Advanced thermochemical conversion of algal biomass to liquid and gaseous biofuels: A comprehensive review of recent advances

Abstract

Algal biomass is considered to be one of the most promising feedstocks of importance for conversion into biofuels. With their benefits over other biomass feedstocks, such as sustainability, renewability and productivity, microalgae are one of the most promising biomass resources for use in thermochemical conversion processes. With this review, we hope to present the most recent information available on the commonly used thermochemical conversion procedures, which are hydrothermal liquefaction, pyrolysis, and gasification processes. The study evaluated both the quality and yield of liquid products (bio-oil) as well as gaseous products (syngas) derived by thermochemical conversion processes, to truly comprehend the effectiveness and feasibility of each method. It was found that the yield of bio-oil obtained through hydrothermal liquefaction was lower than the yield achieved through pyrolysis. However, the energy density, fuel properties and storage stability of hydrothermal liquefaction bio-oil are superior to those of pyrolysis bio-oil. This study also demonstrated that the gasification process has been the most energy-saving approach for the transformation of microalgae to syngas. Microalgae supercritical water gasification might be a good way to turn microalgae into high-heating-value gas without having to dry it first. Finally, the prospects and obstacles of converting microalgal biomass to biofuels were discussed. Overall, the purpose of this work is to present a comprehensive assessment of the most recent developments in microalgal biomass thermochemical conversion for the production of liquid and gaseous biofuels.