Produção de biochar a partir de resíduo agroindustrial da macaúba (Acrocomia aculeata), caracterização e avaliação de sua capacidade de adsorção na remoção de contaminantes

Abstract

This work reports the production of biochar at different temperatures, using a simplified and low-cost procedure, aiming to obtain an adsorbent capable of removing pollutants in aqueous solutions; Methylene Blue (MB) and the Emerging Contaminant (EC) Bisphenol A (BPA) were tested. Biochars were produced from the carbonization of biomass at temperatures of 300 ºC (BC-300), 400 ºC (BC-400), 500 ºC (BC-500), 600 ºC (BC-600), 700 ºC (BC-700), and 800 ºC (BC-800), for 2 hours, in a standard electric muffle furnace, without purge and under limited oxygen conditions (non-inert atmosphere), with no pre-treatment, post-treatment or activation. The precursor used was Macaúba (Acrocomia aculeata) endocarp (EDP), a lignocellulosic material with physical and chemical characteristics favorable to carbonization, besides being accessible and low-cost. The changes in the physical and chemical properties of the precursor biomass and the differences between the biochars themselves were evidenced by TG/DTG, SEM, FT-IR, and XRD analysis and characterization techniques, thus confirming the influence of temperature on the biomass transformation. The results obtained for gravimetric yield (ηG) and the adsorption capacities of MB (qe-MB) and BPA (qe-BPA) were submitted to two-factor Analysis of Variance (ANOVA-2), followed by the Tukey test (p<0.05). The ηG produced under these conditions ranged from 11.05% to 35.98%, and there was a significant influence of the interaction between the evaluated factors (Carbonization Temperature x Atmosphere Condition), whose levels were 6 (six) temperatures between 300 ~ 800 ºC and 2 (two) conditions With Lid (CT) and Without Lid (ST); the CT method presented better yields at all tested temperatures. All biochars produced were able to remove MB and BPA, with better results for MB removal – for which qe-MB ranged from 5.37 to 35.13 mg.g-1 and qe-BPA from 0.92 to 23.17 mg.g-1; a significant interaction of the evaluated factors (Type of Adsorbent x Adsorbent Concentration) was observed; there were 7 (seven) levels for the types of adsorbents (EDP and the biochars) and 4 (four) levels for adsorbent concentrations (between 0.25 and 1.00 g.L-1) for the MB trials, while for BPA trials there were 5 (five) levels – between 0.50 and 5.00 g.L-1; for all tested adsorvates, BC-700 and BC-800 were superior to the others. Complementarily, BC-700 and BC-800 were submitted to textural characterization via N2 adsorption and exhibited maximum adsorbed quantity of 81.89 cm3.g-1 and 69,34 cm3.g-1, respectively; BC-700 was also superior in terms of specific BET surface area with 189.72 m2.g 1and BC-800 with 137.51 m2.g-1. The isotherms obtained for both materials exhibited shapes and hysteresis loops characteristic of mesoporous materials with a significant fraction of micropores. However, it was observed that with this low-cost and simplified carbonization method of Macaúba EDP, it is possible to produce, with yields equivalent to other methods, adsorbents capable of removing MB and BPA in aqueous solution; with those carbonized at the highest temperatures, 700 ºC and 800 ºC, being the most efficient, with BC-700 slightly better.