The role of surface oxygen-containing functional groups in liquid-phase adsorptive denitrogenation by activated carbon

Twelve activated carbon (AC) samples with different physical and chemical properties were selected to investigate their ability for the adsorptive denitrogenation of liquid hydrocarbons using two model fuels containing typical nitrogen compounds, indole and quinoline in decane. The surface oxygen-containing groups of the ACs were characterized by temperature-programmed desorption with a mass spectrometer to identify and quantify the type and concentration of the oxygen-containing functional groups based on the CO- and CO2-evolution profiles. The adsorption behavior of AC for nitrogen compounds in decane was found to obey the Langmuir adsorption isotherm. The adsorption parameters (the maximum capacity and the adsorption constant) were estimated. With these results, the correlation between the adsorption performance of the AC samples and their physical/chemical properties was evaluated by a multiple linear-regression analysis, which indicated that the physical properties were not the key factors for the removal of the nitrogen compounds in decane. Furthermore, the oxygen-containing groups of ACs, especially the carboxylic acid groups, were found to be mainly responsible for nitrogen adsorption.