Online Separation of Biomass Fast-Pyrolysis Liquids via Fractional Condensation

Because biomass fast-pyrolysis oils are a complex mixture comprising hundreds of compounds with a wide range of molecular weights, separating these components is challenging. However, because the composition of the mixture generally renders it reactive and unstable, the separation of bio-oil into more stable fractions remains desirable. This work used a packed column to perform fractional condensation of switchgrass fast-pyrolysis vapors generated in a laboratory-scale fluidized bed system operated at 560 g/h. The bio-oil was collected in nine fractions: the column separation system comprised six separation stages and a flask for the collection of bottoms, and the material escaping the column was collected by an electrostatic precipitator and cold trap. The obtained fractions were analyzed via GC–MS and NMR, and a mass balance was performed. Results were compared with a standard three-stage condensing system and batch distillation of the whole oil. The stability of the bio-oil fractions was compared via the formation of solid residue from bio-oil components from the online separation method, fractional distillation of standard bio-oil, and the evaporation of obtained fractions. A direct correlation between the concentration of compounds that are consumed during batch distillation and the amount of residue formed from each fraction was observed.