Membrane continued degradation

Since in continuous degradation processes it is expected to reach a molecular weight distribution of the products, which is optimal for their further use, the investigation was devoted to test the effect of a key parameter such as the enzyme to substrate ratio (E/S). For a fixed mean retention time in the UF-membrane reactor, the following behaviour can be... 

Most cells continually degrade and replace their membrane lipids. For each hydrolyzable bond in a glycerophospholipid, there is a specific hydrolytic enzyme in the lysosome (Fig. 10-15). Phospholipases of the A type remove one of the two fatty acids, producing a lysophospholipid. (These esterases do not attack the ether link of plasmalogens.) Lysophospholipases remove the remaining fatty acid. 

Polyamide, composite membranes are very sensitive to free chlorine (recall from Chapter 4.2.1 that cellulose acetate membranes can tolerate up to 1 ppm free chlorine continuously). Degradation of the polyamide composite membrane occurs almost immediately upon exposure and can result in significant reduction in rejection after 200 and 1,000-ppm hours of exposure to free chlorine (in other words after 200-1,000 hours exposure to 1 ppm free chlorine). The rate of degradation depends on two important factors 1) degradation is more rapid at high pH than at neutral or low pH, and 2) the presence of transition metals such as iron, will catalyze the oxidation of the membrane. 

Galibiati et al. [147] observed gradually increased hydrogen crossover and short circuit current during continuous operation at 400 mA cm for 6000 h at 180 °C, which is an indication of membrane-related degradation. Post mortem analysis of membrane-electrode assemblies that had been operated at constant load of 200 mA cm at 150 °C, revealed considerable membrane thinning starting after about... 

The interesting applications of polymers are the protection foils and the polymeric components of solar cells. The permanent exposure to the action of weathering agents, the foils are continuously degraded [116, 117]. The studying papers must be focused on the durability of these membranes because the quantum yield of material appoints the performances of electrical generators based by sun light. 

Open-loop systems have inherently long residence times which may be detrimental if the retentate is susceptible to degradation by shear or microbiological contamination. A feed-bleed or closed-loop configuration is a one-stage continuous membrane system. At steady state, the upstream... 

Enzymatic degradation of pectin can be satisfactory performed in UF-membrane reactors which have been proved to be helpful tool for laboratory scale investigations. Reaction products can be continuously recovered in a sequence of filtration stages. The obtained product distribution depends on the enzyme to substrate ratio, which affects particularly the... 

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