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ABSTRACT.A simplex-centroid design was applied to optimize conditions for obtaining B100 biodiesel from sunflower oil using different catalysts with methanol and ethanol as process variable. Sodium methoxide was indicated as the best catalyst in the transesterification reaction with methanol at a 98.30% yield. Reaction yield was optimized only to 89.65% when ethanol as process variable and KOH as catalyst were employed. Tests with the obtained products, in optimal conditions, indicated that they were within the parameters established by Brazilian legislation and by the European Union.

ResumoO processo de obtenção de biodiesel B100, a partir da transesterificação em meio básico, de uma mistura de óleo vegetal e gordura animal foi otimizado utilizando o método simplex supermodificado. Para otimização simultânea foram usados como respostas o rendimento, custo, estabilidade oxidativa e ponto de entupimento de filtro a frio (CFPP), e os limites foram estabelecidos de acordo com os dados experimentais e os parâmetros de conformidade estabelecidos pela legislação. A otimização multirresposta utilizando as equações preditivas, obtidas a partir do delineamento simplex-centroide acopladas às funções de desejabilidade, apresentou uma formulação ótima contendo 38,84% de óleo de soja, 21,90 % de sebo bovino e 39,25 % de gordura de ave com rendimento de 94,94 %, estabilidade oxidativa a 110 ºC de 8,99 horas, CFPP de 2,83 ºC e custo de US$ 864,60. A validação mostrou não haver diferença significativa entre os valores preditos e os valores experimentais. O delineamento de mistura e a otimização simplex-centroide se mostraram metodologias eficazes na obtenção de biodiesel B100, usando uma mistura de diferentes matérias-primas. The process of obtaining B100 biodiesel from vegetable oil and animal fat mixtures by transesterification under basic conditions was optimized using the super-modified simplex method. For simultaneous optimization, yield, cost, oxidative stability and Cold Filter Plugging Point (CFPP), were used as responses, and the limits were established according to the experimental data and the conformity parameters established by legislations. Based on the predictive equations obtained from the simplexcentroid design-coupled functions, the multi-response optimization showed an optimal formulation containing 38.84 % soybean oil, 21.90 % beef tallow and 39.25 % poultry fat, resulting in reaction yield of 94.94 %, 8.99 h for oxidative stability at 110 °C, 2.83 °C of CFPP and cost US$ 864.60. The validation showed that there are no significant differences between the predicted and experimental values. The simplex-centroid mixture design and simplex optimization methods were effective tools in obtaining biodiesel B100, using a mixture of different raw materials.

In the present study an anodic stripping voltammetric method using a bismuth film modified carbon nanotubes paste electrode for simultaneous determination of metals Zn 2+ , Cd 2+ and Pb 2+ in ethanol fuel is described. The metallic ions were preconcentrated on the bismuth film in the time and deposition potential of 500 s and -1.2 V and the stripping step was carried out by square wave voltammetry (frequency of 15 Hz, pulse amplitude of 25 mV and potential step of 5 mV). Acetate buffer at 0.1 mol L -1 concentration and pH 4.5 was used as support electrolyte.