Hollow-fibre membrane modules

Membrane module Hollow-fibre HPRO", 20 cm dia spiral-wound 20 cm diameter 40 cm diameter spiral-... 

Flat-sheet membranes and hollow fibres are traditionally used in MC devices. In the case of flat membranes, the use of plate and frame (Gaeta, 2003) as well as spiral wound (Koschilowski et al, 2003) configurations has been proposed. The modules contain parallel membrane sheets with interposed spacers. Their assembly requires a careful design of spacers and/or use of supported membranes with an active layer, in order to prevent the occurrence of problems related to mechanical abrasions. Co-current flow is usually preferred to counter-current flow, in order to assure constant pressure difference along the membrane and avoid pressure inversion and membrane movement. 

Developments continue on citrus fruit processing. The membrane configurations most often used in juice clarification are tubular membranes or hollow fibre modules, as well as plate and frame systems using flat sheet membranes. The traditional method of concentrating juices and purees has been evaporation, but nowadays reverse osmosis is proving successful. Reverse osmosis plant performance depends on juice viscosity, the osmotic pressure of the solution, and the constraints imposed by the need for a particular product quality. 

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. 

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. 

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. 

Fane, A.G., Chang, S. and Chardon, E. (2002) Submerged hollow fibre membrane module - design options and operational considerations. Desalination, 146, 231-236. 

Guilt, C.M. Air gap membrane distillation 2. Model validation and hollow fibre module performance analysis, Sep. Purif. Technol., 43(3), 245, 2005. 

Wang D, Teo WK, and Li K. Removal of H2S to ultra-low concentrations using an asymmetric hollow fibre membrane module. Sep. Purif. Technol. 2002 27 33-40. 

The principle of ceramic matrix modules is the same as for hollow-fibre systems, with the exception that cells are not separated from the medium circulation by a membrane. Cells are held in the highly porous matrix and are supplied with... 

In order to obtain a sufficiently large membrane area on an industrial scale, hollow fibre ultrafiltration modules are applied (similar types to those used for protein purification). Since the concentration of NAD(H) does not change in the steady state and there is no NAD(H) in the entrance or exit flow, it becomes clear that the actual concentration of pyruvate in the reactor is equal to the concentration in the feed. Since there is a non-zero concentration of pyruvate in the reactor (and in the exit flow), some pyruvate has to be added to the reactor continuously in order to keep the reaction going. The rate equations of both reactions are required to calculate the precise rate of pyruvate addition. 

In general, membrane-supported liquid-liquid extraction is offered as a micro-porous hollow fibre module (Fig. 2.23). The membrane contactor contains thousands of micro-porous hollow fibres knitted into an array that is wound around a distribution tube with a central baffle. The hollow fibres are arranged in a uniform open packing allowing the utilisation of the total membrane surface area. The liquid flows over the shellside (outside of the hollow fibre), is introduced through the distribution tube and moves radially across the array of hollow fibres and then around the baffle and is carried out by the collection tube. 

Ghogomu, J.N. Guigui, C. Roucha, J.C. Clifton, M.J. Aptel, P. Hollow-fibre membrane module design comparison of different curved geometries with Dean vortices. J. Membr. Sci. 2001, 181, 71-80. 

Various modules or contactors have been used ranging from flat sheets to hollow fibres and with various acceptors volumes. Examples of such modules and different types of membranes have been reviewed recently (34). Flat modules are made of two blocks of inert materials and grooves with depth 0.1-... 

A Memcor microfiltration unit with automated air backflush was used for pretreatment. The membrane area of the hollow fibre module is 1 m. ... 

Not only does the bulk chemical industry employ all of the membrane separation processes, but partly because of that, the sector gives home also to all of the various physical embodiments of membranes flat sheets, plate and frame, pleated cartridges, tubular, hollow fibre, capillary module, and spiral w ound. More particularly, this end Use sector has considerable demaitd for membranes able to resist high temperature or highly corrosive fluids, such that metallic membranes and ceramic materials, especially of the monolith type w ith parallel cylindrical chambers, are w idely used. 

Although there are a number of materials with the desired pore structure, for instance silicone rubbers, hydrocarbon rubbers, polyesters, polycarbonates and others, their use for industrial applications is limited to polysulfones and cellulose acetates. While the latt have been used with good success for dehydration, technical gas separation relies exclusively on polysulfones which can be used up to approximately 70 °C (their melting point is around 200 °C) and at pressures between IS and 140 bar. The lowest pressure differential between the feed gas side and the permeate gas side is 3 1 and this differential pressure determines the wall thickness of the membranes. Figure 2.8 shows the design of a membrane element developed by Monsanto Company, USA and marketed by the name of Prism separator. Each of these elements or modules contains thousands of hollow fibres packed to a density of approximately 1(X) per cm. ... 

The invention of the RO membrane stimulated both commercial and academic interest in other membrane processes and applications. For example, Henis and Tripodi, the co-inventors of hollow-fibre GS membranes, made industrial GS economical by drawing on the experience of developments in RO membranes and modules [3]. Technical milestones for the commercial development of various membrane processes are given in Table 1.2. 

Membrane contactor (MC) is a phase-contacting device for use in gas absorption and stripping (degassing) processes as well as in biomedical gas transfer processes [44, 46]. The function of the membrane is to facilitate diflfusive mass transfer between contactir phases such as liquid-liquid, gas-liquid and gas-gas. The membrane phase contactor uses polyolefins, e.g., polypropylene (PP) microporous hollow fibres membranes, which are packed densely in a high surface area module. Since membranes are hydrophobic and have small pores (0.05—0.1 3m), water does not pass through the membrane pores easily. The pressure required to force water to enter the pore is called the breakthrough pressure, which for a PP membrane with a pore size of 0.05 pm is greater than 10 bar g. 

A MC module contains thousands of microporous hollow fibres, which are knitted into a fabric that is wound around a distribution tube with a central baffle as shown in Figure 1.15. The baffle ensures the water is distributed across the fibres, and also results in reduced pressure drop across the contactor. The hollow fibres are packed densely in a membrane module with a surfrce area of up to 4000 n / m. The liquid flows outside (shell side) the membrane, while vacuum is appHed on the inside of the fibre (tube side) forming a film across the pores of the membrane. Mass transfer takes place through this film and the pores due to the difference in the gas partial pressure between the shell side and tube side. Since the membranes are hydrophobic, they are not wetted by water, thereby, efiectively blocking the flow of water through the membrane pores. The membrane provides no selectivity. Rather its purpose is to keep the gas phase and the Hquid phase separated. In effect, the membrane acts as an inert support that allows intimate contact between gas and liquid phases without dispersion. Vacuum on the tube side of the membrane increases the mass transfer rate as in a vacuum tower. The efficiency of the process is enhanced with the aid of nitrogen sweep gas flowing on the permeate side of the membrane. 

Characteristics of membrane modules are summarised in Table 1.12. The spiral wound (SW) module shown in Figure 1.18 is used in all RO and NF applications. The RO hollow-fibre (FIF) module, similar to the one shown in Figure 1.19, is now manufactured by only by Toyobo, and is used for seawater desalination. UF HF membrane (see Figure 1.3) was used extensively in the dairy industry, but it has largely been replaced by SW modules. However, cross-flow HF modules are commorJy used in food processing and industrial wastewater treatment [18, 31]. 

Figure 1.19 A DuPont hollow fibre RO membrane module assembly.

Polydopamine and polydopamine- -PEG coatings increase hydrophdicity of the membrane surfaces and have previously been shown to improve fouling resistance toward model od/water emulsions in laboratory studies. Polyacrylonitrde hollow fibre UF and polyamide spiral wound RO membrane modules were surface-modified with an aqueous solution containing dopamine to deposit polydopamine on the membrane surfaces and other wetted parts inside the modules [76]. UF modules were further... 

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