Lead oxides, separator additives

In a separate investigation MargeHs and Roginekii1107 carried nut catalytic oxidation of ethylene at 350° over vanadium pentoxidc. reportedly similar to metallic silver in catalytic properties. TVv asoertainod that carbon dioxide was formed faster from, ethylene oxide, or from acetaldehyde under comparable conditions, than from ethylene itself. Further, they noted the formation of carbon monoxide, and determined that its rate of formation was considerably greater than that of carbon dioxide, increasing still more in the presence of adtk-d ethylene oxide. The addition of ethylene oxide also appeared to depro both ethylene oxide and acetaldehyde formation. They concluded that reactions leading to carbon dioxide and water did not proceed by wav of ethylene oxide, but by way of some other intermediates, and tlmt-this process could occur either on the catalyst surface or in the gas phase. 

Stirring, and 700 g. (1.03 mole) of red lead oxide (Pt)304) is added in portions of 15-20 g. A fresh addition is made only after the color due to the preceding portion has largely disappeared, and the temperature is kept between 55 and 80°. At the end of the reaction the thick and somewhat dark solution is cooled, and the crystalline lead tetraacetate which separates is collected and washed with acetic acid. The crude product without being dried is dissolved in hot acetic acid, and the solution is clarified with Norit, filtered, and cooled. The colorless crystalline product is dried in a vacuum desiccator over potassium hydroxide in the dark and stored in the desiccator yield 320-350 g. (70-77%). 

PLACID/PLINT process [13,14], The PLACID process (see also Chapter 16) is based on the electrowinning of lead from a chloride solution in a cell where the cathode and anode are separated by a semipermeable membrane. Lead oxide and lead dioxide are converted to soluble lead chloride, whilst lead sulfate is converted in a hot brine circuit. The sulfate ion is removed as gypsum after the addition of lime. The FLINT process is an advanced adaptation of the PLACID process and operates in parallel with a pyrometallurgical route that smelts the metallic lead fractions from the battery. 

The technology of these etectrowinning processes is very simple, The cells are open OD iele tanks lined with rubber or plastic and the lines of anode and cathode plates are placed alternatively with a separation of 5 15 cm the cells are connected monopolar and one arrangement is shown in Fig. 4.S, The anodes are lead alloy sheets which in the sulphate medium form a lead oxide coating the metal additions to the lead (c.g. silver) arc to catalyse oxygen evolution and therefore reduce the anode overpotentiaL The starter sheets for the cathodes are aluminium or titanium and the metal is deposited until there is a layer 3-5 cm thick, at which point the cathodes are removed from the cell. The metal is then Stripped from the starter sheets and these are reused. The electrodes are typically Q,3-0.5 m in area but the anodes are always larger than the cathodes to prevent... 

The water methanol extract is divided into 10-1. batches, and to each is added, with mixing, 15 ml. of 2 JV NaOH and 380 ml. of a solution of the following composition 450 g. lead acetate 150 g. lead oxide -f 2 1. of water. The precipitate is separated by centrifugation, washed, and the supernatant and wash water are pooled. This liquid is acidified by addition of 30 ml. of 2 N sulfuric acid per 10 1., then is vacuum concentrated to one-sixteenth of its volume. The excess lead is removed by addition of sulfuric acid and filtration. 

An additional advantage of this synthetic approach is that the mesopores of silica restrict the size of the TiO species in the mixed oxide materials. Furthermore, Liu et al. were able to control the homogeneity of the mixed oxide materials by changing the pH value of the initial sol-gel mixture. pH values lower than the isoelectric point of sihca (2.0) lead to uniformly dispersed titania domains, whereas at higher pH values phase separation is observed due to the instability of the titanium-citric acid complexes. A similar approach has been reported by Oki et al. [56] for the synthesis of Ti02—Si02 mixed oxides by addition of various alk)d amines such as hexylamine, dodecylamine, and octadecylamine or even... 

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