PEI hollow fiber

Table 5.11. Average pore size of PEI hollow fiber membranes from AFM images (inner surface) and from UF experiments...

Feng et al. [32] measured the pore sizes of PEI hollow fibers prepared at different air gaps by AFM and the solute transport technique. The results are given in Table 5.11. The table also shows that the pore sizes determined by AFM are always larger than those calculated from solute transport data. 

Xu et al. [11] studied the effects of both N,N-dimethylacetamide (DMAc) as a solvent additive in an internal coagulant (water) and acetic acid as a nonsolvent additive in a dope solution (PEI in DMAc) on the morphology and performance of poly(etherimide) (PEI) hollow fiber membranes for UF. Cross-sectional pictures were taken by SEM. The authors observed nodular structures on the inner and outer edges of the cross section when the amount of the acetic acid in the dope solution was increased. Pure water permeation flux increased when the nodules appeared. 

In summary, the following observations were made on the morphology of the PEI hollow fibers fabricated by the dry-wet spinning technique ... 

R. Naim, A.F. Ismail, Effect of polymer concentration on the structure and performance of PEI hollow fiber membrane contactor for CO2 stripping, J. Hazard. Mater. 250-251C (2013)354-361. 

SPPO coated on PEI hollow fibers prepared from PEI (22.5 wt%)/DMAc(76.0 wt%)/LiN03(1.5 wt%) solution... 

For some of the membrane modules permselectivity of 40.8 for a CO2/CH4 was achieved. As mentioned above PEI hollow fibers coated with SPPOBr polymer demonstrated excellent performance for the separation of COj and CH4. However, deterioration of the performance was observed with an... 

Larger membrane modules having surface area about 700 - 800 cm were also prepared and tested. These modules were constructed using about 80 -100 PEI hollow fibers of 35 cm length. These fibers were potted at both ends using epoxy resin into 11/4 inches diameter steel tube having an outlet on the side. The module was sealed at both ends by means of steel end caps fitted with 0-rings. Fiber lumens were open at both ends. 

It was also important to choose an appropriate substrate to coat the active polymer material onto. Hence, TFC membrane modules prepared with SPPOBr as the active layer coated on PEI hollow fibers spun from a PEI/NMP/GBL solution showed superior performances compared to those prepared from PEI/DMAc/LiN03 solutions. Coating on the lumen side of the fibers gave better performance than coating on the shell side. This could be due to the fact that the skin layer of the fibers was formed on the lumen side. Stability of the coated layer was greatly improved when a wet feed stream used instead of a dry feed stream. Water vapor in the feed stream most likely prevented the active layer from stress cracking on drying. Moreover the presence of water vapor in the membrane may have enhanced the permeance of CO2. 

FIGURE 32.8 Effect of structural parameters of hollow-fiber membrane used in the experiments. (From Pei, L. et al., J. Rare Earths, 27, 447, 2009.) (a) Effect of thickness of membrane, (b) Effect of inner diameter of fiber, (c) Effect of membrane porosity. 

L. Pei, L.M. Wang, W. Guo, Stripping dispersion hollow fiber hquid membrane containing carrier PC-88A and HNO3 for the extraction of Sm, Chin. Chem. Lett. 23 (2012) 101-104. 

L. Pei, L.G. Wei, Dispersion hollow fiber hquid membrane using as mobile carrier. Chin. J. Chem. 29 (2011) 1233-1238. 

MAJOR APPLICATIONS PEI offers potential cosmetic uses and new directions for clear antidandruff hair products and antiperspirants. Also used as a wet-strength agent in the paper-making process, a flocculating agent with silica sols, and in the coating of composite hollow-fiber membranes. 

Fig. 1.13 Various types of single fiber structure (a) PEI ribbon fiber, (b) PA6 helix fiber, (c) PS porous fiber, (d) PVA/Si02 necklace-like fiber, (e) PSU/PEO core-sheU fiber, and (f) Ti02 hollow fiber (a Reprinted with permission from Koombhongse et al. [152], 2001 John Wiley Sons, Inc. b Reprinted with permission from Han et al. [57]. 2007, Elsevier, c Reprinted with permission from Lin et al. [59]. 2010, American Chemical Society, d Reprinted with permission from Jin et al. [154]. 2010, American Chemical Society, e Reprinted with permission from Sun et al. [155]. 2003 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim. f Reprinted with permission from Han et al. [57]. 2007, Elsevier)...

In liquid separation, hollow fiber membranes based on PBI have shown excellent performance for pervaporation dehydration of organic liquids. For example, a dual layer PEI-PBI hollow fiber membrane with an outer selective layer of PBI showed better performance than most other polymeric membranes in pervaporation dehydration of ethylene glycol. Sulfonation modifications of PBI membranes have demonstrated excellent separation efficacies in the dehydration of acetic acid. Studies have shown that PBI hollow fiber membranes were effective in separating chromates from solutions. Also, PBI nanofiltration hollow fiber membranes are promising candidates as forward osmosis membranes. In gas separation, recent studies sponsored by the Department of Energy at Los Alamos National Laboratories and SRI International demonstrated potential applications of PBI membranes in carbon capture and Hj purification from synthesis gas streams at elevated temperatures. H2/CO2 selectivity > 40 has been achieved at H2 permeability of 200 GPU at 250°C. ... 

The PEI substrate hollow fibers were prepared using the dry - wet spinning technique to form integrally skinned asymmetric hollow fiber membranes. Two different polymer solution compositions were utilized. In the first case a 22.5 wt% solution of PEI in dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP), containing 1.0 - 1.5 wt% of lithium nitrate was used following the method similar to that described by Deng and others. In the second case a spinning procedure described by Kneifel and Peinemann was adopted. Here NMP was used as the solvent and y-butyrolactone (GBL) was used as the nonsolvent. 

From the initial experiments with PEI - modified PPO TFC hollow fiber membranes it may be concluded that better separation characteristics for SPPOBr was attained compared to that for SPPO for similar gas permeances. 

Figures 12.1.22 and 12.1.23 explain technical principles behind formation of efficient and selective membrane. Figure 12.1.22 shows a micrograph of hollow PEI fiber produced from N-methyl-2-pyrrolidone, NMP, which has thin surface layer and uniform pores and Figure 12.1.23 shows the same fiber obtained from a solution in dimethylformamide, DMF, which has a thick surface layer and less uniform pores. The effect depends on the interaction of polar and non-polar components. The compatibility of components was estimated based on their Hansen s solubility parameter difference. The compatibility increases as the solubility parameter difference decreases. Adjusting temperature is another method of control because the Hansen s solubility parameter decreases as the temperature increases. A procedure was developed to determine precipitation values by titration with non-solvent to a cloud point. Use of this procedure aids in selecting a suitable non-solvent for a given polymer/solvent system. Figure 12.1.24 shows the results from this method. Successfid in membrane production by either non-solvent inversion or thermally-induced phase separation requires careful analysis of the compatibilities between polymer and solvent, polymer and non-solvent, and solvent and non-solvent. Also the processing regime, which includes temperature control, removal of volatile components, uniformity of solvent replacement must be carefully controlled.

Figures 11.24 and 11.25 explain technical principles behind formation of efficient and selective membrane. Figure 11.24 shows a micrograph of hollow PEI fiber produced...

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