ABSTRACT
The increase in demand for energy has provided a tremendous boost for new and alternative approaches to energy generation. Hydrothermal treatment of biomass (high moisture content) is, therefore, a very promising technology that has evolved with time. Significant efforts have been made in assessing various biomass feedstocks for hydrothermal processing based on required end products. The hydrothermal technique is a vital thermochemical conversion method for the conversion of numerous biomass feedstocks into different biofuels and valued products. Operating temperature, pressure and residence time are selected focusing on the target product, i.e., bio-oil, biochar or gas. Hydrothermal processing is generally accomplished in the presence of water at a pressure of 2–22 MPa and a temperature of 180–374°C to produce char or tar and at a higher temperature and pressure to generate gaseous products. It is important to have detailed knowledge of water properties (either subcritical or supercritical) to understand the degradation pathway of biomass under hydrothermal processing. This chapter discusses all the three hydrothermal techniques such as liquefaction, carbonization and gasification, to provide an understanding for possible commercialization. The importance of various operating parameters and catalysts and their impact on the yield is also discussed. Finally, in-depth knowledge of hydrothermal gasification of algal biomass is also incorporated in this chapter.
