Effect of phenolic compound recovery from agro-industrial residues on the performance of pyrolysis process

A biorefinery concept allows the valorization of agro-residues, specifically recovering value-added compounds and energy. In this context, the present study aims to investigate the effect of prior recovery of phenolic compounds from agro-residues in the pyrolysis process. The phenolic compounds were extracted from rotten tomato, unripe tomato, tomato plant, and grape pomace, revealing concentrations between 10 and 56 mg gallic acid equivalents/g. The thermogravimetric analysis and the yields of the pyrolysis products were assessed for raw and extracted residues, and similar patterns were observed for each pair before and after extraction. A maximum of 38.39 wt% can be converted in oil for a temperature ranging from 410 to 500 degrees C, while gas formation is maximum at 900 degrees C. However, the gases formed for all residues presented the highest lower heating value (around 9.5 MJ/Nm(3)) at 700 degrees C. In particular, the pyrolysis of the tomato plant and grape pomace resulted in a more energetic gas (10.3 and 9.32 MJ/Nm(3), respectively) when compared to the other raw materials studied. The energy that can be recovered from syngas formed in pyrolysis and biogas from anaerobic digestion was compared. Anaerobic digestion produced gas with a calorific value higher than 7 MJ/kg of volatile solids, while pyrolysis generated syngas with a maximum calorific value of 2.3 MJ/kg of volatile solids. Overall, this study demonstrated that the ethanolic extraction of phenolic compounds does not affect negatively pyrolysis performance.