Downstream Processing of Drop-In Biofuels

The world urgently requires decarbonizing its energy matrix. However, areas such as industry and transportation will likely rely on high-energy-density liquid fuels in the near future. Drop-in biofuels offer a sustainable solution that seamlessly integrates with existing pipelines, supply chains, and current applications. Examples include bioethanol from various sources (such as sucrose, starch, or lignocellulosic materials), biomethane, biohydrogen, and biohythane. Biodiesel (from plant or microbial sources), lipid-derived hydrocarbons, and pyrolysis gas or gasohol also qualify as drop-in biofuels to some extent. Some highly energetic molecules like higher alcohols, ketones, or ammonia do not fit this category, as they necessitate extensive engine modifications. However, high-energy molecules cannot be considered fuels until they undergo concentration and purification, achieved through a series of processing steps known as downstream processes. This chapter explores the fundamentals of downstream processing for biofuels after their biosynthesis. It includes a material balance for the more technologically mature biofuels, allowing readers to estimate the potential fuel yield from a given amount of biomass.