Obtenção de biocombustíveis líquidos por pirólise e hidropirólise rápida catalítica da microalga Halamphora coffeaeformis.

Abstract

Microalgae biomass has shown great potential for biofuel production. These microorganisms, in various culture media, synthesize compounds that are renewable raw materials for generating green hydrocarbons, used as an alternative to fossil fuels in the energy transition. Microalgae have phytoextractive capacity for certain metals, which can stimulate fatty acid production by the cells. Fast pyrolysis (PY) and fast hydropyrolysis (H2PY), with the aid of catalysts, are technological routes currently used in converting microalgae into green hydrocarbons. In this work, the diatom Halamphora coffeaeformis, the metal ion Ni2+, at 3 ppm, in two Conway culture media were selected. Associated with PY in the production of drop-in biofuels in biogasoline, biojet fuel, and green diesel, alumina (γ-Al2O3) was used at 600°C for 15 seconds. In P. E and H2PY, a synthesized catalyst was also used: nickel and cerium oxide supported on alumina (NiO-CeO2/Al2O3) at 450°C under 1 atm H2 pressure for 2 minutes. Biomass production reached 1 g/L in 30 days, and the highest percentage of free fatty acids was achieved in the condition with the Ni2+ ion in the traditional Conway medium. The biomass was mainly characterized by thermogravimetry (TGA), scanning electron microscopy (SEM), and by fast (thermal) pyrolysis coupled with gas chromatography-mass spectrometry (PY-GC-MS). Fatty acids C14:0, C15:0, C16:0, C16:1, and C18:0 were quantified, representing about 7.8% (w/w), with C16:0 and C16:1 being the most abundant. In the conversions, the deoxygenation effect and hydrocarbon (HC) production were investigated. The presence of a catalyst increased the conversion and selectivity to hydrocarbons, mainly olefinic, paraffinic, and aromatic medium-chain hydrocarbons in PY, obtaining 58.1% of hydrocarbons in the carbon range of C4 to C18. In H2PY, with NiO-CeO2/ Al2O3, 84% of hydrocarbons ranging from C7 to C23 were obtained. This catalyst was more selective to paraffin production compared to Al2O3, with an α/n (olefin/paraffin) ratio of 1.4, while with γ- Al2O3 it was 2.4. In the different reaction processes, hydrocarbons compatible with the desired liquid fuels were obtained. In PY, higher conversion to higher quality biogasoline was achieved, while in H2PY, the production of bio-kerosene and green diesel was maximized, demonstrating the potential of microalgae as a raw material for biorefining in obtaining biofuels, contributing to the energy transition without major technological changes to engines and turbines.