Abstract
Hydrothermal liquefaction (HTL) is an energy-efficient technology that converts biomass with high moisture content, such as lignocellulosic material and aquatic biomass, into bio-oil which can be used as a precursor in the production of renewable biofuels. The current state of technology is mostly at a laboratory scale with relatively low Technology Readiness Levels (TRL). Most HTL research takes place in batch reaction systems, but there is growing interest in scaling up the technology through the use of continuous units. The process is influenced by several factors and operational parameters, which affect the performance of the process in terms of production and bio-oil quality. HTL is highly dependent on the type of biomass used. The main advantages in relation to other thermochemical processes is the possibility of using wet biomass, avoiding the high cost of the drying process. In this work several types of biomasses were studied, different types of micro algae (i. e. Spirulina, Chlorella Vulgaris, algae grown in industrial effluents), and grass. Growing microalgae has a significant cost in the production process of liquid biofuels. So, it was also tested algae cultivated in industrial effluents which has advantages from an economic and environmental point of view. Also, the grass wastes, have high moisture content and so its adequate to be process in HTL. In all the tests, four different products were obtained: gases, aqueous and organic (biocrude) products and solids. All these fractions were characterized to suggest their most favourable application. The gases were mainly composed of Hydrogen, Oxygen, Carbon Monoxide, Carbon Dioxide and Hydrocarbons until C4. Bio oil composition was the parameter most affected by biomass type. So, when microalgae were used, it was observed higher content of nitrogenous compounds, like pyrroles, indoles, pyrazines and other nitrogen-containing compounds, probably formed from the protein fraction of the algae. In all the bio-oils it was also detected the presence of oxygenated compounds, such as ketones, esters, phenols, fatty acids, alcohols, that maybe were produced from the lipids and carbohydrates. Hydrocarbons, including alkanes, alkenes, alkynes and aromatics compounds were also present. The composition of the biomass used has a higher effect on the bio-oil composition, so it is important an extensive characterization of the feedstock in order to select the best raw material to be used in HTL process depending on the intended application. This paper analyses the effect of biomass composition in the HTL to assess its viability to be used to produce biofuels or valuable chemicals.
