5 - Hydrothermal liquefaction of protein-containing feedstocks

Hydrothermal liquefaction (HTL), also refers to as hydrous pyrolysis, is a thermochemical depolymerisation process in an enclosed reactor to convert wet biomass into biocrude oil and chemicals at moderate temperature (typically 200-400°C) and high pressure (typically 10-25. MPa). Protein-containing feedstocks such as food processing waste, manure, and municipal sludge typically have high moisture content and thus make HTL an appropriate process. In HTL processes, water serves as an important reactant. As the reaction condition approaches to the critical point of water, several properties of water are drastically changed and able to bring about fast, homogeneous, and efficient reactions Because subcritical water has a leading role as a heat transfer and extracting medium, HTL is relatively independent of the size of biomass particles or heating rates. The product yield and physiochemical properties of an HTL are primarily affected by the types of feedstock, processing conditions (primarily reaction temperature and time), and existence of catalyst. HTL biocrude oil from protein-containing feedstocks typically contains high nitrogen content and many types of aromatics. Upgrading of the HTL biocrude is necessary for transportation grade fuel. Posthydrothermal wastewater (PHWW) typically has a very high chemical oxygen demand (COD) and various nutrients (primarily nitrogen) that need to be treated before discharge to waterways. Gaseous products of HTL contain malodours and thus must be treated before emitted to the atmosphere. In this chapter, important factors influencing HTL and HTL product characteristics are described.