Improving bio-oil fractions through fractional condensation of pyrolysis vapors from Eucalyptus globulus biomass residues in a prototype auger reactor

Abstract

Bio-oil produced from the pyrolysis of lignocellulosic biomass has potential as a biofuel or chemical precursor. However, its valorization is hindered by its complex composition, high water concentration, and the presence of oxygenated compounds. Operational strategies are therefore required to improve its quality. This study evaluated the technical feasibility of fractional condensation as an alternative to conventional single-stage condensation of vapors produced from pyrolysis of residual Eucalyptus globulus biomass to collect bio-oil fractions with improved properties. The process was carried out using a prototype-scale auger reactor with continuous operation. The fractional condensation system comprised four sequential condensation stages operating at progressively lower temperatures: 140, 100, 80, and 0 ºC. The collected bio-oil fractions were analyzed in terms of product yields, water separation efficiency, elemental composition, heating value, and the presence of volatile and semi-volatile compounds. The results demonstrated that fractional condensation achieved total bio-oil yields comparable to those obtained with the single-stage condensation system, while enabling the recovery of bio-oil fractions with lower water concentration, higher carbon concentration and increased heating value. Notably, the first condensation stage collected heavy fractions with water concentration between 3 % and 6 %wt., oxygen concentration between 17 % and 21 %wt., and carbon concentration between 69 % and 72 %wt., resulting in O/C molar ratios between 0.17 and 0.22, values close to those of biodiesel. These fractions exhibited lower heating values of up to 31 MJ/kg, surpassing those of conventional liquid biofuels such as biomethanol and bioethanol. These findings highlight the potential of fractional condensation of pyrolysis vapors from residual biomass from Eucalyptus globulus as an effective strategy to produce bio-oil with properties more suitable for direct energy use or as an intermediate feedstock for biofuels synthesis. Further research is recommended to optimize the condensation stages and assess the long-term stability of recovered fractions.