Exploring aging kinetic mechanisms of bio-oil from biomass pyrolysis based on change in carbonyl content

Bio-oil from biomass pyrolysis offers a wide range of applications such as transport fuels, value-added chemicals, materials, or heat and power generation. However, fresh bio-oil is unstable due to its physicochemical properties, chemical composition, and multiphase behaviors changing with time. The bio-oil aging kinetic model based on the change in carbonyl content was developed, and the pattern search method was proposed to optimize the model parameters. The accelerated and long-term aging kinetic behaviors of two bio-oil samples could be described accurately by the carbonyl-based aging kinetic model. The reaction rate constant values for the long-term and accelerated aging of bio-oil 1 were 1.694 × 10−4 and 4.589 × 10−2 h−1, whereas 3.084 × 10−4 h−1 and 1.329 × 10−1 h−1 were reported for bio-oil 2, respectively. The reaction order values of the long-term aging (2.452 for bio-oil 1 and 3.973 for bio-oil 2) were higher than that of the accelerated aging (0.943 for bio-oil 1 and 1.000 for bio-oil 2). Two bio-oil samples showed different aging kinetic characteristics due to different raw materials, pyrolysis reactor types and conditions, and bio-oil phases for aging tests. The hydration, hemiacetal, acetal and polymerization reactions of carbonyl compounds were the primary mechanisms for the change in carbonyl content during bio-oil aging.