Sieving and Acid Washing as a Pretreatment to Fast Pyrolysis of a High Ash Hog Fuel

Mineral matter can negatively influence liquid yield and product properties from the fast pyrolysis of woody biomass residuals. Biomass pretreatment approaches to reduce the ash content represent a potential pathway to expand the feedstock flexibility of fast pyrolysis. In this work, ash reduction in biomass pyrolysis oil via sieving the fines portion of a hog fuel as well as washing the fractionated hog fuel with nitric acid was investigated prior to the conversion in CanmetENERGYOttawa's 5-10 kg/h fast pyrolysis system. It was found that sieving the material was much less influential on the liquid yield and product properties relative to nitric acid washing. Product analysis showed up to 40% increase in organic liquid yield and up to 30% decrease in biochar yield on a dry, ash-free basis by nitric acid washing the fractionated hog fuel. Pyrolysis reaction water was minimized when nitric acid washing the feedstock, which has important implications for the phase separation of the pyrolysis liquids. Through nitric acid washing, the ash content in the liquid was reduced up to 87% relative to the liquid produced from the pyrolysis of the untreated material. The chemical quantification of the produced pyrolysis liquids demonstrated that the chemical composition was significantly altered after nitric acid washing the hog fuel, indicating that the removal of the ash species impacted the pyrolysis reaction chemistry.