New composite hollow fiber membrane for nanofiltration

A capillary nanofiltration module would give a better packing density than the tubular module and allows a less demanding pre-treatment and maintenance than the spiral-wound module. This module would be a solution for the treatment of low quality water sources by direct capillary nanofiltration. In this work, a new composite capillary membrane with high permeability was developed by interfacial polymerization of N, N'-diaminopiperazine (DAP) and trimesoylchloride (TMC). The influence of the preparation conditions of the inner thin film on the separating performance of the hollow fibers was studied. The parameters with stronger influence were the concentration of N, N'-diaminopiperazine and the residence times of trimesoylchloride and rinsing solution. By changing the preparation parameters, it was possible to obtain two different hollow fiber membranes. Their performance was evaluated with electrolyte and non-electrolyte solutions. One type gave water permeability in the range 12-22 l/m2/h/bar.The salt rejections for NaCl, MgSO4 and Na2SO4 were 10, 12 and 80%, respectively. The sugar rejections obtained were 12% for glucose and 21% for sucrose and lactose. The other type presented lower water permeability, around 6 l/m2/h/bar, and higher salt rejections for NaCl (14%), MgSO4 (60%) and Na2SO4 (87%). A stronger increase was observed on the sugar rejections which were 57% (glucose),77% (sucrose) and 91% (lactose). Morphological studies of the hollow fiber surface were conducted by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM) and revealed an extreme flat film. It was also possible to conclude that the morphology more similar to the support hollow fiber lead to a more permeable membrane.