Zeolites rejuvenation

A considerable reduction in pumping speed and failure to reach the ultimate pressure which is normally attainable in spite of thermal regeneration having been carried out indicates that the zeolite being used has become contaminated by outside substances. It does not make good sense to attempt to rejuvenate the contaminated zeolite with special thermal processes. The zeolite should simply be replaced. 

Another strategy for the rejuvenation of metal/zeolite catalysts with very large metal particles achieves mobilization by the formation of volatile... 

The chemical stability tests were intended to quantify etructure loss under conditions encountered in either catalyst manufacturing or post-regeneration metal redisperaion processes ("rejuvenations"). Zeolites were first calcined in dry air for two houre at 462 C, after which slurries of 20 g zeolite in 200 mL of treatment solution were prepared and stirred for two hours. The treated zeolites were collected on Buchner funnels, washed twice by reslurrying in 200 mL portions of water, dried at 110°C, and (optionally) calcined In dry air for one hour at 4B2°C. 

Because H2 and H2S are present in synthesis gas, cracked gases, and other gas streams encountered in industry, their effects on the jr-complexation sorbents have been studied. The effects of exposure to 0.5 atm H2 at various temperatures on AgN03/Si02 and AgY zeolite were discussed in detail by Jayaraman et al. (2001). Severe deactivation of both sorbents occurred at temperatures above 120 °C. X-ray photoemission spectroscopy (XPS) studies of the deactivated samples showed that the Ag+ was reduced to Ag . However, these sorbents could be rejuvenated by oxidation with oxygen at 350 °C when the valence of Ag was restored to Ag+. The Tr-complexation ability of the sorbent was tested by adsorption of ethylene, and the deactivation and reoxidation behaviors are shown in Figure 8.7. 

Catalysts new zeolites, improved texture, combination of different catalyst types, regeneration or rejuvenation techniques, disposal of spent catalysts ... 

The first Y-zeolite hydrocracking catalysts contained residual sodium ions in the sodalite cages that were mobile during operation and they entered the supercage. This led to a loss of cracking activity. Treatment of the zeolite with an anunonium salt solution removed the mobile sodium ions and restored acidity. The redistribution of palladium with ammonia solution could be combined with an exchange of sodium ions to rejuvenate the catalyst in one step. This was done before reactivation by burning off the carbon deposits. 

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