Hollow-fiber -type membrane

Figure 15.3 Hollow-fiber-type membrane oxygenator.

In a hollow-fiber-type membrane blood oxygenator, the blood flows outside and across the hollow fibers. The total membrane area (outside fibers) is 4 m . From the data on physical oxygen absorption into water at 20 °C, the following empirical equation (a) for the water-phase oxygen transfer coefficient (cm min ) in this particular oxygenator at 20 °C was obtained. 

A hollow-fiber-type membrane blood oxygenator, in which blood flows inside the hollow fibers, has a total membrane area (outside fibers) of 4.3 m". The inside diameter, membrane thickness, and length of the hollow fibers are 200 pm, 25 pm, and 13 cm, respectively. When venous blood (Ht = 40%, pQ. = 36 mmHg)... 

Iwai, Y., Yamanishi, T., and Nishi, M., A steady-state simulation model of gas separation system by hollow fiber type membrane... 

Figure 6.4 Profile of a hollow-fiber-type membrane and modules (Pall, X-flow, Inge AG, GEwater, Hydracap, Lenntech, Koch).

Membrane reactors, using semi-permeable membranes, usually of sheet or hollow fiber type... 

Figure 8.4 shows the data [2] of the UF of serum solutions with a hollow fiber-type ultrafilter, with hollow fibers 16 cm in length and 200 pm in i.d., at four shear rates on the inner surface of the hollow-fiber membrane. Slopes of the straight lines, which converge at a point C = Cq on the abscissa, give values at the shear rates given in the figure. 

The relative magnitudes of the three terms on the right-hand side of Equation 15.25 vary with the diffusing substance, the flow conditions of both fluids, and especially with the membrane material and thickness. With the hollow-fiber-type hemodialyzers that are widely used today, membrane resistance usually takes a substantial fraction of the total resistance, and the fraction increases with increasing molecular weight of the diffusing component. 

In order for membranes to be used in a commercial separation system they must be packaged in a manner that supports the membrane and facilitates handling of the two product gas streams. These packages are generally referred to as elements or bundles. The most common types of membrane elements in use today include the spiral-wound, hollow fiber, tubular, and plate and frame configurations. The systems currently being marketed for gas separation are of the spiral-wound type, such as the SEPAREX and Delsep processes, and the hollow-fiber type such as the Prism separator and the Cynara Company process. 

Another method of producing composite hollow fibers, described by Kusuki etal. at Ube [108] and Kopp et al. at Memtec [109], is to spin double-layered fibers with a double spinneret of the type shown in Figure 3.37. This system allows different spinning solutions to be used for the outer and inner surface of the fibers and gives more precise control of the final structure. Often, two different polymers are incorporated into the same fiber. The result is a hollow fiber composite membrane equivalent to the flat sheet membrane shown in Figure 3.26. A reason for the popularity of composite hollow fiber membranes is that different polymers can be used to form the mechanically strong support and the selective layer. This can reduce the amount of selective polymer required. The tailor-made polymers developed for gas separation applications can cost as much as... 

The two most common RO membrane configurations used in water treatment today are spiral-wound and hollow fiber. The spiral-wound elements can operate at a higher pressure and at a higher silt density index (SDI) than the hollow fiber type, and thus may require less pretreatment (and are more tolerant of pretreatment upsets). They also are easier to clean than the hollow fiber type. The main advantage of the hollow fiber configuration is that it has the highest amount of membrane area per unit volume, thus requiring less space. Since there is only one hollow fiber element per pressure vessel, it is easier to troubleshoot, and it is easier to replace membrane modules. 

In a hollow-fiber-type hemodialyzer of the total membrane area (based on o.d., A = 1 m2), 200 ml min-1 ofblood (inside fibers) and 500 ml min-1 of dialysate (outside fibers) flow countercurrently. The overall mass transfer coefficient KL for urea (based on the outside diameter of the hollow fiber) is 0.030 cm min-1. Estimate the dialysance for urea. 

For industrial applications, large surface areas are obtained using modules with many tubular or hollow-fiber membranes or by using large sheets in a spiral-wound arrangement. Tubular membranes are 5 to 25 mm inside diameter and up to 3 m long. Hollow-fiber UF membranes have diameters of 0.2 to 2 mm, and thousands of fibers are sealed in each cylindrical module. Spiral-wound modules of the type used for RO are widely used for UF. 

Most commercial membrane separations use natural or synthetic, glassy or rubbery polymers. To achieve high permeability and selectivity, nonporous materials are preferred, with thicknesses ranging from 0.1 to 1.0 micron, either as a surface layer or film onto or as part of much thicker asymmetric or composite membrane materials, which are fabricated primarily into spiral-wound and hollow-fiber-type modules to achieve a high ratio of membrane surface area to module volume. 

In the spiral-wound type, a planar membrane is used and a flat, porous support material is sandwiched between the membranes. Then the membranes, support, and a mesh feed-side spacer are wrapped in a spiral around a tube. In the hollow-fiber type, fibers of 100 to 200 iJ,m diameter with walls about 25 /rm thick are arranged in a bundle similar to a heat exchanger (LI, Rl). 

A demonstration plant that use membranes for biogas upgrading through has been installed at Bruck/Leitha in the south of Austria [61] the membranes used are hollow fiber type and the operative pressure is of about 8-9 bar. The process is carried out in two stages and biomethane concentration was of about 98 %... 

Hollow fiber-type oxygen enrichment membrane... 

Research and development of the hollow-fiber-type module using a cellulose acetate membrane was conducted by Monsanto, Toyobo, and others, in addition to Dow Chemical. Toyobo announced an RO module for one-pass desalination of seawater that used the cellulose triacetate hollow-fiber membrane module in 1979 (Orofino, 1970 Ukai et al., 1980). 

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