Oxygen catalyst regeneration

Ca.ta.lysis, The most important iadustrial use of a palladium catalyst is the Wacker process. The overall reaction, shown ia equations 7—9, iavolves oxidation of ethylene to acetaldehyde by Pd(II) followed by Cu(II)-cataly2ed reoxidation of the Pd(0) by oxygen (204). Regeneration of the catalyst can be carried out in situ or ia a separate reactor after removing acetaldehyde. The acetaldehyde must be distilled to remove chloriaated by-products. 

Catalyst regeneration occurs by the reaction of thallium(I) chloride with copper(II) chloride in the presence of oxygen or air. The formed Cu(I) chloride is reoxidized by the action of oxygen in the presence of HCI ... 

The regeneration process results in the chemical reduction of the adsorbed NO compounds into nitrogen and water vapor. To accomplish the catalyst regeneration in an oxygen-free environment, the system is composed of several separate modules which are alternatively absorbing NO or operated in the regeneration mode. 

The catalyst, used in the form of a ceramic honeycomb monolith, is constituted, as in mobile applications, by a noble metal and an absorber element, such as potassium, deposited on a Y-AI2O3 wash-coat layer. In the oxidation and absorption cycle, the SCON Ox catalyst works by simultaneously oxidizing CO and UHCs to CO2 and H2O, while NOj, are captured on the adsorber compound. Catalyst regeneration is accomplished by passing a controlled mixture of regeneration gases across the surface of the catalyst in the absence of oxygen. 

FIGURE 15.2 Catalyst regeneration versus excess oxygen and temperature. 

Catalyst life depends on several variables. High-pressure oxidation operations (which also operate at higher temperatures, per Table 22.16) require more frequent catalyst regeneration. The presence of trace amounts of iron, calcium, MoS2 (lubricants), and phosphorus in the ammonia feed has been shown to shorten catalyst life. Deposits of iron oxides tend to catalyze the conversion of ammonia and oxygen to nitrogen and water, rather than to nitric oxide. These effects, as well as poor ammonia-air mixing and poor gas distribution across the catalyst, may reduce the yield by up to 10 percent 91,97... 

In the reaction, PdCl2 is reduced to elemental palladium and HC1, and is reoxidized by CuCl2. During catalyst regeneration the CuCl is reoxidized with oxygen. The reaction and regeneration steps can be conducted separately or together. 

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