Corrosion process hydration energy

The best-known corrosion process is the rusting of iron. Luckily this process, which economically speaking Is a disaster, occurs only slowly. As is well knowm, it is due to the conversion of iron atoms fixed in the crystal lattice into hydrated irun(III) oxide, the rust , in the presence of air and water. If the stable lattice is destroyed, the oxygen molecules of the air can react freely with the finely-divided iron particles, so that the corrosion process appears to occur without any energy being supplied. 

The indirect hydration, also called the sulfuric acid process, practiced by the three U.S. domestic producers, was the only process used worldwide until ICI started up the first commercial direct hydration process in 1951. Both processes use propylene and water as raw materials. Early problems of high corrosion, high energy costs, and air pollution using the indirect process led to the development of the direct hydration process in Europe. However, a high purity propylene feedstock is required. In the indirect hydration process, C -feedstock streams from refinery off-gases containing only 40—60 wt % propylene are often used in the United States. 

Isopropyl Alcohol. Propylene may be easily hydrolyzed to isopropyl alcohol. Eady commercial processes involved the use of sulfuric acid in an indirect process (100). The disadvantage was the need to reconcentrate the sulfuric acid after hydrolysis. Direct catalytic hydration of propylene to 2-propanol followed commercialization of the sulfuric acid process and eliniinated the need for acid reconcentration, thus reducing corrosion problems, energy use, and air pollution by SO2 and organic sulfur compounds. Gas-phase hydration takes place over supported oxides of tungsten at 540 K and 25... 

Halide ions, according to the adsorption theory of passivity, tend to break down passivity by competing with the passivator for adsorption sites on the metal surface. Should a halide ion find a vacant site and closely approach the surface, hydration and dissolution of metal ions are favored, and the anodic reaction can proceed with low activation energy, in contrast to the high activation energy required when a passivator is adsorbed. The anode reaction, if it persists, is confined to localized areas where the competitive process first succeeds, because surrounding metal immediately becomes cathode of an electrolytic cell, and is protected by flow of current from further anode activity, a process called cathodic protection. This attack at specific sites leads to corrosion pitting typical of metals otherwise passive that are actually corroded by their environment. 

Studies of kinetics and mechanisms of metal cluster ionization in water solutions are of great importance for deepening of theory of catalyst and corrosion. In this respect the development of micromodels is very urgent, including elementary acts of this constituent process - development of stmctural, electron and energy changes on the way of ionized atom delay from the surface of metals with the formation of hydrated complex is of great importance. 

In addition, the tendency of an ion to deplete would be related to the characteristics of this ion (bond energy in the glass network, valence state, hydrated volume). More generally, the extent of corrosion depends on the nature and concentration of the acid, on the glass composition and on the manufacturing process of the glass fibres (Kumosa, 2001). 

In the indirect ethylene hydratization process ethylene is contacted at 10-15 bar and 65-85 °C with concentrated sulfuric acid in a bubble column reactor. Mono and diethyl sulfate form and are hydrolyzed later (70-100 °C) to ethanol. Diethyl ether is the main side-product of the process (up to 10%). In the downstream of the reactor, ethanol and diethyl ether are distilled from the diluted sulfuric add, neutralized, and separated by rectification. The diluted sulfuric add produced in the process (45-60% sulfuric add after water addition) is reenergy intensive and problematic with resped to corrosion issues. Despite its relatively complex process scheme, the total ethanol yield in the indired ethylene hydratization process is only 86%. One advantage of the indired process, however, is that it also works with diluted ethylene feeds (e.g., feeds containing larger amounts of methane and ethane). 

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