Briquette production as a sustainable alternative for waste management in the tannin extraction industry

Tannins are polyphenols that can be extracted from different parts of the plant and have different known commercial applications. The extraction of tannins generates a significant amount of low-density wastes. An alternative that can be applied to ensure energy reuse of this low-density waste is a densification process, such as briquetting. Thus, this research work aimed to assess the energy potential of the residue from the extraction of tannins of different forest species, aiming at its energy reuse in the form of briquettes. Stem barks of 6 forest species (Acacia mangium, AM; Anacardium occidentale, AO; Anadenanthera colubrina, AC; Azadirachta indica, AI; Mimosa caesalpiniaefolia, MC; Mimosa tenuiflora, MT) were used after tannin extraction. Bulk density, energy (higher, lower, and net heating value) and thermal (TG/DTG) properties, and chemical constitution (extractives, lignin, and holocellulose) of the materials were determined. In addition, briquette compaction ratio, apparent density, volumetric expansion, and water adsorption over the days were evaluated. The highest bulk densities were found in the barks of Anadenanthera colubrina (0.529 g.cm−3) and Mimosa tenuiflora (0.407 g.cm−3), whereas the species that showed the best result of higher heating value was Acacia mangium (20.44 MJ.kg−1), followed by Azadirachta indica (19.39 MJ.kg−1) and Mimosa caesalpiniifolia (18.85 MJ.kg−1). Briquetting increased the density of the evaluated material by 2.3 to 4.9 times. All briquettes produced with wastes from tannin extraction evaluated in this work showed potential for energy production. With more information on the quantification of waste generated and data on the economic viability of production, these tannin-producing industries can benefit both environmentally and economically, by reusing these wastes for energy production.