Membrane separation processes ultrafiltration

Ultrafiltration is one of the most widely used of the pressure-driven membrane separation processes. The solute retained or rejected by ultrafiltration membranes are those with... 

A limitation to the more widespread use of membrane separation processes is membrane fouling, as would be expected in the industrial application of such finely porous materials. Fouling results in a continuous decline in membrane penneation rate, an increased rejection of low molecular weight solutes and eventually blocking of flow channels. On start-up of a process, a reduction in membrane permeation rate to 30-10% of the pure water permeation rate after a few minutes of operation is common for ultrafiltration. Such a rapid decrease may be even more extreme for microfiltration. This is often followed by a more gradual... 

We can use the same filtration principle for the separation of small particles down to small size of the molecular level by using polymeric membranes. Depending upon the size range of the particles separated, membrane separation processes can be classified into three categories microfiltration, ultrafiltration, and reverse osmosis, the major differences of which are summarized in Table 10.2. 

The four developed industrial membrane separation processes are microfiltration, ultrafiltration, reverse osmosis, and electrodialysis. These processes are all well established, and the market is served by a number of experienced companies. 

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). 

The layer of solution immediately adjacent to the membrane surface becomes depleted in the permeating solute on the feed side of the membrane and enriched in this component on the permeate side. Equivalent gradients also form for the other component. This concentration polarization reduces the permeating component s concentration difference across the membrane, thereby lowering its flux and the membrane selectivity. The importance of concentration polarization depends on the membrane separation process. Concentration polarization can significantly affect membrane performance in reverse osmosis, but it is usually well controlled in industrial systems. On the other hand, membrane performance in ultrafiltration, electrodialysis, and some pervaporation processes is seriously affected by concentration polarization. 

Figure 6.1 Schematic illustrating in vivo membrane separation processes. Left microdialysis sampling probe with curved lines indicating analyte tortuous diffusion through the tissue into and out of the probe. Right ultrafiltration representing interstitial fluid flow into the membrane device. Tissue is represented with cells and hlood vessels (dark circles in light circles).

Reverse osmosis retains all components except water, whereas ultrafiltration is primarily a size-exclusion-based pressure-driven membrane separation process. The... 

Mixtures of CO2 (5%-15%) and N2 were used as model feed gas, and monoethanolamine (ME A), diethanolamine (DEA), and 2-amino-2-methyl-l-propanol (AMP) were used as the carriers of CO2. The polyethersulfone capillary ultrafiltration membranes (see Table 13.4) were used in the module. The membrane was very stable over a discontinuous 4-month testing period. The energy consumption was found to be much smaller than those of conventional chemical absorption and membrane separation processes. 

Blatt, WF, Principles and practice of ultrafiltration, in Meares, P, Ed., Membrane Separation Processes, Elsevier Science, Amsterdam, 1976. 

In this chapter, we will introduce fundamental concepts of the membrane and membrane-separation processes, such as membrane definition, membrane classification, membrane formation, module configuration, transport mechanism, system design, and cost evaluation. Four widely used membrane separation processes in water and wastewater treatment, namely, microfiltration (MF), ultrafiltration (UF), nanofiltrafion (NF), and reverse osmosis (RO), will be discussed in detail. The issue of membrane foufing together with its solutions will be addressed. Several examples will be given to illustrate the processes. 

The investigation of Dean vortices and their application to membrane separation processes has been the subject of several experimental and theoretical studies concerning the improvement of microfiltration (ME), ultrafiltration (UF), and nanofiltration (NF),... 

Danger, P., Breitenbach, S., and Schnabel, R., Ultrafiltration with Porous Glass Membranes, Proc. Int. Techn. Conf. on Membrane Separation Processes, Brighten, U. K. (May 24-26, 1989)... 

As with reverse osmosis, ultrafiltration (UF) and microfiltration (MF) are pressure-driven membrane separation processes, with the membrane permselective for the solvent, usually water. MF and UF separate mainly by size exclusion of the solutes. MF retains particles of micrometer size UF retains particles of submicrometer size by ultramicroporous membranes. Typically, UF retains solutes in the 300 to 500,000 molecular weight range including biomolecules, polymers, sugars, and colloidal particles. 

Ultrafiltration, like reverse osmosis, is a pressure-driven membrane separation process. The applied pressures usually range from about 7 X 10" to 7 X 10 Pa, and the solvent, most often water, passes through the membrane. Material that does not pass through the membrane includes particulate matter, colloids, suspensions, and dissolved macromolecules of molecular weight generally greater than 10,000 and often greater than 2000. Rejection is usually close to complete. 

Available techniques for the removal of metal ions include chemical precipitation, ion exchange, evaporation, solvent extraction and a variety of membrane separation processes including reverse osmosis, ultrafiltration and electrodialysis [3]. Each of these methods has its own advantages but all lack the ability of certain electrochemical techniques to produce metal directly in a controlled fashion. 

Bechold [6] reported one of the first careful studies of pressure to drive a membrane separation process. He developed a series of membranes from nitrocellulose with graded porosities and demonstrated how to characterize them through bubble tests [7]. The origin of the word ultrafiltration is attributed to Bechold [8]. Subsequent improvements to Bechold s process led to the first commercially available microporous collodion membranes and the birth of the membrane industry [7]. 

Commercial membrane separation processes include reverse osmosis, gas permeation, dialysis, electrodialysis, pervaporation, ultrafiltration, and microfiltration. Membranes are mainly synthetic or natural polymers in the form of sheets that are spiral wound or hollow fibers that are bundled together. Reverse osmosis, operating at a feed pressure of 1,000 psia, produces water of 99.95% purity from seawater (3.5 wt% dissolved salts) at a 45% recovery, or with a feed pressure of 250 psia from brackish water (less than 0.5 wt% dissolved salts). Bare-module costs of reverse osmosis plants based on purified water rate in gallons per day are included in Table 16.32. Other membrane separation costs in Table 16.32 are f.o.b. purchase costs. 

Ultrafiltration is primarily a size-exclusion-based, pressure-driven membrane separation process. UF membranes typically have pore sizes in the range of 2-500 nm and retain species in the molecular range from 3000 to 500 000 Da [20], while sol-... 

Finally, in Chap. 8, attempts are made to correlate the AFM parameters, such as nodule and pore sizes, to the membrane performance data. Membranes used for a variety of membrane processes, including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, gas and vapor separation, pervaporation, and other membrane separation processes, are covered in this chapter. AFM parameters are also correlated to membrane biofouhng. This chapter also includes appUcations of AFM to characterize biomedical materials, including artificial organs cind drug release. 

Ultrafiltration (UF) Membrane separation process using membranes with a pore size range of about 0.005-0.1 pm, corresponding to MWCO of 1000—500,000. See Section 6.12. 

Khayet, M. and Matsuura, T. 2003a. Progress in membrane surface modification by surface modifying macromolecules using polyethersulfone, polyetherimide and polyvinylidene fluoride base polymers Applications in the separation processes ultrafiltration and per-vaporation. Fluid Particle Sep. J. 15(1) 9-21. 

Membrane separation processes such as gas permeation, pervaporation, reverse osmosis (RO), and ultrafiltration (UF) are not operated as equilibrium-staged processes. Instead, these separations are based on the rate at which solutes transfer though a semipermeable membrane. The key to understanding these membrane processes is the rate of mass transfer not equilibrium. Yet, despite this difference we will see many similarities in the solution methods for different flow patterns with the solution methods developed for equilibrium-staged separations. Because the analyses of these processes are often analogous to the methods used for equilibrium processes, we can use our understanding of equilibrium processes to help understand membrane separators. These membrane processes are usually either conplementary or conpetitive with distillation, absorption, and extraction. 

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