Waste organic acid treatment with polyethyleneimine grafted polystyrene resin

Organic acid is a kind of important fine chemicals with wide application, while impropriate discharges would cause serious damage to environment. In this report, two polyethyleneimine (PEI-600, 1800) functionalized polystyrene (PS) resins were facilely prepared to remediate common organic acids. The heavier PEI-1800 resulted in surprisingly lower nitrogen loading of PSPEI under optimal conditions due to more significant extra grafting. Therefore, PSPEI-600 was used to adsorb two groups (aliphatic and aromatic) of eight common organic acids, and showed highest adsorptive capacities toward salicylic acid (SA) and trifluoroacetic acid (TFA). The adsorption of TFA was faster and was mainly due to strong acid-base interactions by forming ammonium carboxylate. SA possessed lower acidity, but its additional pi-pi stacking and hydrogen bonding interactions with the PSPEI resin led to a slower but overall higher uptake. Kinetic studies indicated that both acid adsorptions conformed to pseudo-second-order kinetics, and the adsorption rate was controlled by intraparticle diffusion. The adsorptions followed Langmuir isotherms and were identified as a spontaneous endothermic process.