Estudo da Pirólise Assistida por Micro-ondas de Biomassas Alternativas Provenientes do Cerrado Brasileiro

Abstract

This study initially investigated the analytical pyrolysis of macaúba epicarp, macaúba endocarp, baru endocarp, coffee husk—biomass from the Brazilian cerrado—as well as carton packaging. The research evaluated the influence of temperature and catalyst use, focusing on the potential of these biomass sources for bio-oil and biochar production. Macaúba epicarp was selected for subsequent stages due to its performance in analytical pyrolysis, particularly in terms of hydrocarbon yield and quality compared to the other biomass samples analyzed. The objective was to obtain bio-oil via microwave-assisted pyrolysis while minimizing oxygenated and nitrogenated compounds. The characterization of macaúba epicarp revealed a moisture content of 6.50%, a high volatile matter fraction (79.65%), and a low ash content (1.35%), which are favorable characteristics for pyrolysis processes. Elemental analysis indicated that the biomass is composed of 48.34% carbon, 5.93% hydrogen, and 43.69% oxygen, resulting in a higher heating value of 18.25 MJ/kg. Non-catalytic microwave-assisted pyrolysis experiments demonstrated a significant temperature effect on product composition and yield, with the highest condensable yield (48.4%) obtained at 550°C. Under these conditions, the bio-oil composition showed a high fraction of oxygenated compounds (93.2%) and hydrocarbons (5.4%). Among the identified hydrocarbons, 62.2% were aromatics, 24.1% alkanes, and 13.7% alkenes. The use of catalysts supported on a SiC foam bed modified the chemical distribution of the products and improved bio-oil quality. In pyrolysis with a single-layer bed supported on SiC foam, calcium oxide (CaO) reduced oxygenated compounds to 85.8%, increasing hydrocarbons to 14.2%. Phosphate mining residue exhibited a similar performance, reducing the oxygenated fraction to 86.2% and increasing hydrocarbons to 13.5%. Nickel oxide supported on niobium (NiONb2O5) achieved 12.0% hydrocarbons while increasing nitrogen-containing compounds to 3.3%. Zeolite use resulted in 11.1% hydrocarbons, whereas Nb2O5 produced 10.9% hydrocarbons and 3.6% nitrogen-containing compounds. The use of a dual-layer bed of catalysts supported on SiC foam proved promising and effective, enhancing hydrocarbon production. The combination of CaO with mining residue led to 59.4% hydrocarbons, distributed as 37.6% aromatics, 49.6% alkenes, and 12.9% alkanes. The combination of NiONb2O5 with mining residue generated 61.7% hydrocarbons, comprising 29.2% alkanes, 27.8% alkenes, 38.4% aromatics, and 4.5% cyclanes. Meanwhile, the association of Nb2O5 with mining residue resulted in 52.2% hydrocarbons, with 25.1% alkanes, 9.3% alkenes, 57.7% aromatics, and 7.9% cyclanes. The biochar from microwave-assisted pyrolysis exhibited high thermal stability, high fixed carbon content, and low ash content, making it suitable for applications in soil conditioning, pollutant adsorption, and energy generation.