Cinética de pirólise para resíduos de abacaxi (Ananas comosus), in natura e torrificados – fator de compensação e modelo de reação

Abstract

Due to its wide availability and reduced environmental damage, biomass has been highlighted as a renewable alternative for generating energy. Torrefaction is a thermal pre-treatment process that can be used to valorize biomass as a fuel, by reducing moisture and increasing energy density. The pineapple crown is the main residue from fruit processing and has no industrial application or specific destination. The present study aimed to evaluate the slow pyrolysis of raw and previously torrefied pineapple crowns through characterization by proximate analysis, chemical composition, and interpretation of mass loss (TGA) and mass loss rate (DTA) profiles at heating rates of 2,5; 5 and 10 K min-1 in an inert nitrogen atmosphere. The isoconversional models (Ozawa-Flynn-Wall, Starink, Vyazovkin, modified Coats-Redfern and Friedman) and the compensation effect methodology were used to estimate the kinetic triplet to represent the thermal decomposition of the material. The raw pineapple crown presented low levels of moisture and ash (8,15 0,28 and 3,06 0,17%, respectively) and similar values of volatile materials (87,69 0,45%), fixed carbon (9,25 0,28%) and higher calorific value (19,04 0,03 MJ kg-1) when compared to other biomasses. Holocellulose represents the largest fraction of the material's composition (66.28 ± 0.92%), to a lesser extent there is total lignin (14.12 ± 0.34) and extractives (6.78 ± 0.26). The torrefaction process mostly decomposed the hemicelluloses and exctratives, what was verified by the smoothing of the DTA curves. Moreover, an increase in the activation energy of pyrolysis was observed, which occurs due to the degradation of the less thermally stable portion of the composition. The estimated kinetic triplet for the slow pyrolysis of the raw pineapple crown was composed of an average activation energy of 154,56 kJ mol-1, global pre-exponential factor of 1,75x1012 s-1 and global conversion function N3 (𝑓(𝛼)==(1 𝛼)3 ; as for the torrefied biomass, the triplet obtained was an average activation energy of 176.33 mol-1, global pre-exponential factor of 1.34×1013 s-1 and global conversion function N2 (𝑓(𝛼 (1 𝛼)22). The obtained results show that the proposed methodology is effective for determining the kinetic triplet and representing the decomposition of the studied heterogeneous material, with low average percentage deviations in relation to experimental data.