Obtenção de hidrocarbonetos verdes similares ao diesel de petróleo por pirólise catalítica da fração lipídica de microalgas

Abstract

Currently, microalgae have been widely studied as a source of biomass to produce biofuels due to their high productivity, high lipid content and ability to grow in a wide variety of climates and spaces without competing with food production. The objective of this work is the production of green hydrocarbons similar to the constituents of conventional diesel, from the rapid thermal pyrolysis of the lipid fraction of microalgae of the Halamphora coffeaeformis (Hc), Chlorella vulgaris (Cv) and Nannochloropsis oculata (No) genera. For the latter, the feasibility of its use was studied when subjected to fast catalytic pyrolysis, using niobium catalysts. This practice emphasizes the important role of catalysis in fast pyrolysis. The catalysts used showed synergy to thermal cracking, amplifying the products of interest. Studies were also carried out using a model molecule, myristic acid, representing the fatty acids that can be found in microalgae. It was verified that the products generated in the micropyrolysis of this molecule in the presence of niobium catalysts (Nb350, Nb700, NbB700,) at two temperature levels, 500 and 600°C, showed formation of ketones and hydrocarbons by fatty acid deoxygenation. Furthermore, experiments using C14 with alumina catalysts (γ-Al2O3) and niobium supported on alumina (Al700 and AlNb700) were used only at a temperature of 600ºC. The experiments were carried out in a Multi-shot Pyrolyzer Model EGA/PY-3030D micro-pyrolyzer, from Frontier Laboratories LTD, connected online with a gas chromatograph coupled to an Agilent GC-MS 5799A mass spectrometry. All micro pyrolyzer were performed by the “Single-Shot” (SS) thermal method. Niobium-based catalysts were prepared from hydrated niobium oxide by calcination at 350 and 700°C, the latter sample being modified with boric acid (Nb350, Nb700 and NbB700). From the purely thermal pyrolysis of the lipid fraction of the microalgae, conducted at a temperature of 600°C, the best response was verified and then tests with the catalysts (Nb350, Nb700 and NbB700) could be carried out. The products of myristic acid micro-pyrolysis were identified through the NIST Data base, assuming a probability of agreement of parameters equal to or greater than 80%. For the pyrolysis of the lipid fraction of microalgae, 70% agreement was admitted. The best yields in hydrocarbons were observed when using the temperature of 600ºC. The Nb350 catalysts proved to be efficient producing ketones that can be considered intermediates in the production of olefins and alkanes hydrocarbons, with a larger carbon chain than the starting acid. The catalysts Nb350 and AL700 both promoted efficient deoxygenation and cracking in the production of hydrocarbons while the catalysts NbB700 and Nb700 provided less efficient deoxygenation and cracking. In the pyrolysis of the lipid fraction of the Nb350 catalysts, I had an important performance, increasing from 18% to 35% the production of hydrocarbons compatible with diesel fuel