Upgrading bio-oil by catalytic fast pyrolysis of acid-washed Saccharina japonica alga in a fluidized-bed reactor

Macroalgae contain significant amounts of inorganic compounds (K, Na, Mg, and Ca) that cause problems during thermal processing (ash fouling or agglomeration of char and bed material). The macroalga Saccharina japonica (S.J) was demineralized with diluted acid solution to remove inorganic species before using this matter for fast pyrolysis in a bubbling fluidized-bed reactor. The effect of acid washing on the product yield and the quality of bio-oil was systematically investigated. When the pyrolysis temperature increased from 400 to 500 °C, the bio-oil yield was 39.70–45.36 wt%. The major compounds in the bio-oil were levoglucosan and di-anhydromannitol. The fractional catalytic pyrolysis of pre-treated S. japonica using HZSM-5 catalyst (calcined at 550 °C) was investigated in fluidized-bed reactor under the same conditions. Pyrolysis of the pretreated sample with catalyst resulted in 35.37–39.05 wt% liquid yield, which was lower than that from using silica sand. Using HZSM-5 catalytic pyrolysis bio-oil showed a decrease in dianhydromannitol and 2-furyl methyl ketone, and an increase in aromatic compounds such as derivatives of phenol, indole, and naphthalene. The effect of pretreatment by acid washing, and the effect of this catalyst on the pyrolysis product distribution and composition were clarified in relation to previous work.