Cleaning procedure membranes

Thermoplastics. There are five elastomeric membranes that are thermoplastic. Two materials, chlorinated polyethylene (CPE) and polyisobutylene (PIB), are relatively obscure. Thermoplastic materials can be either heat-fused or solvent-welded. In contrast to Hypalon and uncured EPDM, this abiHty to fuse the membranes together remains throughout the life of the material. However, cleaning of the membrane surface after exposure to weather is required. Correct cleaning procedures for specific membranes are available from the individual manufacturer. 

Flux response to concentration, cross flow or shear rate, pressure, and temperature should be determined for the allowable plant excursions. Fouling must be quantified and cleaning procedures proven. The final design flux should reflect long-range variables such as feed-composition changes, reduction of membrane performance, long-term compaction, new foulants, and viscosity shifts. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Continued decline in performance indicates a membrane cleaning or compatibihty issue. The adequacy of the cleaning step is determined by the recovery of at least 80 percent of the initial normalized water flux. Although some variability in water flux is typical, any consistent dechne reflects an inadequate cleaning procedure. 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

The first aim of this work was to study the influence of an unwashed membrane filter on the cadmium, lead, and copper concentrations of filtered seawater samples. It was also desirable to ascertain whether, after passage of a reasonable quantity of water, the filter itself could be assumed to be clean so that subsequent portions of filtrate would be uncontaminated. If this were the case, it should be possible to eliminate the cleaning procedure and its contamination risks. The second purpose of the work was to test the possibility of long-term storage of samples at their natural pH (about 8) at 4 °C, kept in low-density polyethylene containers which have been cleaned with acid and conditioned with seawater. 

Zirconia membranes on carbon supports were originally developed by Union Carbide. Ultrafiltration membranes are commercially available now under trade names like Ucarsep and Carbosep. Their outstanding quality is their high chemical resistance which allows steam sterilization and cleaning procedures in the pH range 0-14 at temperatures up to 80°C. These systems consist of a sintered carbon tube with an ultrafiltration layer of a metallic oxide, usually zirconia. Typical tube dimensions are 10 mm (outer diameter) with a wall thickness of 2 mm (Gerster and Veyre 1985). 

In the practical application of electrodialysis there are two main process operation modes. The first one is referred to as the unidirectional electrodialysis and the second as electrodialysis reversal [22]. In a unidirectional operated electrodialysis system the electric field is permanently applied in one direction and the diluate and concentrate cells are also permanently fixed over the period of operation. Unidirectional operated electrodialysis plants are rather sensitive to membrane fouling and scaling and often require a substantial feed-solution pretreatment and stack-cleaning procedures in the form of periodical rinsing of the stack with acid or detergent solutions. The unidirectional operating concept is mainly used today for applications in the... 

Membrane manufacturers and cleaning-chemical vendors typically have cleaning procedures formulated for their specific product(s). While it is impossible to review all cleaning procedures here, a basic cleaning procedure is presented which can be modified to suit the membrane, the cleaning chemical(s), and the specific contaminant(s) to be removed ... 

Hydranautics, "Foulants and Cleaning Procedures for Composite Polyamide RO Membrane Elements," Technical Service Bulletin, TBS107.15,2008. 

The issue of chemical resistance Is relevant not only during applications but also in membrane cleaning procedures which often specify strong acids and bases and sometimes peroxides. Moreover, nonoxidc ceramic membrane materials are prone to reaction upon extended exposure to oxidizing environments. 

The regeneration of membrane properties is key to maintaining its selectivity and yield. Without a safe, practical, reproducible, cost-effective, and efficient cleaning procedure, the viability of crossflow filtration is highly questionable [36], The use of the mechanical means discussed above can help extend the membrane performance over a limited period of time, but the complete... 

The development of an effective cleaning process has to take into account the nature of the foulants, the thermal and chemical resistance of the membrane material, membrane housing and seals. Typically, membrane manufacturers make specific recommendations regarding the cleaning agents and cleaning procedures that need to be used for different membranes and applications. 

Gan Q, Howell JA, Field RW, England R, Bird MR, and McKechinie MT. Synergetic cleaning procedure for a ceramic membrane fouled by beer microfiltration. J. Membr. Sci., 1999 155(2) 277-289. 

To improve the removal of deposits on the membrane surface, Bohner and Bradley [179] modified the cleaning procedure described previously. The modified procedure, which was carried out at 54°C, consisted of a 2 min initial rinsing of the... 

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