Cellulose acetate RO membrane

In 1968 we started investigations of RO applications for desalting brackish water. In the course of the investigations, we have found the spirally wound module of asymmetric cellulose acetate RO membrane shows excellent durabilities against fouling materials and free chlorine. 

Figure 4.3 Cross section of a cellulose acetate RO membrane.

Figure 4.4 Chemical structure of cellulose acetate RO membranes.

In studies to remove organic fouling on RO membranes, it has been reported that several commercial cleaners developed by Pfizer gave excellent results. Differential pressure of the membrane system could be reduced by 42% using a neutral pH liquid formulation (Floclean 107) designed to remove organics, silt, and other particulates from cellulose acetate RO membranes. For polyamide, polysulfone, and thin-film-composite... 

There have been many studies on the application of membrane technology to food Industries. Few have, however, reached a commercial success except those of dairy processes (1) DAICEL has been studying since 1971 the application of its cellulose acetate RO membranes and polyacrylonitrile UF membranes to food, pharmaceutical, medical, paper and other industries. As to the use of membranes in food industries other than dairy processes, only two cases were developed to a semicommercial scale, that is, grape juice concentration for wine must and tomato juice concentration for processing and storage of the juice till next harvest. 

By the way, relatively low flux and rejection values for D-ribose represented in Table I suggest that D-ribose might have a specifically strong interaction with cellulose acetate RO membranes. 

Since acid addition is normally used to prevent scaling in the RO unit and to prevent hydrolysis of cellulose acetate RO membranes, the reaction of the acid with bicarbonate in the feedwater produces carbon dioxide which can further deplete the ion exchange capacity. Forced-draft degasification removes the C02. 

Figure 3.2317 presents rejection data for three different dextrans on the same UF membrane as a function of pressure. Figure 3.2418 shows the effect of pressure on the rejection of 0.1 M NaCI by a cellulose acetate RO membrane. It is obvious that the mechanism for solute transport through the membrane is different for UF and RO. 

Plants are cleaned, sanitized, and rinsed immediately after processing and right before processing to ensure satisfactory initial process conditions from microbiological standpoint [3]. Becanse chlorine is freely permeable to most membranes that it is able to sanitize the permeate side of the system as well as the retentate side, using solutions of sodium hypochlorite containing 100-200 ppm of active chlorine is a common sanitation technique for many membranes, except cellulose acetate RO membranes, which can only tolerate brief exposnre to chlorine at 10-50 ppm level [3]. 

Fujii et al. [13] studied morphological structures of the cross section of various hollow fibers and fiat sheet membranes by high-resolution field emission scanning electron microscopy. Figure 6.8 shows a cross-sectional structure of a flat sheet cellulose acetate RO membrane. The layer near the top surface is composed of a densely packed monolayer of polymeric spheres, which is supported by a layer formed with completely packed spheres. The contours of the spheres in the top layer can be observed. The middle layer is also composed of loosely packed and partly fused spheres, which are larger than the spheres in the surface layer. In the middle layer, there are many microvoids, the sizes of which are the same as the spheres. The layer near the bottom is denser than the middle layer, and the spheres are deformed and fused. Interstitial void spaces between the spheres, which may be called microvoids, are clearly observed. This structure seems common for the flat sheet as well as the hollow fiber membranes. For example. Fig. 6.9 shows a cross section of a hollow fiber made of PMMA B-2 (a copolymer containing methyl methacrylate and a small amount of sulfonate groups). The inside surface layer is composed of the dense structure of compactly packed fine polymeric particles. The particle structure of the middle layer... 

Evaluation of SPPO membrane for the removal of oil from bilge water was done along with cellulose acetate RO membrane and polypropylene MF membrane. Steady flow of SPPO membrane was 30 to 40 gsfd at 400 psig and room temperature, when the feed contained 15 000 ppm salt and 100 ppm oil. The membrane could be readily cleaned and the initial flux could be recovered. 

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