Separation of salicylic acid and two phenols by polyvinyl chloride/N,N-bis (1-methylheptyl) acetamide polymer inclusion membrane

Abstract

The separation behaviour and mass transfer mechanism of salicylic acid (SA) and two phenols by a polymer inclusion membrane (PN-PIM) based on polyvinyl chloride (PVC) as a base polymer and N,N-bis (1-methylheptanyl) acetamide (N503) as a carrier were studied. The correlation between the effects of carrier content and membrane thickness on the morphology, structure and mass transfer stability of PN-PIM was discussed. PN-PIM presented a good mass transfer capability for SA and p-nitrophenol (PNP) through a hydrogen transfer mechanism in weakly acidic environments and with low-concentration NaOH as a stripping phase. The mass transfer rate was in accordance with the first-order kinetic equation. At pH 6, the phenol and PNP coexisting with SA can be selectively removed. The mass transfer of PNP in PN-PIM was consistent with the diffusion mechanism, whereas that of SA exhibited the characteristics of a fixed-site hopping mechanism. When the carrier content was 68.8 %, the permeability coefficient (P) of PNP and SA reached at 9.02 and 8.74 μm/s, respectively. The mass transfer activation energies of PNP and SA totalled 13.23 and 19.08 kJ/mol, respectively. Moreover, intramembrane diffusion was the main controlling step of the mass transfer of PNP and SA in PN-PIM. Given the dual effects of PN-PIM membrane thickness on mass transfer stability and mass transfer rate, the suitable thickness range of PN-PIM was 160–180 μm.