Online separation of biomass fast pyrolysis liquids via fractional condensation

Authors: RAYMUNDO, LUCAS - Federal University Of Rio Grande Do Sul; Mullen, Charles; Elkasabi, Yaseen; Strahan, Gary; BOATENG, AKWASI - Retired ARS Employee; TRIERWEILER, LUCIANE - Federal University Of Rio Grande Do Sul; TRIERWEILER, JORGE - Federal University Of Rio Grande Do Sul

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2022
Publication Date: 10/14/2022
Citation: Raymundo, L.D., Mullen, C.A., Elkasabi, Y.M., Strahan, G.D., Boateng, A.A., Trierweiler, L.F., Trierweiler, J.O. 2022. Online separation of biomass fast pyrolysis liquids via fractional condensation. Energy and Fuels. https://doi.org/10.1021/acs.energyfuels.2c02624.
DOI: https://doi.org/10.1021/acs.energyfuels.2c02624

Interpretive Summary: In order to reduce the environmental impacts of fossil fuel extraction, refining and usage, new processes must be developed to rather refine renewable bioresources into fuels and chemicals. The major potential source of renewable carbon for these applications is lignocellulosic biomass. This includes materials such as crop residues, forest residues, animal wastes and purpose grown energy crops. One process to convert these materials into a liquid for refinement to biofuels and chemicals is fast pyrolysis, in which biomass undergoes rapid heating in an oxygen-free environment to convert the solid biomaterials into a liquid called bio-oil or bio-crude. Refining of the bio-oil requires processing similar to which crude oil undergoes at a refinery, the first step of which is separation by distillation. However, distillation of bio-oil is difficult because unlike crude oil it is subject to chemical reactions that produce intractable solids with heating. Therefore, we modified our standard bio-oil collection process to collect the bio-oil in several fractions before the pyrolysis vapors condensed into an oil, a process called fractional condensation. Compared with post-production distillation, the fractional condensation method produced 86% less solid material. Furthermore, a fraction rich in a high-value chemical product, levoglucosan, was produced. This information will be valuable to those performing pyrolysis biorefining as a method to produce more valuable products from their bio-oils.

Technical Abstract: Because biomass fast pyrolysis oils are a complex mixture comprising hundreds of compounds with a wide range of molecular weights, separation of these components is challenging. However, because the composition of the mixture generally renders it reactive and unstable, separation of bio-oil into more stable fractions remains desirable. In this work a packed column was used to perform fractional condensation of switchgrass fast-pyrolysis vapors generated in a laboratory-scale 560g/h fluidized bed system. 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 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 form each fraction was observed.