The characterization of flat composite nanofiltration membranes and their applications in the separation of Cephalexin

We have characterized two flat composite nanofiltration membranes (NADIR® N30F and NF PES10) by using neutral molecules and electrolytes and investigated their suitability for the separation of Cephalexin. For the first objective, the real rejection was firstly obtained by correcting the observed rejection based on the concentration polarization model. Then both irreversible thermodynamic and steric-hindrance pore (SHP) models were applied in order to estimate membrane structural parameters. It is found that the average pore radius rp are in the range 0.74-1.33 nm and the ratios of membrane porosity to membrane thickness Ak/Δx, are in the range 30,058-35,757 m−1, which are consistent with the experimental results based from the solute transport method. The effective charge density (ϕX) of membranes, determined from the Teorell-Meyer-Sievers (TMS) model through fitting the NaCl rejection data, varies as a function of electrolyte concentration. These two negatively charged membranes express different rejection performance for single electrolytes in aqueous solutions, which in the order of R(Na2SO4) > R(MgSO4) > R(NaCl) > R(MgCl2). When investigating the ion rejection performance in the binary salt mixture solutions (Na2SO4/NaCl) at different pressures, these two membranes also exhibit a negative rejection to Cl− ion due to its lower valence. Through adjusting the pH of aqueous solutions, the separation of Cephalexin can be effectively manipulated up to 98% and 88% for N30F and NF PES10, respectively. In addition, increasing pressure was propitious to enhance the real rejection of solutes with higher permeate flux. N30F membrane shows higher rejection for Cephalexin due to its smaller pore size and larger charge density than NF PES10 membrane.