Membrane processes tubular membrane

The concept of cross-flow microfiltration is shown in Figure 16.11, which represents a cross-section through a rectangular or tubular membrane module. The particle-containing fluid to be filtered is pumped at a velocity in the range 1-8 m/s parallel to the face of the membrane and with a pressure difference of 0.1-0.5 MN/m2 (MPa) across the membrane. The liquid penneates through the membrane and the feed emerges in a more concentrated form at the exit of the module.1617 All of the membrane processes are listed in Table 16.2. Membrane processes are operated with such a cross-flow of the process feed. 

Another factor is the ease with which various membrane materials can be fabricated into a particular module design.1618 Almost all membranes can be formed into plate-and-frame, spiral-wound and tubular modules, but many membrane materials cannot be fabricated into hollow fine fibres or capillary fibres. Finally, the suitability of the module design for high-pressure operation and the relative magnitude of pressure drops on the feed and permeate sides of the membrane can be important factors.4-11 The types of module generally used in some of the major membrane processes are listed in Table 16.2. 

An ultrafiltration plant is required to treat 50m3/day of protein-containing waste stream. The waste contains 0.05% by weight of protein which has to be concentrated to 2% to allow recycling to the main process stream. The tubular membranes to be used are... 

This is a process mainly used in power plants for separation of dissolved matter by filtration through a semipermeable membrane. Tubular membrane, hollow filter modules, or spiral-wound... 

Porous Membrane DS Devices. The applicability of a simple tubular DS based on a porous hydrophobic PTFE membrane tube was demonstrated for the collection of S02 (dilute H202 was used as the scrubber liquid, and conductometric detection was used) (46). The parameters of available tubular membranes that are important in determining the overall behavior of such a device include the following First, the fractional surface porosity, which is typically between 0.4 and 0.7 and represents the probability of an analyte gas molecule entering a pore in the event of a collision with the wall. Second, wall thickness, which is typically between 25 and 1000 xm and determines, together with the pore tortuosity (a measure of how convoluted the path is from one side of the membrane to the other), the overall diffusion distance from one side of the wall to the other. If uptake probability at the air-liquid interface in the pore is not the controlling factor, then items 1 and 2 together determine the collection efficiency. The transport of the analyte gas molecule takes place within the pores, in the gas phase. This process is far faster than the situation with a hydrophilic membrane the relaxation time is well below 100 ms, and the overall response time may in fact be determined by liquid-phase diffusion in the boundary layer within the lumen of the membrane tube, by liquid-phase dispersion within the... 

The effect of concentration polarization on specific membrane processes is discussed in the individual application chapters. However, a brief comparison of the magnitude of concentration polarization is given in Table 4.1 for processes involving liquid feed solutions. The key simplifying assumption is that the boundary layer thickness is 20 p.m for all processes. This boundary layer thickness is typical of values calculated for separation of solutions with spiral-wound modules in reverse osmosis, pervaporation, and ultrafiltration. Tubular, plate-and-ffame, and bore-side feed hollow fiber modules, because of their better flow velocities, generally have lower calculated boundary layer thicknesses. Hollow fiber modules with shell-side feed generally have larger calculated boundary layer thicknesses because of their poor fluid flow patterns. 

The second part of this chapter will treat in detail the, more cumbersome, preparation of high quality tubular membrane supports. This geometry is necessary for upscaling to process industry. Therefore some research has been performed on the production of high quality tubular membrane supports. This part has been published in a concise form [1],... 

To illustrate this approach, we will consider a new example the case of a simple tubular membrane reactor for which we wish to show the dependence between the conversion (rij of the main reactant and other variables which influence the process. 

Over the past decade, there has been an upsurge of interest in the use of gas bubbles to enhance membrane processes. The typical applications include two-phase flow filtration with tubular membranes and submerged membrane systems. A major stimulus for the latter has been the development of MBRs. 

Al-Akoum et al. [82] compared the bubbling. Dean flow, and vibrating-enhanced membrane processes in terms of the shear stress and the permeate fluxes obtained in filtration of yeast suspension. The filtration with two-phase flow was carried out using 15 mm ceramic mono tubular UF (permeability 250 L/m h bar) and MF (permeability 1500 L/m h bar) membranes with TMPs of 100 and 25 kPa for UF and MF, respectively. The yeast concentrations used in the two-phase experiments were 1... 

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