Improving Fast Pyrolysis Bio-Oil Yield and Quality by Alkali Removal from Feedstock

Alkali removal from forest residues, eucalyptus residues, and wheat straw was studied by water and dilute nitric acid leaching. Leaching parameters were optimized for each feedstock in laboratory-scale experiments. After the optimization of leaching on the laboratory scale, nitric acid-leached and untreated feedstocks were pyrolyzed in a bench-scale bubbling fluidized bed unit. In the case of eucalyptus residues and wheat straw, nitric acid leaching was found to increase the organic liquid yield compared to untreated feedstock. In addition, the sugar content of the fast pyrolysis bio-oils was increased, and the alkali content reduced. On the other hand, the pyrolysis experiments with acid-leached forest residues were unsuccessful due to the bed agglomeration. These problems are expected to be a result of the lack of catalytically active elements in biomass which enhance especially the cracking reactions of lignin. Finally, the results were demonstrated in the pilot-scale unit where nitric acid-leached oat straw was pyrolyzed with high organic liquid yield.

Automated summary

This study investigated the removal of alkali from forest residues, eucalyptus residues, and wheat straw through water and dilute nitric acid leaching. The results showed that nitric acid leaching increased the organic liquid yield and reduced the alkali content in eucalyptus residues and wheat straw. However, pyrolysis experiments with acid-leached forest residues were unsuccessful.