Efeito do combustível e da fonte de aquecimento na reação de combustão do ZnAI2O4 e avaliação do seu desempenho na produção de biodiesel por transesterificação.

Abstract

ZnAI204 is a normal spinel of the A B 204 type, whose growth mechanisms and its structural properties have been aim of extensive investigations. An interesting common feature to the spinels is the absorption of a large amount of cations in its structure, which gives each of the resulting phases different physical and chemical properties. Therefore, the present work is based on the synthesis of ZnAI204 by combustion reaction technique, in order to evaluate the influence of the fuel kind and of the external heating kind over the structure and morphology of the synthesized samples, besides evaluation in their performance as catalyst on the transesterification reaction of soybean oil for biodiesel production. As heating source were used a resistive ceramic base and a muffle furnace, and as fuel were used citric acid monohydrate, aniline, carbohydrazide, glycine and urea. During the synthesis were carried out measurements of the time and temperature combustion flame. The samples were characterized by XRD, FTIR, granulometric analysis, textural analysis, carbon content, SEM, and TEM. The transesterification reactions were carried out under two conditions: 1) methanol/oil/catalyst molar ratio of 600/100/1, temperature of 150°C, and reaction time of 1h; and, 2) methanol/oil/catalyst molar ratio of 2700/100/4, temperature of 200°C and reaction time of 4h. The results showed that the syntheses conducted in the muffle furnace reached combustion temperatures greater than those conducted in the ceramic base, and that the fuel kind had a significant influence on the structural and morphological characteristics of the samples. All samples presented the formation of ZnAI204 spinel as majority phase, with exception of the samples synthesized with citric acid that presented amorphous characteristic. ZnAI204 monophasic was only able to be obtained by the sample synthesized with urea using the ceramic base as heating source, the other ones showed ZnO and A l 203 as segregated phases. FTIR spectra confirmed the presence of ZnAI204 by the typical O-AI-0 vibrations bands at around 450-700 cm"1 . The analysis of granulometry, SEM, TEM, and content carbon showed that all samples presented morphologic character based on agglomerates of strongly linked nanoparticles, but with different aspects characteristic of each sample, and carbon content ranging from 0.24 to 17.5%. According to the results of the N2 adsorption, the samples showed surface area with values ranging from 3.9 to 29.7 m2/g. The catalytic test carried out in the transesterification of soybean oil showed that for the mild conditions adopted, the samples presented low catalytic activity, reaching a yield of just 5%, referring to the use of the sample synthesized with glycine in the ceramic base, and that, in more severe conditions, such yield increased to 91.6%.