Characterization of the pyrolysis condensates of birch, spruce and pine bark: Impact of water leaching on the composition

Biocarbon, produced via the pyrolysis of lignocellulosic biomass, is increasingly sought as a sustainable reductant in metallurgical industries. The production of biocarbon also generates significant amounts of condensable liquid by-products, which can be valuable materials subject to detailed characterization and proper upgrading. The current biocarbon production relies mainly on stem wood, but alternative biomass materials of sufficient quality, high availability, and low costs are needed. Bark, a major forestry residue, is a potential feedstock candidate for biocarbon production; however, its high mineral content is a drawback for several industrial applications. In the present work, bark chips of birch, spruce, and pine wood were pyrolyzed in a fixed bed reactor collecting both solid and condensed liquid products. The amount of inorganic elements present in the barks was reduced by an industrially feasible static water leaching method. The chemical composition of the condensates of both leached and unleached bark samples were compared by using GC/MS analysis. A comparison of the composition of bark and stem wood condensates revealed that the summed organic content measured in the bark condensates was much less than that of stem wood. The analysis of bark condensates showed that the birch bark condensates had significantly higher acid content than the bark condensates of conifers, i.e., spruce and pine. The concentration of specific condensate components showed different changes depending on the leached feedstock type. The reduced mineral contents in the leached barks affected the thermal decomposition during pyrolysis, resulting in modest changes in condensate compositions. • Bark condensates contain the same compounds as that of stem wood but with a lower yield. • The volatile organic content of bark condensates mainly differed in the acid content. • Static water leaching of bark chips effectively lowered the alkali contents, but modestly other inorganics. • The condensates of leached barks contained more furfurals and cyclopentenones. • Products of some water-leachable organic substances were reduced in leached bark condensates.