Membrane degradation

Membrane degradation involves the loss of membrane polymer integrity. This can be a result of membrane oxidation, where the oxidizer attacks the membrane polymer, leading to aromatic 

Membranes can also be oxidized in the presence of iron, manganese, and other metals. These metals catalyze the oxidation of RO membranes. This type of oxidation tends to involve the entire RO skid rather than focus on the lead membranes. Again, when this type of degradation occurs, feed water passes into the permeate, resulting in an increase in permeate flow and a decrease in product quality. 

Exposure to high temperature at pH extremes can hydrolyze the membranes, leading to loss of membrane integrity. (See Chapter 4.2.1, Table 4.2, and Chapters 9.2,9.8, and 13.2 for more detailed discussions on the effect of temperature and pH on polyamide composite membranes.) Hydrolysis also tends to involve the entire RO skid rather than focus on only the lead membranes. Just as with oxidation of the membrane, feed water will pass into the permeate resulting in an increase in permeate flow and decrease in the product quality. 

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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... 

Chemical electrical optimisation Predictive analysis of electrode and membrane degradation or anomalies Estimate of electrode state Estimate of membrane state... 

Mittal, V. O., Kunz, H. R. and Fenton, J. M. 2006. Is H2O2 involved in the membrane degradation mechanism in PEMFC Electrochemical and Solid-State Letters 9 A299-A302. 

Early research of ionomer membrane degradation was conducted in the context of PEM electrolyzers. The detection of fluoride and other chain fragments in the condensed effluent water indicates the decomposition of PFSA ionomer and has long been noticed. Baldwin15 reported the detection of fluoride in the effluent of PEM electrolyzer and believed that it is the result of membrane mechanical failure. Extensive research has been conducted to elucidate the reaction pathways for membrane decomposition. Many controversial results and mechanisms have been reported in the literature, demonstrating the complex nature and the current inadequate understanding of the membrane degradation mechanisms. 

Based on our observation, a membrane degradation and failure mechanism under the RH cycling, a pure mechanical effect is theorized as the following sequence electrode-microcracking- - crazing initiation at the electrode/electrolyte interface - crack growth under stress cycling- -fast fracture/instability. 

Based on our observations, we generalize the fuel cell membrane degradation and failure mechanisms as the schematics in Fig. 23. So far, the evidence has shown that defects formation and growth play an important role both in chemical and in mechanical degradation processes. Drawing an analogy with material corrosion behavior,... 

M. Quintus et al., Chemical membrane degradation in automotive fuel cell -Mechanisms and mitigation, 2nd Annual International Symposium on Fuel Cell Durability Performance, Miami Beach, FL,7-8 Dec 2006... 

The clinical utility of electrochemical sensors for continuous glucose monitoring in subcutaneous tissue has been limited by numerous challenges related to sensor component and biocompatibility-based failures.1,2 Sensor component failures include electrical failure, loss of enzyme activity, and membrane degradation,3 4 while examples of biocompatibility-based failures include infection, membrane biofouling (e.g., adsorption of small molecules and proteins to the sensor surface), and bbrous... 

Neplenbroek, A.M., Bargeman, D. and Smolders, C.A. (1992) Mechanism of supported liquid membrane degradation - emulsion formation. Journal of Membrane Science, 67, 133. 

There are two major limitations in the processes described above. First of all, the fact that these fungi are effective only in the sapwood, which in most instances is readily treatable, reduces its usefulness. Secondly, it has been shown by Johnson and Gjovik (41) that extraneous bacteria, rather than fungi, may actually be responsible for the pit membrane degradation... 

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