Fast pyrolysis of fermentation residue derived from Saccharina japonica for a hybrid biological and thermal process

Pyrolysis characteristics of Saccharina japonica fermentation residue (SJFR) were systematically investigated using a thermogravimetric analyzer and a bubbling fluidized-bed reactor. Thermogravimetric (TG) characteristics of the SJFRs with increasing fermentation time (1–6 day) showed a decrease of second peak related to fermentable carbohydrates (e.g., alginate and fucoidan) and an increase of third peak related to non-fermentable carbon sources. The calculated apparent activation energy of the SJFRs ranged from 20.21 to 295.46 kJ/mol, depending on the conversion rate of 5–80%. Between 10 and 40% conversion at 225–310 °C, the apparent activation energies of the SJFRs on each conversion decreased with increasing the fermentation time (1–6 day). The bubbling fluidized-bed pyrolysis of the SJFR-4D and -6D showed the high bio-oil yield of 39.86 and 40.12 wt%, respectively at 375 °C and 4.0 × U_mf, and the HHVs of the organic bio-oils were 28.95–29.34 MJ/kg. The characteristics of the bio-oil derived from SJFRs were analyzed by GC-MS and the TG-based simulated distillation. The fractions of gas oil and heavy gas oil were increased, whereas the one of gasoline decreased with increasing fermentation time. It is attributed to a decrease of the fermented carbohydrates (e.g., alginate and fucoidan) related to the gasoline fraction.