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.