Influence of citric acid leaching on the yield and quality of pyrolytic bio-oils from sugarcane residues

Abstract

The effects of leaching (25 °C and 1 h) sugarcane trash (SCT) and sugarcane bagasse (SCB) with citric acid (CA) on the yields and quality of fast pyrolysis bio-oils were studied. A comparison was made with commonly used leaching agents such as water or solutions of HCl and H2SO4. The quality of the obtained bio-oils was assessed using a set of analytical techniques including elemental analysis, total acid number (TAN) and water content determinations, combustion calorimetry and gas chromatography-mass spectrometry (GC/MS) analysis. Results from the fast pyrolysis of SCT or SCB pretreated with acids reveal higher yields on raw-feedstock basis (38–45 wt.%) of the organic bio-oil fraction than those from raw and water–leached feedstock, but lower yields of water (7.6–10.2 wt.%) and char (13.1–14.9 wt.%). More than 90% of non-condensable gases were CO and CO2. The most important observations related to the effect of leaching with CA on the chemical composition of the bio-oil are a significant increase of the relative abundance of sugars from 15.1% in raw SCT to 44.7% in CA-pretreated SCT, as well as a decrease in carboxylic acids, ketones, furans and phenols with respect to the raw biomasses. These results were close to those obtained from well-known leaching agents such as HCl and H2SO4. The bio-oil from the pyrolysis of CA–leached SCT and SCB have slightly higher HHVs than those obtained from reference leaching solutions (HCl and H2SO4). In addition, the TAN showed the lowest acidity among all pretreated SCB samples.