Comparative study of pyrolysis and hydrothermal liquefaction of microalgal species: Analysis of product yields with reaction temperature.

[Display omitted] • Renewable biofuel production by algal biomass has been discussed in this review. • Two major thermochemical process like pyrolysis and hydrothermal liquefaction are described. • Different pyrolysis and HDL methods in fuel production has been explained. • Temperature, heating rate of the process and product yield have been focused. • Challenges and future benefits of the fuel production using algal biomass is detailed. Renewable and sustainable biofuel production from algal biomass has been explored vigorously due to the owing potential of overcoming the limitations of first and second-generation biofuel feedstocks. Thermochemical conversion technologies are considered promising routes for bioenergy production from algal biomass and have been extensively investigated over the last few years. This paper aims to review the various pyrolysis (slow, fast, and microwave -assisted) processes and hydrothermal liquefaction (HTL) techniques. The fast pyrolysis is involving a higher heating rate and shorter residence time compared to slow pyrolysis. Microwave-assisted pyrolysis (MAP) is considered a highly efficient process due to uniform heating. Due to a high moisture feedstock, the HTL process is considered the most energy-efficient processing option for algal biomass. In all these processes, the process temperature is considered the most critical parameter affecting product yield. This paper provides a detailed analysis and discussion on the effect of temperature and heating rates on the product (biochar, bio-oil, and syngas) yields for various microalgal species. The process details, different approaches, and process conditions investigated, challenges and recent advancements achieved in both technologies have been discussed in detail that provides useful insights to design a sustainable process and understand the process feasibility. [ABSTRACT FROM AUTHOR]