Hollow fibre membranes

Membranes in the form of hollow fibre modules are used commonly for gas dehydration. In comparison to spiral wound modules made from flat sheet membranes, hollow fibre membrane modules contain more membrane surface area per unit volume thereby reducing the size of the module. Additionally, hollow fibre module manufacturing costs are lower [1] and hollow fibre designs easily permit permeate sweep. 

In this case study, an enzymatic hydrolysis reaction, the racemic ibuprofen ester, i.e. (R)-and (S)-ibuprofen esters in equimolar mixture, undergoes a kinetic resolution in a biphasic enzymatic membrane reactor (EMR). In kinetic resolution, the two enantiomers react at different rates lipase originated from Candida rugosa shows a greater stereopreference towards the (S)-enantiomer. The membrane module consisted of multiple bundles of polymeric hydrophilic hollow fibre. The membrane separated the two immiscible phases, i.e. organic in the shell side and aqueous in the lumen. Racemic substrate in the organic phase reacted with immobilised enzyme on the membrane where the hydrolysis reaction took place, and the product (S)-ibuprofen acid was extracted into the aqueous phase. 

Polymeric membranes are most commonly produced in the form of flat sheets, but they are also widely produced as tubes of diameter 10-25 mm and in the form of hollow fibres of diameter 0.1-2 mm. 

Gas separation Hollow-fibre for high-volume applications with low-flux, low-selectivity membranes in which concentration polarisation is easily controlled (nitrogen from air) Spiral-wound when fluxes are higher, feed gases more contaminated, and concentration polarisation a problem (natural gas separations, vapour permeation). 

Industrial membrane plants often require hundreds of thousands of square metres of membrane to perform the separation required on a useful scale. Before a membrane separation can be used industrially, therefore, methods of economically and efficiently packaging large areas of membrane are required. These packages are called membrane modules. The areas of membrane contained in these basic modules are in the range 1-20 m2. The modules may be connected together in series or in parallel to form a plant of the required performance. The four most common types of membrane module are tubular, spiral, wound and hollow fibre. 

New membranes have been developed with significantly enhanced mass-transfer characteristics. These membranes include rotating membrane systems that use a torsional oscillation to produce shear rates as high as 150,000 s. Coiled hollow fibres that exploit Dean vortices to increase solute transport and reduce fouling are receiving attention (Zydney, 2000). 

Kcurentjes et al. (1996) have also reported the separation of racemic mixtures. Two liquids are made oppositely chiral by the addition of R- or S-enantiomers of a chiral selector, respectively. These liquids are miscible, but are kept separated by a non-miscible liquid contained in a porous membrane. These authors have used different types of hollow-fibre modules and optimization of shell-side flow distribution was carried out. The liquid membrane should be permeable to the enantiomers to be separated but non-permeable to the chiral selector molecules. Separation of racemic mixtures like norephedrine, ephedrine, phenyl glycine, salbutanol, etc. was attempted and both enantiomers of 99.3 to 99.8% purity were realized. 

Ricks, E.E., Estrada-Vades, M.C., McLean, T.L. and Iacobucci, G.A. (1992) Highly enantioselective hydrolysis of (/ ,Sl-phenylalanine isopropyl ester by subtilisin Carlsberg. Continuous synthesis of (Sl-phenylalanine in a hollow fibre/liquid membrane reactor. Biotechnology Progress, 8, 197-203. 

Wen et al. [950] used 8-hydroxyquinoline immobilised on a polyarylonitrile hollow fibre membrane to achieve a 300-fold concentration factor for rare earth elements in seawater. 

Yong and Rawliszyn [26] used a multiplex gas chromatograph with a hollow fibre membrane interface in a solventless method for the determination of traces of aliphatic chlorocompounds such as trichloroethane in raw sewage sludge. Down to 0.4pg L 1 of these compounds could be determined. 

Figure 4.3 — Experimental designs using a planar porous membrane (A) and a silicone hollow fibre membrane (B) for the implementation of sensors based on integrated liquid-liquid extraction and detection. (Reproduced from [61] with permission of the American Chemical Society).

A bisphenol A imprinted PES hollow fibre membrane obtained by the dry-wet spinning method was shown to be an interesting alternative to a flat sheet membrane because of its higher surface area [228]. 

Several commercial flat membrane supports have been used including polyethylene [235], polyamide [230, 231], cellulose [236, 237], PVDF [229, 238], PTFE [222, 239], polyurethane [235] and porous alumina [240]. Fibres and hollow fibres of glass [241], polypropylene [233, 234] or PVDF [242] were also employed as support. 

B. Baum, W. Holley, Jr and R.A. White, Hollow Fibres in Reverse Osmosis, Dialysis, and Ultrafiltration, in Membrane Separation Processes, P. Meares (ed.), Elsevier, Amsterdam, pp. 187-228 (1976). 

Keller, O.C., Poitry, S. and BufHe, J. (1994) A hollow fibre supported liquid membrane system for metal speciation and preconcentration calculation of the response time. J. Electroanal. Chem., 378, 165-175. 

Parthasarathy, N., Pelletier, M. and Buffle, J. (1997) Hollow fibre based supported liquid membrane a novel analytical system for trace metal analysis. Anal. Chim. Acta, 350, 183-195. 

Lezamiz, J. and J.A. Jonsson. 2007. Development of a simple hollow fibre supported liquid membrane extraction method to extract and preconcentrate dinitrophenols in environmental samples at ng L-1 level by liquid chromatography. J. Chromatogr. A 1152 226-233. 

Kuosmanen, K., T. Hyotylainen, K. Hartonen, and M.-L. Riekkola. 2003. Analysis of polycyclic aromatic hydrocarbons in soil and sediment with on-line coupled pressurised hot water extraction, hollow fibre microporous membrane liquid-liquid extraction and gas chromatography. Analyst 128 434 -39. 

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