Cellulose acetate membranes effect

For purposes of illustration, the following discussion, unless otherwise specified, is limited to single-solute aqueous feed solutions, cellulose acetate membranes, and reverse osmosis systems for which osmotic pressure effects are essentially negligible. 

Figure 2a. Experimental data on the effect of operating pressure, average pore size on membrane surface, and feed concentration on solute separation and product rate for the reverse osmosis system cellulose acetate membrane-sodium chloride-...

Figure 5. Experimental data on the effect of (a) i vj(acidity) and (h) vdbasicity) of solutes (in centimeters ) on their reverse osmosis separations in systems involving dilute aqueous solutions and cellulose acetate membranes CIS, 16 ...

Using eq 11, 14, 15, 16 and 17, one can for example calculate the effect of feed concentration and feed flow rate on f and (PR) for NaCl-H20 feed solutions obtainable with a cellulose acetate membrane specified in terms of A and (DAM NaCl ... 

Thomas, D.G., and Mixon, W.R., "Effect of Axial Velocity and Initial Flux on Flux Decline of Cellulose Acetate Membrane in Hyperfiltration of Primary Sewage Effluents," I EC Process Design and Development 11, 339-343 (1972). 

Chlorine dioxide has been used as a water disinfectant, showing fewer undesirable side effects than chlorine [6]. This agent was shown by Vos et al. [1] to be unreactive toward cellulose acetate membranes. The compatibility of chlorine dioxide with other membrane types has not been studied. 

The effect of casting solution composition on flux and rejection of formamide-modified cellulose acetate membranes is shown in Figure 1, illustrating the general capability of this membrane type as function of solvent concentration. Membranes of casting solution composition cellulose diacetate/acetone/ formamide 23/52/25 (solvent-to-polymer ratio 2.26) were used as reference membranes in this work. 

As the effects of an annealing step on the properties of cellulose acetate membranes, the increase of crystallinity by means of the X-ray diffraction method (12, 13) and the changes of pore sizes by the BET adsorption method l5) have been reported. 

The successful development of asymmetric cellulose acetate membranes by Loeb and Sourirajan in the early sixties, at the University of California, Los Angeles, has been primarily responsible for the rapid development of Reverse Osmosis (RO) technology for brack sh/sea water desalination. Reverse Osmosis approaches a reversible process when the pressure barely exceeds the osmotic pressure and hence the energy costs are quite low. Theenergy requirement to purify one litre of water by RO is only O.OO3 KW as against 0,7 KV required just to supply the vaporisation energy to change the phase of one litre of water from liquid to vapour by evaporation. Thus RO has an inherent capability to convert brackish water to potable water at economic cost and thus contribute effectively to the health and prosperity of all humanity. 

Figure 5.6 The effect of annealing temperatures on the flux and rejection of cellulose acetate membranes. The anealing temperature is shown on the figure. (Cellulose diacetate membranes tested at 1500 psig with 0.5 M NaCl) [22]. Reprinted with permission from Elsevier...

Acid cleaning agents such as hydrochloric, phosphoric, or citric acids effectively remove common scaling compounds. With cellulose acetate membranes the pH of the solution should not go below 2.0 or else hydrolysis of the membrane will occur. Oxalic acid is particularly effective for removing iron deposits. Acids such as citric acid are not very effective with calcium, magnesium, or barium sulfate scale in this case a chelatant such as ethylene diamine tetraacetic acid (EDTA) may be used. 

Figure 8.6 The difference between selectivities calculated from pure gas measurements and selectivities measured with gas mixtures can be large. Data of Lee et al. [13] for carbon dioxide/methane with cellulose acetate films. Reprinted from S.Y. Lee, B.S. Minhas and M.D. Donohue, Effect of Gas Composition and Pressure on Permeation through Cellulose Acetate Membranes, in New Membrane Materials and Processes for Separation, K.K. Sirkar and D.R. Lloyd (eds), AIChE Symposium Series Number 261, Vol. 84, p. 93 (1988). Reproduced with permission of the American Institute of Chemical Engineers. Copyright 1988 AIChE. All rights reserved...

FIGURE 20.6 Effect of TMP on the permeate flux in beer CMF through a 0.45 p,m cellulose acetate membrane, at 7= 0°C and w = 2 m/s. (From Moraru, C.I., Optimization and membrane processes with applications in the food industry Beer microfiltration. PhD thesis. University Dunarea de Jos Galati, Romania, 1999.)... 

A continuous effect is the decrease in water content and void volume with Increasing temperature. Water is lost from the primary gel during annealing, both because of the formation of virtual crosslinks and because of the decrease in hydrogen bonding and cluster size in the water Itself. An example of a discontinuous effect is the dramatic increase in permselectivity (salt rejection) observed when cellulose acetate membranes are heated above the glass transition temperature 68.6 C. In fact, not one but two... 

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