Membrane processes temperature effect

A rise in temperature can have both a positive and a negative effect on the permeability. Transport through the membrane is an activated process, so it will benefit from a rise in temperature. However, as the temperature increases, the concentration in the membrane diminishes. These effects counteract each other, and one of them will dominate, depending on the difference in activation energy for diffusion and the heat of adsorption and the temperature. This will be discussed further in Section III. 

FIGURE 20.12 Effect of crossflow velocity on the 6 h permeate flux in CMF of beer performed at various TMP values, a process temperature of 0°C, and cellulose acetate membranes of 0.45 p,m pore size. (From Moram, C.I., Optimization and membrane processes with applications in the food industry Beer microfiltration. PhD thesis. University Dunarea de Jos Galati, Romania, 1999.)... 

While higher process temperatures do have a positive effect on permeate flux in membrane separation (Figure 20.15), due to lower product viscosity and enhanced hydrodynamics at the membrane surface, in beer microfiltration the value of this parameter is dictated by the technological requirement that beer be filtered cold, typically at temperatures between — 1.5°C and+2°C. 

Table 35.5 compares the process water, freshwater, and NF permeate values for some parameters at the Eltmann. Water hardness measures divalent cations and is well retained in NF but the retention of conductivity is less than 40%. This is due to the negative retention of chloride ions, as often measured for NF membranes, because of the Dorman effect, which is typical for NF membranes. The reuse of NF permeate decreased the need to heat freshwater to the mill process temperature. The concentrate (36 m /h) is recirculated back to the activated-sludge plant after Erne precipitation. This precipitation process removes iron nearly completely (99.7%). The removal of color, carbonate, silicate, COD, and AOX are 72%, 66%, 61%, 40%, and 39%, respectively. However, only 10% of the conductivity (28% of sulfate) is removed by Erne precipitation [59]. 

The term membrane refers not to a single item, but covers a large variety of structures and materials with very different properties. The same is tme for membrane processes, which can be very different in the way they function. However, all membranes and membrane processes have one feature in common, i.e., they can perform the separation of certain molecular mixrnres effectively and economically at ambient temperature, and without any toxic or harmful reaction by-products. 

The effect of temperature deserves special mention since it represents a major ndvanlage for the liquid-membrane process.9 9 Figure 19.4-5 compares the influence or temperature on extraction of uranium by the SX and LM techniques. In the case of liquid membraues. extraction efficiency increases with tempemiure... 

Formation of vacancies in metals and alloys is an activated process [82]. Diffusion of metals into Pd is decreased exponentially by simply decreasing the absolute temperature at which the membranes are operated. Effects of interdiffusion can also be decreased linearly by increasing the thickness of the Pd. In general, doubling the thickness of a layer of Pd will double the time required for metals to diffuse through the layer and thus double the operation time before decay of the catalytic activity. This assumes that Pd is not poisoned by surface diffusion of impurities originating from pinholes or the membrane seals. It follows that poisoning of supported... 

For the esterification with n-butanol, Liu, Zhang, and Chen (2001) used a cross-linked PVA-ceramic composite membrane (in the temperature range of 60—90 °C). This paper is a rare case of use of the Zr(S04)2 -4H20 catalyst. On the basis of a simple Fickian model, the influence of several esterification process variables, such as process temperature, initial mole ratio of acetic acid to n-butanol, the ratio of the effective membrane area to the volume of reacting mixture, and catalyst content, were discussed. A more rigorous model was defined by Liu and Chen (using a kinetic approach) comparing model outcomes with experimental outcomes (Inoue et al., 2007). 

Ho KC, Hung WT (2001) An amperometric N02 gas sensor based on Pt/Nafion electrode. Sens Actuators B 79 11-18 Ho KC, Liao JY, Yang CC (2005) A kinetic study for electrooxidation of NO gas at a Pt/membrane electrode-apphcation to amperometric NO sensor. Sens Actuators B 108 820-827 Imaya H, Ishiji T, Takahashi K (2005) Detection properties of electrochemical acidic gas sensors using halide-halate electrolytic solutions. Sens Actuators B 108 803-807 Ives DJG, Janz GJ (eds) (1961) Reference electrodes theory and practice. Academic, New York, NY Jordan LR, Hauser PC, Dawson GA (1997) Humidity and temperature effects on the response to ethylene of an amperometric sensor utilizing a gold-Nafion electrode. Electroanalysis 9 1159-1162 Katayama-Aramata A, Nakajima H, Fujikawa K, Kita H (1983) Metal electrodes bonded on sohd polymer electrolyte membranes (SPE)—the behaviour of platinum bonded on SPE for hydrogen and oxygen electrode processes. Electrochim Acta 28 777-780... 

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