Resumo As estruturas de concreto devem ser dimensionadas para garantir estabilidade ao longo da vida útil. Além disso, existem critérios que devem ser seguidos para a verificação da segurança contra incêndio. Nesse contexto, este trabalho teve como objetivo avaliar a influência da substituição parcial e integral do cimento CPII-Z32 pelo cimento refratário em composições de concreto relacionadas às propriedades residuais após exposição a diferentes níveis de temperatura. Para os testes, amostras cilíndricas foram moldadas com percentuais de substituição de cimento de 0% (referência), 50% e 100% e expostas em 450 e 900 °C sem carga. Os resultados dos testes mostraram alteração na cor dos corpos de prova e ainda redução da resistência mecânica com o aumento da temperatura. O incremento no percentual de cimento refratário resultou em menor condução de calor para o concreto fabricado com este material.

Abstract Concrete structures must be sized to ensure stability over their lifetime. Moreover, there are criteria that must be followed for fire safety verification. Given this context, this study aimed to evaluate the influence of the partial and integral replacement of CPII-Z32 cement by a refractory cement in concrete compositions related to the residual properties after exposure to different temperature levels. For the tests, cylindrical specimens were molded with cement replacement percentages of 0% (reference), 50%, and 100%, and exposed at 450 °C and 900 °C without load. The results showed a change in the color of the specimens and a reduction of the mechanical strength with increasing temperature. The increase in the percentage of refractory cement resulted in lower heat conduction for the concrete made with this material.

ABSTRACT This study evaluated the potential of macauba pulp oil (MPO) as a feedstock for continuous ester production using ethanol under pressurized conditions. Experiments were performed in order to obtain data for the effect of process variables on ethyl ester (FAEE) and free fatty acid (FFA) conversion in a catalyst-free process. From the results, it appears that the MPO to ethanol mass ratio and the pressure were the variables with more favorable effect on the evaluated response variables. The addition of n-hexane caused an increase in the production of esters; however, this had a negative effect on FFA conversion. The addition of water was unfavorable for oil processing with high acidity. In this process, esterification and transesterification occur simultaneously, and the high FFA content in MPO provides high yields (85 wt% of esters; 93% FFA conversion) at low temperature, since the esterification reaction rate is higher than the transesterification. The decomposition of fatty acids was evaluated and levels <5% were observed under the evaluated experimental conditions.

The inconveniences of the conventional method for biodiesel production by alkaline catalysis suggests research towards alternative methods, with the non-catalytic transesterification using an alcohol at supercritical conditions proposed as a promising technique for biodiesel production. The so-called supercritical method (SCM) has powerful advantages over conventional techniques, such as fast reaction rates, feedstock flexibility, production efficiency and environmentally friendly benefits. However, application of this methodology has some limitations, like operating conditions (elevated temperature and pressure and higher amounts of alcohol), which result in high energy costs and degradation of the products generated. In this review paper the state of the art in relation to the use of the SCM for biodiesel production is reported and discussed, describing the characteristics of the method, the influence of operational parameters on the ester yield, patents available in the field and the perspectives for application of the technique.