Effect of sulfuric acid concentration on the yield and properties of the bio-oils obtained from the auger and fast pyrolysis of Douglas Fir

The effect of sulfuric acid concentration on the yield and composition of bio-oils obtained from the auger and fluidized bed pyrolysis of Douglas Fir at 500 °C have been investigated as a mean to enhance the production of fermentable sugars. The concentration of sulfuric acid in the feedstock was varied between 0 and 0.6 mass%. The overall yield of pyrolysis products (gas, bio-oil and char) was comparable for both reactors. The presence of sulfuric acid decreases bio-oil yield and increases water and char yields. The yield of pyrolytic water produced in the auger reactor was higher due to the lower heating rates achieved which favor dehydration reactions. Maximum yields of levoglucosan and fermentable sugars were obtained at concentrations of sulfuric acid of 0.3 mass% in the auger reactor and 0.05 mass% in the fluidized bed reactor. Dehydration reactions responsible for water and cross linked sugars formation, as observed by the increase in the band at 1654 cm^-1 fitted in the FTIR, were enhanced as sulfuric acid concentration increases. The dehydration of cellulose in the presence of sulfuric acid also causes a reduction in the yield of acetic acid and acetol. The yields of some lignin derived compounds (lignin oligomers and guaiacols) also decreased substantially when sulfuric acid was added. Potential mechanisms responsible for the phenomena observed are discussed.