Hydrothermal processing of duckweed: Effect of reaction conditions on product distribution and composition

Influences of operating conditions such as temperature (270-380°C), time (10-120min), reactor loading (0.5-5.5g), and K₂CO₃ loading (0-50wt.%) on the product (e.g. crude bio-oil, water soluble, gas and solid residue) distribution from the hydrothermal processing of duckweed were determined. Of the four variables, temperature and K₂CO₃ loading were always the most influential factors to the relative amount of each component. The presence of K₂CO₃ is unfavorable for the production of bio-oil and gas. Hydrothermal processing duckweed produces a bio-oil that is enriched in carbon and hydrogen and has reduced levels of O compared with the original duckweed feedstock. The higher heating values of the bio-oil were estimated within the range of 32-36MJ/kg. Major bio-oil constituents include ketones and their alkylated derivatives, alcohols, heterocyclic nitrogen-containing compounds, saturated fatty acids and hydrocarbons. The gaseous products were mainly CO₂ and H₂, with lesser amounts of CH₄ and CO.