Efeito do pré-tratamento ultrassônico com K3PO4 para a produção de bio-óleo de vagem de feijão

Abstract

The aim of the present work was to study the effect of the ultrasonic pretreatment of cowpea bean pod biomass in the bio-oil production by pyrolysis. The biomass was pretreated during 0.5, 1.5, 03, 06, 08 and 12 hours with the addition of 20% (w/w) potassium phosphate. The biomass presented low oil and protein contents, 0.72% and 8.5%, respectively, and ash content of 4.38% for in natura biomass, being alkali and alkaline earth metals (K, Mg, Na, Ca) and phosphorus the main inorganic compounds. For the pretreated samples, the ash content was around 19.5% (w/w). The elemental analysis showed that the in natura biomass contained 42.01% of carbon, 5.89% of hydrogen, 1.36% of nitrogen and 37.48% of oxygen, presenting lower values for the treated biomass mainly due to the increase of inorganic content by the addition of potassium phosphate. The thermogravimetric curves profiles of the samples changed with different ultrasonic pretreatment times, presenting a decrease in temperature, where the highest mass loss rate occurs, compared to in natura biomass. The pyrolysis was carried out at 600 °C and N2 flow of 5mL min-1, yielding a 25.29% in bio-oil for the in natura biomass, while the samples submitted to pretreatment presented yield between 21 and 23%. The pretreated samples showed a decrease in the biochar yield and an increase in the biogas yield compared to the in natura sample. The chromatographic analysis of the bio-oils, showed that the ultrasonic pretreatment associated with K3PO4 caused a considerable increase in the phenolic compounds content, and the best pretreatment time, 1.5 h, showed 81.21 mg g-1, against 48.90 mg g-1 of phenolics in the bio-oil from in natura biomass.