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Abstract Tangential flow filtration is advantageous for bioreactor clarification as the permeate stream could be introduced directly to the subsequent product capture step. However, membrane fouling coupled with high product rejection has limited its use. Here, the performance of a reverse asymmetric hollow fiber membrane where the more open pore structure faces the feed stream and the barrier layer faces the permeate stream has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of Chinese hamster ovary cell feed streams has been investigated under conditions that could be expected in fed batch operations. The performance of the reverse asymmetric membrane is compared to that of symmetric hollow fiber membranes with nominal pore sizes of 0.2 and 0.65 μm. Laser scanning confocal microscopy was used to observe the locations of particle entrapment. The throughput of the reverse asymmetric membrane is significantly greater than the symmetric membranes. The membrane stabilizes an internal high permeability cake that acts like a depth filter. This stabilized cake can remove particulate matter that would foul the barrier layer if it faced the feed stream. An empirical model has been developed to describe the variation of flux and transmembrane pressure drop during filtration using reverse asymmetric membranes. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor clarification.
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Nanoparticle filtration through microporous ECTFE membrane in an alcoholic solution
Organic solvent filtration is an important industrial process. It is widely used in pharmaceutical manufacturing, chemical processing industry, semiconductor industry, auto assembly etc. Most of the particle filtration studies reported in open literature dealt with aqueous suspension medium. The current work has initiated a study of cross-flow solvent filtration behavior of microporous ethylene chlorotrifluoroethylene (ECTFE) membranes using 12 nm silica nanoparticles suspended in an aqueous solution containing 25% ethanol. In the constant pressure mode of operation of cross-flow microfiltration (MF), permeate samples were collected at different time intervals. The permeate particle size distribution (PSD) results for different experiments were identical. Particle agglomerates having less than 100 nm size can pass through the membrane; some fouling was observed. The governing fouling mechanisms for tests operated using 3.8×10−3 kg/m3 (3.8 ppm) at 6.9×103 Pag and 1.4×104 Pag were pore blocking. For tests conducted using 3.8×10−3 kg/m3 (3.8 ppm) at 27.6×103 Pag (4 psig) and 1.9×10−3 kg/m3 (1.9 ppm) at 6.9×103, 13.8×103 and 27.6×103 Pag (1, 2 and 4 psig), the mechanism was membrane resistance control. Less particles got embedded in membrane pores in experiments operated using suspensions with lower or higher particle concentrations with a higher transmembrane pressure. This is in good agreement with the values of the shear rate in the pore flow and scanning electron microscope images of the membrane after MF. In the dead-end mode of operation of solvent filtration using methanol, ethanol and 2-propanol, the permeate flux behavior follows Jmethanol > Jethanol > J2-propanol at all testing pressures. The values of permeance (kg/m2-s-Pa) determined from the slope of the linear plot of filtration flux vs. the applied pressure difference across the membrane, were 3.9×10−4, 2.3×10−4 and 3.0×10−5 for methanol, ethanol and 2-propanol, respectively. Further exploration was made on solvent sorption results reported earlier. The critical temperature of selected solvents shows a better correlation with solvent sorption rather than the solubility parameter.
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- PAR ID:
- 10097083
- Date Published:
- Journal Name:
- Separation and purification technology
- Volume:
- 210
- Issue:
- 2019
- ISSN:
- 1383-5866
- Page Range / eLocation ID:
- 754-763
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Tangential flow filtration (TFF) has many advantages for bioreactor harvesting, as the permeate could be introduced directly to the subsequent capture step. However, membrane fouling has limited its widespread use. This is particularly problematic given the high cell densities encountered today. Here, a reverse asymmetric membrane, where the more open surface faces the feed stream and the tighter barrier layer faces the permeate stream, has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of yeast suspensions has been conducted under a range of conditions. The yeast cells are trapped in the open pore structure. The membrane stabilizes an internal porous cake that acts like a depth filter. This stabilized cake layer can remove particulate matter that would foul the barrier layer if it faced the feed stream. As filtration continues, a surface cake layer forms on the membrane surface. A resistance in series model has been developed to describe the permeate flux during TFF. The model contains three fitted parameters which can easily be determined from constant pressure normal flow filtration experiments and total recycle constant flux TFF experiments. The model can be used to estimate the capacity of the filter for a given feed stream. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor harvesting.more » « less
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null (Ed.)Simultaneous fouling and pore wetting of the membrane during membrane distillation (MD) is a major concern. In this work, an electrospun bilayer membrane for enhancing fouling and wetting resistance has been developed for treating hydraulic fracture-produced water (PW) by MD. These PWs can contain over 200,000 ppm total dissolved solids, organic compounds and surfactants. The membrane consists of an omniphobic surface that faces the permeate stream and a hydrophilic surface that faces the feed stream. The omniphobic surface was decorated by growing nanoparticles, followed by silanization to lower the surface energy. An epoxied zwitterionic polymer was grafted onto the membrane surface that faces the feed stream to form a tight antifouling hydration layer. The membrane was challenged with an aqueous NaCl solution containing sodium dodecyl sulfate (SDS), an ampholyte and crude oil. In the presence of SDS and crude oil, the membrane was stable and displayed salt rejection (>99.9%). Further, the decrease was much less than the base polyvinylidene difluoride (PVDF) electrospun membrane. The membranes were also challenged with actual PW. Our results highlight the importance of tuning the properties of the membrane surface that faces the feed and permeate streams in order to maximize membrane stability, flux and salt rejection.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1016/j.seppur.2018.08.022
