Perfil termocinético e termodecomposição da leucena (Leucaena Leucocephala)

Abstract

Brazil has abundant and rich vegetation that is used in several industrial and commercial sectors, which is reflected in the high production of plant residues. This, associated with catalytic pyrolysis technology, can be used to produce raw material for the chemical sector, adding economic and environmental value to th e residues. Leucaena (Leucaena leucocephala) has stood out due to its abundance in Brazilian territory. Leucaena is a plant that belongs to the Leguminosae (Fabaceae) family. This work investigated (i) the thermokinetic and thermodecomposition properties of different parts of the biomass (stem, pod and seed), (ii) the thermodecomposition profile in the presence of catalysts composed of niobium and strontium oxides. The material was collected from leucaena trees in the city of Salvador, Bahia, Brazil and its preparation consisted of washing, drying, crushing and sieving. The catalysts were prepared from niobium oxalate and strontium nitrate calcined at different temperatures (400 °C, 600 °C, 800 °C and 1000 °C). The samples were characterized by moisture and ash measurements, Fourier transform infrared spectroscopy and were analyzed in a pyrolyzer at 550 °C coupled to a gas chromatograph with mass spectroscopy. The catalysts were characterized by X-ray diffraction and the biomass presented moisture contents in the range of 2% to 5% and ash below 3%, showing promise for thermodecomposition through pyrolysis. The infrared results showed similar bands among the three parts of leucaena, associated with the presence of cellulose, hemicellulose and lignin. A slight difference in the profile of the seed sample can be attributed to the presence of nitrogenous groups and to the high moisture content compared to the other parts of leucaena. The thermodecomposition results showed differences in the biomass profile when in the presence of the catalysts niobium oxide, strontium oxide and the combination of oxides, indicating a significant effect on the formation of products with potential to be used in the food and pharmaceutical industries, such as acetic acid (samples conta ining the mixture of niobium and strontium oxides), phenols (samples containing strontium oxide) and aldehydes (samples containing niobium oxide). The results of kinetic parameters reveal that, for the conversion range α = 0.15 - 0.70, the isoconversionality principle remained valid, with the seed having the lowest activation energy equal to 91.79 kJmol-1 (Friedman isoconventional method) and even when different thermokinetic methods were applied. Thus, leucaena proved to be a promising biomass for the extraction of products with high added value.