Fuels from bio-oils: Bio-oil production from different residual sources, characterization and thermal conditioning

Abstract

Bio-oils from different residual biomass raw materials (pine wood, mesquite wood and wheat shell) were produced by means of conventional pyrolysis at a temperature of 550°C during 60min. Bio-oils were separated from gases, tar and char, to show yields between about 30wt.% and 45wt.%, and fractionated into water- and ether-soluble fractions in order to know their compositions. Gas chromatography–mass spectrometry was used to identify compounds and complemented with elemental analysis and Conradson carbon residue (CCR), together with water content, density and pH assessments. The composition of the bio-oils varied according to the source biomass. Compounds were considered in eleven main groups: acids, esters, linear aldehydes and ketones, cyclic ketones, furans, alcohols and sugars, phenols, other oxygenated cyclic compounds, hydrocarbons, ethers and nitrogen compounds. The physicochemical properties of bio-oils suggested that it is necessary to upgrade them before co-processing in conventional refining units such as those of catalytic cracking of hydrocarbons. Thermal pre-treatments were conducted with the aim of reducing the CCR of the bio-oils, resulting in a significant average 70% reduction. The concentration of coke precursor phenolic compounds, mainly phenolic ethers, was reduced between 7% and 25%. Another important consequence was the increase in the effective hydrogen index of the mixture, suggesting higher processability in FCC.