Made available in DSpace on 2014-10-09T12:43:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:43Z (GMT). No. of bitstreams: 1 06636.pdf: 4715244 bytes, checksum: 8df295514eae9493e07c3d6352c4bf32 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

>Magister Scientiae - MSc / In recent times, the occurrence and presence of complex recalcitrant toxic contaminants in water and wastewater is increasing and consequently contributes to the non-availability of clean and safe drinking water. Water treatment is complex, time demanding and energy intensive due to the physico-chemical structural complexity and diversity of the pollutants. Non-availability of good drinking water has negatively affected human health and the ecosystem. Over the years, numerous conventional treatment techniques were used to degrade and remove these pollutants, but investigations indicated that some of the pollutants are not susceptible to conventional treatment. Advanced oxidation technology, among which heterogeneous photocatalysis (involving the use of a semiconductor) has emerged as one of the more promising techniques to remediate contaminated water. Titanium dioxide (TiO2) semiconductor photocatalysis is considered to be a good option due to its cost effectiveness, chemical and thermal stability, and inertness in the area of wastewater reclamation and re-use. However the post separation of the titania particles poses a threat to the wastewater remediation. Hence there is a need to develop a supported high surface area photocatalyst that will resolve the post separation challenge. This present study aimed to prepare high surface area TiO2 anatase nanocrystals supported on a stainless steel mesh. These new composite materials were used to remove methylene blue (MB) from aqueous solutions. The supporting procedure involved the thermal decomposition of a sol gel solution coated upon stainless steel mesh. The nanocrystalline anatase phase was formed by thermal decomposition on a stainless steel mesh coated with 8 % PAN/DMF/TiO2 sol gel formation calcined at varying temperatures of 300 °C, 400 °C, 500 °C and 600 °C. The heating rate of 50 °C/min and independent holding time of 1 h, 2 h, 3 h and 4 h were applied to find the optimum supporting conditions. The synthesised TiO2 nanocomposites materials were characterised using the following analytical techniques: XRD, HRSEM, EDS, HRTEM, SAED, FTIR and UV-Vis absorption spectroscopy materials were characterised, and the results indicate that synthesised TiO2 nanocrystals were in the anatase form, polycrystalline in nature, and contained additional carbon-carbon bonds from the polymer used during preparation with TiO2 particle sizes range from 13.6 nm to 2285 nm.

The aim of the diploma thesis was creating a decarbonisation model of lime, implementation the model into CFD tool ANSYS Fluent and to test the decarbonisation model in a model of a real reactor. The required model was based on assumptions for a Shrinking Core Model (SCM). The main objective of this work was the non-catalytic conversion of substances and the search for the most used mathematical models for calcination. The CFD calculation, the sensitivity analysis and the Fluente parametric study were used. Data on the composition of gas flow, temperature, pressure and mass flow of limestone particles were selected for input variables. The particle model called Multiple Surface Reactions (MSR), which is a standard part of Fluent, was used at first. Subsequently, a UDF which was based on the SCM assumptions was written in the programming language C. The results of the CFD calculation were compared with the experimental values from the dissertation. It has been found that the MSR is sufficiently precise for calculation purposes but neglects the internal diffusion of CO2 through the CaO layer which forms behind the reaction front during calcination. It was found that it is possible to solve the flow with ongoing calcination without the need to know the parameters of the Arrhenian equation if the UDF is used. The created UDF incorporates the influence of intraparticular CO2 diffusion on the overall reaction rate.

The topic of this dissertation was the preparation of a high-quality sulphate binder based on secondary raw materials. For this purpose, the work was primarily focused on the laboratory preparation of beta gypsum from the selected industrial gypsum, the design of the technological process of production and its verification by pilot tests. In the next step, the thesis dealt with the modification of beta gypsum by a selected set of liquefiers. In addition to commercial dehumidifiers, the possible beta casting of beta gypsum was tested by increasing the zeta potential of the gypsum suspension. At the end, a complete complex of construction products was developed based on laboratory and semi-prepared beta plasters, consisting of gypsum plasters, mastics, gypsum premix and small plaster casts.

This work is oriented on the preparation of high-voluable sulphate binder based on gypsum waste. One of the potential mineral resources in Moravia is Pregips chemical gypsum, produced by Precheza. This is the raw material, which is characterized by high purity, high quality and is economically acceptable. Beta burned gypsum plaster from this, however, need to modify due to suppression of the high needs of water mixing, which is determined by its morphology. The need for mixing water has a large impact on the strength of gypsum binders. Therefore it is necessary to find a suitable additive, which would reduce the coefficient of water in the preparation of porridge normal consistency.

A highly selective eggshell Fischer-Tropsch catalyst has been fabricated via interaction of hydrophobic and hydrophilic molecules on thermally treated silica gel. The physical interactions of the mesoporous silica support and the effect of catalyst preparation conditions on the performance of the cobalt/SiO2 were explored. It was found that dispersion and performance of the FT cobalt/SiO2 catalyst were significantly affected by the preparation technique used. In this study we focus on two key variables: the solvent used during the precursor loading and the calcination atmosphere. Silanol groups on the silica surface and near-surface regions can alter morphology and dispersion of the supported active metals. Solvents used for precursor such as water or alcohol attach to these silanol sites in specific configurations and compete with metal salts during ion exchange and adsorption. By fine tuning the solvent attachments on heat treated silica we have fabricated a cobalt/silica catalyst with high dispersion and low metal loads. Additionally, since silica has affinity for both polar and non-polar molecule depending on the surface conditions; this property has been exploited in preparing an engineered eggshell profile. This together with simultaneous calcination/ reduction in a dynamic hydrogen environment has been shown to further enhance dispersion and reducibility. Characterization techniques including BET, XPS, XRD, H-chemisorption and FTIR were employed. Catalyst activity, product selectivity, distribution and conversion were studied using a bench scale fixed bed reactor fitted with a GC/MS instrument.

The main objective of this research is to develop a simple and cost effective separation method that captures carbon dioxide from power plant flue gas, as a pure stream that can be stored using regenerable dolomite (calcium magnesium carbonate) as the sorbent. The developed dolomite sorbent was evaluated for carbon dioxide capture capacity using muti-cycle tests of cyclical carbonation/calcination experiments in the thermogravimetric analyzer (TGA) model SDT 600. The variables controlled in the experiment were weight of calcium oxide and sintering time of the sample. The dolomite materials investigated were from two sources Alfa Aesar and Specialty Minerals. The prepared sorbent, after conditioning, is in the oxide form and can adsorb CO2 to form the carbonate and be regenerated back to the oxide. The results showed that the dolomite sorbent developed can be used for reversible CO2 capture. The data from 8 multi-cycle TGA experiments show that the reversible capacity reduced in the first few cycles; however it stabilized to an average value of 34 percent after an average of 10 cycles and an average conditioning time of 15 hours. Data from two multi-cycle TGA experiments show that the dolomite sorbent is capable of an average stabilized conversion of 65% in an average of 13 cycles at a conditioning time of 87 hours.

Calcination is important for modern society as we know it since products from the reaction is used inseveral industries. Calcination is a chemical reaction where a solid particle, e.g., limestone, is exposedto high temperature which causes volatile impurities to be released from the particle.One of the main challenges with lime production is the mere scale of commercial production. Ensuringgood calcination and high-quality lime in laboratory scale is relatively easy, whereas commercial limekilns produce 100 – 800 tons lime each day, causing the conditions to be much more challenging. Theenvironment inside a lime kiln is extreme, with temperatures exceeding 1200°C, and a moving stonebed makes measurements difficult to perform. To obtain information about the calcination processand the extreme environment that arises in commercial lime kilns, companies and researchers havedeveloped simulation programmes to evaluate how changes in ambient condition affect the calcinationprocess.In this project, a shrinking core model has been used to simulate calcination of limestone with variedgeometry and size in different ambient condition. A transient model was used to simulate the heatingphases before and after the calcination phase. The results obtain from the simulation are compared tomeasured data obtain by others.There are many similarities between the measured data and the simulation, a reoccurringphenomenon is that the transit model, during the pre-heating, heats the limestone faster compared tothe measured data. However, in one case, the transient model is slower. A reason for this may be thatthe transient model does not account for morphological effects, as they are included in the heattransfer coefficient instead, such as the thermal conductivity coefficient and specific heat transfercoefficient. The post heating phase, after the reaction phase, required further work.The simulation with the Shrinking core model shows that a cylindrical geometry requires longercalcination duration, or a higher ambient temperature compared to a spherical geometry, even if bothgeometries have same material properties and radius. The factor with the most influence uponcalcination time is the ambient temperature in combination with reaction temperature. A highercarbon dioxide pressure, above atmospheric CO2 partial pressure, has relatively small effect comparedto a low ambient temperature, less than 1000°C.

No description available.

No description available.