CO2 Adsorption on Polybenzoxazine Grafted Activated Carbon: Effects of Amine Precusor

Abstract

CO2 adsorption of polybenzoxazine-modified activated carbon prepared by grafting various polybenzoxazine (PBZ) via ring-opening polymerization of different amine precursors was investigated. Benzoxazine monomer (BZ) was synthesized from phenol, paraformaldehyde, and hexamethylenediamie (HMDA) or triethylenetetramine (TETA). The PBZ loading was varied by different benzoxazine monomer solution concentrations from 0.1 to 0.5 g/L. CO2 adsorption isotherms were obtained at 35 °C, 50 °C, and 75 °C. Adsorbents were characterized by TG-DTA, FT-IR, and surface area and pore size analyses. The amount of PBZ grafted on activated carbon was determined by UV-Vis spectroscopy. The results showed that the CO2 adsorption capacity of the PBZ grafted activated carbon was improved due to the synergistic effects between physical and chemical adsorption. When the adsorption temperature increased, the CO2 adsorption capacity of the grafted adsorbent decreased because the physisorption was more dominated than the chemisorption. The decrease in the capacity due to the temperature increase was more pronounced with the unmodified activated carbon. Using TETA resulted in high CO2 adsorption than using HMDA. It was likely that using TETA to synthesize PBZ contained secondary amine and tertiary amine whereas only tertiary amine was found in PBZ synthesized by HMDA. The secondary amine can directly react with CO2, but the tertiary amine has only van der Waals force to attract CO2. CO2 adsorbed onto PBZ/AC was completely desorbed by heating at 120 °C for 24 h. There was no significant change in the CO2 adsorption capacity of the regenerated adsorbents.