Extract Nitrogen-Containing Compounds in Biocrude Oil Converted from Wet Biowaste via Hydrothermal Liquefaction

This study demonstrates that water can serve as a green solvent to achieve denitrogenation of biocrude oil converted from wet biowaste via hydrothermal liquefaction (HTL) under previously determined optimal reaction conditions (300°C with a 1 h reaction time for swine manure and Chlorella; 300°C with a 0.5 h reaction time for Spirulina). It was hypothesized that water could extract relatively polar chemicals, such as some of the nitrogen-containing compounds, from HTL biocrude oil. This hypothesis was examined by different extraction techniques using water as a solvent to HTL biocrude oil converted from swine manure (SM) and low-lipid algae. The water solubilities of biocrude oil and product yields (water extract, biocrude oil, solid residue, and aqueous and gas products) were measured. Compared to that of the biocrude oil without extraction by water, the nitrogen content of biocrude oil converted from SM decreased from 4.32 to 3.23%. Gas chromatography-mass spectrometry (GC-MS) analyses of treated biocrude oil and water extract demonstrated that water can extract nitrogen-containing compounds and separate fatty acid derivatives that were originally in biocrude oil. When an ultrasonically assisted extraction by water was conducted, the nitrogen content in algal biocrude oil decreased from 6.83 to 5.75% with improved carbon and hydrogen content. In addition, GC-MS analyses of treated biocrude oil and water extract suggest that fatty acid derivatives may behave like surfactants and help in emulsifying nitrogen-containing compounds into water.