Abstract
This chapter focuses on the hydrothermal liquefaction (HTL) process and describes the basic structure, reaction pathway, and kinetics of breakdown of major components in the feedstock during HTL process. It discusses the effect of some of the important operating parameters on bio-oil yield. Products of HTL process include a high heating value biocrude or bio-oil, an aqueous fraction, gases, and solid residues. HTL is a very promising technology for high moisture feedstock conversion. The high solids content is unfavorable for proper mixing in the HTL reactor and reduces the heat and mass transfer, which results in lower conversion and bio-oil yields. The products obtained in bio-oil from cellulose HTL are different under acidic, neutral, and alkaline conditions. The nitrogen gets incorporated in bio-oil during the HTL process. Temperature is an important factor in depolymerization of biomass which is a dominant reaction during initial stages of HTL and requires sufficient temperatures to overcome the activation energies of bond cessation.