Fractionated condensation of pyrolysis vapours from ablative flash pyrolysis
The thermal conversion process pyrolysis converts biomass in the absence of air into 2 primary products: a solid residue (pyrolysis char) and a gaseous vapour (pyrolysis vapor). By cooling the primary vapours the condensable fraction can be separated as liquid phase from the permanent gases. The ablative flash pyrolysis, where heat transfer to the biomass particles happens in direct contact with a hot surface by mechanical force, aims at maximizing the liquid yield. By means of this thermochemical conversion the originally solid biomass becomes accessible for material utilization as platform chemical. Due to the fact that pyrolysis liquids contain on one hand many valuable organic compounds but on the other hand exhibit disadvantageous properties with respect to oxygen and water content, acid number and storage stability, a posttreatment / upgrading is mandatory. Beneath other processes, the thermal fractionation is a possible process to produce separate fractions depending on component boiling temperature. By that an enrichment of components with similar boiling temperature within different fractions can be achieved. As distillation does not lead to a satisfactory result due to polymerization processes the thermal fractionation must be executed directly with the pyrolysis vapours. First results for beech wood obtained in a side stream at the laboratory plant at Fraunhofer UMSICHT indicate, that the middle fraction is well suited for the production of high value phenolic resins, while the two other fractions also concentrate other valuable components. The fraction with low boiling components offer the possibility to produce acetic acid or biogas and the high boiling fraction can substitute biomass in gasification processes or heating oil in residential houses. Other utilization purposes will be evaluated in future research.