Regeneration of catalysts

The process is characterized by high yield (nearly complete hydrogenation of acetylenes) and high selectivity (only a small loss of butadiene by hydrogenation). The process does not lead to polymerization, which might otherwise cause catalyst deactivation, and only infrequent regeneration of catalyst is necessary. 

The spillover effect can be described as the mobility of sorbed species from one phase on which they easily adsorb (donor) to another phase where they do not directly adsorb (acceptor). In this way a seemingly inert material can acquire catalytic activity. In some cases, the acceptor can remain active even after separation from the donor. Also, quite often, as shown by Delmon and coworkers,65 67 simple mechanical mixing of the donor and acceptor phases is sufficient for spillover to occur and influence catalytic kinetics leading to a Remote Control mechanism, a term first introduced by Delmon.65 Spillover may lead, not only to an improvement of catalytic activity and selectivity but also to an increase in lifetime and regenerability of catalysts. 

The purpose of this review is to integrate the literature on this topic, along with some of the work we have performed, to provide a clearer understanding on the role of carbon as a deactivation mechanism. The minimization of carbon by promotion, regeneration of catalysts, and some selectivity implications will also be briefly discussed. 

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. 

In a continuous reformer, some particulate and dust matter can be generated as the catalyst moves from reactor to reactor and is subject to attrition. However, due to catalyst design little attrition occurs, and the only outlet to the atmosphere is the regeneration vent, which is most often scrubbed with a caustic to prevent emission of hydrochloric acid (this also removes particulate matter). Emissions of carbon monoxide and hydrogen sulfide may occur during regeneration of catalyst. 

H-shift is invoked for the formation of 6 and regeneration of catalyst 8. The proposed mechanism is unusual insofar as the tt-bonds of electroneutral alkynes and arenes seldom participate in Diels-Alder reactions. The intermediacy of metal vinylidenes is supported by the failure of internal alkynes to dimerize under the reported conditions. More importantly, mechanistic restrictions imposed by the porphyrin ligand set severely restrict conceivable alternative mechanisms. 

This moderately endothermic process results in the formation of 2 moles of hydrogen per mole of methane consumed above a certain threshold reaction temperature. A gradual catalyst deactivation is expected due to the accumulation of carbon on the catalyst. The catalyst can be regenerated by removing the carbon on the catalyst in a separate step. Thus, hydrogen production by this approach involves two distinct steps (a) catalytic decomposition of methane and (b) regeneration of catalyst. 

B. Design of Recovery and Regeneration of Catalyst for the Primary Stage U38-I40)... 

In 2002, an interesting concept was proposed for coupling a C02-based supercritical extraction with air oxidation in order to remove and decompose pollutants from gases or liquids (134). An exemplary process scheme according to this preliminary concept is shown in Figure 5. Possible (future) environmental applications of such an integrated supercritical extraction-reaction system include treatment of liquid effluents, regeneration of catalysts and adsorption materials, and soil decontamination. 

Subsequent to termination of first cycle, refinery carried out the regeneration of catalyst. Sulfur stripping was performed by circulation of hydrogen in the reaction section at 500-510°C reactor inlet temperature and 5 to 7 kg/cm2 separator pressure. Initially H2S... 

The correct evaluation of catalytic properties demands that heat and mass transfer limitations are eliminated or properly accounted for. It also demands that the catalyst is in the working state, as opposed to the transient state observed at the beginning of most catalytic tests. The absence of gas-phase reactions or reactions catalyzed by the reactor wall should also be verified. This must be kept in mind in the following, in which measurement methods, kinetic analyses including the influence of heat and mass transfer and deactivation or, more generally, time-dependent effects will be examined. Regeneration of catalysts will be examined at the end. 

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