Hydrothermal liquefaction of biomass: Influence of temperature and biomass composition on the bio-oil production

•HTL is a promising process for the production of high quality bio-oil.•The optimum temperature of the process is highly dependent on biomass composition.•A linear relationship between lignin biomass content and bio-oil yield exists.•The maximum bio-oil yield is obtained for biomass with the highest lignin content.

Hydrothermal liquefaction is a promising process for the production of high quality bio-oil from biomass. Aim of this study is to investigate the effect of temperature and biomass composition on the yield and quality of bio-oils produced from three different biomass such as natural hay, oak wood and walnut shell. The hydrothermal liquefaction of cellulose was also investigated. The experimental tests, conducted in water sub-critical conditions, were carried out in a microreactor in a temperature range of 240-320 °C with a reaction time of 30 min. All the products of the process were analyzed and characterized by elemental analysis and GC-MS. It was observed an increase of the bio-oil yields with the lignin content of biomass, being the maximum bio-oil yield obtained for walnut shell and the minimum one for cellulose. This trend is representative of the obtained bio-oils composition, where the phenolic compounds are the major constituents, while the other identified compounds were mainly alcohols, ketones and aldehydes.