Response surface method to optimize bio-oil yield and hydroxyl number from pine pyrolysis using a bubbling fluidized bed reactor

Pyrolysis, a thermochemical conversion method, produces bio-oil, which could be used for resin and bio-fuel synthesis. Despite numerous pyrolysis studies to maximize the bio-oil yield, there is a research gap in optimizing the pyrolysis reactor for both bio-oil yield and hydroxyl group concentration. This study aimed to optimize the pyrolysis operating parameters (pyrolysis temperature, biomass feed rate, and bed height-to-diameter ratio) to maximize the bio-oil yield and hydroxyl group concentration. The Box-Behnken method was used to design the pyrolysis experiments for a laboratory-scale fluidized bed pyrolysis unit. The yield and hydroxyl concentration results were analyzed using the response surface method, which suggested that feed rate (p-value = 0.005) and the square of temperature (p-value = 0.028) significantly affected the bio-oil yield. On the other hand, pyrolysis temperature (p-value = 0.01) and the interaction between feed rate and bed height-to-diameter ratio (p-value = 0.043) were significant parameters for bio-oil hydroxyl concentration. Furthermore, ex-situ catalytic pyrolysis in the presence of Cu/Al2O3 obtained using the optimum pyrolysis conditions led to the catalytic cracking of the sugars and alkoxy phenols in the pyrolysis vapor. Catalytic pyrolysis reduced the water content of the bio-oil from 13.4 to 8.0 % and increased the amount of carbon (from 65.7 to 69.3 %), alkyl phenol (from 7.7 to 22.5 area %), and hydrocarbons (from 1.6 to 11.3 %) in the bio-oil, which were attributed to the deoxygenation and alkylation reactions. Based on the experimental results, it can be concluded that high-temperature pyrolysis is favorable for obtaining bio-oil with higher hydroxyl concentration for resin synthesis application.