Estudo da pirólise para a produção de bio-óleo a partir do resíduo agrícola de Feijão-Caupi (Vigna unguiculata)

Abstract

The valorization of agricultural residues for the production of bio-oil is a promising alternative, as it contributes to minimize the environmental impact. In this study, the Caupi bean pod (Vigna unguiculata) was characterized and used as biomass in the production of bio-oil. Conventional pyrolysis was conducted at 550, 600, and 700 °C and N2 gas flow of 2, 5, and 7 mL min-1 . Five different catalysts were chosen for application in situ (K3PO4, K2HPO4, KH2PO4, K2CO3 e KCl) and the pyrolysis was conducted in the best condition chosen from conventional pyrolysis (600 °C, 5 mL min-1 nitrogen gas flow), catalyst ratio and biomass 20% wt. The bio-oils obtained conventional pyrolysis were analyzed by element analysis, thermogravimetry, infrared and by gas chromatography/mass spectrometry (GC/MS). The bio-oils of catalytic pyrolysis in situ obtained were characterized by gas chromatography coupled with mass spectrometry (GC/MS) and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry GC×GC/TOF-MS. The physicochemical characterization showed that the bean pod presented moisture content below 10%, high carbon (42.01%) and oxygen (46.36%) contents, flow nitrogen (1.36%) and ash (4.36%) contents and superior calorific power (17.55 MJ kg-1 ) The thermogravimetric analyses demonstrate that there can be a relationship between the components of the principal biomass (cellulose, hemicellulose, and lignin) and the compounds present in the bio-oil. The application of GC×GC/TOF-MS was important to resolve coeluted peaks from the GC/MS analysis, resulting in a different distribution of compounds by chemical classes. The data showed that K+ and anions affected primary and secondary reactions, modifying the formation of several chemical species, as carboxylic acids, alcohols, aldehydes, ketones, ethers, esters, phenols and others. This work contributes with relevant information regarding the potential of Caupi bean pod (Vigna unguiculata) for obtaining fine chemicals with commercial value, such phenols and derivatives.