Orientador: Renato Sprung / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-14T09:58:31Z (GMT). No. of bitstreams: 1 CabreraNavarrete_MariaElia_D.pdf: 13508491 bytes, checksum: ed8e83647aa4fc77ef26b506eee4e91a (MD5) Previous issue date: 2007 / Resumo: Materiais do tipo hidrotalcita Mg1-x(Al,Cr)x(OH)2(CO3)x/2yH2O foram sintetizados por coprecipitação a partir de nitratos de magnésio, alumínio e cromo. Os sólidos foram calcinados, caracterizados e testados na conversão de etanol. Na preparação, alumínio foi substituído por cromo na hidrotalcita MgAl nas proporções de 0, 5, 10, 50, 80 e 100% e as frações de cátions trivalentes x foram de 0,20, 0,25 e 0,33. Os materiais mostraram difratogramas de raios-X característicos de hidrotalcitas. A calcinação a 650°C das hidrotalcitas com 0 a 80% de substituição de alumínio resultou em óxidos mistos com estrutura de MgO, e a de materiais com 100% de substituição, em cromita de magnésio. As áreas BET dos materiais calcinados diminuíram com os aumentos do teor de cromo e da fração x, variando entre 90 e 309 m²/g. Os materiais não contêm microporos. A adsorção de CO2 mostrou que a densidade de sítios básicos diminui com os aumentos do teor de cromo e de x. Os testes catalíticos foram realizados num reator de leito fixo, à pressão atmosférica e temperaturas de 300 a 375°C. Os principais produtos foram n-butanol, éter etílico, acetaldeído e etileno, além de quantidades menores de butiraldeído, crotonaldeído e acetato de etila. A substituição de alumínio por cromo inibiu a formação de éter etílico e favoreceu a formação de acetaldeído. A substituição de 5 a 10% de alumínio por cromo resultou nas maiores conversões de etanol e nos maiores rendimentos de n-butanol. A presença da água na alimentação de etanol diminuiu as conversões. A promoção de catalisadores com sódio inibiu as reações, especialmente as de desidratação. / Abstract: Hydrotalcite-type materials, Mg1-x(Al,Cr)x(OH)2(CO3)x/2yH2O, were synthesized by coprecipitation from solutions containing magnesium, aluminium and chromium nitrates, calcined, characterized and tested for the conversion of ethanol. Aluminum was substituted by chromium in MgAl-hydrotalcite in amounts of 0, 5, 10, 50, 80 and 100 mol% and x-values of 0,20, 0,25 and 0,33. Powder X-ray diffraction patterns of the synthesized materials were typical of hydrotalcites. Calcination at 650°C of materials with aluminum yielded mixed oxides with diffraction patterns typical of MgO, and of materials without aluminum, that of magnesium chromite. BET areas of calcined materials increased with increasing chromium contents as well as with increasing x-values, varying between 90 and 309 m²/g. No material contained micropores. CO2 adsorption showed decreasing base site density as either the chromium content or the x-value was increased. Catalysts were tested at atmospheric pressure and temperatures of 300 to 375°C in a fixed bed reactor. Diethyl ether, n-butanol, acetaldehyde and ethylene were the main reaction products; small amounts of crotonaldehyde, butyraldehyde and ethyl acetate were also present. The presence of chromium in the catalysts inhibited diethyl ether formation while favoring acetaldehyde formation. The substitution of 5-10 mol% of aluminum by chromium resulted in the highest ethanol conversions and the largest overall yields of n-butanol. Lower conversions were obtained when water was added into the ethanol feed. Promotion of catalysts with sodium decreased conversions, particularly of dehydration reactions. / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

This work investigates a novel iron Fischer-Tropsch (FT) catalyst preparation and describes the development of a trickle fixed-bed recycle reactor model (TFBRRM) for the FT synthesis applicable to both iron and cobalt catalysts. The iron catalyst preparation was developed using a novel solvent deficient precipitation reaction. Fifteen Fe/Cu/K/SiO2 catalysts were prepared to investigate key preparation variables including timing of promoter addition, washing or not washing after precipitation, and drying temperature. Adding promoters to starting materials before precipitation (1S) gives more uniform promoter distributions which gives higher water-gas shift activity and lower methane selectivity. Unwashed catalysts have smaller average pore and crystallite diameters (3.9-10.8 nm versus 15.3-29.5 nm) and 30% smaller pore volumes, but 65% higher rates of reaction than washed catalysts. Catalysts dried first at 100 °C have up to 50% smaller average pore and crystallite diameters, but 10-20% higher rates of reaction than catalysts dried first at 60 °C. Overall, 1S catalysts, left unwashed, and dried first at 100 °C are best suited in activity, selectivity, and stability for wax production from hydrogen-deficient feed stocks such as coal, biomass, or municipal waste. The activity of the most active catalyst of this study is greater than or equal to the activities of two of three catalysts reported in the literature. This dissertation describes in detail the TFBRRM, reports its validation, and presents results of varying fundamental, theoretically-based parameters (e.g. effective diffusivity, Prandtl number, friction factor, etc.) as well as physical process parameters (i.e. recycle ratio, pressure, flow rate, tube diameter, cooling temperature, and pellet diameter and shape). For example, the model predicts that decreasing effective diffusivity from 7.1E-9 to 2.8E-9 m^2/s results in a lower maximum temperature (from 523 to 518 K) and a longer required bed length to achieve 60% conversion of CO (from 5.7 to 8.5 m). Using the Tallmadge equation to estimate friction losses as recommended by the author results in a pressure drop 40% smaller than using the Ergun equation. Validation of the model was accomplished by matching published full-scale plant data from the SASOL Arge reactors.

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / The subject of maintenance optimisation is not new, and many researchers have explored it. However, it is seen that one optimisation solution cannot be used in all industries. Each industry and equipment thereof are unique as the product streams differ, layouts and operation variables, to name a few. Though Turn-around management is the most used strategy in petrochemical industries. Equipment downtime remains the biggest challenge thus, the purpose of the study was to optimise the maintenance practices used on the critical electromechanical equipment in Sasol Synfuels Catalyst Preparation using both the Analytical Network and Analytical Hierarchy multi-decision approach. Data was collected from the SAP system database, of which the breakdown work orders was obtained from the period of January 2016 to June 2021. The data was collected for each 13 electromechanical equipment identified in the catalyst preparation unit. The applied maintenance strategies employed on the electromechanical equipment in the catalyst preparation unit was also analysed using the Meridium maintenance strategy software tool utilised in Sasol Synfuels. An analysis and identification of the critical equipment within the unit were obtained with the use of two different methods, namely the JADERI, (2019) and AFEFY, (2010) approaches. A theoretical distribution was drawn after that in order to assess the effectiveness of the current maintenance strategy compared to the identified key performance indicators. The theoretical distribution analysis was used to determine the plant utilisation, availability, and maintenance cost. The analytical network and hierarchy process application, and the super decision network model framework, were analysed to obtain the maintenance optimisation solution. Though the ANP and AHP approaches have different problem identification frameworks and cluster dependencies, it is seen that both methods portray more or less similar results. Both methods indicate that in order to achieve an optimised maintenance strategy within the catalyst preparation unit, condition-based maintenance strategy is the most weighed alternative node with 50% for optimal maintenance solution. The least most weighed alternative node is corrective maintenance, weighed at 7%. This is true as corrective maintenance is applied once a breakdown has occurred, of which the aim is to avoid unforeseen breakdowns. Fixed time maintenance is the second most weighed maintenance strategy with 30%, followed then by the operate to failure strategy at 13%. Considering that the operation to failure maintenance strategy is applied based on the consequence of failure and maintenance cost as well as mean time to repair, this is then concluded as practical as RCM priorities predictive and preventative strategies to be employed. It was drawn, for criteria nodes, that the ANP approach resulted in the environmental safety impact as the most important criteria to consider when applying the optimal maintenance strategy in the Sasol Synfuels Catalyst preparation unit. The environmental safety impact was rated at 0.33, followed by availability with a factor of 0.32. The least weighed criteria nodes are then the maintenance cost and MTTR, both with a factor of 0.17. This proves to true considering that the petrochemical industry is considered a high-risk industry as it processes and produces hazardous chemicals The AHP approach structure however, does not consider interdependencies through the criteria and alternative clusters thus the alternative weight could not be defined. The results obtained prove that the ANP approach is the most practical mutli criteria decision making method for maintenance optimisation compared to the AHP approach.