Effect of Dope Flow Rate and Post-Treatment on the Morphology, Permeation and Metal Ion Rejection from PES/LiBr-Based UF Hollow Fiber Membranes.

Muhammad Irfan,Noordin Mohd Yusof,Masooma Irfan,Ani Idris,Khaled H Mahmoud,Nawshad Muhammad,Abdullah Saad Alsubaie

doi:10.3390/membranes12030305

Abstract

This study investigated the influence of dope extrusion rate (DER) and post-treatment effect on the morphology, permeation, and metal ion rejection by polyethersulfone/lithium bromide (PES/LiBr)-based hollow fiber (HF) membranes. HF fibers were spun with 2.25, 2.5, and 3.1 ratios of DER to bore fluid rate (BFR), wherein DER varied from 11.35, 12.5, to 15.6 mL/min with a fixed BFR (5 mL/min). Molecular weight cutoff (MWCO), pore size, water flux, and flux recovery ratio were determined, whereas lake water was used to observe the rejection rate of dissolved metallic ions. Results showed that with the increase of the DER wall thickness (WT), HFs increased from 401.5 to 419.5 um, and furthermore by the post-treatments up to 548.2 um, as confirmed by field emission scanning electron microscope (FESEM) analysis. Moreover, MWCO, pore size, and the pure water permeation (PWP) of the HF membranes decreased, while the separation performance for polyethylene glycol (PEG) solute increased with increasing DER. Post-treated HFs from 11.35 mL/min of DER showed 93.8% of MWCO value with up to 90% and 70% rejection of the arsenic and chromium metallic ions, respectively, in comparison with all other formulated HFs.

Highlights

In recent years, polymeric membranes have gained wide acceptance because of their performance, reliability, flexibility, and cost competitiveness
In a round bottle flask, 20 wt. % PES and 3% lithium bromide (LiBr) were blended in DMF solvent for 20 min in a microwave, and the solution was further homogenized by stirring rod for 30 min without heating
Idris et al reported in detail the effect of LiBr on the performance of PES hollow fiber (HF) in terms of flux rate, hydrophilicity, Molecular weight cutoff (MWCO), and pore size, and the authors concluded that 3 wt. % of LiBr in the formulation provided the best results in terms of MWCO and 2.83 KDa with high flux rate [14,23]

Summary

Introduction

Polymeric membranes have gained wide acceptance because of their performance, reliability, flexibility, and cost competitiveness. Research has been intensified on the effect of DER, causing shear stress within the spinneret because it is observed that the dope rheology has a very important role in the course of HF fabrication in order to obtain desired properties [1–4]. The stress is higher on the wall than the center These stresses may affect molecular orientation and relaxation at the outer surface of the HFs [5]. Shear rate is increased with rise in the DER that will cause the molecules of dope solution to pack nearer to each other, leading to a tighter outer skin structure of HF. This compact and tight packing of HFs result in higher rejection and lower flux. Chung and co-workers investigated the effect of shear stress within the spinneret, finding that high shear lowered the water permeation but increased the selectivity, owing to compact molecular orientation inside the fibers [6]

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Conclusion