Efeito dos extrativos nos processos de combustão e pirólise de resíduos lenhosos da Amazônia

Abstract

The use of residual biomass from forest management, in addition to being a source of renewable energy, is appropriate given the current need to reuse natural resources. Several factors can influence the utilization of these residues, including extractives, which can increase the calorific value of the wood and affect its density, permeability, and the yields of the pyrolysis process. However, studies on the effects of extractives during pyrolysis and combustion are not widely conducted on woody residues from native Amazon species. Therefore, the aim of this study is to evaluate the influence of extractives on wood characteristics and behavior during combustion and pyrolysis processes of woody residues. Woody biomass from five species derived from forest management residues in the Amazon were selected: Dinizia excelsa, Protium cf. altissimum, Parkia pendula, Inga spp., and Manilkara spp. The contents of holocellulose, cellulose, hemicellulose, and lignin in the woody residues were measured. The contents of total extractives, and extractives soluble in acetone, hot water, and cold water were also determined. Analyses of higher heating value and proximate chemical composition were conducted on both the raw material and the extractive-free material, using different removal methods. Thermogravimetric analysis was performed under oxidative and inert atmospheres, and combustion and pyrolysis indices were determined for both the raw and extractive-free materials. The species with the highest holocellulose content was Manilkara spp. (75.10% dry basis), while the lowest was Dinizia excelsa (58.07% db). For total lignin, values ranged from 27.61% db (Inga spp.) to 23,94% db (Dinizia excelsa.). Cellulose content ranged from 47.86% db (Manilkara spp.) to 36.68% db (P. altissimum). The lowest ash content was found in Inga spp. woody residues (0.52% db). Regarding extractives, the highest values were found in Manilkara spp. (5.91%) for cold water, and in D. excelsa (9.95% and 6.61%) for hot water and acetone, respectively. D. excelsa stood out due to its high total extractives content in the wood (16.38% db). In the proximate composition analysis, volatile matter content ranged from 79.35% (P. altissimum) to 85.54% (Inga spp.) in the raw material. Ash content ranged from 0.29% (D. excelsa) to 1.31% (Inga spp.), while fixed carbon ranged from 13.76% (Inga spp.) to 19.84% (D. excelsa), being influenced by the removal of extractives. There was no significant difference in the higher heating value (HHV) between the raw and extractive-free materials, with the highest value observed for D. excelsa (20.49 MJ/kg). In the DTG curves, differences were observed mainly in the maximum decomposition temperature, with the curve shifting to slightly higher temperatures after extractive removal. For D. excelsa and P. altissimum, extractives reduced thermal stability. For P. pendula and Manilkara spp., extractives had little effect on thermal degradation. In Inga spp., they slightly delayed degradation, with little impact on pyrolysis. The results indicate that prior removal of extractives from woody residues is feasible, without causing significant negative impacts on combustion and pyrolysis processes.