is also lost in the purification steps. Another significant improvement brought about by the new bioprocess was a reduced by-product burden. In the commercial chemical process, a total of 1.58 kg by-products are formed for each kilogram of mannitol crystals produced. In the bioprocess, only 0.67 kg by-products are produced per kilogram crystalline mannitol. Using tools of genetic engineering, two key enzymes involved in the primary metabolism of another efficient mannitol-producer, Lactobacillus fermentum, were inactivated. A mutant deficient in D-lactate dehydrogenase and grown in a fructose-glucose medium produced high levels of both mannitol and pure L-lactate. Inactivation of both lactate dehydrogenases resulted in major rerouting of glucose catabolism, which led to the accumulation of pyruvate and production of 2,3-butanediol. Moreover, mutants with lowered fructokinase activity and deficient in acetate kinase were constructed and studied.
  • Effects of prefreezing treatments on the structure of strawberries and jams
    (2002-04-19) Suutarinen, Marjaana
     Doctoral dissertation (article-based)
    Different chemical components and their locations in strawberry (Fragaria x ananassa) achenes, vascular bundles and cortical cell walls were studied by means of bright-field microscopy using different staining systems and by Fourier transform infrared (FT-IR) microscopy. The structural changes in pretreated strawberry tissues during freezing and thawing were studied by means of physical and chemical analyses as well as by bright-field and FT-IR microscopy, and by confocal laser scanning (CLS) microscopy. In addition, traditional jams made from pretreated frozen strawberries were investigated by means of physical and chemical analyses and by sensory evaluation. Basic microstructural studies showed that all the cell walls were complex and consisted of several components. Lignin was an important component of achenes and vascular tissues, whereas the cortical cell walls contained mainly cellulose, pectin and some protein. Cellulose and pectin were also detectable in the intercellular spaces of cortex, in the vascular tissue and pith. Protein was deposited inside the cortical cells, as well as in the vascular tissue and pith. The microscopical methods used gave comparable results. According to microscopical studies both the pretreatments with calcium chloride (CaCl2) and crystallised sucrose as well with CaCl2 and pectin methyesterase (PME) in a vacuum affected the microstructure of strawberry tissues. These pretreatments especially affected pectin, protein, lignin and structural carbohydrates in the vascular tissue and cortex compared to the untreated reference samples. The use of a vacuum appeared to make the pretreatment solutions absorb more efficiently to the cortex and pith, thus improving the stabilisation particularly of pectin and structural carbohydrates. Firmness of thawed and particularly of jam strawberries pretreated with CaCl2 and PME in a vacuum was higher than that of other pretreated or untreated berries. In all the prefreezing treatments studied, dipping of strawberries into a CaCl2 solution with PME in a vacuum resulted in a significantly different sensory profile than was found in the other jams. The sensory attributes wholeness of the berries (p<0.001), firmness, clarity and evenness of the jam medium (p<0.001), softness of the berries (p<0.001) and faultlessness of odour and flavour (p<0.001) in particular were statistically significantly different among the strawberry jams. Sensory quality was perceived to decrease during 4 months of storage, even though the shapes of the sensory profiles of the studied jams did not change significantly from those evaluated after 2 weeks storage. For achieving high quality jams the pretreatment time should be short (about 5-15 min), the temperature low (below 20 °C), the vacuum level high (pressure less than 10 kPa), the CaCl2 concentration moderate (about 1%) and the dosage of PME comparatively low (about 50-100 μkat/kg strawberries).
  • Control of copper and iron oxidation states in some triple- and double-perovskite oxides
    (2002-04-26) Lehmus, Kaisa
     Doctoral dissertation (article-based)
    This thesis consists of eight publications and a summary of the obtained experimental results, reviewed together with the most essential literature related to the topic. The work deals with ways of tuning and analyzing the transition metal oxidation states in the superconductive Cu(Ba,Sr)2(Yb,Ca)Cu2O6+z triple perovskite and the BaRE(Fe,Cu)O5+δ double perovskite, which has aroused interest as a structure potentially exhibiting both superconductivity and magnetoresistivity. These triple- and double-perovskite oxides are compared with regard to their charge distribution at different cation and oxygen stoichiometries. Complementary methods of analysis, including both chemical and physical techniques, are utilized for the determination of the charge distribution in these layered oxide structures with several transition metal ions. Multivariate data analysis is introduced as a novel way for examining the structure-property correlations of complex oxide structures based on the crystallographic data obtained by neutron diffraction. The Ca(II)-for-RE(III) substituted and oxygen-doped Cu(Ba0.8Sr0.2)2(Yb1-xCax)Cu2O6+z triple perovskites (0 <= x <= 0.35 with z ≈ 0 and 0 < z < 1 with x = 0) are described for their fine structures and the charge distribution over the unit cell is determined by two different methods. Bond-valence-sum (BVS) calculations based on structural data obtained by neutron diffraction are shown to be a convenient means to study small gradual changes in the fine structure and the charge distribution. O K-edge and Cu L2,3-edge XANES results independently showed same trends in the charge distribution as did the BVS calculations, i.e. stronger oxidation of the superconductive part of the structure by Ca(II)-for-RE(III) substitution than by oxygen doping. The oxygen stoichiometry of the BaRE(Fe0.5Cu0.5)2O5+δ double perovskite is shown to depend on the size of the RE3+ ion and on the oxygen partial pressure during the final heat treatment of the synthesis. Under ambient pressure, the excess oxygen atom δ can be inserted only in the structures with largest REs (Nd and Pr) whereas high-pressure treatment (p = 5 GPa) was found to stabilize δ also in the structures with smaller REs. The charge distribution between copper and iron is studied by means of coulometric titration and 57Fe Mössbauer spectroscopy. In the normal-pressure oxygenated samples only Fe(III) is oxidized to higher oxidation states, but high-pressure heat treatment enables oxidation of Cu(II) to Cu(III) as well. The excess oxygen can be removed from all compounds by deoxidative post-annealing performed in a controlled way in a thermobalance.
  • Selective conversion of aldehydes to functional esters utilizing the Tishchenko reaction
    (2002-05-03) Törmäkangas, Olli
     Doctoral dissertation (article-based)
    Different modifications of the Tishchenko reaction were studied in order to develop new catalysts and technology to produce 1,3-diol monoester derivatives. Related monoesters are the most common coalescing agents in paint industry with over 100 kilo tonnes total global annual production. The products can also be utilized as solvents and lubricants. During this project a selective process for the preparation of 1,3-diol monoesters with aldol-Tishchenko type mixed Tishchenko reaction via 1,3-dioxan-4-ols was developed and optimized to give a selective and economical method that can be scaled up to industrial scale. The 1,3-dioxan-4-ol type intermediates were initially prepared by dimerization of the isolated β-hydroxy aldehyde and another monofunctional aldehyde. New information concerning the formation, isolation and stability of 1,3-dioxan-4-ol type structures was also obtained. Due to the instability of 1,3-dioxan-4-ol like intermediates the method is temperature sensitive and should be conducted at relatively low temperatures. The catalyst studies in the esterification of 1,3-dioxan-4-ols indicated that the basic nature of the catalyst is essential for the initiation of the reaction. Also sufficient Lewis acidity is required due to the coordination of the counter cation to the oxygens of dioxanol and the formation of the transition state. New 1,3-diol based catalysts were found to give esterification rates of 1,3-dioxan-4-ols faster than previously used metal hydroxides. High yields were obtained without observable product hydrolysis. Another process developed was the homo aldol-Tishchenko reaction of monofunctional enolizable aldehydes to 1,3-diol monoesters under water free reaction conditions. The use of 1,3-diol based monoalcoholate catalysts and one of the formed side products as the solvent provides an advantageous and economical process as the costs due to the formation of wastes are minimized. This work focused on the production of the most important paint industry coalescing agents (2,2-dimethyl-3-hydroxyl-1-isopropyl-propyl)-2-methylpropionate and (3-hydroxy-2,2,4-trimethylpentyl)-2-methylpropionate with the highest yields reported ever. Finally, a new pathway to synthesize a Taxol™ A-ring building block was investigated. In the final step of the synthesis different forms of formaldehyde were utilized successfully as the electrophiles in the Shapiro reaction. The synthesis developed gives the Taxol™ A-ring in good stepwise yields and is clearly superior to the previously described pathways.
  • Etherification of some C8-alkenes to fuel ethers
    (2002-05-17) Karinen, Reetta
     Doctoral dissertation (article-based)
    Tertiary ethers are formed in a reaction between alcohols and alkenes. They are used in gasoline to enhance its burning and to reduce harmful exhaust emissions. They also have high octane rating, which is beneficial for gasoline blending. Regulations in regard to fuel composition and exhaust emissions are tightening and new, cleaner burning high octane gasoline components are of wide interest. This work concerns the etherification of C8-alkenes. Several C8-alkenes were screened for their reactivity. Study of the properties of the resulting ethers showed that some of them are potential for gasoline blending. 2,4,4-Trimethyl pentenes were chosen for more detailed study in view of the availability of the feed stock in industrial scale and the promising properties of the resulting ether. The reactivity of 2,4,4-trimethyl pentenes was tested with various alcohols. The marked effect of the alcohol on the reaction rate was attributed primarily to the polarity of the alcohol, which affects the adsorption of the components and the catalyst. Compared with the ethers currently in commercial production, the C8-alkenes are etherified rather slowly. A new catalyst was sought to enhance the reaction rate. Traditionally, etherification is catalysed by strong cation exchange resin beads, such as Amberlyst resins, but a novel fibrous Smopex-101 catalyst was found to be more active in the etherification of 2,4,4-trimethyl pentenes with methanol, evidently because diffusional limitations were less. A kinetic model was developed for the etherification of 2,4,4-trimethyl pentenes with methanol for purposes of reactor design. Kinetic experiments were performed with Smopex-101 as catalyst. Before the kinetic studies, thermodynamic parameters were derived for the etherification reactions and for the isomerisation reaction between 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene. The results of the kinetic modelling indicated that the adsorption of the alkenes was minor. The best models to describe the data were the Langmuir-Hinshelwood type model where the adsorption of alkenes is assumed to be negligible compared to other reactive components and the Eley-Rideal type model where alkenes are not adsorbed. Adsorption behaviour was different on the fibrous catalyst than on the ion exchange resins: ether was better adsorbed than alcohol on the fibrous catalyst, whereas alcohol is known to better adsorb than ether on the traditional ion exchange resin catalyst. The better adsorption of ether on the fibrous catalyst was attributed to the greater hydrophobicity of this catalyst.
  • Biotechnological production of xylitol with Candida yeasts
    (2002-06-07) Granström, Tom
     Doctoral dissertation (article-based)
    The aim of this study was to develop a biotechnological production process for xylitol. The xylitol production characteristics of Candida millerii, Candida guilliermondii and Candida tropicalis were compared. C. tropicalis was the best xylitol producer. A volumetric productivity of 5.7 g xylitol L-1 h-1 was achieved with 69 % yield from D-xylose on a mineral medium with a modified repeated fed batch production method. The xylitol production mechanism was confirmed by chemostat cultivation studies. Xylitol production is a consequence of an accumulation of intracellular NADH under oxygen limitation. NADH inhibits xylitol dehydrogenase enzyme (XDH) resulting in xylitol excretion out of the cell. The intracellular metabolic fluxes were studied by in vitro enzyme assays and more theoretically by Metabolic Flux Analysis (MFA). The determined enzyme activities revealed that different metabolic pathways are operating simultaneously enabling substrate cycling to maintain ATP turnover and redox balance under oxygen limited conditions. It was possible to calculate the ATP and NAD(P)H turnover by MFA. Connection between the cofactor dependency of xylose reductase (XR) and redox metabolite production was illustrated by a novel experimental set-up using an ascending xylose feed rate and descending oxygen consumption rate profiles simultaneously. This indicated that C. tropicalis, which XR is dual dependent is more responsive in respect to xylitol production under oxygen limited conditions than C. guilliermondii, which XR is only NADPH dependent. The role of additional NADH on xylitol flux was further confirmed by formate feeding. Formate is catabolised to NADH and CO2 in the cell. C. tropicalis resulted in increased xylose uptake and xylitol production compared to C. guilliermondii. XR was purified from C. guilliermondii and its characteristics was studied. C. milleri was able to produce minor amounts of xylitol from xylose in the presence of glucose.
  • Electrochemical characterisation and modelling of passive films on Ni- and Fe-based alloys
    (2002-08-30) Kinnunen, Petri
     Doctoral dissertation (article-based)
    The behaviour of oxide films formed on Ni- and Fe-based alloys in different environments has been studied electrochemically. The aim was to study the effect of pH, temperature and Cr content of the alloy on the protectiveness of the oxide film using a wide combination of electrochemical techniques: conventional linear sweep cyclic voltammetry, rotating ring-disc voltammetry, electrochemical impedance spectroscopy (EIS), contact electric resistance technique (CER) and contact electric impedance technique (CEI). The other goal was to develop modelling tools to describe and predict the oxide film behaviour in different conditions. Increasing pH has been found to decrease oxidation rates in both the passive and transpassive regions. Increasing pH as well as increasing temperature shifts the passive region in the negative direction on the potential scale. A higher amount of Cr in the alloy leads to a more passive oxide film on the metal surface both at low and high temperatures. On the other hand, transpassive dissolution takes place at lower potentials and its rate increases with higher Cr content of the alloy. The potential region of transpassive oxidation and secondary passivation increases and the effect of Cr on the electrochemical behaviour especially on Ni-Cr alloys decreases at high temperatures. The behaviour of oxide films in the passive state in different environments was simulated using the Mixed Conduction Model (MCM). Using this model the diffusion coefficients of current carriers and reaction rate constants at room temperature and profiles of resistances against ionic transport in the oxide films at 200°C were estimated. Also the transpassive dissolution of Ni-Cr alloys at room temperature was studied and a kinetic model proposed to determine quantitatively the reaction rates in the transpassive region. The model describes the oxidation and dissolution reactions of metal cations at the film/solution interface. The proposed model can be used to estimate steady-state current densities as well as dependencies of surface fractions of dissolving species on potential.