Poisoning catalyst regeneration

Poisoning is operationally defined. Often catalysts beheved to be permanently poisoned can be regenerated (5) (see Catalysts, regeneration). A species may be a poison ia some reactions, but not ia others, depending on its adsorption strength relative to that of other species competing for catalytic sites (24), and the temperature of the system. Catalysis poisons have been classified according to chemical species, types of reactions poisoned, and selectivity for active catalyst sites (24). 

Figure 12. Transient HCN yield over platinum catalysts. A and B represent one experiment (Exp. 1) in which a sulfur-poisoned catalyst was regenerated on admission of 1% O2 into the inlet gas mixture between times t, and C shows the resistance of the catalyst to poisoning by SO when oxygen is simultaneously present in the inlet gas mixture. At t only oxygen is removed from the inlet gas mixture. (See Ref. 16 for details.)...

In our mechanism, coke formation is due to the presence of olefins, which occur as intermediate species during the reforming reactions. As discussed in Section II, these olefins can go either to products or to coke precursors. The deactivation caused by feed poison, catalyst sintering during regeneration, or improper regeneration techniques is not considered in this development. 

In summary, the hydrodesulfurization of the low-, middle-, and highboiling distillates can be achieved quite conveniently using a variety of processes. One major advantage of this type of feedstock is that the catalyst does not become poisoned by metal contaminants in the feedstock since only negligible amounts of these contaminants will be present. Thus, the catalyst may be regenerated several times and onstream times between catalyst regeneration (while varying with the process conditions and application) may be of the order of 3 to 4 years (Table 6-6). 

According to Yoo [9] some of the vanadium poisoning is regenerate. While the poisoning effect of Vanadium on the FCC catalyst can at least be partially reversed, this type of regeneration does not take place in conventional FCC operations. 

What are the mechanisms of sulfur removal from surfaces and can these mechanisms be used in the development of regeneration techniques for sulfur-poisoned catalysts ... 

Relatively few studies of regeneration of sulfur-poisoned catalysts have been reported in the literature (/, 9, 11, 83, 92, 178, 194, 237, 269-274). Attempts to regenerate poisoned catalysts have been made using oxygen/air... 

Regeneration of Sulfur-Poisoned Catalysts Using 02 Treatment... 

This type of solution method is possible for reactions where deactivation is slow, and a pseudo steady-state assumption can be made when solving the mass balance equations. Thus, these equations are applicable to reactions where the activity loss is first-order in both the poison and the active sites, and where deactivation is slow compared to the main reaction. A similar type of approach was taken by Johnson et al. (5), for oxygen consumption and carbon content during catalyst regeneration and by Bohart and Adams (6), for chlorine consumption and absorbence capacity of charcoal. 

Supported metal catalysis are employed in a variety of commercially important hydrocarbon conversion processes. Such catalysts consist, in general, of small metal crystallites (0.S to 5 nm diameter) dispersed on non-metallic oxide supports. One of the major ways in which a catalyst becomes deactivated is due to accumulation of carbonaceous deposits on its surface. Catalyst regeneration, or decoking, is normally achieved by gasification of the deposit in air at about 500°C. However, during this process a further problem is frequently encountered, which contributes to catalyst deactivation, namely particle sintering. Other factors which can contribute to catalyst deactivation include the influence of poisons such as sulfur, phosphorus, arsenic and... 

In this paper, we discuss the sulfur-poisoning mechanism of Pd(R)/Al203 catalysts according to the chemical states and the relative quantity of sulfur on/in the catalysts and explore the approaches and procedures to regenerate poisoned catalysts. 

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