Membranes long-term performance

Stable performance was demonstrated to 4,000 hours with Nafion membrane cells having 0.13 mg Pt/cm and cell conditions of 2.4/5.1 atmospheres, H2/air, and 80°C (4000 hour performance was 0.5 V at 600 mA/cm ). These results mean that the previous problem of water management is not severe, particularly after thinner membranes of somewhat lower equivalent weight have become available. Some losses may be caused by slow anode catalyst deactivation, but it has been concluded that the platinum catalyst "ripening" phenomenon does not contribute significantly to the long-term performance losses observed in PEFCs (5). 

The stability of membranes against thermomechanical and chemical stresses is an important factor in determining both their short- and long-term performance. Transport and mechanical properties of membranes affect the fuel cell performance, while the lifetime of a fuel cell is mostly dependent on the thermomechanical and chemical stability of the membrane. Thermomechanical and chemical degradation of a membrane will result in a loss of conductivity, as well as mixing of anode and cathode reactant gases. 

The results obtained were partially reported elsewhere (4) and they are quite similar to those obtained at other experimental sites. Results of long term performance, some of them approaching 10,000 hours are shown in Fig. 3 and Fig. 4. As can be seen in Fig. 3 the initial productivity values for all membranes were better than the specified nominal values and continued to be better than predicted. The results shown in Fig. 4 indicated that the normalized rejection of the membranes tested, except for one of the hollow fiber membranes was better or within the limits specified by the membrane producers. One of the membranes that showed an initially low rejection was successfully restored to the nominal value after treatment as recommended by the manufacturer. 

RO performance of the CTA hollow fiber membrane used in Hollosep was measured under higher pressure and analysed in terms of A and D j j/K value. These values remained almost unchanged under operating pressure of up to 100 Kg/cm G. Moreover, long term performance test of the module at high pressure of 75 Kg/ cm2G was satisfactorily carried out with compaction factor less than 0.03. 

Experience has shown that the best long-term performance of an ultrafiltration membrane is obtained when the applied pressure is maintained at or just below the plateau pressure ps shown in Figure 6.7. Operating at higher pressures does not increase the membrane flux but does increase the thickness and density of retained material at the membrane surface layer. Over time, material on the membrane surface can become compacted or precipitate, forming a layer of deposited material that has a lower permeability the flux then falls from the initial value. 

Figure 11.21 Long-term performance of a composite solid polymer electrolyte membrane consisting of 80 wt% AgBF4 dissolved in a propylene oxide copolymer matrix. Feed gas, 70 vol% ethylene/30 vol% ethane at 50 psig permeate pressure, atmospheric [33,61]...

Galan, B Calzada, M. and Ortiz, I. (2006) Recycling of Cr(VI) by membrane solvent extraction Long term performance with the mathematical model. Chemical Engineering Journal, 124, 71. 

In spite of the advances made by these researchers, it remains unclear how membrane surfaces undergo restructuring and how these changes influence the catalytic and transport properties of the material. Furthermore, there is a need to link surface structure and composition with long-term performance of palladium membranes under continuous reaction conditions. One... 

Voss MA, Ahmed T, and Semmens MJ, Long-term performance of parallel-flow bubbleless hollow flber membrane aerators. Water Environment Research 1999, 71(1), 23-30. 

Before this technology can be applied on a full-scale as envisaged in our conceptual module design, the end-users should gain sufficient trust in long term performance and reliability of this membrane solution. We believe that to achieve this, first, a number of smaller on-site production facilities must be set up. Only through wide publication of the information obtained in those demonstration plants can significant industrial application be expected. 

Figure 11.9 Long-term performance of a Pd/stainless steel H2 separation membrane as manufactured by CRI-Criterion during 7000 h of operation.

It can be seen that membrane cells still have a production capability which is small compared with mercury cells, the limitation being the size of membrane sheet which can be manufactured and handled. In addition it should be recognized that the pipework for electrolyte feeds and product take-off is more numerous and much more complex than for diaphragm or mercury cells and there remains a lack of experience of and confidence in the long-term performance of the membranes. 

This chapter will describe some of the market forces driving m brane growth in natural gas treatment, explore some of the competing technologies to CA membranes, examine membrane compaction and the implication to long-term performance, report both recent laboratory and field studies with CA membranes and comment on some of the technical challenges and trends existing today in natural gas treatment with membrane systems that would benefit from future research and development activities. 

Long-term compaction and decline in flux with asymmetric membranes under gases that plasticize the polymer in use are rarely reported. These experiments confirm that higher pressure and temperature can increase compaction levels to unacceptable levels. Conversely, milder process conditions can allow for stable long-term performance in treatment of natural gas. 

Membrane materials that offer improved resistance to temperature, pressure, high CO2 content, water and other chemical contaminants are all areas that offer gains in long-term performance desired in commercial applications. 

The introduction of membrane technology into chlor-alkali electrolysis has dramatically increased the demands on brine purity [141]. The lifetime of chlor-alkali membrane cells is determined by the operating conditions and the quality and purity of the feed into the electrolyzers. Good long-term performance of the cells may be obtained if brine impurities are kept within the limits recommended in Table 14. 

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