Adsorption of Major Nitrogen-Containing Components in Microalgal Bio-Oil by Activated Carbon: Equilibrium, Kinetics, and Ideal Adsorbed Solution Theory (IAST) Model

This study provides a fundamental understanding of the adsorption process for nitrogenous compound removal from microalgal bio-oil over activated carbon (AC) and offers a useful model based on the carbon adsorption isotherms and kinetics. The results show that AC favors adsorption of hexadacanamide and indole rather than valeramide and 3-phenylpropionitrile. The surface oxygenous functional groups and acidity of the AC play a vital role in the adsorptive performance of AC. The AC presents a Freundlich isotherm in the adsorption of hexadacanamide, indole, valeramide, and 3-phenylpropionitrile. Adsorption removal for the four nitrogen-containing compounds follows pseudo-second-order kinetics. There exists competitive adsorption among different nitrogen-containing compounds which can be simulated by the IAST model. The IAST model can be used to predict the required amount of adsorbent and appropriate initial concentration of adsorbate for maximum enhancement of the removal efficiency of nitrogen-containing compounds from microalgal bio-oil. It can also predict the effects of the specific surface area of the adsorbents and reaction temperature on the carbon adsorption performance.