State-of-the-art co-pyrolysis of lignocellulosic and macroalgae biomass feedstocks for improved bio-oil production- A review

In recent years, there have been emerging studies on developing different techniques to improve the properties of pyrolysis bio-oil. One of such techniques is the co-pyrolysis of biomass with hydrogen-rich feedstock of higher fuel qualities. Co-pyrolysis aims to decrease the water and oxygen contents, increase the calorific and heating values, and eliminate the corrosion and instability problems associated with their direct use in boilers and turbines for heat and power generation and as a transport fuel. Lignocellulosic and macroalgae biomass feedstocks are complementary based on their different compositions, and this combination has been employed in co-pyrolysis techniques. In this review, the biomass feedstock characteristics and their effects on thermal conversion into bio-oil were discussed. Due to the heterogeneous nature of the two biomass feedstocks, investigations of their co-pyrolysis behaviour and their reaction mechanisms in both catalytic and non-catalytic reactions were explored. The synergistic effect which is the key reason behind the improvement in the yield and quality of bio-oil obtained from the co-pyrolysis of these biomass feedstocks was also examined. The resulting bio-oils from the co-pyrolysis were comprehensively analyzed and are characterized by improved properties than the pyrolysis of lignocellulosic or macroalgae biomass alone. However, due to thermal degradation, the existence of high oxygenated compounds in this pyrolysis bio-oil is a challenge that needs to be overcome. Catalytic co-pyrolysis could be implemented for additional upgrading of the pyrolysis bio-oil as liquid fuel for several purposes. Finally, the main bottlenecks, key solutions and future directions for the study were provided.