De-aeration rates

For the de-aeration rate tests, the air supply has to be shut-off suddenly and 2 solenoid valves are used to do this. As one is shut,... 

De-aeration rate Initially fast, then exponential Slow, linear Fast Fast... 

Zembura has made specific use of the rotating disc for investigation of the effect of flow on corrosion reactions. This work has shown that it is possible to determine the type of control (activation or concentration polarisation) of zinc dissolving in 0.1 N Na2S04 (de-aerated), which followed closely the predicted increase in hydrogen ion reduction as the flow rate increased, and proved that in this example... 

In de-aerated 10sulphuric acid (Fig. 3.45) the active dissolution of the austenitic irons occurs at more noble potentials than that of the ferritic irons due to the ennobling effect of nickel in the matrix. This indicates that the austenitic irons should show lower rates of attack when corroding in the active state such as in dilute mineral acids. The current density maximum in the active region, i.e. the critical current density (/ ii) for the austenitic irons tends to decrease with increasing chromium and silicon content. Also the current densities in the passive region are lower for the austenitic irons... 

Fig. 3.50 Corrosion rate versus temperature in de-aerated sea-water continuous test exposure...

Fig. 4.21 Effect of temperature on the anodic behaviour of nickel in 0 025 m H2SO4 -I-0-025 M K2SO4 (pH 1 -3) de-aerated with H2. The curves were determined potentiokinetically at a scan rate of 2 V/h and proceeding from negative to positive (after Cowan and Staehle )...

Variation of pH Between 4 and 8, variation of pH does not appear to have a very significant effect on corrosion rate in de-aerated water. 

In order to control this disadvantageous effect, de-foamers and de-aeraters are added19. The defoamer s task is to control the foam formation due to the tensio-active substances, while the de-aerater removes gas bubbles, in solution and in the fibre structure. In this way, the contact surface between fabric and bleaching solution is kept maximal, which can only favour the rate of the process. By adding the de-aerater, lower quantities of tensio-active substances are needed, which helps to minimise foam formation. 

Cycle the potential between +0.3 and -0.2 V versus Ag/AgCl at a scan rate of 200 mV s 1 and record the voltammograms in an unstirred and not de-aerated 0.1 mol L 1 phosphate buffer solution (pH 7.0), at 25°C. In the DPV technique, sweep the potential from 5 to 30 mV s 1 and the pulse amplitude between 10 and 400 mV. Determine the total phenols concentration present in the samples by DPV using the standard addition method. 

Example. Bitumen is recovered in the form of a froth when a separation-flotation process is applied to surface mined oil sand. Once de aerated, this bituminous froth is a W/O emulsion from which the water must be removed prior to upgrading and refining. At process temperature (80 °C) the emulsion viscosity is similar to that of the bitumen, but the density, due to entrained solids, is higher. Taking t) = 500 mPa-s and f> = 1.04 g/mL, the rate of creaming of 20 pm diameter water droplets under gravitational force will be very slow ... 

Gas holdup and volumetric gas-liquid mass-transfer coefficients are correlated with the gassed power input/volume and with the aeration rate (actual gas superficial velocity), e.g., the correlation of van t Riet [Ind. Eng. Chem. Proc. Des. Dev. 18 357 (1979)] for the volumetric mass-transfer coefficient of coalescing and noncoalescing systems ... 

A variety of feeding arrangements may be employed to ensure that particulate matter of appropriate bulk density is presented to the nip of the rolls. For smoothly flowing materials gravity feed may be used with a control device to adjust feed rate (Fig. 5.4). For fine powders which tend to bridge or stick and are of low bulk density, some form of forced feed (such as the tapered screw feeder shown in Fig. 5.5) must be used to de-aerate, pre-corn-... 

Subbaraman and Santappa found that with de-aerated solutions the rate equation for the oxidation of 2-butanol is the same as that found by Ball et al. for the oxidation of 2-propanol in the absence of oxygen, i.e. equation (19). 

The uncatalysed oxidation in de-aerated solutions is first order with respect to peroxodisulphate, and zero order with respect to the substrate (Subbaraman and Santappa ). Measurements in the temperature range 55-70 C show that the first-order rate coefficient is expressed by... 

Subbaraman and Santappa studied the oxidations of formaldehyde and acetaldehyde in de-aerated solutions, both in the presence and absence of silver ions. When the concentration of aldehyde is much less than that of peroxodisulphate, the rate equation for reaction in absence of silver ions is... 

Acetone and cyclohexanone are oxidised at an appreciable rate only when silver ions are present. Acetone is oxidised to acetic acid and carbon dioxide, and the process is first-order with respect to both peroxodisulphate and silver ions, and zero-order with respect to acetone (Subbaraman and Santappa , Bekier and Kijowski ). The former workers observed that de-aeration has little effect on the rate, and suggested a chain mechanism involving CH3COCH2 radicals. Cyclohexanone is oxidised about 50 % more rapidly than acetone (Subbaraman and Santappa ). 

Early work showed that the rate of the silver ion-catalysed oxidation of oxalate is much faster than the oxidations of other substrates under similar conditions King ). Allen showed that with solutions of very low copper concentration, but not de-aerated, the rate is only slightly faster compared with other substrates. However, Kalb and Allen found that oxygen is a powerful inhibitor of the silver ion-catalysed oxidation, and that in the absence of oxygen low concentrations of copper have no effect on the rate. They studied the silver ion-catalysed reaction in the absence of oxygen. With peroxodisulphate concentrations greater than 0.004 M the rate equation is... 

Finally, the capacity of activated carbons to adsorb surfactants in dynamic conditions has been evaluated. Dynamic adsorption has been carried out in filter columns (diameter 29 nun) in conditions proposed in France [39] bed depth - 6 cm, graining of carbon 0,6—1,2 mm, filtration rate — 6 m/h. Colunuis have been filled with 3 fractions of carbon grain in equal volumes (the total volume of carbon - about 39.6 cm ). Carbons have been flooded with water and then de—aerated in vacuo during Ih. Adsorption has been carried out by passing solution of sodium laurylosulphate SLS (1 mg/dm ) through the bed. 

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