Transformation of nitrogen during microalgae model compounds liquefaction in sub-/supercritical ethanol

Abstract

Nitrogen migration significantly affects the quality of bio-oil and the emission characteristics of pollutants during microalgae thermochemical transformation. To investigate the nitrogen migration and transformation of the main components of microalgae during liquefaction in sub- or supercritical ethanol, three model compounds (soya protein, castor oil, and corn starch) were selected to explore the interaction among various biochemical components and organic solvent at 220 °C and 260 °C. The nitrogen contents in the products were accurately quantified and characterized by GC–MS, element analysis, XPS, and FTIR analysis. The results imply that the addition of castor oil has a negligible effect on the nitrogen transformation during liquefaction, while corn starch promotes more than 22.16 wt% of the nitrogen transfer into the solid residue. Pyrrolidinone is the main nitrogen-containing compound in the oil products; neither pyridine-N nor nitrile-N are detected. It indicates that the hydrogen supply of ethanol is also suitable for the addition of C-N unsaturated bonds in bio-oils. The model compounds containing corn starch generate pyrazines only at the higher temperature and pressure.