Polyethersulfone Hollow Fiber Ultrafiltration Research Articles

Experimental studies on extraction of cobalt ions from dilute aqueous solutions by using complexation-ultrafiltration process

The extraction of cobalt ions from dilute aqueous solutions was investigated by ultrafiltration with the help of poly(acrylic acid) sodium salt (PAASS). Polysulfone and polyethersulfone hollow fiber ultrafiltration membranes were employed in this process. The kinetics of complexation reaction was studied for PAASS with Co2+. Results showed that, under a large excess of PAASS, it takes 65, 55 and 40 min at pH 5, 6 and 7, respectively, to get the equilibrium of complexation. The reaction kinetics can be described by a pseudo-first-order equation. Then, the effects of various parameters on the extraction of Co2+ were examined in detail. Results indicated that loading ratio, pH value and low-molecular competitive complexing agent affect significantly cobalt rejection coefficient R. Furthermore, a concentration experiment was carried out at pH 7. With increasing volume concentration factor, membrane flux declines slowly, and R value is always about 1. The concentrated retentate was used further for a decomplexation experiment. The decomplexation ratio of cobalt-PAASS complex reaches as high as 90.1%. After the decomplexation step, a diafiltration experiment was performed at pH 2.5. Cobalt ions can be extracted satisfactorily from the retentate, and a purified PAASS is obtained.

Separation performance of horizontal and vertical polyethersulfone hollow fiber UF modules

The effect of hollow fiber module positions (horizontal and vertical) on separation performance for PVA solution by using polyethersulfone (PES) hollow fiber ultrafiltration (UF) membrane with the molecular weight cut-off (MWCO) 30 000 has been discussed. Experimental results illustrated that the suitable operation conditions for PVA solution were as follows: trans-membrane pressure 2.1 bar, solution temperature 75 °C and feed velocity 0.32 m/s. Under these suitable operation conditions, the permeate flux is from 36.8 L/(m2·h· bar) to 42.9 L/(m2· h· bar) for the horizontal module and from 39.8 L/(m2· h· bar) to 66.6 L/(m2· h· bar) for the vertical module. Besides, the separation performance of PES hollow fiber UF membrane was better by using vertical hollow fiber module than by using horizontal hollow fiber module. When the trans-membrane pressure increased from 1 bar to 2.1 bar, solution temperature from 50 °C to 75 °C, feed solution velocity from 0.16 m/s to 0.32 m/s, the PVA rejection would increase from 95.8% to 99.7%, 95.4% to 98.6%, 95.8% to 99.2% for horizontal module respectively, and from 98.8% to 99.8%, 98.6% to 99.4%, 98.5% to 99.4% for vertical module respectively. Therefore, PVA rejection in PES hollow fiber UF process was more than 98.5% for vertical module, and it is suitable for PVA recovery from wastewater.