A review on the modelling of hydrothermal liquefaction of biomass and waste feedstocks
Rakesh Kumar
Abstract
Hydrothermal liquefaction is a thermo-chemical conversion process which uses water as a reaction medium at elevated pressure and temperature. It converts biomass and waste feedstock to biofuel and recovers water and fertilizers present in the feedstock. Hydrothermal liquefaction overcomes many technical limitations of the existing technologies such as anaerobic digestion, incineration, gasification, and pyrolysis and it offers a solution to water-energy-climate nexus. Hydrothermal liquefaction has been widely investigated to understand the mechanism and kinetics of hydrothermal liquefaction at different batch scales of operation. Significant efforts have been made recently to develop the kinetic models for various type of feedstocks to predict product yields despite having complex reaction mechanism and pathways. This article critically reviews past work and discuss the different types of mathematical models used to predict products yields and composition for different biomass and waste feedstocks. It encompasses summary of important characteristics of representative biomass and waste feedstocks and quality of biocrude product, experimental studies conducted for various predictive and kinetic model development. A few limitations on existing models were identified to focus for further study. Finally, suggestions have been incorporated with focus on improving hydrothermal liquefaction kinetic model for optimal product yields and composition under varying operating conditions for various feedstocks.