Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals

Abstract

Hydrothermal conversion is an important thermochemical conversion technique that is used to convert waste biomass into valuable products or biofuel. The process is usually performed in the presence of water at high temperature and high pressures. The biomass is depolymerized to form three phases such as biocrude, biogas, and biocarbon into small components in water. Based on the process conditions (temperature, pressure, catalyst, and time), the yield of the phases varies accordingly. Comparing to other thermochemical conversion techniques like combustion, pyrolysis, and gasification, the hydrothermal conversion is highly appropriate for handling biomass with high moisture content. According to the physicochemical properties of water, the process can be classified as hydrothermal carbonization, hydrothermal liquefaction (at subcritical conditions T, 250–374°C, and P, 4–22 MPa), and hydrothermal gasification (at supercritical conditions T > 374°C and P > 22 MPa). There has been significant research reported on the hydrothermal conversion of lignocellulosic biomasses, algal biomasses, and also co-utilization of these two with other waste materials. The interaction of water with the biomass results in formation of various chemicals like acids, alcohols, cyclic ketones, phenols, and methoxyphenols and more condensed structures like naphthols and benzofurans. This chapter focuses on the influence of the process parameters and types of biomass utilized on the hydrothermal conversion of biomass. Additionally, the use of biomass as not only an energy source but also as a viable source for value-added chemicals is discussed.