Hydrothermal Liquefaction of Biomass and Process Intensification

Abstract

Hydrothermal liquefaction (HTL) is considered as a promising thermochemical conversion technology for biomass valorization and crude bio-oil (biocrude) production. However, moving this technology towards commercialization still faces several technical challenges, some of which were partially addressed in this thesis. This project started with evaluating the influence of biocrude recovery methods/solvents on the yield and physicochemical properties of biocrude, and the solvent extraction/filtration with dichloromethane was determined to be a favorable protocol for biocrude recovery. This was followed by the development of prediction models for the yield of HTL products using biomass model components and statistical mixture design, which offered advanced models for predicting HTL product yield as functions of feedstock composition and process variables. The chemical interaction in co-liquefying biomass model components was also explored to better understand the HTL product formation pathways. A variety of actual biomass feedstocks were hydrothermally co-liquefied, and the significance of observed co-liquefaction effect were statistically examined for the first time. The influence of mixing ratio, temperature and their interaction on co-liquefaction effect were evaluated as well. A process intensification technique, microwave irradiation, was applied in HTL of spent coffee grounds, and it was proved to be technically feasible. To gain more insights of heating method’s influence on HTL products formation, HTL of biomass model components and their mixtures were carried out under microwave irradiation and conventional heating. Heating methods did not substantially alter the model components’ interaction, and only slight and/or negligible influence on the chemical composition of obtained biocrudes were observed. The obtained results from this project contributed to new knowledge body in HTL research and advanced the biomass HTL technique from downstream processing methods, product yield prediction, product formation pathways, co-liquefaction of biomass and process intensification perspectives.