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Zéolitas ZSM-12 mesoporosas textura, cristalinidade e atividade ácida para o craqueamento de cicloexano
(Universidade Federal de São Carlos, 2013-09-12) Carvalho, Kele Tatiane Gomes; Urquieta-González, Ernesto Antonio; https://lattes.cnpq.br/7263345705541875
The research addressed the generation of mesoporosity in the zeolite ZSM-12 (MTW). In the first part we studied the synthesis of ZSM-12 via conventional methodology and in the presence of a mesopore directing agent, organosilane [3-(Trimethoxy-silyl)propyl] octadecyldimethylammonium chloride (TPOAC). It was verified to influence the TPOAC/SiO2 and H2O/SiO2 ratios and, also the aging of the reaction mixture, temperature and time of the hydrothermal treatment. In the second part we studied the formation of mesoporosity by post-synthesis treatment with alkaline solution (NaOH). For optimization of such treatment the concentration of the NaOH solution and the temperature were varied. The zeolites were characterized by X-ray diffraction, chemical analysis by energy-dispersive X-ray spectroscopy, N2 adsorption/desorption, scanning electron microscopy, nuclear magnetic resonance of 27Al, and temperature-programmed desorption of ammonia. By the analyses of X-ray diffraction and Rietveld refinement, we verified a decrease in crystallization kinetics with increasing TPOAC/SiO2 ratio and a tendency for simultaneous crystallization of MFI and MTW phases with increasing H2O/SiO2 ratio, temperature and aging time. It was possible to obtain mesoporous ZSM-12 with high purity and crystallinity with only small quantities of TPOAC and relatively long crystallization times. For ZSM-12 zeolites treated in basic medium, there was the formation of mesopores in the range from 2.9 to 23 nm due to the silicon extraction from the crystalline framework, which caused a decrease in the volume of micropores and an increase in the total acidity, assigned to the decrease in Si/Al ratio. In the cracking of cyclohexane at 400 °C, although the presence of mesoporosity had caused a decrease in the total acidity, the zeolites synthesized with TPOAC showed similar conversions to conventional zeolite with minimal catalytic deactivation, which was attributed to the better mass transfer and less coke formation. The ZSM-12 zeolites treated with NaOH exhibited activity and stability similar to those obtained in the presence of TPOAC. By its higher proportion of strong acid sites, the conventional ZSM-12 zeolite showed higher hydrocarbon yields in the range from C2 to C4 in comparison with the mesoporous zeolites, with the latter showing a higher yield for C6 hydrocarbons.
Programação da produção em sistemas flowshop híbrido com buffers limitados
(Universidade Federal de São Carlos, 2013-09-12) Lugo, Pedro Luis Miranda; Teixeira Junior, Rodolfo Florence; https://lattes.cnpq.br/3984827098999832; Armentano, Vinicius Amaral; http://lattes.cnpq.br/2731824199139290; Toso, Eli Angela Vitor
This research studies the hybrid flowshop scheduling problem. In this production configuration, we have a set of jobs that has to be processed in a set of stages. At every stage we have a set of parallel machines available to process the jobs. All jobs have to be processed following the same production flow, from the first to the last stage. Every job has to be processed on one machine at each stage and each machine can process at most one job at a time. Some constraints commonly found in real production systems as unrelated parallel machines, limited buffers, sequence-dependent setup times (both anticipatory and non-anticipatory), machine eligibility, transportation times and release times for machines are also taken into account. The optimization criterion is the makespan, whose minimization is related to the efficient use of production resources. A mixed integer programming model is proposed and solved by the commercial solver CPLEX. The computational evaluation results indicate that the model is suitable just to solve instances up to nine jobs and five stages. Therefore, to solve larger instances (50-100 jobs), several heuristics and an iterated local search (ILS) algorithm are proposed and evaluated computationally. The results indicate that the ILS is able to obtain good quality solutions in short computation times.
Síntese por redução carbotérmica assistida por micro-ondas de carbeto de zircônio
(Universidade Federal de São Carlos, 2013-09-12) Gaviria, Juan Pablo Yasnó; Kiminami, Ruth Herta Goldschmidt Aliaga; https://lattes.cnpq.br/7643216999108223; https://lattes.cnpq.br/8264570604790000
One of the major motivations for the development of new synthesis routes is a continuing need for fast and energy-efficient methods that allow obtaining materials with differentiated technological characteristics and properties. The use of microwaves in materials synthesis has generated great interest in the scientific research due to its speed, simplicity and energy-efficiency. Among different synthesis methods which can be assisted by microwave energy, the carbothermal reduction is the most simple and effective method in ceramic materials production. The conventional carbothermal reduction is used to obtain zirconium carbide (ZrC). In this context, the purpose of this work was to study the synthesis by microwave-assisted carbothermal reduction of ZrC using a mixture of zirconia (ZrO2) and carbon black (C). The synthesis parameters evaluated in this work were: stoichiometry, ZrO2/C-forming process, microwave power, reaction time and pressure of inert gas (argon). Characterization by X-ray diffraction (XRD) analysis of the samples synthesized by this method showed that the formation of ZrC phase was enhanced by controlling the following parameters: microwave power and reaction time increases, conservation of theoretical stoichiometry ZrO2/C:1/3, less compression of the pelleted mixture before the reaction and moderate pressure of argon. The samples with the highest ZrC content were characterized by specific surface area (BET) and scanning electron microscopy (SEM). These characterizations revealed that microwave-assisted carbothermal reduction synthesis produced ZrC samples with average particle size of ~100-200nm, near the nanometer range, homogeneous morphology and reaction time of 30 minutes.