Interaction between ammonium perfluorooctanoate and CO2 and its removal from fluoropolymer in supercritical carbon dioxide

摘要

Ammonium perfluorooctanoate (APFO) is an additive used in synthesis of fluoropolymer and subsequently existed in the final product. However, the residues of APFO in fiuoropolymer caused serious environmental problems. An enhancement in solubility of APFO in supercritical carbon dioxide (scCO(2)) is definitively accomplished via intermolecular interaction. Based on intermolecular interaction, the solvation mechanism of APFO in gaseous and supercritical CO2 was systematically demonstrated by introducing the concepts of transition pressure (P-T). Considering the intermolecular interactions between APFO and CO2 are complicated, perfluorooctanoic acid (PFOA) was used instead of APFO. When the pressure reached P-T, the intermolecular interactions between PFOA and CO2 reached the maximum, and the binary phase changed from heterogeneous to homogeneous phase. P-T of PFOA + CO2 increased from 12.0 +/- 0.26 to 20.2 +/- 0.43 MPa when temperature changed from 333 to 373 K. Under different conditions, the effects of pressure and temperature on the extraction efficiency of APFO were investigated, and the optimized conditions was 12 MPa, and 333 K. An extraction efficiency of 92.3 +/- 0.755% is obtained.