Engineering and Technology Journal

The production of straight and helical hollow fibers plays an important role in developing hollow fiber membrane technology that encompasses a broad range of designs. During the last two decades, scientific studies devoted to straight hollow fibers were more abundant than those focused on helical fibers. Several major applications considering side-by-side testing of these two geometries are discussed in this review. For membrane extraction, desalination, and membrane contactor processes, it is observed that permeability rates are 10%-400 % higher for helical fibers compared to straight fibers. This outcome is justified by the presence of Dean-vortices-induced flow turbulences inherent to the geometry of helical membranes. These conditions give rise to an uptake of mass and heat transfer coefficients and a reduction of temperature and concentration polarization phenomena.  Aside from enhanced flow properties, helical hollow fiber bundles tend to be more robust by design, thus exhibiting better resiliency over long service operations than straight bundles. One persistent shortcoming of the helical fibers seems to be an increase in pressure drop. However, this does not always translate into a higher energy consumption – i.e., versus straight bundles. Given the performance advantage, product robustness, and adaptiveness to a broad range of applications, the adoption of helical hollow fiber technology deserves growing support from the membrane community in academic and industrial settings.

Polyethersulfone (PES) hollow fiber ultrafiltration (UF) membrane with the molecular
weight cut-off (MWCO) 20,000 was used for the recovery of polyvinyl alcohol (PVA) from
the simulated wastewater. An attempt to study the effect of carboxymethyl cellulose as
synthetic warp sizing agents on the PVA recovery was investigated in this case.
Experimental results shown that PVA concentration in the retentate of PES hollow fiber
membrane were lower with addition of carboxymethyl cellulose (CMC) in PVA solution.
Besides, higher trans-membrane pressure from 1.0 to 2.1 bars, solution temperature 50-75℃,
and feed velocity 0.16-0.32 m/s, improved the PVA recovery in two different PVA solutions.
PES hollow fiber ultrafiltration process was efficient for PVA recovery from the simulated
wastewater using PVA solution with low carboxymethyl cellulose (CMC) concentration as
synthetic warp sizing agents.

Hollow fiber ultrafiltration (UF) membranes were prepared using Polyethersulfone
(PES), alcohol (n-Propanol) as additive and N, N-dimethylacetamide (DMAc) as a
solvent. Asymmetric hollow fiber UF membranes were spun by wet phase
inversion method from 17 wt% solids of PES/additive/NMP solutions. The alcohol
additive was n-Propanol while the external coagulant was water. Effects of n-
Propanol concentrations in the dope solution on morphology and separation
performance of PES hollow fiber UF membranes were investigated. UF
membranes were characterized in terms of scanning electron microscope (SEM)
while UF experiments were conducted using polyethylene glycol (PEG20,000MW)
and poly (vinyl pyrrolidone) (PVP 40,000MW), as a solute. It was found that the PES
UF membrane morphology changed from long two finger-like structure through a
short two finger-like structure to the two void-like structure as n-propanol
concentration in the dope solution increased from 5 to 20 wt % using water as a
bore fluid; pure water permeation fluxes (PWP) increased from 47 to 201
L/m2.h.bar while rejections of PEG MW20,000 and PVP MW40,000 for wet-spun
PES hollow fiber membranes were decreased with increased of n-propanol
concentration up to 20%. Using above method, PES hollow fiber UF membrane
with high pure water permeation flux could be prepared while the molecular
weight cut-off of PES hollow fiber membranes is approximately 20,000.

Hollow fiber ultrafiltration (UF) membranes were prepared using
Polyethersulfone (PES), alcohol (n-Propanol) as additive and N, N-dimethylacetamide
(DMAc) as a solvent. Asymmetric hollow fiber UF membranes were spun by wet phase
inversion method from 17 wt% solids of PES/additive/NMP solutions. The alcohol
additive was n-Propanol while the external coagulant was water. Effects of n-Propanol
concentrations in the dope solution on morphology and separation performance of PES
hollow fiber UF membranes were investigated. UF membranes were characterized in
terms of scanning electron microscope (SEM) while UF experiments were conducted
using polyethylene glycol (PEG20,000MW) and poly (vinyl pyrrolidone) (PVP
40,000MW), as a solute. It was found that the PES UF membrane morphology changed
from long two finger-like structure through a short two finger-like structure to the two
void-like structure as n-propanol concentration in the dope solution increased from 5 to
20 wt % using water as a bore fluid; pure water permeation fluxes (PWP) increased from
47 to 201 L/m2.h.bar while rejections of PEG MW20,000 and PVP MW40,000 for wetspun
PES hollow fiber membranes were decreased with the increasing of n-propanol
concentration up to 20%. Using above method, PES hollow fiber UF membrane with
high pure water permeation flux could be prepared while the molecular weight cut-off of
PES hollow fiber membranes is approximately 20,000.