Medidas de tempo de vôo, em cinco diferentes temperaturas, foram realizadas em enxofre ortorrômbico para vários campos elétricos, tanto positivos como negativos. O trânsito dos portadores negativos foi mais extensivamente analisado e para baixas intensidades de luz, isto é, o caso do sinal fraco, os seguintes fatos foram verificados; a) não foi detectada dependência da mobilidade com o campo elétrico; b) a razão da corrente no tempo t para a corrente inicial mostrou não ser uma função universal do tempo, (isto é, independente do campo aplicado). Transporte dispersivo, discernível através da dependência da mobilidade com o campo elétrico, foi detectado pelo fato a. Contudo, para o transporte não dispersivo nós devemos esperar que a corrente normalizada leve a uma função universal do tempo, somente dependente do tempo de captura e, eventualmente, do tempo de soltura dos portadores, contrário ao que foi encontrado em b. A parte principal desta tese foi dedicada a testar nossos resultados com modelos existentes e o efeito esperado da falha das suposições nos resultados. Nós fomos então levados a um novo modelo, o qual explicou razoavelmente os resultados; a luz joga portadores, não só no canal normal de condução, mas também em um nível extra, confinado à região superficial, caracterizado por uma mobilidade dependente da profundidade. Soluções numéricas foram obtidas para confirmar a validade das soluções analíticas aproximadas obtidas. Um modelo aproximado foi desenvolvido para explicar o efeito do campo elétrico na extração de portadores da zona iluminada / Time off light measurements, in five different temperatures, were carried out in orthorhombic sulphur for various electric fields, both positive and negative. The transit of negative carriers were more thoroughly analyzed and at low light intensities, that is, the small signal case, the following facts were well established; a) no electric field dependence of the mobility was detected, b) the ratio of the current at a time t to the initial current was found not to be a universal function of the time (that is, independent of the applied field). Dispersive transport, discernible through its field dependent electron mobility, is ruled out by a. However, for non dispersive transport, we should expect the normalized current to lead to a universal function of time, only dependent of the trapping and, eventually, de-trapping times of the carriers, contrary to what was found in b. The main part of this thesis was devoted to test our results with the existing models and the expected effect of the breakdown of the simplified assumptions on the results. We were thus lead to a new model, which reasonable explained the results: light put carriers, not only in the normal conduction channel, but also in an extra level, confined to the surface region, characterized by a depth dependent mobility. Computer solution were carried out to confirm the validity of approximate analytic solutions thus obtained. An approximate model was also developed to explain the effect of the electronic field on the extraction of carriers from the illuminated zone

Estudou-se o efeito da temperatura na conversão e no coeficiente global de taxa de reação no processo de absorção de SO2 por calcário em reator de leito fluidizado borbulhante atmosférico. O sistema experimental foi constituído por um reator de 160 mm de diâmetro interno e altura de 450 mm e seus periféricos. Os experimentos foram feitos com a introdução de calcário em batelada no leito, fluidizado com ar contendo uma concentração constante e uniforme SO2 e aquecido eletricamente. Utilizou-se granulometria estreita de calcário com diâmetros médios de 545 e 650 &#956m. A areia de quartzo que compunha o leito tinha diâmetro médio de 650 &#956m. Os experimentos foram realizados com bateladas de 50 g de calcário adicionadas ao leito durante o teste, com as demais condições mantidas constantes. As temperaturas utilizadas variaram de 700 a 958°C, a relação entre as velocidades de fluidização e de mínima fluidização foi mantida em 4/1, e fator de fluxo bolha/particulado em torno de 2,6. Os resultados mostraram que a conversão foi relativamente baixa, entre 1,2 e 10,9%, dependendo sobretudo da temperatura utilizada. O coeficiente global de taxa de reação aumentou com a temperatura, atingindo um valor máximo de 500 m/s a 881ºC e decrescendo a partir deste valor. / The effect of temperature in both the conversion and the overall rate of reaction coefficient for the process of SO2 absorption by limestone within a fluidized bed was studied on a bench scale atmospheric bubbling fluidized bed reactor. The reactor had an internal diameter of 160 mm and was 450 mm high. The bed was fluidized with air with a concentration of about 950 ppm of SO2. This mixture was electrically heated. The bed material was quartz sand with a narrow size distribution of around 650 &#956m. Limestone was fed to the bed with narrow sized particles of 545 and 650 &#956m. The experiments were carried out on a batch mode introducing samples of 50 g of limestone into the bed with the other variables kept constant. Process temperatures ranged from 700 to 958°C, the relation between gas fluidization velocity and minimum gas fluidization velocity was fixed at 4/1 and the cross flow factor was around 2.6. The results showed a relatively low conversion of limestone, from 1.2 to 10.9%, depending mostly on temperature. The overall rate of reaction coefficient increased with temperature, reaching a maximum value of 500 m/s at 881°C, and decreasing afterwards.

The No-Tillage (NT) diffused in about 70 % of producing grain crops and has emerged as an alternative to soil losses due to the conventional tillage. However, it has been observed in recent years that the basic assumptions of this system are not being considered, reflecting in densification of layers and therefore lower infiltration and soil water storage. Furthermore, due to the characteristics of the system itself, it has been observed the formation of a fertility gradient with high nutrient concentrations in the superficial layers of the soil. With this, the highest goal to be accomplished is to create physical and chemical soil conditions, able to permit greater infiltration and water storage, root growth and absorption capacity of both water and nutrients in depth, depending the vulnerability of soybean and maize recurrent water deficits in the state of RS. The gypsum has been touted as enhancing the chemical characteristics of the subsoil, as his ability to deliver cation and sulphur to lower layers of the listing, in addition to eliminating toxic forms of aluminium to plants. Farmers from the northern region of RS are speculating using this product without observing large returns to grain production, which lacks scientific technical soil and climate in the local conditions. In this sense, this study aimed to verify the effect of gypsum combined with mechanical interventions of a consolidated system of zero tillage on the gradient of cation in the soil profile and the cultivation of soybeans and corn. Application rates of gypsum were performed on the soil surface, with and without mechanical intervention, making it the cultivation of soybeans/corn plants under cover for four seasons (2009/10, 2010/11, 2011/12 and 2012/13). The results showed that the mechanical operations of the soil did not influence the effects of gypsum on the gradient of cations in the soil profile and grain yield of corn and soybeans; Intervention soil with plowing+disking alters the Ca2+ gradient in the soil under NT and the plaster has little potential to mobilize cations vertically soil, and the effects are limited to 0.10 m depth; Use of gypsum shows little maximizing soybean production and maximizing good for corn production, being the contribution of sulfur in soil maximizing main factor. / O Sistema de Plantio Direto (SPD), difundido em cerca de 70% das lavouras produtoras de grãos, surgiu como alternativa conservacionista às perdas de solo por conta do sistema de preparo convencional. No entanto, tem-se observado nos últimos anos que as premissas básicas desse sistema não estão sendo consideradas, repercutindo em adensamento de camadas e consequentemente menor infiltração e armazenamento de água no solo. Além disso, e por conta das características do próprio sistema, tem-se observado a formação de um gradiente de fertilidade com altas concentrações de nutrientes nas camadas superficiais do solo. Com isso, a maior meta a ser cumprida é a de criar condições físico-químicas do solo, capazes de permitirem a maior infiltração e armazenamento de água, o crescimento de raízes e a capacidade de absorção tanto da água quanto dos nutrientes em profundidade, em função da vulnerabilidade das lavouras de soja e milho a déficits hídricos recorrentes no estado do RS. O gesso agrícola tem sido apontado como melhorador das características químicas do subsolo, visto sua capacidade de carrear cátions e enxofre para camadas inferiores do perfil, além de alterar formas tóxicas de alumínio às plantas. Agricultores da região norte do RS estão especulando a utilização deste produto, sem observarem grandes retornos à produção de grãos, que carece de respaldo técnico científico nas condições edafoclimáticas locais. Neste sentido, o presente trabalho teve por objetivo verificar o efeito do gesso agrícola aliado a intervenções mecânicas de um sistema de plantio direto, sobre o gradiente de cátions no perfil do solo e no cultivo de soja e milho. Foram realizada aplicação de doses de gesso agrícola sobre a superfície de solo, com e sem intervenção mecânica, efetuando-se o cultivo da sucessão soja/milho sob plantas de cobertura por quatro safras (2009/10, 2010/11, 2011/12 e 2012/13). Os resultados apontaram que as intervenções mecânicas do solo não influenciam os efeitos do gesso sobre o gradiente de cátions no perfil do solo e as produtividade de grãos do milho e soja; A intervenção do solo com aração+gradagem altera o gradiente de Ca2+ no solo sob SPD e, o gesso tem pouco potencial de mobilizar verticalmente os cátions do solo, sendo que os efeitos são limitados aos 0,10 m de profundidade; O uso do gesso agrícola mostra pouca maximização na produção de soja e boa maximização na produção de milho, sendo o aporte de enxofre no solo o principal fator maximizador.

This diploma thesis deals with the stereoselective addition reaction of benzothiophenone derivatives to ketimines derived from isatin using bifunctional organocatalysis. The stereoselective addition reaction was optimized to provide the appropriate reaction conditions which were subsequently used to study the scope of the reaction. Keywords Organocatalysis, stereoselective synthesis, bifunctional organocatalysts, ketimines, sulphur heterocykles.

Please read the abstract in the section, 00front, of this document / Dissertation (MSc (Microbiology))--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted

Nitrogen-alloyed austenitic stainless steels are becoming increasingly popular, mainly due to their excellent combination of strength and toughness. Nitrogen desorption to the atmosphere during the autogenous welding of these steels is often a major problem, resulting in porosity and nitrogen losses from the weld. In order to counteract this problem, the addition of nitrogen to the shielding gas has been proposed. This study deals with the absorption and desorption of nitrogen during the autogenous arc welding of a number of experimental stainless steels. These steels are similar in composition to type 310 stainless steel, but with varying levels of nitrogen and sulphur. The project investigated the influence of the base metal nitrogen content, the nitrogen partial pressure in the shielding gas and the weld surface active element concentration on the nitrogen content of autogenous welds. The results confirm that Sievert's law is not obeyed during welding. The weld nitrogen content increases with an increase in the shielding gas nitrogen content at low nitrogen partial pressures, but at higher partial pressures a dynamic equilibrium is created where the amount of nitrogen absorbed by the weld metal is balanced by the amount of nitrogen evolved from the weld pool. In alloys with low sulphur contents, this steady-state nitrogen content is not influenced to any significant extent by the base metal nitrogen content, but in high sulphur alloys, an increase in the initial nitrogen concentration results in higher weld nitrogen contents over the entire range of nitrogen partial pressures evaluated. A kinetic model can be used to describe nitrogen absorption and desorption during welding. The nitrogen desorption rate constant decreases with an increase in the sulphur concentration. This is consistent with a site blockage model, where surface active elements occupy a fraction of the available surface sites. The absorption rate constant is, however, not a strong function of the surface active element concentration. Alloys with higher base metal nitrogen contents require increased levels of supersaturation prior to the onset of nitrogen evolution as bubbles. These increased levels of supersaturation for the higher-nitrogen alloys is probably related to the higher rate of nitrogen removal as N2 the onset of bubble formation. Given that nitrogen bubble formation and detachment require nucleation and growth, it is assumed that a higher nitrogen removal rate would require a higher degree of supersaturation. Nitrogen losses from nitrogen-alloyed stainless steels can be expected during welding in pure argon shielding gas. Small amounts of nitrogen can be added to the shielding gas to counteract this effect, but this should be done with care to avoid bubble formation. Supersaturation before bubble formation does, however, extend the range of shielding gas compositions which can be used. Due to the lower desorption rates associated with higher surface active element concentrations, these elements have a beneficial influence during the welding of high nitrogen stainless steels. Although higher sulphur contents may not be viable in practice, small amounts of oxygen added to the shielding gas during welding will have a similar effect. / Dissertation (PHD)--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / unrestricted

No description available.

South Africa (SA) currently faces a major pollution problem from mining impacted water, including acid rock drainage (ARD), as a consequence of the mining activities upon which the economy has been largely built. The environmental impact of ARD has been further exacerbated by the country's water scarce status. Increasingly scarce freshwater reserves require the preservation and strategic management of the country's existing water resources to ensure sustainable water security. In SA, the primary focus on remediation of ARDcontaminated water has been based on established active technologies. However, these approaches are costly, lead to secondary challenges and are not always appropriate for the remediation of lower volume discharges. Mostly overlooked, ARD discharges from diffuse sources, associated with the SA coal mining industry, have a marked impact on the environment, similar to those originating from underground mine basins. This is due to the large number of deposits and their broad geographic distribution across largely rural areas of SA. Semi-passive ARD treatment systems present an attractive alternative treatment approach for diffuse sources, with lower capital and operational costs than active systems as well as better process control and predictability than traditional passive systems. These semi-passive systems typically target sulphate salinity through biological sulphate reduction catalysed by sulphate reducing bacteria (SRB). These anaerobic bacteria reduce sulphate, in the presence of a suitable electron donor, to sulphide and bicarbonate. However, the hydrogen sulphide product generated is highly toxic, unstable, easily re-oxidised and poses a significant threat to the environment and human health, so requires appropriate management. An attractive strategy is the reduction of sulphate to sulphide, followed by its partial oxidation to elemental sulphur, which is stable and has potential as a value-added product. A promising approach to achieve partial oxidation is the use of sulphide oxidising bacteria (SOB) in a floating sulphur biofilm (FSB). These biofilms develop naturally on the surfaces of sulphide rich wastewater streams. Its application in wastewater treatment and the feasibility of obtaining high partial oxidation rates in a linear flow channel reactor (LFCR) has been described. The use of a floating sulphur biofilm overcomes many of the drawbacks associated with conventional sulphide oxidation technologies that are costly and require precise operational control to maintain oxygen limiting conditions for partial oxidation. In the current study a hybrid LFCR, incorporating a FSB with biological sulphate reduction in a single reactor unit, was developed. The integration of the two biological processes in a single LFCR unit was successfully demonstrated as a ‘proof of concept'. The success of this system relies greatly on the development of discrete anaerobic and microaerobic zones, in the bulk liquid and at the airliquid interface, that facilitate sulphate reduction and partial sulphide oxidation, respectively. In the LFCR these environments are established as a result of the hydrodynamic properties associated with its design. Key elements of the hybrid LFCR system include the presence of a sulphate-reducing microbial community immobilised onto carbon fibres and the rapid development of a floating sulphur biofilm at the air-liquid interface. The floating sulphur biofilm consists of a complex network of bacterial cells and deposits of elemental sulphur held together by an extracellular polysaccharide matrix. During the Initial stages of FSB development, a thin transparent biofilm layer is formed by heterotrophic microorganisms. This serves as ‘scaffolding' for the subsequent attachment and colonisation of SOB. As the biofilm forms at the air-liquid interface it impedes oxygen mass transfer into the bulk volume and creates a suitable pH-redox microenvironment for partial sulphide oxidation. Under these conditions the sulphide generated in the bulk volume is oxidised at the surface. The biofilm gradually thickens as sulphur is deposited. The produced sulphur, localised within the biofilm, serves as an effective mechanism for recovering elemental sulphur while the resulting water stream is safe for discharge into the environment. The results from the initial demonstration achieved near complete reduction of the sulphate (96%) at a sulphate feed concentration of 1 g/L with effective management of the generated sulphide (95-100% removal) and recovery of a portion of the sulphur through harvesting the elemental sulphur-rich biofilm. The colonisation of the carbon microfibres by SRB ensured high biomass retention within the LFCR. This facilitated high volumetric sulphate reduction rates under the experimental conditions. Despite the lack of active mixing, at a 4-day hydraulic residence time, the system achieved volumetric sulphate reduction rates similar to that previously shown in a continuous stirred-tank reactor. The outcome of the demonstration at laboratory scale generated interest to evaluate the technology at pilot scale. This interest necessitated further development of the process with a particular focus on evaluating key challenges that would be experienced at a larger scale. A comprehensive kinetic analysis on the performance of the hybrid LFCR was conducted as a function of operational parameters, including the effect of hydraulic residence time, temperature and sulphate loading on system performance. Concurrently, the study compared the utilisation of lactate and acetate as carbon source and electron donor as well as the effect of reactor configuration on system performance. Comparative assessment of the performance between the original 2 L LFCR and an 8 L LFCR variant that reflected the pilot scale design with respect to aspect ratio was conducted. Pseudo-steady state kinetics was assessed based on carbon source utilisation, volumetric sulphate reduction, sulphide removal efficiency and elemental sulphur recovery. Additionally, the hybrid LFCR provided a unique synergistic environment for studying the co-existence of the sulphate reducing (SRB) and sulphide oxidising (SOB) microbial communities. The investigation into the microbial ecology was performed using 16S rRNA amplicon sequencing. This enabled the community structure and the relative abundance of key microbial genera to be resolved. These results were used to examine the link between process kinetics and the community dynamics as a function of hydraulic residence time. Results from this study showed that both temperature and volumetric sulphate loading rate, the latter mediated through both sulphate concentration in the feed and dilution rate, significantly influenced the kinetics of biological sulphate reduction. Partial sulphide oxidation was highly dependent on the availability and rate of sulphide production. Volumetric sulphate reduction rates (VSRR) increased linearly as hydraulic residence time (HRT) decreased. The optimal residence time was determined to be 2 days, as this supported the highest volumetric sulphate reduction rate (0.21 mmol/L.h) and conversion (98%) with effective sulphide removal (82%) in the 2 L lactate-fed LFCR. Lactate as a sole carbon source proved effective for achieving high sulphate reduction rates. Its utilisation within the process was highly dependent on the dominant metabolic pathway. The operation at high dilution rates resulted in a decrease in sulphate conversion and subsequent increase in lactate metabolism toward fermentation. This was attributed to the competitive interaction between SRB and fermentative bacteria under varying availability of lactate and concentrations of sulphate and sulphide. Acetate as a sole carbon source supported a different microbial community to lactate. The lower growth rate associated with acetate utilising SRB required longer start-up period and was highly sensitive to operational perturbations, especially the introduction of oxygen. However, biomass accumulation over long continuous operation led to an increase in performance and system stability. Microbial ecology analysis revealed that a similar community structure developed between the 2 L and 8 L lactate-fed LFCR configurations. This, in conjunction with the kinetic data analysis, confirmed that the difference in aspect ratio and scale had minimal impact on process stability and that system performance can be reproduced. The choice of carbon source selected for distinctly different, highly diverse microbial communities. This was determined using principle co-ordinate analysis (PCoA) which highlighted the variation in microbial communities as a function of diversity and relative abundance. The SRB genera Desulfarculus, Desulfovibrio and Desulfomicrobium were detected across both carbon sources. However, Desulfocurvus was found in the lactate-fed system and Desulfobacter in acetate-fed system. Other genera that predominated within the system belonged to the classes Bacteroidetes, Firmicutes and Synergistetes. The presence of Veillonella, a lactate fermenter known for competing with SRB, was detected in the lactate-fed systems. Its relative abundance corresponded well with the lactate fermentation and oxidation performance, where an apparent shift in the dominant metabolic pathway was observed at high dilution rates. Furthermore, the data also revealed preferential attachment of selective SRB onto carbon microfibers, particularly among the Desulfarculus and Desulfocurvus genera. The microbial ecology of the floating sulphur biofilm was consistent across both carbon sources. Key sulphur oxidising genera detected were Paracoccus, Halothiobacillus and Arcobacter. The most dominant genera present in the FSB were Rhizobium, well-known nitrogen fixing bacteria, and Pannonibacter. Both genera are members of the class Alphaproteobacteria, a well-known phylogenetic grouping in which the complete sulphur-oxidising, sox, enzyme system is highly conserved. An aspect often not considered in the operation of these industrial bioprocess systems is the microbial community dynamics within the system. This is particularly evident within biomass accumulating systems where the proliferation of non-SRB over time can compromise the performance and efficiency of the process. Therefore, the selection and development of robust microbial inoculums is critical for overcoming the challenges associated with scaling up, particularly with regards to start-up period, and long-term viability of sulphate reducing bioreactor systems. In the current study, long-term operation demonstrated the robustness of the hybrid LFCR process to maintain relatively stable system performance. Additionally, this study showed that process performance can be recovered through re-establishing suitable operational conditions that favor biological sulphate reduction. The ability of the system to recover after being exposed to multiple perturbations, as explored in this study, confirms the resilience and long-term viability of the hybrid process. A key feature of the hybrid process was the ability to recover the FSB intermittently without compromising biological sulphate reduction. The current research successfully demonstrated the concept of the hybrid LFCR and characterised sulphate reduction and sulphide oxidation performance across a range of operating conditions. This, in conjunction with a clearer understanding of the complex microbial ecology, illustrated that the hybrid LFCR has potential as part of a semi-passive approach for the remediation of low volume sulphate-rich waste streams, critical for treatment of diffuse ARD sources.

The aim of this thesis is to design a desulphurization device for the fluid boiler. In the fluid boiler, fuel with extremely high sulphur content is burnt and the combustion products are not desulphurized to the required level, therefore it is necessary to build a desulphurization device. The thesis consists of two parts – theoretical and practical. In the theoretical part I stated the emission limits of sulphur dioxide, elaborated possible desulphurization methods and described the sorbets suitable for desulphurization. In the practical part I chose a dry desulphurization method with fluid reactor, to which a dry sorbent on the basis of lime hydrate is dosed. For the required parameters, I designed the whole desulphurization equipment including cloth filters, all necessary silos and major components. It is a design proposal with a layout and a spatial model.

The aim of this thesis is to design a desulphurisation device for the pulverized coal boiler K3 in heating plant Olomouc. In this boiler, coal with sulphur content is burnt. Emissions SOx from the boiler output are much higher than the emission limits for SOx, which comes into force 1.1.2016. Therefore it is necessary to build a desulphurisation device, which will cause a significant reduction of SOx emissions and compliance with the emission limits. The thesis consists of two parts - theoretical and practical. The theoretical part states SO2 emission limits and describes various methods for flue gas desulphurisation. In the practical part I chose a semi-dry desulphurisation method with fluid reactor. It determines a stoichiometric amount of combustion air and determines the boiler efficiency. For the required parametres is given a calculation of desulphurisation, the design of some parts of the device and design arrangement.