Regeneration of coked catalyst

The catalyst pore system may, however, be blocked if the catalyst does not contain macropores [381], 

The newly formed carbon whiskers are very reactive when there is a thermodynamic potential for gasification (reverse Reaction R6 in Table 5. 2). This was demonstrated in the TGA tests close to equilibrium. In situ electron microscopy [33] has shown how nickel crystals may eat channels through carbon by a reverse whisker growth mechanism. Similar observations have been made for catalytic filters for car exhaust where cerium oxide crystals react with soot deposits [460]. The gum layer is also reactive in hydrogen [205]. 

Newly formed carbon may be removed by steaming (600-700°C) [381] according to Equation (5.13) which shows potential for gasification at a H20/H2=10, which is sufficient to keep the nickel catalyst in a reduced state (refer to Chapter 4). In practice fresh whisker carbon can be removed by simply increasing the steam-to-carbon ratio. 

With ageing, the whisker stracture collapses and the reactivity diminishes. The same is true for the gum layer and eventually the coke deposits can only be removed by means of oxygen (air). 

If whisker carbon has resulted in breakage of the catalyst pellets, a high pressure drop will remain after the removal of carbon. 

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Regeneration of coked catalysts may be accomplished by gasification with oxygen, steam, hydrogen, or carbon dioxide ... 

The regeneration of coked catalysts (Section 8.6.5) can be represented by coke burning with air ... 

These reactions may serve as a means of regeneration of coked catalysts. Both reactions are exothermic, and the improved temperature control provided by a fluidized bed is critical for regeneration of catalysts prone to sintering. 

Analysis of Fractions. Surface areas and pore size distributions for both coked and regenerated catalyst fractions were determined by low temperature (Digisorb) N2 adsorption isotherms. Relative zeolite (micropore volume) and matrix (external surface area) contributions to the BET surface area were determined by t-plot analyses (3). Carbon and hydrogen on catalyst were determined using a Perkin Elmer 240 C instrument. Unit cell size and crystallinity for the molecular zeolite component were determined for coked and for regenerated catalyst fractions by x-ray diffraction. Elemental compositions for Ni, Fe, and V on each fraction were determined by ICP. Regeneration of coked catalyst fractions was accomplished in an air muffle furnace heated to 538°C at 2.8°C/min and held at that temperature for 6 hr. 

TPO regeneration of coked catalysts indicates that different minima occurred in the oxygen concentration downstream from the reactor (Figure 2). Those at lower... 

Regeneration of coked catalyst is an important step in FCC operation as the effective activity of the catalyst entering the riser is determined by the coke on regenerated catalyst... 

Coke formation is a common cause of catalyst deactivation. Regeneration of coked catalyst can generally be achieved by gasification of the coke deposits with oxygen, carbon dioxide, steam or hydrogen. The first of these methods gives rise to oxidative regeneration processes with which this work is concerned. 

Gas-solid noncatalytic reactions are encountered in a broad range of industrial processes, including coal combustion and gasification, mineral processing, the capture of contaminants from gas streams, and the regeneration of coked catalysts. In applications such as combustion and gasification, the solid phase disappears as the reaction proceeds, while in others such as the capture of sulfur from gas streams, the solid reactant is converted into a solid product. 

Kern, C. and (ess, A. (2005) Regeneration of coked catalysts - modelling and verification of coke bmn-off in single particles and fixed bed reactors. Chem. Eng. Sci., 60, 4249-4264. 

Analogous equations are used to simulate the regeneration of coked catalysts, and similar waves are obtained [Olson et al., 1968 and Hughes et al., 1987]. 

Examples of such a system are the regeneration of coked catalysts, the reduction of some metal oxides, and the roasting of sulfide ores. 

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